single-page-ref.rst
Author: Arvid Norberg, arvid@libtorrent.org

| libtorrent

Author: | Arvid Norberg, arvid@libtorrent.org
Version: | 1.2.9

# libtorrent API Documentation

Table of contents

- libtorrent API Documentation
- Upgrading to libtorrent 1.2

## overview

The interface of libtorrent consists of a few classes. The main class is the `session`, it contains the main loop that serves all torrents.

The basic usage is as follows:

- construct a session

- load session state from settings file (see load_state())

- start extensions (see add_extension()).

- start DHT, LSD, UPnP, NAT-PMP etc (see start_dht(), start_lsd(), start_upnp() and start_natpmp()).

- parse .torrent-files and add them to the session (see torrent_info, async_add_torrent() and add_torrent())

- main loop (see session)

  > - poll for alerts (see wait_for_alert(), pop_alerts())
  > - handle updates to torrents, (see state_update_alert).
  > - handle other alerts, (see alert).
  > - query the session for information (see session::status()).
  > - add and remove torrents from the session (remove_torrent())

- save resume data for all torrent_handles (optional, see save_resume_data())

- save session state (see save_state())

- destruct session object

Each class and function is described in this manual, you may want to have a look at the tutorial as well.

For a description on how to create torrent files, see create_torrent.

## forward declarations

Forward declaring types from the libtorrent namespace is discouraged as it may break in future releases. Instead include `libtorrent/fwd.hpp` for forward declarations of all public types in libtorrent.

## trouble shooting

A common problem developers are facing is torrents stopping without explanation. Here is a description on which conditions libtorrent will stop your torrents, how to find out about it and what to do about it.

Make sure to keep track of the paused state, the error state and the upload mode of your torrents. By default, torrents are auto-managed, which means libtorrent will pause, resume, scrape them and take them out of upload-mode automatically.

Whenever a torrent encounters a fatal error, it will be stopped, and the `torrent_status::error` will describe the error that caused it. If a torrent is auto managed, it is scraped periodically and paused or resumed based on the number of downloaders per seed. This will effectively seed torrents that are in the greatest need of seeds.

If a torrent hits a disk write error, it will be put into upload mode. This means it will not download anything, but only upload. The assumption is that the write error is caused by a full disk or write permission errors. If the torrent is auto-managed, it will periodically be taken out of the upload mode, trying to write things to the disk again. This means torrent will recover from certain disk errors if the problem is resolved. If the torrent is not auto managed, you have to call set_upload_mode() to turn downloading back on again.

For a more detailed guide on how to trouble shoot performance issues, see troubleshooting

## ABI considerations

libtorrent maintains a stable ABI for versions with the same major and minor versions.

e.g. libtorrent-1.2.0 is ABI compatible with libtorrent-1.2.1 but not with libtorrent-1.1

## network primitives

There are a few typedefs in the `libtorrent` namespace which pulls in network types from the `boost::asio` namespace. These are:

    using address = boost::asio::ip::address;
    using address_v4 = boost::asio::ip::address_v4;
    using address_v6 = boost::asio::ip::address_v6;
    using boost::asio::ip::tcp;
    using boost::asio::ip::udp;

These are declared in the `<libtorrent/socket.hpp>` header.

The `using` statements will give easy access to:

    tcp::endpoint
    udp::endpoint

Which are the endpoint types used in libtorrent. An endpoint is an address with an associated port.

For documentation on these types, please refer to the asio documentation.

## exceptions

Many functions in libtorrent have two versions, one that throws exceptions on errors and one that takes an `error_code` reference which is filled with the error code on errors.

On exceptions, libtorrent will throw `boost::system::system_error` exceptions carrying an `error_code` describing the underlying error.

### translating error codes

The error_code::message() function will typically return a localized error string, for system errors. That is, errors that belong to the generic or system category.

Errors that belong to the libtorrent error category are not localized however, they are only available in English. In order to translate libtorrent errors, compare the error category of the `error_code` object against `lt::libtorrent_category()`, and if matches, you know the error code refers to the list above. You can provide your own mapping from error code to string, which is localized. In this case, you cannot rely on `error_code::message()` to generate your strings.

The numeric values of the errors are part of the API and will stay the same, although new error codes may be appended at the end.

Here's a simple example of how to translate error codes:

    std::string error_code_to_string(boost::system::error_code const& ec)
    {
            if (ec.category() != lt::libtorrent_category())
            {
                    return ec.message();
            }
            // the error is a libtorrent error

            int code = ec.value();
            static const char const* swedish[] =
            {
                    "inget fel",
                    "en fil i torrenten kolliderar med en fil fran en annan torrent",
                    "hash check misslyckades",
                    "torrentfilen ar inte en dictionary",
                    "'info'-nyckeln saknas eller ar korrupt i torrentfilen",
                    "'info'-faltet ar inte en dictionary",
                    "'piece length' faltet saknas eller ar korrupt i torrentfilen",
                    "torrentfilen saknar namnfaltet",
                    "ogiltigt namn i torrentfilen (kan vara en attack)",
                    // ... more strings here
            };

            // use the default error string in case we don't have it
            // in our translated list
            if (code < 0 || code >= sizeof(swedish)/sizeof(swedish[0]))
                    return ec.message();

            return swedish[code];
    }

## magnet links

Magnet links are URIs that includes an info-hash, a display name and optionally a tracker url. The idea behind magnet links is that an end user can click on a link in a browser and have it handled by a bittorrent application, to start a download, without any .torrent file.

The format of the magnet URI is:

magnet:?xt=urn:btih: Base16 encoded info-hash [ &dn= name of download ] [ &tr= tracker URL ]*

In order to download just the metadata (.torrent file) from a magnet link, set the torrent_flags::upload_mode flag in add_torrent_params before adding the it.

In this case, when the metadata is received from the swarm, the torrent will still be running, but it will disconnect the majority of peers (since connections to peers that already have the metadata are redundant). It will keep seeding the metadata only.

Note that this doesn't prevent empty files from being created, if the torrent contains any. If you need to prevent that, you can either set `file_priority` to a long list of zeros (since the number of files is not known in advance), or set `save_path` to an invalid path.

## queuing

libtorrent supports queuing. Queuing is a mechanism to automatically pause and resume torrents based on certain criteria. The criteria depends on the overall state the torrent is in (checking, downloading or seeding).

To opt-out of the queuing logic, make sure your torrents are added with the torrent_flags::auto_managed bit cleared from `add_torrent_params::flags`. Or call torrent_handle::unset_flags() and pass in torrent_flags::auto_managed on the torrent handle.

The overall purpose of the queuing logic is to improve performance under arbitrary torrent downloading and seeding load. For example, if you want to download 100 torrents on a limited home connection, you improve performance by downloading them one at a time (or maybe two at a time), over downloading them all in parallel. The benefits are:

- the average completion time of a torrent is half of what it would be if all downloaded in parallel.
- The amount of upload capacity is more likely to reach the reciprocation rate of your peers, and is likely to improve your return on investment (download to upload ratio)
- your disk I/O load is likely to be more local which may improve I/O performance and decrease fragmentation.

There are fundamentally 3 separate queues:

- checking torrents
- downloading torrents
- seeding torrents

Every torrent that is not seeding has a queue number associated with it, this is its place in line to be started. See torrent_status::queue_position.

On top of the limits of each queue, there is an over arching limit, set in settings_pack::active_limit. The auto manager will never start more than this number of torrents (with one exception described below). Non-auto-managed torrents are exempt from this logic, and not counted.

At a regular interval, torrents are checked if there needs to be any re-ordering of which torrents are active and which are queued. This interval can be controlled via settings_pack::auto_manage_interval.

For queuing to work, resume data needs to be saved and restored for all torrents. See torrent_handle::save_resume_data().

### queue position

The torrents in the front of the queue are started and the rest are ordered by their queue position. Any newly added torrent is placed at the end of the queue. Once a torrent is removed or turns into a seed, its queue position is -1 and all torrents that used to be after it in the queue, decreases their position in order to fill the gap.

The queue positions are always contiguous, in a sequence without any gaps.

Lower queue position means closer to the front of the queue, and will be started sooner than torrents with higher queue positions.

To query a torrent for its position in the queue, or change its position, see: torrent_handle::queue_position(), torrent_handle::queue_position_up(), torrent_handle::queue_position_down(), torrent_handle::queue_position_top() and torrent_handle::queue_position_bottom().

### checking queue

The checking queue affects torrents in the torrent_status::checking or torrent_status::allocating state that are auto-managed.

The checking queue will make sure that (of the torrents in its queue) no more than settings_pack::active_checking_limit torrents are started at any given time. Once a torrent completes checking and moves into a different state, the next in line will be started for checking.

Any torrent added force-started or force-stopped (i.e. the auto managed flag is not set), will not be subject to this limit and they will all check independently and in parallel.

Once a torrent completes the checking of its files, or resume data, it will be put in the queue for downloading and potentially start downloading immediately. In order to add a torrent and check its files without starting the download, it can be added in `stop_when_ready` mode. See add_torrent_params::flag_stop_when_ready. This flag will stop the torrent once it is ready to start downloading.

This is conceptually the same as waiting for the `torrent_checked_alert` and then call:

    h.set_flags(torrent_flags::paused, torrent_flags::paused | torrent_flags::auto_managed);

With the important distinction that it entirely avoids the brief window where the torrent is in downloading state.

### downloading queue

Similarly to the checking queue, the downloading queue will make sure that no more than settings_pack::active_downloads torrents are in the downloading state at any given time.

The torrent_status::queue_position is used again here to determine who is next in line to be started once a downloading torrent completes or is stopped/removed.

### seeding queue

The seeding queue does not use torrent_status::queue_position to determine which torrent to seed. Instead, it estimates the demand for the torrent to be seeded. A torrent with few other seeds and many downloaders is assumed to have a higher demand of more seeds than one with many seeds and few downloaders.

It limits the number of started seeds to settings_pack::active_seeds.

On top of this basic bias, seed priority can be controller by specifying a seed ratio (the upload to download ratio), a seed-time ratio (the download time to seeding time ratio) and a seed-time (the absolute time to be seeding a torrent). Until all those targets are hit, the torrent will be prioritized for seeding.

Among torrents that have met their seed target, torrents where we don't know of any other seed take strict priority.

In order to avoid flapping, torrents that were started less than 30 minutes ago also have priority to keep seeding.

Finally, for torrents where none of the above apply, they are prioritized based on the download to seed ratio.

The relevant settings to control these limits are settings_pack::share_ratio_limit, settings_pack::seed_time_ratio_limit and settings_pack::seed_time_limit.

### queuing options

In addition to simply starting and stopping torrents, the queuing mechanism can have more fine grained control of the resources used by torrents.

#### half-started torrents

In addition to the downloading and seeding limits, there are limits on actions torrents perform. The downloading and seeding limits control whether peers are allowed at all, and if peers are not allowed, torrents are stopped and don't do anything. If peers are allowed, torrents may:

1. announce to trackers
2. announce to the DHT
3. announce to local peer discovery (local service discovery)

Each of those actions are associated with a cost and hence may need a separate limit. These limits are controlled by settings_pack::active_tracker_limit, settings_pack::active_dht_limit and settings_pack::active_lsd_limit respectively.

Specifically, announcing to a tracker is typically cheaper than announcing to the DHT. settings_pack::active_dht_limit will limit the number of torrents that are allowed to announce to the DHT. The highest priority ones will, and the lower priority ones won't. The will still be considered started though, and any incoming peers will still be accepted.

If you do not wish to impose such limits (basically, if you do not wish to have half-started torrents) make sure to set these limits to -1 (infinite).

#### prefer seeds

In the case where `active_downloads` + `active_seeds` > `active_limit`, there's an ambiguity whether the downloads should be satisfied first or the seeds. To disambiguate this case, the settings_pack::auto_manage_prefer_seeds determines whether seeds are preferred or not.

#### inactive torrents

Torrents that are not transferring any bytes (downloading or uploading) have a relatively low cost to be started. It's possible to exempt such torrents from the download and seed queues by setting settings_pack::dont_count_slow_torrents to true.

Since it sometimes may take a few minutes for a newly started torrent to find peers and be unchoked, or find peers that are interested in requesting data, torrents are not considered inactive immediately. There must be an extended period of no transfers before it is considered inactive and exempt from the queuing limits.

## fast resume

The fast resume mechanism is a way to remember which pieces are downloaded and where they are put between sessions. You can generate fast resume data by calling save_resume_data() on torrent_handle. You can then save this data to disk and use it when resuming the torrent. libtorrent will not check the piece hashes then, and rely on the information given in the fast-resume data. The fast-resume data also contains information about which blocks, in the unfinished pieces, were downloaded, so it will not have to start from scratch on the partially downloaded pieces.

To use the fast-resume data you pass it to read_resume_data(), which will return an add_torrent_params object. Fields of this object can then be altered before passing it to async_add_torrent() or add_torrent(). The session will then skip the time consuming checks. It may have to do the checking anyway, if the fast-resume data is corrupt or doesn't fit the storage for that torrent.

### file format

The file format is a bencoded dictionary containing the following fields:

`file-format` | string: "libtorrent resume file"
`info-hash` | string, the info hash of the torrent this data is saved for.
`pieces` | A string with piece flags, one character per piece. Bit 1 means we have that piece. Bit 2 means we have verified that this piece is correct. This only applies when the torrent is in seed_mode.
`total_uploaded` | integer. The number of bytes that have been uploaded in total for this torrent.
`total_downloaded` | integer. The number of bytes that have been downloaded in total for this torrent.
`active_time` | integer. The number of seconds this torrent has been active. i.e. not paused.
`seeding_time` | integer. The number of seconds this torrent has been active and seeding.
`last_upload` | integer. The number of seconds since epoch when we last uploaded payload to a peer on this torrent.
`last_download` | integer. The number of seconds since epoch when we last downloaded payload from a peer on this torrent.
`upload_rate_limit` | integer. In case this torrent has a per-torrent upload rate limit, this is that limit. In bytes per second.
`download_rate_limit` | integer. The download rate limit for this torrent in case one is set, in bytes per second.
`max_connections` | integer. The max number of peer connections this torrent may have, if a limit is set.
`max_uploads` | integer. The max number of unchoked peers this torrent may have, if a limit is set.
`file_priority` | list of integers. One entry per file in the torrent. Each entry is the priority of the file with the same index.
`piece_priority` | string of bytes. Each byte is interpreted as an integer and is the priority of that piece.
`seed_mode` | integer. 1 if the torrent is in seed mode, 0 otherwise.
`upload_mode` | integer. 1 if the torrent_flags::upload_mode is set.
`share_mode` | integer. 1 if the torrent_flags::share_mode is set.
`apply_ip_filter` | integer. 1 if the torrent_flags::apply_ip_filter is set.
`paused` | integer. 1 if the torrent is paused, 0 otherwise.
`auto_managed` | integer. 1 if the torrent is auto managed, otherwise 0.
`super_seeding` | integer. 1 if the torrent_flags::super_seeding is set.
`sequential_download` | integer. 1 if the torrent is in sequential download mode, 0 otherwise.
`stop_when_ready` | integer. 1 if the torrent_flags::stop_when_ready is set.
`disable_dht` | integer. 1 if the torrent_flags::disable_dht is set.
`disable_lsd` | integer. 1 if the torrent_flags::disable_lsd is set.
`disable_pex` | integer. 1 if the torrent_flags::disable_pex is set.
`trackers` | list of lists of strings. The top level list lists all tracker tiers. Each second level list is one tier of trackers.
`mapped_files` | list of strings. If any file in the torrent has been renamed, this entry contains a list of all the filenames. In the same order as in the torrent file.
`url-list` | list of strings. List of url-seed URLs used by this torrent. The URLs are expected to be properly encoded and not contain any illegal url characters.
`httpseeds` | list of strings. List of HTTP seed URLs used by this torrent. The URLs are expected to be properly encoded and not contain any illegal url characters.
`merkle tree` | string. In case this torrent is a merkle torrent, this is a string containing the entire merkle tree, all nodes, including the root and all leaves. The tree is not necessarily complete, but complete enough to be able to send any piece that we have, indicated by the have bitmask.
`save_path` | string. The save path where this torrent was saved. This is especially useful when moving torrents with move_storage() since this will be updated.
`peers` | string. This string contains IPv4 and port pairs of peers we were connected to last session. The endpoints are in compact representation. 4 bytes IPv4 address followed by 2 bytes port. Hence, the length of this string should be divisible by 6.
`banned_peers` | string. This string has the same format as `peers` but instead represent IPv4 peers that we have banned.
`peers6` | string. This string contains IPv6 and port pairs of peers we were connected to last session. The endpoints are in compact representation. 16 bytes IPv6 address followed by 2 bytes port. The length of this string should be divisible by 18.
`banned_peers6` | string. This string has the same format as `peers6` but instead represent IPv6 peers that we have banned.
`info` | If this field is present, it should be the info-dictionary of the torrent this resume data is for. Its SHA-1 hash must match the one in the `info-hash` field. When present, the torrent is loaded from here, meaning the torrent can be added purely from resume data (no need to load the .torrent file separately). This may have performance advantages.
`unfinished` | list of dictionaries. Each dictionary represents an piece, and has the following layout:
`piece` | integer, the index of the piece this entry refers to.
`bitmask` | string, a binary bitmask representing the blocks that have been downloaded in this piece.
`adler32` | The adler32 checksum of the data in the blocks specified by `bitmask`.
`allocation` | The allocation mode for the storage. Can be either `allocate` or `sparse`.

## storage allocation

There are two modes in which storage (files on disk) are allocated in libtorrent.

1. The traditional full allocation mode, where the entire files are filled up with zeros before anything is downloaded. Files are allocated on demand, the first time anything is written to them. The main benefit of this mode is that it avoids creating heavily fragmented files.
2. The sparse allocation, sparse files are used, and pieces are downloaded directly to where they belong. This is the recommended (and default) mode.

### sparse allocation

On filesystems that supports sparse files, this allocation mode will only use as much space as has been downloaded.

The main drawback of this mode is that it may create heavily fragmented files.

> - It does not require an allocation pass on startup.

### full allocation

When a torrent is started in full allocation mode, the disk-io thread will make sure that the entire storage is allocated, and fill any gaps with zeros. It will of course still check for existing pieces and fast resume data. The main drawbacks of this mode are:

> - It may take longer to start the torrent, since it will need to fill the files with zeros. This delay is linear to the size of the download.
> - The download may occupy unnecessary disk space between download sessions.
> - Disk caches usually perform poorly with random access to large files and may slow down the download some.

The benefits of this mode are:

> - Downloaded pieces are written directly to their final place in the files and the total number of disk operations will be fewer and may also play nicer to the filesystem file allocation, and reduce fragmentation.
> - No risk of a download failing because of a full disk during download, once all files have been created.

## HTTP seeding

There are two kinds of HTTP seeding. One with that assumes a smart (and polite) client and one that assumes a smart server. These are specified in BEP 19 and BEP 17 respectively.

libtorrent supports both. In the libtorrent source code and API, BEP 19 URLs are typically referred to as url seeds and BEP 17 URLs are typically referred to as HTTP seeds.

The libtorrent implementation of BEP 19 assumes that, if the URL ends with a slash ('/'), the filename should be appended to it in order to request pieces from that file. The way this works is that if the torrent is a single-file torrent, only that filename is appended. If the torrent is a multi-file torrent, the torrent's name '/' the file name is appended. This is the same directory structure that libtorrent will download torrents into.

There is limited support for HTTP redirects. In case some files are redirected to different hosts, the files must be piece aligned or padded to be piece aligned.

## piece picker

The piece picker in libtorrent has the following features:

- rarest first
- sequential download
- random pick
- reverse order picking
- parole mode
- prioritize partial pieces
- prefer whole pieces
- piece affinity by speed category
- piece priorities

### internal representation

It is optimized by, at all times, keeping a list of pieces ordered by rarity, randomly shuffled within each rarity class. This list is organized as a single vector of contiguous memory in RAM, for optimal memory locality and to eliminate heap allocations and frees when updating rarity of pieces.

Expensive events, like a peer joining or leaving, are evaluated lazily, since it's cheaper to rebuild the whole list rather than updating every single piece in it. This means as long as no blocks are picked, peers joining and leaving is no more costly than a single peer joining or leaving. Of course the special cases of peers that have all or no pieces are optimized to not require rebuilding the list.

### picker strategy

The normal mode of the picker is of course rarest first, meaning pieces that few peers have are preferred to be downloaded over pieces that more peers have. This is a fundamental algorithm that is the basis of the performance of bittorrent. However, the user may set the piece picker into sequential download mode. This mode simply picks pieces sequentially, always preferring lower piece indices.

When a torrent starts out, picking the rarest pieces means increased risk that pieces won't be completed early (since there are only a few peers they can be downloaded from), leading to a delay of having any piece to offer to other peers. This lack of pieces to trade, delays the client from getting started into the normal tit-for-tat mode of bittorrent, and will result in a long ramp-up time. The heuristic to mitigate this problem is to, for the first few pieces, pick random pieces rather than rare pieces. The threshold for when to leave this initial picker mode is determined by settings_pack::initial_picker_threshold.

### reverse order

An orthogonal setting is reverse order, which is used for snubbed peers. Snubbed peers are peers that appear very slow, and might have timed out a piece request. The idea behind this is to make all snubbed peers more likely to be able to do download blocks from the same piece, concentrating slow peers on as few pieces as possible. The reverse order means that the most common pieces are picked, instead of the rarest pieces (or in the case of sequential download, the last pieces, instead of the first).

### parole mode

Peers that have participated in a piece that failed the hash check, may be put in parole mode. This means we prefer downloading a full piece from this peer, in order to distinguish which peer is sending corrupt data. Whether to do this is or not is controlled by settings_pack::use_parole_mode.

In parole mode, the piece picker prefers picking one whole piece at a time for a given peer, avoiding picking any blocks from a piece any other peer has contributed to (since that would defeat the purpose of parole mode).

### prioritize partial pieces

This setting determines if partially downloaded or requested pieces should always be preferred over other pieces. The benefit of doing this is that the number of partial pieces is minimized (and hence the turn-around time for downloading a block until it can be uploaded to others is minimized). It also puts less stress on the disk cache, since fewer partial pieces need to be kept in the cache. Whether or not to enable this is controlled by setting_pack::prioritize_partial_pieces.

The main benefit of not prioritizing partial pieces is that the rarest first algorithm gets to have more influence on which pieces are picked. The picker is more likely to truly pick the rarest piece, and hence improving the performance of the swarm.

This setting is turned on automatically whenever the number of partial pieces in the piece picker exceeds the number of peers we're connected to times 1.5. This is in order to keep the waste of partial pieces to a minimum, but still prefer rarest pieces.

### prefer whole pieces

The prefer whole pieces setting makes the piece picker prefer picking entire pieces at a time. This is used by web connections (both http seeding standards), in order to be able to coalesce the small bittorrent requests to larger HTTP requests. This significantly improves performance when downloading over HTTP.

It is also used by peers that are downloading faster than a certain threshold. The main advantage is that these peers will better utilize the other peer's disk cache, by requesting all blocks in a single piece, from the same peer.

This threshold is controlled by the settings_pack::whole_pieces_threshold setting.

TODO: piece priorities

## Multi-homed hosts

The settings_pack::listen_interfaces setting is used to specify which interfaces/IP addresses to listen on, and accept incoming connections via.

Each item in `listen_interfaces` is an IP address or a device name, followed by a listen port number. Each item (called `listen_socket_t`) will have the following objects associated with it:

- a listen socket accepting incoming TCP connections
- a UDP socket: 1. to accept incoming uTP connections 2. to run a DHT instance on 3. to announce to UDP trackers from 4. a SOCKS5 UDP tunnel (if applicable)
- a listen address and netmask, describing the network the sockets are bound to
- a Local service discovery object, broadcasting to the specified subnet
- a NAT-PMP/PCP port mapper (if applicable), to map ports on the gateway for the specified subnet.
- a UPnP port mapper (if applicable), to map ports on any
- `InternetGatewayDevice` found on the specified local subnet.

A `listen_socket_t` item may be specified to only be a local network (with the `l` suffix). Such listen socket will only be used to talk to peers and trackers within the same local network. The netmask defining the network is queried from the operating system by enumerating network interfaces.

An item that's considered to be "local network" will not be used to announce to trackers outside of that network. For example, `10.0.0.2:6881l` is marked as "local network" and it will only be used as the source address announcing to a tracker if the tracker is also within the same local network (e.g. `10.0.0.0/8`).

The NAT-PMP/PCP and UPnP port mapper objects are only created for networks that are expected to be externally available (i.e. not "local network"). If there are multiple subnets connected to the internet, they will have separate port mappings.

### expanding device names

If a device name is specified, libtorrent will expand it to the IP addresses associated with that device, but also retain the device name in order to attempt to bind the listen sockets to that specific device.

### expanding unspecified addresses

If an IP address is the unspecified address (i.e. `0.0.0.0` or `::`), libtorrent will expand it to specific IP addresses. This expansion will enumerate all addresses it can find for the corresponding address family. The expanded IP addresses are considered "local network" if any of the following conditions are met:

- the IP address is in a known link-local range
- the IP address is in a known loopback range
- the item the IP address was expanded from was marked local (`l`)
- the network interface has the `loopback` flag set
- NONE of the following conditions are met: 1. the IP address is in a globally reachable IP address range 2. the network interface has the `point-to-point` flag set 3. the routing table contains a route for at least one global internet address (e.g. a default route) for the address family of the expanded IP that points to the network interface of the expanded IP.

### routing

A `listen_socket_t` item is considered able to route to a destination address if any of these hold:

- the destination address falls inside its subnet (i.e. interface address masked by netmask is the same as the destination address masked by the netmask).
- the `listen_socket_t` does not have the "local network" flag set, and the address family matches the destination address.

The ability to route to an address is used when determining whether to announce to a tracker from a `listen_socket_t` and whether to open a SOCKS5 UDP tunnel for a `listen_socket_t`.

Note that the actual IP stack routing table is not considered for this purpose. This mechanism is to determine which IP addresses should be announced to trackers.

### tracker announces

Trackers are announced to from all network interfaces listening for incoming connections. However, interfaces that cannot be used to reach the tracker, such as loopback, are not used as the source address for announces. A `listen_socket_t` item that can route to at least one of the tracker IP addresses will be used as the source address for an announce. Each such item will also have an announce_endpoint item associated with it, in the tracker list.

If a tracker can be reached on a loopback address, then the loopback interface will be used to announce to that tracker. But under normal circumstances, loopback will not be used for announcing to trackers.

For more details, see BEP 7.

### SOCKS5 UDP tunnels

When using a SOCKS5 proxy, each interface that can route to one of the SOCKS5 proxy's addresses will be used to open a UDP tunnel, via that proxy. For example, if a client has both IPv4 and IPv6 connectivity, but the socks5 proxy only resolves to IPv4, only the IPv4 address will have a UDP tunnel. In that case, the IPv6 connection will not be used, since it cannot use the proxy.

## rate based choking

libtorrent supports a choking algorithm that automatically determines the number of upload slots (unchoke slots) based on the upload rate to peers. It is controlled by the settings_pack::choking_algorithm setting. The settings_pack::unchoke_slots_limit is ignored in this mode.

The algorithm is designed to stay stable, and not oscillate the number of upload slots.

The initial rate threshold is set to settings_pack::rate_choker_initial_threshold.

It sorts all peers by on the rate at which we are uploading to them.

1. Compare the fastest peer against the initial threshold.
2. Increment the threshold by 2 kiB/s.
3. The next fastest peer is compared against the threshold. If the peer rate is higher than the threshold. goto 2
4. Terminate. The number of peers visited is the number of unchoke slots, but never less than 2.

In other words, the more upload slots you have, the higher rate does the slowest unchoked peer upload at in order to open another slot.

## predictive piece announce

In order to improve performance, libtorrent supports a feature called `predictive piece announce`. When enabled, it will make libtorrent announce that we have pieces to peers, before we truly have them. The most important case is to announce a piece as soon as it has been downloaded and passed the hash check, but not yet been written to disk. In this case, there is a risk the piece will fail to be written to disk, in which case we won't have the piece anymore, even though we announced it to peers.

The other case is when we're very close to completing the download of a piece and assume it will pass the hash check, we can announce it to peers to make it available one round-trip sooner than otherwise. This lets libtorrent start uploading the piece to interested peers immediately when the piece complete, instead of waiting one round-trip for the peers to request it.

This makes for the implementation slightly more complicated, since piece will have more states and more complicated transitions. For instance, a piece could be:

1. hashed but not fully written to disk
2. fully written to disk but not hashed
3. not fully downloaded
4. downloaded and hash checked

Once a piece is fully downloaded, the hash check could complete before any of the write operations or it could complete after all write operations are complete.

## peer classes

The peer classes feature in libtorrent allows a client to define custom groups of peers and rate limit them individually. Each such group is called a peer class. There are a few default peer classes that are always created:

- global - all peers belong to this class, except peers on the local network
- local peers - all peers on the local network belongs to this class TCP peers
- tcp class - all peers connected over TCP belong to this class

The TCP peers class is used by the uTP/TCP balancing logic, if it's enabled, to throttle TCP peers. The global and local classes are used to adjust the global rate limits.

When the rate limits are adjusted for a specific torrent, a class is created implicitly for that torrent.

The default peer class IDs are defined as enums in the `session` class:

    enum {
            global_peer_class_id,
            tcp_peer_class_id,
            local_peer_class_id
    };

The default peer classes are automatically created on session startup, and configured to apply to each respective type of connection. There's nothing preventing a client from reconfiguring the peer class ip- and type filters to disable or customize which peers they apply to. See set_peer_class_filter() and set_peer_class_type_filter().

A peer class can be considered a more general form of labels that some clients have. Peer classes however are not just applied to torrents, but ultimately the peers.

Peer classes can be created with the create_peer_class() call (on the session object), and deleted with the delete_peer_class() call.

Peer classes are configured with the set_peer_class() get_peer_class() calls.

Custom peer classes can be assigned based on the peer's IP address or the type of transport protocol used. See set_peer_class_filter() and set_peer_class_type_filter() for more information.

### peer class examples

Here are a few examples of common peer class operations.

To make the global rate limit apply to local peers as well, update the IP-filter based peer class assignment:

    std::uint32_t const mask = 1 << lt::session::global_peer_class_id;
    ip_filter f;

    // for every IPv4 address, assign the global peer class
    f.add_rule(make_address("0.0.0.0"), make_address("255.255.255.255"), mask);

    // for every IPv6 address, assign the global peer class
    f.add_rule(make_address("::")
            , make_address("ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff")
            , mask);
    ses.set_peer_class_filter(f);

To make uTP sockets exempt from rate limiting:

    peer_class_type_filter flt = ses.get_peer_class_type_filter();
    // filter out the global and local peer class for uTP sockets, if these
    // classes are set by the IP filter
    flt.disallow(peer_class_type_filter::utp_socket, session::global_peer_class_id);
    flt.disallow(peer_class_type_filter::utp_socket, session::local_peer_class_id);

    // this filter should not add the global or local peer class to utp sockets
    flt.remove(peer_class_type_filter::utp_socket, session::global_peer_class_id);
    flt.remove(peer_class_type_filter::utp_socket, session::local_peer_class_id);

    ses.set_peer_class_type_filter(flt);

To make all peers on the internal network not subject to throttling:

    std::uint32_t const mask = 1 << lt::session::global_peer_class_id;
    ip_filter f;

    // for every IPv4 address, assign the global peer class
    f.add_rule(make_address("0.0.0.0"), make_address("255.255.255.255"), mask);

    // for every address on the local metwork, set the mask to 0
    f.add_rule(make_address("10.0.0.0"), make_address("10.255.255.255"), 0);
    ses.set_peer_class_filter(f);

## SSL torrents

Torrents may have an SSL root (CA) certificate embedded in them. Such torrents are called SSL torrents. An SSL torrent talks to all bittorrent peers over SSL. The protocols are layered like this:

During the SSL handshake, both peers need to authenticate by providing a certificate that is signed by the CA certificate found in the .torrent file. These peer certificates are expected to be provided to peers through some other means than bittorrent. Typically by a peer generating a certificate request which is sent to the publisher of the torrent, and the publisher returning a signed certificate.

In libtorrent, set_ssl_certificate() in torrent_handle is used to tell libtorrent where to find the peer certificate and the private key for it. When an SSL torrent is loaded, the torrent_need_cert_alert is posted to remind the user to provide a certificate.

A peer connecting to an SSL torrent MUST provide the SNI TLS extension (server name indication). The server name is the hex encoded info-hash of the torrent to connect to. This is required for the client accepting the connection to know which certificate to present.

SSL connections are accepted on a separate socket from normal bittorrent connections. To enable support for SSL torrents, add a listen interface to the settings_pack::listen_interfaces setting with the `s` suffix. For example:

    0.0.0.0:6881,0.0.0.0:6882s

That will listen for normal bittorrent connections on port 6881 and for SSL torrent connections on port 6882.

This feature is only available if libtorrent is build with openssl support (`TORRENT_USE_OPENSSL`) and requires at least OpenSSL version 1.0, since it needs SNI support.

Peer certificates must have at least one SubjectAltName field of type DNSName. At least one of the fields must exactly match the name of the torrent. This is a byte-by-byte comparison, the UTF-8 encoding must be identical (i.e. there's no unicode normalization going on). This is the recommended way of verifying certificates for HTTPS servers according to RFC 2818. Note the difference that for torrents only DNSName fields are taken into account (not IP address fields). The most specific (i.e. last) Common Name field is also taken into account if no SubjectAltName did not match.

If any of these fields contain a single asterisk ("*"), the certificate is considered covering any torrent, allowing it to be reused for any torrent.

The purpose of matching the torrent name with the fields in the peer certificate is to allow a publisher to have a single root certificate for all torrents it distributes, and issue separate peer certificates for each torrent. A peer receiving a certificate will not necessarily be able to access all torrents published by this root certificate (only if it has a "star cert").

### testing

To test incoming SSL connections to an SSL torrent, one can use the following openssl command:

    openssl s_client -cert <peer-certificate>.pem -key <peer-private-key>.pem -CAfile \
       <torrent-cert>.pem -debug -connect 127.0.0.1:4433 -tls1 -servername <info-hash>

To create a root certificate, the Distinguished Name (DN) is not taken into account by bittorrent peers. You still need to specify something, but from libtorrent's point of view, it doesn't matter what it is. libtorrent only makes sure the peer certificates are signed by the correct root certificate.

One way to create the certificates is to use the `CA.sh` script that comes with openssl, like this (don't forget to enter a common Name for the certificate):

    CA.sh -newca
    CA.sh -newreq
    CA.sh -sign

The torrent certificate is located in `./demoCA/private/demoCA/cacert.pem`, this is the pem file to include in the .torrent file.

The peer's certificate is located in `./newcert.pem` and the certificate's private key in `./newkey.pem`.

## session statistics

libtorrent provides a mechanism to query performance and statistics counters from its internals.

The statistics consists of two fundamental types. counters and gauges. A counter is a monotonically increasing value, incremented every time some event occurs. For example, every time the network thread wakes up because a socket became readable will increment a counter. Another example is every time a socket receives n bytes, a counter is incremented by n.

Counters are the most flexible of metrics. It allows the program to sample the counter at any interval, and calculate average rates of increments to the counter. Some events may be rare and need to be sampled over a longer period in order to get useful rates, where other events may be more frequent and evenly distributed that sampling it frequently yields useful values. Counters also provides accurate overall counts. For example, converting samples of a download rate into a total transfer count is not accurate and takes more samples. Converting an increasing counter into a rate is easy and flexible.

Gauges measure the instantaneous state of some kind. This is used for metrics that are not counting events or flows, but states that can fluctuate. For example, the number of torrents that are currently being downloaded.

It's important to know whether a value is a counter or a gauge in order to interpret it correctly. In order to query libtorrent for which counters and gauges are available, call session_stats_metrics(). This will return metadata about the values available for inspection in libtorrent. It will include whether a value is a counter or a gauge. The key information it includes is the index used to extract the actual measurements for a specific counter or gauge.

In order to take a sample, call post_session_stats() in the session object. This will result in a session_stats_alert being posted. In this alert object, there is an array of values, these values make up the sample. The value index in the stats metric indicates which index the metric's value is stored in.

The mapping between metric and value is not stable across versions of libtorrent. Always query the metrics first, to find out the index at which the value is stored, before interpreting the values array in the session_stats_alert. The mapping will not change during the runtime of your process though, it's tied to a specific libtorrent version. You only have to query the mapping once on startup (or every time `libtorrent.so` is loaded, if it's done dynamically).

The available stats metrics are:

name | type
--- | ---
peer.error_peers | counter
peer.disconnected_peers | counter

`error_peers` is the total number of peer disconnects caused by an error (not initiated by this client) and disconnected initiated by this client (`disconnected_peers`).

name | type
--- | ---
peer.eof_peers | counter
peer.connreset_peers | counter
peer.connrefused_peers | counter
peer.connaborted_peers | counter
peer.notconnected_peers | counter
peer.perm_peers | counter
peer.buffer_peers | counter
peer.unreachable_peers | counter
peer.broken_pipe_peers | counter
peer.addrinuse_peers | counter
peer.no_access_peers | counter
peer.invalid_arg_peers | counter
peer.aborted_peers | counter

these counters break down the peer errors into more specific categories. These errors are what the underlying transport reported (i.e. TCP or uTP)

name | type
--- | ---
peer.piece_requests | counter
peer.max_piece_requests | counter
peer.invalid_piece_requests | counter
peer.choked_piece_requests | counter
peer.cancelled_piece_requests | counter
peer.piece_rejects | counter

the total number of incoming piece requests we've received followed by the number of rejected piece requests for various reasons. max_piece_requests mean we already had too many outstanding requests from this peer, so we rejected it. cancelled_piece_requests are ones where the other end explicitly asked for the piece to be rejected.

name | type
--- | ---
peer.error_incoming_peers | counter
peer.error_outgoing_peers | counter

these counters break down the peer errors into whether they happen on incoming or outgoing peers.

name | type
--- | ---
peer.error_rc4_peers | counter
peer.error_encrypted_peers | counter

these counters break down the peer errors into whether they happen on encrypted peers (just encrypted handshake) and rc4 peers (full stream encryption). These can indicate whether encrypted peers are more or less likely to fail

name | type
--- | ---
peer.error_tcp_peers | counter
peer.error_utp_peers | counter

these counters break down the peer errors into whether they happen on uTP peers or TCP peers. these may indicate whether one protocol is more error prone

name | type
--- | ---
peer.connect_timeouts | counter
peer.uninteresting_peers | counter
peer.timeout_peers | counter
peer.no_memory_peers | counter
peer.too_many_peers | counter
peer.transport_timeout_peers | counter
peer.num_banned_peers | counter
peer.banned_for_hash_failure | counter
peer.connection_attempts | counter
peer.connection_attempt_loops | counter
peer.boost_connection_attempts | counter
peer.missed_connection_attempts | counter
peer.no_peer_connection_attempts | counter
peer.incoming_connections | counter

these counters break down the reasons to disconnect peers.

name | type
--- | ---
peer.num_tcp_peers | gauge
peer.num_socks5_peers | gauge
peer.num_http_proxy_peers | gauge
peer.num_utp_peers | gauge
peer.num_i2p_peers | gauge
peer.num_ssl_peers | gauge
peer.num_ssl_socks5_peers | gauge
peer.num_ssl_http_proxy_peers | gauge
peer.num_ssl_utp_peers | gauge
peer.num_peers_half_open | gauge
peer.num_peers_connected | gauge
peer.num_peers_up_interested | gauge
peer.num_peers_down_interested | gauge
peer.num_peers_up_unchoked_all | gauge
peer.num_peers_up_unchoked_optimistic | gauge
peer.num_peers_up_unchoked | gauge
peer.num_peers_down_unchoked | gauge
peer.num_peers_up_requests | gauge
peer.num_peers_down_requests | gauge
peer.num_peers_end_game | gauge
peer.num_peers_up_disk | gauge
peer.num_peers_down_disk | gauge

the number of peer connections for each kind of socket. `num_peers_half_open` counts half-open (connecting) peers, no other count includes those peers. `num_peers_up_unchoked_all` is the total number of unchoked peers, whereas `num_peers_up_unchoked` only are unchoked peers that count against the limit (i.e. excluding peers that are unchoked because the limit doesn't apply to them). `num_peers_up_unchoked_optimistic` is the number of optimistically unchoked peers.

name | type
--- | ---
net.on_read_counter | counter
net.on_write_counter | counter
net.on_tick_counter | counter
net.on_lsd_counter | counter
net.on_lsd_peer_counter | counter
net.on_udp_counter | counter
net.on_accept_counter | counter
net.on_disk_queue_counter | counter
net.on_disk_counter | counter

These counters count the number of times the network thread wakes up for each respective reason. If these counters are very large, it may indicate a performance issue, causing the network thread to wake up too ofte, wasting CPU. mitigate it by increasing buffers and limits for the specific trigger that wakes up the thread.

name | type
--- | ---
net.sent_payload_bytes | counter
net.sent_bytes | counter
net.sent_ip_overhead_bytes | counter
net.sent_tracker_bytes | counter
net.recv_payload_bytes | counter
net.recv_bytes | counter
net.recv_ip_overhead_bytes | counter
net.recv_tracker_bytes | counter

total number of bytes sent and received by the session

name | type
--- | ---
net.limiter_up_queue | gauge
net.limiter_down_queue | gauge

the number of sockets currently waiting for upload and download bandwidth from the rate limiter.

name | type
--- | ---
net.limiter_up_bytes | gauge
net.limiter_down_bytes | gauge

the number of upload and download bytes waiting to be handed out from the rate limiter.

name | type
--- | ---
net.recv_failed_bytes | counter

the number of bytes downloaded that had to be discarded because they failed the hash check

name | type
--- | ---
net.recv_redundant_bytes | counter

the number of downloaded bytes that were discarded because they were downloaded multiple times (from different peers)

name | type
--- | ---
net.has_incoming_connections | gauge

is false by default and set to true when the first incoming connection is established this is used to know if the client is behind NAT or not.

name | type
--- | ---
ses.num_checking_torrents | gauge
ses.num_stopped_torrents | gauge
ses.num_upload_only_torrents | gauge
ses.num_downloading_torrents | gauge
ses.num_seeding_torrents | gauge
ses.num_queued_seeding_torrents | gauge
ses.num_queued_download_torrents | gauge
ses.num_error_torrents | gauge

these gauges count the number of torrents in different states. Each torrent only belongs to one of these states. For torrents that could belong to multiple of these, the most prominent in picked. For instance, a torrent with an error counts as an error-torrent, regardless of its other state.

name | type
--- | ---
ses.non_filter_torrents | gauge

the number of torrents that don't have the IP filter applied to them.

name | type
--- | ---
ses.num_piece_passed | counter
ses.num_piece_failed | counter
ses.num_have_pieces | counter
ses.num_total_pieces_added | counter

these count the number of times a piece has passed the hash check, the number of times a piece was successfully written to disk and the number of total possible pieces added by adding torrents. e.g. when adding a torrent with 1000 piece, num_total_pieces_added is incremented by 1000.

name | type
--- | ---
ses.num_unchoke_slots | gauge

the number of allowed unchoked peers

name | type
--- | ---
ses.num_outstanding_accept | gauge

the number of listen sockets that are currently accepting incoming connections

name | type
--- | ---
ses.num_incoming_choke | counter
ses.num_incoming_unchoke | counter
ses.num_incoming_interested | counter
ses.num_incoming_not_interested | counter
ses.num_incoming_have | counter
ses.num_incoming_bitfield | counter
ses.num_incoming_request | counter
ses.num_incoming_piece | counter
ses.num_incoming_cancel | counter
ses.num_incoming_dht_port | counter
ses.num_incoming_suggest | counter
ses.num_incoming_have_all | counter
ses.num_incoming_have_none | counter
ses.num_incoming_reject | counter
ses.num_incoming_allowed_fast | counter
ses.num_incoming_ext_handshake | counter
ses.num_incoming_pex | counter
ses.num_incoming_metadata | counter
ses.num_incoming_extended | counter
ses.num_outgoing_choke | counter
ses.num_outgoing_unchoke | counter
ses.num_outgoing_interested | counter
ses.num_outgoing_not_interested | counter
ses.num_outgoing_have | counter
ses.num_outgoing_bitfield | counter
ses.num_outgoing_request | counter
ses.num_outgoing_piece | counter
ses.num_outgoing_cancel | counter
ses.num_outgoing_dht_port | counter
ses.num_outgoing_suggest | counter
ses.num_outgoing_have_all | counter
ses.num_outgoing_have_none | counter
ses.num_outgoing_reject | counter
ses.num_outgoing_allowed_fast | counter
ses.num_outgoing_ext_handshake | counter
ses.num_outgoing_pex | counter
ses.num_outgoing_metadata | counter
ses.num_outgoing_extended | counter

bittorrent message counters. These counters are incremented every time a message of the corresponding type is received from or sent to a bittorrent peer.

name | type
--- | ---
ses.waste_piece_timed_out | counter
ses.waste_piece_cancelled | counter
ses.waste_piece_unknown | counter
ses.waste_piece_seed | counter
ses.waste_piece_end_game | counter
ses.waste_piece_closing | counter

the number of wasted downloaded bytes by reason of the bytes being wasted.

name | type
--- | ---
picker.piece_picker_partial_loops | counter
picker.piece_picker_suggest_loops | counter
picker.piece_picker_sequential_loops | counter
picker.piece_picker_reverse_rare_loops | counter
picker.piece_picker_rare_loops | counter
picker.piece_picker_rand_start_loops | counter
picker.piece_picker_rand_loops | counter
picker.piece_picker_busy_loops | counter

the number of pieces considered while picking pieces

name | type
--- | ---
picker.reject_piece_picks | counter
picker.unchoke_piece_picks | counter
picker.incoming_redundant_piece_picks | counter
picker.incoming_piece_picks | counter
picker.end_game_piece_picks | counter
picker.snubbed_piece_picks | counter
picker.interesting_piece_picks | counter
picker.hash_fail_piece_picks | counter

This breaks down the piece picks into the event that triggered it

name | type
--- | ---
disk.write_cache_blocks | gauge
disk.read_cache_blocks | gauge

These gauges indicate how many blocks are currently in use as dirty disk blocks (`write_cache_blocks`) and read cache blocks, respectively. deprecates `cache_status::read_cache_size`. The sum of these gauges deprecates `cache_status::cache_size`.

name | type
--- | ---
disk.request_latency | gauge

the number of microseconds it takes from receiving a request from a peer until we're sending the response back on the socket.

name | type
--- | ---
disk.pinned_blocks | gauge
disk.disk_blocks_in_use | gauge

`disk_blocks_in_use` indicates how many disk blocks are currently in use, either as dirty blocks waiting to be written or blocks kept around in the hope that a peer will request it or in a peer send buffer. This gauge deprecates `cache_status::total_used_buffers`.

name | type
--- | ---
disk.queued_disk_jobs | gauge
disk.num_running_disk_jobs | gauge
disk.num_read_jobs | gauge
disk.num_write_jobs | gauge
disk.num_jobs | gauge
disk.blocked_disk_jobs | gauge
disk.num_writing_threads | gauge
disk.num_running_threads | gauge

`queued_disk_jobs` is the number of disk jobs currently queued, waiting to be executed by a disk thread. Deprecates `cache_status::job_queue_length`.

name | type
--- | ---
disk.queued_write_bytes | gauge
disk.arc_mru_size | gauge
disk.arc_mru_ghost_size | gauge
disk.arc_mfu_size | gauge
disk.arc_mfu_ghost_size | gauge
disk.arc_write_size | gauge
disk.arc_volatile_size | gauge

the number of bytes we have sent to the disk I/O thread for writing. Every time we hear back from the disk I/O thread with a completed write job, this is updated to the number of bytes the disk I/O thread is actually waiting for to be written (as opposed to bytes just hanging out in the cache)

name | type
--- | ---
disk.num_blocks_written | counter
disk.num_blocks_read | counter

the number of blocks written and read from disk in total. A block is 16 kiB. `num_blocks_written` and `num_blocks_read` deprecates `cache_status::blocks_written` and `cache_status::blocks_read` respectively.

name | type
--- | ---
disk.num_blocks_hashed | counter

the total number of blocks run through SHA-1 hashing

name | type
--- | ---
disk.num_blocks_cache_hits | counter

the number of blocks read from the disk cache Deprecates `cache_info::blocks_read_hit`.

name | type
--- | ---
disk.num_write_ops | counter
disk.num_read_ops | counter

the number of disk I/O operation for reads and writes. One disk operation may transfer more then one block. These counters deprecates `cache_status::writes` and `cache_status::reads`.

name | type
--- | ---
disk.num_read_back | counter

the number of blocks that had to be read back from disk in order to hash a piece (when verifying against the piece hash)

name | type
--- | ---
disk.disk_read_time | counter
disk.disk_write_time | counter
disk.disk_hash_time | counter
disk.disk_job_time | counter

cumulative time spent in various disk jobs, as well as total for all disk jobs. Measured in microseconds

name | type
--- | ---
disk.num_fenced_read | gauge
disk.num_fenced_write | gauge
disk.num_fenced_hash | gauge
disk.num_fenced_move_storage | gauge
disk.num_fenced_release_files | gauge
disk.num_fenced_delete_files | gauge
disk.num_fenced_check_fastresume | gauge
disk.num_fenced_save_resume_data | gauge
disk.num_fenced_rename_file | gauge
disk.num_fenced_stop_torrent | gauge
disk.num_fenced_flush_piece | gauge
disk.num_fenced_flush_hashed | gauge
disk.num_fenced_flush_storage | gauge
disk.num_fenced_trim_cache | gauge
disk.num_fenced_file_priority | gauge
disk.num_fenced_load_torrent | gauge
disk.num_fenced_clear_piece | gauge
disk.num_fenced_tick_storage | gauge

for each kind of disk job, a counter of how many jobs of that kind are currently blocked by a disk fence

name | type
--- | ---
dht.dht_nodes | gauge

The number of nodes in the DHT routing table

name | type
--- | ---
dht.dht_node_cache | gauge

The number of replacement nodes in the DHT routing table

name | type
--- | ---
dht.dht_torrents | gauge

the number of torrents currently tracked by our DHT node

name | type
--- | ---
dht.dht_peers | gauge

the number of peers currently tracked by our DHT node

name | type
--- | ---
dht.dht_immutable_data | gauge

the number of immutable data items tracked by our DHT node

name | type
--- | ---
dht.dht_mutable_data | gauge

the number of mutable data items tracked by our DHT node

name | type
--- | ---
dht.dht_allocated_observers | gauge

the number of RPC observers currently allocated

name | type
--- | ---
dht.dht_messages_in | counter
dht.dht_messages_out | counter

the total number of DHT messages sent and received

name | type
--- | ---
dht.dht_messages_in_dropped | counter

the number of incoming DHT requests that were dropped. There are a few different reasons why incoming DHT packets may be dropped:

1. there wasn't enough send quota to respond to them.
2. the Denial of service logic kicked in, blocking the peer
3. ignore_dark_internet is enabled, and the packet came from a non-public IP address
4. the bencoding of the message was invalid

name | type
--- | ---
dht.dht_messages_out_dropped | counter

the number of outgoing messages that failed to be sent

name | type
--- | ---
dht.dht_bytes_in | counter
dht.dht_bytes_out | counter

the total number of bytes sent and received by the DHT

name | type
--- | ---
dht.dht_ping_in | counter
dht.dht_ping_out | counter
dht.dht_find_node_in | counter
dht.dht_find_node_out | counter
dht.dht_get_peers_in | counter
dht.dht_get_peers_out | counter
dht.dht_announce_peer_in | counter
dht.dht_announce_peer_out | counter
dht.dht_get_in | counter
dht.dht_get_out | counter
dht.dht_put_in | counter
dht.dht_put_out | counter
dht.dht_sample_infohashes_in | counter
dht.dht_sample_infohashes_out | counter

the number of DHT messages we've sent and received by kind.

name | type
--- | ---
dht.dht_invalid_announce | counter
dht.dht_invalid_get_peers | counter
dht.dht_invalid_find_node | counter
dht.dht_invalid_put | counter
dht.dht_invalid_get | counter
dht.dht_invalid_sample_infohashes | counter

the number of failed incoming DHT requests by kind of request

name | type
--- | ---
utp.utp_packet_loss | counter
utp.utp_timeout | counter
utp.utp_packets_in | counter
utp.utp_packets_out | counter
utp.utp_fast_retransmit | counter
utp.utp_packet_resend | counter
utp.utp_samples_above_target | counter
utp.utp_samples_below_target | counter
utp.utp_payload_pkts_in | counter
utp.utp_payload_pkts_out | counter
utp.utp_invalid_pkts_in | counter
utp.utp_redundant_pkts_in | counter

uTP counters. Each counter represents the number of time each event has occurred.

name | type
--- | ---
utp.num_utp_idle | gauge
utp.num_utp_syn_sent | gauge
utp.num_utp_connected | gauge
utp.num_utp_fin_sent | gauge
utp.num_utp_close_wait | gauge
utp.num_utp_deleted | gauge

the number of uTP sockets in each respective state

name | type
--- | ---
sock_bufs.socket_send_size3 | counter
sock_bufs.socket_send_size4 | counter
sock_bufs.socket_send_size5 | counter
sock_bufs.socket_send_size6 | counter
sock_bufs.socket_send_size7 | counter
sock_bufs.socket_send_size8 | counter
sock_bufs.socket_send_size9 | counter
sock_bufs.socket_send_size10 | counter
sock_bufs.socket_send_size11 | counter
sock_bufs.socket_send_size12 | counter
sock_bufs.socket_send_size13 | counter
sock_bufs.socket_send_size14 | counter
sock_bufs.socket_send_size15 | counter
sock_bufs.socket_send_size16 | counter
sock_bufs.socket_send_size17 | counter
sock_bufs.socket_send_size18 | counter
sock_bufs.socket_send_size19 | counter
sock_bufs.socket_send_size20 | counter
sock_bufs.socket_recv_size3 | counter
sock_bufs.socket_recv_size4 | counter
sock_bufs.socket_recv_size5 | counter
sock_bufs.socket_recv_size6 | counter
sock_bufs.socket_recv_size7 | counter
sock_bufs.socket_recv_size8 | counter
sock_bufs.socket_recv_size9 | counter
sock_bufs.socket_recv_size10 | counter
sock_bufs.socket_recv_size11 | counter
sock_bufs.socket_recv_size12 | counter
sock_bufs.socket_recv_size13 | counter
sock_bufs.socket_recv_size14 | counter
sock_bufs.socket_recv_size15 | counter
sock_bufs.socket_recv_size16 | counter
sock_bufs.socket_recv_size17 | counter
sock_bufs.socket_recv_size18 | counter
sock_bufs.socket_recv_size19 | counter
sock_bufs.socket_recv_size20 | counter

the buffer sizes accepted by socket send and receive calls respectively. The larger the buffers are, the more efficient, because it reqire fewer system calls per byte. The size is 1 << n, where n is the number at the end of the counter name. i.e. 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384, 32768, 65536, 131072, 262144, 524288, 1048576 bytes

name | type
--- | ---
tracker.num_queued_tracker_announces | gauge

if the outstanding tracker announce limit is reached, tracker announces are queued, to be issued when an announce slot opens up. this measure the number of tracker announces currently in the queue

## glossary

The libtorrent documentation use words that are bittorrent terms of art. This section defines some of these words. For an overview of what bittorrent is and how it works, see these slides. For an introduction to the bittorrent DHT, see this presentation.

announce
  The act of telling a tracker or the DHT network about the existence of oneself and how other peers can connect, by specifying port one is listening on.
block
  A subset of a piece. Almost always 16 kiB of payload, unless the piece size is smaller. This is the granularity file payload is requested from peers on the network.
DHT
  The distributed hash table is a cross-swarm, world-wide network of bittorrent peers. It's loosely connected, implementing the Kademlia protocol. Its purpose is to act as a tracker. Peers can announce their presence to nodes on the DHT and other peers can discover them to join the swarm.
HTTP tracker
  A tracker that uses the HTTP protocol for announces.
info dictionary
  The subset of a torrent file that describes piece hashes and file names. This is the only mandatory part necessary to join the swarm (network of peers) for the torrent.
info hash
  The hash of the info dictionary. This uniquely identifies a torrent and is used by the protocol to ensure peers talking to each other agree on which swarm they are participating in. Sometimes spelled info-hash.
leecher
  A peer that is still interested in downloading more pieces for the torrent. It is not a seed.
magnet link
  A URI containing the info hash for a torrent, allowing peers to join its swarm. May optionally contain a display name, trackers and web seeds. Typically magnet links rely on peers joining the swarm via the DHT.
metadata
  Synonymous to a torrent file
peer
  A computer running bittorrent client software that participates in the network for a particular torrent/set of files.
piece
  The smallest number of bytes that can be validated when downloading (no longer the case in bittorrent V2). The smallest part of the files that can be advertised to other peers. The size of a piece is determined by the info dictionary inside the torrent file.
seed
  A computer running bittorrent client software that has the complete files for a specific torrent, able to share any piece for that file with other peers in the network
swarm
  The network of peers participating in sharing and downloading of a specific torrent.
torrent
  May refer to a torrent file or the swarm (network of peers) created around the torrent file.
torrent file
  A file ending in .torrent describing the content of a set of files (but not containing the content). Importantly, it contains hashes of all files, split up into pieces. It may optionally contain references to trackers and nodes on the DHT network to aid peers in joining the network of peers sharing these files.
tracker
  A server peers can announce to and receive other peers back belonging to the same swarm. Trackers are used to introduce peers to each other, within a swarm. When announcing, the info hash of the torrent is included. Trackers can introduce peers to any info-hash that's specified, given other peers also use the same tracker. Some trackers restrict which info hashes they support based on a white list.
UDP tracker
  A tracker that uses a UDP based protocol for announces.
web seed
  A web server that is acting a seed, providing access to all pieces of all files over HTTP. This is an extension that client software may or may not support.

Author: | Arvid Norberg, arvid@libtorrent.org
Version: | 1.2.9

## tuning libtorrent

libtorrent expose most parameters used in the bittorrent engine for customization through the settings_pack. This makes it possible to test and tweak the parameters for certain algorithms to make a client that fits a wide range of needs. From low memory embedded devices to servers seeding thousands of torrents. The default settings in libtorrent are tuned for an end-user bittorrent client running on a normal desktop computer.

This document describes techniques to benchmark libtorrent performance and how parameters are likely to affect it.

## profiling

libtorrent is instrumented with a number of counters and gauges you can have access to via the `session_stats_alert`. First, enable these alerts in the alert mask:

    settings_pack p;
    p.set_int(settings_mask::alert_mask, alert::stats_notification);
    ses.apply_settings(p);

Then print alerts to a file:

    std::vector<alert*> alerts;
    ses.pop_alerts(&alerts);

    for (auto* a : alerts) {
            std::cout << a->message() << "\n";
    }

If you want to separate generic alerts from session stats, you can filter on the alert category in the alert, `alert::category()`.

The alerts with data will have the type session_stats_alert and there is one session_log_alert that will be posted on startup containing the column names for all metrics. Logging this line will greatly simplify interpreting the output.

The python scrip in `tools/parse_session_stats.py` can parse the resulting file and produce graphs of relevant stats. It requires gnuplot.

## reducing memory footprint

These are things you can do to reduce the memory footprint of libtorrent. You get some of this by basing your default settings_pack on the min_memory_usage() setting preset function.

