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# gen_sctp (kernel v10.4)

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Interface to SCTP sockets.

This module provides functions for communicating over SCTP sockets. The implementation assumes that the OS kernel supports SCTP (RFC 2960) through the user-level Sockets API Extensions.

During development, this implementation was tested on:

- Linux Fedora Core 5.0 (kernel 2.6.15-2054 or later is needed)
- Solaris 10, 11

During OTP adaptation it was tested on:

- SUSE Linux Enterprise Server 10 (x86_64) kernel 2.6.16.27-0.6-smp, with lksctp-tools-1.0.6
- Briefly on Solaris 10
- SUSE Linux Enterprise Server 10 Service Pack 1 (x86_64) kernel 2.6.16.54-0.2.3-smp with lksctp-tools-1.0.7
- FreeBSD 8.2

This module was written for one-to-many style sockets (type `seqpacket`). With the addition of `peeloff/2`, one-to-one style sockets (type `stream`) were introduced.

Record definitions for this module can be found using:

    -include_lib("kernel/include/inet_sctp.hrl").

These record definitions use the "new" spelling 'adaptation', not the deprecated 'adaption', regardless of which spelling the underlying C API uses.

## SCTP Socket Options

The set of admissible SCTP socket options is by construction orthogonal to the sets of TCP, UDP, and generic `inet` options. Here are only options listed that are allowed for SCTP sockets.

Options can be set on the socket when calling `open/1,2`, and changed when calling `connect/4,5` or by calling `inet:setopts/2`. They can be retrieved using `inet:getopts/2`.

- `{mode, list|binary} | list | binary` - Determines the type of data returned from `recv/1,2` or in active mode data messages.

- `{active, false|true|once|N}`

  - If `false` (passive mode, the default), the caller must do an explicit `recv` call to retrieve the available data from the socket.

  - If `true|once|N` (active modes) received data or events are sent to the owning process. See `open/0..2` for the message format.

  - If `true` (fully active mode) there is no flow control.

    #### Note

    Note that this can cause the message queue to overflow causing for example the virtual machine to run out of memory and crash.

  - If `once`, only one message is automatically placed in the message queue, and the mode resets to passive. This provides flow control and the possibility for the receiver to listen for incoming SCTP data interleaved with other inter-process messages.

  - If `active` is specified as an integer `N` in the range -32768 to 32767 (inclusive), that number is added to the socket's data messages counter. If the result of the addition is negative, the counter is set to `0`. Once the counter reaches `0`, either through the delivery of messages or by being explicitly set with `inet:setopts/2`, the socket mode resets to passive (`{active, false}`). When a socket in `{active, N}` mode transitions to passive mode, the message `{sctp_passive, Socket}` is sent to the controlling process to notify that if it wants to receive more data messages from the socket, it must call `inet:setopts/2` to set the socket back into an active mode.

- `{tos, integer()}` - Sets the Type-Of-Service field on the IP datagrams that are sent, to the specified value. This effectively determines a prioritization policy for the outbound packets. The acceptable values are system-dependent.

- `{priority, integer()}` - A protocol-independent equivalent of `tos` above. Setting priority implies setting `tos` as well.

- `{dontroute, true|false}` - Defaults to `false`. If `true`, the kernel does not send packets through any gateway, but only sends them to directly connected hosts.

- `{reuseaddr, true|false}` - Defaults to `false`. If `true`, the local binding address `{IP,Port}` of the socket can be reused immediately. No waiting in state `CLOSE_WAIT` is performed (can be required for some types of servers).

- `{sndbuf, integer()}` - The size, in bytes, of the OS kernel send buffer for this socket. Sending errors would occur for datagrams larger than `val(sndbuf)`. Setting this option also adjusts the size of the driver buffer (see `buffer` above).

- `{recbuf, integer()}` - The size, in bytes, of the OS kernel receive buffer for this socket. Sending errors would occur for datagrams larger than `val(recbuf)`. Setting this option also adjusts the size of the driver buffer (see `buffer` above).

###

- `{non_block_send, boolean()}` - A send call that would otherwise block (hang), will instead immediately return with e.g. `{error, eagain}` if this option has been set to `true`. Defaults to `false`.

- `{sctp_module, module()}` - Overrides which callback module is used. Defaults to `inet_sctp` for IPv4 and `inet6_sctp` for IPv6.

- `{sctp_rtoinfo, #sctp_rtoinfo{}}`

      #sctp_rtoinfo{
            assoc_id = assoc_id(),
            initial  = integer(),
            max      = integer(),
            min      = integer()
      }

  Determines retransmission time-out parameters, in milliseconds, for the association(s) specified by `assoc_id`.

  `assoc_id = 0` (default) indicates the whole endpoint. See RFC 2960 and Sockets API Extensions for SCTP for the exact semantics of the field values.

- `{sctp_associnfo, #sctp_assocparams{}}`

      #sctp_assocparams{
            assoc_id                 = assoc_id(),
            asocmaxrxt               = integer(),
            number_peer_destinations = integer(),
            peer_rwnd                = integer(),
            local_rwnd               = integer(),
            cookie_life              = integer()
      }

  Determines association parameters for the association(s) specified by `assoc_id`.

  `assoc_id = 0` (default) indicates the whole endpoint. See Sockets API Extensions for SCTP for the discussion of their semantics. Rarely used.

- `{sctp_initmsg, #sctp_initmsg{}}`

      #sctp_initmsg{
           num_ostreams   = integer(),
           max_instreams  = integer(),
           max_attempts   = integer(),
           max_init_timeo = integer()
      }

  Determines the default parameters that this socket tries to negotiate with its peer while establishing an association with it. Is to be set after `open/*` but before the first `connect/*`. `#sctp_initmsg{}` can also be used as ancillary data with the first call of `send/*` to a new peer (when a new association is created).

