= ranch_transport(3)

== Name

ranch_transport - Transport modules

== Description

The module `ranch_transport` defines the interface used
by Ranch transports.

== Callbacks

Ranch transports implement the following interface:

=== accept

[source,erlang]
----
accept(LSocket :: socket(), Timeout :: timeout())
    -> {ok, Socket :: socket()}
     | {error, closed | timeout | atom()}
----

Use the listening socket returned by `listen/1`
to accept a new connection. The timeout is specified
in milliseconds.

=== close

[source,erlang]
----
close(Socket :: socket()) -> ok
----

Close the socket.

=== controlling_process

[source,erlang]
----
controlling_process(Socket :: socket(), Pid :: pid())
    -> ok | {error, closed | not_owner | atom()}
----

Assign a new controlling process to the socket. The
controlling process is the process that is linked to
and receives messages from the socket.

=== format_error

[source,erlang]
----
format_error(Reason :: term())
    -> ReasonString :: string()
----

Format a listen error into a human-readable diagnostic string.

This callback is optional, but implementing it is highly
recommended. It will become mandatory in Ranch 3.0.

=== getopts

[source,erlang]
----
getopts(Socket :: socket(), SockOpts :: [atom()])
    -> {ok, any()} | {error, atom()}
----

Get one or more options for the socket.

=== getstat

[source,erlang]
----
getstat(Socket :: socket())
    -> {ok, SockStatValues :: any()} | {error, atom()}
----

Get all statistics for the socket.

[source,erlang]
----
getstat(Socket :: socket(), SockStats :: [atom()])
    -> {ok, SockStatValues :: any()} | {error, atom()}
----

Get one or more statistic options for the socket.

=== handshake

[source,erlang]
----
handshake(Socket0  :: socket(),
          Timeout  :: timeout())
    -> {ok, Socket :: socket()}
     | {ok, Socket :: socket(), Info :: any()}
     | {error, any()}

handshake(Socket0  :: socket(),
          SockOpts :: opts(),
          Timeout  :: timeout())
    -> {ok, Socket :: socket()}
     | {ok, Socket :: socket(), Info :: any()}
     | {error, any()}
----

Perform the transport-level handshake.

This function will be called by connection processes
before performing any socket operation. It allows
transports that require extra initialization to perform
their task and return a socket that is ready to use.

If the handshake is completed by this call, the function will
return `{ok, Socket}`. However, some transports (notably,
`ranch_ssl` if `{handshake, hello}` is specified in the socket
options) may pause the handshake at a certain point and return
`{ok, Socket, Info}` instead, in order to allow for
additional decisions to be made before resuming the handshake
with `handshake_continue/3` or cancelling it with
`handshake_cancel/1`.

This function may also be used to upgrade a connection
from a transport to another depending on the capabilities
of the transports. For example a `ranch_tcp` socket may
be upgraded to a `ranch_ssl` one using this function.

=== handshake_continue

[source,erlang]
----
handshake_continue(Socket0  :: socket(),
                   Timeout  :: timeout())
    -> {ok, Socket :: socket()}
     | {error, any()}

handshake_continue(Socket0  :: socket(),
                   SockOpts :: opts(),
                   Timeout  :: timeout())
    -> {ok, Socket :: socket()}
     | {error, any()}
----

Resume the paused transport-level handshake and return a socket
that is ready to use.

This function will be called by connection processes
to resume a paused handshake.

=== handshake_cancel

[source,erlang]
----
handshake_cancel(Socket :: socket()) -> ok
----

Cancel the paused transport-level handshake.

=== listen

[source,erlang]
----
listen(TransportOpts :: ranch:transport_opts(any()))
    -> {ok, LSocket :: socket()} | {error, atom()}
----

Create a socket that listens on the port given in the
socket options.

The port may not be specified or may be set to 0, which
means a random available port number will be chosen.

=== messages

[source,erlang]
----
messages()
    -> {OK      :: atom(),
        Closed  :: atom(),
        Error   :: atom(),
        Passive :: atom()}
----

Return the tuple keys for the messages sent by the socket.