Keep in mind that lowering memory usage will affect performance, always profile and benchmark your settings to determine if it's worth the trade-off.

The typical buffer usage of libtorrent, for a single download, with the cache size set to 256 blocks (256 * 16 kiB = 4 MiB) is:

    read cache:      128.6 (2058 kiB)
    write cache:     103.5 (1656 kiB)
    receive buffers: 7.3   (117 kiB)
    send buffers:    4.8   (77 kiB)
    hash temp:       0.001 (19 Bytes)

The receive buffers is proportional to the number of connections we make, and is limited by the total number of connections in the session (default is 200).

The send buffers is proportional to the number of upload slots that are allowed in the session. The default is auto configured based on the observed upload rate.

The read and write cache can be controlled (see section below).

The "hash temp" entry size depends on whether or not hashing is optimized for speed or memory usage. In this test run it was optimized for memory usage.

### disable disk cache

The bulk of the memory libtorrent will use is used for the disk cache. To save the absolute most amount of memory, you can disable the cache by setting settings_pack::cache_size to 0. You might want to consider using the cache but just disable caching read operations. You do this by settings settings_pack::use_read_cache to false. This is the main factor in how much memory will be used by the client. Keep in mind that you will degrade performance by disabling the cache. You should benchmark the disk access in order to make an informed trade-off.

### remove torrents

Torrents that have been added to libtorrent will inevitably use up memory, even when it's paused. A paused torrent will not use any peer connection objects or any send or receive buffers though. Any added torrent holds the entire .torrent file in memory, it also remembers the entire list of peers that it's heard about (which can be fairly long unless it's capped). It also retains information about which blocks and pieces we have on disk, which can be significant for torrents with many pieces.

If you need to minimize the memory footprint, consider removing torrents from the session rather than pausing them. This will likely only make a difference when you have a very large number of torrents in a session.

The downside of removing them is that they will no longer be auto-managed. Paused auto managed torrents are scraped periodically, to determine which torrents are in the greatest need of seeding, and libtorrent will prioritize to seed those.

### socket buffer sizes

You can make libtorrent explicitly set the kernel buffer sizes of all its peer sockets. If you set this to a low number, you may see reduced throughput, especially for high latency connections. It is however an opportunity to save memory per connection, and might be worth considering if you have a very large number of peer connections. This memory will not be visible in your process, this sets the amount of kernel memory is used for your sockets.

Change this by setting settings_pack::recv_socket_buffer_size and settings_pack::send_socket_buffer_size.

### peer list size

The default maximum for the peer list is 4000 peers. For IPv4 peers, each peer entry uses 32 bytes, which ends up using 128 kB per torrent. If seeding 4 popular torrents, the peer lists alone uses about half a megabyte.

The default limit is the same for paused torrents as well, so if you have a large number of paused torrents (that are popular) it will be even more significant.

If you're short of memory, you should consider lowering the limit. 500 is probably enough. You can do this by setting settings_pack::max_peerlist_size to the max number of peers you want in a torrent's peer list. This limit applies per torrent. For 5 torrents, the total number of peers in peer lists will be 5 times the setting.

You should also lower the same limit but for paused torrents. It might even make sense to set that even lower, since you only need a few peers to start up while waiting for the tracker and DHT to give you fresh ones. The max peer list size for paused torrents is set by settings_pack::max_paused_peerlist_size.

The drawback of lowering this number is that if you end up in a position where the tracker is down for an extended period of time, your only hope of finding live peers is to go through your list of all peers you've ever seen. Having a large peer list will also help increase performance when starting up, since the torrent can start connecting to peers in parallel with connecting to the tracker.

### send buffer watermark

The send buffer watermark controls when libtorrent will ask the disk I/O thread to read blocks from disk, and append it to a peer's send buffer.

When the send buffer has fewer than or equal number of bytes as settings_pack::send_buffer_watermark, the peer will ask the disk I/O thread for more data to send. The trade-off here is between wasting memory by having too much data in the send buffer, and hurting send rate by starving out the socket, waiting for the disk read operation to complete.

If your main objective is memory usage and you're not concerned about being able to achieve high send rates, you can set the watermark to 9 bytes. This will guarantee that no more than a single (16 kiB) block will be on the send buffer at a time, for all peers. This is the least amount of memory possible for the send buffer.

You should benchmark your max send rate when adjusting this setting. If you have a very fast disk, you are less likely see a performance hit.

### reduce executable size

Compilers generally add a significant number of bytes to executables that make use of C++ exceptions. By disabling exceptions (-fno-exceptions on GCC), you can reduce the executable size with up to 45%. In order to build without exception support, you need to patch parts of boost.

Also make sure to optimize for size when compiling.

Another way of reducing the executable size is to disable code that isn't used. There are a number of `TORRENT_*` macros that control which features are included in libtorrent. If these macros are used to strip down libtorrent, make sure the same macros are defined when building libtorrent as when linking against it. If these are different the structures will look different from the libtorrent side and from the client side and memory corruption will follow.

One, probably, safe macro to define is `TORRENT_NO_DEPRECATE` which removes all deprecated functions and struct members. As long as no deprecated functions are relied upon, this should be a simple way to eliminate a little bit of code.

For all available options, see the building libtorrent section.

## high performance seeding

In the case of a high volume seed, there are two main concerns. Performance and scalability. This translates into high send rates, and low memory and CPU usage per peer connection.

### file pool

libtorrent keeps an LRU file cache. Each file that is opened, is stuck in the cache. The main purpose of this is because of anti-virus software that hooks on file-open and file close to scan the file. Anti-virus software that does that will significantly increase the cost of opening and closing files. However, for a high performance seed, the file open/close might be so frequent that it becomes a significant cost. It might therefore be a good idea to allow a large file descriptor cache. Adjust this though settings_pack::file_pool_size.

Don't forget to set a high rlimit for file descriptors in your process as well. This limit must be high enough to keep all connections and files open.

### disk cache

You typically want to set the cache size to as high as possible. The settings_pack::cache_size is specified in 16 kiB blocks. Since you're seeding, the cache would be useless unless you also set settings_pack::use_read_cache to true.

In order to increase the possibility of read cache hits, set the settings_pack::cache_expiry to a large number. This won't degrade anything as long as the client is only seeding, and not downloading any torrents.

There's a guided cache mode. This means the size of the read cache line that's stored in the cache is determined based on the upload rate to the peer that triggered the read operation. The idea being that slow peers don't use up a disproportional amount of space in the cache. This is enabled through settings_pack::guided_read_cache.

In cases where the assumption is that the cache is only used as a read-ahead, and that no other peer will ever request the same block while it's still in the cache, the read cache can be set to be volatile. This means that every block that is requested out of the read cache is removed immediately. This saves a significant amount of cache space which can be used as read-ahead for other peers. To enable volatile read cache, set settings_pack::volatile_read_cache to true.

### uTP-TCP mixed mode

libtorrent supports uTP, which has a delay based congestion controller. In order to avoid having a single TCP bittorrent connection completely starve out any uTP connection, there is a mixed mode algorithm. This attempts to detect congestion on the uTP peers and throttle TCP to avoid it taking over all bandwidth. This balances the bandwidth resources between the two protocols. When running on a network where the bandwidth is in such an abundance that it's virtually infinite, this algorithm is no longer necessary, and might even be harmful to throughput. It is advised to experiment with the settings_pack::mixed_mode_algorithm, setting it to settings_pack::prefer_tcp. This setting entirely disables the balancing and un-throttles all connections. On a typical home connection, this would mean that none of the benefits of uTP would be preserved (the modem's send buffer would be full at all times) and uTP connections would for the most part be squashed by the TCP traffic.

### send buffer low watermark

libtorrent uses a low watermark for send buffers to determine when a new piece should be requested from the disk I/O subsystem, to be appended to the send buffer. The low watermark is determined based on the send rate of the socket. It needs to be large enough to not draining the socket's send buffer before the disk operation completes.

The watermark is bound to a max value, to avoid buffer sizes growing out of control. The default max send buffer size might not be enough to sustain very high upload rates, and you might have to increase it. It's specified in bytes in settings_pack::send_buffer_watermark.

### peers

First of all, in order to allow many connections, set the global connection limit high, settings_pack::connections_limit. Also set the upload rate limit to infinite, settings_pack::upload_rate_limit, 0 means infinite.

When dealing with a large number of peers, it might be a good idea to have slightly stricter timeouts, to get rid of lingering connections as soon as possible.

There are a couple of relevant settings: settings_pack::request_timeout, settings_pack::peer_timeout and settings_pack::inactivity_timeout.

For seeds that are critical for a delivery system, you most likely want to allow multiple connections from the same IP. That way two people from behind the same NAT can use the service simultaneously. This is controlled by settings_pack::allow_multiple_connections_per_ip.

In order to always unchoke peers, turn off automatic unchoke by setting settings_pack::choking_algorithm to settings_pack::fixed_slot_choker and set the number of upload slots to a large number via settings_pack::unchoke_slots_limit, or use -1 (which means infinite).

### torrent limits

To seed thousands of torrents, you need to increase the settings_pack::active_limit and settings_pack::active_seeds.

### SHA-1 hashing

When downloading at very high rates, it is possible to have the CPU be the bottleneck for passing every downloaded byte through SHA-1. In order to enable calculating SHA-1 hashes in parallel, on multi-core systems, set settings_pack::aio_threads to the number of threads libtorrent should perform I/O and do SHA-1 hashing in. Only if that thread is close to saturating one core does it make sense to increase the number of threads.

## scalability

In order to make more efficient use of the libtorrent interface when running a large number of torrents simultaneously, one can use the `session::get_torrent_status()` call together with `session::post_torrent_updates()`. Keep in mind that every call into libtorrent that return some value have to block your thread while posting a message to the main network thread and then wait for a response. Calls that don't return any data will simply post the message and then immediately return, performing the work asynchronously. The time this takes might become significant once you reach a few hundred torrents, depending on how many calls you make to each torrent and how often. `session::get_torrent_status()` lets you query the status of all torrents in a single call. This will actually loop through all torrents and run a provided predicate function to determine whether or not to include it in the returned vector.

To use `session::post_torrent_updates()` torrents need to have the `flag_update_subscribe` flag set. When post_torrent_updates() is called, a state_update_alert alert is posted, with all the torrents that have updated since the last time this function was called. The client have to keep its own state of all torrents, and update it based on this alert.

## benchmarking

There is a bunch of built-in instrumentation of libtorrent that can be used to get an insight into what it's doing and how well it performs. This instrumentation is enabled by defining preprocessor symbols when building.

There are also a number of scripts that parses the log files and generates graphs (requires gnuplot and python).

## understanding the disk threads

This section is somewhat outdated, there are potentially more than one disk thread

All disk operations are funneled through a separate thread, referred to as the disk thread. The main interface to the disk thread is a queue where disk jobs are posted, and the results of these jobs are then posted back on the main thread's io_service.

A disk job is essentially one of:

1. write this block to disk, i.e. a write job. For the most part this is just a
     matter of sticking the block in the disk cache, but if we've run out of cache space or completed a whole piece, we'll also flush blocks to disk. This is typically very fast, since the OS just sticks these buffers in its write cache which will be flushed at a later time, presumably when the drive head will pass the place on the platter where the blocks go.
2. read this block from disk. The first thing that happens is we look in the
     cache to see if the block is already in RAM. If it is, we'll return immediately with this block. If it's a cache miss, we'll have to hit the disk. Here we decide to defer this job. We find the physical offset on the drive for this block and insert the job in an ordered queue, sorted by the physical location. At a later time, once we don't have any more non-read jobs left in the queue, we pick one read job out of the ordered queue and service it. The order we pick jobs out of the queue is according to an elevator cursor moving up and down along the ordered queue of read jobs. If we have enough space in the cache we'll read read_cache_line_size number of blocks and stick those in the cache. This defaults to 32 blocks. If the system supports asynchronous I/O (Windows, Linux, Mac OS X, BSD, Solars for instance), jobs will be issued immediately to the OS. This especially increases read throughput, since the OS has a much greater flexibility to reorder the read jobs.

Other disk job consist of operations that needs to be synchronized with the disk I/O, like renaming files, closing files, flushing the cache, updating the settings etc. These are relatively rare though.

## contributions

If you have added instrumentation for some part of libtorrent that is not covered here, or if you have improved any of the parser scrips, please consider contributing it back to the project.

If you have run tests and found that some algorithm or default value in libtorrent are suboptimal, please contribute that knowledge back as well, to allow us to improve the library.

If you have additional suggestions on how to tune libtorrent for any specific use case, please let us know and we'll update this document.

# Upgrading to libtorrent 1.2

libtorrent version 1.2 comes with some significant updates in the API. This document summarizes the changes affecting library users.

## C++98 no longer supported

With libtorrent 1.2, C++98 is no longer supported, you need a compiler capable of at least C++11 to build libtorrent.

This also means libtorrent types now support move.

## listen interfaces

There's a subtle change in how the `listen_interfaces` setting is interpreted in 1.2 compared to 1.1.

In libtorrent-1.1, if you listen to `0.0.0.0:6881` (which was the default), not only would an IPv4 listen socket be opened (bound to INADDR_ANY) but also an IPv6 socket would be opened.

In libtorrent-1.2, if you listen to `0.0.0.0:6881` only the IPv4 INADDR_ANY is opened as a listen socket. If you want to listen to both IPv4 and IPv6, you need to listen to `0.0.0.0:6881,[::]:6881`.

## forward declaring libtorrent types deprecated

Clients are discouraged from forward declaring types from libtorrent. Instead, include the <libtorrent/fwd.hpp> header.

A future release will introduce ABI versioning using an inline namespace, which will break any forward declarations by clients.

There is a new namespace alias, `lt` which is shorthand for `libtorrent`. In the future, `libtorrent` will be the alias and `lt` the namespace name. With no forward declarations inside libtorrent's namespace though, there should not be any reason for clients to re-open the namespace.

## resume data handling

To significantly simplify handling of resume data, the previous way of handling it is deprecated. resume data is no longer passed in as a flat buffer in the add_torrent_params. The add_torrent_params structure itself is the resume data now.

In order to parse the bencoded fast resume file (which is still the same format, and backwards compatible) use the read_resume_data() function.

Similarly, when saving resume data, the save_resume_data_alert now has a `params` field of type add_torrent_params which contains the resume data. This object can be serialized into the bencoded form using write_resume_data().

This give the client full control over which properties should be loaded from the resume data and which should be controlled by the client directly. The flags `flag_override_resume_data`, `flag_merge_resume_trackers`, `flag_use_resume_save_path` and `flag_merge_resume_http_seeds` have all been deprecated, since they are no longer needed.

The old API is still supported as long as libtorrent is built with deprecated functions enabled (which is the default). It will be performing slightly better without deprecated functions present.

## rate_limit_utp changed defaults

The setting `rate_limit_utp` was deprecated in libtorrent 1.1. When building without deprecated features (`deprecated-functions=off`) the default behavior also changed to have rate limits apply to utp sockets too. In order to be more consistent between the two build configurations, the default value has changed to true. The new mechanism provided to apply special rate limiting rules is peer classes. In order to implement the old behavior of not rate limiting uTP peers, one can set up a peer class for all uTP peers, to make the normal peer classes not apply to them (which is where the rate limits are set).

## announce entry multi-home support

The announce_entry type now captures status on individual endpoints, as opposed to treating every tracker behind the same name as a single tracker. This means some properties has moved into the `announce_endpoint` structure, and an announce entry has 0 or more endpoints.

## alerts no longer cloneable

As part of the transition to a more efficient handling of alerts, 1.1 allocated them in a contiguous, heterogeneous, vector. This means they are no longer heap allocated nor held by a smart pointer. The `clone()` member on alerts was deprecated in 1.1 and removed in 1.2. To pass alerts across threads, instead pull out the relevant information from the alerts and pass that across.

## progress alert category

The `alert::progress_notification` category has been deprecated. Alerts posted in this category are now also posted in one of these new categories:

- `alert::block_progress_notification`
- `alert::piece_progress_notification`
- `alert::file_progress_notification`
- `alert::upload_notification`

## boost replaced by std

`boost::shared_ptr` has been replaced by `std::shared_ptr` in the libtorrent API. The same goes for `<cstdint>` types, instead of `boost::int64_t`, libtorrent now uses `std::int64_t`. Instead of `boost::array`, `std::array` is used, and `boost::function` has been replaced by `std::function`.

## strong typedefs

In order to strengthen type-safety, libtorrent now uses special types to represent certain indexes and ID types. Any integer referring to a piece index, now has the type `piece_index_t`, and indices to files in a torrent, use `file_index_t`. Similarly, time points and duration now use `time_point` and `duration` from the `<chrono>` standard library.

The specific types have typedefs at `lt::time_point` and `lt::duration`, and the clock used by libtorrent is `lt::clock_type`.`

## strongly typed flags

Enum flags have been replaced by strongly typed flags. This means their implicit conversion to and from `int` is deprecated. For example, the following expressions are deprecated:

    if ((atp.flags & add_torrent_params::flag_paused) == 0)

    atp.flags = 0;

Insted say:

    if (!(atp.flags & torrent_flags::paused))

    atp.flags = {};

(Also note that in this specific example, the flags moved out of the `add_torrent_params` structure, but this is unrelated to them also having stronger types).

## span<> and string_view

The interface has adopted `string_view` (from boost for now) and `span<>` (custom implementation for now). This means some function calls that previously took `char const*` or `std::string` may now take an `lt::string_view`. Similarly, functions that previously would take a pointer and length pair will now take a `span<>`.

## periphery utility functions no longer exported

Historically, libtorrent has exported functions not essential to its core bittorrent functionality. Such as filesystem functions like `directory`, `file` classes and `remove`, `create_directory` functions. Path manipulation functions like `combine_path`, `extension`, `split_path` etc. String manipulation functions like `from_hex` and `to_hex`. Time functions like `time_now`. These functions are no longer available to clients, and some have been removed from the library. Instead, it is recommended to use boost.filesystem or the experimental filesystem TS.

## plugins

libtorrent session plugins no longer have all callbacks called unconditionally. The plugin has to register which callbacks it's interested in receiving by returning a bitmask from `feature_flags_t implemented_features()`. The return value is documented in the plugin class.

## RSS functions removed

The deprecated RSS functions have been removed from the library interface.

Author: | Arvid Norberg, arvid@libtorrent.org
Version: | 1.2.9

home

## Core

[report issue]

### peer_class_info

Declared in "libtorrent/peer_class.hpp"

holds settings for a peer class. Used in set_peer_class() and get_peer_class() calls.

    struct peer_class_info
    {
       bool ignore_unchoke_slots;
       int connection_limit_factor;
       std::string label;
       int upload_limit;
       int download_limit;
       int upload_priority;
       int download_priority;
    };

[report issue]

ignore_unchoke_slots
  `ignore_unchoke_slots` determines whether peers should always unchoke a peer, regardless of the choking algorithm, or if it should honor the unchoke slot limits. It's used for local peers by default. If any of the peer classes a peer belongs to has this set to true, that peer will be unchoked at all times.

[report issue]

connection_limit_factor
  adjusts the connection limit (global and per torrent) that applies to this peer class. By default, local peers are allowed to exceed the normal connection limit for instance. This is specified as a percent factor. 100 makes the peer class apply normally to the limit. 200 means as long as there are fewer connections than twice the limit, we accept this peer. This factor applies both to the global connection limit and the per-torrent limit. Note that if not used carefully one peer class can potentially completely starve out all other over time.

[report issue]

label
  not used by libtorrent. It's intended as a potentially user-facing identifier of this peer class.

[report issue]

upload_limit download_limit
  transfer rates limits for the whole peer class. They are specified in bytes per second and apply to the sum of all peers that are members of this class.

[report issue]

upload_priority download_priority
  relative priorities used by the bandwidth allocator in the rate limiter. If no rate limits are in use, the priority is not used either. Priorities start at 1 (0 is not a valid priority) and may not exceed 255.

[report issue]

### peer_connection_handle

Declared in "libtorrent/peer_connection_handle.hpp"

the peer_connection_handle class provides a handle to the internal peer connection object, to be used by plugins. This is a low level interface that may not be stable across libtorrent versions

    struct peer_connection_handle
    {
       explicit peer_connection_handle (std::weak_ptr<peer_connection> impl);
       connection_type type () const;
       void add_extension (std::shared_ptr<peer_plugin>);
       peer_plugin const* find_plugin (string_view type) const;
       bool is_seed () const;
       bool upload_only () const;
       bool has_piece (piece_index_t i) const;
       peer_id const& pid () const;
       bool is_interesting () const;
       bool is_choked () const;
       bool has_peer_choked () const;
       bool is_peer_interested () const;
       void choke_this_peer ();
       void maybe_unchoke_this_peer ();
       void get_peer_info (peer_info& p) const;
       torrent_handle associated_torrent () const;
       tcp::endpoint local_endpoint () const;
       tcp::endpoint const& remote () const;
       bool is_connecting () const;
       void disconnect (error_code const& ec, operation_t op
          , disconnect_severity_t = peer_connection_interface::normal);
       bool is_outgoing () const;
       bool is_disconnecting () const;
       bool on_local_network () const;
       bool ignore_unchoke_slots () const;
       bool failed () const;
       bool should_log (peer_log_alert::direction_t direction) const;
       void peer_log (peer_log_alert::direction_t direction
          , char const* event, char const* fmt = "", ...) const TORRENT_FORMAT(4,5);
       bool can_disconnect (error_code const& ec) const;
       bool has_metadata () const;
       bool in_handshake () const;
       void send_buffer (char const* begin, int size);
       std::time_t last_seen_complete () const;
       time_point time_of_last_unchoke () const;
       bool operator== (peer_connection_handle const& o) const;
       bool operator!= (peer_connection_handle const& o) const;
       bool operator< (peer_connection_handle const& o) const;
       std::shared_ptr<peer_connection> native_handle () const;
    };

[report issue]

### bt_peer_connection_handle

Declared in "libtorrent/peer_connection_handle.hpp"

The bt_peer_connection_handle provides a handle to the internal bittorrent peer connection object to plugins. It's low level and may not be a stable API across libtorrent versions.

    struct bt_peer_connection_handle : peer_connection_handle
    {
       explicit bt_peer_connection_handle (peer_connection_handle pc);
       bool support_extensions () const;
       bool packet_finished () const;
       bool supports_encryption () const;
       void switch_recv_crypto (std::shared_ptr<crypto_plugin> crypto);
       void switch_send_crypto (std::shared_ptr<crypto_plugin> crypto);
       std::shared_ptr<bt_peer_connection> native_handle () const;
    };

[report issue]

### torrent_status

Declared in "libtorrent/torrent_status.hpp"

holds a snapshot of the status of a torrent, as queried by torrent_handle::status().

    struct torrent_status
    {
       bool operator== (torrent_status const& st) const;
       time_duration next_announce = seconds (0);

       enum state_t
       {
          checking_files,
          downloading_metadata,
          downloading,
          finished,
          seeding,
          allocating,
          checking_resume_data,
       };

       torrent_handle handle;
       error_code errc;
       file_index_t error_file  = torrent_status::error_file_none;
       static constexpr file_index_t error_file_none {-1};
       static constexpr file_index_t error_file_ssl_ctx {-3};
       static constexpr file_index_t error_file_metadata {-4};
       static constexpr file_index_t error_file_exception {-5};
       static constexpr file_index_t error_file_partfile {-6};
       std::string save_path;
       std::string name;
       std::weak_ptr<const torrent_info> torrent_file;
       std::string current_tracker;
       std::int64_t total_download  = 0;
       std::int64_t total_upload  = 0;
       std::int64_t total_payload_download  = 0;
       std::int64_t total_payload_upload  = 0;
       std::int64_t total_failed_bytes  = 0;
       std::int64_t total_redundant_bytes  = 0;
       typed_bitfield<piece_index_t> pieces;
       typed_bitfield<piece_index_t> verified_pieces;
       std::int64_t total_done  = 0;
       std::int64_t total  = 0;
       std::int64_t total_wanted_done  = 0;
       std::int64_t total_wanted  = 0;
       std::int64_t all_time_upload  = 0;
       std::int64_t all_time_download  = 0;
       std::time_t added_time  = 0;
       std::time_t completed_time  = 0;
       std::time_t last_seen_complete  = 0;
       storage_mode_t storage_mode  = storage_mode_sparse;
       float progress  = 0.f;
       int progress_ppm  = 0;
       queue_position_t queue_position {};
       int download_rate  = 0;
       int upload_rate  = 0;
       int download_payload_rate  = 0;
       int upload_payload_rate  = 0;
       int num_seeds  = 0;
       int num_peers  = 0;
       int num_complete  = -1;
       int num_incomplete  = -1;
       int list_seeds  = 0;
       int list_peers  = 0;
       int connect_candidates  = 0;
       int num_pieces  = 0;
       int distributed_full_copies  = 0;
       int distributed_fraction  = 0;
       float distributed_copies  = 0.f;
       int block_size  = 0;
       int num_uploads  = 0;
       int num_connections  = 0;
       int uploads_limit  = 0;
       int connections_limit  = 0;
       int up_bandwidth_queue  = 0;
       int down_bandwidth_queue  = 0;
       int seed_rank  = 0;
       state_t state  = checking_resume_data;
       bool need_save_resume  = false;
       bool is_seeding  = false;
       bool is_finished  = false;
       bool has_metadata  = false;
       bool has_incoming  = false;
       bool moving_storage  = false;
       bool announcing_to_trackers  = false;
       bool announcing_to_lsd  = false;
       bool announcing_to_dht  = false;
       sha1_hash info_hash;
       time_point last_upload;
       time_point last_download;
       seconds active_duration;
       seconds finished_duration;
       seconds seeding_duration;
       torrent_flags_t flags {};
    };

[report issue]

#### operator==()

    bool operator== (torrent_status const& st) const;

compares if the torrent status objects come from the same torrent. i.e. only the torrent_handle field is compared.

[report issue]

#### seconds()

    time_duration next_announce = seconds (0);

the time until the torrent will announce itself to the tracker.

[report issue]

#### enum state_t

Declared in "libtorrent/torrent_status.hpp"

name | value | description
--- | --- | ---
checking_files | 1 | The torrent has not started its download yet, and is currently checking existing files.
downloading_metadata | 2 | The torrent is trying to download metadata from peers. This implies the ut_metadata extension is in use.
downloading | 3 | The torrent is being downloaded. This is the state most torrents will be in most of the time. The progress meter will tell how much of the files that has been downloaded.
finished | 4 | In this state the torrent has finished downloading but still doesn't have the entire torrent. i.e. some pieces are filtered and won't get downloaded.
seeding | 5 | In this state the torrent has finished downloading and is a pure seeder.
allocating | 6 | If the torrent was started in full allocation mode, this indicates that the (disk) storage for the torrent is allocated.
checking_resume_data | 7 | The torrent is currently checking the fast resume data and comparing it to the files on disk. This is typically completed in a fraction of a second, but if you add a large number of torrents at once, they will queue up.

[report issue]

handle
  a handle to the torrent whose status the object represents.

[report issue]

errc
  may be set to an error code describing why the torrent was paused, in case it was paused by an error. If the torrent is not paused or if it's paused but not because of an error, this error_code is not set. if the error is attributed specifically to a file, error_file is set to the index of that file in the .torrent file.

[report issue]

error_file
  if the torrent is stopped because of an disk I/O error, this field contains the index of the file in the torrent that encountered the error. If the error did not originate in a file in the torrent, there are a few special values this can be set to: error_file_none, error_file_ssl_ctx, error_file_exception, error_file_partfile or error_file_metadata;

[report issue]

error_file_none
  special values for error_file to describe which file or component encountered the error (`errc`). the error did not occur on a file

[report issue]

error_file_ssl_ctx
  the error occurred setting up the SSL context

[report issue]

error_file_metadata
  the error occurred while loading the .torrent file via the user supplied load function

[report issue]

error_file_exception
  there was a serious error reported in this torrent. The error code or a torrent log alert may provide more information.

[report issue]

error_file_partfile
  the error occurred with the partfile

[report issue]

save_path
  the path to the directory where this torrent's files are stored. It's typically the path as was given to async_add_torrent() or add_torrent() when this torrent was started. This field is only included if the torrent status is queried with `torrent_handle::query_save_path`.

[report issue]

name
  the name of the torrent. Typically this is derived from the .torrent file. In case the torrent was started without metadata, and hasn't completely received it yet, it returns the name given to it when added to the session. See `session::add_torrent`. This field is only included if the torrent status is queried with `torrent_handle::query_name`.

[report issue]

torrent_file
  set to point to the `torrent_info` object for this torrent. It's only included if the torrent status is queried with `torrent_handle::query_torrent_file`.

[report issue]

current_tracker
  the URL of the last working tracker. If no tracker request has been successful yet, it's set to an empty string.

[report issue]

total_download total_upload
  the number of bytes downloaded and uploaded to all peers, accumulated, this session only. The session is considered to restart when a torrent is paused and restarted again. When a torrent is paused, these counters are reset to 0. If you want complete, persistent, stats, see `all_time_upload` and `all_time_download`.

[report issue]

total_payload_download total_payload_upload
  counts the amount of bytes send and received this session, but only the actual payload data (i.e the interesting data), these counters ignore any protocol overhead. The session is considered to restart when a torrent is paused and restarted again. When a torrent is paused, these counters are reset to 0.

[report issue]

total_failed_bytes
  the number of bytes that has been downloaded and that has failed the piece hash test. In other words, this is just how much crap that has been downloaded since the torrent was last started. If a torrent is paused and then restarted again, this counter will be reset.

[report issue]

total_redundant_bytes
  the number of bytes that has been downloaded even though that data already was downloaded. The reason for this is that in some situations the same data can be downloaded by mistake. When libtorrent sends requests to a peer, and the peer doesn't send a response within a certain timeout, libtorrent will re-request that block. Another situation when libtorrent may re-request blocks is when the requests it sends out are not replied in FIFO-order (it will re-request blocks that are skipped by an out of order block). This is supposed to be as low as possible. This only counts bytes since the torrent was last started. If a torrent is paused and then restarted again, this counter will be reset.

[report issue]

pieces
  a bitmask that represents which pieces we have (set to true) and the pieces we don't have. It's a pointer and may be set to 0 if the torrent isn't downloading or seeding.

[report issue]

verified_pieces
  a bitmask representing which pieces has had their hash checked. This only applies to torrents in seed mode. If the torrent is not in seed mode, this bitmask may be empty.

[report issue]

total_done
  the total number of bytes of the file(s) that we have. All this does not necessarily has to be downloaded during this session (that's `total_payload_download`).

[report issue]

total
  the total number of bytes to download for this torrent. This may be less than the size of the torrent in case there are pad files. This number only counts bytes that will actually be requested from peers.

[report issue]

total_wanted_done
  the number of bytes we have downloaded, only counting the pieces that we actually want to download. i.e. excluding any pieces that we have but have priority 0 (i.e. not wanted).

[report issue]

total_wanted
  The total number of bytes we want to download. This may be smaller than the total torrent size in case any pieces are prioritized to 0, i.e. not wanted

[report issue]

all_time_upload all_time_download
  are accumulated upload and download payload byte counters. They are saved in and restored from resume data to keep totals across sessions.

[report issue]

added_time
  the posix-time when this torrent was added. i.e. what `time(nullptr)` returned at the time.

[report issue]

completed_time
  the posix-time when this torrent was finished. If the torrent is not yet finished, this is 0.

[report issue]

last_seen_complete
  the time when we, or one of our peers, last saw a complete copy of this torrent.

[report issue]

storage_mode
  The allocation mode for the torrent. See storage_mode_t for the options. For more information, see storage allocation.

[report issue]

progress
  a value in the range [0, 1], that represents the progress of the torrent's current task. It may be checking files or downloading.

[report issue]

progress_ppm

  progress parts per million (progress * 1000000) when disabling floating point operations, this is the only option to query progress

  reflects the same value as `progress`, but instead in a range [0, 1000000] (ppm = parts per million). When floating point operations are disabled, this is the only alternative to the floating point value in progress.

[report issue]

queue_position
  the position this torrent has in the download queue. If the torrent is a seed or finished, this is -1.

[report issue]

download_rate upload_rate
  the total rates for all peers for this torrent. These will usually have better precision than summing the rates from all peers. The rates are given as the number of bytes per second.

[report issue]

download_payload_rate upload_payload_rate
  the total transfer rate of payload only, not counting protocol chatter. This might be slightly smaller than the other rates, but if projected over a long time (e.g. when calculating ETA:s) the difference may be noticeable.

[report issue]

num_seeds
  the number of peers that are seeding that this client is currently connected to.

[report issue]

num_peers
  the number of peers this torrent currently is connected to. Peer connections that are in the half-open state (is attempting to connect) or are queued for later connection attempt do not count. Although they are visible in the peer list when you call get_peer_info().

[report issue]

num_complete num_incomplete
  if the tracker sends scrape info in its announce reply, these fields will be set to the total number of peers that have the whole file and the total number of peers that are still downloading. set to -1 if the tracker did not send any scrape data in its announce reply.

[report issue]

list_seeds list_peers
  the number of seeds in our peer list and the total number of peers (including seeds). We are not necessarily connected to all the peers in our peer list. This is the number of peers we know of in total, including banned peers and peers that we have failed to connect to.

[report issue]

connect_candidates
  the number of peers in this torrent's peer list that is a candidate to be connected to. i.e. It has fewer connect attempts than the max fail count, it is not a seed if we are a seed, it is not banned etc. If this is 0, it means we don't know of any more peers that we can try.

[report issue]

num_pieces
  the number of pieces that has been downloaded. It is equivalent to: `std::accumulate(pieces->begin(), pieces->end())`. So you don't have to count yourself. This can be used to see if anything has updated since last time if you want to keep a graph of the pieces up to date.

[report issue]

distributed_full_copies
  the number of distributed copies of the torrent. Note that one copy may be spread out among many peers. It tells how many copies there are currently of the rarest piece(s) among the peers this client is connected to.

[report issue]

distributed_fraction

  tells the share of pieces that have more copies than the rarest piece(s). Divide this number by 1000 to get the fraction.

  For example, if `distributed_full_copies` is 2 and `distributed_fraction` is 500, it means that the rarest pieces have only 2 copies among the peers this torrent is connected to, and that 50% of all the pieces have more than two copies.

  If we are a seed, the piece picker is deallocated as an optimization, and piece availability is no longer tracked. In this case the distributed copies members are set to -1.

[report issue]

distributed_copies

  the number of distributed copies of the file. note that one copy may be spread out among many peers. This is a floating point representation of the distributed copies.

  the integer part tells how many copies
    there are of the rarest piece(s)
  the fractional part tells the fraction of pieces that
    have more copies than the rarest piece(s).

[report issue]

block_size
  the size of a block, in bytes. A block is a sub piece, it is the number of bytes that each piece request asks for and the number of bytes that each bit in the `partial_piece_info`'s bitset represents, see get_download_queue(). This is typically 16 kB, but it may be smaller, if the pieces are smaller.

[report issue]

num_uploads
  the number of unchoked peers in this torrent.

[report issue]

num_connections
  the number of peer connections this torrent has, including half-open connections that hasn't completed the bittorrent handshake yet. This is always >= `num_peers`.

[report issue]

uploads_limit
  the set limit of upload slots (unchoked peers) for this torrent.

[report issue]

connections_limit
  the set limit of number of connections for this torrent.

[report issue]

up_bandwidth_queue down_bandwidth_queue
  the number of peers in this torrent that are waiting for more bandwidth quota from the torrent rate limiter. This can determine if the rate you get from this torrent is bound by the torrents limit or not. If there is no limit set on this torrent, the peers might still be waiting for bandwidth quota from the global limiter, but then they are counted in the `session_status` object.

[report issue]

seed_rank
  A rank of how important it is to seed the torrent, it is used to determine which torrents to seed and which to queue. It is based on the peer to seed ratio from the tracker scrape. For more information, see queuing. Higher value means more important to seed

[report issue]

state
  the main state the torrent is in. See torrent_status::state_t.

[report issue]

need_save_resume
  true if this torrent has unsaved changes to its download state and statistics since the last resume data was saved.

[report issue]

is_seeding
  true if all pieces have been downloaded.

[report issue]

is_finished
  true if all pieces that have a priority > 0 are downloaded. There is only a distinction between finished and seeding if some pieces or files have been set to priority 0, i.e. are not downloaded.

[report issue]

has_metadata
  true if this torrent has metadata (either it was started from a .torrent file or the metadata has been downloaded). The only scenario where this can be false is when the torrent was started torrent-less (i.e. with just an info-hash and tracker ip, a magnet link for instance).

[report issue]

has_incoming
  true if there has ever been an incoming connection attempt to this torrent.

[report issue]

moving_storage
  this is true if this torrent's storage is currently being moved from one location to another. This may potentially be a long operation if a large file ends up being copied from one drive to another.

[report issue]

announcing_to_trackers announcing_to_lsd announcing_to_dht
  these are set to true if this torrent is allowed to announce to the respective peer source. Whether they are true or false is determined by the queue logic/auto manager. Torrents that are not auto managed will always be allowed to announce to all peer sources.

[report issue]

info_hash
  the info-hash for this torrent

[report issue]

last_upload last_download
  the timestamps of the last time this torrent uploaded or downloaded payload to any peer.

[report issue]

active_duration finished_duration seeding_duration
  these are cumulative counters of for how long the torrent has been in different states. active means not paused and added to session. Whether it has found any peers or not is not relevant. finished means all selected files/pieces were downloaded and available to other peers (this is always a subset of active time). seeding means all files/pieces were downloaded and available to peers. Being available to peers does not imply there are other peers asking for the payload.

[report issue]

flags
  reflects several of the torrent's flags. For more information, see `torrent_handle::flags()`.

[report issue]

### announce_endpoint

Declared in "libtorrent/announce_entry.hpp"

announces are sent to each tracker using every listen socket this class holds information about one listen socket for one tracker

    struct announce_endpoint
    {
       void reset ();
       void failed (int backoff_ratio, seconds32 retry_interval = seconds32(0));
       bool can_announce (time_point now, bool is_seed, std::uint8_t fail_limit) const;
       bool is_working () const;

       std::string message;
       error_code last_error;
       tcp::endpoint local_endpoint;
       int scrape_incomplete  = -1;
       int scrape_complete  = -1;
       int scrape_downloaded  = -1;
       std::uint8_t fails : 7;
       bool updating : 1;
       bool start_sent : 1;
       bool complete_sent : 1;
       bool enabled : 1;
    };

[report issue]

#### reset()

    void reset ();

reset announce counters and clears the started sent flag. The announce_endpoint will look like we've never talked to the tracker.

[report issue]

#### failed()

    void failed (int backoff_ratio, seconds32 retry_interval = seconds32(0));

updates the failure counter and time-outs for re-trying. This is called when the tracker announce fails.

[report issue]

#### can_announce()

    bool can_announce (time_point now, bool is_seed, std::uint8_t fail_limit) const;

returns true if we can announce to this tracker now. The current time is passed in as `now`. The `is_seed` argument is necessary because once we become a seed, we need to announce right away, even if the re-announce timer hasn't expired yet.

[report issue]

#### is_working()

    bool is_working () const;

returns true if the last time we tried to announce to this tracker succeeded, or if we haven't tried yet.

[report issue]

message
  if this tracker has returned an error or warning message that message is stored here

[report issue]

last_error
  if this tracker failed the last time it was contacted this error code specifies what error occurred

[report issue]

local_endpoint
  the local endpoint of the listen interface associated with this endpoint

[report issue]

scrape_incomplete scrape_complete scrape_downloaded
  if this tracker has returned scrape data, these fields are filled in with valid numbers. Otherwise they are set to -1. `incomplete` counts the number of current downloaders. `complete` counts the number of current peers completed the download, or "seeds". `downloaded` is the cumulative number of completed downloads.

[report issue]

fails
  the number of times in a row we have failed to announce to this tracker.

[report issue]

updating
  true while we're waiting for a response from the tracker.

[report issue]

start_sent
  set to true when we get a valid response from an announce with event=started. If it is set, we won't send start in the subsequent announces.

[report issue]

complete_sent
  set to true when we send a event=completed.

[report issue]

enabled
  set to false to not announce from this endpoint

[report issue]

### announce_entry

Declared in "libtorrent/announce_entry.hpp"

this class holds information about one bittorrent tracker, as it relates to a specific torrent.

    struct announce_entry
    {
       explicit announce_entry (string_view u);
       announce_entry (announce_entry const&);
       announce_entry ();
       announce_entry& operator= (announce_entry const&);
       ~announce_entry ();
       void reset ();
       void trim ();

       enum tracker_source
       {
          source_torrent,
          source_client,
          source_magnet_link,
          source_tex,
       };

       std::string url;
       std::string trackerid;
       std::vector<announce_endpoint> endpoints;
       std::uint8_t tier  = 0;
       std::uint8_t fail_limit  = 0;
       std::uint8_t source:4;
       bool verified:1;
    };

[report issue]

#### ~announce_entry() operator=() announce_entry()

    explicit announce_entry (string_view u);
    announce_entry (announce_entry const&);
    announce_entry ();
    announce_entry& operator= (announce_entry const&);
    ~announce_entry ();

constructs a tracker announce entry with `u` as the URL.

[report issue]

#### reset()

    void reset ();

reset announce counters and clears the started sent flag. The announce_entry will look like we've never talked to the tracker.

[report issue]

#### trim()

    void trim ();

trims whitespace characters from the beginning of the URL.

[report issue]

#### enum tracker_source

Declared in "libtorrent/announce_entry.hpp"

name | value | description
--- | --- | ---
source_torrent | 1 | the tracker was part of the .torrent file
source_client | 2 | the tracker was added programmatically via the add_tracker() function
source_magnet_link | 4 | the tracker was part of a magnet link
source_tex | 8 | the tracker was received from the swarm via tracker exchange

[report issue]

url
  tracker URL as it appeared in the torrent file

[report issue]

trackerid
  the current `&trackerid=` argument passed to the tracker. this is optional and is normally empty (in which case no trackerid is sent).

[report issue]

endpoints
  each local listen socket (endpoint) will announce to the tracker. This list contains state per endpoint.

[report issue]

tier
  the tier this tracker belongs to

[report issue]

fail_limit
  the max number of failures to announce to this tracker in a row, before this tracker is not used anymore. 0 means unlimited

[report issue]

source
  a bitmask specifying which sources we got this tracker from.

[report issue]

verified
  set to true the first time we receive a valid response from this tracker.

[report issue]

### open_file_state

Declared in "libtorrent/disk_interface.hpp"

this contains information about a file that's currently open by the libtorrent disk I/O subsystem. It's associated with a single torrent.

    struct open_file_state
    {
       file_index_t file_index;
       file_open_mode_t open_mode;
       time_point last_use;
    };

[report issue]

file_index
  the index of the file this entry refers to into the `file_storage` file list of this torrent. This starts indexing at 0.

[report issue]

open_mode

  `open_mode` is a bitmask of the file flags this file is currently opened with. These are the flags used in the `file::open()` function. For possible flags, see file_open_mode_t.

  Note that the read/write mode is not a bitmask. The two least significant bits are used to represent the read/write mode. Those bits can be masked out using the `rw_mask` constant.

[report issue]

last_use
  a (high precision) timestamp of when the file was last used.

[report issue]

### peer_class_type_filter

Declared in "libtorrent/peer_class_type_filter.hpp"

`peer_class_type_filter` is a simple container for rules for adding and subtracting peer-classes from peers. It is applied after the peer class filter is applied (which is based on the peer's IP address).

    struct peer_class_type_filter
    {
       void remove (socket_type_t const st, peer_class_t const peer_class);
       void add (socket_type_t const st, peer_class_t const peer_class);
       void disallow (socket_type_t const st, peer_class_t const peer_class);
       void allow (socket_type_t const st, peer_class_t const peer_class);
       std::uint32_t apply (socket_type_t const st, std::uint32_t peer_class_mask);

       enum socket_type_t
       {
          tcp_socket,
          utp_socket,
          ssl_tcp_socket,
          ssl_utp_socket,
          i2p_socket,
          num_socket_types,
       };
    };

[report issue]

#### add() remove()

    void remove (socket_type_t const st, peer_class_t const peer_class);
    void add (socket_type_t const st, peer_class_t const peer_class);

`add()` and `remove()` adds and removes a peer class to be added to new peers based on socket type.

[report issue]

#### disallow() allow()

    void disallow (socket_type_t const st, peer_class_t const peer_class);
    void allow (socket_type_t const st, peer_class_t const peer_class);

`disallow()` and `allow()` adds and removes a peer class to be removed from new peers based on socket type.

The `peer_class` argument cannot be greater than 31. The bitmasks representing peer classes in the `peer_class_type_filter` are 32 bits.

[report issue]

#### apply()

    std::uint32_t apply (socket_type_t const st, std::uint32_t peer_class_mask);

takes a bitmask of peer classes and returns a new bitmask of peer classes after the rules have been applied, based on the socket type argument (`st`).

[report issue]

#### enum socket_type_t

Declared in "libtorrent/peer_class_type_filter.hpp"

name | value | description
--- | --- | ---
tcp_socket | 0 | these match the socket types from socket_type.hpp shifted one down
utp_socket | 1 |
ssl_tcp_socket | 2 |
ssl_utp_socket | 3 |
i2p_socket | 4 |
num_socket_types | 5 |

[report issue]

### block_info

Declared in "libtorrent/torrent_handle.hpp"

holds the state of a block in a piece. Who we requested it from and how far along we are at downloading it.

    struct block_info
    {
       void set_peer (tcp::endpoint const& ep);
       tcp::endpoint peer () const;

       enum block_state_t
       {
          none,
          requested,
          writing,
          finished,
       };

       unsigned bytes_progress:15;
       unsigned block_size:15;
       unsigned state:2;
       unsigned num_peers:14;
    };

[report issue]

#### peer() set_peer()

    void set_peer (tcp::endpoint const& ep);
    tcp::endpoint peer () const;

The peer is the ip address of the peer this block was downloaded from.

[report issue]

#### enum block_state_t

Declared in "libtorrent/torrent_handle.hpp"

name | value | description
--- | --- | ---
none | 0 | This block has not been downloaded or requested form any peer.
requested | 1 | The block has been requested, but not completely downloaded yet.
writing | 2 | The block has been downloaded and is currently queued for being written to disk.
finished | 3 | The block has been written to disk.

[report issue]

bytes_progress
  the number of bytes that have been received for this block

[report issue]

block_size
  the total number of bytes in this block.

[report issue]

state
  the state this block is in (see block_state_t)

[report issue]

num_peers
  the number of peers that is currently requesting this block. Typically this is 0 or 1, but at the end of the torrent blocks may be requested by more peers in parallel to speed things up.

[report issue]

### partial_piece_info

Declared in "libtorrent/torrent_handle.hpp"

This class holds information about pieces that have outstanding requests or outstanding writes

    struct partial_piece_info
    {
       piece_index_t piece_index;
       int blocks_in_piece;
       int finished;
       int writing;
       int requested;
       block_info* blocks;
    };

[report issue]

piece_index
  the index of the piece in question. `blocks_in_piece` is the number of blocks in this particular piece. This number will be the same for most pieces, but the last piece may have fewer blocks than the standard pieces.

[report issue]

blocks_in_piece
  the number of blocks in this piece

[report issue]

finished
  the number of blocks that are in the finished state

[report issue]

writing
  the number of blocks that are in the writing state

[report issue]

requested
  the number of blocks that are in the requested state

[report issue]

blocks

  this is an array of `blocks_in_piece` number of items. One for each block in the piece.

  Warning

  This is a pointer that points to an array that's owned by the session object. The next time get_download_queue() is called, it will be invalidated.

[report issue]

### torrent_handle

Declared in "libtorrent/torrent_handle.hpp"

You will usually have to store your torrent handles somewhere, since it's the object through which you retrieve information about the torrent and aborts the torrent.

Warning

Any member function that returns a value or fills in a value has to be made synchronously. This means it has to wait for the main thread to complete the query before it can return. This might potentially be expensive if done from within a GUI thread that needs to stay responsive. Try to avoid querying for information you don't need, and try to do it in as few calls as possible. You can get most of the interesting information about a torrent from the torrent_handle::status() call.

The default constructor will initialize the handle to an invalid state. Which means you cannot perform any operation on it, unless you first assign it a valid handle. If you try to perform any operation on an uninitialized handle, it will throw `invalid_handle`.

Warning

All operations on a torrent_handle may throw system_error exception, in case the handle is no longer referring to a torrent. There is one exception is_valid() will never throw. Since the torrents are processed by a background thread, there is no guarantee that a handle will remain valid between two calls.

    struct torrent_handle
    {
       torrent_handle () noexcept = default;
       void add_piece (piece_index_t piece, char const* data, add_piece_flags_t flags = {}) const;
       void read_piece (piece_index_t piece) const;
       bool have_piece (piece_index_t piece) const;
       void get_peer_info (std::vector<peer_info>& v) const;
       torrent_status status (status_flags_t flags = status_flags_t::all()) const;
       void get_download_queue (std::vector<partial_piece_info>& queue) const;
       void set_piece_deadline (piece_index_t index, int deadline, deadline_flags_t flags = {}) const;
       void reset_piece_deadline (piece_index_t index) const;
       void clear_piece_deadlines () const;
       void file_progress (std::vector<std::int64_t>& progress, int flags = 0) const;
       std::vector<open_file_state> file_status () const;
       void clear_error () const;
       void replace_trackers (std::vector<announce_entry> const&) const;
       std::vector<announce_entry> trackers () const;
       void add_tracker (announce_entry const&) const;
       std::set<std::string> url_seeds () const;
       void add_url_seed (std::string const& url) const;
       void remove_url_seed (std::string const& url) const;
       void add_http_seed (std::string const& url) const;
       void remove_http_seed (std::string const& url) const;
       std::set<std::string> http_seeds () const;
       void add_extension (
          std::function<std::shared_ptr<torrent_plugin>(torrent_handle const&, void*)> const& ext
          , void* userdata = nullptr);
       bool set_metadata (span<char const> metadata) const;
       bool is_valid () const;
       void resume () const;
       void pause (pause_flags_t flags = {}) const;
       void unset_flags (torrent_flags_t flags) const;
       void set_flags (torrent_flags_t flags) const;
       torrent_flags_t flags () const;
       void set_flags (torrent_flags_t flags, torrent_flags_t mask) const;
       void flush_cache () const;
       void force_recheck () const;
       void save_resume_data (resume_data_flags_t flags = {}) const;
       bool need_save_resume_data () const;
       queue_position_t queue_position () const;
       void queue_position_down () const;
       void queue_position_up () const;
       void queue_position_top () const;
       void queue_position_bottom () const;
       void queue_position_set (queue_position_t p) const;
       void set_ssl_certificate (std::string const& certificate
          , std::string const& private_key
          , std::string const& dh_params
          , std::string const& passphrase = "");
       void set_ssl_certificate_buffer (std::string const& certificate
          , std::string const& private_key
          , std::string const& dh_params);
       storage_interface* get_storage_impl () const;
       std::shared_ptr<const torrent_info> torrent_file () const;
       void piece_availability (std::vector<int>& avail) const;
       download_priority_t piece_priority (piece_index_t index) const;
       void prioritize_pieces (std::vector<std::pair<piece_index_t, download_priority_t>> const& pieces) const;
       std::vector<download_priority_t> get_piece_priorities () const;
       void piece_priority (piece_index_t index, download_priority_t priority) const;
       void prioritize_pieces (std::vector<download_priority_t> const& pieces) const;
       std::vector<download_priority_t> get_file_priorities () const;
       void file_priority (file_index_t index, download_priority_t priority) const;
       download_priority_t file_priority (file_index_t index) const;
       void prioritize_files (std::vector<download_priority_t> const& files) const;
       void force_dht_announce () const;
       void force_reannounce (int seconds = 0, int tracker_index = -1, reannounce_flags_t = {}) const;
       void scrape_tracker (int idx = -1) const;
       void set_download_limit (int limit) const;
       int download_limit () const;
       void set_upload_limit (int limit) const;
       int upload_limit () const;
       void connect_peer (tcp::endpoint const& adr, peer_source_flags_t source = {}
          , pex_flags_t flags = pex_encryption | pex_utp | pex_holepunch) const;
       void clear_peers ();
       void set_max_uploads (int max_uploads) const;
       int max_uploads () const;
       void set_max_connections (int max_connections) const;
       int max_connections () const;
       void move_storage (std::string const& save_path
          , move_flags_t flags = move_flags_t::always_replace_files
          ) const;
       void rename_file (file_index_t index, std::string const& new_name) const;
       sha1_hash info_hash () const;
       bool operator== (const torrent_handle& h) const;
       bool operator!= (const torrent_handle& h) const;
       bool operator< (const torrent_handle& h) const;
       std::uint32_t id () const;
       std::shared_ptr<torrent> native_handle () const;

       enum file_progress_flags_t
       {
          piece_granularity,
       };

       static constexpr add_piece_flags_t overwrite_existing  = 0_bit;
       static constexpr status_flags_t query_distributed_copies  = 0_bit;
       static constexpr status_flags_t query_accurate_download_counters  = 1_bit;
       static constexpr status_flags_t query_last_seen_complete  = 2_bit;
       static constexpr status_flags_t query_pieces  = 3_bit;
       static constexpr status_flags_t query_verified_pieces  = 4_bit;
       static constexpr status_flags_t query_torrent_file  = 5_bit;
       static constexpr status_flags_t query_name  = 6_bit;
       static constexpr status_flags_t query_save_path  = 7_bit;
       static constexpr deadline_flags_t alert_when_available  = 0_bit;
       static constexpr pause_flags_t graceful_pause  = 0_bit;
       static constexpr pause_flags_t clear_disk_cache  = 1_bit;
       static constexpr resume_data_flags_t flush_disk_cache  = 0_bit;
       static constexpr resume_data_flags_t save_info_dict  = 1_bit;
       static constexpr resume_data_flags_t only_if_modified  = 2_bit;
       static constexpr reannounce_flags_t ignore_min_interval  = 0_bit;
    };

[report issue]

#### torrent_handle()

    torrent_handle () noexcept = default;

constructs a torrent handle that does not refer to a torrent. i.e. is_valid() will return false.

[report issue]

#### add_piece()

    void add_piece (piece_index_t piece, char const* data, add_piece_flags_t flags = {}) const;

This function will write `data` to the storage as piece `piece`, as if it had been downloaded from a peer. `data` is expected to point to a buffer of as many bytes as the size of the specified piece. The data in the buffer is copied and passed on to the disk IO thread to be written at a later point.

By default, data that's already been downloaded is not overwritten by this buffer. If you trust this data to be correct (and pass the piece hash check) you may pass the overwrite_existing flag. This will instruct libtorrent to overwrite any data that may already have been downloaded with this data.

Since the data is written asynchronously, you may know that is passed or failed the hash check by waiting for piece_finished_alert or hash_failed_alert.

Adding pieces while the torrent is being checked (i.e. in torrent_status::checking_files state) is not supported.

[report issue]

#### read_piece()

    void read_piece (piece_index_t piece) const;

This function starts an asynchronous read operation of the specified piece from this torrent. You must have completed the download of the specified piece before calling this function.

When the read operation is completed, it is passed back through an alert, read_piece_alert. Since this alert is a response to an explicit call, it will always be posted, regardless of the alert mask.

Note that if you read multiple pieces, the read operations are not guaranteed to finish in the same order as you initiated them.

[report issue]

#### have_piece()

    bool have_piece (piece_index_t piece) const;

Returns true if this piece has been completely downloaded and written to disk, and false otherwise.

[report issue]

#### get_peer_info()

    void get_peer_info (std::vector<peer_info>& v) const;

takes a reference to a vector that will be cleared and filled with one entry for each peer connected to this torrent, given the handle is valid. If the torrent_handle is invalid, it will throw system_error exception. Each entry in the vector contains information about that particular peer. See peer_info.

[report issue]

#### status()

    torrent_status status (status_flags_t flags = status_flags_t::all()) const;

`status()` will return a structure with information about the status of this torrent. If the torrent_handle is invalid, it will throw system_error exception. See torrent_status. The `flags` argument filters what information is returned in the torrent_status. Some information in there is relatively expensive to calculate, and if you're not interested in it (and see performance issues), you can filter them out.

By default everything is included. The flags you can use to decide what to include are defined in this class.

[report issue]

#### get_download_queue()

    void get_download_queue (std::vector<partial_piece_info>& queue) const;

`get_download_queue()` takes a non-const reference to a vector which it will fill with information about pieces that are partially downloaded or not downloaded at all but partially requested. See partial_piece_info for the fields in the returned vector.

[report issue]

#### reset_piece_deadline() clear_piece_deadlines() set_piece_deadline()

    void set_piece_deadline (piece_index_t index, int deadline, deadline_flags_t flags = {}) const;
    void reset_piece_deadline (piece_index_t index) const;
    void clear_piece_deadlines () const;

This function sets or resets the deadline associated with a specific piece index (`index`). libtorrent will attempt to download this entire piece before the deadline expires. This is not necessarily possible, but pieces with a more recent deadline will always be prioritized over pieces with a deadline further ahead in time. The deadline (and flags) of a piece can be changed by calling this function again.

If the piece is already downloaded when this call is made, nothing happens, unless the alert_when_available flag is set, in which case it will have the same effect as calling read_piece() for `index`.

`deadline` is the number of milliseconds until this piece should be completed.

`reset_piece_deadline` removes the deadline from the piece. If it hasn't already been downloaded, it will no longer be considered a priority.

`clear_piece_deadlines()` removes deadlines on all pieces in the torrent. As if reset_piece_deadline() was called on all pieces.

[report issue]

#### file_progress()

    void file_progress (std::vector<std::int64_t>& progress, int flags = 0) const;

This function fills in the supplied vector with the number of bytes downloaded of each file in this torrent. The progress values are ordered the same as the files in the torrent_info. This operation is not very cheap. Its complexity is O(n + mj). Where n is the number of files, m is the number of downloading pieces and j is the number of blocks in a piece.

The `flags` parameter can be used to specify the granularity of the file progress. If left at the default value of 0, the progress will be as accurate as possible, but also more expensive to calculate. If `torrent_handle::piece_granularity` is specified, the progress will be specified in piece granularity. i.e. only pieces that have been fully downloaded and passed the hash check count. When specifying piece granularity, the operation is a lot cheaper, since libtorrent already keeps track of this internally and no calculation is required.

[report issue]

#### file_status()

    std::vector<open_file_state> file_status () const;

This function returns a vector with status about files that are open for this torrent. Any file that is not open will not be reported in the vector, i.e. it's possible that the vector is empty when returning, if none of the files in the torrent are currently open.

See open_file_state

[report issue]

#### clear_error()

    void clear_error () const;

If the torrent is in an error state (i.e. `torrent_status::error` is non-empty), this will clear the error and start the torrent again.

[report issue]

#### add_tracker() replace_trackers() trackers()

    void replace_trackers (std::vector<announce_entry> const&) const;
    std::vector<announce_entry> trackers () const;
    void add_tracker (announce_entry const&) const;

`trackers()` will return the list of trackers for this torrent. The announce entry contains both a string `url` which specify the announce url for the tracker as well as an int `tier`, which is specifies the order in which this tracker is tried. If you want libtorrent to use another list of trackers for this torrent, you can use `replace_trackers()` which takes a list of the same form as the one returned from `trackers()` and will replace it. If you want an immediate effect, you have to call force_reannounce(). See announce_entry.