  - `num_ostreams` - Number of outbound streams

  - `max_instreams` - Maximum number of inbound streams

  - `max_attempts` - Maximum retransmissions while establishing an association

  - `max_init_timeo` - Time-out, in milliseconds, for establishing an association

- `{sctp_autoclose, integer() >= 0}` - Determines the time, in seconds, after which an idle association is automatically closed. `0` means that the association is never automatically closed.

- `{sctp_nodelay, true|false}` - Turns off (`true`) / on (`false`) the Nagle algorithm for merging small packets into larger ones. This improves throughput at the expense of latency.

- `{sctp_disable_fragments, true|false}` - If `true`, induces an error on an attempt to send a message larger than the current PMTU size (which would require fragmentation/reassembling). Notice that message fragmentation does not affect the logical atomicity of its delivery; this option is provided for performance reasons only.

- `{sctp_i_want_mapped_v4_addr, true|false}` - Turns on|off automatic mapping of IPv4 addresses into IPv6 ones (if the socket address family is `AF_INET6`).

- `{sctp_maxseg, integer()}` - Determines the maximum chunk size if message fragmentation is used. If `0`, the chunk size is limited by the Path MTU only.

- `{sctp_primary_addr, #sctp_prim{}}`

      #sctp_prim{
            assoc_id = assoc_id(),
            addr     = {IP, Port}
      }
       IP = ip_address()
       Port = port_number()

  For the association specified by `assoc_id`, `{IP,Port}` must be one of the peer addresses. This option determines that the specified address is treated by the local SCTP stack as the primary address of the peer.

- `{sctp_set_peer_primary_addr, #sctp_setpeerprim{}}`

      #sctp_setpeerprim{
            assoc_id = assoc_id(),
            addr     = {IP, Port}
      }
       IP = ip_address()
       Port = port_number()

  When set, informs the peer to use `{IP, Port}` as the primary address of the local endpoint for the association specified by `assoc_id`.

- `{sctp_adaptation_layer, #sctp_setadaptation{}}`

      #sctp_setadaptation{
            adaptation_ind = integer()
      }

  When set, requests that the local endpoint uses the value specified by `adaptation_ind` as the Adaptation Indication parameter for establishing new associations. For details, see RFC 2960 and Sockets API Extensions for SCTP.

- `{sctp_peer_addr_params, #sctp_paddrparams{}}`

      #sctp_paddrparams{
            assoc_id   = assoc_id(),
            address    = {IP, Port},
            hbinterval = integer(),
            pathmaxrxt = integer(),
            pathmtu    = integer(),
            sackdelay  = integer(),
            flags      = list()
      }
      IP = ip_address()
      Port = port_number()

  Determines various per-address parameters for the association specified by `assoc_id` and the peer address `address` (the SCTP protocol supports multi-homing, so more than one address can correspond to a specified association).

  - `hbinterval` - Heartbeat interval, in milliseconds

  - `pathmaxrxt` - Maximum number of retransmissions before this address is considered unreachable (and an alternative address is selected)

  - `pathmtu` - Fixed Path MTU, if automatic discovery is disabled (see `flags` below)

  - `sackdelay` - Delay, in milliseconds, for SAC messages (if the delay is enabled, see `flags` below)

  - `flags` - The following flags are available:

    - `hb_enable` - Enables heartbeat

    - `hb_disable` - Disables heartbeat

    - `hb_demand` - Initiates heartbeat immediately

    - `pmtud_enable` - Enables automatic Path MTU discovery

    - `pmtud_disable` - Disables automatic Path MTU discovery

    - `sackdelay_enable` - Enables SAC delay

    - `sackdelay_disable` - Disables SAC delay

- `{sctp_default_send_param, #sctp_sndrcvinfo{}}`

      #sctp_sndrcvinfo{
            stream     = integer(),
            ssn        = integer(),
            flags      = list(),
            ppid       = integer(),
            context    = integer(),
            timetolive = integer(),
            tsn        = integer(),
            cumtsn     = integer(),
            assoc_id   = assoc_id()
      }

  `#sctp_sndrcvinfo{}` is used both in this socket option, and as ancillary data while sending or receiving SCTP messages. When set as an option, it provides default values for subsequent `send` calls on the association specified by `assoc_id`.

  `assoc_id = 0` (default) indicates the whole endpoint.

  The following fields typically must be specified by the sender:

  - `sinfo_stream` - Stream number (0-base) within the association to send the messages through;

  - `sinfo_flags` - The following flags are recognised:

    - `unordered` - The message is to be sent unordered

    - `addr_over` - The address specified in `send` overwrites the primary peer address

    - `abort` - Aborts the current association without flushing any unsent data

    - `eof` - Gracefully shuts down the current association, with flushing of unsent data

    Other fields are rarely used. For complete information, see RFC 2960 and Sockets API Extensions for SCTP.

- `{sctp_events, #sctp_event_subscribe{}}`

      #sctp_event_subscribe{
              data_io_event          = true | false,
              association_event      = true | false,
              address_event          = true | false,
              send_failure_event     = true | false,
              peer_error_event       = true | false,
              shutdown_event         = true | false,
              partial_delivery_event = true | false,
              adaptation_layer_event = true | false
      }

  This option determines which SCTP Events that are to be received (through `recv/*`) along with the data. The only exception is `data_io_event`, which enables or disables receiving of `#sctp_sndrcvinfo{}` ancillary data, not events. By default, all flags except `adaptation_layer_event` are enabled, although `sctp_data_io_event` and `association_event` are used by the driver itself and not exported to the user level.

- `{sctp_delayed_ack_time, #sctp_assoc_value{}}`

      #sctp_assoc_value{
            assoc_id    = assoc_id(),
            assoc_value = integer()
      }

  Rarely used. Determines the ACK time (specified by `assoc_value`, in milliseconds) for the specified association or the whole endpoint if `assoc_value = 0` (default).