=== name

[source,erlang]
----
name() -> Name :: atom()
----

Return the name of the transport.

=== peername

[source,erlang]
----
peername(Socket :: socket())
    -> {ok, {inet:ip_address(), inet:port_number()}}
     | {local, binary()} | {error, atom()}.
----

Return the address and port number for the other end of
the connection.

For UNIX Domain sockets the return value will be
`{local, PeerSocket}`, with `PeerSocket` typically
an empty binary.

=== recv

[source,erlang]
----
recv(Socket :: socket(),
     Length :: non_neg_integer(),
     Timeout :: timeout())
    -> {ok, Packet :: any()}
     | {error, closed | timeout | atom()}
----

Receive a packet from the socket in passive mode.

Attempting to receive data from a socket that is
in active mode will return an error.

A length of 0 will return the data available on
the socket as soon as possible, regardless of length.

While it is possible to use the timeout value `infinity`,
it is highly discouraged as it could cause your process
to get stuck waiting for data that will never come. This may
happen when a socket becomes half-open due to a crash of the
remote endpoint. Wi-Fi going down is another common culprit.

=== secure

[source,erlang]
----
secure() -> boolean()
----

Return whether the transport can be used for secure connections.

=== send

[source,erlang]
----
send(Socket :: socket(), Packet :: iodata())
    -> ok | {error, atom()}
----

Send a packet on the socket.

=== sendfile

[source,erlang]
----
sendfile(Socket, File)
    -> sendfile(Socket, File, 0, 0, [])

sendfile(Socket, File, Offset, Bytes)
    -> sendfile(Socket, File, Offset, Bytes, [])

sendfile(Socket :: socket(),
         File   :: file:name_all() | file:fd(),
         Offset :: non_neg_integer(),
         Bytes  :: non_neg_integer(),
         Opts   :: sendfile_opts())
    -> {ok, SentBytes :: non_neg_integer()} | {error, atom()}
----

Send a file on the socket.

The file may be sent full or in parts, and may be specified
by its filename or by an already open file descriptor.

Transports that manipulate TCP directly may use the
`file:sendfile/2,4,5` function, which calls the `sendfile`
syscall where applicable (on Linux, for example). Other
transports can use the `sendfile/6` function exported from
this module.

=== setopts

[source,erlang]
----
setopts(Socket :: socket(), SockOpts :: any())
    -> ok | {error, atom()}
----

Set one or more options for the socket.

=== shutdown

[source,erlang]
----
shutdown(Socket :: socket(),
         How    :: read | write | read_write)
    -> ok | {error, atom()}
----

Close the socket for reading and/or writing.

=== sockname

[source,erlang]
----
sockname(Socket :: socket())
    -> {ok, {inet:ip_address(), inet:port_number()}}
     | {error, atom()}.
----

Return the address and port number for the local end
of the connection.

For UNIX Domain sockets the return value will be
`{local, SocketFile}`.

== Exports

The following function can be used when implementing
transport modules:

* link:man:ranch_transport:sendfile(3)[ranch_transport:sendfile(3)] - Send a file on the socket

== Types

=== sendfile_opts()

[source,erlang]
----
sendfile_opts() :: [{chunk_size, non_neg_integer()}]
----

Options accepted by the sendfile function and callbacks:

chunk_size (8191)::

The chunk size, in bytes.

=== socket()

[source,erlang]
----
socket() :: any()
----

The socket.

The exact type will vary depending on the transport module.

== Changelog

* *2.2*: The callback `format_error/1` was added.
* *2.0*: The callback `listen/1` has changed to accept a map of
         transport options instead of socket options.
* *2.0*: The callback `messages/0` return value was updated to
         include the passive message for `{active, N}`.
* *1.6*: The `socket()` type was added for documentation purposes.
* *1.6*: The type of the sendfile filename was extended.

== See also

link:man:ranch(7)[ranch(7)],
link:man:ranch_tcp(3)[ranch_tcp(3)],
link:man:ranch_ssl(3)[ranch_ssl(3)]