`add_tracker()` will look if the specified tracker is already in the set. If it is, it doesn't do anything. If it's not in the current set of trackers, it will insert it in the tier specified in the announce_entry.

The updated set of trackers will be saved in the resume data, and when a torrent is started with resume data, the trackers from the resume data will replace the original ones.

[report issue]

#### url_seeds() remove_url_seed() add_url_seed()

    std::set<std::string> url_seeds () const;
    void add_url_seed (std::string const& url) const;
    void remove_url_seed (std::string const& url) const;

`add_url_seed()` adds another url to the torrent's list of url seeds. If the given url already exists in that list, the call has no effect. The torrent will connect to the server and try to download pieces from it, unless it's paused, queued, checking or seeding. `remove_url_seed()` removes the given url if it exists already. `url_seeds()` return a set of the url seeds currently in this torrent. Note that URLs that fails may be removed automatically from the list.

See http seeding for more information.

[report issue]

#### add_http_seed() remove_http_seed() http_seeds()

    void add_http_seed (std::string const& url) const;
    void remove_http_seed (std::string const& url) const;
    std::set<std::string> http_seeds () const;

These functions are identical as the `*_url_seed()` variants, but they operate on BEP 17 web seeds instead of BEP 19.

See http seeding for more information.

[report issue]

#### add_extension()

    void add_extension (
          std::function<std::shared_ptr<torrent_plugin>(torrent_handle const&, void*)> const& ext
          , void* userdata = nullptr);

add the specified extension to this torrent. The `ext` argument is a function that will be called from within libtorrent's context passing in the internal torrent object and the specified userdata pointer. The function is expected to return a shared pointer to a torrent_plugin instance.

[report issue]

#### set_metadata()

    bool set_metadata (span<char const> metadata) const;

`set_metadata` expects the info section of metadata. i.e. The buffer passed in will be hashed and verified against the info-hash. If it fails, a `metadata_failed_alert` will be generated. If it passes, a `metadata_received_alert` is generated. The function returns true if the metadata is successfully set on the torrent, and false otherwise. If the torrent already has metadata, this function will not affect the torrent, and false will be returned.

[report issue]

#### is_valid()

    bool is_valid () const;

Returns true if this handle refers to a valid torrent and false if it hasn't been initialized or if the torrent it refers to has been aborted. Note that a handle may become invalid after it has been added to the session. Usually this is because the storage for the torrent is somehow invalid or if the filenames are not allowed (and hence cannot be opened/created) on your filesystem. If such an error occurs, a file_error_alert is generated and all handles that refers to that torrent will become invalid.

[report issue]

#### pause() resume()

    void resume () const;
    void pause (pause_flags_t flags = {}) const;

`pause()`, and `resume()` will disconnect all peers and reconnect all peers respectively. When a torrent is paused, it will however remember all share ratios to all peers and remember all potential (not connected) peers. Torrents may be paused automatically if there is a file error (e.g. disk full) or something similar. See file_error_alert.

To know if a torrent is paused or not, call `torrent_handle::status()` and inspect `torrent_status::paused`.

Note

Torrents that are auto-managed may be automatically resumed again. It does not make sense to pause an auto-managed torrent without making it not auto-managed first. Torrents are auto-managed by default when added to the session. For more information, see queuing.

[report issue]

#### flags() set_flags() unset_flags()

    void unset_flags (torrent_flags_t flags) const;
    void set_flags (torrent_flags_t flags) const;
    torrent_flags_t flags () const;
    void set_flags (torrent_flags_t flags, torrent_flags_t mask) const;

sets and gets the torrent state flags. See torrent_flags_t. The `set_flags` overload that take a mask will affect all flags part of the mask, and set their values to what the `flags` argument is set to. This allows clearing and setting flags in a single function call. The `set_flags` overload that just takes flags, sets all the specified flags and leave any other flags unchanged. `unset_flags` clears the specified flags, while leaving any other flags unchanged.

The seed_mode flag is special, it can only be cleared once the torrent has been added, and it can only be set as part of the add_torrent_params flags, when adding the torrent.

[report issue]

#### flush_cache()

    void flush_cache () const;

Instructs libtorrent to flush all the disk caches for this torrent and close all file handles. This is done asynchronously and you will be notified that it's complete through cache_flushed_alert.

Note that by the time you get the alert, libtorrent may have cached more data for the torrent, but you are guaranteed that whatever cached data libtorrent had by the time you called `torrent_handle::flush_cache()` has been written to disk.

[report issue]

#### force_recheck()

    void force_recheck () const;

`force_recheck` puts the torrent back in a state where it assumes to have no resume data. All peers will be disconnected and the torrent will stop announcing to the tracker. The torrent will be added to the checking queue, and will be checked (all the files will be read and compared to the piece hashes). Once the check is complete, the torrent will start connecting to peers again, as normal. The torrent will be placed last in queue, i.e. its queue position will be the highest of all torrents in the session.

[report issue]

#### save_resume_data()

    void save_resume_data (resume_data_flags_t flags = {}) const;

`save_resume_data()` asks libtorrent to generate fast-resume data for this torrent.

This operation is asynchronous, `save_resume_data` will return immediately. The resume data is delivered when it's done through an save_resume_data_alert.

The fast resume data will be empty in the following cases:

> 1. The torrent handle is invalid.
> 2. The torrent hasn't received valid metadata and was started without metadata (see libtorrent's metadata from peers extension)

Note that by the time you receive the fast resume data, it may already be invalid if the torrent is still downloading! The recommended practice is to first pause the session, then generate the fast resume data, and then close it down. Make sure to not remove_torrent() before you receive the save_resume_data_alert though. There's no need to pause when saving intermittent resume data.

Warning

If you pause every torrent individually instead of pausing the session, every torrent will have its paused state saved in the resume data!

Note

It is typically a good idea to save resume data whenever a torrent is completed or paused. In those cases you don't need to pause the torrent or the session, since the torrent will do no more writing to its files. If you save resume data for torrents when they are paused, you can accelerate the shutdown process by not saving resume data again for paused torrents. Completed torrents should have their resume data saved when they complete and on exit, since their statistics might be updated.

> In full allocation mode the resume data is never invalidated by subsequent writes to the files, since pieces won't move around. This means that you don't need to pause before writing resume data in full or sparse mode. If you don't, however, any data written to disk after you saved resume data and before the session closed is lost.

It also means that if the resume data is out dated, libtorrent will not re-check the files, but assume that it is fairly recent. The assumption is that it's better to loose a little bit than to re-check the entire file.

It is still a good idea to save resume data periodically during download as well as when closing down.

Example code to pause and save resume data for all torrents and wait for the alerts:

    extern int outstanding_resume_data; // global counter of outstanding resume data
    std::vector<torrent_handle> handles = ses.get_torrents();
    ses.pause();
    for (torrent_handle const& h : handles)
    {
            if (!h.is_valid()) continue;
            torrent_status s = h.status();
            if (!s.has_metadata || !s.need_save_resume_data()) continue;

            h.save_resume_data();
            ++outstanding_resume_data;
    }

    while (outstanding_resume_data > 0)
    {
            alert const* a = ses.wait_for_alert(seconds(10));

            // if we don't get an alert within 10 seconds, abort
            if (a == nullptr) break;

            std::vector<alert*> alerts;
            ses.pop_alerts(&alerts);

            for (alert* i : alerts)
            {
                    if (alert_cast<save_resume_data_failed_alert>(i))
                    {
                            process_alert(i);
                            --outstanding_resume_data;
                            continue;
                    }

                    save_resume_data_alert const* rd = alert_cast<save_resume_data_alert>(i);
                    if (rd == nullptr)
                    {
                            process_alert(i);
                            continue;
                    }

                    torrent_handle h = rd->handle;
                    torrent_status st = h.status(torrent_handle::query_save_path
                            | torrent_handle::query_name);
                    std::ofstream out((st.save_path
                            + "/" + st.name + ".fastresume").c_str()
                            , std::ios_base::binary);
                    std::vector<char> buf = write_resume_data_buf(rd->params);
                    out.write(buf.data(), buf.size());
                    --outstanding_resume_data;
            }
    }

Note

Note how `outstanding_resume_data` is a global counter in this example. This is deliberate, otherwise there is a race condition for torrents that was just asked to save their resume data, they posted the alert, but it has not been received yet. Those torrents would report that they don't need to save resume data again, and skipped by the initial loop, and thwart the counter otherwise.

[report issue]

#### need_save_resume_data()

    bool need_save_resume_data () const;

This function returns true if any whole chunk has been downloaded since the torrent was first loaded or since the last time the resume data was saved. When saving resume data periodically, it makes sense to skip any torrent which hasn't downloaded anything since the last time.

Note

A torrent's resume data is considered saved as soon as the save_resume_data_alert is posted. It is important to make sure this alert is received and handled in order for this function to be meaningful.

[report issue]

#### queue_position_top() queue_position_bottom() queue_position() queue_position_down() queue_position_up()

    queue_position_t queue_position () const;
    void queue_position_down () const;
    void queue_position_up () const;
    void queue_position_top () const;
    void queue_position_bottom () const;

Every torrent that is added is assigned a queue position exactly one greater than the greatest queue position of all existing torrents. Torrents that are being seeded have -1 as their queue position, since they're no longer in line to be downloaded.

When a torrent is removed or turns into a seed, all torrents with greater queue positions have their positions decreased to fill in the space in the sequence.

`queue_position()` returns the torrent's position in the download queue. The torrents with the smallest numbers are the ones that are being downloaded. The smaller number, the closer the torrent is to the front of the line to be started.

The queue position is also available in the torrent_status.

The `queue_position_*()` functions adjust the torrents position in the queue. Up means closer to the front and down means closer to the back of the queue. Top and bottom refers to the front and the back of the queue respectively.

[report issue]

#### queue_position_set()

    void queue_position_set (queue_position_t p) const;

updates the position in the queue for this torrent. The relative order of all other torrents remain intact but their numerical queue position shifts to make space for this torrent's new position

[report issue]

#### set_ssl_certificate() set_ssl_certificate_buffer()

    void set_ssl_certificate (std::string const& certificate
          , std::string const& private_key
          , std::string const& dh_params
          , std::string const& passphrase = "");
    void set_ssl_certificate_buffer (std::string const& certificate
          , std::string const& private_key
          , std::string const& dh_params);

For SSL torrents, use this to specify a path to a .pem file to use as this client's certificate. The certificate must be signed by the certificate in the .torrent file to be valid.

The set_ssl_certificate_buffer() overload takes the actual certificate, private key and DH params as strings, rather than paths to files.

`cert` is a path to the (signed) certificate in .pem format corresponding to this torrent.

`private_key` is a path to the private key for the specified certificate. This must be in .pem format.

`dh_params` is a path to the Diffie-Hellman parameter file, which needs to be in .pem format. You can generate this file using the openssl command like this: `openssl dhparam -outform PEM -out dhparams.pem 512`.

`passphrase` may be specified if the private key is encrypted and requires a passphrase to be decrypted.

Note that when a torrent first starts up, and it needs a certificate, it will suspend connecting to any peers until it has one. It's typically desirable to resume the torrent after setting the SSL certificate.

If you receive a torrent_need_cert_alert, you need to call this to provide a valid cert. If you don't have a cert you won't be allowed to connect to any peers.

[report issue]

#### get_storage_impl()

    storage_interface* get_storage_impl () const;

Returns the storage implementation for this torrent. This depends on the storage constructor function that was passed to add_torrent.

[report issue]

#### torrent_file()

    std::shared_ptr<const torrent_info> torrent_file () const;

Returns a pointer to the torrent_info object associated with this torrent. The torrent_info object may be a copy of the internal object. If the torrent doesn't have metadata, the pointer will not be initialized (i.e. a nullptr). The torrent may be in a state without metadata only if it was started without a .torrent file, e.g. by being added by magnet link

[report issue]

#### piece_availability()

    void piece_availability (std::vector<int>& avail) const;

Fills the specified `std::vector<int>` with the availability for each piece in this torrent. libtorrent does not keep track of availability for seeds, so if the torrent is seeding the availability for all pieces is reported as 0.

The piece availability is the number of peers that we are connected that has advertised having a particular piece. This is the information that libtorrent uses in order to prefer picking rare pieces.

[report issue]

#### prioritize_pieces() get_piece_priorities() piece_priority()

    download_priority_t piece_priority (piece_index_t index) const;
    void prioritize_pieces (std::vector<std::pair<piece_index_t, download_priority_t>> const& pieces) const;
    std::vector<download_priority_t> get_piece_priorities () const;
    void piece_priority (piece_index_t index, download_priority_t priority) const;
    void prioritize_pieces (std::vector<download_priority_t> const& pieces) const;

These functions are used to set and get the priority of individual pieces. By default all pieces have priority 4. That means that the random rarest first algorithm is effectively active for all pieces. You may however change the priority of individual pieces. There are 8 priority levels. 0 means not to download the piece at all. Otherwise, lower priority values means less likely to be picked. Piece priority takes precedence over piece availability. Every piece with priority 7 will be attempted to be picked before a priority 6 piece and so on.

The default priority of pieces is 4.

Piece priorities can not be changed for torrents that have not downloaded the metadata yet. Magnet links won't have metadata immediately. see the metadata_received_alert.

`piece_priority` sets or gets the priority for an individual piece, specified by `index`.

`prioritize_pieces` takes a vector of integers, one integer per piece in the torrent. All the piece priorities will be updated with the priorities in the vector. The second overload of `prioritize_pieces` that takes a vector of pairs will update the priorities of only select pieces, and leave all other unaffected. Each pair is (piece, priority). That is, the first item is the piece index and the second item is the priority of that piece. Invalid entries, where the piece index or priority is out of range, are not allowed.

`get_piece_priorities` returns a vector with one element for each piece in the torrent. Each element is the current priority of that piece.

It's possible to cancel the effect of file priorities by setting the priorities for the affected pieces. Care has to be taken when mixing usage of file- and piece priorities.

[report issue]

#### file_priority() prioritize_files() get_file_priorities()

    std::vector<download_priority_t> get_file_priorities () const;
    void file_priority (file_index_t index, download_priority_t priority) const;
    download_priority_t file_priority (file_index_t index) const;
    void prioritize_files (std::vector<download_priority_t> const& files) const;

`index` must be in the range [0, number_of_files).

`file_priority()` queries or sets the priority of file `index`.

`prioritize_files()` takes a vector that has at as many elements as there are files in the torrent. Each entry is the priority of that file. The function sets the priorities of all the pieces in the torrent based on the vector.

`get_file_priorities()` returns a vector with the priorities of all files.

The priority values are the same as for piece_priority(). See download_priority_t.

Whenever a file priority is changed, all other piece priorities are reset to match the file priorities. In order to maintain special priorities for particular pieces, piece_priority() has to be called again for those pieces.

You cannot set the file priorities on a torrent that does not yet have metadata or a torrent that is a seed. `file_priority(int, int)` and prioritize_files() are both no-ops for such torrents.

Since changing file priorities may involve disk operations (of moving files in- and out of the part file), the internal accounting of file priorities happen asynchronously. i.e. setting file priorities and then immediately querying them may not yield the same priorities just set. However, the piece priorities are updated immediately.

when combining file- and piece priorities, the resume file will record both. When loading the resume data, the file priorities will be applied first, then the piece priorities.

[report issue]

#### force_reannounce() force_dht_announce()

    void force_dht_announce () const;
    void force_reannounce (int seconds = 0, int tracker_index = -1, reannounce_flags_t = {}) const;

`force_reannounce()` will force this torrent to do another tracker request, to receive new peers. The `seconds` argument specifies how many seconds from now to issue the tracker announces.

If the tracker's `min_interval` has not passed since the last announce, the forced announce will be scheduled to happen immediately as the `min_interval` expires. This is to honor trackers minimum re-announce interval settings.

The `tracker_index` argument specifies which tracker to re-announce. If set to -1 (which is the default), all trackers are re-announce.

The `flags` argument can be used to affect the re-announce. See ignore_min_interval.

`force_dht_announce` will announce the torrent to the DHT immediately.

[report issue]

#### scrape_tracker()

    void scrape_tracker (int idx = -1) const;

`scrape_tracker()` will send a scrape request to a tracker. By default (`idx` = -1) it will scrape the last working tracker. If `idx` is >= 0, the tracker with the specified index will scraped.

A scrape request queries the tracker for statistics such as total number of incomplete peers, complete peers, number of downloads etc.

This request will specifically update the `num_complete` and `num_incomplete` fields in the torrent_status struct once it completes. When it completes, it will generate a scrape_reply_alert. If it fails, it will generate a scrape_failed_alert.

[report issue]

#### set_download_limit() upload_limit() download_limit() set_upload_limit()

    void set_download_limit (int limit) const;
    int download_limit () const;
    void set_upload_limit (int limit) const;
    int upload_limit () const;

`set_upload_limit` will limit the upload bandwidth used by this particular torrent to the limit you set. It is given as the number of bytes per second the torrent is allowed to upload. `set_download_limit` works the same way but for download bandwidth instead of upload bandwidth. Note that setting a higher limit on a torrent then the global limit (`settings_pack::upload_rate_limit`) will not override the global rate limit. The torrent can never upload more than the global rate limit.

`upload_limit` and `download_limit` will return the current limit setting, for upload and download, respectively.

Local peers are not rate limited by default. see peer classes.

[report issue]

#### connect_peer()

    void connect_peer (tcp::endpoint const& adr, peer_source_flags_t source = {}
          , pex_flags_t flags = pex_encryption | pex_utp | pex_holepunch) const;

`connect_peer()` is a way to manually connect to peers that one believe is a part of the torrent. If the peer does not respond, or is not a member of this torrent, it will simply be disconnected. No harm can be done by using this other than an unnecessary connection attempt is made. If the torrent is uninitialized or in queued or checking mode, this will throw system_error. The second (optional) argument will be bitwise ORed into the source mask of this peer. Typically this is one of the source flags in peer_info. i.e. `tracker`, `pex`, `dht` etc.

For possible values of `flags`, see pex_flags_t.

[report issue]

#### clear_peers()

    void clear_peers ();

This will disconnect all peers and clear the peer list for this torrent. New peers will have to be acquired before resuming, from trackers, DHT or local service discovery, for example.

[report issue]

#### set_max_uploads() max_uploads()

    void set_max_uploads (int max_uploads) const;
    int max_uploads () const;

`set_max_uploads()` sets the maximum number of peers that's unchoked at the same time on this torrent. If you set this to -1, there will be no limit. This defaults to infinite. The primary setting controlling this is the global unchoke slots limit, set by unchoke_slots_limit in settings_pack.

`max_uploads()` returns the current settings.

[report issue]

#### max_connections() set_max_connections()

    void set_max_connections (int max_connections) const;
    int max_connections () const;

`set_max_connections()` sets the maximum number of connection this torrent will open. If all connections are used up, incoming connections may be refused or poor connections may be closed. This must be at least 2. The default is unlimited number of connections. If -1 is given to the function, it means unlimited. There is also a global limit of the number of connections, set by `connections_limit` in settings_pack.

`max_connections()` returns the current settings.

[report issue]

#### move_storage()

    void move_storage (std::string const& save_path
          , move_flags_t flags = move_flags_t::always_replace_files
          ) const;

Moves the file(s) that this torrent are currently seeding from or downloading to. If the given `save_path` is not located on the same drive as the original save path, the files will be copied to the new drive and removed from their original location. This will block all other disk IO, and other torrents download and upload rates may drop while copying the file.

Since disk IO is performed in a separate thread, this operation is also asynchronous. Once the operation completes, the `storage_moved_alert` is generated, with the new path as the message. If the move fails for some reason, `storage_moved_failed_alert` is generated instead, containing the error message.

The `flags` argument determines the behavior of the copying/moving of the files in the torrent. see move_flags_t.

`always_replace_files` is the default and replaces any file that exist in both the source directory and the target directory.

`fail_if_exist` first check to see that none of the copy operations would cause an overwrite. If it would, it will fail. Otherwise it will proceed as if it was in `always_replace_files` mode. Note that there is an inherent race condition here. If the files in the target directory appear after the check but before the copy or move completes, they will be overwritten. When failing because of files already existing in the target path, the `error` of `move_storage_failed_alert` is set to `boost::system::errc::file_exists`.

The intention is that a client may use this as a probe, and if it fails, ask the user which mode to use. The client may then re-issue the `move_storage` call with one of the other modes.

`dont_replace` always keeps the existing file in the target directory, if there is one. The source files will still be removed in that case. Note that it won't automatically re-check files. If an incomplete torrent is moved into a directory with the complete files, pause, move, force-recheck and resume. Without the re-checking, the torrent will keep downloading and files in the new download directory will be overwritten.

Files that have been renamed to have absolute paths are not moved by this function. Keep in mind that files that don't belong to the torrent but are stored in the torrent's directory may be moved as well. This goes for files that have been renamed to absolute paths that still end up inside the save path.

[report issue]

#### rename_file()

    void rename_file (file_index_t index, std::string const& new_name) const;

Renames the file with the given index asynchronously. The rename operation is complete when either a file_renamed_alert or file_rename_failed_alert is posted.

[report issue]

#### info_hash()

    sha1_hash info_hash () const;

`info_hash()` returns the info-hash of the torrent. If this handle is to a torrent that hasn't loaded yet (for instance by being added) by a URL, the returned value is undefined.

[report issue]

#### operator==() operator!=() operator<()

    bool operator== (const torrent_handle& h) const;
    bool operator!= (const torrent_handle& h) const;
    bool operator< (const torrent_handle& h) const;

comparison operators. The order of the torrents is unspecified but stable.

[report issue]

#### id()

    std::uint32_t id () const;

returns a unique identifier for this torrent. It's not a dense index. It's not preserved across sessions.

[report issue]

#### native_handle()

    std::shared_ptr<torrent> native_handle () const;

This function is intended only for use by plugins and the alert dispatch function. This type does not have a stable ABI and should be relied on as little as possible. Accessing the handle returned by this function is not thread safe outside of libtorrent's internal thread (which is used to invoke plugin callbacks). The `torrent` class is not only eligible for changing ABI across minor versions of libtorrent, its layout is also dependent on build configuration. This adds additional requirements on a client to be built with the exact same build configuration as libtorrent itself. i.e. the `TORRENT_` macros must match between libtorrent and the client builds.

[report issue]

#### enum file_progress_flags_t

Declared in "libtorrent/torrent_handle.hpp"

name | value | description
--- | --- | ---
piece_granularity | 1 | only calculate file progress at piece granularity. This makes the file_progress() call cheaper and also only takes bytes that have passed the hash check into account, so progress cannot regress in this mode.

[report issue]

overwrite_existing
  instruct libtorrent to overwrite any data that may already have been downloaded with the data of the new piece being added.

[report issue]

query_distributed_copies
  calculates `distributed_copies`, `distributed_full_copies` and `distributed_fraction`.

[report issue]

query_accurate_download_counters
  includes partial downloaded blocks in `total_done` and `total_wanted_done`.

[report issue]

query_last_seen_complete
  includes `last_seen_complete`.

[report issue]

query_pieces
  populate the `pieces` field in torrent_status.

[report issue]

query_verified_pieces
  includes `verified_pieces` (only applies to torrents in seed mode).

[report issue]

query_torrent_file
  includes `torrent_file`, which is all the static information from the .torrent file.

[report issue]

query_name
  includes `name`, the name of the torrent. This is either derived from the .torrent file, or from the `&dn=` magnet link argument or possibly some other source. If the name of the torrent is not known, this is an empty string.

[report issue]

query_save_path
  includes `save_path`, the path to the directory the files of the torrent are saved to.

[report issue]

alert_when_available
  used to ask libtorrent to send an alert once the piece has been downloaded, by passing alert_when_available. When set, the read_piece_alert alert will be delivered, with the piece data, when it's downloaded.

[report issue]

graceful_pause clear_disk_cache
  will delay the disconnect of peers that we're still downloading outstanding requests from. The torrent will not accept any more requests and will disconnect all idle peers. As soon as a peer is done transferring the blocks that were requested from it, it is disconnected. This is a graceful shut down of the torrent in the sense that no downloaded bytes are wasted.

[report issue]

flush_disk_cache
  the disk cache will be flushed before creating the resume data. This avoids a problem with file timestamps in the resume data in case the cache hasn't been flushed yet.

[report issue]

save_info_dict
  the resume data will contain the metadata from the torrent file as well. This is default for any torrent that's added without a torrent file (such as a magnet link or a URL).

[report issue]

only_if_modified
  if nothing significant has changed in the torrent since the last time resume data was saved, fail this attempt. Significant changes primarily include more data having been downloaded, file or piece priorities having changed etc. If the resume data doesn't need saving, a save_resume_data_failed_alert is posted with the error resume_data_not_modified.

[report issue]

ignore_min_interval
  by default, force-reannounce will still honor the min-interval published by the tracker. If this flag is set, it will be ignored and the tracker is announced immediately.

[report issue]

### cache_status

Declared in "libtorrent/disk_io_thread.hpp"

this struct holds a number of statistics counters relevant for the disk io thread and disk cache.

    struct cache_status
    {
       cache_status ();

       std::vector<cached_piece_info> pieces;
    };

[report issue]

#### cache_status()

    cache_status ();

initializes all counters to 0

[report issue]

### web_seed_entry

Declared in "libtorrent/torrent_info.hpp"

the web_seed_entry holds information about a web seed (also known as URL seed or HTTP seed). It is essentially a URL with some state associated with it. For more information, see BEP 17 and BEP 19.

    struct web_seed_entry
    {
       bool operator== (web_seed_entry const& e) const;
       bool operator< (web_seed_entry const& e) const;

       enum type_t
       {
          url_seed,
          http_seed,
       };

       std::string url;
       std::string auth;
       headers_t extra_headers;
       std::uint8_t type;
    };

[report issue]

#### operator==()

    bool operator== (web_seed_entry const& e) const;

URL and type comparison

[report issue]

#### operator<()

    bool operator< (web_seed_entry const& e) const;

URL and type less-than comparison

[report issue]

#### enum type_t

Declared in "libtorrent/torrent_info.hpp"

name | value | description
--- | --- | ---
url_seed | 0 |
http_seed | 1 |

[report issue]

url
  The URL of the web seed

[report issue]

auth
  Optional authentication. If this is set, it's passed in as HTTP basic auth to the web seed. The format is: username:password.

[report issue]

extra_headers
  Any extra HTTP headers that need to be passed to the web seed

[report issue]

type
  The type of web seed (see type_t)

[report issue]

### load_torrent_limits

Declared in "libtorrent/torrent_info.hpp"

this object holds configuration options for limits to use when loading torrents. They are meant to prevent loading potentially malicious torrents that cause excessive memory allocations.

    struct load_torrent_limits
    {
       int max_buffer_size  = 10000000;
       int max_pieces  = 0x200000;
       int max_decode_depth  = 100;
       int max_decode_tokens  = 3000000;
    };

[report issue]

max_buffer_size
  the max size of a .torrent file to load into RAM

[report issue]

max_pieces
  the max number of pieces allowed in the torrent

[report issue]

max_decode_depth
  the max recursion depth in the bdecoded structure

[report issue]

max_decode_tokens
  the max number of bdecode tokens

[report issue]

### torrent_info

Declared in "libtorrent/torrent_info.hpp"

the torrent_info class holds the information found in a .torrent file.

    class torrent_info
    {
       torrent_info (std::string const& filename, load_torrent_limits const& cfg);
       explicit torrent_info (bdecode_node const& torrent_file);
       torrent_info (torrent_info const& t);
       explicit torrent_info (span<char const> buffer, from_span_t);
       torrent_info (span<char const> buffer, load_torrent_limits const& cfg, from_span_t);
       explicit torrent_info (sha1_hash const& info_hash);
       torrent_info (char const* buffer, int size, error_code& ec);
       torrent_info (std::string const& filename, error_code& ec);
       torrent_info (bdecode_node const& torrent_file, error_code& ec);
       torrent_info (char const* buffer, int size);
       explicit torrent_info (std::string const& filename);
       torrent_info (bdecode_node const& torrent_file, load_torrent_limits const& cfg);
       torrent_info (span<char const> buffer, error_code& ec, from_span_t);
       ~torrent_info ();
       file_storage const& files () const;
       file_storage const& orig_files () const;
       void rename_file (file_index_t index, std::string const& new_filename);
       void remap_files (file_storage const& f);
       void add_tracker (std::string const& url, int tier
          , announce_entry::tracker_source source);
       void add_tracker (std::string const& url, int tier = 0);
       std::vector<announce_entry> const& trackers () const;
       std::vector<std::string> collections () const;
       std::vector<sha1_hash> similar_torrents () const;
       std::vector<web_seed_entry> const& web_seeds () const;
       void add_url_seed (std::string const& url
          , std::string const& extern_auth = std::string()
          , web_seed_entry::headers_t const& extra_headers = web_seed_entry::headers_t());
       void add_http_seed (std::string const& url
          , std::string const& extern_auth = std::string()
          , web_seed_entry::headers_t const& extra_headers = web_seed_entry::headers_t());
       void set_web_seeds (std::vector<web_seed_entry> seeds);
       std::int64_t total_size () const;
       int piece_length () const;
       int num_pieces () const;
       piece_index_t end_piece () const;
       piece_index_t last_piece () const;
       index_range<piece_index_t> piece_range () const;
       const sha1_hash& info_hash () const;
       int num_files () const;
       std::vector<file_slice> map_block (piece_index_t const piece
          , std::int64_t offset, int size) const;
       peer_request map_file (file_index_t const file, std::int64_t offset, int size) const;
       string_view ssl_cert () const;
       bool is_valid () const;
       bool priv () const;
       bool is_i2p () const;
       int piece_size (piece_index_t index) const;
       char const* hash_for_piece_ptr (piece_index_t const index) const;
       sha1_hash hash_for_piece (piece_index_t index) const;
       bool is_loaded () const;
       std::vector<sha1_hash> const& merkle_tree () const;
       void set_merkle_tree (std::vector<sha1_hash>& h);
       const std::string& name () const;
       std::time_t creation_date () const;
       const std::string& creator () const;
       const std::string& comment () const;
       std::vector<std::pair<std::string, int>> const& nodes () const;
       void add_node (std::pair<std::string, int> const& node);
       bool parse_info_section (bdecode_node const& e, error_code& ec);
       bool parse_info_section (bdecode_node const& e, error_code& ec, int piece_limit);
       bdecode_node info (char const* key) const;
       void swap (torrent_info& ti);
       boost::shared_array<char> metadata () const;
       int metadata_size () const;
       bool is_merkle_torrent () const;
    };

[report issue]

#### torrent_info()

    torrent_info (std::string const& filename, load_torrent_limits const& cfg);
    explicit torrent_info (bdecode_node const& torrent_file);
    torrent_info (torrent_info const& t);
    explicit torrent_info (span<char const> buffer, from_span_t);
    torrent_info (span<char const> buffer, load_torrent_limits const& cfg, from_span_t);
    explicit torrent_info (sha1_hash const& info_hash);
    torrent_info (char const* buffer, int size, error_code& ec);
    torrent_info (std::string const& filename, error_code& ec);
    torrent_info (bdecode_node const& torrent_file, error_code& ec);
    torrent_info (char const* buffer, int size);
    explicit torrent_info (std::string const& filename);
    torrent_info (bdecode_node const& torrent_file, load_torrent_limits const& cfg);
    torrent_info (span<char const> buffer, error_code& ec, from_span_t);

The constructor that takes an info-hash will initialize the info-hash to the given value, but leave all other fields empty. This is used internally when downloading torrents without the metadata. The metadata will be created by libtorrent as soon as it has been downloaded from the swarm.

The constructor that takes a bdecode_node will create a torrent_info object from the information found in the given torrent_file. The bdecode_node represents a tree node in an bencoded file. To load an ordinary .torrent file into a bdecode_node, use bdecode().

The version that takes a buffer pointer and a size will decode it as a .torrent file and initialize the torrent_info object for you.

The version that takes a filename will simply load the torrent file and decode it inside the constructor, for convenience. This might not be the most suitable for applications that want to be able to report detailed errors on what might go wrong.

There is an upper limit on the size of the torrent file that will be loaded by the overload taking a filename. If it's important that even very large torrent files are loaded, use one of the other overloads.

The overloads that takes an `error_code const&` never throws if an error occur, they will simply set the error code to describe what went wrong and not fully initialize the torrent_info object. The overloads that do not take the extra error_code parameter will always throw if an error occurs. These overloads are not available when building without exception support.

The overload that takes a `span` also needs an extra parameter of type `from_span_t` to disambiguate the `std::string` overload for string literals. There is an object in the libtorrent namespace of this type called `from_span`.

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#### ~torrent_info()

    ~torrent_info ();

frees all storage associated with this torrent_info object

[report issue]

#### files() orig_files()

    file_storage const& files () const;
    file_storage const& orig_files () const;

The file_storage object contains the information on how to map the pieces to files. It is separated from the torrent_info object because when creating torrents a storage object needs to be created without having a torrent file. When renaming files in a storage, the storage needs to make its own copy of the file_storage in order to make its mapping differ from the one in the torrent file.

`orig_files()` returns the original (unmodified) file storage for this torrent. This is used by the web server connection, which needs to request files with the original names. Filename may be changed using `torrent_info::rename_file()`.

For more information on the file_storage object, see the separate document on how to create torrents.

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#### rename_file()

    void rename_file (file_index_t index, std::string const& new_filename);

Renames the file with the specified index to the new name. The new filename is reflected by the `file_storage` returned by `files()` but not by the one returned by `orig_files()`.

If you want to rename the base name of the torrent (for a multi file torrent), you can copy the `file_storage` (see files() and orig_files() ), change the name, and then use remap_files().

The `new_filename` can both be a relative path, in which case the file name is relative to the `save_path` of the torrent. If the `new_filename` is an absolute path (i.e. `is_complete(new_filename) == true`), then the file is detached from the `save_path` of the torrent. In this case the file is not moved when move_storage() is invoked.

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#### remap_files()

    void remap_files (file_storage const& f);

Remaps the file storage to a new file layout. This can be used to, for instance, download all data in a torrent to a single file, or to a number of fixed size sector aligned files, regardless of the number and sizes of the files in the torrent.

The new specified `file_storage` must have the exact same size as the current one.

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#### add_tracker() trackers()

    void add_tracker (std::string const& url, int tier
          , announce_entry::tracker_source source);
    void add_tracker (std::string const& url, int tier = 0);
    std::vector<announce_entry> const& trackers () const;

`add_tracker()` adds a tracker to the announce-list. The `tier` determines the order in which the trackers are to be tried. The `trackers()` function will return a sorted vector of `announce_entry`. Each announce entry contains a string, which is the tracker url, and a tier index. The tier index is the high-level priority. No matter which trackers that works or not, the ones with lower tier will always be tried before the one with higher tier number. For more information, see announce_entry.

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#### similar_torrents() collections()

    std::vector<std::string> collections () const;
    std::vector<sha1_hash> similar_torrents () const;

These two functions are related to BEP 38 (mutable torrents). The vectors returned from these correspond to the "similar" and "collections" keys in the .torrent file. Both info-hashes and collections from within the info-dict and from outside of it are included.

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#### add_http_seed() web_seeds() set_web_seeds() add_url_seed()

    std::vector<web_seed_entry> const& web_seeds () const;
    void add_url_seed (std::string const& url
          , std::string const& extern_auth = std::string()
          , web_seed_entry::headers_t const& extra_headers = web_seed_entry::headers_t());
    void add_http_seed (std::string const& url
          , std::string const& extern_auth = std::string()
          , web_seed_entry::headers_t const& extra_headers = web_seed_entry::headers_t());
    void set_web_seeds (std::vector<web_seed_entry> seeds);

`web_seeds()` returns all url seeds and http seeds in the torrent. Each entry is a `web_seed_entry` and may refer to either a url seed or http seed.

`add_url_seed()` and `add_http_seed()` adds one url to the list of url/http seeds. Currently, the only transport protocol supported for the url is http.

`set_web_seeds()` replaces all web seeds with the ones specified in the `seeds` vector.

The `extern_auth` argument can be used for other authorization schemes than basic HTTP authorization. If set, it will override any username and password found in the URL itself. The string will be sent as the HTTP authorization header's value (without specifying "Basic").

The `extra_headers` argument defaults to an empty list, but can be used to insert custom HTTP headers in the requests to a specific web seed.

See http seeding for more information.

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#### num_pieces() total_size() piece_length()

    std::int64_t total_size () const;
    int piece_length () const;
    int num_pieces () const;

`total_size()`, `piece_length()` and `num_pieces()` returns the total number of bytes the torrent-file represents (all the files in it), the number of byte for each piece and the total number of pieces, respectively. The difference between `piece_size()` and `piece_length()` is that `piece_size()` takes the piece index as argument and gives you the exact size of that piece. It will always be the same as `piece_length()` except in the case of the last piece, which may be smaller.

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#### end_piece() last_piece() piece_range()

    piece_index_t end_piece () const;
    piece_index_t last_piece () const;
    index_range<piece_index_t> piece_range () const;

`last_piece()` returns the index to the last piece in the torrent and `end_piece()` returns the index to the one-past-end piece in the torrent `piece_range()` returns an implementation-defined type that can be used as the container in a range-for loop. Where the values are the indices of all pieces in the file_storage.

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#### info_hash()

    const sha1_hash& info_hash () const;

returns the info-hash of the torrent

[report issue]

#### num_files()

    int num_files () const;

If you need index-access to files you can use the `num_files()` along with the `file_path()`, `file_size()`-family of functions to access files using indices.

[report issue]

#### map_block()

    std::vector<file_slice> map_block (piece_index_t const piece
          , std::int64_t offset, int size) const;

This function will map a piece index, a byte offset within that piece and a size (in bytes) into the corresponding files with offsets where that data for that piece is supposed to be stored. See file_slice.

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#### map_file()

    peer_request map_file (file_index_t const file, std::int64_t offset, int size) const;

This function will map a range in a specific file into a range in the torrent. The `file_offset` parameter is the offset in the file, given in bytes, where 0 is the start of the file. See peer_request.

The input range is assumed to be valid within the torrent. `file_offset` + `size` is not allowed to be greater than the file size. `file_index` must refer to a valid file, i.e. it cannot be >= `num_files()`.

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#### ssl_cert()

    string_view ssl_cert () const;

Returns the SSL root certificate for the torrent, if it is an SSL torrent. Otherwise returns an empty string. The certificate is the public certificate in x509 format.

[report issue]

#### is_valid()

    bool is_valid () const;

returns true if this torrent_info object has a torrent loaded. This is primarily used to determine if a magnet link has had its metadata resolved yet or not.

[report issue]

#### priv()

    bool priv () const;

returns true if this torrent is private. i.e., the client should not advertise itself on the trackerless network (the Kademlia DHT) for this torrent.

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#### is_i2p()

    bool is_i2p () const;

returns true if this is an i2p torrent. This is determined by whether or not it has a tracker whose URL domain name ends with ".i2p". i2p torrents disable the DHT and local peer discovery as well as talking to peers over anything other than the i2p network.

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#### piece_size()

    int piece_size (piece_index_t index) const;

returns the piece size of file with `index`. This will be the same as piece_length(), except for the last piece, which may be shorter.

[report issue]

#### hash_for_piece_ptr() hash_for_piece()

    char const* hash_for_piece_ptr (piece_index_t const index) const;
    sha1_hash hash_for_piece (piece_index_t index) const;

`hash_for_piece()` takes a piece-index and returns the 20-bytes sha1-hash for that piece and `info_hash()` returns the 20-bytes sha1-hash for the info-section of the torrent file. `hash_for_piece_ptr()` returns a pointer to the 20 byte sha1 digest for the piece. Note that the string is not 0-terminated.

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#### merkle_tree() set_merkle_tree()

    std::vector<sha1_hash> const& merkle_tree () const;
    void set_merkle_tree (std::vector<sha1_hash>& h);

`merkle_tree()` returns a reference to the merkle tree for this torrent, if any. `set_merkle_tree()` moves the passed in merkle tree into the torrent_info object. i.e. `h` will not be identical after the call. You need to set the merkle tree for a torrent that you've just created (as a merkle torrent). The merkle tree is retrieved from the `create_torrent::merkle_tree()` function, and need to be saved separately from the torrent file itself. Once it's added to libtorrent, the merkle tree will be persisted in the resume data.

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#### name()

    const std::string& name () const;

`name()` returns the name of the torrent. name contains UTF-8 encoded string.

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#### creation_date()

    std::time_t creation_date () const;

`creation_date()` returns the creation date of the torrent as time_t (posix time). If there's no time stamp in the torrent file, the optional object will be uninitialized. .. posix time: http://www.opengroup.org/onlinepubs/009695399/functions/time.html

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#### creator()

    const std::string& creator () const;

`creator()` returns the creator string in the torrent. If there is no creator string it will return an empty string.

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#### comment()

    const std::string& comment () const;

`comment()` returns the comment associated with the torrent. If there's no comment, it will return an empty string. comment contains UTF-8 encoded string.

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#### nodes()

    std::vector<std::pair<std::string, int>> const& nodes () const;

If this torrent contains any DHT nodes, they are put in this vector in their original form (host name and port number).

[report issue]

#### add_node()

    void add_node (std::pair<std::string, int> const& node);

This is used when creating torrent. Use this to add a known DHT node. It may be used, by the client, to bootstrap into the DHT network.

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#### parse_info_section()

    bool parse_info_section (bdecode_node const& e, error_code& ec);
    bool parse_info_section (bdecode_node const& e, error_code& ec, int piece_limit);

populates the torrent_info by providing just the info-dict buffer. This is used when loading a torrent from a magnet link for instance, where we only have the info-dict. The bdecode_node `e` points to a parsed info-dictionary. `ec` returns an error code if something fails (typically if the info dictionary is malformed). the piece_limit parameter allows limiting the amount of memory dedicated to loading the torrent, and fails for torrents that exceed the limit

[report issue]

#### info()

    bdecode_node info (char const* key) const;

This function looks up keys from the info-dictionary of the loaded torrent file. It can be used to access extension values put in the .torrent file. If the specified key cannot be found, it returns nullptr.

[report issue]

#### swap()

    void swap (torrent_info& ti);

swap the content of this and `ti`.

[report issue]

#### metadata() metadata_size()

    boost::shared_array<char> metadata () const;
    int metadata_size () const;

`metadata()` returns a the raw info section of the torrent file. The size of the metadata is returned by `metadata_size()`.

[report issue]

#### is_merkle_torrent()

    bool is_merkle_torrent () const;

returns whether or not this is a merkle torrent. see BEP 30.

[report issue]

### add_torrent_params

Declared in "libtorrent/add_torrent_params.hpp"

The add_torrent_params is a parameter pack for adding torrents to a session. The key fields when adding a torrent are:

- ti - when you have loaded a .torrent file into a torrent_info object
- info_hash - when you don't have the metadata (.torrent file) but. This is set when adding a magnet link.

one of those fields must be set. Another mandatory field is `save_path`. The add_torrent_params object is passed into one of the `session::add_torrent()` overloads or `session::async_add_torrent()`.

If you only specify the info-hash, the torrent file will be downloaded from peers, which requires them to support the metadata extension. For the metadata extension to work, libtorrent must be built with extensions enabled (`TORRENT_DISABLE_EXTENSIONS` must not be defined). It also takes an optional `name` argument. This may be left empty in case no name should be assigned to the torrent. In case it's not, the name is used for the torrent as long as it doesn't have metadata. See `torrent_handle::name`.

The `add_torrent_params` is also used when requesting resume data for a torrent. It can be saved to and restored from a file and added back to a new session. For serialization and de-serialization of `add_torrent_params` objects, see read_resume_data() and write_resume_data().

    struct add_torrent_params
    {
       add_torrent_params (add_torrent_params&&) noexcept;
       add_torrent_params& operator= (add_torrent_params&&) = default;
       add_torrent_params& operator= (add_torrent_params const&);
       explicit add_torrent_params (storage_constructor_type sc = default_storage_constructor);
       add_torrent_params (add_torrent_params const&);

       int version  = LIBTORRENT_VERSION_NUM;
       std::shared_ptr<torrent_info> ti;
       aux::noexcept_movable<std::vector<std::string>> trackers;
       aux::noexcept_movable<std::vector<int>> tracker_tiers;
       aux::noexcept_movable<std::vector<std::pair<std::string, int>>> dht_nodes;
       std::string name;
       std::string save_path;
       storage_mode_t storage_mode  = storage_mode_sparse;
       aux::noexcept_movable<storage_constructor_type> storage;
       void* userdata  = nullptr;
       aux::noexcept_movable<std::vector<download_priority_t>> file_priorities;
       std::string trackerid;
       torrent_flags_t flags  = torrent_flags::default_flags;
       sha1_hash info_hash;
       int max_uploads  = -1;
       int max_connections  = -1;
       int upload_limit  = -1;
       int download_limit  = -1;
       std::int64_t total_uploaded  = 0;
       std::int64_t total_downloaded  = 0;
       int active_time  = 0;
       int finished_time  = 0;
       int seeding_time  = 0;
       std::time_t added_time  = 0;
       std::time_t completed_time  = 0;
       std::time_t last_seen_complete  = 0;
       int num_complete  = -1;
       int num_incomplete  = -1;
       int num_downloaded  = -1;
       aux::noexcept_movable<std::vector<std::string>> http_seeds;
       aux::noexcept_movable<std::vector<std::string>> url_seeds;
       aux::noexcept_movable<std::vector<tcp::endpoint>> peers;
       aux::noexcept_movable<std::vector<tcp::endpoint>> banned_peers;
       aux::noexcept_movable<std::map<piece_index_t, bitfield>> unfinished_pieces;
       typed_bitfield<piece_index_t> have_pieces;
       typed_bitfield<piece_index_t> verified_pieces;
       aux::noexcept_movable<std::vector<download_priority_t>> piece_priorities;
       aux::noexcept_movable<std::vector<sha1_hash>> merkle_tree;
       aux::noexcept_movable<std::map<file_index_t, std::string>> renamed_files;
       std::time_t last_download  = 0;
       std::time_t last_upload  = 0;
    };

[report issue]

#### add_torrent_params() operator=()

    add_torrent_params (add_torrent_params&&) noexcept;
    add_torrent_params& operator= (add_torrent_params&&) = default;
    add_torrent_params& operator= (add_torrent_params const&);
    explicit add_torrent_params (storage_constructor_type sc = default_storage_constructor);
    add_torrent_params (add_torrent_params const&);

The constructor can be used to initialize the storage constructor, which determines the storage mechanism for the downloaded or seeding data for the torrent. For more information, see the `storage` field.

[report issue]

version
  filled in by the constructor and should be left untouched. It is used for forward binary compatibility.

[report issue]

ti
  torrent_info object with the torrent to add. Unless the info_hash is set, this is required to be initialized.

[report issue]

trackers
  If the torrent doesn't have a tracker, but relies on the DHT to find peers, the `trackers` can specify tracker URLs for the torrent.

[report issue]

tracker_tiers
  the tiers the URLs in `trackers` belong to. Trackers belonging to different tiers may be treated differently, as defined by the multi tracker extension. This is optional, if not specified trackers are assumed to be part of tier 0, or whichever the last tier was as iterating over the trackers.

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dht_nodes
  a list of hostname and port pairs, representing DHT nodes to be added to the session (if DHT is enabled). The hostname may be an IP address.

[report issue]

name
  in case there's no other name in this torrent, this name will be used. The name out of the torrent_info object takes precedence if available.

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save_path

  the path where the torrent is or will be stored.

  Note

  On windows this path (and other paths) are interpreted as UNC paths. This means they must use backslashes as directory separators and may not contain the special directories "." or "..".

  Setting this to an absolute path performs slightly better than a relative path.

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storage_mode
  One of the values from storage_mode_t. For more information, see storage allocation.

[report issue]

storage
  can be used to customize how the data is stored. The default storage will simply write the data to the files it belongs to, but it could be overridden to save everything to a single file at a specific location or encrypt the content on disk for instance. For more information about the storage_interface that needs to be implemented for a custom storage, see storage_interface.

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userdata
  The `userdata` parameter is optional and will be passed on to the extension constructor functions, if any (see torrent_handle::add_extension()).

[report issue]

file_priorities
  can be set to control the initial file priorities when adding a torrent. The semantics are the same as for `torrent_handle::prioritize_files()`. The file priorities specified in here take precedence over those specified in the resume data, if any.

[report issue]

trackerid
  the default tracker id to be used when announcing to trackers. By default this is empty, and no tracker ID is used, since this is an optional argument. If a tracker returns a tracker ID, that ID is used instead of this.

[report issue]

flags

  flags controlling aspects of this torrent and how it's added. See torrent_flags_t for details.

  Note

  The `flags` field is initialized with default flags by the constructor. In order to preserve default behavior when clearing or setting other flags, make sure to bitwise OR or in a flag or bitwise AND the inverse of a flag to clear it.

[report issue]

info_hash
  set this to the info hash of the torrent to add in case the info-hash is the only known property of the torrent. i.e. you don't have a .torrent file nor a magnet link. To add a magnet link, use parse_magnet_uri() to populate fields in the add_torrent_params object.

[report issue]

max_uploads max_connections

  `max_uploads`, `max_connections`, `upload_limit`, `download_limit` correspond to the `set_max_uploads()`, `set_max_connections()`, `set_upload_limit()` and `set_download_limit()` functions on torrent_handle. These values let you initialize these settings when the torrent is added, instead of calling these functions immediately following adding it.

  -1 means unlimited on these settings just like their counterpart functions on torrent_handle

  For fine grained control over rate limits, including making them apply to local peers, see peer classes.

[report issue]

upload_limit download_limit
  the upload and download rate limits for this torrent, specified in bytes per second. -1 means unlimited.

[report issue]

total_uploaded total_downloaded
  the total number of bytes uploaded and downloaded by this torrent so far.

[report issue]

active_time finished_time seeding_time
  the number of seconds this torrent has spent in started, finished and seeding state so far, respectively.

[report issue]

added_time completed_time
  if set to a non-zero value, this is the posix time of when this torrent was first added, including previous runs/sessions. If set to zero, the internal added_time will be set to the time of when add_torrent() is called.

[report issue]

last_seen_complete
  if set to non-zero, initializes the time (expressed in posix time) when we last saw a seed or peers that together formed a complete copy of the torrent. If left set to zero, the internal counterpart to this field will be updated when we see a seed or a distributed copies >= 1.0.

[report issue]

num_complete num_incomplete num_downloaded

  these field can be used to initialize the torrent's cached scrape data. The scrape data is high level metadata about the current state of the swarm, as returned by the tracker (either when announcing to it or by sending a specific scrape request). `num_complete` is the number of peers in the swarm that are seeds, or have every piece in the torrent. `num_incomplete` is the number of peers in the swarm that do not have every piece. `num_downloaded` is the number of times the torrent has been downloaded (not initiated, but the number of times a download has completed).

  Leaving any of these values set to -1 indicates we don't know, or we have not received any scrape data.

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http_seeds url_seeds

  URLs can be added to these two lists to specify additional web seeds to be used by the torrent. If the `flag_override_web_seeds` is set, these will be the _only_ ones to be used. i.e. any web seeds found in the .torrent file will be overridden.

  http_seeds expects URLs to web servers implementing the original HTTP seed specification BEP 17.

  url_seeds expects URLs to regular web servers, aka "get right" style, specified in BEP 19.

[report issue]

peers
  peers to add to the torrent, to be tried to be connected to as bittorrent peers.

[report issue]

banned_peers
  peers banned from this torrent. The will not be connected to

[report issue]

unfinished_pieces
  this is a map of partially downloaded piece. The key is the piece index and the value is a bitfield where each bit represents a 16 kiB block. A set bit means we have that block.

[report issue]

have_pieces
  this is a bitfield indicating which pieces we already have of this torrent.

[report issue]

verified_pieces
  when in seed_mode, pieces with a set bit in this bitfield have been verified to be valid. Other pieces will be verified the first time a peer requests it.

[report issue]

piece_priorities
  this sets the priorities for each individual piece in the torrent. Each element in the vector represent the piece with the same index. If you set both file- and piece priorities, file priorities will take precedence.

[report issue]

merkle_tree
  if this is a merkle tree torrent, and you're seeding, this field must be set. It is all the hashes in the binary tree, with the root as the first entry. See torrent_info::set_merkle_tree() for more info.

[report issue]

renamed_files
  this is a map of file indices in the torrent and new filenames to be applied before the torrent is added.

[report issue]

last_download last_upload
  the posix time of the last time payload was received or sent for this torrent, respectively.

[report issue]

### peer_info

Declared in "libtorrent/peer_info.hpp"

holds information and statistics about one peer that libtorrent is connected to

    struct peer_info
    {
       enum connection_type_t
       {
          standard_bittorrent,
          web_seed,
          http_seed,
       };

       std::string client;
       typed_bitfield<piece_index_t> pieces;
       std::int64_t total_download;
       std::int64_t total_upload;
       time_duration last_request;
       time_duration last_active;
       time_duration download_queue_time;
       static constexpr peer_flags_t interesting  = 0_bit;
       static constexpr peer_flags_t choked  = 1_bit;
       static constexpr peer_flags_t remote_interested  = 2_bit;
       static constexpr peer_flags_t remote_choked  = 3_bit;
       static constexpr peer_flags_t supports_extensions  = 4_bit;
       static constexpr peer_flags_t local_connection  = 5_bit;
       static constexpr peer_flags_t handshake  = 6_bit;
       static constexpr peer_flags_t connecting  = 7_bit;
       static constexpr peer_flags_t on_parole  = 9_bit;
       static constexpr peer_flags_t seed  = 10_bit;
       static constexpr peer_flags_t optimistic_unchoke  = 11_bit;
       static constexpr peer_flags_t snubbed  = 12_bit;
       static constexpr peer_flags_t upload_only  = 13_bit;
       static constexpr peer_flags_t endgame_mode  = 14_bit;
       static constexpr peer_flags_t holepunched  = 15_bit;
       static constexpr peer_flags_t i2p_socket  = 16_bit;
       static constexpr peer_flags_t utp_socket  = 17_bit;
       static constexpr peer_flags_t ssl_socket  = 18_bit;
       static constexpr peer_flags_t rc4_encrypted  = 19_bit;
       static constexpr peer_flags_t plaintext_encrypted  = 20_bit;
       peer_flags_t flags;
       static constexpr peer_source_flags_t tracker  = 0_bit;
       static constexpr peer_source_flags_t dht  = 1_bit;
       static constexpr peer_source_flags_t pex  = 2_bit;
       static constexpr peer_source_flags_t lsd  = 3_bit;
       static constexpr peer_source_flags_t resume_data  = 4_bit;
       static constexpr peer_source_flags_t incoming  = 5_bit;
       peer_source_flags_t source;
       int up_speed;
       int down_speed;
       int payload_up_speed;
       int payload_down_speed;
       peer_id pid;
       int queue_bytes;
       int request_timeout;
       int send_buffer_size;
       int used_send_buffer;
       int receive_buffer_size;
       int used_receive_buffer;
       int receive_buffer_watermark;
       int num_hashfails;
       int download_queue_length;
       int timed_out_requests;
       int busy_requests;
       int requests_in_buffer;
       int target_dl_queue_length;
       int upload_queue_length;
       int failcount;
       piece_index_t downloading_piece_index;
       int downloading_block_index;
       int downloading_progress;
       int downloading_total;
       int connection_type;
       int pending_disk_bytes;
       int pending_disk_read_bytes;
       int send_quota;
       int receive_quota;
       int rtt;
       int num_pieces;
       int download_rate_peak;
       int upload_rate_peak;
       float progress;
       int progress_ppm;
       int deprecated_estimated_reciprocation_rate;
       tcp::endpoint ip;
       tcp::endpoint local_endpoint;
       static constexpr bandwidth_state_flags_t bw_idle  = 0_bit;
       static constexpr bandwidth_state_flags_t bw_limit  = 1_bit;
       static constexpr bandwidth_state_flags_t bw_network  = 2_bit;
       static constexpr bandwidth_state_flags_t bw_disk  = 4_bit;
       bandwidth_state_flags_t read_state;
       bandwidth_state_flags_t write_state;
    };

[report issue]

#### enum connection_type_t

Declared in "libtorrent/peer_info.hpp"

name | value | description
--- | --- | ---
standard_bittorrent | 0 | Regular bittorrent connection
web_seed | 1 | HTTP connection using the BEP 19 protocol
http_seed | 2 | HTTP connection using the BEP 17 protocol

[report issue]

client
  a string describing the software at the other end of the connection. In some cases this information is not available, then it will contain a string that may give away something about which software is running in the other end. In the case of a web seed, the server type and version will be a part of this string.

[report issue]

pieces
  a bitfield, with one bit per piece in the torrent. Each bit tells you if the peer has that piece (if it's set to 1) or if the peer miss that piece (set to 0).

[report issue]

total_download total_upload
  the total number of bytes downloaded from and uploaded to this peer. These numbers do not include the protocol chatter, but only the payload data.

[report issue]

last_request last_active
  the time since we last sent a request to this peer and since any transfer occurred with this peer

[report issue]

download_queue_time
  the time until all blocks in the request queue will be downloaded

[report issue]

interesting
  we are interested in pieces from this peer.

[report issue]

choked
  we have choked this peer.

[report issue]

remote_interested
  the peer is interested in us

[report issue]

remote_choked
  the peer has choked us.

[report issue]

supports_extensions
  means that this peer supports the extension protocol.

[report issue]

local_connection
  The connection was initiated by us, the peer has a listen port open, and that port is the same as in the address of this peer. If this flag is not set, this peer connection was opened by this peer connecting to us.

[report issue]

handshake
  The connection is opened, and waiting for the handshake. Until the handshake is done, the peer cannot be identified.

[report issue]

connecting
  The connection is in a half-open state (i.e. it is being connected).

[report issue]

on_parole
  The peer has participated in a piece that failed the hash check, and is now "on parole", which means we're only requesting whole pieces from this peer until it either fails that piece or proves that it doesn't send bad data.

[report issue]

seed
  This peer is a seed (it has all the pieces).

[report issue]

optimistic_unchoke
  This peer is subject to an optimistic unchoke. It has been unchoked for a while to see if it might unchoke us in return an earn an upload/unchoke slot. If it doesn't within some period of time, it will be choked and another peer will be optimistically unchoked.

[report issue]

snubbed
  This peer has recently failed to send a block within the request timeout from when the request was sent. We're currently picking one block at a time from this peer.

[report issue]

upload_only
  This peer has either explicitly (with an extension) or implicitly (by becoming a seed) told us that it will not downloading anything more, regardless of which pieces we have.

[report issue]

endgame_mode
  This means the last time this peer picket a piece, it could not pick as many as it wanted because there were not enough free ones. i.e. all pieces this peer has were already requested from other peers.

[report issue]

holepunched
  This flag is set if the peer was in holepunch mode when the connection succeeded. This typically only happens if both peers are behind a NAT and the peers connect via the NAT holepunch mechanism.

[report issue]

i2p_socket
  indicates that this socket is running on top of the I2P transport.

[report issue]

utp_socket
  indicates that this socket is a uTP socket

[report issue]

ssl_socket
  indicates that this socket is running on top of an SSL (TLS) channel

[report issue]

rc4_encrypted
  this connection is obfuscated with RC4

[report issue]

plaintext_encrypted
  the handshake of this connection was obfuscated with a Diffie-Hellman exchange

[report issue]

flags
  tells you in which state the peer is in. It is set to any combination of the peer_flags_t flags above.