- `{sctp_status, #sctp_status{}}`

      #sctp_status{
            assoc_id            = assoc_id(),
            state               = atom(),
            rwnd                = integer(),
            unackdata           = integer(),
            penddata            = integer(),
            instrms             = integer(),
            outstrms            = integer(),
            fragmentation_point = integer(),
            primary             = #sctp_paddrinfo{}
      }

  This option is read-only. It determines the status of the SCTP association specified by `assoc_id`. The following are the possible values of `state` (the state designations are mostly self-explanatory):

  - `sctp_state_empty` - Default. Means that no other state is active.

  - `sctp_state_closed`

  - `sctp_state_cookie_wait`

  - `sctp_state_cookie_echoed`

  - `sctp_state_established`

  - `sctp_state_shutdown_pending`

  - `sctp_state_shutdown_sent`

  - `sctp_state_shutdown_received`

  - `sctp_state_shutdown_ack_sent`

  Semantics of the other fields:

  - `sstat_rwnd` - Current receiver window size of the association

  - `sstat_unackdata` - Number of unacked data chunks

  - `sstat_penddata` - Number of data chunks pending receipt

  - `sstat_instrms` - Number of inbound streams

  - `sstat_outstrms` - Number of outbound streams

  - `sstat_fragmentation_point` - Message size at which SCTP fragmentation occurs

  - `sstat_primary` - Information on the current primary peer address (see below for the format of `#sctp_paddrinfo{}`)

- `{sctp_get_peer_addr_info, #sctp_paddrinfo{}}`

      #sctp_paddrinfo{
            assoc_id  = assoc_id(),
            address   = {IP, Port},
            state     = inactive | active | unconfirmed,
            cwnd      = integer(),
            srtt      = integer(),
            rto       = integer(),
            mtu       = integer()
      }
      IP = ip_address()
      Port = port_number()

  This option is read-only. It determines the parameters specific to the peer address specified by `address` within the association specified by `assoc_id`. Field `address` fmust be set by the caller; all other fields are filled in on return. If `assoc_id = 0` (default), the `address` is automatically translated into the corresponding association ID. This option is rarely used. For the semantics of all fields, see RFC 2960 and Sockets API Extensions for SCTP.

## SCTP Examples

Example of an Erlang SCTP server that receives SCTP messages and prints them on the standard output:

    -module(sctp_server).

    -export([server/0,server/1,server/2]).
    -include_lib("kernel/include/inet.hrl").
    -include_lib("kernel/include/inet_sctp.hrl").

    server() ->
        server(any, 2006).

    server([Host,Port]) when is_list(Host), is_list(Port) ->
        {ok, #hostent{h_addr_list = [IP|_]}} = inet:gethostbyname(Host),
        io:format("~w -> ~w~n", [Host, IP]),
        server([IP, list_to_integer(Port)]).

    server(IP, Port) when is_tuple(IP) orelse IP == any orelse IP == loopback,
                          is_integer(Port) ->
        {ok,S} = gen_sctp:open(Port, [{recbuf,65536}, {ip,IP}]),
        io:format("Listening on ~w:~w. ~w~n", [IP,Port,S]),
        ok     = gen_sctp:listen(S, true),
        server_loop(S).

    server_loop(S) ->
        case gen_sctp:recv(S) of
        {error, Error} ->
            io:format("SCTP RECV ERROR: ~p~n", [Error]);
        Data ->
            io:format("Received: ~p~n", [Data])
        end,
        server_loop(S).

Example of an Erlang SCTP client interacting with the above server. Note that in this example the client creates an association with the server with 5 outbound streams. Therefore, sending of `"Test 0"` over stream 0 succeeds, but sending of `"Test 5"` over stream 5 fails. The client then `abort`s the association, which results in that the corresponding event is received on the server side.

    -module(sctp_client).

    -export([client/0, client/1, client/2]).
    -include_lib("kernel/include/inet.hrl").
    -include_lib("kernel/include/inet_sctp.hrl").

    client() ->
        client([localhost]).

    client([Host]) ->
        client(Host, 2006);

    client([Host, Port]) when is_list(Host), is_list(Port) ->
        client(Host,list_to_integer(Port)),
        init:stop().

    client(Host, Port) when is_integer(Port) ->
        {ok,S}     = gen_sctp:open(),
        {ok,Assoc} = gen_sctp:connect
            (S, Host, Port, [{sctp_initmsg,#sctp_initmsg{num_ostreams=5}}]),
        io:format("Connection Successful, Assoc=~p~n", [Assoc]),

        io:write(gen_sctp:send(S, Assoc, 0, <<"Test 0">>)),
        io:nl(),
        timer:sleep(10000),
        io:write(gen_sctp:send(S, Assoc, 5, <<"Test 5">>)),
        io:nl(),
        timer:sleep(10000),
        io:write(gen_sctp:abort(S, Assoc)),
        io:nl(),

        timer:sleep(1000),
        gen_sctp:close(S).

A simple Erlang SCTP client that uses the `connect_init` API:

    -module(ex3).

    -export([client/4]).
    -include_lib("kernel/include/inet.hrl").
    -include_lib("kernel/include/inet_sctp.hrl").

    client(Peer1, Port1, Peer2, Port2)
      when is_tuple(Peer1), is_integer(Port1), is_tuple(Peer2), is_integer(Port2) ->
        {ok,S}     = gen_sctp:open(),
        SctpInitMsgOpt = {sctp_initmsg,#sctp_initmsg{num_ostreams=5}},
        ActiveOpt = {active, true},
        Opts = [SctpInitMsgOpt, ActiveOpt],
        ok = gen_sctp:connect(S, Peer1, Port1, Opts),
        ok = gen_sctp:connect(S, Peer2, Port2, Opts),
        io:format("Connections initiated~n", []),
        client_loop(S, Peer1, Port1, undefined, Peer2, Port2, undefined).

