= ranch(3)

== Name

ranch - Socket acceptor pool

== Description

The module `ranch` provides functions for starting and
manipulating Ranch listeners.

== Exports

Start/stop:

* link:man:ranch:start_listener(3)[ranch:start_listener(3)] - Start a listener
* link:man:ranch:stop_listener(3)[ranch:stop_listener(3)] - Stop a listener
* link:man:ranch:child_spec(3)[ranch:child_spec(3)] - Build child specifications for a new listener

Suspend/resume:

* link:man:ranch:suspend_listener(3)[ranch:suspend_listener(3)] - Suspend a running listener
* link:man:ranch:resume_listener(3)[ranch:resume_listener(3)] - Resume a suspended listener
* link:man:ranch:get_status(3)[ranch:get_status(3)] - Get a listener's running state

Connections:

* link:man:ranch:handshake(3)[ranch:handshake(3)] - Perform the transport handshake
* link:man:ranch:handshake_continue(3)[ranch:handshake_continue(3)] - Resume the paused transport handshake
* link:man:ranch:handshake_cancel(3)[ranch:handshake_cancel(3)] - Cancel the paused transport handshake
* link:man:ranch:recv_proxy_header(3)[ranch:recv_proxy_header(3)] - Receive the PROXY protocol header
* link:man:ranch:remove_connection(3)[ranch:remove_connection(3)] - Remove connection from the count

Options:

* link:man:ranch:get_max_connections(3)[ranch:get_max_connections(3)] - Get the max number of connections per connection supervisor
* link:man:ranch:get_protocol_options(3)[ranch:get_protocol_options(3)] - Get the current protocol options
* link:man:ranch:get_transport_options(3)[ranch:get_transport_options(3)] - Get the current transport options
* link:man:ranch:set_max_connections(3)[ranch:set_max_connections(3)] - Set the max number of connections per connection supervisor
* link:man:ranch:set_protocol_options(3)[ranch:set_protocol_options(3)] - Set the protocol options
* link:man:ranch:set_transport_options(3)[ranch:set_transport_options(3)] - Set the transport options

Introspection:

* link:man:ranch:get_addr(3)[ranch:get_addr(3)] - Get the listening address
* link:man:ranch:get_port(3)[ranch:get_port(3)] - Get the listening port
* link:man:ranch:info(3)[ranch:info(3)] - Overview of Ranch listeners
* link:man:ranch:procs(3)[ranch:procs(3)] - Retrieve pids from a listener
* link:man:ranch:wait_for_connections(3)[ranch:wait_for_connections(3)] - Wait for a specific number of connections

== Types

=== max_conns()

[source,erlang]
----
max_conns() = non_neg_integer() | infinity
----

Maximum number of connections allowed per connection supervisor.

This is a soft limit. The actual number of connections
might be slightly above the limit due to concurrency
when accepting new connections. Some connections may
also be removed from this count explicitly by the user
code.

=== opts()

[source,erlang]
----
opts() = any() | transport_opts(any())
----

Transport or socket options.

=== ref()

[source,erlang]
----
ref() = any()
----

Unique name used to refer to a listener.

=== transport_opts(SocketOpts)

[source,erlang]
----
transport_opts(SocketOpts) = #{
    alarms               => #{
                                term() => #{
                                    type := num_connections,
                                    threshold := non_neg_integer(),
                                    callback := fun((ref(), term(), pid(), [pid()]) -> any()),
                                    cooldown => non_neg_integer()
                                }
                            },
    connection_type      => worker | supervisor,
    handshake_timeout    => timeout(),
    max_connections      => max_conns(),
    logger               => module(),
    num_acceptors        => pos_integer(),
    num_conns_sups       => pos_integer(),
    post_listen_callback => fun((term()) -> ok | {error, term()}),
    shutdown             => timeout() | brutal_kill,
    socket_opts          => SocketOpts
}
----

Transport options.

The transport options are a combination of Ranch-specific
options and transport-specific socket options.

None of the options are required.

alarms (#{})::

Alarms to call a function when the number of connections tracked
by one connection supervisor reaches or exceeds a defined threshold.
+
The map keys are the alarm names, which can be any `term`. The
associated values are the respective alarm options, again in a map
with the following keys:

type:::

Must be set to `num_connections`.

threshold:::

Threshold value, which must be a `non_neg_integer`. When the
number of connections tracked by a single connection supervisor
reaches or exceeds this value, The alarm will trigger and call
the function defined in the `callback` key (see below).

callback:::

The alarm function, which takes the listener name, the alarm
name, the pid of the connection supervisor and a list of the pids
of all connection processes under that supervisor as arguments.
The return value is ignored.

cooldown (5000):::

The minimum time after which the alarm can be triggered again,
in milliseconds.

connection_type (worker)::

Type of process that will handle the connection.

handshake_timeout (5000)::

Maximum allowed time for the `ranch:handshake/1,2` call to finish.

logger (logger)::

The module that will be used to write log messages.

max_connections (1024)::

Maximum number of active connections per connection supervisor.
Soft limit. Use `infinity` to disable the limit entirely.

num_acceptors (10)::

Number of processes that accept connections.

num_conns_sups - see below::

Number of processes that supervise connection processes.
If not specified, defaults to be equal to `num_acceptors`.

post_listen_callback (fun(_ListenSock) -> ok end)::

A function which will be called after a listen socket has been successfully
created, with the socket as argument. It can be used to perform any
necessary setup steps on the socket.
+
If the callback function returns `ok`, the listener will start accepting
connections on the socket. If it returns `{error, Reason}`, the listener
will fail to start.

shutdown (5000)::

Maximum allowed time for children to stop on listener shutdown.

socket_opts::

Socket options to be used by `Transport:listen/1`. Please refer to the
documentation of the transport module you are using for more details.

== Changelog

* *2.1*: The `post_listen_callback` transport option was added.
* *2.0*: The type `transport_opts(SocketOpts)` was added.
* *2.0*: The function `ranch:accept_ack/1` was removed in favor of
         link:man:ranch:handshake(3)[ranch:handshake(3)].
* *2.0*: The option `max_connections` is now per connection supervisor.
* *2.0*: The `num_conns_sup` option was added.
* *2.0*: The `socket` option was removed.
* *2.0*: The `logger` option is no longer experimental. It now defaults
         to `logger` instead of `error_logger`.
* *2.0*: The `opt()` type was removed.
* *1.6*: The experimental `logger` option was added.
* *1.6*: The `opt()` type was deprecated in favor of the new `opts()` type.

== See also

link:man:ranch(7)[ranch(7)]