[report issue]

tracker
  The peer was received from the tracker.

[report issue]

dht
  The peer was received from the kademlia DHT.

[report issue]

pex
  The peer was received from the peer exchange extension.

[report issue]

lsd
  The peer was received from the local service discovery (The peer is on the local network).

[report issue]

resume_data
  The peer was added from the fast resume data.

[report issue]

incoming
  we received an incoming connection from this peer

[report issue]

source
  a combination of flags describing from which sources this peer was received. A combination of the peer_source_flags_t above.

[report issue]

up_speed down_speed
  the current upload and download speed we have to and from this peer (including any protocol messages). updated about once per second

[report issue]

payload_up_speed payload_down_speed
  The transfer rates of payload data only updated about once per second

[report issue]

pid
  the peer's id as used in the bit torrent protocol. This id can be used to extract 'fingerprints' from the peer. Sometimes it can tell you which client the peer is using. See identify_client()_

[report issue]

queue_bytes
  the number of bytes we have requested from this peer, but not yet received.

[report issue]

request_timeout
  the number of seconds until the current front piece request will time out. This timeout can be adjusted through `settings_pack::request_timeout`. -1 means that there is not outstanding request.

[report issue]

send_buffer_size used_send_buffer
  the number of bytes allocated and used for the peer's send buffer, respectively.

[report issue]

receive_buffer_size used_receive_buffer receive_buffer_watermark
  the number of bytes allocated and used as receive buffer, respectively.

[report issue]

num_hashfails
  the number of pieces this peer has participated in sending us that turned out to fail the hash check.

[report issue]

download_queue_length
  this is the number of requests we have sent to this peer that we haven't got a response for yet

[report issue]

timed_out_requests
  the number of block requests that have timed out, and are still in the download queue

[report issue]

busy_requests
  the number of busy requests in the download queue. A busy request is a request for a block we've also requested from a different peer

[report issue]

requests_in_buffer
  the number of requests messages that are currently in the send buffer waiting to be sent.

[report issue]

target_dl_queue_length
  the number of requests that is tried to be maintained (this is typically a function of download speed)

[report issue]

upload_queue_length
  the number of piece-requests we have received from this peer that we haven't answered with a piece yet.

[report issue]

failcount
  the number of times this peer has "failed". i.e. failed to connect or disconnected us. The failcount is decremented when we see this peer in a tracker response or peer exchange message.

[report issue]

downloading_piece_index downloading_block_index downloading_progress downloading_total
  You can know which piece, and which part of that piece, that is currently being downloaded from a specific peer by looking at these four members. `downloading_piece_index` is the index of the piece that is currently being downloaded. This may be set to -1 if there's currently no piece downloading from this peer. If it is >= 0, the other three members are valid. `downloading_block_index` is the index of the block (or sub-piece) that is being downloaded. `downloading_progress` is the number of bytes of this block we have received from the peer, and `downloading_total` is the total number of bytes in this block.

[report issue]

connection_type
  the kind of connection this peer uses. See connection_type_t.

[report issue]

pending_disk_bytes
  the number of bytes this peer has pending in the disk-io thread. Downloaded and waiting to be written to disk. This is what is capped by `settings_pack::max_queued_disk_bytes`.

[report issue]

pending_disk_read_bytes
  number of outstanding bytes to read from disk

[report issue]

send_quota receive_quota
  the number of bytes this peer has been assigned to be allowed to send and receive until it has to request more quota from the bandwidth manager.

[report issue]

rtt
  an estimated round trip time to this peer, in milliseconds. It is estimated by timing the TCP `connect()`. It may be 0 for incoming connections.

[report issue]

num_pieces
  the number of pieces this peer has.

[report issue]

download_rate_peak upload_rate_peak
  the highest download and upload rates seen on this connection. They are given in bytes per second. This number is reset to 0 on reconnect.

[report issue]

progress
  the progress of the peer in the range [0, 1]. This is always 0 when floating point operations are disabled, instead use `progress_ppm`.

[report issue]

progress_ppm
  indicates the download progress of the peer in the range [0, 1000000] (parts per million).

[report issue]

ip
  the IP-address to this peer. The type is an asio endpoint. For more info, see the asio documentation.

[report issue]

local_endpoint
  the IP and port pair the socket is bound to locally. i.e. the IP address of the interface it's going out over. This may be useful for multi-homed clients with multiple interfaces to the internet.

[report issue]

bw_idle
  The peer is not waiting for any external events to send or receive data.

[report issue]

bw_limit
  The peer is waiting for the rate limiter.

[report issue]

bw_network
  The peer has quota and is currently waiting for a network read or write operation to complete. This is the state all peers are in if there are no bandwidth limits.

[report issue]

bw_disk
  The peer is waiting for the disk I/O thread to catch up writing buffers to disk before downloading more.

[report issue]

read_state write_state
  bitmasks indicating what state this peer is in with regards to sending and receiving data. The states are defined as independent flags of type bandwidth_state_flags_t, in this class.

[report issue]

### peer_request

Declared in "libtorrent/peer_request.hpp"

represents a byte range within a piece. Internally this is is used for incoming piece requests.

    struct peer_request
    {
       bool operator== (peer_request const& r) const;

       piece_index_t piece;
       int start;
       int length;
    };

[report issue]

#### operator==()

    bool operator== (peer_request const& r) const;

returns true if the right hand side peer_request refers to the same range as this does.

[report issue]

piece
  the index of the piece in which the range starts.

[report issue]

start
  the offset within that piece where the range starts.

[report issue]

length
  the size of the range, in bytes.

[report issue]

### write_resume_data() write_resume_data_buf()

Declared in "libtorrent/write_resume_data.hpp"

    std::vector<char> write_resume_data_buf (add_torrent_params const& atp);
    entry write_resume_data (add_torrent_params const& atp);

this function turns the resume data in an `add_torrent_params` object into a bencoded structure

[report issue]

### make_magnet_uri()

Declared in "libtorrent/magnet_uri.hpp"

    std::string make_magnet_uri (torrent_info const& info);
    std::string make_magnet_uri (torrent_handle const& handle);

Generates a magnet URI from the specified torrent. If the torrent handle is invalid, an empty string is returned.

For more information about magnet links, see magnet links.

[report issue]

### parse_magnet_uri()

Declared in "libtorrent/magnet_uri.hpp"

    void parse_magnet_uri (string_view uri, add_torrent_params& p, error_code& ec);
    add_torrent_params parse_magnet_uri (string_view uri);
    add_torrent_params parse_magnet_uri (string_view uri, error_code& ec);

This function parses out information from the magnet link and populates the add_torrent_params object. The overload that does not take an `error_code` reference will throw a system_error on error The overload taking an `add_torrent_params` reference will fill in the fields specified in the magnet URI.

[report issue]

### version()

Declared in "libtorrent/version.hpp"

    char const* version ();

returns the libtorrent version as string form in this format: "<major>.<minor>.<tiny>.<tag>"

[report issue]

### generate_fingerprint()

Declared in "libtorrent/fingerprint.hpp"

    std::string generate_fingerprint (std::string name
       , int major, int minor = 0, int revision = 0, int tag = 0);

This is a utility function to produce a client ID fingerprint formatted to the most common convention. The fingerprint can be set via the `peer_fingerprint` setting, in settings_pack.

The name string should contain exactly two characters. These are the characters unique to your client, used to identify it. Make sure not to clash with anybody else. Here are some taken id's:

id chars | client
--- | ---
LT | libtorrent (default)
UT | uTorrent
UM | uTorrent Mac
qB | qBittorrent
BP | BitTorrent Pro
BT | BitTorrent
DE | Deluge
AZ | Azureus
TL | Tribler

There's an informal directory of client id's here.

The `major`, `minor`, `revision` and `tag` parameters are used to identify the version of your client.

[report issue]

### hash_value()

Declared in "libtorrent/torrent_handle.hpp"

    std::size_t hash_value (torrent_handle const& h);

for std::hash (and to support using this type in unordered_map etc.)

[report issue]

### is_utp_stream_logging()

Declared in "libtorrent/utp_stream.hpp"

    bool is_utp_stream_logging ();

[report issue]

### set_utp_stream_logging()

Declared in "libtorrent/utp_stream.hpp"

    void set_utp_stream_logging (bool enable);

This function should be used at the very beginning and very end of your program.

[report issue]

### read_resume_data()

Declared in "libtorrent/read_resume_data.hpp"

    add_torrent_params read_resume_data (span<char const> buffer);
    add_torrent_params read_resume_data (span<char const> buffer
       , error_code& ec);
    add_torrent_params read_resume_data (bdecode_node const& rd
       , error_code& ec);
    add_torrent_params read_resume_data (bdecode_node const& rd);

these functions are used to parse resume data and populate the appropriate fields in an add_torrent_params object. This object can then be used to add the actual torrent_info object to and pass to session::add_torrent() or session::async_add_torrent().

If the client wants to override any field that was loaded from the resume data, e.g. save_path, those fields must be changed after loading resume data but before adding the torrent.

[report issue]

### enum connection_type

Declared in "libtorrent/peer_connection.hpp"

name | value | description
--- | --- | ---
bittorrent | 0 |
url_seed | 1 |
http_seed | 2 |

[report issue]

### enum portmap_transport

Declared in "libtorrent/portmap.hpp"

name | value | description
--- | --- | ---
natpmp | 0 | natpmp can be NAT-PMP or PCP
upnp | 1 |

[report issue]

### enum portmap_protocol

Declared in "libtorrent/portmap.hpp"

name | value | description
--- | --- | ---
none | 0 |
tcp | 1 |
udp | 2 |

[report issue]

### torrent_flags_t

Declared in "libtorrent/torrent_flags.hpp"

seed_mode

  If `seed_mode` is set, libtorrent will assume that all files are present for this torrent and that they all match the hashes in the torrent file. Each time a peer requests to download a block, the piece is verified against the hash, unless it has been verified already. If a hash fails, the torrent will automatically leave the seed mode and recheck all the files. The use case for this mode is if a torrent is created and seeded, or if the user already know that the files are complete, this is a way to avoid the initial file checks, and significantly reduce the startup time.

  Setting `seed_mode` on a torrent without metadata (a .torrent file) is a no-op and will be ignored.

  It is not possible to set the `seed_mode` flag on a torrent after it has been added to a session. It is possible to clear it though.

upload_mode

  If `upload_mode` is set, the torrent will be initialized in upload-mode, which means it will not make any piece requests. This state is typically entered on disk I/O errors, and if the torrent is also auto managed, it will be taken out of this state periodically (see `settings_pack::optimistic_disk_retry`).

  This mode can be used to avoid race conditions when adjusting priorities of pieces before allowing the torrent to start downloading.

  If the torrent is auto-managed (`auto_managed`), the torrent will eventually be taken out of upload-mode, regardless of how it got there. If it's important to manually control when the torrent leaves upload mode, don't make it auto managed.

share_mode

  determines if the torrent should be added in share mode or not. Share mode indicates that we are not interested in downloading the torrent, but merely want to improve our share ratio (i.e. increase it). A torrent started in share mode will do its best to never download more than it uploads to the swarm. If the swarm does not have enough demand for upload capacity, the torrent will not download anything. This mode is intended to be safe to add any number of torrents to, without manual screening, without the risk of downloading more than is uploaded.

  A torrent in share mode sets the priority to all pieces to 0, except for the pieces that are downloaded, when pieces are decided to be downloaded. This affects the progress bar, which might be set to "100% finished" most of the time. Do not change file or piece priorities for torrents in share mode, it will make it not work.

  The share mode has one setting, the share ratio target, see `settings_pack::share_mode_target` for more info.

apply_ip_filter
  determines if the IP filter should apply to this torrent or not. By default all torrents are subject to filtering by the IP filter (i.e. this flag is set by default). This is useful if certain torrents needs to be exempt for some reason, being an auto-update torrent for instance.

paused
  specifies whether or not the torrent is paused. i.e. it won't connect to the tracker or any of the peers until it's resumed. Note that a paused torrent that also has the auto_managed flag set can be started at any time by libtorrent's queuing logic. See queuing.

auto_managed

  If the torrent is auto-managed (`auto_managed`), the torrent may be resumed at any point, regardless of how it paused. If it's important to manually control when the torrent is paused and resumed, don't make it auto managed.

  If `auto_managed` is set, the torrent will be queued, started and seeded automatically by libtorrent. When this is set, the torrent should also be started as paused. The default queue order is the order the torrents were added. They are all downloaded in that order. For more details, see queuing.

duplicate_is_error
  used in add_torrent_params to indicate that it's an error to attempt to add a torrent that's already in the session. If it's not considered an error, a handle to the existing torrent is returned. This flag is not saved by write_resume_data(), since it is only meant for adding torrents.

update_subscribe
  on by default and means that this torrent will be part of state updates when calling post_torrent_updates(). This flag is not saved by write_resume_data().

super_seeding
  sets the torrent into super seeding/initial seeding mode. If the torrent is not a seed, this flag has no effect.

sequential_download
  sets the sequential download state for the torrent. In this mode the piece picker will pick pieces with low index numbers before pieces with high indices. The actual pieces that are picked depend on other factors still, such as which pieces a peer has and whether it is in parole mode or "prefer whole pieces"-mode. Sequential mode is not ideal for streaming media. For that, see set_piece_deadline() instead.

stop_when_ready

  When this flag is set, the torrent will force stop whenever it transitions from a non-data-transferring state into a data-transferring state (referred to as being ready to download or seed). This is useful for torrents that should not start downloading or seeding yet, but want to be made ready to do so. A torrent may need to have its files checked for instance, so it needs to be started and possibly queued for checking (auto-managed and started) but as soon as it's done, it should be stopped.

  Force stopped means auto-managed is set to false and it's paused. As if the auto_manages flag is cleared and the paused flag is set on the torrent.

  Note that the torrent may transition into a downloading state while setting this flag, and since the logic is edge triggered you may miss the edge. To avoid this race, if the torrent already is in a downloading state when this call is made, it will trigger the stop-when-ready immediately.

  When the stop-when-ready logic fires, the flag is cleared. Any subsequent transitions between downloading and non-downloading states will not be affected, until this flag is set again.

  The behavior is more robust when setting this flag as part of adding the torrent. See add_torrent_params.

  The stop-when-ready flag fixes the inherent race condition of waiting for the state_changed_alert and then call pause(). The download/seeding will most likely start in between posting the alert and receiving the call to pause.

  A downloading state is one where peers are being connected. Which means just downloading the metadata via the `ut_metadata` extension counts as a downloading state. In order to stop a torrent once the metadata has been downloaded, instead set all file priorities to dont_download

override_trackers
  when this flag is set, the tracker list in the add_torrent_params object override any trackers from the torrent file. If the flag is not set, the trackers from the add_torrent_params object will be added to the list of trackers used by the torrent. This flag is set by read_resume_data() if there are trackers present in the resume data file. This effectively makes the trackers saved in the resume data take precedence over the original trackers. This includes if there's an empty list of trackers, to support the case where they were explicitly removed in the previous session. This flag is not saved by write_resume_data()

override_web_seeds
  If this flag is set, the web seeds from the add_torrent_params object will override any web seeds in the torrent file. If it's not set, web seeds in the add_torrent_params object will be added to the list of web seeds used by the torrent. This flag is set by read_resume_data() if there are web seeds present in the resume data file. This effectively makes the web seeds saved in the resume data take precedence over the original ones. This includes if there's an empty list of web seeds, to support the case where they were explicitly removed in the previous session. This flag is not saved by write_resume_data()

need_save_resume
  if this flag is set (which it is by default) the torrent will be considered needing to save its resume data immediately as it's added. New torrents that don't have any resume data should do that. This flag is cleared by a successful call to save_resume_data() This flag is not saved by write_resume_data(), since it represents an ephemeral state of a running torrent.

disable_dht
  set this flag to disable DHT for this torrent. This lets you have the DHT enabled for the whole client, and still have specific torrents not participating in it. i.e. not announcing to the DHT nor picking up peers from it.

disable_lsd
  set this flag to disable local service discovery for this torrent.

disable_pex
  set this flag to disable peer exchange for this torrent.

all
  all torrent flags combined. Can conveniently be used when creating masks for flags

[report issue]

### download_priority_t

Declared in "libtorrent/download_priority.hpp"

dont_download
  Don't download the file or piece. Partial pieces may still be downloaded when setting file priorities.

default_priority
  The default priority for files and pieces.

low_priority
  The lowest priority for files and pieces.

top_priority
  The highest priority for files and pieces.

[report issue]

### pex_flags_t

Declared in "libtorrent/pex_flags.hpp"

pex_encryption
  the peer supports protocol encryption

pex_seed
  the peer is a seed

pex_utp
  the peer supports the uTP, transport protocol over UDP.

pex_holepunch
  the peer supports the holepunch extension If this flag is received from a peer, it can be used as a rendezvous point in case direct connections to the peer fail

[report issue]

### file_open_mode_t

Declared in "libtorrent/disk_interface.hpp"

read_only
  open the file for reading only

write_only
  open the file for writing only

read_write
  open the file for reading and writing

rw_mask
  the mask for the bits determining read or write mode

sparse
  open the file in sparse mode (if supported by the filesystem).

no_atime
  don't update the access timestamps on the file (if supported by the operating system and filesystem). this generally improves disk performance.

random_access
  open the file for random access. This disables read-ahead logic

[report issue]

### open_mode_t

Declared in "libtorrent/file.hpp"

read_only
  open the file for reading only

write_only
  open the file for writing only

read_write
  open the file for reading and writing

rw_mask
  the mask for the bits making up the read-write mode.

sparse
  open the file in sparse mode (if supported by the filesystem).

no_atime
  don't update the access timestamps on the file (if supported by the operating system and filesystem). this generally improves disk performance.

random_access
  open the file for random access. This disables read-ahead logic

no_cache
  don't put any pressure on the OS disk cache because of access to this file. We expect our files to be fairly large, and there is already a cache at the bittorrent block level. This may improve overall system performance by leaving running applications in the page cache

coalesce_buffers
  this is only used for readv/writev flags

attribute_hidden
  when creating a file, set the hidden attribute (windows only)

attribute_executable
  when creating a file, set the executable attribute

attribute_mask
  the mask of all attribute bits

Author: | Arvid Norberg, arvid@libtorrent.org
Version: | 1.2.9

home

## DHT

[report issue]

### dht_settings

Declared in "libtorrent/kademlia/dht_settings.hpp"

structure used to hold configuration options for the DHT

The `dht_settings` struct used to contain a `service_port` member to control which port the DHT would listen on and send messages from. This field is deprecated and ignored. libtorrent always tries to open the UDP socket on the same port as the TCP socket.

    struct dht_settings
    {
       int max_peers_reply  = 100;
       int search_branching  = 5;
       int max_fail_count  = 20;
       int max_torrents  = 2000;
       int max_dht_items  = 700;
       int max_peers  = 500;
       int max_torrent_search_reply  = 20;
       bool restrict_routing_ips  = true;
       bool restrict_search_ips  = true;
       bool extended_routing_table  = true;
       bool aggressive_lookups  = true;
       bool privacy_lookups  = false;
       bool enforce_node_id  = false;
       bool ignore_dark_internet  = true;
       int block_timeout  = 5 * 60;
       int block_ratelimit  = 5;
       bool read_only  = false;
       int item_lifetime  = 0;
       int upload_rate_limit  = 8000;
       int sample_infohashes_interval  = 21600;
       int max_infohashes_sample_count  = 20;
    };

[report issue]

max_peers_reply
  the maximum number of peers to send in a reply to `get_peers`

[report issue]

search_branching
  the number of concurrent search request the node will send when announcing and refreshing the routing table. This parameter is called alpha in the kademlia paper

[report issue]

max_fail_count
  the maximum number of failed tries to contact a node before it is removed from the routing table. If there are known working nodes that are ready to replace a failing node, it will be replaced immediately, this limit is only used to clear out nodes that don't have any node that can replace them.

[report issue]

max_torrents
  the total number of torrents to track from the DHT. This is simply an upper limit to make sure malicious DHT nodes cannot make us allocate an unbounded amount of memory.

[report issue]

max_dht_items
  max number of items the DHT will store

[report issue]

max_peers
  the max number of peers to store per torrent (for the DHT)

[report issue]

max_torrent_search_reply
  the max number of torrents to return in a torrent search query to the DHT

[report issue]

restrict_routing_ips

  determines if the routing table entries should restrict entries to one per IP. This defaults to true, which helps mitigate some attacks on the DHT. It prevents adding multiple nodes with IPs with a very close CIDR distance.

  when set, nodes whose IP address that's in the same /24 (or /64 for IPv6) range in the same routing table bucket. This is an attempt to mitigate node ID spoofing attacks also restrict any IP to only have a single entry in the whole routing table

[report issue]

restrict_search_ips
  determines if DHT searches should prevent adding nodes with IPs with very close CIDR distance. This also defaults to true and helps mitigate certain attacks on the DHT.

[report issue]

extended_routing_table
  makes the first buckets in the DHT routing table fit 128, 64, 32 and 16 nodes respectively, as opposed to the standard size of 8. All other buckets have size 8 still.

[report issue]

aggressive_lookups
  slightly changes the lookup behavior in terms of how many outstanding requests we keep. Instead of having branch factor be a hard limit, we always keep branch factor outstanding requests to the closest nodes. i.e. every time we get results back with closer nodes, we query them right away. It lowers the lookup times at the cost of more outstanding queries.

[report issue]

privacy_lookups
  when set, perform lookups in a way that is slightly more expensive, but which minimizes the amount of information leaked about you.

[report issue]

enforce_node_id
  when set, node's whose IDs that are not correctly generated based on its external IP are ignored. When a query arrives from such node, an error message is returned with a message saying "invalid node ID".

[report issue]

ignore_dark_internet
  ignore DHT messages from parts of the internet we wouldn't expect to see any traffic from

[report issue]

block_timeout
  the number of seconds a DHT node is banned if it exceeds the rate limit. The rate limit is averaged over 10 seconds to allow for bursts above the limit.

[report issue]

block_ratelimit
  the max number of packets per second a DHT node is allowed to send without getting banned.

[report issue]

read_only
  when set, the other nodes won't keep this node in their routing tables, it's meant for low-power and/or ephemeral devices that cannot support the DHT, it is also useful for mobile devices which are sensitive to network traffic and battery life. this node no longer responds to 'query' messages, and will place a 'ro' key (value = 1) in the top-level message dictionary of outgoing query messages.

[report issue]

item_lifetime
  the number of seconds a immutable/mutable item will be expired. default is 0, means never expires.

[report issue]

upload_rate_limit
  the number of bytes per second (on average) the DHT is allowed to send. If the incoming requests causes to many bytes to be sent in responses, incoming requests will be dropped until the quota has been replenished.

[report issue]

sample_infohashes_interval
  the info-hashes sample recomputation interval (in seconds). The node will precompute a subset of the tracked info-hashes and return that instead of calculating it upon each request. The permissible range is between 0 and 21600 seconds (inclusive).

[report issue]

max_infohashes_sample_count
  the maximum number of elements in the sampled subset of info-hashes. If this number is too big, expect the DHT storage implementations to clamp it in order to allow UDP packets go through

[report issue]

### dht_storage_counters

Declared in "libtorrent/kademlia/dht_storage.hpp"

This structure hold the relevant counters for the storage

    struct dht_storage_counters
    {
       void reset ();

       std::int32_t torrents  = 0;
       std::int32_t peers  = 0;
       std::int32_t immutable_data  = 0;
       std::int32_t mutable_data  = 0;
    };

[report issue]

#### reset()

    void reset ();

This member function set the counters to zero.

[report issue]

### dht_storage_interface

Declared in "libtorrent/kademlia/dht_storage.hpp"

The DHT storage interface is a pure virtual class that can be implemented to customize how the data for the DHT is stored.

The default storage implementation uses three maps in RAM to save the peers, mutable and immutable items and it's designed to provide a fast and fully compliant behavior of the BEPs.

libtorrent comes with one built-in storage implementation: `dht_default_storage` (private non-accessible class). Its constructor function is called dht_default_storage_constructor(). You should know that if this storage becomes full of DHT items, the current implementation could degrade in performance.

    struct dht_storage_interface
    {
       virtual void update_node_ids (std::vector<node_id> const& ids) = 0;
       virtual bool get_peers (sha1_hash const& info_hash
          , bool noseed, bool scrape, address const& requester
          , entry& peers) const = 0;
       virtual void announce_peer (sha1_hash const& info_hash
          , tcp::endpoint const& endp
          , string_view name, bool seed) = 0;
       virtual bool get_immutable_item (sha1_hash const& target
          , entry& item) const = 0;
       virtual void put_immutable_item (sha1_hash const& target
          , span<char const> buf
          , address const& addr) = 0;
       virtual bool get_mutable_item_seq (sha1_hash const& target
          , sequence_number& seq) const = 0;
       virtual bool get_mutable_item (sha1_hash const& target
          , sequence_number seq, bool force_fill
          , entry& item) const = 0;
       virtual void put_mutable_item (sha1_hash const& target
          , span<char const> buf
          , signature const& sig
          , sequence_number seq
          , public_key const& pk
          , span<char const> salt
          , address const& addr) = 0;
       virtual int get_infohashes_sample (entry& item) = 0;
       virtual void tick () = 0;
       virtual dht_storage_counters counters () const = 0;
    };

[report issue]

#### update_node_ids()

    virtual void update_node_ids (std::vector<node_id> const& ids) = 0;

This member function notifies the list of all node's ids of each DHT running inside libtorrent. It's advisable that the concrete implementation keeps a copy of this list for an eventual prioritization when deleting an element to make room for a new one.

[report issue]

#### get_peers()

    virtual bool get_peers (sha1_hash const& info_hash
          , bool noseed, bool scrape, address const& requester
          , entry& peers) const = 0;

This function retrieve the peers tracked by the DHT corresponding to the given info_hash. You can specify if you want only seeds and/or you are scraping the data.

For future implementers: If the torrent tracked contains a name, such a name must be stored as a string in peers["n"]

If the scrape parameter is true, you should fill these keys:

> peers["BFpe"]
>   with the standard bit representation of a 256 bloom filter containing the downloaders
> peers["BFsd"]
>   with the standard bit representation of a 256 bloom filter containing the seeders

If the scrape parameter is false, you should fill the key peers["values"] with a list containing a subset of peers tracked by the given info_hash. Such a list should consider the value of dht_settings::max_peers_reply. If noseed is true only peers marked as no seed should be included.

returns true if the maximum number of peers are stored for this info_hash.

[report issue]

#### announce_peer()

    virtual void announce_peer (sha1_hash const& info_hash
          , tcp::endpoint const& endp
          , string_view name, bool seed) = 0;

This function is named announce_peer for consistency with the upper layers, but has nothing to do with networking. Its only responsibility is store the peer in such a way that it's returned in the entry with the lookup_peers.

The `name` parameter is the name of the torrent if provided in the announce_peer DHT message. The length of this value should have a maximum length in the final storage. The default implementation truncate the value for a maximum of 50 characters.

[report issue]

#### get_immutable_item()

    virtual bool get_immutable_item (sha1_hash const& target
          , entry& item) const = 0;

This function retrieves the immutable item given its target hash.

For future implementers: The value should be returned as an entry in the key item["v"].

returns true if the item is found and the data is returned inside the (entry) out parameter item.

[report issue]

#### put_immutable_item()

    virtual void put_immutable_item (sha1_hash const& target
          , span<char const> buf
          , address const& addr) = 0;

Store the item's data. This layer is only for storage. The authentication of the item is performed by the upper layer.

For implementers: This data can be stored only if the target is not already present. The implementation should consider the value of dht_settings::max_dht_items.

[report issue]

#### get_mutable_item_seq()

    virtual bool get_mutable_item_seq (sha1_hash const& target
          , sequence_number& seq) const = 0;

This function retrieves the sequence number of a mutable item.

returns true if the item is found and the data is returned inside the out parameter seq.

[report issue]

#### get_mutable_item()

    virtual bool get_mutable_item (sha1_hash const& target
          , sequence_number seq, bool force_fill
          , entry& item) const = 0;

This function retrieves the mutable stored in the DHT.

For implementers: The item sequence should be stored in the key item["seq"]. if force_fill is true or (0 <= seq and seq < item["seq"]) the following keys should be filled item["v"] - with the value no encoded. item["sig"] - with a string representation of the signature. item["k"] - with a string representation of the public key.

returns true if the item is found and the data is returned inside the (entry) out parameter item.

[report issue]

#### put_mutable_item()

    virtual void put_mutable_item (sha1_hash const& target
          , span<char const> buf
          , signature const& sig
          , sequence_number seq
          , public_key const& pk
          , span<char const> salt
          , address const& addr) = 0;

Store the item's data. This layer is only for storage. The authentication of the item is performed by the upper layer.

For implementers: The sequence number should be checked if the item is already present. The implementation should consider the value of dht_settings::max_dht_items.

[report issue]

#### get_infohashes_sample()

    virtual int get_infohashes_sample (entry& item) = 0;

This function retrieves a sample info-hashes

For implementers: The info-hashes should be stored in ["samples"] (N x 20 bytes). the following keys should be filled item["interval"] - the subset refresh interval in seconds. item["num"] - number of info-hashes in storage.

Internally, this function is allowed to lazily evaluate, cache and modify the actual sample to put in `item`

returns the number of info-hashes in the sample.

[report issue]

#### tick()

    virtual void tick () = 0;

This function is called periodically (non-constant frequency).

For implementers: Use this functions for expire peers or items or any other storage cleanup.

[report issue]

#### counters()

    virtual dht_storage_counters counters () const = 0;

return stats counters for the store

[report issue]

### dht_state

Declared in "libtorrent/kademlia/dht_state.hpp"

This structure helps to store and load the state of the `dht_tracker`. At this moment the library is only a dual stack implementation of the DHT. See BEP 32

    struct dht_state
    {
       void clear ();

       node_ids_t nids;
       std::vector<udp::endpoint> nodes;
       std::vector<udp::endpoint> nodes6;
    };

[report issue]

nodes
  the bootstrap nodes saved from the buckets node

[report issue]

nodes6
  the bootstrap nodes saved from the IPv6 buckets node

[report issue]

### dht_default_storage_constructor()

Declared in "libtorrent/kademlia/dht_storage.hpp"

    std::unique_ptr<dht_storage_interface> dht_default_storage_constructor (
       dht_settings const& settings);

constructor for the default DHT storage. The DHT storage is responsible for maintaining peers and mutable and immutable items announced and stored/put to the DHT node.

[report issue]

### sign_mutable_item()

Declared in "libtorrent/kademlia/item.hpp"

    signature sign_mutable_item (
       span<char const> v
       , span<char const> salt
       , sequence_number seq
       , public_key const& pk
       , secret_key const& sk);

given a byte range `v` and an optional byte range `salt`, a sequence number, public key `pk` (must be 32 bytes) and a secret key `sk` (must be 64 bytes), this function produces a signature which is written into a 64 byte buffer pointed to by `sig`. The caller is responsible for allocating the destination buffer that's passed in as the `sig` argument. Typically it would be allocated on the stack.

[report issue]

### announce_flags_t

Declared in "libtorrent/kademlia/announce_flags.hpp"

seed
  announce to DHT as a seed

implied_port
  announce to DHT with the implied-port flag set. This tells the network to use your source UDP port as your listen port, rather than the one specified in the message. This may improve the chances of traversing NATs when using uTP.

ssl_torrent
  Specify the port number for the SSL listen socket in the DHT announce.

Author: | Arvid Norberg, arvid@libtorrent.org
Version: | 1.2.9

home

## Session

[report issue]

### stats_metric

Declared in "libtorrent/session_stats.hpp"

describes one statistics metric from the session. For more information, see the session statistics section.

    struct stats_metric
    {
       char const* name;
       int value_index;
       metric_type_t type;
    };

[report issue]

name
  the name of the counter or gauge

[report issue]

value_index type
  the index into the session stats array, where the underlying value of this counter or gauge is found. The session stats array is part of the session_stats_alert object.

[report issue]

### session_handle

Declared in "libtorrent/session_handle.hpp"

this class provides a non-owning handle to a session and a subset of the interface of the session class. If the underlying session is destructed any handle to it will no longer be valid. is_valid() will return false and any operation on it will throw a system_error exception, with error code invalid_session_handle.

    struct session_handle
    {
       bool is_valid () const;
       void load_state (bdecode_node const& e, save_state_flags_t flags = save_state_flags_t::all());
       void save_state (entry& e, save_state_flags_t flags = save_state_flags_t::all()) const;
       std::vector<torrent_status> get_torrent_status (
          std::function<bool(torrent_status const&)> const& pred
          , status_flags_t flags = {}) const;
       void refresh_torrent_status (std::vector<torrent_status>* ret
          , status_flags_t flags = {}) const;
       void post_torrent_updates (status_flags_t flags = status_flags_t::all());
       void post_session_stats ();
       void post_dht_stats ();
       std::vector<torrent_handle> get_torrents () const;
       torrent_handle find_torrent (sha1_hash const& info_hash) const;
       void async_add_torrent (add_torrent_params const& params);
       torrent_handle add_torrent (add_torrent_params const& params);
       torrent_handle add_torrent (add_torrent_params&& params);
       torrent_handle add_torrent (add_torrent_params&& params, error_code& ec);
       void async_add_torrent (add_torrent_params&& params);
       torrent_handle add_torrent (add_torrent_params const& params, error_code& ec);
       void resume ();
       bool is_paused () const;
       void pause ();
       void get_cache_info (cache_status* ret, torrent_handle h = torrent_handle(), int flags = 0) const;
       dht::dht_settings get_dht_settings () const;
       bool is_dht_running () const;
       void set_dht_settings (dht::dht_settings const& settings);
       void set_dht_storage (dht::dht_storage_constructor_type sc);
       void add_dht_node (std::pair<std::string, int> const& node);
       void dht_get_item (sha1_hash const& target);
       void dht_get_item (std::array<char, 32> key
          , std::string salt = std::string());
       sha1_hash dht_put_item (entry data);
       void dht_put_item (std::array<char, 32> key
          , std::function<void(entry&, std::array<char, 64>&
          , std::int64_t&, std::string const&)> cb
          , std::string salt = std::string());
       void dht_announce (sha1_hash const& info_hash, int port = 0, dht::announce_flags_t flags = {});
       void dht_get_peers (sha1_hash const& info_hash);
       void dht_live_nodes (sha1_hash const& nid);
       void dht_sample_infohashes (udp::endpoint const& ep, sha1_hash const& target);
       void dht_direct_request (udp::endpoint const& ep, entry const& e, void* userdata = nullptr);
       void add_extension (std::function<std::shared_ptr<torrent_plugin>(
          torrent_handle const&, void*)> ext);
       void add_extension (std::shared_ptr<plugin> ext);
       void set_ip_filter (ip_filter const& f);
       ip_filter get_ip_filter () const;
       void set_port_filter (port_filter const& f);
       unsigned short listen_port () const;
       bool is_listening () const;
       unsigned short ssl_listen_port () const;
       ip_filter get_peer_class_filter () const;
       void set_peer_class_filter (ip_filter const& f);
       void set_peer_class_type_filter (peer_class_type_filter const& f);
       peer_class_type_filter get_peer_class_type_filter () const;
       peer_class_t create_peer_class (char const* name);
       void delete_peer_class (peer_class_t cid);
       void set_peer_class (peer_class_t cid, peer_class_info const& pci);
       peer_class_info get_peer_class (peer_class_t cid) const;
       void remove_torrent (const torrent_handle& h, remove_flags_t options = {});
       void apply_settings (settings_pack const& s);
       settings_pack get_settings () const;
       void apply_settings (settings_pack&& s);
       void pop_alerts (std::vector<alert*>* alerts);
       alert* wait_for_alert (time_duration max_wait);
       void set_alert_notify (std::function<void()> const& fun);
       void delete_port_mapping (port_mapping_t handle);
       std::vector<port_mapping_t> add_port_mapping (portmap_protocol t, int external_port, int local_port);
       void reopen_network_sockets (reopen_network_flags_t options = reopen_map_ports);
       std::shared_ptr<aux::session_impl> native_handle () const;

       static constexpr save_state_flags_t save_settings  = 0_bit;
       static constexpr save_state_flags_t save_dht_settings  = 1_bit;
       static constexpr save_state_flags_t save_dht_state  = 2_bit;
       static constexpr peer_class_t global_peer_class_id {0};
       static constexpr peer_class_t tcp_peer_class_id {1};
       static constexpr peer_class_t local_peer_class_id {2};
       static constexpr remove_flags_t delete_files  = 0_bit;
       static constexpr remove_flags_t delete_partfile  = 1_bit;
       static constexpr session_flags_t add_default_plugins  = 0_bit;
       static constexpr portmap_protocol udp  = portmap_protocol::udp;
       static constexpr portmap_protocol tcp  = portmap_protocol::tcp;
       static constexpr reopen_network_flags_t reopen_map_ports  = 0_bit;
    };

[report issue]

#### is_valid()

    bool is_valid () const;

returns true if this handle refers to a valid session object. If the session has been destroyed, all session_handle objects will expire and not be valid.

[report issue]

#### save_state() load_state()

    void load_state (bdecode_node const& e, save_state_flags_t flags = save_state_flags_t::all());
    void save_state (entry& e, save_state_flags_t flags = save_state_flags_t::all()) const;

loads and saves all session settings, including dht_settings, encryption settings and proxy settings. `save_state` writes all keys to the `entry` that's passed in, which needs to either not be initialized, or initialized as a dictionary.

`load_state` expects a bdecode_node which can be built from a bencoded buffer with bdecode().

The `flags` argument is used to filter which parts of the session state to save or load. By default, all state is saved/restored (except for the individual torrents).

When saving settings, there are two fields that are not loaded. `peer_fingerprint` and `user_agent`. Those are left as configured by the `session_settings` passed to the session constructor or subsequently set via apply_settings().

[report issue]

#### get_torrent_status() refresh_torrent_status()

    std::vector<torrent_status> get_torrent_status (
          std::function<bool(torrent_status const&)> const& pred
          , status_flags_t flags = {}) const;
    void refresh_torrent_status (std::vector<torrent_status>* ret
          , status_flags_t flags = {}) const;

Note

these calls are potentially expensive and won't scale well with lots of torrents. If you're concerned about performance, consider using `post_torrent_updates()` instead.

`get_torrent_status` returns a vector of the torrent_status for every torrent which satisfies `pred`, which is a predicate function which determines if a torrent should be included in the returned set or not. Returning true means it should be included and false means excluded. The `flags` argument is the same as to torrent_handle::status(). Since `pred` is guaranteed to be called for every torrent, it may be used to count the number of torrents of different categories as well.

`refresh_torrent_status` takes a vector of torrent_status structs (for instance the same vector that was returned by get_torrent_status() ) and refreshes the status based on the `handle` member. It is possible to use this function by first setting up a vector of default constructed `torrent_status` objects, only initializing the `handle` member, in order to request the torrent status for multiple torrents in a single call. This can save a significant amount of time if you have a lot of torrents.

Any torrent_status object whose `handle` member is not referring to a valid torrent are ignored.

The intended use of these functions is to start off by calling `get_torrent_status()` to get a list of all torrents that match your criteria. Then call `refresh_torrent_status()` on that list. This will only refresh the status for the torrents in your list, and thus ignore all other torrents you might be running. This may save a significant amount of time, especially if the number of torrents you're interested in is small. In order to keep your list of interested torrents up to date, you can either call `get_torrent_status()` from time to time, to include torrents you might have become interested in since the last time. In order to stop refreshing a certain torrent, simply remove it from the list.

[report issue]

#### post_torrent_updates()

    void post_torrent_updates (status_flags_t flags = status_flags_t::all());

This functions instructs the session to post the state_update_alert, containing the status of all torrents whose state changed since the last time this function was called.

Only torrents who has the state subscription flag set will be included. This flag is on by default. See add_torrent_params. the `flags` argument is the same as for torrent_handle::status(). see status_flags_t in torrent_handle.

[report issue]

#### post_session_stats()

    void post_session_stats ();

This function will post a session_stats_alert object, containing a snapshot of the performance counters from the internals of libtorrent. To interpret these counters, query the session via session_stats_metrics().

For more information, see the session statistics section.

[report issue]

#### post_dht_stats()

    void post_dht_stats ();

This will cause a dht_stats_alert to be posted.

[report issue]

#### get_torrents() find_torrent()

    std::vector<torrent_handle> get_torrents () const;
    torrent_handle find_torrent (sha1_hash const& info_hash) const;

`find_torrent()` looks for a torrent with the given info-hash. In case there is such a torrent in the session, a torrent_handle to that torrent is returned. In case the torrent cannot be found, an invalid torrent_handle is returned.

See `torrent_handle::is_valid()` to know if the torrent was found or not.

`get_torrents()` returns a vector of torrent_handles to all the torrents currently in the session.

[report issue]

#### add_torrent() async_add_torrent()

    void async_add_torrent (add_torrent_params const& params);
    torrent_handle add_torrent (add_torrent_params const& params);
    torrent_handle add_torrent (add_torrent_params&& params);
    torrent_handle add_torrent (add_torrent_params&& params, error_code& ec);
    void async_add_torrent (add_torrent_params&& params);
    torrent_handle add_torrent (add_torrent_params const& params, error_code& ec);

You add torrents through the add_torrent() function where you give an object with all the parameters. The add_torrent() overloads will block until the torrent has been added (or failed to be added) and returns an error code and a torrent_handle. In order to add torrents more efficiently, consider using async_add_torrent() which returns immediately, without waiting for the torrent to add. Notification of the torrent being added is sent as add_torrent_alert.

The overload that does not take an error_code throws an exception on error and is not available when building without exception support. The torrent_handle returned by add_torrent() can be used to retrieve information about the torrent's progress, its peers etc. It is also used to abort a torrent.

If the torrent you are trying to add already exists in the session (is either queued for checking, being checked or downloading) `add_torrent()` will throw system_error which derives from `std::exception` unless duplicate_is_error is set to false. In that case, add_torrent() will return the handle to the existing torrent.

The add_torrent_params class has a flags field. It can be used to control what state the new torrent will be added in. Common flags to want to control are torrent_flags::paused and torrent_flags::auto_managed. In order to add a magnet link that will just download the metadata, but no payload, set the torrent_flags::upload_mode flag.

[report issue]

#### pause() resume() is_paused()

    void resume ();
    bool is_paused () const;
    void pause ();

Pausing the session has the same effect as pausing every torrent in it, except that torrents will not be resumed by the auto-manage mechanism. Resuming will restore the torrents to their previous paused state. i.e. the session pause state is separate from the torrent pause state. A torrent is inactive if it is paused or if the session is paused.

[report issue]

#### get_cache_info()

    void get_cache_info (cache_status* ret, torrent_handle h = torrent_handle(), int flags = 0) const;

Fills in the cache_status struct with information about the given torrent. If `flags` is `session::disk_cache_no_pieces` the `cache_status::pieces` field will not be set. This may significantly reduce the cost of this call.

[report issue]

#### is_dht_running() get_dht_settings() set_dht_settings()

    dht::dht_settings get_dht_settings () const;
    bool is_dht_running () const;
    void set_dht_settings (dht::dht_settings const& settings);

`set_dht_settings` sets some parameters available to the dht node. See dht_settings for more information.

`is_dht_running()` returns true if the DHT support has been started and false otherwise.

`get_dht_settings()` returns the current settings

[report issue]

#### set_dht_storage()

    void set_dht_storage (dht::dht_storage_constructor_type sc);

`set_dht_storage` set a dht custom storage constructor function to be used internally when the dht is created.

Since the dht storage is a critical component for the dht behavior, this function will only be effective the next time the dht is started. If you never touch this feature, a default map-memory based storage is used.

If you want to make sure the dht is initially created with your custom storage, create a session with the setting `settings_pack::enable_dht` to false, set your constructor function and call `apply_settings` with `settings_pack::enable_dht` to true.

[report issue]

#### add_dht_node()

    void add_dht_node (std::pair<std::string, int> const& node);

`add_dht_node` takes a host name and port pair. That endpoint will be pinged, and if a valid DHT reply is received, the node will be added to the routing table.

[report issue]

#### dht_get_item()

    void dht_get_item (sha1_hash const& target);

query the DHT for an immutable item at the `target` hash. the result is posted as a dht_immutable_item_alert.

[report issue]

#### dht_get_item()

    void dht_get_item (std::array<char, 32> key
          , std::string salt = std::string());

query the DHT for a mutable item under the public key `key`. this is an ed25519 key. `salt` is optional and may be left as an empty string if no salt is to be used. if the item is found in the DHT, a dht_mutable_item_alert is posted.

[report issue]

#### dht_put_item()

    sha1_hash dht_put_item (entry data);

store the given bencoded data as an immutable item in the DHT. the returned hash is the key that is to be used to look the item up again. It's just the SHA-1 hash of the bencoded form of the structure.

[report issue]

#### dht_put_item()

    void dht_put_item (std::array<char, 32> key
          , std::function<void(entry&, std::array<char, 64>&
          , std::int64_t&, std::string const&)> cb
          , std::string salt = std::string());

store a mutable item. The `key` is the public key the blob is to be stored under. The optional `salt` argument is a string that is to be mixed in with the key when determining where in the DHT the value is to be stored. The callback function is called from within the libtorrent network thread once we've found where to store the blob, possibly with the current value stored under the key. The values passed to the callback functions are:

entry& value
  the current value stored under the key (may be empty). Also expected to be set to the value to be stored by the function.
std::array<char,64>& signature
  the signature authenticating the current value. This may be zeros if there is currently no value stored. The function is expected to fill in this buffer with the signature of the new value to store. To generate the signature, you may want to use the `sign_mutable_item` function.
std::int64_t& seq
  current sequence number. May be zero if there is no current value. The function is expected to set this to the new sequence number of the value that is to be stored. Sequence numbers must be monotonically increasing. Attempting to overwrite a value with a lower or equal sequence number will fail, even if the signature is correct.
std::string const& salt
  this is the salt that was used for this put call.

Since the callback function `cb` is called from within libtorrent, it is critical to not perform any blocking operations. Ideally not even locking a mutex. Pass any data required for this function along with the function object's context and make the function entirely self-contained. The only reason data blob's value is computed via a function instead of just passing in the new value is to avoid race conditions. If you want to update the value in the DHT, you must first retrieve it, then modify it, then write it back. The way the DHT works, it is natural to always do a lookup before storing and calling the callback in between is convenient.

[report issue]

#### dht_get_peers() dht_announce()

    void dht_announce (sha1_hash const& info_hash, int port = 0, dht::announce_flags_t flags = {});
    void dht_get_peers (sha1_hash const& info_hash);

`dht_get_peers()` will issue a DHT get_peer request to the DHT for the specified info-hash. The response (the peers) will be posted back in a dht_get_peers_reply_alert.

`dht_announce()` will issue a DHT announce request to the DHT to the specified info-hash, advertising the specified port. If the port is left at its default, 0, the port will be implied by the DHT message's source port (which may improve connectivity through a NAT).

Both these functions are exposed for advanced custom use of the DHT. All torrents eligible to be announce to the DHT will be automatically, by libtorrent.

For possible flags, see announce_flags_t.

[report issue]

#### dht_live_nodes()

    void dht_live_nodes (sha1_hash const& nid);

Retrieve all the live DHT (identified by `nid`) nodes. All the nodes id and endpoint will be returned in the list of nodes in the alert `dht_live_nodes_alert`. Since this alert is a response to an explicit call, it will always be posted, regardless of the alert mask.

[report issue]

#### dht_sample_infohashes()

    void dht_sample_infohashes (udp::endpoint const& ep, sha1_hash const& target);

Query the DHT node specified by `ep` to retrieve a sample of the info-hashes that the node currently have in their storage. The `target` is included for iterative lookups so that indexing nodes can perform a key space traversal with a single RPC per node by adjusting the target value for each RPC. It has no effect on the returned sample value. The result is posted as a `dht_sample_infohashes_alert`.

[report issue]

#### dht_direct_request()

    void dht_direct_request (udp::endpoint const& ep, entry const& e, void* userdata = nullptr);

Send an arbitrary DHT request directly to the specified endpoint. This function is intended for use by plugins. When a response is received or the request times out, a dht_direct_response_alert will be posted with the response (if any) and the userdata pointer passed in here. Since this alert is a response to an explicit call, it will always be posted, regardless of the alert mask.

[report issue]

#### add_extension()

    void add_extension (std::function<std::shared_ptr<torrent_plugin>(
          torrent_handle const&, void*)> ext);
    void add_extension (std::shared_ptr<plugin> ext);

This function adds an extension to this session. The argument is a function object that is called with a `torrent_handle` and which should return a `std::shared_ptr<torrent_plugin>`. To write custom plugins, see libtorrent plugins. For the typical bittorrent client all of these extensions should be added. The main plugins implemented in libtorrent are:

uTorrent metadata
  Allows peers to download the metadata (.torrent files) from the swarm directly. Makes it possible to join a swarm with just a tracker and info-hash.

    #include <libtorrent/extensions/ut_metadata.hpp>
    ses.add_extension(&lt::create_ut_metadata_plugin);

uTorrent peer exchange
  Exchanges peers between clients.

    #include <libtorrent/extensions/ut_pex.hpp>
    ses.add_extension(&lt::create_ut_pex_plugin);

smart ban plugin
  A plugin that, with a small overhead, can ban peers that sends bad data with very high accuracy. Should eliminate most problems on poisoned torrents.

    #include <libtorrent/extensions/smart_ban.hpp>
    ses.add_extension(&lt::create_smart_ban_plugin);

[report issue]

#### get_ip_filter() set_ip_filter()

    void set_ip_filter (ip_filter const& f);
    ip_filter get_ip_filter () const;

Sets a filter that will be used to reject and accept incoming as well as outgoing connections based on their originating ip address. The default filter will allow connections to any ip address. To build a set of rules for which addresses are accepted and not, see ip_filter.

Each time a peer is blocked because of the IP filter, a peer_blocked_alert is generated. `get_ip_filter()` Returns the ip_filter currently in the session. See ip_filter.

[report issue]

#### set_port_filter()

    void set_port_filter (port_filter const& f);

apply port_filter `f` to incoming and outgoing peers. a port filter will reject making outgoing peer connections to certain remote ports. The main intention is to be able to avoid triggering certain anti-virus software by connecting to SMTP, FTP ports.

[report issue]

#### listen_port() ssl_listen_port() is_listening()

    unsigned short listen_port () const;
    bool is_listening () const;
    unsigned short ssl_listen_port () const;

`is_listening()` will tell you whether or not the session has successfully opened a listening port. If it hasn't, this function will return false, and then you can set a new settings_pack::listen_interfaces to try another interface and port to bind to.

`listen_port()` returns the port we ended up listening on.

[report issue]

#### get_peer_class_filter() set_peer_class_filter()

    ip_filter get_peer_class_filter () const;
    void set_peer_class_filter (ip_filter const& f);

Sets the peer class filter for this session. All new peer connections will take this into account and be added to the peer classes specified by this filter, based on the peer's IP address.

The ip-filter essentially maps an IP -> uint32. Each bit in that 32 bit integer represents a peer class. The least significant bit represents class 0, the next bit class 1 and so on.

For more info, see ip_filter.

For example, to make all peers in the range 200.1.1.0 - 200.1.255.255 belong to their own peer class, apply the following filter:

    ip_filter f = ses.get_peer_class_filter();
    peer_class_t my_class = ses.create_peer_class("200.1.x.x IP range");
    f.add_rule(make_address("200.1.1.0"), make_address("200.1.255.255")
            , 1 << static_cast<std::uint32_t>(my_class));
    ses.set_peer_class_filter(f);

This setting only applies to new connections, it won't affect existing peer connections.

This function is limited to only peer class 0-31, since there are only 32 bits in the IP range mapping. Only the set bits matter; no peer class will be removed from a peer as a result of this call, peer classes are only added.

The `peer_class` argument cannot be greater than 31. The bitmasks representing peer classes in the `peer_class_filter` are 32 bits.

The `get_peer_class_filter()` function returns the current filter.

For more information, see peer classes.

[report issue]

#### get_peer_class_type_filter() set_peer_class_type_filter()

    void set_peer_class_type_filter (peer_class_type_filter const& f);
    peer_class_type_filter get_peer_class_type_filter () const;

Sets and gets the peer class type filter. This is controls automatic peer class assignments to peers based on what kind of socket it is.

It does not only support assigning peer classes, it also supports removing peer classes based on socket type.

The order of these rules being applied are:

1. peer-class IP filter
2. peer-class type filter, removing classes
3. peer-class type filter, adding classes

For more information, see peer classes.

[report issue]

#### create_peer_class()

    peer_class_t create_peer_class (char const* name);

Creates a new peer class (see peer classes) with the given name. The returned integer is the new peer class identifier. Peer classes may have the same name, so each invocation of this function creates a new class and returns a unique identifier.

Identifiers are assigned from low numbers to higher. So if you plan on using certain peer classes in a call to set_peer_class_filter(), make sure to create those early on, to get low identifiers.

For more information on peer classes, see peer classes.

[report issue]

#### delete_peer_class()

    void delete_peer_class (peer_class_t cid);

This call dereferences the reference count of the specified peer class. When creating a peer class it's automatically referenced by 1. If you want to recycle a peer class, you may call this function. You may only call this function once per peer class you create. Calling it more than once for the same class will lead to memory corruption.

Since peer classes are reference counted, this function will not remove the peer class if it's still assigned to torrents or peers. It will however remove it once the last peer and torrent drops their references to it.

There is no need to call this function for custom peer classes. All peer classes will be properly destructed when the session object destructs.

For more information on peer classes, see peer classes.

[report issue]

#### set_peer_class() get_peer_class()

    void set_peer_class (peer_class_t cid, peer_class_info const& pci);
    peer_class_info get_peer_class (peer_class_t cid) const;

These functions queries information from a peer class and updates the configuration of a peer class, respectively.

`cid` must refer to an existing peer class. If it does not, the return value of `get_peer_class()` is undefined.

`set_peer_class()` sets all the information in the peer_class_info object in the specified peer class. There is no option to only update a single property.

A peer or torrent belonging to more than one class, the highest priority among any of its classes is the one that is taken into account.

For more information, see peer classes.

[report issue]

#### remove_torrent()

    void remove_torrent (const torrent_handle& h, remove_flags_t options = {});

`remove_torrent()` will close all peer connections associated with the torrent and tell the tracker that we've stopped participating in the swarm. This operation cannot fail. When it completes, you will receive a torrent_removed_alert.

The optional second argument `options` can be used to delete all the files downloaded by this torrent. To do so, pass in the value `session_handle::delete_files`. The removal of the torrent is asynchronous, there is no guarantee that adding the same torrent immediately after it was removed will not throw a system_error exception. Once the torrent is deleted, a torrent_deleted_alert is posted.

Note that when a queued or downloading torrent is removed, its position in the download queue is vacated and every subsequent torrent in the queue has their queue positions updated. This can potentially cause a large state_update to be posted. When removing all torrents, it is advised to remove them from the back of the queue, to minimize the shifting.

[report issue]

#### get_settings() apply_settings()

    void apply_settings (settings_pack const& s);
    settings_pack get_settings () const;
    void apply_settings (settings_pack&& s);

Applies the settings specified by the settings_pack `s`. This is an asynchronous operation that will return immediately and actually apply the settings to the main thread of libtorrent some time later.

[report issue]

#### wait_for_alert() set_alert_notify() pop_alerts()

    void pop_alerts (std::vector<alert*>* alerts);
    alert* wait_for_alert (time_duration max_wait);
    void set_alert_notify (std::function<void()> const& fun);

Alerts is the main mechanism for libtorrent to report errors and events. `pop_alerts` fills in the vector passed to it with pointers to new alerts. The session still owns these alerts and they will stay valid until the next time `pop_alerts` is called. You may not delete the alert objects.

It is safe to call `pop_alerts` from multiple different threads, as long as the alerts themselves are not accessed once another thread calls `pop_alerts`. Doing this requires manual synchronization between the popping threads.

`wait_for_alert` will block the current thread for `max_wait` time duration, or until another alert is posted. If an alert is available at the time of the call, it returns immediately. The returned alert pointer is the head of the alert queue. `wait_for_alert` does not pop alerts from the queue, it merely peeks at it. The returned alert will stay valid until `pop_alerts` is called twice. The first time will pop it and the second will free it.

If there is no alert in the queue and no alert arrives within the specified timeout, `wait_for_alert` returns nullptr.

In the python binding, `wait_for_alert` takes the number of milliseconds to wait as an integer.

The alert queue in the session will not grow indefinitely. Make sure to pop periodically to not miss notifications. To control the max number of alerts that's queued by the session, see `settings_pack::alert_queue_size`.

Some alerts are considered so important that they are posted even when the alert queue is full. Some alerts are considered mandatory and cannot be disabled by the `alert_mask`. For instance, save_resume_data_alert and save_resume_data_failed_alert are always posted, regardless of the alert mask.

To control which alerts are posted, set the alert_mask (settings_pack::alert_mask).

If the alert queue fills up to the point where alerts are dropped, this will be indicated by a alerts_dropped_alert, which contains a bitmask of which types of alerts were dropped. Generally it is a good idea to make sure the alert queue is large enough, the alert_mask doesn't have unnecessary categories enabled and to call pop_alert() frequently, to avoid alerts being dropped.

the `set_alert_notify` function lets the client set a function object to be invoked every time the alert queue goes from having 0 alerts to 1 alert. This function is called from within libtorrent, it may be the main thread, or it may be from within a user call. The intention of of the function is that the client wakes up its main thread, to poll for more alerts using `pop_alerts()`. If the notify function fails to do so, it won't be called again, until `pop_alerts` is called for some other reason. For instance, it could signal an eventfd, post a message to an HWND or some other main message pump. The actual retrieval of alerts should not be done in the callback. In fact, the callback should not block. It should not perform any expensive work. It really should just notify the main application thread.

The type of an alert is returned by the polymorphic function `alert::type()` but can also be queries from a concrete type via `T::alert_type`, as a static constant.

[report issue]

#### add_port_mapping() delete_port_mapping()

    void delete_port_mapping (port_mapping_t handle);
    std::vector<port_mapping_t> add_port_mapping (portmap_protocol t, int external_port, int local_port);

add_port_mapping adds one or more port forwards on UPnP and/or NAT-PMP, whichever is enabled. A mapping is created for each listen socket in the session. The return values are all handles referring to the port mappings that were just created. Pass them to delete_port_mapping() to remove them.

[report issue]

#### reopen_network_sockets()

    void reopen_network_sockets (reopen_network_flags_t options = reopen_map_ports);

Instructs the session to reopen all listen and outgoing sockets.

It's useful in the case your platform doesn't support the built in IP notifier mechanism, or if you have a better more reliable way to detect changes in the IP routing table.

[report issue]

#### native_handle()

    std::shared_ptr<aux::session_impl> native_handle () const;

This function is intended only for use by plugins. This type does not have a stable API and should be relied on as little as possible.

[report issue]

save_settings
  saves settings (i.e. the settings_pack)

[report issue]

save_dht_settings
  saves dht_settings

[report issue]

save_dht_state
  saves dht state such as nodes and node-id, possibly accelerating joining the DHT if provided at next session startup.

[report issue]

global_peer_class_id tcp_peer_class_id local_peer_class_id
  built-in peer classes

[report issue]

delete_files
  delete the files belonging to the torrent from disk. including the part-file, if there is one

[report issue]

delete_partfile
  delete just the part-file associated with this torrent

[report issue]

add_default_plugins
  this will add common extensions like ut_pex, ut_metadata, lt_tex smart_ban and possibly others.