    client_loop(S, Peer1, Port1, AssocId1, Peer2, Port2, AssocId2) ->
        receive
            {sctp, S, Peer1, Port1, {_Anc, SAC}}
              when is_record(SAC, sctp_assoc_change), AssocId1 == undefined ->
                io:format("Association 1 connect result: ~p. AssocId: ~p~n",
                          [SAC#sctp_assoc_change.state,
                           SAC#sctp_assoc_change.assoc_id]),
                client_loop(S, Peer1, Port1, SAC#sctp_assoc_change.assoc_id,
                            Peer2, Port2, AssocId2);

            {sctp, S, Peer2, Port2, {_Anc, SAC}}
              when is_record(SAC, sctp_assoc_change), AssocId2 == undefined ->
                io:format("Association 2 connect result: ~p. AssocId: ~p~n",
                          [SAC#sctp_assoc_change.state, SAC#sctp_assoc_change.assoc_id]),
                client_loop(S, Peer1, Port1, AssocId1, Peer2, Port2,
                           SAC#sctp_assoc_change.assoc_id);

            {sctp, S, Peer1, Port1, Data} ->
                io:format("Association 1: received ~p~n", [Data]),
                client_loop(S, Peer1, Port1, AssocId1,
                            Peer2, Port2, AssocId2);

            {sctp, S, Peer2, Port2, Data} ->
                io:format("Association 2: received ~p~n", [Data]),
                client_loop(S, Peer1, Port1, AssocId1,
                            Peer2, Port2, AssocId2);

            Other ->
                io:format("Other ~p~n", [Other]),
                client_loop(S, Peer1, Port1, AssocId1,
                            Peer2, Port2, AssocId2)

        after 5000 ->
                ok
        end.

## See Also

`gen_tcp`, `gen_udp`, `inet`, RFC 2960 (Stream Control Transmission Protocol), Sockets API Extensions for SCTP

# Summary

## Types: Exported data types

assoc_id()

Association ID.

option()

SCTP Socket Option name and value, to set.

option_name()

SCTP Socket Option name, to get.

option_value()

SCTP Socket Option name and value, what you get.

sctp_socket()

Socket identifier returned from `open/*`.

## Types: Internal data types

elementary_option()
elementary_option_name()
record_option()
ro_option()

## Functions

abort(Socket, Assoc)

Abort an association.

close(Socket)

Close an SCTP socket.

connect(Socket, SockAddr, Opts)

Equivalent to `connect(Socket, SockAddr, Opts, infinity)`.

connect/4

Establish an association with a peer.

connect(Socket, Addr, Port, Opts, Timeout)

Establish an association with a peer.

connect_init(Socket, SockAddr, Opts)

Equivalent to `connect_init(Socket, SockAddr, Opts, infinity)`.

connect_init/4

Start establishing an association with a peer.

connect_init(Socket, Addr, Port, Opts, Timeout)

Start establishing an association with a peer.

connectx_init(Socket, SockAddrs, Opts)

Start establishing an association with a peer (multiple addresses).

connectx_init(Socket, Addrs, Port, Opts)

Equivalent to `connectx_init(Socket, Addrs, Port, Opts, infinity)`.

connectx_init(Socket, Addrs, Port, Opts, Timeout)

Start establishing an association with a peer (multiple addresses).

controlling_process(Socket, Pid)

Change the controlling process (owner) of a socket.

eof(Socket, Assoc)

Terminate an association gracefully.

error_string(ErrorNumber)

Translate an error number into a string or atom.

listen/2

Make an SCTP socket listen to incoming associations.

open()

Equivalent to `open([])`.

open/1

Create an SCTP socket.

open(Port, Opts)

Equivalent to `open([{port, Port} | Opts])`.

peeloff(Socket, Assoc)

Branch off an association into a new socket of type `stream`.

recv(Socket)

Equivalent to `recv(Socket, infinity)`.

recv(Socket, Timeout)

Receive a `Data` message.

send(Socket, SndRcvInfo, Data)

Send a `Data` message, full-featured.

send(Socket, Assoc, Stream, Data)

Send a data message.

# Types: Exported data types

# assoc_id()

    -type assoc_id() :: term().

Association ID.

An opaque term returned in, for example, `#sctp_paddr_change{}`, which identifies an association for an SCTP socket. The term is opaque except for the special value `0`, which has a meaning such as "the whole endpoint" or "all future associations".

# option()

    -type option() :: elementary_option() | record_option().

SCTP Socket Option name and value, to set.

# option_name()

    -type option_name() :: elementary_option_name() | record_option() | ro_option().

SCTP Socket Option name, to get.

# option_value()

    -type option_value() :: elementary_option() | record_option() | ro_option().

SCTP Socket Option name and value, what you get.

# sctp_socket()

    -type sctp_socket() :: port().

Socket identifier returned from `open/*`.

# Types: Internal data types

# elementary_option()

(not exported)

    -type elementary_option() ::
              {active, true | false | once | -32768..32767} |
              {buffer, non_neg_integer()} |
              {non_block_send, boolean()} |
              {debug, boolean()} |
              {dontroute, boolean()} |
              {exclusiveaddruse, boolean()} |
              {high_msgq_watermark, pos_integer()} |
              {linger, {boolean(), non_neg_integer()}} |
              {low_msgq_watermark, pos_integer()} |
              {mode, list | binary} |
              list | binary |
              {priority, non_neg_integer()} |
              {recbuf, non_neg_integer()} |
              {reuseaddr, boolean()} |
              {reuseport, boolean()} |
              {reuseport_lb, boolean()} |
              {ipv6_v6only, boolean()} |
              {sndbuf, non_neg_integer()} |
              {sctp_autoclose, non_neg_integer()} |
              {sctp_disable_fragments, boolean()} |
              {sctp_i_want_mapped_v4_addr, boolean()} |
              {sctp_maxseg, non_neg_integer()} |
              {sctp_nodelay, boolean()} |
              {tos, non_neg_integer()} |
              {tclass, non_neg_integer()} |
              {ttl, non_neg_integer()} |
              {recvtos, boolean()} |
              {recvtclass, boolean()} |
              {recvttl, boolean()}.

# elementary_option_name()

(not exported)

    -type elementary_option_name() ::
              active | buffer | non_block_send | debug | dontroute | exclusiveaddruse |
              high_msgq_watermark | linger | low_msgq_watermark | mode | priority | recbuf | reuseaddr |
              reuseport | reuseport_lb | ipv6_v6only | sctp_autoclose | sctp_disable_fragments |
              sctp_i_want_mapped_v4_addr | sctp_maxseg | sctp_nodelay | sndbuf | tos | tclass | ttl |
              recvtos | recvtclass | recvttl.

# record_option()

(not exported)

    -type record_option() ::
              {sctp_adaptation_layer, #sctp_setadaptation{adaptation_ind :: term()}} |
              {sctp_associnfo,
               #sctp_assocparams{assoc_id :: term(),
                                 asocmaxrxt :: term(),
                                 number_peer_destinations :: term(),
                                 peer_rwnd :: term(),
                                 local_rwnd :: term(),
                                 cookie_life :: term()}} |
              {sctp_default_send_param,
               #sctp_sndrcvinfo{stream :: term(),
                                ssn :: term(),
                                flags :: term(),
                                ppid :: term(),
                                context :: term(),
                                timetolive :: term(),
                                tsn :: term(),
                                cumtsn :: term(),
                                assoc_id :: term()}} |
              {sctp_delayed_ack_time, #sctp_assoc_value{assoc_id :: term(), assoc_value :: term()}} |
              {sctp_events,
               #sctp_event_subscribe{data_io_event :: term(),
                                     association_event :: term(),
                                     address_event :: term(),
                                     send_failure_event :: term(),
                                     peer_error_event :: term(),
                                     shutdown_event :: term(),
                                     partial_delivery_event :: term(),
                                     adaptation_layer_event :: term(),
                                     authentication_event :: term()}} |
              {sctp_initmsg,
               #sctp_initmsg{num_ostreams :: term(),
                             max_instreams :: term(),
                             max_attempts :: term(),
                             max_init_timeo :: term()}} |
              {sctp_peer_addr_params,
               #sctp_paddrparams{assoc_id :: term(),
                                 address :: term(),
                                 hbinterval :: term(),
                                 pathmaxrxt :: term(),
                                 pathmtu :: term(),
                                 sackdelay :: term(),
                                 flags :: term()}} |
              {sctp_primary_addr, #sctp_prim{assoc_id :: term(), addr :: term()}} |
              {sctp_rtoinfo,
               #sctp_rtoinfo{assoc_id :: term(), initial :: term(), max :: term(), min :: term()}} |
              {sctp_set_peer_primary_addr, #sctp_setpeerprim{assoc_id :: term(), addr :: term()}}.

# ro_option()

(not exported)

    -type ro_option() ::
              {sctp_get_peer_addr_info,
               #sctp_paddrinfo{assoc_id :: term(),
                               address :: term(),
                               state :: term(),
                               cwnd :: term(),
                               srtt :: term(),
                               rto :: term(),
                               mtu :: term()}} |
              {sctp_status,
               #sctp_status{assoc_id :: term(),
                            state :: term(),
                            rwnd :: term(),
                            unackdata :: term(),
                            penddata :: term(),
                            instrms :: term(),
                            outstrms :: term(),
                            fragmentation_point :: term(),
                            primary :: term()}}.

# Functions

# abort(Socket, Assoc)

    -spec abort(Socket, Assoc) -> ok | {error, inet:posix()}
                   when
                       Socket :: sctp_socket(),
                       Assoc ::
                           #sctp_assoc_change{state :: term(),
                                              error :: term(),
                                              outbound_streams :: term(),
                                              inbound_streams :: term(),
                                              assoc_id :: term()}.

Abort an association.

Abnormally terminates the association specified by `Assoc`, without flushing unsent data. The socket itself remains open. Other associations opened on this socket are still valid, and the socket can be used in new associations.

# close(Socket)

    -spec close(Socket) -> ok | {error, inet:posix()} when Socket :: sctp_socket().

Close an SCTP socket.

Closes the socket and all associations on it. The unsent data is flushed as for `eof/2`. The `close/1` call is blocking depending of the value of the `linger` socket [option]. If it is `false` or the linger time-out expires, the call returns and unsent data is flushed in the background.

# connect(Socket, SockAddr, Opts)

(since OTP 24.3)

    -spec connect(Socket, SockAddr, Opts) ->
                     {ok,
                      #sctp_assoc_change{state :: comm_up,
                                         error :: term(),
                                         outbound_streams :: term(),
                                         inbound_streams :: term(),
                                         assoc_id :: term()}} |
                     {error,
                      #sctp_assoc_change{state :: cant_assoc,
                                         error :: term(),
                                         outbound_streams :: term(),
                                         inbound_streams :: term(),
                                         assoc_id :: term()}} |
                     {error, inet:posix()}
                     when
                         Socket :: sctp_socket(),
                         SockAddr :: socket:sockaddr_in() | socket:sockaddr_in6(),
                         Opts :: [Opt :: option()].

Equivalent to `connect(Socket, SockAddr, Opts, infinity)`.