[report issue]

udp tcp
  protocols used by add_port_mapping()

[report issue]

reopen_map_ports
  This option indicates if the ports are mapped using natpmp and upnp. If mapping was already made, they are deleted and added again. This only works if natpmp and/or upnp are configured to be enable.

[report issue]

### session_proxy

Declared in "libtorrent/session.hpp"

this is a holder for the internal session implementation object. Once the session destruction is explicitly initiated, this holder is used to synchronize the completion of the shutdown. The lifetime of this object may outlive session, causing the session destructor to not block. The session_proxy destructor will block however, until the underlying session is done shutting down.

    class session_proxy
    {
       session_proxy (session_proxy const&);
       session_proxy& operator= (session_proxy const&);
       ~session_proxy ();
       session_proxy& operator= (session_proxy&&) noexcept;
       session_proxy ();
       session_proxy (session_proxy&&) noexcept;
    };

[report issue]

#### ~session_proxy() session_proxy() operator=()

    session_proxy (session_proxy const&);
    session_proxy& operator= (session_proxy const&);
    ~session_proxy ();
    session_proxy& operator= (session_proxy&&) noexcept;
    session_proxy ();
    session_proxy (session_proxy&&) noexcept;

default constructor, does not refer to any session implementation object.

[report issue]

### session_params

Declared in "libtorrent/session.hpp"

The session_params is a parameters pack for configuring the session before it's started.

    struct session_params
    {
       explicit session_params (settings_pack&& sp);
       session_params ();
       explicit session_params (settings_pack const& sp);
       session_params (settings_pack const& sp
          , std::vector<std::shared_ptr<plugin>> exts);
       session_params (settings_pack&& sp
          , std::vector<std::shared_ptr<plugin>> exts);

       settings_pack settings;
       std::vector<std::shared_ptr<plugin>> extensions;
       dht::dht_settings dht_settings;
       dht::dht_state dht_state;
       dht::dht_storage_constructor_type dht_storage_constructor;
    };

[report issue]

#### session_params()

    explicit session_params (settings_pack&& sp);
    session_params ();
    explicit session_params (settings_pack const& sp);

This constructor can be used to start with the default plugins (ut_metadata, ut_pex and smart_ban). The default values in the settings is to start the default features like upnp, NAT-PMP, and dht for example.

[report issue]

#### session_params()

    session_params (settings_pack const& sp
          , std::vector<std::shared_ptr<plugin>> exts);
    session_params (settings_pack&& sp
          , std::vector<std::shared_ptr<plugin>> exts);

This constructor helps to configure the set of initial plugins to be added to the session before it's started.

[report issue]

### session

Declared in "libtorrent/session.hpp"

The session holds all state that spans multiple torrents. Among other things it runs the network loop and manages all torrents. Once it's created, the session object will spawn the main thread that will do all the work. The main thread will be idle as long it doesn't have any torrents to participate in.

You have some control over session configuration through the `session_handle::apply_settings()` member function. To change one or more configuration options, create a settings_pack. object and fill it with the settings to be set and pass it in to `session::apply_settings()`.

see apply_settings().

    class session : public session_handle
    {
       explicit session (session_params&& params);
       session ();
       explicit session (session_params const& params);
       session (session_params const& params, io_service& ios);
       session (session_params&& params, io_service& ios);
       session (settings_pack&& pack
          , session_flags_t const flags = add_default_plugins);
       session (settings_pack const& pack
          , session_flags_t const flags = add_default_plugins);
       session& operator= (session&&) = default;
       session (session&&) = default;
       session& operator= (session const&) = delete;
       session (session const&) = delete;
       session (settings_pack&& pack
          , io_service& ios
          , session_flags_t const flags = add_default_plugins);
       session (settings_pack const& pack
          , io_service& ios
          , session_flags_t const flags = add_default_plugins);
       ~session ();
       session_proxy abort ();
    };

[report issue]

#### session()

    explicit session (session_params&& params);
    session ();
    explicit session (session_params const& params);

Constructs the session objects which acts as the container of torrents. In order to avoid a race condition between starting the session and configuring it, you can pass in a session_params object. Its settings will take effect before the session starts up.

[report issue]

#### session()

    session (session_params const& params, io_service& ios);
    session (session_params&& params, io_service& ios);

Overload of the constructor that takes an external io_service to run the session object on. This is primarily useful for tests that may want to run multiple sessions on a single io_service, or low resource systems where additional threads are expensive and sharing an io_service with other events is fine.

Warning

The session object does not cleanly terminate with an external `io_service`. The `io_service::run()` call _must_ have returned before it's safe to destruct the session. Which means you MUST call session::abort() and save the session_proxy first, then destruct the session object, then sync with the io_service, then destruct the session_proxy object.

[report issue]

#### session()

    session (settings_pack&& pack
          , session_flags_t const flags = add_default_plugins);
    session (settings_pack const& pack
          , session_flags_t const flags = add_default_plugins);

Constructs the session objects which acts as the container of torrents. It provides configuration options across torrents (such as rate limits, disk cache, ip filter etc.). In order to avoid a race condition between starting the session and configuring it, you can pass in a settings_pack object. Its settings will take effect before the session starts up.

The `flags` parameter can be used to start default features (UPnP & NAT-PMP) and default plugins (ut_metadata, ut_pex and smart_ban). The default is to start those features. If you do not want them to start, pass 0 as the flags parameter.

[report issue]

#### session() operator=()

    session& operator= (session&&) = default;
    session (session&&) = default;

movable

[report issue]

#### session() operator=()

    session& operator= (session const&) = delete;
    session (session const&) = delete;

non-copyable

[report issue]

#### session()

    session (settings_pack&& pack
          , io_service& ios
          , session_flags_t const flags = add_default_plugins);
    session (settings_pack const& pack
          , io_service& ios
          , session_flags_t const flags = add_default_plugins);

overload of the constructor that takes an external io_service to run the session object on. This is primarily useful for tests that may want to run multiple sessions on a single io_service, or low resource systems where additional threads are expensive and sharing an io_service with other events is fine.

Warning

The session object does not cleanly terminate with an external `io_service`. The `io_service::run()` call _must_ have returned before it's safe to destruct the session. Which means you MUST call session::abort() and save the session_proxy first, then destruct the session object, then sync with the io_service, then destruct the session_proxy object.

[report issue]

#### ~session()

    ~session ();

The destructor of session will notify all trackers that our torrents have been shut down. If some trackers are down, they will time out. All this before the destructor of session returns. So, it's advised that any kind of interface (such as windows) are closed before destructing the session object. Because it can take a few second for it to finish. The timeout can be set with apply_settings().

[report issue]

#### abort()

    session_proxy abort ();

In case you want to destruct the session asynchronously, you can request a session destruction proxy. If you don't do this, the destructor of the session object will block while the trackers are contacted. If you keep one `session_proxy` to the session when destructing it, the destructor will not block, but start to close down the session, the destructor of the proxy will then synchronize the threads. So, the destruction of the session is performed from the `session` destructor call until the `session_proxy` destructor call. The `session_proxy` does not have any operations on it (since the session is being closed down, no operations are allowed on it). The only valid operation is calling the destructor:

    class session_proxy
    {
    public:
            session_proxy();
            ~session_proxy()
    };

[report issue]

### session_stats_metrics()

Declared in "libtorrent/session_stats.hpp"

    std::vector<stats_metric> session_stats_metrics ();

This free function returns the list of available metrics exposed by libtorrent's statistics API. Each metric has a name and a value index. The value index is the index into the array in session_stats_alert where this metric's value can be found when the session stats is sampled (by calling post_session_stats()).

[report issue]

### find_metric_idx()

Declared in "libtorrent/session_stats.hpp"

    int find_metric_idx (string_view name);

given a name of a metric, this function returns the counter index of it, or -1 if it could not be found. The counter index is the index into the values array returned by session_stats_alert.

[report issue]

### read_session_params()

Declared in "libtorrent/session.hpp"

    session_params read_session_params (bdecode_node const& e
       , save_state_flags_t flags = save_state_flags_t::all());

This function helps to construct a `session_params` from a bencoded data generated by `session_handle::save_state`

[report issue]

### enum metric_type_t

Declared in "libtorrent/session_stats.hpp"

name | value | description
--- | --- | ---
counter | 0 |
gauge | 1 |

Author: | Arvid Norberg, arvid@libtorrent.org
Version: | 1.2.9

home

## Plugins

libtorrent has a plugin interface for implementing extensions to the protocol. These can be general extensions for transferring metadata or peer exchange extensions, or it could be used to provide a way to customize the protocol to fit a particular (closed) network.

In short, the plugin interface makes it possible to:

- register extension messages (sent in the extension handshake), see extensions.
- add data and parse data from the extension handshake.
- send extension messages and standard bittorrent messages.
- override or block the handling of standard bittorrent messages.
- save and restore state via the session state
- see all alerts that are posted

### a word of caution

Writing your own plugin is a very easy way to introduce serious bugs such as dead locks and race conditions. Since a plugin has access to internal structures it is also quite easy to sabotage libtorrent's operation.

All the callbacks are always called from the libtorrent network thread. In case portions of your plugin are called from other threads, typically the main thread, you cannot use any of the member functions on the internal structures in libtorrent, since those require being called from the libtorrent network thread . Furthermore, you also need to synchronize your own shared data within the plugin, to make sure it is not accessed at the same time from the libtorrent thread (through a callback). If you need to send out a message from another thread, it is advised to use an internal queue, and do the actual sending in `tick()`.

Since the plugin interface gives you easy access to internal structures, it is not supported as a stable API. Plugins should be considered specific to a specific version of libtorrent. Although, in practice the internals mostly don't change that dramatically.

## plugin-interface

The plugin interface consists of three base classes that the plugin may implement. These are called plugin, torrent_plugin and peer_plugin. They are found in the `<libtorrent/extensions.hpp>` header.

These plugins are instantiated for each session, torrent and possibly each peer, respectively.

For plugins that only need per torrent state, it is enough to only implement `torrent_plugin` and pass a constructor function or function object to `session::add_extension()` or `torrent_handle::add_extension()` (if the torrent has already been started and you want to hook in the extension at run-time).

The signature of the function is:

    std::shared_ptr<torrent_plugin> (*)(torrent_handle const&, void*);

The second argument is the userdata passed to `session::add_torrent()` or `torrent_handle::add_extension()`.

The function should return a `std::shared_ptr<torrent_plugin>` which may or may not be 0. If it is a nullptr, the extension is simply ignored for this torrent. If it is a valid pointer (to a class inheriting `torrent_plugin`), it will be associated with this torrent and callbacks will be made on torrent events.

For more elaborate plugins which require session wide state, you would implement `plugin`, construct an object (in a `std::shared_ptr`) and pass it in to `session::add_extension()`.

## custom alerts

Since plugins are running within internal libtorrent threads, one convenient way to communicate with the client is to post custom alerts.

The expected interface of any alert, apart from deriving from the alert base class, looks like this:

    static const int alert_type = <unique alert ID>;
    virtual int type() const { return alert_type; }

    virtual std::string message() const;

    static const alert_category_t static_category = <bitmask of alert::category_t flags>;
    virtual alert_category_t category() const { return static_category; }

    virtual char const* what() const { return <string literal of the name of this alert>; }

The `alert_type` is used for the type-checking in `alert_cast`. It must not collide with any other alert. The built-in alerts in libtorrent will not use alert type IDs greater than `user_alert_id`. When defining your own alert, make sure it's greater than this constant.

`type()` is the run-time equivalence of the `alert_type`.

The `message()` virtual function is expected to construct a useful string representation of the alert and the event or data it represents. Something convenient to put in a log file for instance.

`clone()` is used internally to copy alerts. The suggested implementation of simply allocating a new instance as a copy of `*this` is all that's expected.

The static category is required for checking whether or not the category for a specific alert is enabled or not, without instantiating the alert. The `category` virtual function is the run-time equivalence.

The `what()` virtual function may simply be a string literal of the class name of your alert.

For more information, see the alert section.

[report issue]

### plugin

Declared in "libtorrent/extensions.hpp"

this is the base class for a session plugin. One primary feature is that it is notified of all torrents that are added to the session, and can add its own torrent_plugins.

    struct plugin
    {
       virtual feature_flags_t implemented_features ();
       virtual std::shared_ptr<torrent_plugin> new_torrent (torrent_handle const&, void*);
       virtual void added (session_handle const&);
       virtual bool on_dht_request (string_view /* query */
          , udp::endpoint const& /* source */, bdecode_node const& /* message */
          , entry& /* response */);
       virtual void on_alert (alert const*);
       virtual bool on_unknown_torrent (sha1_hash const& /* info_hash */
          , peer_connection_handle const& /* pc */, add_torrent_params& /* p */);
       virtual void on_tick ();
       virtual uint64_t get_unchoke_priority (peer_connection_handle const& /* peer */);
       virtual void save_state (entry&);
       virtual void load_state (bdecode_node const&);

       static constexpr feature_flags_t optimistic_unchoke_feature  = 1_bit;
       static constexpr feature_flags_t tick_feature  = 2_bit;
       static constexpr feature_flags_t dht_request_feature  = 3_bit;
       static constexpr feature_flags_t alert_feature  = 4_bit;
    };

[report issue]

#### implemented_features()

    virtual feature_flags_t implemented_features ();

This function is expected to return a bitmask indicating which features this plugin implements. Some callbacks on this object may not be called unless the corresponding feature flag is returned here. Note that callbacks may still be called even if the corresponding feature is not specified in the return value here. See feature_flags_t for possible flags to return.

[report issue]

#### new_torrent()

    virtual std::shared_ptr<torrent_plugin> new_torrent (torrent_handle const&, void*);

this is called by the session every time a new torrent is added. The `torrent*` points to the internal torrent object created for the new torrent. The `void*` is the userdata pointer as passed in via add_torrent_params.

If the plugin returns a torrent_plugin instance, it will be added to the new torrent. Otherwise, return an empty shared_ptr to a torrent_plugin (the default).

[report issue]

#### added()

    virtual void added (session_handle const&);

called when plugin is added to a session

[report issue]

#### on_dht_request()

    virtual bool on_dht_request (string_view /* query */
          , udp::endpoint const& /* source */, bdecode_node const& /* message */
          , entry& /* response */);

called when a dht request is received. If your plugin expects this to be called, make sure to include the flag `dht_request_feature` in the return value from implemented_features().

[report issue]

#### on_alert()

    virtual void on_alert (alert const*);

called when an alert is posted alerts that are filtered are not posted. If your plugin expects this to be called, make sure to include the flag `alert_feature` in the return value from implemented_features().

[report issue]

#### on_unknown_torrent()

    virtual bool on_unknown_torrent (sha1_hash const& /* info_hash */
          , peer_connection_handle const& /* pc */, add_torrent_params& /* p */);

return true if the add_torrent_params should be added

[report issue]

#### on_tick()

    virtual void on_tick ();

called once per second. If your plugin expects this to be called, make sure to include the flag `tick_feature` in the return value from implemented_features().

[report issue]

#### get_unchoke_priority()

    virtual uint64_t get_unchoke_priority (peer_connection_handle const& /* peer */);

called when choosing peers to optimistically unchoke. The return value indicates the peer's priority for unchoking. Lower return values correspond to higher priority. Priorities above 2^63-1 are reserved. If your plugin has no priority to assign a peer it should return 2^64-1. If your plugin expects this to be called, make sure to include the flag `optimistic_unchoke_feature` in the return value from implemented_features(). If multiple plugins implement this function the lowest return value (i.e. the highest priority) is used.

[report issue]

#### save_state()

    virtual void save_state (entry&);

called when saving settings state

[report issue]

#### load_state()

    virtual void load_state (bdecode_node const&);

called when loading settings state

[report issue]

optimistic_unchoke_feature
  include this bit if your plugin needs to alter the order of the optimistic unchoke of peers. i.e. have the on_optimistic_unchoke() callback be called.

[report issue]

tick_feature
  include this bit if your plugin needs to have on_tick() called

[report issue]

dht_request_feature
  include this bit if your plugin needs to have on_dht_request() called

[report issue]

alert_feature
  include this bit if your plugin needs to have on_alert() called

[report issue]

### torrent_plugin

Declared in "libtorrent/extensions.hpp"

Torrent plugins are associated with a single torrent and have a number of functions called at certain events. Many of its functions have the ability to change or override the default libtorrent behavior.

    struct torrent_plugin
    {
       virtual std::shared_ptr<peer_plugin> new_connection (peer_connection_handle const&);
       virtual void on_piece_failed (piece_index_t);
       virtual void on_piece_pass (piece_index_t);
       virtual void tick ();
       virtual bool on_pause ();
       virtual bool on_resume ();
       virtual void on_files_checked ();
       virtual void on_state (torrent_status::state_t);
       virtual void on_add_peer (tcp::endpoint const&,
          peer_source_flags_t, add_peer_flags_t);

       static constexpr add_peer_flags_t first_time  = 1_bit;
       static constexpr add_peer_flags_t filtered  = 2_bit;
    };

[report issue]

#### new_connection()

    virtual std::shared_ptr<peer_plugin> new_connection (peer_connection_handle const&);

This function is called each time a new peer is connected to the torrent. You may choose to ignore this by just returning a default constructed `shared_ptr` (in which case you don't need to override this member function).

If you need an extension to the peer connection (which most plugins do) you are supposed to return an instance of your peer_plugin class. Which in turn will have its hook functions called on event specific to that peer.

The `peer_connection_handle` will be valid as long as the `shared_ptr` is being held by the torrent object. So, it is generally a good idea to not keep a `shared_ptr` to your own peer_plugin. If you want to keep references to it, use `weak_ptr`.

If this function throws an exception, the connection will be closed.

[report issue]

#### on_piece_failed() on_piece_pass()

    virtual void on_piece_failed (piece_index_t);
    virtual void on_piece_pass (piece_index_t);

These hooks are called when a piece passes the hash check or fails the hash check, respectively. The `index` is the piece index that was downloaded. It is possible to access the list of peers that participated in sending the piece through the `torrent` and the `piece_picker`.

[report issue]

#### tick()

    virtual void tick ();

This hook is called approximately once per second. It is a way of making it easy for plugins to do timed events, for sending messages or whatever.

[report issue]

#### on_resume() on_pause()

    virtual bool on_pause ();
    virtual bool on_resume ();

These hooks are called when the torrent is paused and resumed respectively. The return value indicates if the event was handled. A return value of `true` indicates that it was handled, and no other plugin after this one will have this hook function called, and the standard handler will also not be invoked. So, returning true effectively overrides the standard behavior of pause or resume.

Note that if you call `pause()` or `resume()` on the torrent from your handler it will recurse back into your handler, so in order to invoke the standard handler, you have to keep your own state on whether you want standard behavior or overridden behavior.

[report issue]

#### on_files_checked()

    virtual void on_files_checked ();

This function is called when the initial files of the torrent have been checked. If there are no files to check, this function is called immediately.

i.e. This function is always called when the torrent is in a state where it can start downloading.

[report issue]

#### on_state()

    virtual void on_state (torrent_status::state_t);

called when the torrent changes state the state is one of torrent_status::state_t enum members

[report issue]

#### on_add_peer()

    virtual void on_add_peer (tcp::endpoint const&,
          peer_source_flags_t, add_peer_flags_t);

called every time a new peer is added to the peer list. This is before the peer is connected to. For `flags`, see torrent_plugin::flags_t. The `source` argument refers to the source where we learned about this peer from. It's a bitmask, because many sources may have told us about the same peer. For peer source flags, see peer_info::peer_source_flags.

[report issue]

first_time
  this is the first time we see this peer

[report issue]

filtered
  this peer was not added because it was filtered by the IP filter

[report issue]

### peer_plugin

Declared in "libtorrent/extensions.hpp"

peer plugins are associated with a specific peer. A peer could be both a regular bittorrent peer (`bt_peer_connection`) or one of the web seed connections (`web_peer_connection` or `http_seed_connection`). In order to only attach to certain peers, make your torrent_plugin::new_connection only return a plugin for certain peer connection types

    struct peer_plugin
    {
       virtual string_view type () const;
       virtual void add_handshake (entry&);
       virtual void on_disconnect (error_code const&);
       virtual void on_connected ();
       virtual bool on_handshake (span<char const>);
       virtual bool on_extension_handshake (bdecode_node const&);
       virtual bool on_interested ();
       virtual bool on_allowed_fast (piece_index_t);
       virtual bool on_choke ();
       virtual bool on_not_interested ();
       virtual bool on_dont_have (piece_index_t);
       virtual bool on_have (piece_index_t);
       virtual bool on_bitfield (bitfield const& /*bitfield*/);
       virtual bool on_have_all ();
       virtual bool on_request (peer_request const&);
       virtual bool on_have_none ();
       virtual bool on_unchoke ();
       virtual bool on_piece (peer_request const& /*piece*/
          , span<char const> /*buf*/);
       virtual bool on_cancel (peer_request const&);
       virtual bool on_reject (peer_request const&);
       virtual bool on_suggest (piece_index_t);
       virtual void sent_unchoke ();
       virtual void sent_payload (int /* bytes */);
       virtual bool can_disconnect (error_code const& /*ec*/);
       virtual bool on_extended (int /*length*/, int /*msg*/,
          span<char const> /*body*/);
       virtual bool on_unknown_message (int /*length*/, int /*msg*/,
          span<char const> /*body*/);
       virtual void on_piece_failed (piece_index_t);
       virtual void on_piece_pass (piece_index_t);
       virtual void tick ();
       virtual bool write_request (peer_request const&);
    };

[report issue]

#### type()

    virtual string_view type () const;

This function is expected to return the name of the plugin.

[report issue]

#### add_handshake()

    virtual void add_handshake (entry&);

can add entries to the extension handshake this is not called for web seeds

[report issue]

#### on_disconnect()

    virtual void on_disconnect (error_code const&);

called when the peer is being disconnected.

[report issue]

#### on_connected()

    virtual void on_connected ();

called when the peer is successfully connected. Note that incoming connections will have been connected by the time the peer plugin is attached to it, and won't have this hook called.

[report issue]

#### on_handshake()

    virtual bool on_handshake (span<char const>);

this is called when the initial bittorrent handshake is received. Returning false means that the other end doesn't support this extension and will remove it from the list of plugins. this is not called for web seeds

[report issue]

#### on_extension_handshake()

    virtual bool on_extension_handshake (bdecode_node const&);

called when the extension handshake from the other end is received if this returns false, it means that this extension isn't supported by this peer. It will result in this peer_plugin being removed from the peer_connection and destructed. this is not called for web seeds

[report issue]

#### on_have_all() on_have() on_request() on_interested() on_bitfield() on_unchoke() on_have_none() on_not_interested() on_allowed_fast() on_choke() on_dont_have()

    virtual bool on_interested ();
    virtual bool on_allowed_fast (piece_index_t);
    virtual bool on_choke ();
    virtual bool on_not_interested ();
    virtual bool on_dont_have (piece_index_t);
    virtual bool on_have (piece_index_t);
    virtual bool on_bitfield (bitfield const& /*bitfield*/);
    virtual bool on_have_all ();
    virtual bool on_request (peer_request const&);
    virtual bool on_have_none ();
    virtual bool on_unchoke ();

returning true from any of the message handlers indicates that the plugin has handled the message. it will break the plugin chain traversing and not let anyone else handle the message, including the default handler.

[report issue]

#### on_piece()

    virtual bool on_piece (peer_request const& /*piece*/
          , span<char const> /*buf*/);

This function is called when the peer connection is receiving a piece. `buf` points (non-owning pointer) to the data in an internal immutable disk buffer. The length of the data is specified in the `length` member of the `piece` parameter. returns true to indicate that the piece is handled and the rest of the logic should be ignored.

[report issue]

#### sent_unchoke()

    virtual void sent_unchoke ();

called after a choke message has been sent to the peer

[report issue]

#### sent_payload()

    virtual void sent_payload (int /* bytes */);

called after piece data has been sent to the peer this can be used for stats book keeping

[report issue]

#### can_disconnect()

    virtual bool can_disconnect (error_code const& /*ec*/);

called when libtorrent think this peer should be disconnected. if the plugin returns false, the peer will not be disconnected.

[report issue]

#### on_extended()

    virtual bool on_extended (int /*length*/, int /*msg*/,
          span<char const> /*body*/);

called when an extended message is received. If returning true, the message is not processed by any other plugin and if false is returned the next plugin in the chain will receive it to be able to handle it. This is not called for web seeds. thus function may be called more than once per incoming message, but only the last of the calls will the `body` size equal the `length`. i.e. Every time another fragment of the message is received, this function will be called, until finally the whole message has been received. The purpose of this is to allow early disconnects for invalid messages and for reporting progress of receiving large messages.

[report issue]

#### on_unknown_message()

    virtual bool on_unknown_message (int /*length*/, int /*msg*/,
          span<char const> /*body*/);

this is not called for web seeds

[report issue]

#### on_piece_failed() on_piece_pass()

    virtual void on_piece_failed (piece_index_t);
    virtual void on_piece_pass (piece_index_t);

called when a piece that this peer participated in either fails or passes the hash_check

[report issue]

#### tick()

    virtual void tick ();

called approximately once every second

[report issue]

#### write_request()

    virtual bool write_request (peer_request const&);

called each time a request message is to be sent. If true is returned, the original request message won't be sent and no other plugin will have this function called.

[report issue]

### crypto_plugin

Declared in "libtorrent/extensions.hpp"

    struct crypto_plugin
    {
       virtual void set_outgoing_key (span<char const> key) = 0;
       virtual void set_incoming_key (span<char const> key) = 0;
       encrypt (span<span<char>> /*send_vec*/) = 0;
       virtual std::tuple<int, int, int> decrypt (span<span<char>> /*receive_vec*/) = 0;
    };

[report issue]

#### decrypt()

    virtual std::tuple<int, int, int> decrypt (span<span<char>> /*receive_vec*/) = 0;

decrypt the provided buffers. returns is a tuple representing the values (consume, produce, packet_size)

consume is set to the number of bytes which should be trimmed from the head of the buffers, default is 0

produce is set to the number of bytes of payload which are now ready to be sent to the upper layer. default is the number of bytes passed in receive_vec

packet_size is set to the minimum number of bytes which must be read to advance the next step of decryption. default is 0

[report issue]

### create_ut_metadata_plugin()

Declared in "libtorrent/extensions/ut_metadata.hpp"

    std::shared_ptr<torrent_plugin> create_ut_metadata_plugin (torrent_handle const&, void*);

constructor function for the ut_metadata extension. The ut_metadata extension allows peers to request the .torrent file (or more specifically the info-dictionary of the .torrent file) from each other. This is the main building block in making magnet links work. This extension is enabled by default unless explicitly disabled in the session constructor.

This can either be passed in the add_torrent_params::extensions field, or via torrent_handle::add_extension().

[report issue]

### create_smart_ban_plugin()

Declared in "libtorrent/extensions/smart_ban.hpp"

    std::shared_ptr<torrent_plugin> create_smart_ban_plugin (torrent_handle const&, void*);

constructor function for the smart ban extension. The extension keeps track of the data peers have sent us for failing pieces and once the piece completes and passes the hash check bans the peers that turned out to have sent corrupt data. This function can either be passed in the add_torrent_params::extensions field, or via torrent_handle::add_extension().

[report issue]

### create_ut_pex_plugin()

Declared in "libtorrent/extensions/ut_pex.hpp"

    std::shared_ptr<torrent_plugin> create_ut_pex_plugin (torrent_handle const&, void*);

constructor function for the ut_pex extension. The ut_pex extension allows peers to gossip about their connections, allowing the swarm stay well connected and peers aware of more peers in the swarm. This extension is enabled by default unless explicitly disabled in the session constructor.

This can either be passed in the add_torrent_params::extensions field, or via torrent_handle::add_extension().

Author: | Arvid Norberg, arvid@libtorrent.org
Version: | 1.2.9

home

## Create Torrents

This section describes the functions and classes that are used to create torrent files. It is a layered API with low level classes and higher level convenience functions. A torrent is created in 4 steps:

1. first the files that will be part of the torrent are determined.
2. the torrent properties are set, such as tracker url, web seeds, DHT nodes etc.
3. Read through all the files in the torrent, SHA-1 all the data and set the piece hashes.
4. The torrent is bencoded into a file or buffer.

If there are a lot of files and or deep directory hierarchies to traverse, step one can be time consuming.

Typically step 3 is by far the most time consuming step, since it requires to read all the bytes from all the files in the torrent.

All of these classes and functions are declared by including `libtorrent/create_torrent.hpp`.

example:

    file_storage fs;

    // recursively adds files in directories
    add_files(fs, "./my_torrent");

    create_torrent t(fs);
    t.add_tracker("http://my.tracker.com/announce");
    t.set_creator("libtorrent example");

    // reads the files and calculates the hashes
    set_piece_hashes(t, ".");

    ofstream out("my_torrent.torrent", std::ios_base::binary);
    bencode(std::ostream_iterator<char>(out), t.generate());

[report issue]

### create_torrent

Declared in "libtorrent/create_torrent.hpp"

This class holds state for creating a torrent. After having added all information to it, call create_torrent::generate() to generate the torrent. The entry that's returned can then be bencoded into a .torrent file using bencode().

    struct create_torrent
    {
       explicit create_torrent (torrent_info const& ti);
       explicit create_torrent (file_storage& fs, int piece_size = 0
          , int pad_file_limit = -1, create_flags_t flags = optimize_alignment
          , int alignment = -1);
       entry generate () const;
       file_storage const& files () const;
       void set_comment (char const* str);
       void set_creator (char const* str);
       void set_hash (piece_index_t index, sha1_hash const& h);
       void set_file_hash (file_index_t index, sha1_hash const& h);
       void add_http_seed (string_view url);
       void add_url_seed (string_view url);
       void add_node (std::pair<std::string, int> node);
       void add_tracker (string_view url, int tier = 0);
       void set_root_cert (string_view pem);
       bool priv () const;
       void set_priv (bool p);
       int num_pieces () const;
       int piece_length () const;
       int piece_size (piece_index_t i) const;
       std::vector<sha1_hash> const& merkle_tree () const;
       void add_similar_torrent (sha1_hash ih);
       void add_collection (string_view c);

       static constexpr create_flags_t optimize_alignment  = 0_bit;
       static constexpr create_flags_t merkle  = 1_bit;
       static constexpr create_flags_t modification_time  = 2_bit;
       static constexpr create_flags_t symlinks  = 3_bit;
       static constexpr create_flags_t mutable_torrent_support  = 4_bit;
    };

[report issue]

#### create_torrent()

    explicit create_torrent (torrent_info const& ti);
    explicit create_torrent (file_storage& fs, int piece_size = 0
          , int pad_file_limit = -1, create_flags_t flags = optimize_alignment
          , int alignment = -1);

The `piece_size` is the size of each piece in bytes. It must be a multiple of 16 kiB. If a piece size of 0 is specified, a piece_size will be calculated such that the torrent file is roughly 40 kB.

If a `pad_file_limit` is specified (other than -1), any file larger than the specified number of bytes will be preceded by a pad file to align it with the start of a piece. The pad_file_limit is ignored unless the `optimize_alignment` flag is passed. Typically it doesn't make sense to set this any lower than 4 kiB.

The overload that takes a `torrent_info` object will make a verbatim copy of its info dictionary (to preserve the info-hash). The copy of the info dictionary will be used by create_torrent::generate(). This means that none of the member functions of create_torrent that affects the content of the info dictionary (such as `set_hash()`), will have any affect.

The `flags` arguments specifies options for the torrent creation. It can be any combination of the flags defined by create_flags_t.

`alignment` is used when pad files are enabled. This is the size eligible files are aligned to. The default is -1, which means the piece size of the torrent.

[report issue]

#### generate()

    entry generate () const;

This function will generate the .torrent file as a bencode tree. In order to generate the flat file, use the bencode() function.

It may be useful to add custom entries to the torrent file before bencoding it and saving it to disk.

If anything goes wrong during torrent generation, this function will return an empty `entry` structure. You can test for this condition by querying the type of the entry:

    file_storage fs;
    // add file ...
    create_torrent t(fs);
    // add trackers and piece hashes ...
    e = t.generate();

    if (e.type() == entry::undefined_t)
    {
            // something went wrong
    }

For instance, you cannot generate a torrent with 0 files in it. If you don't add any files to the `file_storage`, torrent generation will fail.

[report issue]

#### files()

    file_storage const& files () const;

returns an immutable reference to the file_storage used to create the torrent from.

[report issue]

#### set_comment()

    void set_comment (char const* str);

Sets the comment for the torrent. The string `str` should be utf-8 encoded. The comment in a torrent file is optional.

[report issue]

#### set_creator()

    void set_creator (char const* str);

Sets the creator of the torrent. The string `str` should be utf-8 encoded. This is optional.

[report issue]

#### set_hash()

    void set_hash (piece_index_t index, sha1_hash const& h);

This sets the SHA-1 hash for the specified piece (`index`). You are required to set the hash for every piece in the torrent before generating it. If you have the files on disk, you can use the high level convenience function to do this. See set_piece_hashes().

[report issue]

#### set_file_hash()

    void set_file_hash (file_index_t index, sha1_hash const& h);

This sets the sha1 hash for this file. This hash will end up under the key `sha1` associated with this file (for multi-file torrents) or in the root info dictionary for single-file torrents.

[report issue]

#### add_http_seed() add_url_seed()

    void add_http_seed (string_view url);
    void add_url_seed (string_view url);

This adds a url seed to the torrent. You can have any number of url seeds. For a single file torrent, this should be an HTTP url, pointing to a file with identical content as the file of the torrent. For a multi-file torrent, it should point to a directory containing a directory with the same name as this torrent, and all the files of the torrent in it.

The second function, `add_http_seed()` adds an HTTP seed instead.

[report issue]

#### add_node()

    void add_node (std::pair<std::string, int> node);

This adds a DHT node to the torrent. This especially useful if you're creating a tracker less torrent. It can be used by clients to bootstrap their DHT node from. The node is a hostname and a port number where there is a DHT node running. You can have any number of DHT nodes in a torrent.

[report issue]

#### add_tracker()

    void add_tracker (string_view url, int tier = 0);

Adds a tracker to the torrent. This is not strictly required, but most torrents use a tracker as their main source of peers. The url should be an http:// or udp:// url to a machine running a bittorrent tracker that accepts announces for this torrent's info-hash. The tier is the fallback priority of the tracker. All trackers with tier 0 are tried first (in any order). If all fail, trackers with tier 1 are tried. If all of those fail, trackers with tier 2 are tried, and so on.

[report issue]

#### set_root_cert()

    void set_root_cert (string_view pem);

This function sets an X.509 certificate in PEM format to the torrent. This makes the torrent an SSL torrent. An SSL torrent requires that each peer has a valid certificate signed by this root certificate. For SSL torrents, all peers are connecting over SSL connections. For more information, see the section on ssl torrents.

The string is not the path to the cert, it's the actual content of the certificate.

[report issue]

#### priv() set_priv()

    bool priv () const;
    void set_priv (bool p);

Sets and queries the private flag of the torrent. Torrents with the private flag set ask the client to not use any other sources than the tracker for peers, and to not use DHT to advertise itself publicly, only the tracker.

[report issue]

#### num_pieces()

    int num_pieces () const;

returns the number of pieces in the associated file_storage object.

[report issue]

#### piece_size() piece_length()

    int piece_length () const;
    int piece_size (piece_index_t i) const;

`piece_length()` returns the piece size of all pieces but the last one. `piece_size()` returns the size of the specified piece. these functions are just forwarding to the associated file_storage.

[report issue]

#### merkle_tree()

    std::vector<sha1_hash> const& merkle_tree () const;

This function returns the merkle hash tree, if the torrent was created as a merkle torrent. The tree is created by `generate()` and won't be valid until that function has been called. When creating a merkle tree torrent, the actual tree itself has to be saved off separately and fed into libtorrent the first time you start seeding it, through the `torrent_info::set_merkle_tree()` function. From that point onwards, the tree will be saved in the resume data.

[report issue]

#### add_collection() add_similar_torrent()

    void add_similar_torrent (sha1_hash ih);
    void add_collection (string_view c);

Add similar torrents (by info-hash) or collections of similar torrents. Similar torrents are expected to share some files with this torrent. Torrents sharing a collection name with this torrent are also expected to share files with this torrent. A torrent may have more than one collection and more than one similar torrents. For more information, see BEP 38.

[report issue]

optimize_alignment
  This will insert pad files to align the files to piece boundaries, for optimized disk-I/O. This will minimize the number of bytes of pad- files, to keep the impact down for clients that don't support them.

[report issue]

merkle
  This will create a merkle hash tree torrent. A merkle torrent cannot be opened in clients that don't specifically support merkle torrents. The benefit is that the resulting torrent file will be much smaller and not grow with more pieces. When this option is specified, it is recommended to have a fairly small piece size, say 64 kiB. When creating merkle torrents, the full hash tree is also generated and should be saved off separately. It is accessed through the create_torrent::merkle_tree() function.

[report issue]

modification_time
  This will include the file modification time as part of the torrent. This is not enabled by default, as it might cause problems when you create a torrent from separate files with the same content, hoping to yield the same info-hash. If the files have different modification times, with this option enabled, you would get different info-hashes for the files.

[report issue]

symlinks
  If this flag is set, files that are symlinks get a symlink attribute set on them and their data will not be included in the torrent. This is useful if you need to reconstruct a file hierarchy which contains symlinks.

[report issue]

mutable_torrent_support
  to create a torrent that can be updated via a mutable torrent (see BEP 38). This also needs to be enabled for torrents that update another torrent.

[report issue]

### add_files()

Declared in "libtorrent/create_torrent.hpp"

    void add_files (file_storage& fs, std::string const& file
       , create_flags_t flags = {});
    void add_files (file_storage& fs, std::string const& file
       , std::function<bool(std::string)> p, create_flags_t flags = {});

Adds the file specified by `path` to the file_storage object. In case `path` refers to a directory, files will be added recursively from the directory.

If specified, the predicate `p` is called once for every file and directory that is encountered. Files for which `p` returns true are added, and directories for which `p` returns true are traversed. `p` must have the following signature:

    bool Pred(std::string const& p);

The path that is passed in to the predicate is the full path of the file or directory. If no predicate is specified, all files are added, and all directories are traversed.

The ".." directory is never traversed.

The `flags` argument should be the same as the flags passed to the create_torrent constructor.

[report issue]

### set_piece_hashes()

Declared in "libtorrent/create_torrent.hpp"

    inline void set_piece_hashes (create_torrent& t, std::string const& p);
    void set_piece_hashes (create_torrent& t, std::string const& p
       , std::function<void(piece_index_t)> const& f, error_code& ec);
    inline void set_piece_hashes (create_torrent& t, std::string const& p
       , std::function<void(piece_index_t)> const& f);
    inline void set_piece_hashes (create_torrent& t, std::string const& p, error_code& ec);

This function will assume that the files added to the torrent file exists at path `p`, read those files and hash the content and set the hashes in the `create_torrent` object. The optional function `f` is called in between every hash that is set. `f` must have the following signature:

    void Fun(piece_index_t);

The overloads that don't take an `error_code&` may throw an exception in case of a file error, the other overloads sets the error code to reflect the error, if any.

Author: | Arvid Norberg, arvid@libtorrent.org
Version: | 1.2.9

home

## Error Codes

[report issue]

### storage_error

Declared in "libtorrent/error_code.hpp"

used by storage to return errors also includes which underlying file the error happened on

    struct storage_error
    {
       explicit operator bool () const;
       file_index_t file () const;
       void file (file_index_t f);

       error_code ec;
       operation_t operation;
    };

[report issue]

#### bool()

    explicit operator bool () const;

explicitly converts to true if this object represents an error, and false if it does not.

[report issue]

#### file()

    file_index_t file () const;
    void file (file_index_t f);

set and query the index (in the torrent) of the file this error occurred on. This may also have special values defined in torrent_status.

[report issue]

ec
  the error that occurred

[report issue]

operation
  A code from operation_t enum, indicating what kind of operation failed.

[report issue]

### libtorrent_category()

Declared in "libtorrent/error_code.hpp"

    boost::system::error_category& libtorrent_category ();

return the instance of the libtorrent_error_category which maps libtorrent error codes to human readable error messages.

[report issue]

### http_category()

Declared in "libtorrent/error_code.hpp"

    boost::system::error_category& http_category ();

returns the error_category for HTTP errors

[report issue]

### pcp_category()

Declared in "libtorrent/natpmp.hpp"

    boost::system::error_category& pcp_category ();

[report issue]

### upnp_category()

Declared in "libtorrent/upnp.hpp"

    boost::system::error_category& upnp_category ();

the boost.system error category for UPnP errors

[report issue]

### gzip_category()

Declared in "libtorrent/gzip.hpp"

    boost::system::error_category& gzip_category ();

get the `error_category` for zip errors

[report issue]

### bdecode_category()

Declared in "libtorrent/bdecode.hpp"

    boost::system::error_category& bdecode_category ();

[report issue]

### socks_category()

Declared in "libtorrent/socks5_stream.hpp"

    boost::system::error_category& socks_category ();

returns the error_category for SOCKS5 errors

[report issue]

### i2p_category()

Declared in "libtorrent/i2p_stream.hpp"

    boost::system::error_category& i2p_category ();

returns the error category for I2P errors

[report issue]

### enum error_code_enum

Declared in "libtorrent/error_code.hpp"

name | value | description
--- | --- | ---
no_error | 0 | Not an error
file_collision | 1 | Two torrents has files which end up overwriting each other
failed_hash_check | 2 | A piece did not match its piece hash
torrent_is_no_dict | 3 | The .torrent file does not contain a bencoded dictionary at its top level
torrent_missing_info | 4 | The .torrent file does not have an `info` dictionary
torrent_info_no_dict | 5 | The .torrent file's `info` entry is not a dictionary
torrent_missing_piece_length | 6 | The .torrent file does not have a `piece length` entry
torrent_missing_name | 7 | The .torrent file does not have a `name` entry
torrent_invalid_name | 8 | The .torrent file's name entry is invalid
torrent_invalid_length | 9 | The length of a file, or of the whole .torrent file is invalid. Either negative or not an integer
torrent_file_parse_failed | 10 | Failed to parse a file entry in the .torrent
torrent_missing_pieces | 11 | The `pieces` field is missing or invalid in the .torrent file
torrent_invalid_hashes | 12 | The `pieces` string has incorrect length
too_many_pieces_in_torrent | 13 | The .torrent file has more pieces than is supported by libtorrent
invalid_swarm_metadata | 14 | The metadata (.torrent file) that was received from the swarm matched the info-hash, but failed to be parsed
invalid_bencoding | 15 | The file or buffer is not correctly bencoded
no_files_in_torrent | 16 | The .torrent file does not contain any files
invalid_escaped_string | 17 | The string was not properly url-encoded as expected
session_is_closing | 18 | Operation is not permitted since the session is shutting down
duplicate_torrent | 19 | There's already a torrent with that info-hash added to the session
invalid_torrent_handle | 20 | The supplied torrent_handle is not referring to a valid torrent
invalid_entry_type | 21 | The type requested from the entry did not match its type
missing_info_hash_in_uri | 22 | The specified URI does not contain a valid info-hash
file_too_short | 23 | One of the files in the torrent was unexpectedly small. This might be caused by files being changed by an external process
unsupported_url_protocol | 24 | The URL used an unknown protocol. Currently `http` and `https` (if built with openssl support) are recognized. For trackers `udp` is recognized as well.
url_parse_error | 25 | The URL did not conform to URL syntax and failed to be parsed
peer_sent_empty_piece | 26 | The peer sent a piece message of length 0
parse_failed | 27 | A bencoded structure was corrupt and failed to be parsed
invalid_file_tag | 28 | The fast resume file was missing or had an invalid file version tag
missing_info_hash | 29 | The fast resume file was missing or had an invalid info-hash
mismatching_info_hash | 30 | The info-hash did not match the torrent
invalid_hostname | 31 | The URL contained an invalid hostname
invalid_port | 32 | The URL had an invalid port
port_blocked | 33 | The port is blocked by the port-filter, and prevented the connection
expected_close_bracket_in_address | 34 | The IPv6 address was expected to end with "]"
destructing_torrent | 35 | The torrent is being destructed, preventing the operation to succeed
timed_out | 36 | The connection timed out
upload_upload_connection | 37 | The peer is upload only, and we are upload only. There's no point in keeping the connection
uninteresting_upload_peer | 38 | The peer is upload only, and we're not interested in it. There's no point in keeping the connection
invalid_info_hash | 39 | The peer sent an unknown info-hash
torrent_paused | 40 | The torrent is paused, preventing the operation from succeeding
invalid_have | 41 | The peer sent an invalid have message, either wrong size or referring to a piece that doesn't exist in the torrent
invalid_bitfield_size | 42 | The bitfield message had the incorrect size
too_many_requests_when_choked | 43 | The peer kept requesting pieces after it was choked, possible abuse attempt.
invalid_piece | 44 | The peer sent a piece message that does not correspond to a piece request sent by the client
no_memory | 45 | memory allocation failed
torrent_aborted | 46 | The torrent is aborted, preventing the operation to succeed
self_connection | 47 | The peer is a connection to ourself, no point in keeping it
invalid_piece_size | 48 | The peer sent a piece message with invalid size, either negative or greater than one block
timed_out_no_interest | 49 | The peer has not been interesting or interested in us for too long, no point in keeping it around
timed_out_inactivity | 50 | The peer has not said anything in a long time, possibly dead
timed_out_no_handshake | 51 | The peer did not send a handshake within a reasonable amount of time, it might not be a bittorrent peer
timed_out_no_request | 52 | The peer has been unchoked for too long without requesting any data. It might be lying about its interest in us
invalid_choke | 53 | The peer sent an invalid choke message
invalid_unchoke | 54 | The peer send an invalid unchoke message
invalid_interested | 55 | The peer sent an invalid interested message
invalid_not_interested | 56 | The peer sent an invalid not-interested message
invalid_request | 57 | The peer sent an invalid piece request message
invalid_hash_list | 58 | The peer sent an invalid hash-list message (this is part of the merkle-torrent extension)
invalid_hash_piece | 59 | The peer sent an invalid hash-piece message (this is part of the merkle-torrent extension)
invalid_cancel | 60 | The peer sent an invalid cancel message
invalid_dht_port | 61 | The peer sent an invalid DHT port-message
invalid_suggest | 62 | The peer sent an invalid suggest piece-message
invalid_have_all | 63 | The peer sent an invalid have all-message
invalid_have_none | 64 | The peer sent an invalid have none-message
invalid_reject | 65 | The peer sent an invalid reject message
invalid_allow_fast | 66 | The peer sent an invalid allow fast-message
invalid_extended | 67 | The peer sent an invalid extension message ID
invalid_message | 68 | The peer sent an invalid message ID
sync_hash_not_found | 69 | The synchronization hash was not found in the encrypted handshake
invalid_encryption_constant | 70 | The encryption constant in the handshake is invalid
no_plaintext_mode | 71 | The peer does not support plain text, which is the selected mode
no_rc4_mode | 72 | The peer does not support RC4, which is the selected mode
unsupported_encryption_mode | 73 | The peer does not support any of the encryption modes that the client supports
unsupported_encryption_mode_selected | 74 | The peer selected an encryption mode that the client did not advertise and does not support
invalid_pad_size | 75 | The pad size used in the encryption handshake is of invalid size
invalid_encrypt_handshake | 76 | The encryption handshake is invalid
no_incoming_encrypted | 77 | The client is set to not support incoming encrypted connections and this is an encrypted connection
no_incoming_regular | 78 | The client is set to not support incoming regular bittorrent connections, and this is a regular connection
duplicate_peer_id | 79 | The client is already connected to this peer-ID
torrent_removed | 80 | Torrent was removed
packet_too_large | 81 | The packet size exceeded the upper sanity check-limit
reserved | 82 |
http_error | 83 | The web server responded with an error
missing_location | 84 | The web server response is missing a location header
invalid_redirection | 85 | The web seed redirected to a path that no longer matches the .torrent directory structure
redirecting | 86 | The connection was closed because it redirected to a different URL
invalid_range | 87 | The HTTP range header is invalid
no_content_length | 88 | The HTTP response did not have a content length
banned_by_ip_filter | 89 | The IP is blocked by the IP filter
too_many_connections | 90 | At the connection limit
peer_banned | 91 | The peer is marked as banned
stopping_torrent | 92 | The torrent is stopping, causing the operation to fail
too_many_corrupt_pieces | 93 | The peer has sent too many corrupt pieces and is banned
torrent_not_ready | 94 | The torrent is not ready to receive peers
peer_not_constructed | 95 | The peer is not completely constructed yet
session_closing | 96 | The session is closing, causing the operation to fail
optimistic_disconnect | 97 | The peer was disconnected in order to leave room for a potentially better peer
torrent_finished | 98 | The torrent is finished
no_router | 99 | No UPnP router found
metadata_too_large | 100 | The metadata message says the metadata exceeds the limit
invalid_metadata_request | 101 | The peer sent an invalid metadata request message
invalid_metadata_size | 102 | The peer advertised an invalid metadata size
invalid_metadata_offset | 103 | The peer sent a message with an invalid metadata offset
invalid_metadata_message | 104 | The peer sent an invalid metadata message
pex_message_too_large | 105 | The peer sent a peer exchange message that was too large
invalid_pex_message | 106 | The peer sent an invalid peer exchange message
invalid_lt_tracker_message | 107 | The peer sent an invalid tracker exchange message
too_frequent_pex | 108 | The peer sent an pex messages too often. This is a possible attempt of and attack
no_metadata | 109 | The operation failed because it requires the torrent to have the metadata (.torrent file) and it doesn't have it yet. This happens for magnet links before they have downloaded the metadata, and also torrents added by URL.
invalid_dont_have | 110 | The peer sent an invalid `dont_have` message. The don't have message is an extension to allow peers to advertise that the no longer has a piece they previously had.
requires_ssl_connection | 111 | The peer tried to connect to an SSL torrent without connecting over SSL.
invalid_ssl_cert | 112 | The peer tried to connect to a torrent with a certificate for a different torrent.
not_an_ssl_torrent | 113 | the torrent is not an SSL torrent, and the operation requires an SSL torrent
banned_by_port_filter | 114 | peer was banned because its listen port is within a banned port range, as specified by the port_filter.
invalid_session_handle | 115 | The session_handle is not referring to a valid session_impl
invalid_listen_socket | 116 | the listen socket associated with this request was closed
deprecated_120 | 120 |
deprecated_121 | 121 |
deprecated_122 | 122 |
deprecated_123 | 123 |
deprecated_124 | 124 |
missing_file_sizes | 130 | The resume data file is missing the `file sizes` entry
no_files_in_resume_data | 131 | The resume data file `file sizes` entry is empty
missing_pieces | 132 | The resume data file is missing the `pieces` and `slots` entry
mismatching_number_of_files | 133 | The number of files in the resume data does not match the number of files in the torrent
mismatching_file_size | 134 | One of the files on disk has a different size than in the fast resume file
mismatching_file_timestamp | 135 | One of the files on disk has a different timestamp than in the fast resume file
not_a_dictionary | 136 | The resume data file is not a dictionary
invalid_blocks_per_piece | 137 | The `blocks per piece` entry is invalid in the resume data file
missing_slots | 138 | The resume file is missing the `slots` entry, which is required for torrents with compact allocation. DEPRECATED
too_many_slots | 139 | The resume file contains more slots than the torrent
invalid_slot_list | 140 | The `slot` entry is invalid in the resume data
invalid_piece_index | 141 | One index in the `slot` list is invalid
pieces_need_reorder | 142 | The pieces on disk needs to be re-ordered for the specified allocation mode. This happens if you specify sparse allocation and the files on disk are using compact storage. The pieces needs to be moved to their right position. DEPRECATED
resume_data_not_modified | 143 | this error is returned when asking to save resume data and specifying the flag to only save when there's anything new to save (torrent_handle::only_if_modified) and there wasn't anything changed.
http_parse_error | 150 | The HTTP header was not correctly formatted
http_missing_location | 151 | The HTTP response was in the 300-399 range but lacked a location header
http_failed_decompress | 152 | The HTTP response was encoded with gzip or deflate but decompressing it failed
no_i2p_router | 160 | The URL specified an i2p address, but no i2p router is configured
no_i2p_endpoint | 161 | i2p acceptor is not available yet, can't announce without endpoint
scrape_not_available | 170 | The tracker URL doesn't support transforming it into a scrape URL. i.e. it doesn't contain "announce.
invalid_tracker_response | 171 | invalid tracker response
invalid_peer_dict | 172 | invalid peer dictionary entry. Not a dictionary
tracker_failure | 173 | tracker sent a failure message
invalid_files_entry | 174 | missing or invalid `files` entry
invalid_hash_entry | 175 | missing or invalid `hash` entry
invalid_peers_entry | 176 | missing or invalid `peers` and `peers6` entry
invalid_tracker_response_length | 177 | UDP tracker response packet has invalid size
invalid_tracker_transaction_id | 178 | invalid transaction id in UDP tracker response
invalid_tracker_action | 179 | invalid action field in UDP tracker response
no_entropy | 200 | random number generation failed
error_code_max | 201 | the number of error codes

[report issue]

### enum http_errors

Declared in "libtorrent/error_code.hpp"

name | value | description
--- | --- | ---
cont | 100 |
ok | 200 |
created | 201 |
accepted | 202 |
no_content | 204 |
multiple_choices | 300 |
moved_permanently | 301 |
moved_temporarily | 302 |
not_modified | 304 |
bad_request | 400 |
unauthorized | 401 |
forbidden | 403 |
not_found | 404 |
internal_server_error | 500 |
not_implemented | 501 |
bad_gateway | 502 |
service_unavailable | 503 |

[report issue]

### enum pcp_errors

Declared in "libtorrent/natpmp.hpp"

name | value | description
--- | --- | ---
pcp_success | 0 |
pcp_unsupp_version | 1 |
pcp_not_authorized | 2 |
pcp_malformed_request | 3 |
pcp_unsupp_opcode | 4 |
pcp_unsupp_option | 5 |
pcp_malformed_option | 6 |
pcp_network_failure | 7 |
pcp_no_resources | 8 |
pcp_unsupp_protocol | 9 |
pcp_user_ex_quota | 10 |
pcp_cannot_provide_external | 11 |
pcp_address_mismatch | 12 |
pcp_excessive_remote_peers | 13 |

[report issue]

### enum error_code_enum

Declared in "libtorrent/upnp.hpp"

name | value | description
--- | --- | ---
no_error | 0 | No error
invalid_argument | 402 | One of the arguments in the request is invalid
action_failed | 501 | The request failed
value_not_in_array | 714 | The specified value does not exist in the array
source_ip_cannot_be_wildcarded | 715 | The source IP address cannot be wild-carded, but must be fully specified
external_port_cannot_be_wildcarded | 716 | The external port cannot be a wildcard, but must be specified
port_mapping_conflict | 718 | The port mapping entry specified conflicts with a mapping assigned previously to another client
internal_port_must_match_external | 724 | Internal and external port value must be the same
only_permanent_leases_supported | 725 | The NAT implementation only supports permanent lease times on port mappings
remote_host_must_be_wildcard | 726 | RemoteHost must be a wildcard and cannot be a specific IP address or DNS name
external_port_must_be_wildcard | 727 | ExternalPort must be a wildcard and cannot be a specific port

[report issue]

### enum error_code_enum

Declared in "libtorrent/gzip.hpp"

name | value | description
--- | --- | ---
no_error | 0 | Not an error
invalid_gzip_header | 1 | the supplied gzip buffer has invalid header
inflated_data_too_large | 2 | the gzip buffer would inflate to more bytes than the specified maximum size, and was rejected.
data_did_not_terminate | 3 | available inflate data did not terminate
space_exhausted | 4 | output space exhausted before completing inflate
invalid_block_type | 5 | invalid block type (type == 3)
invalid_stored_block_length | 6 | stored block length did not match one's complement
too_many_length_or_distance_codes | 7 | dynamic block code description: too many length or distance codes
code_lengths_codes_incomplete | 8 | dynamic block code description: code lengths codes incomplete
repeat_lengths_with_no_first_length | 9 | dynamic block code description: repeat lengths with no first length
repeat_more_than_specified_lengths | 10 | dynamic block code description: repeat more than specified lengths
invalid_literal_length_code_lengths | 11 | dynamic block code description: invalid literal/length code lengths
invalid_distance_code_lengths | 12 | dynamic block code description: invalid distance code lengths
invalid_literal_code_in_block | 13 | invalid literal/length or distance code in fixed or dynamic block
distance_too_far_back_in_block | 14 | distance is too far back in fixed or dynamic block
unknown_gzip_error | 15 | an unknown error occurred during gzip inflation
error_code_max | 16 | the number of error codes

[report issue]

### enum error_code_enum

Declared in "libtorrent/bdecode.hpp"

name | value | description
--- | --- | ---
no_error | 0 | Not an error
expected_digit | 1 | expected digit in bencoded string
expected_colon | 2 | expected colon in bencoded string
unexpected_eof | 3 | unexpected end of file in bencoded string
expected_value | 4 | expected value (list, dict, int or string) in bencoded string
depth_exceeded | 5 | bencoded recursion depth limit exceeded
limit_exceeded | 6 | bencoded item count limit exceeded
overflow | 7 | integer overflow
error_code_max | 8 | the number of error codes

[report issue]

### enum socks_error_code

Declared in "libtorrent/socks5_stream.hpp"

name | value | description
--- | --- | ---
no_error | 0 |
unsupported_version | 1 |
unsupported_authentication_method | 2 |
unsupported_authentication_version | 3 |
authentication_error | 4 |
username_required | 5 |
general_failure | 6 |
command_not_supported | 7 |
no_identd | 8 |
identd_error | 9 |
num_errors | 10 |

[report issue]

### enum i2p_error_code

Declared in "libtorrent/i2p_stream.hpp"

name | value | description
--- | --- | ---
no_error | 0 |
parse_failed | 1 |
cant_reach_peer | 2 |
i2p_error | 3 |
invalid_key | 4 |
invalid_id | 5 |
timeout | 6 |
key_not_found | 7 |
duplicated_id | 8 |
num_errors | 9 |

Author: | Arvid Norberg, arvid@libtorrent.org
Version: | 1.2.9

home

## Storage

[report issue]

### storage_params

Declared in "libtorrent/storage_defs.hpp"

    struct storage_params
    {
       storage_params (file_storage const& f, file_storage const* mf
          , std::string const& sp, storage_mode_t const sm
          , aux::vector<download_priority_t, file_index_t> const& prio
          , sha1_hash const& ih);

       file_storage const& files;
       file_storage const* mapped_files  = nullptr;
       std::string const& path;
       storage_mode_t mode {storage_mode_sparse};
       aux::vector<download_priority_t, file_index_t> const& priorities;
       sha1_hash const& info_hash;
    };

[report issue]

### file_slice

Declared in "libtorrent/file_storage.hpp"

represents a window of a file in a torrent.