# connect/4

    -spec connect(Socket, SockAddr, Opts, Timeout) ->
                     {ok,
                      #sctp_assoc_change{state :: comm_up,
                                         error :: term(),
                                         outbound_streams :: term(),
                                         inbound_streams :: term(),
                                         assoc_id :: term()}} |
                     {error,
                      #sctp_assoc_change{state :: cant_assoc,
                                         error :: term(),
                                         outbound_streams :: term(),
                                         inbound_streams :: term(),
                                         assoc_id :: term()}} |
                     {error, inet:posix()}
                     when
                         Socket :: sctp_socket(),
                         SockAddr :: socket:sockaddr_in() | socket:sockaddr_in6(),
                         Opts :: [Opt :: option()],
                         Timeout :: timeout();
                 (Socket, Addr, Port, Opts) ->
                     {ok,
                      #sctp_assoc_change{state :: comm_up,
                                         error :: term(),
                                         outbound_streams :: term(),
                                         inbound_streams :: term(),
                                         assoc_id :: term()}} |
                     {error,
                      #sctp_assoc_change{state :: cant_assoc,
                                         error :: term(),
                                         outbound_streams :: term(),
                                         inbound_streams :: term(),
                                         assoc_id :: term()}} |
                     {error, inet:posix()}
                     when
                         Socket :: sctp_socket(),
                         Addr :: inet:ip_address() | inet:hostname(),
                         Port :: inet:port_number(),
                         Opts :: [Opt :: option()].

Establish an association with a peer.

With arguments `Addr` and `Port`, equivalent to `connect(Socket, Addr, Port, Opts, infinity)`.

With arguments `SockAddr` and `Opts` (since OTP 24.3), equivalent to `connect(Socket, Addr, Port, Opts, Timeout)` where `Addr` and `Port` are extracted from `SockAddr`.

# connect(Socket, Addr, Port, Opts, Timeout)

    -spec connect(Socket, Addr, Port, Opts, Timeout) ->
                     {ok,
                      #sctp_assoc_change{state :: comm_up,
                                         error :: term(),
                                         outbound_streams :: term(),
                                         inbound_streams :: term(),
                                         assoc_id :: term()}} |
                     {error,
                      #sctp_assoc_change{state :: cant_assoc,
                                         error :: term(),
                                         outbound_streams :: term(),
                                         inbound_streams :: term(),
                                         assoc_id :: term()}} |
                     {error, inet:posix()}
                     when
                         Socket :: sctp_socket(),
                         Addr :: inet:ip_address() | inet:hostname(),
                         Port :: inet:port_number(),
                         Opts :: [Opt :: option()],
                         Timeout :: timeout().

Establish an association with a peer.

Establishes a new association for socket `Socket`, with the peer (SCTP server socket) specified by `Addr` and `Port`. `Timeout`, is expressed in milliseconds. A socket can be associated with multiple peers. The socket has to be of type `seqpacket`.

#### Warning

Using a value of `Timeout` less than the maximum time taken by the OS to establish an association (around 4.5 minutes if the default values from RFC 4960 are used), can result in inconsistent or incorrect return values. This is especially relevant for associations sharing the same `Socket` (that is, source address and port), as the controlling process blocks until `connect/*` returns. `connect_init/*` provides an alternative without this limitation.

### `#sctp_assoc_change{}`

The result of `connect/*` is an `#sctp_assoc_change{}` event that contains, in particular, the new Association ID: l

    #sctp_assoc_change{
          state             = atom(),
          error             = integer(),
          outbound_streams  = integer(),
          inbound_streams   = integer(),
          assoc_id          = assoc_id()
    }

The number of outbound and inbound streams for the association can be set by giving an `sctp_initmsg` option to `connect` as in:

    connect(Socket, Ip, Port>,
          [{sctp_initmsg,#sctp_initmsg{num_ostreams=OutStreams,
                                       max_instreams=MaxInStreams}}])

All options `Opt` are set on the socket before the association is attempted. If an option record has undefined field values, the options record is first read from the socket for those values. In effect, `Opt` option records only need to define field values to change before connecting.

The returned `outbound_streams` and `inbound_streams` are the number of stream on the socket. These can be different from the requested values (`OutStreams` and `MaxInStreams`, respectively), if the peer requires lower values.

`state` can have the following values:

- `comm_up` - Association is successfully established. This indicates a successful completion of `connect`.

- `cant_assoc` - The association cannot be established (`connect/*` failure).

Other states do not normally occur in the output from `connect/*`. Rather, they can occur in `#sctp_assoc_change{}` events received instead of data from `recv/*` calls or socket messages. All of them indicate losing the association because of various error conditions, and are listed here for the sake of completeness:

- `comm_lost`

- `restart`

- `shutdown_comp`

The field `error` can provide more detailed diagnostics. Its value can be converted into a string using `error_string/1`.

# connect_init(Socket, SockAddr, Opts)

(since OTP 24.3)

    -spec connect_init(Socket, SockAddr, Opts) -> ok | {error, inet:posix()}
                          when
                              Socket :: sctp_socket(),
                              SockAddr :: socket:sockaddr_in() | socket:sockaddr_in6(),
                              Opts :: [option()].

Equivalent to `connect_init(Socket, SockAddr, Opts, infinity)`.

# connect_init/4

(since OTP R13B04)

    -spec connect_init(Socket, SockAddr, Opts, Timeout) -> ok | {error, inet:posix()}
                          when
                              Socket :: sctp_socket(),
                              SockAddr :: socket:sockaddr_in() | socket:sockaddr_in6(),
                              Opts :: [option()],
                              Timeout :: timeout();
                      (Socket, Addr, Port, Opts) -> ok | {error, inet:posix()}
                          when
                              Socket :: sctp_socket(),
                              Addr :: inet:ip_address() | inet:hostname(),
                              Port :: inet:port_number(),
                              Opts :: [option()].

Start establishing an association with a peer.

With arguments `Addr` and `Port`, equivalent to `connect_init(Socket, Addr, Port, Opts, infinity)`.

With arguments `SockAddr` and `Opts` (since OTP 24.3), equivalent to `connect_init(Socket, Addr, Port, Opts, Timeout)` where `Addr` and `Port` are extracted from `SockAddr`.

# connect_init(Socket, Addr, Port, Opts, Timeout)

(since OTP R13B04)

    -spec connect_init(Socket, Addr, Port, Opts, Timeout) -> ok | {error, inet:posix()}
                          when
                              Socket :: sctp_socket(),
                              Addr :: inet:ip_address() | inet:hostname(),
                              Port :: inet:port_number(),
                              Opts :: [option()],
                              Timeout :: timeout().