The `file_index` refers to the index of the file (in the torrent_info). To get the path and filename, use `file_path()` and give the `file_index` as argument. The `offset` is the byte offset in the file where the range starts, and `size` is the number of bytes this range is. The size + offset will never be greater than the file size.

    struct file_slice
    {
       file_index_t file_index;
       std::int64_t offset;
       std::int64_t size;
    };

[report issue]

file_index
  the index of the file

[report issue]

offset
  the offset from the start of the file, in bytes

[report issue]

size
  the size of the window, in bytes

[report issue]

### file_storage

Declared in "libtorrent/file_storage.hpp"

The `file_storage` class represents a file list and the piece size. Everything necessary to interpret a regular bittorrent storage file structure.

    class file_storage
    {
       bool is_valid () const;
       void reserve (int num_files);
       void add_file (std::string const& path, std::int64_t file_size
          , file_flags_t file_flags = {}
          , std::time_t mtime = 0, string_view symlink_path = string_view());
       void add_file_borrow (string_view filename
          , std::string const& path, std::int64_t file_size
          , file_flags_t file_flags = {}, char const* filehash = nullptr
          , std::int64_t mtime = 0, string_view symlink_path = string_view());
       void rename_file (file_index_t index, std::string const& new_filename);
       std::vector<file_slice> map_block (piece_index_t piece, std::int64_t offset
          , int size) const;
       peer_request map_file (file_index_t file, std::int64_t offset, int size) const;
       int num_files () const noexcept;
       file_index_t end_file () const noexcept;
       index_range<file_index_t> file_range () const noexcept;
       std::int64_t total_size () const;
       void set_num_pieces (int n);
       int num_pieces () const;
       piece_index_t end_piece () const;
       piece_index_t last_piece () const;
       index_range<piece_index_t> piece_range () const noexcept;
       int piece_length () const;
       void set_piece_length (int l);
       int piece_size (piece_index_t index) const;
       std::string const& name () const;
       void set_name (std::string const& n);
       void swap (file_storage& ti) noexcept;
       void optimize (int pad_file_limit = -1, int alignment = -1
          , bool tail_padding = false);
       std::string const& symlink (file_index_t index) const;
       bool pad_file_at (file_index_t index) const;
       std::time_t mtime (file_index_t index) const;
       std::int64_t file_offset (file_index_t index) const;
       std::int64_t file_size (file_index_t index) const;
       string_view file_name (file_index_t index) const;
       sha1_hash hash (file_index_t index) const;
       std::string file_path (file_index_t index, std::string const& save_path = "") const;
       std::uint32_t file_path_hash (file_index_t index, std::string const& save_path) const;
       void all_path_hashes (std::unordered_set<std::uint32_t>& table) const;
       std::vector<std::string> const& paths () const;
       file_flags_t file_flags (file_index_t index) const;
       bool file_absolute_path (file_index_t index) const;
       file_index_t file_index_at_offset (std::int64_t offset) const;
       int file_name_len (file_index_t index) const;
       char const* file_name_ptr (file_index_t index) const;
       void apply_pointer_offset (std::ptrdiff_t off);
       void sanitize_symlinks ();

       static constexpr file_flags_t flag_pad_file  = 0_bit;
       static constexpr file_flags_t flag_hidden  = 1_bit;
       static constexpr file_flags_t flag_executable  = 2_bit;
       static constexpr file_flags_t flag_symlink  = 3_bit;
    };

[report issue]

#### is_valid()

    bool is_valid () const;

returns true if the piece length has been initialized on the file_storage. This is typically taken as a proxy of whether the file_storage as a whole is initialized or not.

[report issue]

#### reserve()

    void reserve (int num_files);

allocates space for `num_files` in the internal file list. This can be used to avoid reallocating the internal file list when the number of files to be added is known up-front.

[report issue]

#### add_file_borrow() add_file()

    void add_file (std::string const& path, std::int64_t file_size
          , file_flags_t file_flags = {}
          , std::time_t mtime = 0, string_view symlink_path = string_view());
    void add_file_borrow (string_view filename
          , std::string const& path, std::int64_t file_size
          , file_flags_t file_flags = {}, char const* filehash = nullptr
          , std::int64_t mtime = 0, string_view symlink_path = string_view());

Adds a file to the file storage. The `add_file_borrow` version expects that `filename` is the file name (without a path) of the file that's being added. This memory is borrowed, i.e. it is the caller's responsibility to make sure it stays valid throughout the lifetime of this file_storage object or any copy of it. The same thing applies to `filehash`, which is an optional pointer to a 20 byte binary SHA-1 hash of the file.

if `filename` is empty, the filename from `path` is used and not borrowed.

The `path` argument is the full path (in the torrent file) to the file to add. Note that this is not supposed to be an absolute path, but it is expected to include the name of the torrent as the first path element.

`file_size` is the size of the file in bytes.

The `file_flags` argument sets attributes on the file. The file attributes is an extension and may not work in all bittorrent clients.

For possible file attributes, see file_storage::flags_t.

The `mtime` argument is optional and can be set to 0. If non-zero, it is the posix time of the last modification time of this file.

`symlink_path` is the path the file is a symlink to. To make this a symlink you also need to set the file_storage::flag_symlink file flag.

If more files than one are added, certain restrictions to their paths apply. In a multi-file file storage (torrent), all files must share the same root directory.

That is, the first path element of all files must be the same. This shared path element is also set to the name of the torrent. It can be changed by calling `set_name`.

[report issue]

#### rename_file()

    void rename_file (file_index_t index, std::string const& new_filename);

renames the file at `index` to `new_filename`. Keep in mind that filenames are expected to be UTF-8 encoded.

[report issue]

#### map_block()

    std::vector<file_slice> map_block (piece_index_t piece, std::int64_t offset
          , int size) const;

returns a list of file_slice objects representing the portions of files the specified piece index, byte offset and size range overlaps. this is the inverse mapping of map_file().

Preconditions of this function is that the input range is within the torrents address space. `piece` may not be negative and

> `piece` * piece_size + `offset` + `size`

may not exceed the total size of the torrent.

[report issue]

#### map_file()

    peer_request map_file (file_index_t file, std::int64_t offset, int size) const;

returns a peer_request representing the piece index, byte offset and size the specified file range overlaps. This is the inverse mapping over map_block(). Note that the `peer_request` return type is meant to hold bittorrent block requests, which may not be larger than 16 kiB. Mapping a range larger than that may return an overflown integer.

[report issue]

#### num_files()

    int num_files () const noexcept;

returns the number of files in the file_storage

[report issue]

#### end_file()

    file_index_t end_file () const noexcept;

returns the index of the one-past-end file in the file storage

[report issue]

#### file_range()

    index_range<file_index_t> file_range () const noexcept;

returns an implementation-defined type that can be used as the container in a range-for loop. Where the values are the indices of all files in the file_storage.

[report issue]

#### total_size()

    std::int64_t total_size () const;

returns the total number of bytes all the files in this torrent spans

[report issue]

#### num_pieces() set_num_pieces()

    void set_num_pieces (int n);
    int num_pieces () const;

set and get the number of pieces in the torrent

[report issue]

#### end_piece()

    piece_index_t end_piece () const;

returns the index of the one-past-end piece in the file storage

[report issue]

#### last_piece()

    piece_index_t last_piece () const;

returns the index of the last piece in the torrent. The last piece is special in that it may be smaller than the other pieces (and the other pieces are all the same size).

[report issue]

#### piece_range()

    index_range<piece_index_t> piece_range () const noexcept;

returns an implementation-defined type that can be used as the container in a range-for loop. Where the values are the indices of all pieces in the file_storage.

[report issue]

#### set_piece_length() piece_length()

    int piece_length () const;
    void set_piece_length (int l);

set and get the size of each piece in this torrent. This size is typically an even power of 2. It doesn't have to be though. It should be divisible by 16 kiB however.

[report issue]

#### piece_size()

    int piece_size (piece_index_t index) const;

returns the piece size of `index`. This will be the same as piece_length(), except for the last piece, which may be shorter.

[report issue]

#### name() set_name()

    std::string const& name () const;
    void set_name (std::string const& n);

set and get the name of this torrent. For multi-file torrents, this is also the name of the root directory all the files are stored in.

[report issue]

#### swap()

    void swap (file_storage& ti) noexcept;

swap all content of this with ti.

[report issue]

#### optimize()

    void optimize (int pad_file_limit = -1, int alignment = -1
          , bool tail_padding = false);

if pad_file_limit >= 0, files larger than that limit will be padded, default is to not add any padding (-1). The alignment specifies the alignment files should be padded to. This defaults to the piece size (-1) but it may also make sense to set it to 16 kiB, or something divisible by 16 kiB. If pad_file_limit is 0, every file will be padded (except empty ones). `tail_padding` indicates whether aligned files also are padded at the end to make them end aligned. This is required for mutable torrents, since piece hashes are compared

[report issue]

#### file_size() mtime() file_path() file_name() hash() file_offset() pad_file_at() symlink()

    std::string const& symlink (file_index_t index) const;
    bool pad_file_at (file_index_t index) const;
    std::time_t mtime (file_index_t index) const;
    std::int64_t file_offset (file_index_t index) const;
    std::int64_t file_size (file_index_t index) const;
    string_view file_name (file_index_t index) const;
    sha1_hash hash (file_index_t index) const;
    std::string file_path (file_index_t index, std::string const& save_path = "") const;

These functions are used to query attributes of files at a given index.

The `hash()` is a SHA-1 hash of the file, or 0 if none was provided in the torrent file. This can potentially be used to join a bittorrent network with other file sharing networks.

The `mtime()` is the modification time is the posix time when a file was last modified when the torrent was created, or 0 if it was not included in the torrent file.

`file_path()` returns the full path to a file.

`file_size()` returns the size of a file.

`pad_file_at()` returns true if the file at the given index is a pad-file.

`file_name()` returns just the name of the file, whereas `file_path()` returns the path (inside the torrent file) with the filename appended.

`file_offset()` returns the byte offset within the torrent file where this file starts. It can be used to map the file to a piece index (given the piece size).

[report issue]

#### file_path_hash()

    std::uint32_t file_path_hash (file_index_t index, std::string const& save_path) const;

returns the crc32 hash of file_path(index)

[report issue]

#### all_path_hashes()

    void all_path_hashes (std::unordered_set<std::uint32_t>& table) const;

this will add the CRC32 hash of all directory entries to the table. No filename will be included, just directories. Every depth of directories are added separately to allow test for collisions with files at all levels. i.e. if one path in the torrent is `foo/bar/baz`, the CRC32 hashes for `foo`, `foo/bar` and `foo/bar/baz` will be added to the set.

[report issue]

#### paths()

    std::vector<std::string> const& paths () const;

returns all directories used in the torrent. Files in the torrent are located in one of these directories. This is not a tree, it's a flat list of all leaf directories. i.e. the union of the parent paths of all files.

[report issue]

#### file_flags()

    file_flags_t file_flags (file_index_t index) const;

returns a bitmask of flags from file_flags_t that apply to file at `index`.

[report issue]

#### file_absolute_path()

    bool file_absolute_path (file_index_t index) const;

returns true if the file at the specified index has been renamed to have an absolute path, i.e. is not anchored in the save path of the torrent.

[report issue]

#### file_index_at_offset()

    file_index_t file_index_at_offset (std::int64_t offset) const;

returns the index of the file at the given offset in the torrent

[report issue]

#### file_name_len() file_name_ptr()

    int file_name_len (file_index_t index) const;
    char const* file_name_ptr (file_index_t index) const;

low-level function. returns a pointer to the internal storage for the filename. This string may not be 0-terminated! the `file_name_len()` function returns the length of the filename. prefer to use `file_name()` instead, which returns a `string_view`.

[report issue]

#### apply_pointer_offset()

    void apply_pointer_offset (std::ptrdiff_t off);

if the backing buffer changed for this storage, this is the pointer offset to add to any pointers to make them point into the new buffer

[report issue]

#### sanitize_symlinks()

    void sanitize_symlinks ();

validate any symlinks, to ensure they all point to other files or directories inside this storage. Any invalid symlinks are updated to point to themselves.

[report issue]

flag_pad_file
  the file is a pad file. It's required to contain zeros at it will not be saved to disk. Its purpose is to make the following file start on a piece boundary.

[report issue]

flag_hidden
  this file has the hidden attribute set. This is primarily a windows attribute

[report issue]

flag_executable
  this file has the executable attribute set.

[report issue]

flag_symlink
  this file is a symbolic link. It should have a link target string associated with it.

[report issue]

### default_storage_constructor()

Declared in "libtorrent/storage_defs.hpp"

    storage_interface* default_storage_constructor (storage_params const&
       , file_pool& p);

the constructor function for the regular file storage. This is the default value for add_torrent_params::storage.

[report issue]

### disabled_storage_constructor()

Declared in "libtorrent/storage_defs.hpp"

    storage_interface* disabled_storage_constructor (storage_params const&, file_pool&);

the constructor function for the disabled storage. This can be used for testing and benchmarking. It will throw away any data written to it and return garbage for anything read from it.

[report issue]

### zero_storage_constructor()

Declared in "libtorrent/storage_defs.hpp"

    storage_interface* zero_storage_constructor (storage_params const&, file_pool&);

the constructor function for the "zero" storage. This will always read zeros and ignore all writes.

[report issue]

### enum storage_mode_t

Declared in "libtorrent/storage_defs.hpp"

name | value | description
--- | --- | ---
storage_mode_allocate | 0 | All pieces will be written to their final position, all files will be allocated in full when the torrent is first started. This is done with `fallocate()` and similar calls. This mode minimizes fragmentation.
storage_mode_sparse | 1 | All pieces will be written to the place where they belong and sparse files will be used. This is the recommended, and default mode.

[report issue]

### enum status_t

Declared in "libtorrent/storage_defs.hpp"

name | value | description
--- | --- | ---
no_error | 0 |
fatal_disk_error | 1 |
need_full_check | 2 |
file_exist | 3 |

[report issue]

### enum move_flags_t

Declared in "libtorrent/storage_defs.hpp"

name | value | description
--- | --- | ---
always_replace_files | 0 | replace any files in the destination when copying or moving the storage
fail_if_exist | 1 | if any files that we want to copy exist in the destination exist, fail the whole operation and don't perform any copy or move. There is an inherent race condition in this mode. The files are checked for existence before the operation starts. In between the check and performing the copy, the destination files may be created, in which case they are replaced.
dont_replace | 2 | if any file exist in the target, take those files instead of the ones we may have in the source.

Author: | Arvid Norberg, arvid@libtorrent.org
Version: | 1.2.9

home

## Custom Storage

libtorrent provides a customization point for storage of data. By default, (`default_storage`) downloaded files are saved to disk according with the general conventions of bittorrent clients, mimicking the original file layout when the torrent was created. The libtorrent user may define a custom storage to store piece data in a different way.

A custom storage implementation must derive from and implement the storage_interface. You must also provide a function that constructs the custom storage object and provide this function to the add_torrent() call via add_torrent_params. Either passed in to the constructor or by setting the add_torrent_params::storage field.

This is an example storage implementation that stores all pieces in a `std::map`, i.e. in RAM. It's not necessarily very useful in practice, but illustrates the basics of implementing a custom storage.

    struct temp_storage : lt::storage_interface
    {
      explicit temp_storage(lt::file_storage const& fs) : lt::storage_interface(fs) {}
      void initialize(lt::storage_error&) override {}
      bool has_any_file(lt::storage_error&) override { return false; }
      void set_file_priority(lt::aux::vector<lt::download_priority_t, lt::file_index_t>&
        , lt::storage_error&) override {}
      int readv(lt::span<lt::iovec_t const> bufs, lt::piece_index_t piece
        , int offset, lt::open_mode_t, lt::storage_error&) override
      {
        auto const i = m_file_data.find(piece);
        if (i == m_file_data.end()) return 0;
        if (int(i->second.size()) <= offset) return 0;
        lt::iovec_t data{ i->second.data() + offset, int(i->second.size() - offset) };
        int ret = 0;
        for (lt::iovec_t const& b : bufs) {
          int const to_copy = std::min(int(b.size()), int(data.size()));
          memcpy(b.data(), data.data(), to_copy);
          data = data.subspan(to_copy);
          ret += to_copy;
          if (data.empty()) break;
        }
        return ret;
      }
      int writev(lt::span<lt::iovec_t const> bufs
        , lt::piece_index_t const piece, int offset, lt::open_mode_t, lt::storage_error&) override
      {
        auto& data = m_file_data[piece];
        int ret = 0;
        for (auto& b : bufs) {
          if (int(data.size()) < offset + b.size()) data.resize(offset + b.size());
          std::memcpy(data.data() + offset, b.data(), b.size());
          offset += int(b.size());
          ret += int(b.size());
        }
        return ret;
      }
      void rename_file(lt::file_index_t, std::string const&, lt::storage_error&) override
      { assert(false); }
      lt::status_t move_storage(std::string const&
        , lt::move_flags_t, lt::storage_error&) override { return lt::status_t::no_error; }
      bool verify_resume_data(lt::add_torrent_params const&
        , lt::aux::vector<std::string, lt::file_index_t> const&
        , lt::storage_error&) override
      { return false; }
      void release_files(lt::storage_error&) override {}
      void delete_files(lt::remove_flags_t, lt::storage_error&) override {}

      std::map<lt::piece_index_t, std::vector<char>> m_file_data;
    };

    lt::storage_interface* temp_storage_constructor(lt::storage_params const& params, lt::file_pool&)
    {
      return new temp_storage(params.files);
    }

[report issue]

### storage_interface

Declared in "libtorrent/storage.hpp"

The storage interface is a pure virtual class that can be implemented to customize how and where data for a torrent is stored. The default storage implementation uses regular files in the filesystem, mapping the files in the torrent in the way one would assume a torrent is saved to disk. Implementing your own storage interface makes it possible to store all data in RAM, or in some optimized order on disk (the order the pieces are received for instance), or saving multi file torrents in a single file in order to be able to take advantage of optimized disk-I/O.

It is also possible to write a thin class that uses the default storage but modifies some particular behavior, for instance encrypting the data before it's written to disk, and decrypting it when it's read again.

The storage interface is based on pieces. Every read and write operation happens in the piece-space. Each piece fits `piece_size` number of bytes. All access is done by writing and reading whole or partial pieces.

libtorrent comes with two built-in storage implementations; `default_storage` and `disabled_storage`. Their constructor functions are called default_storage_constructor() and `disabled_storage_constructor` respectively. The disabled storage does just what it sounds like. It throws away data that's written, and it reads garbage. It's useful mostly for benchmarking and profiling purpose.

    struct storage_interface: std::enable_shared_from_this<storage_interface>, aux::disk_job_fence, aux::storage_piece_set
    {
       explicit storage_interface (file_storage const& fs);
       storage_interface (storage_interface const&) = delete;
       storage_interface& operator= (storage_interface const&) = delete;
       virtual void initialize (storage_error& ec) = 0;
       virtual int writev (span<iovec_t const> bufs
          , piece_index_t piece, int offset, open_mode_t flags, storage_error& ec) = 0;
       virtual int readv (span<iovec_t const> bufs
          , piece_index_t piece, int offset, open_mode_t flags, storage_error& ec) = 0;
       virtual bool has_any_file (storage_error& ec) = 0;
       virtual void set_file_priority (aux::vector<download_priority_t, file_index_t>& prio
          , storage_error& ec) = 0;
       virtual status_t move_storage (std::string const& save_path
          , move_flags_t flags, storage_error& ec) = 0;
       virtual bool verify_resume_data (add_torrent_params const& rd
          , aux::vector<std::string, file_index_t> const& links
          , storage_error& ec) = 0;
       virtual void release_files (storage_error& ec) = 0;
       virtual void rename_file (file_index_t index, std::string const& new_filename
          , storage_error& ec) = 0;
       virtual void delete_files (remove_flags_t options, storage_error& ec) = 0;
       virtual bool tick ();
       file_storage const& files () const;
       bool set_need_tick ();
       void do_tick ();
       void set_owner (std::shared_ptr<void> const& tor);
       aux::session_settings const& settings () const;
       void set_storage_index (storage_index_t st);
       storage_index_t storage_index () const;
       void inc_refcount ();
       int dec_refcount ();

       aux::session_settings const* m_settings  = nullptr;
    };

[report issue]

#### initialize()

    virtual void initialize (storage_error& ec) = 0;

This function is called when the storage on disk is to be initialized. The default storage will create directories and empty files at this point. If `allocate_files` is true, it will also `ftruncate` all files to their target size.

This function may be called multiple time on a single instance. When a torrent is force-rechecked, the storage is re-initialized to trigger the re-check from scratch.

The function is not necessarily called before other member functions. For instance has_any_files() and verify_resume_data() are called early to determine whether we may have to check all files or not. If we're doing a full check of the files every piece will be hashed, causing readv() to be called as well.

Any required internals that need initialization should be done in the constructor. This function is called before the torrent starts to download.

If an error occurs, `storage_error` should be set to reflect it.

[report issue]

#### readv() writev()

    virtual int writev (span<iovec_t const> bufs
          , piece_index_t piece, int offset, open_mode_t flags, storage_error& ec) = 0;
    virtual int readv (span<iovec_t const> bufs
          , piece_index_t piece, int offset, open_mode_t flags, storage_error& ec) = 0;

These functions should read and write the data in or to the given `piece` at the given `offset`. It should read or write `num_bufs` buffers sequentially, where the size of each buffer is specified in the buffer array `bufs`. The iovec_t type has the following members:

    struct iovec_t { void* iov_base; size_t iov_len; };

These functions may be called simultaneously from multiple threads. Make sure they are thread safe. The `file` in libtorrent is thread safe when it can fall back to `pread`, `preadv` or the windows equivalents. On targets where read operations cannot be thread safe (i.e one has to seek first and then read), only one disk thread is used.

The `offset` is aligned to 16 kiB boundaries most of the time, but there are rare exceptions when it's not. Specifically if the read cache is disabled/or full and a peer requests unaligned data. Most clients request aligned data.

The number of bytes read or written should be returned, or -1 on error. If there's an error, the `storage_error` must be filled out to represent the error that occurred.

For possible values of `flags`, see open_mode_t.

[report issue]

#### has_any_file()

    virtual bool has_any_file (storage_error& ec) = 0;

This function is called when first checking (or re-checking) the storage for a torrent. It should return true if any of the files that is used in this storage exists on disk. If so, the storage will be checked for existing pieces before starting the download.

If an error occurs, `storage_error` should be set to reflect it.

[report issue]

#### set_file_priority()

    virtual void set_file_priority (aux::vector<download_priority_t, file_index_t>& prio
          , storage_error& ec) = 0;

change the priorities of files. This is a fenced job and is guaranteed to be the only running function on this storage when called

[report issue]

#### move_storage()

    virtual status_t move_storage (std::string const& save_path
          , move_flags_t flags, storage_error& ec) = 0;

This function should move all the files belonging to the storage to the new save_path. The default storage moves the single file or the directory of the torrent.

Before moving the files, any open file handles may have to be closed, like `release_files()`.

If an error occurs, `storage_error` should be set to reflect it.

[report issue]

#### verify_resume_data()

    virtual bool verify_resume_data (add_torrent_params const& rd
          , aux::vector<std::string, file_index_t> const& links
          , storage_error& ec) = 0;

This function should verify the resume data `rd` with the files on disk. If the resume data seems to be up-to-date, return true. If not, set `error` to a description of what mismatched and return false.

The default storage may compare file sizes and time stamps of the files.

If an error occurs, `storage_error` should be set to reflect it.

This function should verify the resume data `rd` with the files on disk. If the resume data seems to be up-to-date, return true. If not, set `error` to a description of what mismatched and return false.

If the `links` pointer is non-empty, it has the same number of elements as there are files. Each element is either empty or contains the absolute path to a file identical to the corresponding file in this torrent. The storage must create hard links (or copy) those files. If any file does not exist or is inaccessible, the disk job must fail.

[report issue]

#### release_files()

    virtual void release_files (storage_error& ec) = 0;

This function should release all the file handles that it keeps open to files belonging to this storage. The default implementation just calls file_pool::release_files().

If an error occurs, `storage_error` should be set to reflect it.

[report issue]

#### rename_file()

    virtual void rename_file (file_index_t index, std::string const& new_filename
          , storage_error& ec) = 0;

Rename the file with index `file` to name `new_name`.

If an error occurs, `storage_error` should be set to reflect it.

[report issue]

#### delete_files()

    virtual void delete_files (remove_flags_t options, storage_error& ec) = 0;

This function should delete some or all of the storage for this torrent. The `options` parameter specifies whether to delete all files or just the partfile. `options` are set to the same value as the options passed to session::remove_torrent().

If an error occurs, `storage_error` should be set to reflect it.

The `disk_buffer_pool` is used to allocate and free disk buffers. It has the following members:

    struct disk_buffer_pool
    {
            char* allocate_buffer(char const* category);
            void free_buffer(char* buf);

            char* allocate_buffers(int blocks, char const* category);
            void free_buffers(char* buf, int blocks);

            int block_size() const { return m_block_size; }

    };

[report issue]

#### tick()

    virtual bool tick ();

called periodically (useful for deferred flushing). When returning false, it means no more ticks are necessary. Any disk job submitted will re-enable ticking. The default will always turn ticking back off again.

[report issue]

#### settings()

    aux::session_settings const& settings () const;

access global session_settings

[report issue]

m_settings
  initialized in disk_io_thread::perform_async_job

[report issue]

### default_storage

Declared in "libtorrent/storage.hpp"

The default implementation of storage_interface. Behaves as a normal bittorrent client. It is possible to derive from this class in order to override some of its behavior, when implementing a custom storage.

    class default_storage : public storage_interface
    {
       explicit default_storage (storage_params const& params, file_pool&);
       void delete_files (remove_flags_t options, storage_error& ec) override;
       status_t move_storage (std::string const& save_path
          , move_flags_t flags, storage_error& ec) override;
       bool tick () override;
       bool verify_resume_data (add_torrent_params const& rd
          , aux::vector<std::string, file_index_t> const& links
          , storage_error& error) override;
       void release_files (storage_error& ec) override;
       void initialize (storage_error& ec) override;
       void rename_file (file_index_t index, std::string const& new_filename
          , storage_error& ec) override;
       void set_file_priority (aux::vector<download_priority_t, file_index_t>& prio
          , storage_error& ec) override;
       bool has_any_file (storage_error& ec) override;
       int readv (span<iovec_t const> bufs
          , piece_index_t piece, int offset, open_mode_t flags, storage_error& ec) override;
       int writev (span<iovec_t const> bufs
          , piece_index_t piece, int offset, open_mode_t flags, storage_error& ec) override;
       file_storage const& files () const;
    };

[report issue]

#### default_storage()

    explicit default_storage (storage_params const& params, file_pool&);

constructs the default_storage based on the give file_storage (fs). `mapped` is an optional argument (it may be nullptr). If non-nullptr it represents the file mapping that have been made to the torrent before adding it. That's where files are supposed to be saved and looked for on disk. `save_path` is the root save folder for this torrent. `file_pool` is the cache of file handles that the storage will use. All files it opens will ask the file_pool to open them. `file_prio` is a vector indicating the priority of files on startup. It may be an empty vector. Any file whose index is not represented by the vector (because the vector is too short) are assumed to have priority 1. this is used to treat files with priority 0 slightly differently.

[report issue]

#### files()

    file_storage const& files () const;

if the files in this storage are mapped, returns the mapped file_storage, otherwise returns the original file_storage object.

[report issue]

### file_pool

Declared in "libtorrent/file_pool.hpp"

this is an internal cache of open file handles. It's primarily used by storage_interface implementations. It provides semi weak guarantees of not opening more file handles than specified. Given multiple threads, each with the ability to lock a file handle (via smart pointer), there may be windows where more file handles are open.

    struct file_pool : boost::noncopyable
    {
       ~file_pool ();
       explicit file_pool (int size = 40);
       file_handle open_file (storage_index_t st, std::string const& p
          , file_index_t file_index, file_storage const& fs, open_mode_t m
          , error_code& ec);
       void release ();
       void release (storage_index_t st);
       void release (storage_index_t st, file_index_t file_index);
       void resize (int size);
       int size_limit () const;
       void close_oldest ();
    };

[report issue]

#### file_pool() ~file_pool()

    ~file_pool ();
    explicit file_pool (int size = 40);

`size` specifies the number of allowed files handles to hold open at any given time.

[report issue]

#### open_file()

    file_handle open_file (storage_index_t st, std::string const& p
          , file_index_t file_index, file_storage const& fs, open_mode_t m
          , error_code& ec);

return an open file handle to file at `file_index` in the file_storage `fs` opened at save path `p`. `m` is the file open mode (see file::open_mode_t).

[report issue]

#### release()

    void release ();
    void release (storage_index_t st);
    void release (storage_index_t st, file_index_t file_index);

release all files belonging to the specified storage_interface (`st`) the overload that takes `file_index` releases only the file with that index in storage `st`.

[report issue]

#### resize()

    void resize (int size);

update the allowed number of open file handles to `size`.

[report issue]

#### size_limit()

    int size_limit () const;

returns the current limit of number of allowed open file handles held by the file_pool.

[report issue]

#### close_oldest()

    void close_oldest ();

close the file that was opened least recently (i.e. not accessed least recently). The purpose is to make the OS (really just windows) clear and flush its disk cache associated with this file. We don't want any file to stay open for too long, allowing the disk cache to accrue.

Author: | Arvid Norberg, arvid@libtorrent.org
Version: | 1.2.9

home

## Utility

[report issue]

### bitfield

Declared in "libtorrent/bitfield.hpp"

The bitfield type stores any number of bits as a bitfield in a heap allocated array.

    struct bitfield
    {
       bitfield () noexcept = default;
       bitfield (bitfield const& rhs);
       explicit bitfield (int bits);
       bitfield (bitfield&& rhs) noexcept = default;
       bitfield (int bits, bool val);
       bitfield (char const* b, int bits);
       void assign (char const* b, int const bits);
       bool operator[] (int index) const noexcept;
       bool get_bit (int index) const noexcept;
       void set_bit (int index) noexcept;
       void clear_bit (int index) noexcept;
       bool all_set () const noexcept;
       bool none_set () const noexcept;
       int size () const noexcept;
       int num_words () const noexcept;
       bool empty () const noexcept;
       char* data () noexcept;
       char const* data () const noexcept;
       void swap (bitfield& rhs) noexcept;
       int count () const noexcept;
       int find_first_set () const noexcept;
       int find_last_clear () const noexcept;
    };

[report issue]

#### bitfield()

    bitfield () noexcept = default;
    bitfield (bitfield const& rhs);
    explicit bitfield (int bits);
    bitfield (bitfield&& rhs) noexcept = default;
    bitfield (int bits, bool val);
    bitfield (char const* b, int bits);

constructs a new bitfield. The default constructor creates an empty bitfield. `bits` is the size of the bitfield (specified in bits). `val` is the value to initialize the bits to. If not specified all bits are initialized to 0.

The constructor taking a pointer `b` and `bits` copies a bitfield from the specified buffer, and `bits` number of bits (rounded up to the nearest byte boundary).

[report issue]

#### assign()

    void assign (char const* b, int const bits);

copy bitfield from buffer `b` of `bits` number of bits, rounded up to the nearest byte boundary.

[report issue]

#### get_bit() operator[]()

    bool operator[] (int index) const noexcept;
    bool get_bit (int index) const noexcept;

query bit at `index`. Returns true if bit is 1, otherwise false.

[report issue]

#### set_bit() clear_bit()

    void set_bit (int index) noexcept;
    void clear_bit (int index) noexcept;

set bit at `index` to 0 (clear_bit) or 1 (set_bit).

[report issue]

#### all_set()

    bool all_set () const noexcept;

returns true if all bits in the bitfield are set

[report issue]

#### none_set()

    bool none_set () const noexcept;

returns true if no bit in the bitfield is set

[report issue]

#### size()

    int size () const noexcept;

returns the size of the bitfield in bits.

[report issue]

#### num_words()

    int num_words () const noexcept;

returns the number of 32 bit words are needed to represent all bits in this bitfield.

[report issue]

#### empty()

    bool empty () const noexcept;

returns true if the bitfield has zero size.

[report issue]

#### data()

    char* data () noexcept;
    char const* data () const noexcept;

returns a pointer to the internal buffer of the bitfield, or `nullptr` if it's empty.

[report issue]

#### swap()

    void swap (bitfield& rhs) noexcept;

swaps the bit-fields two variables refer to

[report issue]

#### count()

    int count () const noexcept;

count the number of bits in the bitfield that are set to 1.

[report issue]

#### find_first_set()

    int find_first_set () const noexcept;

returns the index of the first set bit in the bitfield, i.e. 1 bit.

[report issue]

#### find_last_clear()

    int find_last_clear () const noexcept;

returns the index to the last cleared bit in the bitfield, i.e. 0 bit.

[report issue]

### hasher

Declared in "libtorrent/hasher.hpp"

this is a SHA-1 hash class.

You use it by first instantiating it, then call `update()` to feed it with data. i.e. you don't have to keep the entire buffer of which you want to create the hash in memory. You can feed the hasher parts of it at a time. When You have fed the hasher with all the data, you call `final()` and it will return the sha1-hash of the data.

The constructor that takes a `char const*` and an integer will construct the sha1 context and feed it the data passed in.

If you want to reuse the hasher object once you have created a hash, you have to call `reset()` to reinitialize it.

The built-in software version of sha1-algorithm was implemented by Steve Reid and released as public domain. For more info, see `src/sha1.cpp`.

    class hasher
    {
       hasher ();
       hasher& operator= (hasher const&) &;
       hasher (hasher const&);
       explicit hasher (span<char const> data);
       hasher (char const* data, int len);
       hasher& update (span<char const> data);
       hasher& update (char const* data, int len);
       sha1_hash final ();
       void reset ();
    };

[report issue]

#### hasher() operator=()

    hasher& operator= (hasher const&) &;
    hasher (hasher const&);
    explicit hasher (span<char const> data);
    hasher (char const* data, int len);

this is the same as default constructing followed by a call to `update(data, len)`.

[report issue]

#### update()

    hasher& update (span<char const> data);
    hasher& update (char const* data, int len);

append the following bytes to what is being hashed

[report issue]

#### final()

    sha1_hash final ();

returns the SHA-1 digest of the buffers previously passed to update() and the hasher constructor.

[report issue]

#### reset()

    void reset ();

restore the hasher state to be as if the hasher has just been default constructed.

[report issue]

### operator<<()

Declared in "libtorrent/sha1_hash.hpp"

    std::ostream& operator<< (std::ostream& os, sha1_hash const& peer);

print a sha1_hash object to an ostream as 40 hexadecimal digits

[report issue]

### operator>>()

Declared in "libtorrent/sha1_hash.hpp"

    std::istream& operator>> (std::istream& is, sha1_hash& peer);

read 40 hexadecimal digits from an istream into a sha1_hash

Author: | Arvid Norberg, arvid@libtorrent.org
Version: | 1.2.9

home

## Bencoding

Bencoding is a common representation in bittorrent used for dictionary, list, int and string hierarchies. It's used to encode .torrent files and some messages in the network protocol. libtorrent also uses it to store settings, resume data and other session state.

Strings in bencoded structures do not necessarily represent text. Strings are raw byte buffers of a certain length. If a string is meant to be interpreted as text, it is required to be UTF-8 encoded. See BEP 3.

The function for decoding bencoded data bdecode(), returning a bdecode_node. This function builds a tree that points back into the original buffer. The returned bdecode_node will not be valid once the buffer it was parsed out of is discarded.

It's possible to construct an entry from a bdecode_node, if a structure needs to be altered and re-encoded.

[report issue]

### entry

Declared in "libtorrent/entry.hpp"

The `entry` class represents one node in a bencoded hierarchy. It works as a variant type, it can be either a list, a dictionary (`std::map`), an integer or a string.

    class entry
    {
       data_type type () const;
       entry& operator= (list_type) &;
       entry (list_type); // NOLINT;
       entry (dictionary_type); // NOLINT;
       entry& operator= (integer_type) &;
       entry& operator= (preformatted_type) &;
       list_type& list ();
       preformatted_type& preformatted ();
       integer_type& integer ();
       string_type& string ();
       const string_type& string () const;
       const dictionary_type& dict () const;
       const preformatted_type& preformatted () const;
       const integer_type& integer () const;
       dictionary_type& dict ();
       const list_type& list () const;
       void swap (entry& e);
       entry& operator[] (string_view key);
       const entry& operator[] (string_view key) const;
       entry const* find_key (string_view key) const;
       entry* find_key (string_view key);
       std::string to_string (bool single_line = false) const;

       enum data_type
       {
          int_t,
          string_t,
          list_t,
          dictionary_t,
          undefined_t,
          preformatted_t,
       };

       mutable std::uint8_t m_type_queried:1;
    };

[report issue]

#### type()

    data_type type () const;

returns the concrete type of the entry

[report issue]

#### operator=() entry()

    entry& operator= (list_type) &;
    entry (list_type); // NOLINT;
    entry (dictionary_type); // NOLINT;
    entry& operator= (integer_type) &;
    entry& operator= (preformatted_type) &;

constructors directly from a specific type. The content of the argument is copied into the newly constructed entry

[report issue]

#### string() dict() list() integer() preformatted()

    list_type& list ();
    preformatted_type& preformatted ();
    integer_type& integer ();
    string_type& string ();
    const string_type& string () const;
    const dictionary_type& dict () const;
    const preformatted_type& preformatted () const;
    const integer_type& integer () const;
    dictionary_type& dict ();
    const list_type& list () const;

The `integer()`, `string()`, `list()` and `dict()` functions are accessors that return the respective type. If the `entry` object isn't of the type you request, the accessor will throw system_error. You can ask an `entry` for its type through the `type()` function.

If you want to create an `entry` you give it the type you want it to have in its constructor, and then use one of the non-const accessors to get a reference which you then can assign the value you want it to have.

The typical code to get info from a torrent file will then look like this:

    entry torrent_file;
    // ...

    // throws if this is not a dictionary
    entry::dictionary_type const& dict = torrent_file.dict();
    entry::dictionary_type::const_iterator i;
    i = dict.find("announce");
    if (i != dict.end())
    {
            std::string tracker_url = i->second.string();
            std::cout << tracker_url << "\n";
    }

The following code is equivalent, but a little bit shorter:

    entry torrent_file;
    // ...

    // throws if this is not a dictionary
    if (entry* i = torrent_file.find_key("announce"))
    {
            std::string tracker_url = i->string();
            std::cout << tracker_url << "\n";
    }

To make it easier to extract information from a torrent file, the class torrent_info exists.

[report issue]

#### swap()

    void swap (entry& e);

swaps the content of this with `e`.

[report issue]

#### operator[]()

    entry& operator[] (string_view key);
    const entry& operator[] (string_view key) const;

All of these functions requires the entry to be a dictionary, if it isn't they will throw `system_error`.

The non-const versions of the `operator[]` will return a reference to either the existing element at the given key or, if there is no element with the given key, a reference to a newly inserted element at that key.

The const version of `operator[]` will only return a reference to an existing element at the given key. If the key is not found, it will throw `system_error`.

[report issue]

#### find_key()

    entry const* find_key (string_view key) const;
    entry* find_key (string_view key);

These functions requires the entry to be a dictionary, if it isn't they will throw `system_error`.

They will look for an element at the given key in the dictionary, if the element cannot be found, they will return nullptr. If an element with the given key is found, the return a pointer to it.

[report issue]

#### to_string()

    std::string to_string (bool single_line = false) const;

returns a pretty-printed string representation of the bencoded structure, with JSON-style syntax

[report issue]

#### enum data_type

Declared in "libtorrent/entry.hpp"

name | value | description
--- | --- | ---
int_t | 0 |
string_t | 1 |
list_t | 2 |
dictionary_t | 3 |
undefined_t | 4 |
preformatted_t | 5 |

[report issue]

m_type_queried
  in debug mode this is set to false by bdecode to indicate that the program has not yet queried the type of this entry, and should not assume that it has a certain type. This is asserted in the accessor functions. This does not apply if exceptions are used.

[report issue]

### bencode()

Declared in "libtorrent/bencode.hpp"

    template<class OutIt> int bencode (OutIt out, const entry& e);

This function will encode data to bencoded form.

The entry class is the internal representation of the bencoded data and it can be used to retrieve information, an entry can also be build by the program and given to `bencode()` to encode it into the `OutIt` iterator.

`OutIt` is an OutputIterator. It's a template and usually instantiated as ostream_iterator or back_insert_iterator. This function assumes the value_type of the iterator is a `char`. In order to encode entry `e` into a buffer, do:

    std::vector<char> buffer;
    bencode(std::back_inserter(buf), e);

[report issue]

### operator<<()

Declared in "libtorrent/entry.hpp"

    inline std::ostream& operator<< (std::ostream& os, const entry& e);

prints the bencoded structure to the ostream as a JSON-style structure.

Author: | Arvid Norberg, arvid@libtorrent.org
Version: | 1.2.9

home

## Alerts

The pop_alerts() function on session is the main interface for retrieving alerts (warnings, messages and errors from libtorrent). If no alerts have been posted by libtorrent pop_alerts() will return an empty list.

By default, only errors are reported. settings_pack::alert_mask can be used to specify which kinds of events should be reported. The alert mask is a combination of the alert_category_t flags in the alert class.

Every alert belongs to one or more category. There is a cost associated with posting alerts. Only alerts that belong to an enabled category are posted. Setting the alert bitmask to 0 will disable all alerts (except those that are non-discardable). Alerts that are responses to API calls such as save_resume_data() and post_session_stats() are non-discardable and will be posted even if their category is disabled.

There are other alert base classes that some alerts derive from, all the alerts that are generated for a specific torrent are derived from torrent_alert, and tracker events derive from tracker_alert.

Alerts returned by pop_alerts() are only valid until the next call to pop_alerts(). You may not copy an alert object to access it after the next call to pop_alerts(). Internal members of alerts also become invalid once pop_alerts() is called again.

[report issue]

### alert

Declared in "libtorrent/alert.hpp"

The `alert` class is the base class that specific messages are derived from. alert types are not copyable, and cannot be constructed by the client. The pointers returned by libtorrent are short lived (the details are described under session_handle::pop_alerts())

    class alert
    {
       time_point timestamp () const;
       virtual int type () const noexcept = 0;
       virtual char const* what () const noexcept = 0;
       virtual std::string message () const = 0;
       virtual alert_category_t category () const noexcept = 0;

       static constexpr alert_category_t error_notification  = 0_bit;
       static constexpr alert_category_t peer_notification  = 1_bit;
       static constexpr alert_category_t port_mapping_notification  = 2_bit;
       static constexpr alert_category_t storage_notification  = 3_bit;
       static constexpr alert_category_t tracker_notification  = 4_bit;
       static constexpr alert_category_t connect_notification  = 5_bit;
       static constexpr alert_category_t status_notification  = 6_bit;
       static constexpr alert_category_t ip_block_notification  = 8_bit;
       static constexpr alert_category_t performance_warning  = 9_bit;
       static constexpr alert_category_t dht_notification  = 10_bit;
       static constexpr alert_category_t stats_notification  = 11_bit;
       static constexpr alert_category_t session_log_notification  = 13_bit;
       static constexpr alert_category_t torrent_log_notification  = 14_bit;
       static constexpr alert_category_t peer_log_notification  = 15_bit;
       static constexpr alert_category_t incoming_request_notification  = 16_bit;
       static constexpr alert_category_t dht_log_notification  = 17_bit;
       static constexpr alert_category_t dht_operation_notification  = 18_bit;
       static constexpr alert_category_t port_mapping_log_notification  = 19_bit;
       static constexpr alert_category_t picker_log_notification  = 20_bit;
       static constexpr alert_category_t file_progress_notification  = 21_bit;
       static constexpr alert_category_t piece_progress_notification  = 22_bit;
       static constexpr alert_category_t upload_notification  = 23_bit;
       static constexpr alert_category_t block_progress_notification  = 24_bit;
       static constexpr alert_category_t all_categories  = alert_category_t::all();
    };

[report issue]

#### timestamp()

    time_point timestamp () const;

a timestamp is automatically created in the constructor

[report issue]

#### type()

    virtual int type () const noexcept = 0;

returns an integer that is unique to this alert type. It can be compared against a specific alert by querying a static constant called `alert_type` in the alert. It can be used to determine the run-time type of an alert* in order to cast to that alert type and access specific members.

e.g:

    std::vector<alert*> alerts;
    ses.pop_alerts(&alerts);
    for (alert* a : alerts) {
            switch (a->type()) {

                    case read_piece_alert::alert_type:
                    {
                            auto* p = static_cast<read_piece_alert*>(a);
                            if (p->ec) {
                                    // read_piece failed
                                    break;
                            }
                            // use p
                            break;
                    }
                    case file_renamed_alert::alert_type:
                    {
                            // etc...
                    }
            }
    }

[report issue]

#### what()

    virtual char const* what () const noexcept = 0;

returns a string literal describing the type of the alert. It does not include any information that might be bundled with the alert.

[report issue]

#### message()

    virtual std::string message () const = 0;

generate a string describing the alert and the information bundled with it. This is mainly intended for debug and development use. It is not suitable to use this for applications that may be localized. Instead, handle each alert type individually and extract and render the information from the alert depending on the locale.

[report issue]

#### category()

    virtual alert_category_t category () const noexcept = 0;

returns a bitmask specifying which categories this alert belong to.

[report issue]

### dht_routing_bucket

Declared in "libtorrent/alert_types.hpp"

struct to hold information about a single DHT routing table bucket

    struct dht_routing_bucket
    {
       int num_nodes;
       int num_replacements;
       int last_active;
    };

[report issue]

num_nodes num_replacements
  the total number of nodes and replacement nodes in the routing table

[report issue]

last_active
  number of seconds since last activity

[report issue]

### torrent_alert

Declared in "libtorrent/alert_types.hpp"

This is a base class for alerts that are associated with a specific torrent. It contains a handle to the torrent.

    struct torrent_alert : alert
    {
       std::string message () const override;
       char const* torrent_name () const;

       torrent_handle handle;
    };

[report issue]

#### message()

    std::string message () const override;

returns the message associated with this alert

[report issue]

handle
  The torrent_handle pointing to the torrent this alert is associated with.

[report issue]

### peer_alert

Declared in "libtorrent/alert_types.hpp"

The peer alert is a base class for alerts that refer to a specific peer. It includes all the information to identify the peer. i.e. `ip` and `peer-id`.

    struct peer_alert : torrent_alert
    {
       std::string message () const override;

       aux::noexcept_movable<tcp::endpoint> endpoint;
       peer_id pid;
    };

[report issue]

endpoint
  The peer's IP address and port.

[report issue]

pid
  the peer ID, if known.

[report issue]

### tracker_alert

Declared in "libtorrent/alert_types.hpp"

This is a base class used for alerts that are associated with a specific tracker. It derives from torrent_alert since a tracker is also associated with a specific torrent.

    struct tracker_alert : torrent_alert
    {
       std::string message () const override;
       char const* tracker_url () const;

       aux::noexcept_movable<tcp::endpoint> local_endpoint;
    };

[report issue]

#### tracker_url()

    char const* tracker_url () const;

returns a 0-terminated string of the tracker's URL

[report issue]

local_endpoint
  endpoint of the listen interface being announced

[report issue]

### torrent_removed_alert

Declared in "libtorrent/alert_types.hpp"

The `torrent_removed_alert` is posted whenever a torrent is removed. Since the torrent handle in its base class will always be invalid (since the torrent is already removed) it has the info hash as a member, to identify it. It's posted when the `status_notification` bit is set in the alert_mask.

Even though the `handle` member doesn't point to an existing torrent anymore, it is still useful for comparing to other handles, which may also no longer point to existing torrents, but to the same non-existing torrents.

The `torrent_handle` acts as a `weak_ptr`, even though its object no longer exists, it can still compare equal to another weak pointer which points to the same non-existent object.

    struct torrent_removed_alert final : torrent_alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::status;
       sha1_hash info_hash;
    };

[report issue]

### read_piece_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted when the asynchronous read operation initiated by a call to torrent_handle::read_piece() is completed. If the read failed, the torrent is paused and an error state is set and the buffer member of the alert is 0. If successful, `buffer` points to a buffer containing all the data of the piece. `piece` is the piece index that was read. `size` is the number of bytes that was read.

If the operation fails, `error` will indicate what went wrong.

    struct read_piece_alert final : torrent_alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::storage;
       error_code const error;
       boost::shared_array<char> const buffer;
       piece_index_t const piece;
       int const size;
    };

[report issue]

### file_completed_alert

Declared in "libtorrent/alert_types.hpp"

This is posted whenever an individual file completes its download. i.e. All pieces overlapping this file have passed their hash check.

    struct file_completed_alert final : torrent_alert
    {
       std::string message () const override;

       file_index_t const index;
    };

[report issue]

index
  refers to the index of the file that completed.

[report issue]

### file_renamed_alert

Declared in "libtorrent/alert_types.hpp"

This is posted as a response to a torrent_handle::rename_file() call, if the rename operation succeeds.

    struct file_renamed_alert final : torrent_alert
    {
       std::string message () const override;
       char const* new_name () const;

       static constexpr alert_category_t static_category  = alert_category::storage;
       file_index_t const index;
    };

[report issue]

index
  refers to the index of the file that was renamed,

[report issue]

### file_rename_failed_alert

Declared in "libtorrent/alert_types.hpp"

This is posted as a response to a torrent_handle::rename_file() call, if the rename operation failed.

    struct file_rename_failed_alert final : torrent_alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::storage;
       file_index_t const index;
       error_code const error;
    };

[report issue]

index error
  refers to the index of the file that was supposed to be renamed, `error` is the error code returned from the filesystem.

[report issue]

### performance_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a limit is reached that might have a negative impact on upload or download rate performance.

    struct performance_alert final : torrent_alert
    {
       std::string message () const override;

       enum performance_warning_t
       {
          outstanding_disk_buffer_limit_reached,
          outstanding_request_limit_reached,
          upload_limit_too_low,
          download_limit_too_low,
          send_buffer_watermark_too_low,
          too_many_optimistic_unchoke_slots,
          too_high_disk_queue_limit,
          aio_limit_reached,
          deprecated_bittyrant_with_no_uplimit,
          too_few_outgoing_ports,
          too_few_file_descriptors,
          num_warnings,
       };

       static constexpr alert_category_t static_category  = alert_category::performance_warning;
       performance_warning_t const warning_code;
    };

[report issue]

#### enum performance_warning_t

Declared in "libtorrent/alert_types.hpp"

name | value | description
--- | --- | ---
outstanding_disk_buffer_limit_reached | 0 | This warning means that the number of bytes queued to be written to disk exceeds the max disk byte queue setting (`settings_pack::max_queued_disk_bytes`). This might restrict the download rate, by not queuing up enough write jobs to the disk I/O thread. When this alert is posted, peer connections are temporarily stopped from downloading, until the queued disk bytes have fallen below the limit again. Unless your `max_queued_disk_bytes` setting is already high, you might want to increase it to get better performance.
outstanding_request_limit_reached | 1 | This is posted when libtorrent would like to send more requests to a peer, but it's limited by `settings_pack::max_out_request_queue`. The queue length libtorrent is trying to achieve is determined by the download rate and the assumed round-trip-time (`settings_pack::request_queue_time`). The assumed round-trip-time is not limited to just the network RTT, but also the remote disk access time and message handling time. It defaults to 3 seconds. The target number of outstanding requests is set to fill the bandwidth-delay product (assumed RTT times download rate divided by number of bytes per request). When this alert is posted, there is a risk that the number of outstanding requests is too low and limits the download rate. You might want to increase the `max_out_request_queue` setting.
upload_limit_too_low | 2 | This warning is posted when the amount of TCP/IP overhead is greater than the upload rate limit. When this happens, the TCP/IP overhead is caused by a much faster download rate, triggering TCP ACK packets. These packets eat into the rate limit specified to libtorrent. When the overhead traffic is greater than the rate limit, libtorrent will not be able to send any actual payload, such as piece requests. This means the download rate will suffer, and new requests can be sent again. There will be an equilibrium where the download rate, on average, is about 20 times the upload rate limit. If you want to maximize the download rate, increase the upload rate limit above 5% of your download capacity.
download_limit_too_low | 3 | This is the same warning as `upload_limit_too_low` but referring to the download limit instead of upload. This suggests that your download rate limit is much lower than your upload capacity. Your upload rate will suffer. To maximize upload rate, make sure your download rate limit is above 5% of your upload capacity.
send_buffer_watermark_too_low | 4 | We're stalled on the disk. We want to write to the socket, and we can write but our send buffer is empty, waiting to be refilled from the disk. This either means the disk is slower than the network connection or that our send buffer watermark is too small, because we can send it all before the disk gets back to us. The number of bytes that we keep outstanding, requested from the disk, is calculated as follows:
    min(512, max(upload_rate * send_buffer_watermark_factor / 100, send_buffer_watermark))
If you receive this alert, you might want to either increase your `send_buffer_watermark` or `send_buffer_watermark_factor`.
too_many_optimistic_unchoke_slots | 5 | If the half (or more) of all upload slots are set as optimistic unchoke slots, this warning is issued. You probably want more regular (rate based) unchoke slots.
too_high_disk_queue_limit | 6 | If the disk write queue ever grows larger than half of the cache size, this warning is posted. The disk write queue eats into the total disk cache and leaves very little left for the actual cache. This causes the disk cache to oscillate in evicting large portions of the cache before allowing peers to download any more, onto the disk write queue. Either lower `max_queued_disk_bytes` or increase `cache_size`.
aio_limit_reached | 7 |
deprecated_bittyrant_with_no_uplimit | 8 |
too_few_outgoing_ports | 9 | This is generated if outgoing peer connections are failing because of address in use errors, indicating that `settings_pack::outgoing_ports` is set and is too small of a range. Consider not using the `outgoing_ports` setting at all, or widen the range to include more ports.
too_few_file_descriptors | 10 |
num_warnings | 11 |

[report issue]

### state_changed_alert

Declared in "libtorrent/alert_types.hpp"

Generated whenever a torrent changes its state.

    struct state_changed_alert final : torrent_alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::status;
       torrent_status::state_t const state;
       torrent_status::state_t const prev_state;
    };

[report issue]

state
  the new state of the torrent.

[report issue]

prev_state
  the previous state.

[report issue]

### tracker_error_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated on tracker time outs, premature disconnects, invalid response or a HTTP response other than "200 OK". From the alert you can get the handle to the torrent the tracker belongs to.

The `times_in_row` member says how many times in a row this tracker has failed. `status_code` is the code returned from the HTTP server. 401 means the tracker needs authentication, 404 means not found etc. If the tracker timed out, the code will be set to 0.

    struct tracker_error_alert final : tracker_alert
    {
       std::string message () const override;
       char const* error_message () const;

       static constexpr alert_category_t static_category  = alert_category::tracker | alert_category::error;
       int const times_in_row;
       error_code const error;
    };

[report issue]

#### error_message()

    char const* error_message () const;

the message associated with this error

[report issue]

### tracker_warning_alert

Declared in "libtorrent/alert_types.hpp"

This alert is triggered if the tracker reply contains a warning field. Usually this means that the tracker announce was successful, but the tracker has a message to the client.

    struct tracker_warning_alert final : tracker_alert
    {
       std::string message () const override;
       char const* warning_message () const;

       static constexpr alert_category_t static_category  = alert_category::tracker | alert_category::error;
    };

[report issue]

#### warning_message()

    char const* warning_message () const;

the message associated with this warning

[report issue]

### scrape_reply_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a scrape request succeeds.

    struct scrape_reply_alert final : tracker_alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::tracker;
       int const incomplete;
       int const complete;
    };

[report issue]

incomplete complete
  the data returned in the scrape response. These numbers may be -1 if the response was malformed.

[report issue]

### scrape_failed_alert

Declared in "libtorrent/alert_types.hpp"

If a scrape request fails, this alert is generated. This might be due to the tracker timing out, refusing connection or returning an http response code indicating an error.

    struct scrape_failed_alert final : tracker_alert
    {
       std::string message () const override;
       char const* error_message () const;

       static constexpr alert_category_t static_category  = alert_category::tracker | alert_category::error;
       error_code const error;
    };

[report issue]

#### error_message()

    char const* error_message () const;

if the error indicates there is an associated message, this returns that message. Otherwise and empty string.

[report issue]

error
  the error itself. This may indicate that the tracker sent an error message (`error::tracker_failure`), in which case it can be retrieved by calling `error_message()`.

[report issue]

### tracker_reply_alert

Declared in "libtorrent/alert_types.hpp"

This alert is only for informational purpose. It is generated when a tracker announce succeeds. It is generated regardless what kind of tracker was used, be it UDP, HTTP or the DHT.

    struct tracker_reply_alert final : tracker_alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::tracker;
       int const num_peers;
    };

[report issue]

num_peers
  tells how many peers the tracker returned in this response. This is not expected to be greater than the `num_want` settings. These are not necessarily all new peers, some of them may already be connected.

[report issue]

### dht_reply_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated each time the DHT receives peers from a node. `num_peers` is the number of peers we received in this packet. Typically these packets are received from multiple DHT nodes, and so the alerts are typically generated a few at a time.

    struct dht_reply_alert final : tracker_alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::dht | alert_category::tracker;
       int const num_peers;
    };

[report issue]

### tracker_announce_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated each time a tracker announce is sent (or attempted to be sent). There are no extra data members in this alert. The url can be found in the base class however.

    struct tracker_announce_alert final : tracker_alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::tracker;
       int const event;
    };

[report issue]

event

  specifies what event was sent to the tracker. It is defined as:

  0. None
  1. Completed
  2. Started
  3. Stopped

[report issue]

### hash_failed_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a finished piece fails its hash check. You can get the handle to the torrent which got the failed piece and the index of the piece itself from the alert.

    struct hash_failed_alert final : torrent_alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::status;
       piece_index_t const piece_index;
    };

[report issue]

### peer_ban_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a peer is banned because it has sent too many corrupt pieces to us. `ip` is the endpoint to the peer that was banned.

    struct peer_ban_alert final : peer_alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::peer;
    };

[report issue]

### peer_unsnubbed_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a peer is un-snubbed. Essentially when it was snubbed for stalling sending data, and now it started sending data again.

    struct peer_unsnubbed_alert final : peer_alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::peer;
    };

[report issue]

### peer_snubbed_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a peer is snubbed, when it stops sending data when we request it.

    struct peer_snubbed_alert final : peer_alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::peer;
    };

[report issue]

### peer_error_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a peer sends invalid data over the peer-peer protocol. The peer will be disconnected, but you get its ip address from the alert, to identify it.

    struct peer_error_alert final : peer_alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::peer;
       operation_t op;
       error_code const error;
    };

[report issue]

op
  a 0-terminated string of the low-level operation that failed, or nullptr if there was no low level disk operation.

[report issue]

error
  tells you what error caused this alert.

[report issue]

### peer_connect_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted every time an outgoing peer connect attempts succeeds.

    struct peer_connect_alert final : peer_alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::connect;
       int const socket_type;
    };

[report issue]

### peer_disconnected_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a peer is disconnected for any reason (other than the ones covered by peer_error_alert ).

    struct peer_disconnected_alert final : peer_alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::connect;
       int const socket_type;
       operation_t const op;
       error_code const error;
       close_reason_t const reason;
    };

[report issue]

socket_type
  the kind of socket this peer was connected over

[report issue]

op
  the operation or level where the error occurred. Specified as an value from the operation_t enum. Defined in operations.hpp.

[report issue]

error
  tells you what error caused peer to disconnect.

[report issue]

reason
  the reason the peer disconnected (if specified)

[report issue]

### invalid_request_alert

Declared in "libtorrent/alert_types.hpp"

This is a debug alert that is generated by an incoming invalid piece request. `ip` is the address of the peer and the `request` is the actual incoming request from the peer. See peer_request for more info.

    struct invalid_request_alert final : peer_alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::peer;
       peer_request const request;
       bool const we_have;
       bool const peer_interested;
       bool const withheld;
    };

[report issue]

request
  the request we received from the peer

[report issue]

we_have
  true if we have this piece

[report issue]

peer_interested
  true if the peer indicated that it was interested to download before sending the request

[report issue]

withheld
  if this is true, the peer is not allowed to download this piece because of super-seeding rules.

[report issue]

### torrent_finished_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a torrent switches from being a downloader to a seed. It will only be generated once per torrent. It contains a torrent_handle to the torrent in question.

    struct torrent_finished_alert final : torrent_alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::status;
    };

[report issue]

### piece_finished_alert

Declared in "libtorrent/alert_types.hpp"

this alert is posted every time a piece completes downloading and passes the hash check. This alert derives from torrent_alert which contains the torrent_handle to the torrent the piece belongs to. Note that being downloaded and passing the hash check may happen before the piece is also fully flushed to disk. So torrent_handle::have_piece() may still return false

    struct piece_finished_alert final : torrent_alert
    {
       std::string message () const override;

       piece_index_t const piece_index;
    };

[report issue]

piece_index
  the index of the piece that finished

[report issue]

### request_dropped_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a peer rejects or ignores a piece request.

    struct request_dropped_alert final : peer_alert
    {
       std::string message () const override;

       int const block_index;
       piece_index_t const piece_index;
    };

[report issue]

### block_timeout_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a block request times out.

    struct block_timeout_alert final : peer_alert
    {
       std::string message () const override;

       int const block_index;
       piece_index_t const piece_index;
    };

[report issue]

### block_finished_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a block request receives a response.

    struct block_finished_alert final : peer_alert
    {
       std::string message () const override;

       int const block_index;
       piece_index_t const piece_index;
    };

[report issue]

### block_downloading_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a block request is sent to a peer.

    struct block_downloading_alert final : peer_alert
    {
       std::string message () const override;

       int const block_index;
       piece_index_t const piece_index;
    };

[report issue]

### unwanted_block_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a block is received that was not requested or whose request timed out.

    struct unwanted_block_alert final : peer_alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::peer;
       int const block_index;
       piece_index_t const piece_index;
    };

[report issue]

### storage_moved_alert

Declared in "libtorrent/alert_types.hpp"

The `storage_moved_alert` is generated when all the disk IO has completed and the files have been moved, as an effect of a call to `torrent_handle::move_storage`. This is useful to synchronize with the actual disk. The `storage_path()` member return the new path of the storage.

    struct storage_moved_alert final : torrent_alert
    {
       std::string message () const override;
       char const* storage_path () const;

       static constexpr alert_category_t static_category  = alert_category::storage;
    };

[report issue]

#### storage_path()

    char const* storage_path () const;

the path the torrent was moved to

[report issue]

### storage_moved_failed_alert

Declared in "libtorrent/alert_types.hpp"

The `storage_moved_failed_alert` is generated when an attempt to move the storage, via torrent_handle::move_storage(), fails.

    struct storage_moved_failed_alert final : torrent_alert
    {
       std::string message () const override;
       char const* file_path () const;

       static constexpr alert_category_t static_category  = alert_category::storage;
       error_code const error;
       operation_t op;
    };

[report issue]

#### file_path()

    char const* file_path () const;

If the error happened for a specific file, this returns its path.

[report issue]

op
  this indicates what underlying operation caused the error

[report issue]

### torrent_deleted_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a request to delete the files of a torrent complete.

The `info_hash` is the info-hash of the torrent that was just deleted. Most of the time the torrent_handle in the `torrent_alert` will be invalid by the time this alert arrives, since the torrent is being deleted. The `info_hash` member is hence the main way of identifying which torrent just completed the delete.

This alert is posted in the `storage_notification` category, and that bit needs to be set in the alert_mask.

    struct torrent_deleted_alert final : torrent_alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::storage;
       sha1_hash info_hash;
    };

[report issue]

### torrent_delete_failed_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a request to delete the files of a torrent fails. Just removing a torrent from the session cannot fail

    struct torrent_delete_failed_alert final : torrent_alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::storage
       | alert_category::error;
       error_code const error;
       sha1_hash info_hash;
    };

[report issue]

error
  tells you why it failed.

[report issue]

info_hash
  the info hash of the torrent whose files failed to be deleted

[report issue]

### save_resume_data_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated as a response to a `torrent_handle::save_resume_data` request. It is generated once the disk IO thread is done writing the state for this torrent.

    struct save_resume_data_alert final : torrent_alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::storage;
       add_torrent_params params;
    };

[report issue]

params
  the `params` structure is populated with the fields to be passed to add_torrent() or async_add_torrent() to resume the torrent. To save the state to disk, you may pass it on to write_resume_data().

[report issue]

### save_resume_data_failed_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated instead of `save_resume_data_alert` if there was an error generating the resume data. `error` describes what went wrong.

    struct save_resume_data_failed_alert final : torrent_alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::storage
       | alert_category::error;
       error_code const error;
    };

[report issue]

error
  the error code from the resume_data failure

[report issue]

### torrent_paused_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated as a response to a `torrent_handle::pause` request. It is generated once all disk IO is complete and the files in the torrent have been closed. This is useful for synchronizing with the disk.

    struct torrent_paused_alert final : torrent_alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::status;
    };

[report issue]

### torrent_resumed_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated as a response to a torrent_handle::resume() request. It is generated when a torrent goes from a paused state to an active state.

    struct torrent_resumed_alert final : torrent_alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::status;
    };

[report issue]

### torrent_checked_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted when a torrent completes checking. i.e. when it transitions out of the `checking files` state into a state where it is ready to start downloading

    struct torrent_checked_alert final : torrent_alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::status;
    };

[report issue]

### url_seed_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a HTTP seed name lookup fails.

    struct url_seed_alert final : torrent_alert
    {
       std::string message () const override;
       char const* server_url () const;
       char const* error_message () const;

       static constexpr alert_category_t static_category  = alert_category::peer | alert_category::error;
       error_code const error;
    };

[report issue]

#### server_url()

    char const* server_url () const;

the URL the error is associated with

[report issue]

#### error_message()

    char const* error_message () const;

in case the web server sent an error message, this function returns it.

[report issue]

error
  the error the web seed encountered. If this is not set, the server sent an error message, call `error_message()`.

[report issue]

### file_error_alert

Declared in "libtorrent/alert_types.hpp"

If the storage fails to read or write files that it needs access to, this alert is generated and the torrent is paused.

    struct file_error_alert final : torrent_alert
    {
       std::string message () const override;
       char const* filename () const;

       static constexpr alert_category_t static_category  = alert_category::status
       | alert_category::storage;
       error_code const error;
       operation_t op;
    };

[report issue]

#### filename()

    char const* filename () const;

the file that experienced the error

[report issue]

error
  the error code describing the error.

[report issue]

op
  indicates which underlying operation caused the error

[report issue]

### metadata_failed_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when the metadata has been completely received and the info-hash failed to match it. i.e. the metadata that was received was corrupt. libtorrent will automatically retry to fetch it in this case. This is only relevant when running a torrent-less download, with the metadata extension provided by libtorrent.

    struct metadata_failed_alert final : torrent_alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::error;
       error_code const error;
    };

[report issue]

error
  indicates what failed when parsing the metadata. This error is what's returned from lazy_bdecode().

[report issue]

### metadata_received_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when the metadata has been completely received and the torrent can start downloading. It is not generated on torrents that are started with metadata, but only those that needs to download it from peers (when utilizing the libtorrent extension).

There are no additional data members in this alert.

Typically, when receiving this alert, you would want to save the torrent file in order to load it back up again when the session is restarted. Here's an example snippet of code to do that:

    torrent_handle h = alert->handle();
    if (h.is_valid()) {
            std::shared_ptr<torrent_info const> ti = h.torrent_file();
            create_torrent ct(*ti);
            entry te = ct.generate();
            std::vector<char> buffer;
            bencode(std::back_inserter(buffer), te);
            FILE* f = fopen((to_hex(ti->info_hash().to_string()) + ".torrent").c_str(), "wb+");
            if (f) {
                    fwrite(&buffer[0], 1, buffer.size(), f);
                    fclose(f);
            }
    }

    struct metadata_received_alert final : torrent_alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::status;
    };

[report issue]

### udp_error_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted when there is an error on a UDP socket. The UDP sockets are used for all uTP, DHT and UDP tracker traffic. They are global to the session.

    struct udp_error_alert final : alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::error;
       aux::noexcept_movable<udp::endpoint> endpoint;
       operation_t operation;
       error_code const error;
    };

[report issue]

endpoint
  the source address associated with the error (if any)

[report issue]

operation
  the operation that failed

[report issue]

error
  the error code describing the error

[report issue]

### external_ip_alert

Declared in "libtorrent/alert_types.hpp"

Whenever libtorrent learns about the machines external IP, this alert is generated. The external IP address can be acquired from the tracker (if it supports that) or from peers that supports the extension protocol. The address can be accessed through the `external_address` member.

    struct external_ip_alert final : alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::status;
       aux::noexcept_movable<address> external_address;
    };

[report issue]

external_address
  the IP address that is believed to be our external IP

[report issue]

### listen_failed_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when none of the ports, given in the port range, to session can be opened for listening. The `listen_interface` member is the interface that failed, `error` is the error code describing the failure.

In the case an endpoint was created before generating the alert, it is represented by `address` and `port`. The combinations of socket type and operation in which such address and port are not valid are: accept - i2p accept - socks5 enum_if - tcp

libtorrent may sometimes try to listen on port 0, if all other ports failed. Port 0 asks the operating system to pick a port that's free). If that fails you may see a listen_failed_alert with port 0 even if you didn't ask to listen on it.

    struct listen_failed_alert final : alert
    {
       listen_failed_alert (aux::stack_allocator& alloc, string_view iface
          , tcp::endpoint const& ep, operation_t op, error_code const& ec
          , lt::socket_type_t t);
       listen_failed_alert (aux::stack_allocator& alloc, string_view iface
          , udp::endpoint const& ep, operation_t op, error_code const& ec
          , lt::socket_type_t t);
       listen_failed_alert (aux::stack_allocator& alloc, string_view iface
          , operation_t op, error_code const& ec, lt::socket_type_t t);
       std::string message () const override;
       char const* listen_interface () const;

       static constexpr alert_category_t static_category  = alert_category::status | alert_category::error;
       error_code const error;
       operation_t op;
       lt::socket_type_t const socket_type;
       aux::noexcept_movable<lt::address> address;
       int const port;
    };

[report issue]

#### listen_interface()

    char const* listen_interface () const;

the network device libtorrent attempted to listen on, or the IP address

[report issue]

error
  the error the system returned

[report issue]

op
  the underlying operation that failed

[report issue]

socket_type
  the type of listen socket this alert refers to.

[report issue]

address
  the address libtorrent attempted to listen on see alert documentation for validity of this value

[report issue]

port
  the port libtorrent attempted to listen on see alert documentation for validity of this value

[report issue]

### listen_succeeded_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted when the listen port succeeds to be opened on a particular interface. `address` and `port` is the endpoint that successfully was opened for listening.

    struct listen_succeeded_alert final : alert
    {
       listen_succeeded_alert (aux::stack_allocator& alloc
          , tcp::endpoint const& ep
          , lt::socket_type_t t);
       listen_succeeded_alert (aux::stack_allocator& alloc
          , udp::endpoint const& ep
          , lt::socket_type_t t);
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::status;
       aux::noexcept_movable<lt::address> address;
       int const port;
       lt::socket_type_t const socket_type;
    };

[report issue]

address
  the address libtorrent ended up listening on. This address refers to the local interface.

[report issue]

port
  the port libtorrent ended up listening on.

[report issue]

socket_type
  the type of listen socket this alert refers to.

[report issue]

### portmap_error_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a NAT router was successfully found but some part of the port mapping request failed. It contains a text message that may help the user figure out what is wrong. This alert is not generated in case it appears the client is not running on a NAT:ed network or if it appears there is no NAT router that can be remote controlled to add port mappings.

    struct portmap_error_alert final : alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::port_mapping
       | alert_category::error;
       port_mapping_t const mapping;
       portmap_transport map_transport;
       error_code const error;
    };

[report issue]

mapping
  refers to the mapping index of the port map that failed, i.e. the index returned from add_mapping().

[report issue]

map_transport
  UPnP or NAT-PMP

[report issue]

error
  tells you what failed.

[report issue]

### portmap_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a NAT router was successfully found and a port was successfully mapped on it. On a NAT:ed network with a NAT-PMP capable router, this is typically generated once when mapping the TCP port and, if DHT is enabled, when the UDP port is mapped.

    struct portmap_alert final : alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::port_mapping;
       port_mapping_t const mapping;
       int const external_port;
       portmap_protocol const map_protocol;
       portmap_transport const map_transport;
    };

[report issue]

mapping
  refers to the mapping index of the port map that failed, i.e. the index returned from add_mapping().

[report issue]

external_port
  the external port allocated for the mapping.

[report issue]

### portmap_log_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated to log informational events related to either UPnP or NAT-PMP. They contain a log line and the type (0 = NAT-PMP and 1 = UPnP). Displaying these messages to an end user is only useful for debugging the UPnP or NAT-PMP implementation. This alert is only posted if the alert_category::port_mapping_log flag is enabled in the alert mask.

    struct portmap_log_alert final : alert
    {
       std::string message () const override;
       char const* log_message () const;

       static constexpr alert_category_t static_category  = alert_category::port_mapping_log;
       portmap_transport const map_transport;
    };

[report issue]

#### log_message()

    char const* log_message () const;

the message associated with this log line

[report issue]

### fastresume_rejected_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a fast resume file has been passed to add_torrent() but the files on disk did not match the fast resume file. The error_code explains the reason why the resume file was rejected.

    struct fastresume_rejected_alert final : torrent_alert
    {
       std::string message () const override;
       char const* file_path () const;

       static constexpr alert_category_t static_category  = alert_category::status
       | alert_category::error;
       error_code error;
       operation_t op;
    };

[report issue]

#### file_path()

    char const* file_path () const;

If the error happened to a specific file, this returns the path to it.

[report issue]

op
  the underlying operation that failed

[report issue]

### peer_blocked_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted when an incoming peer connection, or a peer that's about to be added to our peer list, is blocked for some reason. This could be any of:

- the IP filter
- i2p mixed mode restrictions (a normal peer is not allowed on an i2p swarm)
- the port filter
- the peer has a low port and `no_connect_privileged_ports` is enabled
- the protocol of the peer is blocked (uTP/TCP blocking)

    struct peer_blocked_alert final : peer_alert
    {
       std::string message () const override;

       enum reason_t
       {
          ip_filter,
          port_filter,
          i2p_mixed,
          privileged_ports,
          utp_disabled,
          tcp_disabled,
          invalid_local_interface,
       };

       static constexpr alert_category_t static_category  = alert_category::ip_block;
       int const reason;
    };

[report issue]

#### enum reason_t

Declared in "libtorrent/alert_types.hpp"

name | value | description
--- | --- | ---
ip_filter | 0 |
port_filter | 1 |
i2p_mixed | 2 |
privileged_ports | 3 |
utp_disabled | 4 |
tcp_disabled | 5 |
invalid_local_interface | 6 |

[report issue]

reason
  the reason for the peer being blocked. Is one of the values from the reason_t enum.

[report issue]

### dht_announce_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a DHT node announces to an info-hash on our DHT node. It belongs to the `dht_notification` category.

    struct dht_announce_alert final : alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::dht;
       aux::noexcept_movable<address> ip;
       int port;
       sha1_hash info_hash;
    };

[report issue]

### dht_get_peers_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a DHT node sends a `get_peers` message to our DHT node. It belongs to the `dht_notification` category.

    struct dht_get_peers_alert final : alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::dht;
       sha1_hash info_hash;
    };

[report issue]

### stats_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted approximately once every second, and it contains byte counters of most statistics that's tracked for torrents. Each active torrent posts these alerts regularly. This alert has been superseded by calling `post_torrent_updates()` regularly on the session object. This alert will be removed

    struct stats_alert final : torrent_alert
    {
       std::string message () const override;

       enum stats_channel
       {
          upload_payload,
          upload_protocol,
          download_payload,
          download_protocol,
          upload_ip_protocol,
          deprecated1,
          deprecated2,
          download_ip_protocol,
          deprecated3,
          deprecated4,
          num_channels,
       };

       static constexpr alert_category_t static_category  = alert_category::stats;
       std::array<int, num_channels> const transferred;
       int const interval;
    };

[report issue]

#### enum stats_channel

Declared in "libtorrent/alert_types.hpp"

name | value | description
--- | --- | ---
upload_payload | 0 |
upload_protocol | 1 |
download_payload | 2 |
download_protocol | 3 |
upload_ip_protocol | 4 |
deprecated1 | 5 |
deprecated2 | 6 |
download_ip_protocol | 7 |
deprecated3 | 8 |
deprecated4 | 9 |
num_channels | 10 |

[report issue]

transferred
  an array of samples. The enum describes what each sample is a measurement of. All of these are raw, and not smoothing is performed.

[report issue]

interval
  the number of milliseconds during which these stats were collected. This is typically just above 1000, but if CPU is limited, it may be higher than that.

[report issue]

### cache_flushed_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted when the disk cache has been flushed for a specific torrent as a result of a call to torrent_handle::flush_cache(). This alert belongs to the `storage_notification` category, which must be enabled to let this alert through. The alert is also posted when removing a torrent from the session, once the outstanding cache flush is complete and the torrent does no longer have any files open.

    struct cache_flushed_alert final : torrent_alert
    {
       static constexpr alert_category_t static_category  = alert_category::storage;
    };

[report issue]

### lsd_peer_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when we receive a local service discovery message from a peer for a torrent we're currently participating in.

    struct lsd_peer_alert final : peer_alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::peer;
    };

[report issue]

### trackerid_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted whenever a tracker responds with a `trackerid`. The tracker ID is like a cookie. libtorrent will store the tracker ID for this tracker and repeat it in subsequent announces.

    struct trackerid_alert final : tracker_alert
    {
       std::string message () const override;
       char const* tracker_id () const;

       static constexpr alert_category_t static_category  = alert_category::status;
    };

[report issue]

#### tracker_id()

    char const* tracker_id () const;

The tracker ID returned by the tracker

[report issue]

### dht_bootstrap_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted when the initial DHT bootstrap is done.

    struct dht_bootstrap_alert final : alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::dht;
    };

[report issue]

### torrent_error_alert

Declared in "libtorrent/alert_types.hpp"

This is posted whenever a torrent is transitioned into the error state.

    struct torrent_error_alert final : torrent_alert
    {
       std::string message () const override;
       char const* filename () const;

       static constexpr alert_category_t static_category  = alert_category::error | alert_category::status;
       error_code const error;
    };

[report issue]

#### filename()

    char const* filename () const;

the filename (or object) the error occurred on.

[report issue]

error
  specifies which error the torrent encountered.

[report issue]

### torrent_need_cert_alert

Declared in "libtorrent/alert_types.hpp"

This is always posted for SSL torrents. This is a reminder to the client that the torrent won't work unless torrent_handle::set_ssl_certificate() is called with a valid certificate. Valid certificates MUST be signed by the SSL certificate in the .torrent file.

    struct torrent_need_cert_alert final : torrent_alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::status;
    };

[report issue]

### incoming_connection_alert

Declared in "libtorrent/alert_types.hpp"

The incoming connection alert is posted every time we successfully accept an incoming connection, through any mean. The most straight-forward ways of accepting incoming connections are through the TCP listen socket and the UDP listen socket for uTP sockets. However, connections may also be accepted through a Socks5 or i2p listen socket, or via an SSL listen socket.

    struct incoming_connection_alert final : alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::peer;
       int const socket_type;
       aux::noexcept_movable<tcp::endpoint> endpoint;
    };

[report issue]

socket_type

  tells you what kind of socket the connection was accepted as:

  0. none (no socket instantiated)
  1. TCP
  2. Socks5
  3. HTTP
  4. uTP
  5. i2p
  6. SSL/TCP
  7. SSL/Socks5
  8. HTTPS (SSL/HTTP)
  9. SSL/uTP

[report issue]

endpoint
  is the IP address and port the connection came from.

[report issue]

### add_torrent_alert

Declared in "libtorrent/alert_types.hpp"

This alert is always posted when a torrent was attempted to be added and contains the return status of the add operation. The torrent handle of the new torrent can be found as the `handle` member in the base class. If adding the torrent failed, `error` contains the error code.

    struct add_torrent_alert final : torrent_alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::status;
       add_torrent_params params;
       error_code error;
    };

[report issue]

params
  a copy of the parameters used when adding the torrent, it can be used to identify which invocation to `async_add_torrent()` caused this alert.

[report issue]

error
  set to the error, if one occurred while adding the torrent.

[report issue]

### state_update_alert

Declared in "libtorrent/alert_types.hpp"

This alert is only posted when requested by the user, by calling session::post_torrent_updates() on the session. It contains the torrent status of all torrents that changed since last time this message was posted. Its category is `status_notification`, but it's not subject to filtering, since it's only manually posted anyway.

    struct state_update_alert final : alert
    {
       state_update_alert (aux::stack_allocator& alloc
          , std::vector<torrent_status> st);
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::status;
       std::vector<torrent_status> status;
    };

[report issue]

status
  contains the torrent status of all torrents that changed since last time this message was posted. Note that you can map a torrent status to a specific torrent via its `handle` member. The receiving end is suggested to have all torrents sorted by the torrent_handle or hashed by it, for efficient updates.

[report issue]

### session_stats_alert

Declared in "libtorrent/alert_types.hpp"

The session_stats_alert is posted when the user requests session statistics by calling post_session_stats() on the session object. Its category is `status_notification`, but it is not subject to filtering, since it's only manually posted anyway.

the `message()` member function returns a string representation of the values that properly match the line returned in `session_stats_header_alert::message()`.

this specific output is parsed by tools/parse_session_stats.py if this is changed, that parser should also be changed

    struct session_stats_alert final : alert
    {
       std::string message () const override;
       span<std::int64_t const> counters () const;

       static constexpr alert_category_t static_category  = alert_category::stats;
    };

[report issue]

#### counters()

    span<std::int64_t const> counters () const;

An array are a mix of counters and gauges, which meanings can be queries via the session_stats_metrics() function on the session. The mapping from a specific metric to an index into this array is constant for a specific version of libtorrent, but may differ for other versions. The intended usage is to request the mapping, i.e. call session_stats_metrics(), once on startup, and then use that mapping to interpret these values throughout the process' runtime.

For more information, see the session statistics section.

[report issue]

### dht_error_alert

Declared in "libtorrent/alert_types.hpp"

posted when something fails in the DHT. This is not necessarily a fatal error, but it could prevent proper operation

    struct dht_error_alert final : alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::error | alert_category::dht;
       error_code error;
       operation_t op;
    };

[report issue]

error
  the error code

[report issue]

op
  the operation that failed

[report issue]

### dht_immutable_item_alert

Declared in "libtorrent/alert_types.hpp"

this alert is posted as a response to a call to session::get_item(), specifically the overload for looking up immutable items in the DHT.

    struct dht_immutable_item_alert final : alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::dht;
       sha1_hash target;
       entry item;
    };

[report issue]

target
  the target hash of the immutable item. This must match the SHA-1 hash of the bencoded form of `item`.

[report issue]

item
  the data for this item

[report issue]

### dht_mutable_item_alert

Declared in "libtorrent/alert_types.hpp"

this alert is posted as a response to a call to session::get_item(), specifically the overload for looking up mutable items in the DHT.

    struct dht_mutable_item_alert final : alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::dht;
       std::array<char, 32> key;
       std::array<char, 64> signature;
       std::int64_t seq;
       std::string salt;
       entry item;
       bool authoritative;
    };

[report issue]

key
  the public key that was looked up

[report issue]

signature
  the signature of the data. This is not the signature of the plain encoded form of the item, but it includes the sequence number and possibly the hash as well. See the dht_store document for more information. This is primarily useful for echoing back in a store request.

[report issue]

seq
  the sequence number of this item

[report issue]

salt
  the salt, if any, used to lookup and store this item. If no salt was used, this is an empty string

[report issue]

item
  the data for this item

[report issue]

authoritative
  the last response for mutable data is authoritative.

[report issue]

### dht_put_alert

Declared in "libtorrent/alert_types.hpp"

this is posted when a DHT put operation completes. This is useful if the client is waiting for a put to complete before shutting down for instance.

    struct dht_put_alert final : alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::dht;
       sha1_hash target;
       std::array<char, 32> public_key;
       std::array<char, 64> signature;
       std::string salt;
       std::int64_t seq;
       int num_success;
    };

[report issue]

target
  the target hash the item was stored under if this was an immutable item.

[report issue]

public_key signature salt seq
  if a mutable item was stored, these are the public key, signature, salt and sequence number the item was stored under.

[report issue]

num_success
  DHT put operation usually writes item to k nodes, maybe the node is stale so no response, or the node doesn't support 'put', or the token for write is out of date, etc. num_success is the number of successful responses we got from the puts.

[report issue]

### i2p_alert

Declared in "libtorrent/alert_types.hpp"

this alert is used to report errors in the i2p SAM connection

    struct i2p_alert final : alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::error;
       error_code error;
    };

[report issue]

error
  the error that occurred in the i2p SAM connection

[report issue]

### dht_outgoing_get_peers_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when we send a get_peers request It belongs to the `dht_notification` category.

    struct dht_outgoing_get_peers_alert final : alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::dht;
       sha1_hash info_hash;
       sha1_hash obfuscated_info_hash;
       aux::noexcept_movable<udp::endpoint> endpoint;
    };

[report issue]

info_hash
  the info_hash of the torrent we're looking for peers for.

[report issue]

obfuscated_info_hash
  if this was an obfuscated lookup, this is the info-hash target actually sent to the node.

[report issue]

endpoint
  the endpoint we're sending this query to

[report issue]

### log_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted by some session wide event. Its main purpose is trouble shooting and debugging. It's not enabled by the default alert mask and is enabled by the `alert_category::session_log` bit. Furthermore, it's by default disabled as a build configuration.

    struct log_alert final : alert
    {
       std::string message () const override;
       char const* log_message () const;

       static constexpr alert_category_t static_category  = alert_category::session_log;
    };

[report issue]

#### log_message()

    char const* log_message () const;

returns the log message

[report issue]

### torrent_log_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted by torrent wide events. It's meant to be used for trouble shooting and debugging. It's not enabled by the default alert mask and is enabled by the `alert_category::torrent_log` bit. By default it is disabled as a build configuration.

    struct torrent_log_alert final : torrent_alert
    {
       std::string message () const override;
       char const* log_message () const;

       static constexpr alert_category_t static_category  = alert_category::torrent_log;
    };

[report issue]

#### log_message()

    char const* log_message () const;

returns the log message

[report issue]

### peer_log_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted by events specific to a peer. It's meant to be used for trouble shooting and debugging. It's not enabled by the default alert mask and is enabled by the `alert_category::peer_log` bit. By default it is disabled as a build configuration.

    struct peer_log_alert final : peer_alert
    {
       std::string message () const override;
       char const* log_message () const;

       enum direction_t
       {
          incoming_message,
          outgoing_message,
          incoming,
          outgoing,
          info,
       };

       static constexpr alert_category_t static_category  = alert_category::peer_log;
       char const* event_type;
       direction_t direction;
    };

[report issue]

#### log_message()

    char const* log_message () const;

returns the log message

[report issue]

#### enum direction_t

Declared in "libtorrent/alert_types.hpp"

name | value | description
--- | --- | ---
incoming_message | 0 |
outgoing_message | 1 |
incoming | 2 |
outgoing | 3 |
info | 4 |

[report issue]

event_type
  string literal indicating the kind of event. For messages, this is the message name.

[report issue]

### lsd_error_alert

Declared in "libtorrent/alert_types.hpp"

posted if the local service discovery socket fails to start properly. it's categorized as `error_notification`.

    struct lsd_error_alert final : alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::error;
       error_code error;
    };

[report issue]

error
  The error code

[report issue]

### dht_lookup

Declared in "libtorrent/alert_types.hpp"

holds statistics about a current dht_lookup operation. a DHT lookup is the traversal of nodes, looking up a set of target nodes in the DHT for retrieving and possibly storing information in the DHT

    struct dht_lookup
    {
       char const* type;
       int outstanding_requests;
       int timeouts;
       int responses;
       int branch_factor;
       int nodes_left;
       int last_sent;
       int first_timeout;
       sha1_hash target;
    };

[report issue]

type
  string literal indicating which kind of lookup this is

[report issue]

outstanding_requests
  the number of outstanding request to individual nodes this lookup has right now

[report issue]

timeouts
  the total number of requests that have timed out so far for this lookup

[report issue]

responses
  the total number of responses we have received for this lookup so far for this lookup

[report issue]

branch_factor
  the branch factor for this lookup. This is the number of nodes we keep outstanding requests to in parallel by default. when nodes time out we may increase this.

[report issue]

nodes_left
  the number of nodes left that could be queries for this lookup. Many of these are likely to be part of the trail while performing the lookup and would never end up actually being queried.

[report issue]

last_sent
  the number of seconds ago the last message was sent that's still outstanding

[report issue]

first_timeout
  the number of outstanding requests that have exceeded the short timeout and are considered timed out in the sense that they increased the branch factor

[report issue]

target
  the node-id or info-hash target for this lookup

[report issue]

### dht_stats_alert

Declared in "libtorrent/alert_types.hpp"

contains current DHT state. Posted in response to session::post_dht_stats().

    struct dht_stats_alert final : alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::stats;
       std::vector<dht_lookup> active_requests;
       std::vector<dht_routing_bucket> routing_table;
    };

[report issue]

active_requests
  a vector of the currently running DHT lookups.

[report issue]

routing_table
  contains information about every bucket in the DHT routing table.

[report issue]

### incoming_request_alert

Declared in "libtorrent/alert_types.hpp"

posted every time an incoming request from a peer is accepted and queued up for being serviced. This alert is only posted if the alert_category::incoming_request flag is enabled in the alert mask.

    struct incoming_request_alert final : peer_alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::incoming_request;
       peer_request req;
    };

[report issue]

req
  the request this peer sent to us

[report issue]

### dht_log_alert

Declared in "libtorrent/alert_types.hpp"

debug logging of the DHT when dht_log_notification is set in the alert mask.

    struct dht_log_alert final : alert
    {
       std::string message () const override;
       char const* log_message () const;

       enum dht_module_t
       {
          tracker,
          node,
          routing_table,
          rpc_manager,
          traversal,
       };

       static constexpr alert_category_t static_category  = alert_category::dht_log;
       dht_module_t module;
    };

[report issue]

#### log_message()

    char const* log_message () const;

the log message

[report issue]

#### enum dht_module_t

Declared in "libtorrent/alert_types.hpp"

name | value | description
--- | --- | ---
tracker | 0 |
node | 1 |
routing_table | 2 |
rpc_manager | 3 |
traversal | 4 |

[report issue]

module
  the module, or part, of the DHT that produced this log message.

[report issue]

### dht_pkt_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted every time a DHT message is sent or received. It is only posted if the `alert_category::dht_log` alert category is enabled. It contains a verbatim copy of the message.

    struct dht_pkt_alert final : alert
    {
       std::string message () const override;
       span<char const> pkt_buf () const;

       enum direction_t
       {
          incoming,
          outgoing,
       };

       static constexpr alert_category_t static_category  = alert_category::dht_log;
       direction_t direction;
       aux::noexcept_movable<udp::endpoint> node;
    };

[report issue]

#### pkt_buf()

    span<char const> pkt_buf () const;

returns a pointer to the packet buffer and size of the packet, respectively. This buffer is only valid for as long as the alert itself is valid, which is owned by libtorrent and reclaimed whenever pop_alerts() is called on the session.

[report issue]

#### enum direction_t

Declared in "libtorrent/alert_types.hpp"

name | value | description
--- | --- | ---
incoming | 0 |
outgoing | 1 |

[report issue]

direction
  whether this is an incoming or outgoing packet.

[report issue]

node
  the DHT node we received this packet from, or sent this packet to (depending on `direction`).

[report issue]

### dht_get_peers_reply_alert

Declared in "libtorrent/alert_types.hpp"

Posted when we receive a response to a DHT get_peers request.

    struct dht_get_peers_reply_alert final : alert
    {
       std::string message () const override;
       int num_peers () const;
       std::vector<tcp::endpoint> peers () const;

       static constexpr alert_category_t static_category  = alert_category::dht_operation;
       sha1_hash info_hash;
    };

[report issue]

### dht_direct_response_alert

Declared in "libtorrent/alert_types.hpp"

This is posted exactly once for every call to session_handle::dht_direct_request. If the request failed, response() will return a default constructed bdecode_node.

    struct dht_direct_response_alert final : alert
    {
       dht_direct_response_alert (aux::stack_allocator& alloc, void* userdata
          , udp::endpoint const& addr);
       std::string message () const override;
       bdecode_node response () const;

       static constexpr alert_category_t static_category  = alert_category::dht;
       void const* userdata;
       aux::noexcept_movable<udp::endpoint> endpoint;
    };

[report issue]

#### dht_direct_response_alert() message()

    dht_direct_response_alert (aux::stack_allocator& alloc, void* userdata
          , udp::endpoint const& addr);
    std::string message () const override;

for when there was a timeout so we don't have a response

[report issue]

### picker_log_alert

Declared in "libtorrent/alert_types.hpp"

this is posted when one or more blocks are picked by the piece picker, assuming the verbose piece picker logging is enabled (see picker_log_notification).

    struct picker_log_alert final : peer_alert
    {
       std::string message () const override;
       std::vector<piece_block> blocks () const;

       static constexpr alert_category_t static_category  = alert_category::picker_log;
       static constexpr picker_flags_t partial_ratio  = 0_bit;
       static constexpr picker_flags_t prioritize_partials  = 1_bit;
       static constexpr picker_flags_t rarest_first_partials  = 2_bit;
       static constexpr picker_flags_t rarest_first  = 3_bit;
       static constexpr picker_flags_t reverse_rarest_first  = 4_bit;
       static constexpr picker_flags_t suggested_pieces  = 5_bit;
       static constexpr picker_flags_t prio_sequential_pieces  = 6_bit;
       static constexpr picker_flags_t sequential_pieces  = 7_bit;
       static constexpr picker_flags_t reverse_pieces  = 8_bit;
       static constexpr picker_flags_t time_critical  = 9_bit;
       static constexpr picker_flags_t random_pieces  = 10_bit;
       static constexpr picker_flags_t prefer_contiguous  = 11_bit;
       static constexpr picker_flags_t reverse_sequential  = 12_bit;
       static constexpr picker_flags_t backup1  = 13_bit;
       static constexpr picker_flags_t backup2  = 14_bit;
       static constexpr picker_flags_t end_game  = 15_bit;
       static constexpr picker_flags_t extent_affinity  = 16_bit;
       picker_flags_t const picker_flags;
    };

[report issue]

picker_flags
  this is a bitmask of which features were enabled for this particular pick. The bits are defined in the picker_flags_t enum.

[report issue]

### session_error_alert

Declared in "libtorrent/alert_types.hpp"

this alert is posted when the session encounters a serious error, potentially fatal

    struct session_error_alert final : alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::error;
       error_code const error;
    };

[report issue]

error
  The error code, if one is associated with this error

[report issue]

### dht_live_nodes_alert

Declared in "libtorrent/alert_types.hpp"

posted in response to a call to session::dht_live_nodes(). It contains the live nodes from the DHT routing table of one of the DHT nodes running locally.

    struct dht_live_nodes_alert final : alert
    {
       std::string message () const override;
       int num_nodes () const;
       std::vector<std::pair<sha1_hash, udp::endpoint>> nodes () const;

       static constexpr alert_category_t static_category  = alert_category::dht;
       sha1_hash node_id;
    };

[report issue]

#### num_nodes() nodes()

    int num_nodes () const;
    std::vector<std::pair<sha1_hash, udp::endpoint>> nodes () const;

the number of nodes in the routing table and the actual nodes.

[report issue]

node_id
  the local DHT node's node-ID this routing table belongs to

[report issue]

### session_stats_header_alert

Declared in "libtorrent/alert_types.hpp"

The session_stats_header alert is posted the first time post_session_stats() is called

the `message()` member function returns a string representation of the header that properly match the stats values string returned in `session_stats_alert::message()`.

this specific output is parsed by tools/parse_session_stats.py if this is changed, that parser should also be changed

    struct session_stats_header_alert final : alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::stats;
    };

[report issue]

### dht_sample_infohashes_alert

Declared in "libtorrent/alert_types.hpp"

posted as a response to a call to session::dht_sample_infohashes() with the information from the DHT response message.

    struct dht_sample_infohashes_alert final : alert
    {
       std::string message () const override;
       int num_samples () const;
       std::vector<sha1_hash> samples () const;
       int num_nodes () const;
       std::vector<std::pair<sha1_hash, udp::endpoint>> nodes () const;

       static constexpr alert_category_t static_category  = alert_category::dht_operation;
       aux::noexcept_movable<udp::endpoint> endpoint;
       time_duration const interval;
       int const num_infohashes;
    };

[report issue]

#### samples() num_samples()

    int num_samples () const;
    std::vector<sha1_hash> samples () const;

returns the number of info-hashes returned by the node, as well as the actual info-hashes. `num_samples()` is more efficient than `samples().size()`.

[report issue]

#### num_nodes()

    int num_nodes () const;

The total number of nodes returned by `nodes()`.

[report issue]

#### nodes()

    std::vector<std::pair<sha1_hash, udp::endpoint>> nodes () const;

This is the set of more DHT nodes returned by the request.

The information is included so that indexing nodes can perform a key space traversal with a single RPC per node by adjusting the target value for each RPC.

[report issue]

endpoint
  the node the request was sent to (and this response was received from)

[report issue]

interval
  the interval to wait before making another request to this node

[report issue]

num_infohashes
  This field indicates how many info-hash keys are currently in the node's storage. If the value is larger than the number of returned samples it indicates that the indexer may obtain additional samples after waiting out the interval.

[report issue]

### block_uploaded_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted when a block intended to be sent to a peer is placed in the send buffer. Note that if the connection is closed before the send buffer is sent, the alert may be posted without the bytes having been sent to the peer. It belongs to the `upload_notification` category.

    struct block_uploaded_alert final : peer_alert
    {
       std::string message () const override;

       int const block_index;
       piece_index_t const piece_index;
    };

[report issue]

### alerts_dropped_alert

Declared in "libtorrent/alert_types.hpp"

this alert is posted to indicate to the client that some alerts were dropped. Dropped meaning that the alert failed to be delivered to the client. The most common cause of such failure is that the internal alert queue grew too big (controlled by alert_queue_size).

    struct alerts_dropped_alert final : alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::error;
       std::bitset<num_alert_types> dropped_alerts;
    };

[report issue]

dropped_alerts
  a bitmask indicating which alerts were dropped. Each bit represents the alert type ID, where bit 0 represents whether any alert of type 0 has been dropped, and so on.

[report issue]

### socks5_alert

Declared in "libtorrent/alert_types.hpp"

this alert is posted with SOCKS5 related errors, when a SOCKS5 proxy is configured. It's enabled with the error_notification alert category.

    struct socks5_alert final : alert
    {
       std::string message () const override;

       static constexpr alert_category_t static_category  = alert_category::error;
       error_code error;
       operation_t op;
       aux::noexcept_movable<tcp::endpoint> ip;
    };

[report issue]

error
  the error

[report issue]

op
  the operation that failed

[report issue]

ip
  the endpoint configured as the proxy

[report issue]

### alert_cast()

Declared in "libtorrent/alert.hpp"

    template <class T> T const* alert_cast (alert const* a);
    template <class T> T* alert_cast (alert* a);

When you get an alert, you can use `alert_cast<>` to attempt to cast the pointer to a specific alert type, in order to query it for more information.

Note

`alert_cast<>` can only cast to an exact alert type, not a base class

[report issue]

### operation_name()

Declared in "libtorrent/operations.hpp"

    char const* operation_name (operation_t op);

maps an operation id (from peer_error_alert and peer_disconnected_alert) to its name. See operation_t for the constants

[report issue]

### enum operation_t

Declared in "libtorrent/operations.hpp"

name | value | description
--- | --- | ---
unknown | 0 | the error was unexpected and it is unknown which operation caused it
bittorrent | 1 | this is used when the bittorrent logic determines to disconnect
iocontrol | 2 | a call to iocontrol failed
getpeername | 3 | a call to `getpeername()` failed (querying the remote IP of a connection)
getname | 4 | a call to getname failed (querying the local IP of a connection)
alloc_recvbuf | 5 | an attempt to allocate a receive buffer failed
alloc_sndbuf | 6 | an attempt to allocate a send buffer failed
file_write | 7 | writing to a file failed
file_read | 8 | reading from a file failed
file | 9 | a non-read and non-write file operation failed
sock_write | 10 | a socket write operation failed
sock_read | 11 | a socket read operation failed
sock_open | 12 | a call to open(), to create a socket socket failed
sock_bind | 13 | a call to bind() on a socket failed
available | 14 | an attempt to query the number of bytes available to read from a socket failed
encryption | 15 | a call related to bittorrent protocol encryption failed
connect | 16 | an attempt to connect a socket failed
ssl_handshake | 17 | establishing an SSL connection failed
get_interface | 18 | a connection failed to satisfy the bind interface setting
sock_listen | 19 | a call to listen() on a socket
sock_bind_to_device | 20 | a call to the ioctl to bind a socket to a specific network device or adapter
sock_accept | 21 | a call to accept() on a socket
parse_address | 22 | convert a string into a valid network address
enum_if | 23 | enumeration network devices or adapters
file_stat | 24 | invoking stat() on a file
file_copy | 25 | copying a file
file_fallocate | 26 | allocating storage for a file
file_hard_link | 27 | creating a hard link
file_remove | 28 | removing a file
file_rename | 29 | renaming a file
file_open | 30 | opening a file
mkdir | 31 | creating a directory
check_resume | 32 | check fast resume data against files on disk
exception | 33 | an unknown exception
alloc_cache_piece | 34 | allocate space for a piece in the cache
partfile_move | 35 | move a part-file
partfile_read | 36 | read from a part file
partfile_write | 37 | write to a part-file
hostname_lookup | 38 | a hostname lookup
symlink | 39 | create or read a symlink
handshake | 40 | handshake with a peer or server
sock_option | 41 | set socket option
enum_route | 42 | enumeration network routes

[report issue]

### enum socket_type_t

Declared in "libtorrent/alert_types.hpp"

name | value | description
--- | --- | ---
tcp | 0 |
tcp_ssl | 1 |
udp | 2 |
i2p | 3 |
socks5 | 4 |
utp_ssl | 5 |

[report issue]

### alert_category_t

Declared in "libtorrent/alert.hpp"

error

  Enables alerts that report an error. This includes:

  - tracker errors
  - tracker warnings
  - file errors
  - resume data failures
  - web seed errors
  - .torrent files errors
  - listen socket errors
  - port mapping errors

peer
  Enables alerts when peers send invalid requests, get banned or snubbed.

port_mapping
  Enables alerts for port mapping events. For NAT-PMP and UPnP.

storage
  Enables alerts for events related to the storage. File errors and synchronization events for moving the storage, renaming files etc.

tracker
  Enables all tracker events. Includes announcing to trackers, receiving responses, warnings and errors.

connect
  Low level alerts for when peers are connected and disconnected.

status
  Enables alerts for when a torrent or the session changes state.

ip_block
  Alerts when a peer is blocked by the ip blocker or port blocker.

performance_warning
  Alerts when some limit is reached that might limit the download or upload rate.

dht
  Alerts on events in the DHT node. For incoming searches or bootstrapping being done etc.

stats
  If you enable these alerts, you will receive a stats_alert approximately once every second, for every active torrent. These alerts contain all statistics counters for the interval since the lasts stats alert.

session_log
  Enables debug logging alerts. These are available unless libtorrent was built with logging disabled (`TORRENT_DISABLE_LOGGING`). The alerts being posted are log_alert and are session wide.

torrent_log
  Enables debug logging alerts for torrents. These are available unless libtorrent was built with logging disabled (`TORRENT_DISABLE_LOGGING`). The alerts being posted are torrent_log_alert and are torrent wide debug events.

peer_log
  Enables debug logging alerts for peers. These are available unless libtorrent was built with logging disabled (`TORRENT_DISABLE_LOGGING`). The alerts being posted are peer_log_alert and low-level peer events and messages.

incoming_request
  enables the incoming_request_alert.

dht_log
  enables dht_log_alert, debug logging for the DHT

dht_operation
  enable events from pure dht operations not related to torrents

port_mapping_log
  enables port mapping log events. This log is useful for debugging the UPnP or NAT-PMP implementation

picker_log
  enables verbose logging from the piece picker.

file_progress
  alerts when files complete downloading

piece_progress
  alerts when pieces complete downloading or fail hash check

upload
  alerts when we upload blocks to other peers

block_progress
  alerts on individual blocks being requested, downloading, finished, rejected, time-out and cancelled. This is likely to post alerts at a high rate.

all

  The full bitmask, representing all available categories.

  since the enum is signed, make sure this isn't interpreted as -1. For instance, boost.python does that and fails when assigning it to an unsigned parameter.

[report issue]

### int

Declared in "libtorrent/alert_types.hpp"

user_alert_id
  user defined alerts should use IDs greater than this

num_alert_types
  this constant represents "max_alert_index" + 1

Author: | Arvid Norberg, arvid@libtorrent.org
Version: | 1.2.9

home

## Filter

[report issue]

### ip_filter

Declared in "libtorrent/ip_filter.hpp"

The `ip_filter` class is a set of rules that uniquely categorizes all ip addresses as allowed or disallowed. The default constructor creates a single rule that allows all addresses (0.0.0.0 - 255.255.255.255 for the IPv4 range, and the equivalent range covering all addresses for the IPv6 range).

A default constructed ip_filter does not filter any address.

    struct ip_filter
    {
       void add_rule (address const& first, address const& last, std::uint32_t flags);
       std::uint32_t access (address const& addr) const;
       filter_tuple_t export_filter () const;

       enum access_flags
       {
          blocked,
       };
    };

[report issue]

#### add_rule()

    void add_rule (address const& first, address const& last, std::uint32_t flags);

Adds a rule to the filter. `first` and `last` defines a range of ip addresses that will be marked with the given flags. The `flags` can currently be 0, which means allowed, or `ip_filter::blocked`, which means disallowed.

precondition: `first.is_v4() == last.is_v4() && first.is_v6() == last.is_v6()`

postcondition: `access(x) == flags` for every `x` in the range [`first`, `last`]

This means that in a case of overlapping ranges, the last one applied takes precedence.

[report issue]

#### access()

    std::uint32_t access (address const& addr) const;

Returns the access permissions for the given address (`addr`). The permission can currently be 0 or `ip_filter::blocked`. The complexity of this operation is O(`log` n), where n is the minimum number of non-overlapping ranges to describe the current filter.

[report issue]

#### export_filter()

    filter_tuple_t export_filter () const;

This function will return the current state of the filter in the minimum number of ranges possible. They are sorted from ranges in low addresses to high addresses. Each entry in the returned vector is a range with the access control specified in its `flags` field.

The return value is a tuple containing two range-lists. One for IPv4 addresses and one for IPv6 addresses.

[report issue]

#### enum access_flags

Declared in "libtorrent/ip_filter.hpp"

name | value | description
--- | --- | ---
blocked | 1 | indicates that IPs in this range should not be connected to nor accepted as incoming connections

[report issue]

### port_filter

Declared in "libtorrent/ip_filter.hpp"

the port filter maps non-overlapping port ranges to flags. This is primarily used to indicate whether a range of ports should be connected to or not. The default is to have the full port range (0-65535) set to flag 0.

    class port_filter
    {
       void add_rule (std::uint16_t first, std::uint16_t last, std::uint32_t flags);
       std::uint32_t access (std::uint16_t port) const;

       enum access_flags
       {
          blocked,
       };
    };

[report issue]

#### add_rule()

    void add_rule (std::uint16_t first, std::uint16_t last, std::uint32_t flags);

set the flags for the specified port range (`first`, `last`) to `flags` overwriting any existing rule for those ports. The range is inclusive, i.e. the port `last` also has the flag set on it.

[report issue]

#### access()

    std::uint32_t access (std::uint16_t port) const;

test the specified port (`port`) for whether it is blocked or not. The returned value is the flags set for this port. see access_flags.

[report issue]

#### enum access_flags

Declared in "libtorrent/ip_filter.hpp"

name | value | description
--- | --- | ---
blocked | 1 | this flag indicates that destination ports in the range should not be connected to

Author: | Arvid Norberg, arvid@libtorrent.org
Version: | 1.2.9

home

## Settings

You have some control over session configuration through the session::apply_settings() member function. To change one or more configuration options, create a settings_pack object and fill it with the settings to be set and pass it in to session::apply_settings().

The settings_pack object is a collection of settings updates that are applied to the session when passed to session::apply_settings(). It's empty when constructed.

You have control over proxy and authorization settings and also the user-agent that will be sent to the tracker. The user-agent will also be used to identify the client with other peers.

Each configuration option is named with an enum value inside the settings_pack class. These are the available settings:

[report issue]

### settings_pack

Declared in "libtorrent/settings_pack.hpp"

The `settings_pack` struct, contains the names of all settings as enum values. These values are passed in to the `set_str()`, `set_int()`, `set_bool()` functions, to specify the setting to change.

name | type | default
--- | --- | ---
user_agent | string | libtorrent/

this is the client identification to the tracker. The recommended format of this string is: "client-name/client-version libtorrent/libtorrent-version". This name will not only be used when making HTTP requests, but also when sending extended headers to peers that support that extension. It may not contain r or n

name | type | default
--- | --- | ---
announce_ip | string | nullptr

`announce_ip` is the ip address passed along to trackers as the `&ip=` parameter. If left as the default, that parameter is omitted.

Note

This setting is only meant for very special cases where a seed is running on the same host as the tracker, and the tracker accepts the IP parameter (which normal trackers don't). Do not set this option unless you also control the tracker.

name | type | default
--- | --- | ---
handshake_client_version | string | nullptr

this is the client name and version identifier sent to peers in the handshake message. If this is an empty string, the user_agent is used instead. This string must be a UTF-8 encoded unicode string.

name | type | default
--- | --- | ---
outgoing_interfaces | string |

This controls which IP address outgoing TCP peer connections are bound to, in addition to controlling whether such connections are also bound to a specific network interface/adapter (bind-to-device). This string is a comma-separated list of IP addresses and interface names. An empty string will not bind TCP sockets to a device, and let the network stack assign the local address. A list of names will be used to bind outgoing TCP sockets in a round-robin fashion. An IP address will simply be used to bind() the socket. An interface name will attempt to bind the socket to that interface. If that fails, or is unsupported, one of the IP addresses configured for that interface is used to bind() the socket to. If the interface or adapter doesn't exist, the outgoing peer connection will fail with an error message suggesting the device cannot be found. Adapter names on Unix systems are of the form "eth0", "eth1", "tun0", etc. This may be useful for clients that are multi-homed. Binding an outgoing connection to a local IP does not necessarily make the connection via the associated NIC/Adapter.

name | type | default
--- | --- | ---
listen_interfaces | string | 0.0.0.0:6881,[::]:6881

a comma-separated list of (IP or device name, port) pairs. These are the listen ports that will be opened for accepting incoming uTP and TCP peer connections. These are also used for outgoing uTP and UDP tracker connections and DHT nodes.

It is possible to listen on multiple interfaces and multiple ports. Binding to port 0 will make the operating system pick the port.

Note

There are reasons to stick to the same port across sessions, which would mean only using port 0 on the first start, and recording the port that was picked for subsequent startups. Trackers, the DHT and other peers will remember the port they see you use and hand that port out to other peers trying to connect to you, as well as trying to connect to you themselves.

A port that has an "s" suffix will accept SSL peer connections. (note that SSL sockets are only available in builds with SSL support)

A port that has an "l" suffix will be considered a local network. i.e. it's assumed to only be able to reach hosts in the same local network as the IP address (based on the netmask associated with the IP, queried from the operating system).

if binding fails, the listen_failed_alert is posted. Once a socket binding succeeds (if it does), the listen_succeeded_alert is posted. There may be multiple failures before a success.

If a device name that does not exist is configured, no listen socket will be opened for that interface. If this is the only interface configured, it will be as if no listen ports are configured.

If no listen ports are configured (e.g. listen_interfaces is an empty string), networking will be disabled. No DHT will start, no outgoing uTP or tracker connections will be made. No incoming TCP or uTP connections will be accepted. (outgoing TCP connections will still be possible, depending on settings_pack::outgoing_interfaces).

For example: `[::1]:8888` - will only accept connections on the IPv6 loopback address on port 8888.

`eth0:4444,eth1:4444` - will accept connections on port 4444 on any IP address bound to device `eth0` or `eth1`.

`[::]:0s` - will accept SSL connections on a port chosen by the OS. And not accept non-SSL connections at all.

`0.0.0.0:6881,[::]:6881` - binds to all interfaces on port 6881.

`10.0.1.13:6881l` - binds to the local IP address, port 6881, but only allow talking to peers on the same local network. The netmask is queried from the operating system. Interfaces marked `l` are not announced to trackers, unless the tracker is also on the same local network.

Windows OS network adapter device name must be specified with GUID. It can be obtained from "netsh lan show interfaces" command output. GUID must be uppercased string embraced in curly brackets. `{E4F0B674-0DFC-48BB-98A5-2AA730BDB6D6}:7777` - will accept connections on port 7777 on adapter with this GUID.

For more information, see the Multi-homed hosts section.

name | type | default
--- | --- | ---
proxy_hostname | string |

when using a proxy, this is the hostname where the proxy is running see proxy_type. Note that when using a proxy, the settings_pack::listen_interfaces setting is overridden and only a single interface is created, just to contact the proxy. This means a proxy cannot be combined with SSL torrents or multiple listen interfaces. This proxy listen interface will not accept incoming TCP connections, will not map ports with any gateway and will not enable local service discovery. All traffic is supposed to be channeled through the proxy.

name | type | default
--- | --- | ---
proxy_username | string |
proxy_password | string |

when using a proxy, these are the credentials (if any) to use when connecting to it. see proxy_type

name | type | default
--- | --- | ---
i2p_hostname | string |

sets the i2p SAM bridge to connect to. set the port with the `i2p_port` setting.

name | type | default
--- | --- | ---
peer_fingerprint | string | -LT1290-

this is the fingerprint for the client. It will be used as the prefix to the peer_id. If this is 20 bytes (or longer) it will be truncated to 20 bytes and used as the entire peer-id

There is a utility function, generate_fingerprint() that can be used to generate a standard client peer ID fingerprint prefix.

name | type | default
--- | --- | ---
dht_bootstrap_nodes | string | dht.libtorrent.org:25401

This is a comma-separated list of IP port-pairs. They will be added to the DHT node (if it's enabled) as back-up nodes in case we don't know of any.

Changing these after the DHT has been started may not have any effect until the DHT is restarted.

name | type | default
--- | --- | ---
allow_multiple_connections_per_ip | bool | false

determines if connections from the same IP address as existing connections should be rejected or not. Rejecting multiple connections from the same IP address will prevent abusive behavior by peers. The logic for determining whether connections are to the same peer is more complicated with this enabled, and more likely to fail in some edge cases. It is not recommended to enable this feature.

name | type | default
--- | --- | ---
send_redundant_have | bool | true

`send_redundant_have` controls if have messages will be sent to peers that already have the piece. This is typically not necessary, but it might be necessary for collecting statistics in some cases.

name | type | default
--- | --- | ---
use_dht_as_fallback | bool | false

`use_dht_as_fallback` determines how the DHT is used. If this is true, the DHT will only be used for torrents where all trackers in its tracker list has failed. Either by an explicit error message or a time out. If this is false, the DHT is used regardless of if the trackers fail or not.

name | type | default
--- | --- | ---
upnp_ignore_nonrouters | bool | false

`upnp_ignore_nonrouters` indicates whether or not the UPnP implementation should ignore any broadcast response from a device whose address is not on our subnet. i.e. it's a way to not talk to other people's routers by mistake.

name | type | default
--- | --- | ---
use_parole_mode | bool | true

`use_parole_mode` specifies if parole mode should be used. Parole mode means that peers that participate in pieces that fail the hash check are put in a mode where they are only allowed to download whole pieces. If the whole piece a peer in parole mode fails the hash check, it is banned. If a peer participates in a piece that passes the hash check, it is taken out of parole mode.

name | type | default
--- | --- | ---
use_read_cache | bool | true

enable and disable caching of blocks read from disk. the purpose of the read cache is partly read-ahead of requests but also to avoid reading blocks back from the disk multiple times for popular pieces.

name | type | default
--- | --- | ---
coalesce_reads | bool | false
coalesce_writes | bool | false

allocate separate, contiguous, buffers for read and write calls. Only used where writev/readv cannot be used will use more RAM but may improve performance

name | type | default
--- | --- | ---
auto_manage_prefer_seeds | bool | false

if true, prefer seeding torrents when determining which torrents to give active slots to. If false, give preference to downloading torrents

name | type | default
--- | --- | ---
dont_count_slow_torrents | bool | true

if `dont_count_slow_torrents` is true, torrents without any payload transfers are not subject to the `active_seeds` and `active_downloads` limits. This is intended to make it more likely to utilize all available bandwidth, and avoid having torrents that don't transfer anything block the active slots.

name | type | default
--- | --- | ---
close_redundant_connections | bool | true

`close_redundant_connections` specifies whether libtorrent should close connections where both ends have no utility in keeping the connection open. For instance if both ends have completed their downloads, there's no point in keeping it open.

name | type | default
--- | --- | ---
prioritize_partial_pieces | bool | false

If `prioritize_partial_pieces` is true, partial pieces are picked before pieces that are more rare. If false, rare pieces are always prioritized, unless the number of partial pieces is growing out of proportion.

name | type | default
--- | --- | ---
rate_limit_ip_overhead | bool | true

if set to true, the estimated TCP/IP overhead is drained from the rate limiters, to avoid exceeding the limits with the total traffic

name | type | default
--- | --- | ---
announce_to_all_tiers | bool | false
announce_to_all_trackers | bool | false

`announce_to_all_trackers` controls how multi tracker torrents are treated. If this is set to true, all trackers in the same tier are announced to in parallel. If all trackers in tier 0 fails, all trackers in tier 1 are announced as well. If it's set to false, the behavior is as defined by the multi tracker specification.