Start establishing an association with a peer.

Initiates a new association for socket `Socket`, with the peer (SCTP server socket) specified by `Addr` and `Port`.

The fundamental difference between this API and `connect/*` is that the return value is that of the underlying OS `connect(2)` system call. If `ok` is returned, the operation has been succesfully initiated, and the final result result of the association establishment is sent to the socket owner (controlling process) as an `#sctp_assoc_change{}` event. The socket owner must be prepared to receive this, the `recv/*` call has to be polled, depending on the value of the active option.

The parameters are as described for `connect/*`, except the `Timeout` value since for this function, the time-out only applies to the name resolving of `Addr` when it is a `inet:hostname/0`.

# connectx_init(Socket, SockAddrs, Opts)

(since OTP 25.0)

    -spec connectx_init(Socket, SockAddrs, Opts) -> {ok, assoc_id()} | {error, inet:posix()}
                           when
                               Socket :: sctp_socket(),
                               SockAddrs ::
                                   [{inet:ip_address(), inet:port_number()} |
                                    inet:family_address() |
                                    socket:sockaddr_in() |
                                    socket:sockaddr_in6()],
                               Opts :: [option()].

Start establishing an association with a peer (multiple addresses).

Similar to `connectx_init/5` except using socket addresses, and not having a `Timeout`. Since the addresses do not need lookup and the connect is non-blocking this call returns immediately.

The value of each socket address `port` must be the same or zero. At least one socket address must have a non-zero `port`

# connectx_init(Socket, Addrs, Port, Opts)

(since OTP 25.0)

    -spec connectx_init(Socket, Addrs, Port, Opts) -> {ok, assoc_id()} | {error, inet:posix()}
                           when
                               Socket :: sctp_socket(),
                               Addrs :: [inet:ip_address() | inet:hostname()],
                               Port :: inet:port_number() | atom(),
                               Opts :: [option()].

Equivalent to `connectx_init(Socket, Addrs, Port, Opts, infinity)`.

# connectx_init(Socket, Addrs, Port, Opts, Timeout)

(since OTP 25.0)

    -spec connectx_init(Socket, Addrs, Port, Opts, Timeout) -> {ok, assoc_id()} | {error, inet:posix()}
                           when
                               Socket :: sctp_socket(),
                               Addrs :: [inet:ip_address() | inet:hostname()],
                               Port :: inet:port_number() | atom(),
                               Opts :: [option()],
                               Timeout :: timeout().

Start establishing an association with a peer (multiple addresses).

Initiates a new association for socket `Socket`, with the peer (SCTP server socket) specified by `Addrs` and `Port`.

This API is similar to `connect_init/*` except the underlying OS `sctp_connectx(3)` system call is used, that accepts multiple destination addresses.

If successful, the association ID is returned which will be received in a subsequent `#sctp_assoc_change{}` event.

The parameters are as described in `connect_init/5`

#### Note

This API allows the OS to use all Addrs when establishing an association, but does not guarantee it will. Therefore, if the connection fails, the user may want to rotate the order of addresses for a subsequent call.

# controlling_process(Socket, Pid)

    -spec controlling_process(Socket, Pid) -> ok | {error, Reason}
                                 when
                                     Socket :: sctp_socket(),
                                     Pid :: pid(),
                                     Reason :: closed | not_owner | badarg | inet:posix().

Change the controlling process (owner) of a socket.

Assigns a new controlling process `Pid` to `Socket`. See `gen_udp:controlling_process/2`.

# eof(Socket, Assoc)

    -spec eof(Socket, Assoc) -> ok | {error, Reason}
                 when
                     Socket :: sctp_socket(),
                     Assoc ::
                         #sctp_assoc_change{state :: term(),
                                            error :: term(),
                                            outbound_streams :: term(),
                                            inbound_streams :: term(),
                                            assoc_id :: term()},
                     Reason :: term().

Terminate an association gracefully.

Gracefully terminates the association specified by `Assoc`, flushing all unsent data. The socket itself remains open. Other associations opened on this socket are still valid. The socket can be used in new associations.

# error_string(ErrorNumber)

    -spec error_string(ErrorNumber) -> ok | string() | unknown_error when ErrorNumber :: integer().

Translate an error number into a string or atom.

Translates an SCTP error number from, for example, `#sctp_remote_error{}` or `#sctp_send_failed{}` into an explanatory string, or into one of the atoms `ok` for no error, or `unknown_error` for an unrecognized integer.

# listen/2

    -spec listen(Socket, IsServer) -> ok | {error, Reason}
                    when Socket :: sctp_socket(), IsServer :: boolean(), Reason :: term();
                (Socket, Backlog) -> ok | {error, Reason}
                    when Socket :: sctp_socket(), Backlog :: integer(), Reason :: term().

Make an SCTP socket listen to incoming associations.

The socket will listen on the IP address(es) and port number it is bound to.

For type `seqpacket`, sockets (the default), the argument`IsServer` must be a `boolean/0`. In contrast to `stream` sockets, there is no listening queue length. If `IsServer` is `true`, the socket accepts new associations, that is, it becomes an SCTP server socket.

For type `stream` sockets, the argument `Backlog` sets the backlog queue length just like for TCP.

# open()

    -spec open() -> {ok, Socket} | {error, inet:posix()} when Socket :: sctp_socket().

Equivalent to `open([])`.

# open/1

    -spec open(Port) -> {ok, Socket} | {error, inet:posix()}
                  when Port :: inet:port_number(), Socket :: sctp_socket();
              (Opts) -> {ok, Socket} | {error, inet:posix()}
                  when
                      Opts :: [Opt],
                      Opt ::
                          {ifaddr, IP | SockAddr} |
                          {ip, IP} |
                          {port, Port} |
                          inet:address_family() |
                          {type, SockType} |
                          {netns, file:filename_all()} |
                          {bind_to_device, binary()} |
                          option(),
                      IP :: inet:ip_address() | any | loopback,
                      SockAddr :: socket:sockaddr_in() | socket:sockaddr_in6(),
                      Port :: inet:port_number(),
                      SockType :: seqpacket | stream,
                      Socket :: sctp_socket().