`announce_to_all_tiers` also controls how multi tracker torrents are treated. When this is set to true, one tracker from each tier is announced to. This is the uTorrent behavior. To be compliant with the Multi-tracker specification, set it to false.

name | type | default
--- | --- | ---
prefer_udp_trackers | bool | true

`prefer_udp_trackers`: true means that trackers may be rearranged in a way that udp trackers are always tried before http trackers for the same hostname. Setting this to false means that the tracker's tier is respected and there's no preference of one protocol over another.

name | type | default
--- | --- | ---
disable_hash_checks | bool | false

when set to true, all data downloaded from peers will be assumed to be correct, and not tested to match the hashes in the torrent this is only useful for simulation and testing purposes (typically combined with disabled_storage)

name | type | default
--- | --- | ---
allow_i2p_mixed | bool | false

if this is true, i2p torrents are allowed to also get peers from other sources than the tracker, and connect to regular IPs, not providing any anonymization. This may be useful if the user is not interested in the anonymization of i2p, but still wants to be able to connect to i2p peers.

name | type | default
--- | --- | ---
volatile_read_cache | bool | false

`volatile_read_cache`, if this is set to true, read cache blocks that are hit by peer read requests are removed from the disk cache to free up more space. This is useful if you don't expect the disk cache to create any cache hits from other peers than the one who triggered the cache line to be read into the cache in the first place.

name | type | default
--- | --- | ---
no_atime_storage | bool | true

`no_atime_storage` this is a Linux-only option and passes in the `O_NOATIME` to `open()` when opening files. This may lead to some disk performance improvements.

name | type | default
--- | --- | ---
incoming_starts_queued_torrents | bool | false

`incoming_starts_queued_torrents`. If a torrent has been paused by the auto managed feature in libtorrent, i.e. the torrent is paused and auto managed, this feature affects whether or not it is automatically started on an incoming connection. The main reason to queue torrents, is not to make them unavailable, but to save on the overhead of announcing to the trackers, the DHT and to avoid spreading one's unchoke slots too thin. If a peer managed to find us, even though we're no in the torrent anymore, this setting can make us start the torrent and serve it.

name | type | default
--- | --- | ---
report_true_downloaded | bool | false

when set to true, the downloaded counter sent to trackers will include the actual number of payload bytes downloaded including redundant bytes. If set to false, it will not include any redundancy bytes

name | type | default
--- | --- | ---
strict_end_game_mode | bool | true

`strict_end_game_mode` controls when a block may be requested twice. If this is `true`, a block may only be requested twice when there's at least one request to every piece that's left to download in the torrent. This may slow down progress on some pieces sometimes, but it may also avoid downloading a lot of redundant bytes. If this is `false`, libtorrent attempts to use each peer connection to its max, by always requesting something, even if it means requesting something that has been requested from another peer already.

name | type | default
--- | --- | ---
enable_outgoing_utp | bool | true
enable_incoming_utp | bool | true
enable_outgoing_tcp | bool | true
enable_incoming_tcp | bool | true

when set to true, libtorrent will try to make outgoing utp connections controls whether libtorrent will accept incoming connections or make outgoing connections of specific type.

name | type | default
--- | --- | ---
no_recheck_incomplete_resume | bool | false

`no_recheck_incomplete_resume` determines if the storage should check the whole files when resume data is incomplete or missing or whether it should simply assume we don't have any of the data. If false, any existing files will be checked. By setting this setting to true, the files won't be checked, but will go straight to download mode.

name | type | default
--- | --- | ---
anonymous_mode | bool | false

`anonymous_mode`: When set to true, the client tries to hide its identity to a certain degree. The user-agent will be reset to an empty string (except for private torrents). Trackers will only be used if they are using a proxy server. The listen sockets are closed, and incoming connections will only be accepted through a SOCKS5 or I2P proxy (if a peer proxy is set up and is run on the same machine as the tracker proxy). Since no incoming connections are accepted, NAT-PMP, UPnP, DHT and local peer discovery are all turned off when this setting is enabled.

If you're using I2P, it might make sense to enable anonymous mode as well.

name | type | default
--- | --- | ---
report_web_seed_downloads | bool | true

specifies whether downloads from web seeds is reported to the tracker or not. Turning it off also excludes web seed traffic from other stats and download rate reporting via the libtorrent API.

name | type | default
--- | --- | ---
seeding_outgoing_connections | bool | true

`seeding_outgoing_connections` determines if seeding (and finished) torrents should attempt to make outgoing connections or not. It may be set to false in very specific applications where the cost of making outgoing connections is high, and there are no or small benefits of doing so. For instance, if no nodes are behind a firewall or a NAT, seeds don't need to make outgoing connections.

name | type | default
--- | --- | ---
no_connect_privileged_ports | bool | false

when this is true, libtorrent will not attempt to make outgoing connections to peers whose port is < 1024. This is a safety precaution to avoid being part of a DDoS attack

name | type | default
--- | --- | ---
smooth_connects | bool | true

`smooth_connects` means the number of connection attempts per second may be limited to below the `connection_speed`, in case we're close to bump up against the limit of number of connections. The intention of this setting is to more evenly distribute our connection attempts over time, instead of attempting to connect in batches, and timing them out in batches.

name | type | default
--- | --- | ---
always_send_user_agent | bool | false

always send user-agent in every web seed request. If false, only the first request per http connection will include the user agent

name | type | default
--- | --- | ---
apply_ip_filter_to_trackers | bool | true

`apply_ip_filter_to_trackers` determines whether the IP filter applies to trackers as well as peers. If this is set to false, trackers are exempt from the IP filter (if there is one). If no IP filter is set, this setting is irrelevant.

name | type | default
--- | --- | ---
ban_web_seeds | bool | true

when true, web seeds sending bad data will be banned

name | type | default
--- | --- | ---
allow_partial_disk_writes | bool | true

when set to false, the `write_cache_line_size` will apply across piece boundaries. this is a bad idea unless the piece picker also is configured to have an affinity to pick pieces belonging to the same write cache line as is configured in the disk cache.

name | type | default
--- | --- | ---
support_share_mode | bool | true

if false, prevents libtorrent to advertise share-mode support

name | type | default
--- | --- | ---
support_merkle_torrents | bool | true

if this is false, don't advertise support for the Tribler merkle tree piece message

name | type | default
--- | --- | ---
report_redundant_bytes | bool | true

if this is true, the number of redundant bytes is sent to the tracker

name | type | default
--- | --- | ---
listen_system_port_fallback | bool | true

if this is true, libtorrent will fall back to listening on a port chosen by the operating system (i.e. binding to port 0). If a failure is preferred, set this to false.

name | type | default
--- | --- | ---
announce_crypto_support | bool | true

when this is true, and incoming encrypted connections are enabled, &supportcrypt=1 is included in http tracker announces

name | type | default
--- | --- | ---
enable_upnp | bool | true

Starts and stops the UPnP service. When started, the listen port and the DHT port are attempted to be forwarded on local UPnP router devices.

The upnp object returned by `start_upnp()` can be used to add and remove arbitrary port mappings. Mapping status is returned through the portmap_alert and the portmap_error_alert. The object will be valid until `stop_upnp()` is called. See upnp and nat pmp.

name | type | default
--- | --- | ---
enable_natpmp | bool | true

Starts and stops the NAT-PMP service. When started, the listen port and the DHT port are attempted to be forwarded on the router through NAT-PMP.

The natpmp object returned by `start_natpmp()` can be used to add and remove arbitrary port mappings. Mapping status is returned through the portmap_alert and the portmap_error_alert. The object will be valid until `stop_natpmp()` is called. See upnp and nat pmp.

name | type | default
--- | --- | ---
enable_lsd | bool | true

Starts and stops Local Service Discovery. This service will broadcast the info-hashes of all the non-private torrents on the local network to look for peers on the same swarm within multicast reach.

name | type | default
--- | --- | ---
enable_dht | bool | true

starts the dht node and makes the trackerless service available to torrents.

name | type | default
--- | --- | ---
prefer_rc4 | bool | false

if the allowed encryption level is both, setting this to true will prefer RC4 if both methods are offered, plain text otherwise

name | type | default
--- | --- | ---
proxy_hostnames | bool | true

if true, hostname lookups are done via the configured proxy (if any). This is only supported by SOCKS5 and HTTP.

name | type | default
--- | --- | ---
proxy_peer_connections | bool | true

if true, peer connections are made (and accepted) over the configured proxy, if any. Web seeds as well as regular bittorrent peer connections are considered "peer connections". Anything transporting actual torrent payload (trackers and DHT traffic are not considered peer connections).

name | type | default
--- | --- | ---
auto_sequential | bool | true

if this setting is true, torrents with a very high availability of pieces (and seeds) are downloaded sequentially. This is more efficient for the disk I/O. With many seeds, the download order is unlikely to matter anyway

name | type | default
--- | --- | ---
proxy_tracker_connections | bool | true

if true, tracker connections are made over the configured proxy, if any.

name | type | default
--- | --- | ---
enable_ip_notifier | bool | true

Starts and stops the internal IP table route changes notifier.

The current implementation supports multiple platforms, and it is recommended to have it enable, but you may want to disable it if it's supported but unreliable, or if you have a better way to detect the changes. In the later case, you should manually call `session_handle::reopen_network_sockets` to ensure network changes are taken in consideration.

name | type | default
--- | --- | ---
dht_prefer_verified_node_ids | bool | true

when this is true, nodes whose IDs are derived from their source IP according to BEP 42 are preferred in the routing table.

name | type | default
--- | --- | ---
piece_extent_affinity | bool | false

when this is true, create an affinity for downloading 4 MiB extents of adjacent pieces. This is an attempt to achieve better disk I/O throughput by downloading larger extents of bytes, for torrents with small piece sizes

name | type | default
--- | --- | ---
validate_https_trackers | bool | false

when set to true, the certificate of HTTPS trackers will be validated against the system's certificate store (as defined by OpenSSL). If the system does not have one, enabling this may cause HTTPS trackers to fail.

name | type | default
--- | --- | ---
tracker_completion_timeout | int | 30

`tracker_completion_timeout` is the number of seconds the tracker connection will wait from when it sent the request until it considers the tracker to have timed-out.

name | type | default
--- | --- | ---
tracker_receive_timeout | int | 10

`tracker_receive_timeout` is the number of seconds to wait to receive any data from the tracker. If no data is received for this number of seconds, the tracker will be considered as having timed out. If a tracker is down, this is the kind of timeout that will occur.

name | type | default
--- | --- | ---
stop_tracker_timeout | int | 5

`stop_tracker_timeout` is the number of seconds to wait when sending a stopped message before considering a tracker to have timed out. This is usually shorter, to make the client quit faster. If the value is set to 0, the connections to trackers with the stopped event are suppressed.

name | type | default
--- | --- | ---
tracker_maximum_response_length | int | 1024*1024

this is the maximum number of bytes in a tracker response. If a response size passes this number of bytes it will be rejected and the connection will be closed. On gzipped responses this size is measured on the uncompressed data. So, if you get 20 bytes of gzip response that'll expand to 2 megabytes, it will be interrupted before the entire response has been uncompressed (assuming the limit is lower than 2 MiB).

name | type | default
--- | --- | ---
piece_timeout | int | 20

the number of seconds from a request is sent until it times out if no piece response is returned.

name | type | default
--- | --- | ---
request_timeout | int | 60

the number of seconds one block (16 kiB) is expected to be received within. If it's not, the block is requested from a different peer

name | type | default
--- | --- | ---
request_queue_time | int | 3

the length of the request queue given in the number of seconds it should take for the other end to send all the pieces. i.e. the actual number of requests depends on the download rate and this number.

name | type | default
--- | --- | ---
max_allowed_in_request_queue | int | 500

the number of outstanding block requests a peer is allowed to queue up in the client. If a peer sends more requests than this (before the first one has been sent) the last request will be dropped. the higher this is, the faster upload speeds the client can get to a single peer.

name | type | default
--- | --- | ---
max_out_request_queue | int | 500

`max_out_request_queue` is the maximum number of outstanding requests to send to a peer. This limit takes precedence over `request_queue_time`. i.e. no matter the download speed, the number of outstanding requests will never exceed this limit.

name | type | default
--- | --- | ---
whole_pieces_threshold | int | 20

if a whole piece can be downloaded in this number of seconds, or less, the peer_connection will prefer to request whole pieces at a time from this peer. The benefit of this is to better utilize disk caches by doing localized accesses and also to make it easier to identify bad peers if a piece fails the hash check.

name | type | default
--- | --- | ---
peer_timeout | int | 120

`peer_timeout` is the number of seconds the peer connection should wait (for any activity on the peer connection) before closing it due to time out. 120 seconds is specified in the protocol specification. After half the time out, a keep alive message is sent.

name | type | default
--- | --- | ---
urlseed_timeout | int | 20

same as peer_timeout, but only applies to url-seeds. this is usually set lower, because web servers are expected to be more reliable.

name | type | default
--- | --- | ---
urlseed_pipeline_size | int | 5

controls the pipelining size of url and http seeds. i.e. the number of HTTP request to keep outstanding before waiting for the first one to complete. It's common for web servers to limit this to a relatively low number, like 5

name | type | default
--- | --- | ---
urlseed_wait_retry | int | 30

number of seconds until a new retry of a url-seed takes place. Default retry value for http-seeds that don't provide a valid `retry-after` header.

name | type | default
--- | --- | ---
file_pool_size | int | 40

sets the upper limit on the total number of files this session will keep open. The reason why files are left open at all is that some anti virus software hooks on every file close, and scans the file for viruses. deferring the closing of the files will be the difference between a usable system and a completely hogged down system. Most operating systems also has a limit on the total number of file descriptors a process may have open.

name | type | default
--- | --- | ---
max_failcount | int | 3

`max_failcount` is the maximum times we try to connect to a peer before stop connecting again. If a peer succeeds, the failure counter is reset. If a peer is retrieved from a peer source (other than DHT) the failcount is decremented by one, allowing another try.

name | type | default
--- | --- | ---
min_reconnect_time | int | 60

the number of seconds to wait to reconnect to a peer. this time is multiplied with the failcount.

name | type | default
--- | --- | ---
peer_connect_timeout | int | 15

`peer_connect_timeout` the number of seconds to wait after a connection attempt is initiated to a peer until it is considered as having timed out. This setting is especially important in case the number of half-open connections are limited, since stale half-open connection may delay the connection of other peers considerably.

name | type | default
--- | --- | ---
connection_speed | int | 30

`connection_speed` is the number of connection attempts that are made per second. If a number < 0 is specified, it will default to 200 connections per second. If 0 is specified, it means don't make outgoing connections at all.

name | type | default
--- | --- | ---
inactivity_timeout | int | 600

if a peer is uninteresting and uninterested for longer than this number of seconds, it will be disconnected.

name | type | default
--- | --- | ---
unchoke_interval | int | 15

`unchoke_interval` is the number of seconds between chokes/unchokes. On this interval, peers are re-evaluated for being choked/unchoked. This is defined as 30 seconds in the protocol, and it should be significantly longer than what it takes for TCP to ramp up to it's max rate.

name | type | default
--- | --- | ---
optimistic_unchoke_interval | int | 30

`optimistic_unchoke_interval` is the number of seconds between each optimistic unchoke. On this timer, the currently optimistically unchoked peer will change.

name | type | default
--- | --- | ---
num_want | int | 200

`num_want` is the number of peers we want from each tracker request. It defines what is sent as the `&num_want=` parameter to the tracker.

name | type | default
--- | --- | ---
initial_picker_threshold | int | 4

`initial_picker_threshold` specifies the number of pieces we need before we switch to rarest first picking. The first `initial_picker_threshold` pieces in any torrent are picked at random , the following pieces are picked in rarest first order.

name | type | default
--- | --- | ---
allowed_fast_set_size | int | 5

the number of allowed pieces to send to peers that supports the fast extensions

name | type | default
--- | --- | ---
suggest_mode | int | settings_pack::no_piece_suggestions

`suggest_mode` controls whether or not libtorrent will send out suggest messages to create a bias of its peers to request certain pieces. The modes are:

- `no_piece_suggestions` which will not send out suggest messages.
- `suggest_read_cache` which will send out suggest messages for the most recent pieces that are in the read cache.

name | type | default
--- | --- | ---
max_queued_disk_bytes | int | 1024 * 1024

`max_queued_disk_bytes` is the maximum number of bytes, to be written to disk, that can wait in the disk I/O thread queue. This queue is only for waiting for the disk I/O thread to receive the job and either write it to disk or insert it in the write cache. When this limit is reached, the peer connections will stop reading data from their sockets, until the disk thread catches up. Setting this too low will severely limit your download rate.

name | type | default
--- | --- | ---
handshake_timeout | int | 10

the number of seconds to wait for a handshake response from a peer. If no response is received within this time, the peer is disconnected.

name | type | default
--- | --- | ---
send_buffer_low_watermark | int | 10 * 1024
send_buffer_watermark | int | 500 * 1024
send_buffer_watermark_factor | int | 50

`send_buffer_low_watermark` the minimum send buffer target size (send buffer includes bytes pending being read from disk). For good and snappy seeding performance, set this fairly high, to at least fit a few blocks. This is essentially the initial window size which will determine how fast we can ramp up the send rate

if the send buffer has fewer bytes than `send_buffer_watermark`, we'll read another 16 kiB block onto it. If set too small, upload rate capacity will suffer. If set too high, memory will be wasted. The actual watermark may be lower than this in case the upload rate is low, this is the upper limit.

the current upload rate to a peer is multiplied by this factor to get the send buffer watermark. The factor is specified as a percentage. i.e. 50 -> 0.5 This product is clamped to the `send_buffer_watermark` setting to not exceed the max. For high speed upload, this should be set to a greater value than 100. For high capacity connections, setting this higher can improve upload performance and disk throughput. Setting it too high may waste RAM and create a bias towards read jobs over write jobs.

name | type | default
--- | --- | ---
choking_algorithm | int | settings_pack::fixed_slots_choker
seed_choking_algorithm | int | settings_pack::round_robin

`choking_algorithm` specifies which algorithm to use to determine how many peers to unchoke. The unchoking algorithm for downloading torrents is always "tit-for-tat", i.e. the peers we download the fastest from are unchoked.

The options for choking algorithms are defined in the choking_algorithm_t enum.

`seed_choking_algorithm` controls the seeding unchoke behavior. i.e. How we select which peers to unchoke for seeding torrents. Since a seeding torrent isn't downloading anything, the tit-for-tat mechanism cannot be used. The available options are defined in the seed_choking_algorithm_t enum.

name | type | default
--- | --- | ---
cache_size | int | 2048
cache_expiry | int | 300

`cache_size` is the disk write and read cache. It is specified in units of 16 kiB blocks. Buffers that are part of a peer's send or receive buffer also count against this limit. Send and receive buffers will never be denied to be allocated, but they will cause the actual cached blocks to be flushed or evicted. If this is set to -1, the cache size is automatically set based on the amount of physical RAM on the machine. If the amount of physical RAM cannot be determined, it's set to 1024 (= 16 MiB).

`cache_expiry` is the number of seconds from the last cached write to a piece in the write cache, to when it's forcefully flushed to disk.

On 32 bit builds, the effective cache size will be limited to 3/4 of 2 GiB to avoid exceeding the virtual address space limit.

name | type | default
--- | --- | ---
disk_io_write_mode | int | settings_pack::enable_os_cache
disk_io_read_mode | int | settings_pack::enable_os_cache

determines how files are opened when they're in read only mode versus read and write mode. The options are:

enable_os_cache
  Files are opened normally, with the OS caching reads and writes.
disable_os_cache
  This opens all files in no-cache mode. This corresponds to the OS not letting blocks for the files linger in the cache. This makes sense in order to avoid the bittorrent client to potentially evict all other processes' cache by simply handling high throughput and large files. If libtorrent's read cache is disabled, enabling this may reduce performance.

One reason to disable caching is that it may help the operating system from growing its file cache indefinitely.

name | type | default
--- | --- | ---
outgoing_port | int | 0
num_outgoing_ports | int | 0

this is the first port to use for binding outgoing connections to. This is useful for users that have routers that allow QoS settings based on local port. when binding outgoing connections to specific ports, `num_outgoing_ports` is the size of the range. It should be more than a few

Warning

setting outgoing ports will limit the ability to keep multiple connections to the same client, even for different torrents. It is not recommended to change this setting. Its main purpose is to use as an escape hatch for cheap routers with QoS capability but can only classify flows based on port numbers.

It is a range instead of a single port because of the problems with failing to reconnect to peers if a previous socket to that peer and port is in `TIME_WAIT` state.

name | type | default
--- | --- | ---
peer_tos | int | 0x20

`peer_tos` determines the TOS byte set in the IP header of every packet sent to peers (including web seeds). `0x0` means no marking, `0x20` represents the QBone scavenger service. For more details, see QBSS.

name | type | default
--- | --- | ---
active_downloads | int | 3
active_seeds | int | 5
active_checking | int | 1
active_dht_limit | int | 88
active_tracker_limit | int | 1600
active_lsd_limit | int | 60
active_limit | int | 500

for auto managed torrents, these are the limits they are subject to. If there are too many torrents some of the auto managed ones will be paused until some slots free up. `active_downloads` and `active_seeds` controls how many active seeding and downloading torrents the queuing mechanism allows. The target number of active torrents is `min(active_downloads + active_seeds, active_limit)`. `active_downloads` and `active_seeds` are upper limits on the number of downloading torrents and seeding torrents respectively. Setting the value to -1 means unlimited.

For example if there are 10 seeding torrents and 10 downloading torrents, and `active_downloads` is 4 and `active_seeds` is 4, there will be 4 seeds active and 4 downloading torrents. If the settings are `active_downloads` = 2 and `active_seeds` = 4, then there will be 2 downloading torrents and 4 seeding torrents active. Torrents that are not auto managed are not counted against these limits.

`active_checking` is the limit of number of simultaneous checking torrents.

`active_limit` is a hard limit on the number of active (auto managed) torrents. This limit also applies to slow torrents.

`active_dht_limit` is the max number of torrents to announce to the DHT.

`active_tracker_limit` is the max number of torrents to announce to their trackers.

`active_lsd_limit` is the max number of torrents to announce to the local network over the local service discovery protocol.

You can have more torrents active, even though they are not announced to the DHT, lsd or their tracker. If some peer knows about you for any reason and tries to connect, it will still be accepted, unless the torrent is paused, which means it won't accept any connections.

name | type | default
--- | --- | ---
auto_manage_interval | int | 30

`auto_manage_interval` is the number of seconds between the torrent queue is updated, and rotated.

name | type | default
--- | --- | ---
seed_time_limit | int | 24 * 60 * 60

this is the limit on the time a torrent has been an active seed (specified in seconds) before it is considered having met the seed limit criteria. See queuing.

name | type | default
--- | --- | ---
auto_scrape_interval | int | 1800
auto_scrape_min_interval | int | 300

`auto_scrape_interval` is the number of seconds between scrapes of queued torrents (auto managed and paused torrents). Auto managed torrents that are paused, are scraped regularly in order to keep track of their downloader/seed ratio. This ratio is used to determine which torrents to seed and which to pause.

`auto_scrape_min_interval` is the minimum number of seconds between any automatic scrape (regardless of torrent). In case there are a large number of paused auto managed torrents, this puts a limit on how often a scrape request is sent.

name | type | default
--- | --- | ---
max_peerlist_size | int | 3000
max_paused_peerlist_size | int | 1000

`max_peerlist_size` is the maximum number of peers in the list of known peers. These peers are not necessarily connected, so this number should be much greater than the maximum number of connected peers. Peers are evicted from the cache when the list grows passed 90% of this limit, and once the size hits the limit, peers are no longer added to the list. If this limit is set to 0, there is no limit on how many peers we'll keep in the peer list.

`max_paused_peerlist_size` is the max peer list size used for torrents that are paused. This can be used to save memory for paused torrents, since it's not as important for them to keep a large peer list.

name | type | default
--- | --- | ---
min_announce_interval | int | 5 * 60

this is the minimum allowed announce interval for a tracker. This is specified in seconds and is used as a sanity check on what is returned from a tracker. It mitigates hammering mis-configured trackers.

name | type | default
--- | --- | ---
auto_manage_startup | int | 60

this is the number of seconds a torrent is considered active after it was started, regardless of upload and download speed. This is so that newly started torrents are not considered inactive until they have a fair chance to start downloading.

name | type | default
--- | --- | ---
seeding_piece_quota | int | 20

`seeding_piece_quota` is the number of pieces to send to a peer, when seeding, before rotating in another peer to the unchoke set.

name | type | default
--- | --- | ---
max_rejects | int | 50

`max_rejects` is the number of piece requests we will reject in a row while a peer is choked before the peer is considered abusive and is disconnected.

name | type | default
--- | --- | ---
recv_socket_buffer_size | int | 0
send_socket_buffer_size | int | 0

specifies the buffer sizes set on peer sockets. 0 means the OS default (i.e. don't change the buffer sizes). The socket buffer sizes are changed using setsockopt() with SOL_SOCKET/SO_RCVBUF and SO_SNDBUFFER.

name | type | default
--- | --- | ---
max_peer_recv_buffer_size | int | 2 * 1024 * 1024

the max number of bytes a single peer connection's receive buffer is allowed to grow to.

name | type | default
--- | --- | ---
read_cache_line_size | int | 32
write_cache_line_size | int | 16

`read_cache_line_size` is the number of blocks to read into the read cache when a read cache miss occurs. Setting this to 0 is essentially the same thing as disabling read cache. The number of blocks read into the read cache is always capped by the piece boundary.

When a piece in the write cache has `write_cache_line_size` contiguous blocks in it, they will be flushed. Setting this to 1 effectively disables the write cache.

name | type | default
--- | --- | ---
optimistic_disk_retry | int | 10 * 60

`optimistic_disk_retry` is the number of seconds from a disk write errors occur on a torrent until libtorrent will take it out of the upload mode, to test if the error condition has been fixed.

libtorrent will only do this automatically for auto managed torrents.

You can explicitly take a torrent out of upload only mode using set_upload_mode().

name | type | default
--- | --- | ---
max_suggest_pieces | int | 16

`max_suggest_pieces` is the max number of suggested piece indices received from a peer that's remembered. If a peer floods suggest messages, this limit prevents libtorrent from using too much RAM.

name | type | default
--- | --- | ---
local_service_announce_interval | int | 5 * 60

`local_service_announce_interval` is the time between local network announces for a torrent. This interval is specified in seconds.

name | type | default
--- | --- | ---
dht_announce_interval | int | 15 * 60

`dht_announce_interval` is the number of seconds between announcing torrents to the distributed hash table (DHT).

name | type | default
--- | --- | ---
udp_tracker_token_expiry | int | 60

`udp_tracker_token_expiry` is the number of seconds libtorrent will keep UDP tracker connection tokens around for. This is specified to be 60 seconds. The higher this value is, the fewer packets have to be sent to the UDP tracker. In order for higher values to work, the tracker needs to be configured to match the expiration time for tokens.

name | type | default
--- | --- | ---
num_optimistic_unchoke_slots | int | 0

`num_optimistic_unchoke_slots` is the number of optimistic unchoke slots to use. Having a higher number of optimistic unchoke slots mean you will find the good peers faster but with the trade-off to use up more bandwidth. 0 means automatic, where libtorrent opens up 20% of your allowed upload slots as optimistic unchoke slots.

name | type | default
--- | --- | ---
max_pex_peers | int | 50

the max number of peers we accept from pex messages from a single peer. this limits the number of concurrent peers any of our peers claims to be connected to. If they claim to be connected to more than this, we'll ignore any peer that exceeds this limit

name | type | default
--- | --- | ---
tick_interval | int | 500

`tick_interval` specifies the number of milliseconds between internal ticks. This is the frequency with which bandwidth quota is distributed to peers. It should not be more than one second (i.e. 1000 ms). Setting this to a low value (around 100) means higher resolution bandwidth quota distribution, setting it to a higher value saves CPU cycles.

name | type | default
--- | --- | ---
share_mode_target | int | 3

`share_mode_target` specifies the target share ratio for share mode torrents. If set to 3, we'll try to upload 3 times as much as we download. Setting this very high, will make it very conservative and you might end up not downloading anything ever (and not affecting your share ratio). It does not make any sense to set this any lower than 2. For instance, if only 3 peers need to download the rarest piece, it's impossible to download a single piece and upload it more than 3 times. If the share_mode_target is set to more than 3, nothing is downloaded.

name | type | default
--- | --- | ---
upload_rate_limit | int | 0
download_rate_limit | int | 0

`upload_rate_limit` and `download_rate_limit` sets the session-global limits of upload and download rate limits, in bytes per second. By default peers on the local network are not rate limited.

A value of 0 means unlimited.

For fine grained control over rate limits, including making them apply to local peers, see peer classes.

name | type | default
--- | --- | ---
dht_upload_rate_limit | int | 8000

`dht_upload_rate_limit` sets the rate limit on the DHT. This is specified in bytes per second. For busy boxes with lots of torrents that requires more DHT traffic, this should be raised.

name | type | default
--- | --- | ---
unchoke_slots_limit | int | 8

`unchoke_slots_limit` is the max number of unchoked peers in the session. The number of unchoke slots may be ignored depending on what `choking_algorithm` is set to. Setting this limit to -1 means unlimited, i.e. all peers will always be unchoked.

name | type | default
--- | --- | ---
connections_limit | int | 200

`connections_limit` sets a global limit on the number of connections opened. The number of connections is set to a hard minimum of at least two per torrent, so if you set a too low connections limit, and open too many torrents, the limit will not be met.

name | type | default
--- | --- | ---
connections_slack | int | 10

`connections_slack` is the number of incoming connections exceeding the connection limit to accept in order to potentially replace existing ones.

name | type | default
--- | --- | ---
utp_target_delay | int | 100
utp_gain_factor | int | 3000
utp_min_timeout | int | 500
utp_syn_resends | int | 2
utp_fin_resends | int | 2
utp_num_resends | int | 3
utp_connect_timeout | int | 3000
utp_loss_multiplier | int | 50

`utp_target_delay` is the target delay for uTP sockets in milliseconds. A high value will make uTP connections more aggressive and cause longer queues in the upload bottleneck. It cannot be too low, since the noise in the measurements would cause it to send too slow. `utp_gain_factor` is the number of bytes the uTP congestion window can increase at the most in one RTT. If this is set too high, the congestion controller reacts too hard to noise and will not be stable, if it's set too low, it will react slow to congestion and not back off as fast.

`utp_min_timeout` is the shortest allowed uTP socket timeout, specified in milliseconds. The timeout depends on the RTT of the connection, but is never smaller than this value. A connection times out when every packet in a window is lost, or when a packet is lost twice in a row (i.e. the resent packet is lost as well).

The shorter the timeout is, the faster the connection will recover from this situation, assuming the RTT is low enough. `utp_syn_resends` is the number of SYN packets that are sent (and timed out) before giving up and closing the socket. `utp_num_resends` is the number of times a packet is sent (and lost or timed out) before giving up and closing the connection. `utp_connect_timeout` is the number of milliseconds of timeout for the initial SYN packet for uTP connections. For each timed out packet (in a row), the timeout is doubled. `utp_loss_multiplier` controls how the congestion window is changed when a packet loss is experienced. It's specified as a percentage multiplier for `cwnd`. Do not change this value unless you know what you're doing. Never set it higher than 100.

name | type | default
--- | --- | ---
mixed_mode_algorithm | int | settings_pack::peer_proportional

The `mixed_mode_algorithm` determines how to treat TCP connections when there are uTP connections. Since uTP is designed to yield to TCP, there's an inherent problem when using swarms that have both TCP and uTP connections. If nothing is done, uTP connections would often be starved out for bandwidth by the TCP connections. This mode is `prefer_tcp`. The `peer_proportional` mode simply looks at the current throughput and rate limits all TCP connections to their proportional share based on how many of the connections are TCP. This works best if uTP connections are not rate limited by the global rate limiter (which they aren't by default).

name | type | default
--- | --- | ---
listen_queue_size | int | 5

`listen_queue_size` is the value passed in to listen() for the listen socket. It is the number of outstanding incoming connections to queue up while we're not actively waiting for a connection to be accepted. 5 should be sufficient for any normal client. If this is a high performance server which expects to receive a lot of connections, or used in a simulator or test, it might make sense to raise this number. It will not take affect until the `listen_interfaces` settings is updated.

name | type | default
--- | --- | ---
torrent_connect_boost | int | 30

`torrent_connect_boost` is the number of peers to try to connect to immediately when the first tracker response is received for a torrent. This is a boost to given to new torrents to accelerate them starting up. The normal connect scheduler is run once every second, this allows peers to be connected immediately instead of waiting for the session tick to trigger connections. This may not be set higher than 255.

name | type | default
--- | --- | ---
alert_queue_size | int | 1000

`alert_queue_size` is the maximum number of alerts queued up internally. If alerts are not popped, the queue will eventually fill up to this level. Once the alert queue is full, additional alerts will be dropped, and not delivered to the client. Once the client drains the queue, new alerts may be delivered again. In order to know that alerts have been dropped, see session_handle::dropped_alerts().

name | type | default
--- | --- | ---
max_metadata_size | int | 3 * 1024 * 10240

`max_metadata_size` is the maximum allowed size (in bytes) to be received by the metadata extension, i.e. magnet links.

name | type | default
--- | --- | ---
checking_mem_usage | int | 1024

the number of blocks to keep outstanding at any given time when checking torrents. Higher numbers give faster re-checks but uses more memory. Specified in number of 16 kiB blocks

name | type | default
--- | --- | ---
predictive_piece_announce | int | 0

if set to > 0, pieces will be announced to other peers before they are fully downloaded (and before they are hash checked). The intention is to gain 1.5 potential round trip times per downloaded piece. When non-zero, this indicates how many milliseconds in advance pieces should be announced, before they are expected to be completed.

name | type | default
--- | --- | ---
aio_threads | int | 4

for some aio back-ends, `aio_threads` specifies the number of io-threads to use.

name | type | default
--- | --- | ---
tracker_backoff | int | 250

`tracker_backoff` determines how aggressively to back off from retrying failing trackers. This value determines x in the following formula, determining the number of seconds to wait until the next retry:

> delay = 5 + 5 * x / 100 * fails^2

This setting may be useful to make libtorrent more or less aggressive in hitting trackers.

name | type | default
--- | --- | ---
share_ratio_limit | int | 200
seed_time_ratio_limit | int | 700

when a seeding torrent reaches either the share ratio (bytes up / bytes down) or the seed time ratio (seconds as seed / seconds as downloader) or the seed time limit (seconds as seed) it is considered done, and it will leave room for other torrents. These are specified as percentages. Torrents that are considered done will still be allowed to be seeded, they just won't have priority anymore. For more, see queuing.

name | type | default
--- | --- | ---
peer_turnover | int | 4
peer_turnover_cutoff | int | 90
peer_turnover_interval | int | 300

peer_turnover is the percentage of peers to disconnect every turnover peer_turnover_interval (if we're at the peer limit), this is specified in percent when we are connected to more than limit * peer_turnover_cutoff peers disconnect peer_turnover fraction of the peers. It is specified in percent peer_turnover_interval is the interval (in seconds) between optimistic disconnects if the disconnects happen and how many peers are disconnected is controlled by peer_turnover and peer_turnover_cutoff

name | type | default
--- | --- | ---
connect_seed_every_n_download | int | 10

this setting controls the priority of downloading torrents over seeding or finished torrents when it comes to making peer connections. Peer connections are throttled by the connection_speed and the half-open connection limit. This makes peer connections a limited resource. Torrents that still have pieces to download are prioritized by default, to avoid having many seeding torrents use most of the connection attempts and only give one peer every now and then to the downloading torrent. libtorrent will loop over the downloading torrents to connect a peer each, and every n:th connection attempt, a finished torrent is picked to be allowed to connect to a peer. This setting controls n.

name | type | default
--- | --- | ---
max_http_recv_buffer_size | int | 4*1024*204

the max number of bytes to allow an HTTP response to be when announcing to trackers or downloading .torrent files via the `url` provided in `add_torrent_params`.

name | type | default
--- | --- | ---
max_retry_port_bind | int | 10

if binding to a specific port fails, should the port be incremented by one and tried again? This setting specifies how many times to retry a failed port bind

name | type | default
--- | --- | ---
alert_mask | int | int

a bitmask combining flags from alert_category_t defining which kinds of alerts to receive

name | type | default
--- | --- | ---
out_enc_policy | int | settings_pack::pe_enabled
in_enc_policy | int | settings_pack::pe_enabled

control the settings for incoming and outgoing connections respectively. see enc_policy enum for the available options. Keep in mind that protocol encryption degrades performance in several respects:

1. It prevents "zero copy" disk buffers being sent to peers, since each peer needs to mutate the data (i.e. encrypt it) the data must be copied per peer connection rather than sending the same buffer to multiple peers.
2. The encryption itself requires more CPU than plain bittorrent protocol. The highest cost is the Diffie Hellman exchange on connection setup.
3. The encryption handshake adds several round-trips to the connection setup, and delays transferring data.

name | type | default
--- | --- | ---
allowed_enc_level | int | settings_pack::pe_both

determines the encryption level of the connections. This setting will adjust which encryption scheme is offered to the other peer, as well as which encryption scheme is selected by the client. See enc_level enum for options.

name | type | default
--- | --- | ---
inactive_down_rate | int | 2048
inactive_up_rate | int | 2048

the download and upload rate limits for a torrent to be considered active by the queuing mechanism. A torrent whose download rate is less than `inactive_down_rate` and whose upload rate is less than `inactive_up_rate` for `auto_manage_startup` seconds, is considered inactive, and another queued torrent may be started. This logic is disabled if `dont_count_slow_torrents` is false.

name | type | default
--- | --- | ---
proxy_type | int | settings_pack::none

proxy to use. see proxy_type_t.

name | type | default
--- | --- | ---
proxy_port | int | 0

the port of the proxy server

name | type | default
--- | --- | ---
i2p_port | int | 0

sets the i2p SAM bridge port to connect to. set the hostname with the `i2p_hostname` setting.

name | type | default
--- | --- | ---
cache_size_volatile | int | 256

this determines the max number of volatile disk cache blocks. If the number of volatile blocks exceed this limit, other volatile blocks will start to be evicted. A disk cache block is volatile if it has low priority, and should be one of the first blocks to be evicted under pressure. For instance, blocks pulled into the cache as the result of calculating a piece hash are volatile. These blocks don't represent potential interest among peers, so the value of keeping them in the cache is limited.

name | type | default
--- | --- | ---
urlseed_max_request_bytes | int | 16 * 1024 * 1024

The maximum request range of an url seed in bytes. This value defines the largest possible sequential web seed request. Lower values are possible but will be ignored if they are lower then piece size. This value should be related to your download speed to prevent libtorrent from creating too many expensive http requests per second. You can select a value as high as you want but keep in mind that libtorrent can't create parallel requests if the first request did already select the whole file. If you combine bittorrent seeds with web seeds and pick strategies like rarest first you may find your web seed requests split into smaller parts because we don't download already picked pieces twice.

name | type | default
--- | --- | ---
web_seed_name_lookup_retry | int | 1800

time to wait until a new retry of a web seed name lookup

name | type | default
--- | --- | ---
close_file_interval | int | CLOSE_FILE_INTERVAL

the number of seconds between closing the file opened the longest ago. 0 means to disable the feature. The purpose of this is to periodically close files to trigger the operating system flushing disk cache. Specifically it has been observed to be required on windows to not have the disk cache grow indefinitely. This defaults to 120 seconds on windows, and disabled on other systems.

name | type | default
--- | --- | ---
utp_cwnd_reduce_timer | int | 100

When uTP experiences packet loss, it will reduce the congestion window, and not reduce it again for this many milliseconds, even if experiencing another lost packet.

name | type | default
--- | --- | ---
max_web_seed_connections | int | 3

the max number of web seeds to have connected per torrent at any given time.

name | type | default
--- | --- | ---
resolver_cache_timeout | int | 1200

the number of seconds before the internal host name resolver considers a cache value timed out, negative values are interpreted as zero.

name | type | default
--- | --- | ---
send_not_sent_low_watermark | int | 16384

specify the not-sent low watermark for socket send buffers. This corresponds to the, Linux-specific, `TCP_NOTSENT_LOWAT` TCP socket option.

name | type | default
--- | --- | ---
rate_choker_initial_threshold | int | 1024

the rate based choker compares the upload rate to peers against a threshold that increases proportionally by its size for every peer it visits, visiting peers in decreasing upload rate. The number of upload slots is determined by the number of peers whose upload rate exceeds the threshold. This option sets the start value for this threshold. A higher value leads to fewer unchoke slots, a lower value leads to more.

name | type | default
--- | --- | ---
upnp_lease_duration | int | 3600

The expiration time of UPnP port-mappings, specified in seconds. 0 means permanent lease. Some routers do not support expiration times on port-maps (nor correctly returning an error indicating lack of support). In those cases, set this to 0. Otherwise, don't set it any lower than 5 minutes.

name | type | default
--- | --- | ---
max_concurrent_http_announces | int | 50

limits the number of concurrent HTTP tracker announces. Once the limit is hit, tracker requests are queued and issued when an outstanding announce completes.

    struct settings_pack
    {
       void set_str (int name, std::string val);
       void set_int (int name, flags::bitfield_flag<Type, Tag> const val);
       void set_bool (int name, bool val);
       void set_int (int name, int val);
       bool has_val (int name) const;
       void clear ();
       void clear (int name);
       bool get_bool (int name) const;
       std::string const& get_str (int name) const;
       int get_int (int name) const;

       enum type_bases
       {
          string_type_base,
          int_type_base,
          bool_type_base,
          type_mask,
          index_mask,
       };

       enum suggest_mode_t
       {
          no_piece_suggestions,
          suggest_read_cache,
       };

       enum choking_algorithm_t
       {
          fixed_slots_choker,
          rate_based_choker,
          deprecated_bittyrant_choker,
       };

       enum seed_choking_algorithm_t
       {
          round_robin,
          fastest_upload,
          anti_leech,
       };

       enum io_buffer_mode_t
       {
          enable_os_cache,
          deprecated_disable_os_cache_for_aligned_files,
          disable_os_cache,
       };

       enum bandwidth_mixed_algo_t
       {
          prefer_tcp,
          peer_proportional,
       };

       enum enc_policy
       {
          pe_forced,
          pe_enabled,
          pe_disabled,
       };

       enum enc_level
       {
          pe_plaintext,
          pe_rc4,
          pe_both,
       };

       enum proxy_type_t
       {
          none,
          socks4,
          socks5,
          socks5_pw,
          http,
          http_pw,
          i2p_proxy,
       };
    };

[report issue]

#### set_str() set_bool() set_int()

    void set_str (int name, std::string val);
    void set_int (int name, flags::bitfield_flag<Type, Tag> const val);
    void set_bool (int name, bool val);
    void set_int (int name, int val);

set a configuration option in the settings_pack. `name` is one of the enum values from string_types, int_types or bool_types. They must match the respective type of the set_* function.

[report issue]

#### has_val()

    bool has_val (int name) const;

queries whether the specified configuration option has a value set in this pack. `name` can be any enumeration value from string_types, int_types or bool_types.

[report issue]

#### clear()

    void clear ();

clear the settings pack from all settings

[report issue]

#### clear()

    void clear (int name);

clear a specific setting from the pack

[report issue]

#### get_str() get_int() get_bool()

    bool get_bool (int name) const;
    std::string const& get_str (int name) const;
    int get_int (int name) const;

queries the current configuration option from the settings_pack. `name` is one of the enumeration values from string_types, int_types or bool_types. The enum value must match the type of the get_* function.

[report issue]

#### enum type_bases

Declared in "libtorrent/settings_pack.hpp"

name | value | description
--- | --- | ---
string_type_base | 0 |
int_type_base | 16384 |
bool_type_base | 32768 |
type_mask | 49152 |
index_mask | 16383 |

[report issue]

#### enum suggest_mode_t

Declared in "libtorrent/settings_pack.hpp"

name | value | description
--- | --- | ---
no_piece_suggestions | 0 |
suggest_read_cache | 1 |

[report issue]

#### enum choking_algorithm_t

Declared in "libtorrent/settings_pack.hpp"

name | value | description
--- | --- | ---
fixed_slots_choker | 0 | This is the traditional choker with a fixed number of unchoke slots (as specified by settings_pack::unchoke_slots_limit).
rate_based_choker | 2 | This opens up unchoke slots based on the upload rate achieved to peers. The more slots that are opened, the marginal upload rate required to open up another slot increases. Configure the initial threshold with settings_pack::rate_choker_initial_threshold. For more information, see rate based choking.
deprecated_bittyrant_choker | 3 |

[report issue]

#### enum seed_choking_algorithm_t

Declared in "libtorrent/settings_pack.hpp"

name | value | description
--- | --- | ---
round_robin | 0 | which round-robins the peers that are unchoked when seeding. This distributes the upload bandwidth uniformly and fairly. It minimizes the ability for a peer to download everything without redistributing it.
fastest_upload | 1 | unchokes the peers we can send to the fastest. This might be a bit more reliable in utilizing all available capacity.
anti_leech | 2 | prioritizes peers who have just started or are just about to finish the download. The intention is to force peers in the middle of the download to trade with each other. This does not just take into account the pieces a peer is reporting having downloaded, but also the pieces we have sent to it.

[report issue]

#### enum io_buffer_mode_t

Declared in "libtorrent/settings_pack.hpp"

name | value | description
--- | --- | ---
enable_os_cache | 0 |
deprecated_disable_os_cache_for_aligned_files | 1 |
disable_os_cache | 2 |

[report issue]

#### enum bandwidth_mixed_algo_t

Declared in "libtorrent/settings_pack.hpp"

name | value | description
--- | --- | ---
prefer_tcp | 0 | disables the mixed mode bandwidth balancing
peer_proportional | 1 | does not throttle uTP, throttles TCP to the same proportion of throughput as there are TCP connections

[report issue]

#### enum enc_policy

Declared in "libtorrent/settings_pack.hpp"

name | value | description
--- | --- | ---
pe_forced | 0 | Only encrypted connections are allowed. Incoming connections that are not encrypted are closed and if the encrypted outgoing connection fails, a non-encrypted retry will not be made.
pe_enabled | 1 | encrypted connections are enabled, but non-encrypted connections are allowed. An incoming non-encrypted connection will be accepted, and if an outgoing encrypted connection fails, a non- encrypted connection will be tried.
pe_disabled | 2 | only non-encrypted connections are allowed.

[report issue]

#### enum enc_level

Declared in "libtorrent/settings_pack.hpp"

name | value | description
--- | --- | ---
pe_plaintext | 1 | use only plain text encryption
pe_rc4 | 2 | use only RC4 encryption
pe_both | 3 | allow both

[report issue]

#### enum proxy_type_t

Declared in "libtorrent/settings_pack.hpp"

name | value | description
--- | --- | ---
none | 0 | No proxy server is used and all other fields are ignored.
socks4 | 1 | The server is assumed to be a SOCKS4 server that requires a username.
socks5 | 2 | The server is assumed to be a SOCKS5 server (RFC 1928) that does not require any authentication. The username and password are ignored.
socks5_pw | 3 | The server is assumed to be a SOCKS5 server that supports plain text username and password authentication (RFC 1929). The username and password specified may be sent to the proxy if it requires.
http | 4 | The server is assumed to be an HTTP proxy. If the transport used for the connection is non-HTTP, the server is assumed to support the CONNECT method. i.e. for web seeds and HTTP trackers, a plain proxy will suffice. The proxy is assumed to not require authorization. The username and password will not be used.
http_pw | 5 | The server is assumed to be an HTTP proxy that requires user authorization. The username and password will be sent to the proxy.
i2p_proxy | 6 | route through a i2p SAM proxy

[report issue]

### high_performance_seed() min_memory_usage()

Declared in "libtorrent/session.hpp"

    settings_pack high_performance_seed ();
    settings_pack min_memory_usage ();

The default values of the session settings are set for a regular bittorrent client running on a desktop system. There are functions that can set the session settings to pre set settings for other environments. These can be used for the basis, and should be tweaked to fit your needs better.

`min_memory_usage` returns settings that will use the minimal amount of RAM, at the potential expense of upload and download performance. It adjusts the socket buffer sizes, disables the disk cache, lowers the send buffer watermarks so that each connection only has at most one block in use at any one time. It lowers the outstanding blocks send to the disk I/O thread so that connections only have one block waiting to be flushed to disk at any given time. It lowers the max number of peers in the peer list for torrents. It performs multiple smaller reads when it hashes pieces, instead of reading it all into memory before hashing.

This configuration is intended to be the starting point for embedded devices. It will significantly reduce memory usage.

`high_performance_seed` returns settings optimized for a seed box, serving many peers and that doesn't do any downloading. It has a 128 MB disk cache and has a limit of 400 files in its file pool. It support fast upload rates by allowing large send buffers.

[report issue]

### setting_by_name() name_for_setting()

Declared in "libtorrent/settings_pack.hpp"

    char const* name_for_setting (int s);
    int setting_by_name (string_view name);

converts a setting integer (from the enums string_types, int_types or bool_types) to a string, and vice versa.

[report issue]

### default_settings()

Declared in "libtorrent/settings_pack.hpp"

    settings_pack default_settings ();

returns a settings_pack with every setting set to its default value

Author: | Arvid Norberg, arvid@libtorrent.org
Version: | 1.2.9

home

## Bdecoding

[report issue]

### bdecode_node

Declared in "libtorrent/bdecode.hpp"

Sometimes it's important to get a non-owning reference to the root node ( to be able to copy it as a reference for instance). For that, use the non_owning() member function.

There are 5 different types of nodes, see type_t.

    struct bdecode_node
    {
       bdecode_node () = default;
       bdecode_node (bdecode_node&&) noexcept;
       bdecode_node& operator= (bdecode_node&&) = default;
       bdecode_node& operator= (bdecode_node const&);
       bdecode_node (bdecode_node const&);
       type_t type () const noexcept;
       explicit operator bool () const noexcept;
       bdecode_node non_owning () const;
       span<char const> data_section () const noexcept;
       int list_size () const;
       std::int64_t list_int_value_at (int i
          , std::int64_t default_val = 0) const;
       bdecode_node list_at (int i) const;
       string_view list_string_value_at (int i
          , string_view default_val = string_view()) const;
       std::pair<string_view, bdecode_node> dict_at (int i) const;
       string_view dict_find_string_value (string_view key
          , string_view default_value = string_view()) const;
       bdecode_node dict_find_int (string_view key) const;
       bdecode_node dict_find (string_view key) const;
       bdecode_node dict_find_list (string_view key) const;
       int dict_size () const;
       std::int64_t dict_find_int_value (string_view key
          , std::int64_t default_val = 0) const;
       bdecode_node dict_find_dict (string_view key) const;
       bdecode_node dict_find_string (string_view key) const;
       std::int64_t int_value () const;
       char const* string_ptr () const;
       int string_length () const;
       string_view string_value () const;
       void clear ();
       void swap (bdecode_node& n);
       void reserve (int tokens);
       void switch_underlying_buffer (char const* buf) noexcept;
       bool has_soft_error (span<char> error) const;

       enum type_t
       {
          none_t,
          dict_t,
          list_t,
          string_t,
          int_t,
       };
    };

[report issue]

#### bdecode_node()

    bdecode_node () = default;

creates a default constructed node, it will have the type `none_t`.

[report issue]

#### bdecode_node() operator=()

    bdecode_node (bdecode_node&&) noexcept;
    bdecode_node& operator= (bdecode_node&&) = default;
    bdecode_node& operator= (bdecode_node const&);
    bdecode_node (bdecode_node const&);

For owning nodes, the copy will create a copy of the tree, but the underlying buffer remains the same.

[report issue]

#### type()

    type_t type () const noexcept;

the type of this node. See type_t.

[report issue]

#### bool()

    explicit operator bool () const noexcept;

returns true if type() != none_t.

[report issue]

#### non_owning()

    bdecode_node non_owning () const;

return a non-owning reference to this node. This is useful to refer to the root node without copying it in assignments.

[report issue]

#### data_section()

    span<char const> data_section () const noexcept;

returns the buffer and length of the section in the original bencoded buffer where this node is defined. For a dictionary for instance, this starts with `d` and ends with `e`, and has all the content of the dictionary in between.

[report issue]

#### list_at() list_string_value_at() list_int_value_at() list_size()

    int list_size () const;
    std::int64_t list_int_value_at (int i
          , std::int64_t default_val = 0) const;
    bdecode_node list_at (int i) const;
    string_view list_string_value_at (int i
          , string_view default_val = string_view()) const;

functions with the `list_` prefix operate on lists. These functions are only valid if `type()` == `list_t`. `list_at()` returns the item in the list at index `i`. `i` may not be greater than or equal to the size of the list. `size()` returns the size of the list.

[report issue]

#### dict_find_dict() dict_find_list() dict_at() dict_find_string() dict_find() dict_size() dict_find_int() dict_find_int_value() dict_find_string_value()

    std::pair<string_view, bdecode_node> dict_at (int i) const;
    string_view dict_find_string_value (string_view key
          , string_view default_value = string_view()) const;
    bdecode_node dict_find_int (string_view key) const;
    bdecode_node dict_find (string_view key) const;
    bdecode_node dict_find_list (string_view key) const;
    int dict_size () const;
    std::int64_t dict_find_int_value (string_view key
          , std::int64_t default_val = 0) const;
    bdecode_node dict_find_dict (string_view key) const;
    bdecode_node dict_find_string (string_view key) const;

Functions with the `dict_` prefix operates on dictionaries. They are only valid if `type()` == `dict_t`. In case a key you're looking up contains a 0 byte, you cannot use the 0-terminated string overloads, but have to use `std::string` instead. `dict_find_list` will return a valid `bdecode_node` if the key is found _and_ it is a list. Otherwise it will return a default-constructed bdecode_node.

Functions with the `_value` suffix return the value of the node directly, rather than the nodes. In case the node is not found, or it has a different type, a default value is returned (which can be specified).

[report issue]

#### int_value()

    std::int64_t int_value () const;

this function is only valid if `type()` == `int_t`. It returns the value of the integer.

[report issue]

#### string_length() string_ptr() string_value()

    char const* string_ptr () const;
    int string_length () const;
    string_view string_value () const;

these functions are only valid if `type()` == `string_t`. They return the string values. Note that `string_ptr()` is not 0-terminated. `string_length()` returns the number of bytes in the string.

[report issue]

#### clear()

    void clear ();

resets the `bdecoded_node` to a default constructed state. If this is an owning node, the tree is freed and all child nodes are invalidated.

[report issue]

#### swap()

    void swap (bdecode_node& n);

Swap contents.

[report issue]

#### reserve()

    void reserve (int tokens);

preallocate memory for the specified numbers of tokens. This is useful if you know approximately how many tokens are in the file you are about to parse. Doing so will save realloc operations while parsing. You should only call this on the root node, before passing it in to bdecode().

[report issue]

#### switch_underlying_buffer()

    void switch_underlying_buffer (char const* buf) noexcept;

this buffer MUST be identical to the one originally parsed. This operation is only defined on owning root nodes, i.e. the one passed in to decode().

[report issue]

#### has_soft_error()

    bool has_soft_error (span<char> error) const;

returns true if there is a non-fatal error in the bencoding of this node or its children

[report issue]

#### enum type_t

Declared in "libtorrent/bdecode.hpp"

name | value | description
--- | --- | ---
none_t | 0 | uninitialized or default constructed. This is also used to indicate that a node was not found in some cases.
dict_t | 1 | a dictionary node. The `dict_find_` functions are valid.
list_t | 2 | a list node. The `list_` functions are valid.
string_t | 3 | a string node, the `string_` functions are valid.
int_t | 4 | an integer node. The `int_` functions are valid.

[report issue]

### print_entry()

Declared in "libtorrent/bdecode.hpp"

    std::string print_entry (bdecode_node const& e
       , bool single_line = false, int indent = 0);

print the bencoded structure in a human-readable format to a string that's returned.

[report issue]

### bdecode()

Declared in "libtorrent/bdecode.hpp"

    int bdecode (char const* start, char const* end, bdecode_node& ret
       , error_code& ec, int* error_pos = nullptr, int depth_limit = 100
       , int token_limit = 2000000);
    bdecode_node bdecode (span<char const> buffer
       , error_code& ec, int* error_pos = nullptr, int depth_limit = 100
       , int token_limit = 2000000);
    bdecode_node bdecode (span<char const> buffer
       , int depth_limit = 100, int token_limit = 2000000);

This function decodes/parses bdecoded data (for example a .torrent file). The data structure is returned in the `ret` argument. the buffer to parse is specified by the `start` of the buffer as well as the `end`, i.e. one byte past the end. If the buffer fails to parse, the function returns a non-zero value and fills in `ec` with the error code. The optional argument `error_pos`, if set to non-nullptr, will be set to the byte offset into the buffer where the parse failure occurred.

`depth_limit` specifies the max number of nested lists or dictionaries are allowed in the data structure. (This affects the stack usage of the function, be careful not to set it too high).

`token_limit` is the max number of tokens allowed to be parsed from the buffer. This is simply a sanity check to not have unbounded memory usage.

The resulting `bdecode_node` is an owning node. That means it will be holding the whole parsed tree. When iterating lists and dictionaries, those `bdecode_node` objects will simply have references to the root or owning `bdecode_node`. If the root node is destructed, all other nodes that refer to anything in that tree become invalid.

However, the underlying buffer passed in to this function (`start`, `end`) must also remain valid while the bdecoded tree is used. The parsed tree produced by this function does not copy any data out of the buffer, but simply produces references back into it.

Author: | Arvid Norberg, arvid@libtorrent.org
Version: | 1.2.9

home

## ed25519

[report issue]

### ed25519_create_seed()

Declared in "libtorrent/kademlia/ed25519.hpp"

    std::array<char, 32> ed25519_create_seed ();

See documentation of internal random_bytes

[report issue]

### ed25519_create_keypair()

Declared in "libtorrent/kademlia/ed25519.hpp"

    std::tuple<public_key, secret_key> ed25519_create_keypair (
       std::array<char, 32> const& seed);

Creates a new key pair from the given seed.

It's important to clarify that the seed completely determines the key pair. Then it's enough to save the seed and the public key as the key-pair in a buffer of 64 bytes. The standard is (32 bytes seed, 32 bytes public key).

This function does work with a given seed, giving you a pair of (64 bytes private key, 32 bytes public key). It's a trade-off between space and CPU, saving in one format or another.

The smaller format is not weaker by any means, in fact, it is only the seed (32 bytes) that determines the point in the curve.

[report issue]

### ed25519_sign()

Declared in "libtorrent/kademlia/ed25519.hpp"

    signature ed25519_sign (span<char const> msg
       , public_key const& pk, secret_key const& sk);

Creates a signature of the given message with the given key pair.

[report issue]

### ed25519_verify()

Declared in "libtorrent/kademlia/ed25519.hpp"

    bool ed25519_verify (signature const& sig
       , span<char const> msg, public_key const& pk);

Verifies the signature on the given message using `pk`

[report issue]

### ed25519_add_scalar()

Declared in "libtorrent/kademlia/ed25519.hpp"

    secret_key ed25519_add_scalar (secret_key const& sk
       , std::array<char, 32> const& scalar);
    public_key ed25519_add_scalar (public_key const& pk
       , std::array<char, 32> const& scalar);

Adds a scalar to the given key pair where scalar is a 32 byte buffer (possibly generated with ed25519_create_seed), generating a new key pair.

You can calculate the public key sum without knowing the private key and vice versa by passing in null for the key you don't know. This is useful when a third party (an authoritative server for example) needs to enforce randomness on a key pair while only knowing the public key of the other side.

Warning: the last bit of the scalar is ignored - if comparing scalars make sure to clear it with scalar[31] &= 127.

see http://crypto.stackexchange.com/a/6215/4697 see test_ed25519 for a practical example

[report issue]

### ed25519_key_exchange()

Declared in "libtorrent/kademlia/ed25519.hpp"

    std::array<char, 32> ed25519_key_exchange (
       public_key const& pk, secret_key const& sk);

Performs a key exchange on the given public key and private key, producing a shared secret. It is recommended to hash the shared secret before using it.

This is useful when two parties want to share a secret but both only knows their respective public keys. see test_ed25519 for a practical example