Create an SCTP socket.

With argument `Port`, equivalent to`open([{port, Port}]`.

Creates an SCTP socket and binds it to the local addresses specified by all `{ip,IP}` (or synonymously `{ifaddr,IP}`) options (this feature is called SCTP multi-homing). The default `IP` and `Port` are `any` and `0`, meaning bind to all local addresses on any free port.

It is also possible to use `{ifaddr, SockAddr}`, in which case it takes precedence over the `ip` and `port` options. These options can however be used to update the address and port of ifaddr (if they occur after ifaddr in the options list), although this is not recommended.

Other options:

- `inet6` - Sets up the socket for IPv6.

- `inet` - Sets up the socket for IPv4. This is the default.

A default set of socket options is used. In particular, the socket is opened in binary and passive mode, with SockType `seqpacket`, and with reasonably large kernel and driver buffers.

When the socket is in passive mode, data can be received through the `recv/1,2` calls.

When the socket is in active mode, data received data is delivered to the controlling process as messages:

    {sctp, Socket, FromIP, FromPort, {AncData, Data}}

See `recv/1,2` for a description of the message fields.

#### Note

This message format unfortunately differs slightly from the `gen_udp` message format with ancillary data, and from the `recv/1,2` return tuple format.

# open(Port, Opts)

    -spec open(Port :: integer(), Opts :: [term()]) -> _.

Equivalent to `open([{port, Port} | Opts])`.

# peeloff(Socket, Assoc)

(since OTP R15B)

    -spec peeloff(Socket, Assoc) -> {ok, NewSocket} | {error, Reason}
                     when
                         Socket :: sctp_socket(),
                         Assoc ::
                             #sctp_assoc_change{state :: term(),
                                                error :: term(),
                                                outbound_streams :: term(),
                                                inbound_streams :: term(),
                                                assoc_id :: term()} |
                             assoc_id(),
                         NewSocket :: sctp_socket(),
                         Reason :: term().

Branch off an association into a new socket of type `stream`.

The existing association `Assoc` in the socket `Socket` (that has to be of type `seqpacket`; one-to-many style) is branched off into a new socket `NewSocket` of type `stream` (one-to-one style).

The existing association argument `Assoc` can be a `#sctp_assoc_change{}` record as returned from, for example, `recv/*`, `connect/*`, or from a listening socket in active mode. It can also be just the field `assoc_id` `integer/0` from such a record.

# recv(Socket)

    -spec recv(Socket) -> {ok, {FromIP, FromPort, AncData, Data}} | {error, Reason}
                  when
                      Socket :: sctp_socket(),
                      FromIP :: inet:ip_address(),
                      FromPort :: inet:port_number(),
                      AncData ::
                          [#sctp_sndrcvinfo{stream :: term(),
                                            ssn :: term(),
                                            flags :: term(),
                                            ppid :: term(),
                                            context :: term(),
                                            timetolive :: term(),
                                            tsn :: term(),
                                            cumtsn :: term(),
                                            assoc_id :: term()} |
                           inet:ancillary_data()],
                      Data ::
                          binary() |
                          string() |
                          #sctp_sndrcvinfo{stream :: term(),
                                           ssn :: term(),
                                           flags :: term(),
                                           ppid :: term(),
                                           context :: term(),
                                           timetolive :: term(),
                                           tsn :: term(),
                                           cumtsn :: term(),
                                           assoc_id :: term()} |
                          #sctp_assoc_change{state :: term(),
                                             error :: term(),
                                             outbound_streams :: term(),
                                             inbound_streams :: term(),
                                             assoc_id :: term()} |
                          #sctp_paddr_change{addr :: term(),
                                             state :: term(),
                                             error :: term(),
                                             assoc_id :: term()} |
                          #sctp_adaptation_event{adaptation_ind :: term(), assoc_id :: term()},
                      Reason ::
                          inet:posix() |
                          #sctp_send_failed{flags :: term(),
                                            error :: term(),
                                            info :: term(),
                                            assoc_id :: term(),
                                            data :: term()} |
                          #sctp_paddr_change{addr :: term(),
                                             state :: term(),
                                             error :: term(),
                                             assoc_id :: term()} |
                          #sctp_pdapi_event{indication :: term(), assoc_id :: term()} |
                          #sctp_remote_error{error :: term(), assoc_id :: term(), data :: term()} |
                          #sctp_shutdown_event{assoc_id :: term()}.

Equivalent to `recv(Socket, infinity)`.

# recv(Socket, Timeout)

    -spec recv(Socket, Timeout) -> {ok, {FromIP, FromPort, AncData, Data}} | {error, Reason}
                  when
                      Socket :: sctp_socket(),
                      Timeout :: timeout(),
                      FromIP :: inet:ip_address(),
                      FromPort :: inet:port_number(),
                      AncData ::
                          [#sctp_sndrcvinfo{stream :: term(),
                                            ssn :: term(),
                                            flags :: term(),
                                            ppid :: term(),
                                            context :: term(),
                                            timetolive :: term(),
                                            tsn :: term(),
                                            cumtsn :: term(),
                                            assoc_id :: term()} |
                           inet:ancillary_data()],
                      Data ::
                          binary() |
                          string() |
                          #sctp_sndrcvinfo{stream :: term(),
                                           ssn :: term(),
                                           flags :: term(),
                                           ppid :: term(),
                                           context :: term(),
                                           timetolive :: term(),
                                           tsn :: term(),
                                           cumtsn :: term(),
                                           assoc_id :: term()} |
                          #sctp_assoc_change{state :: term(),
                                             error :: term(),
                                             outbound_streams :: term(),
                                             inbound_streams :: term(),
                                             assoc_id :: term()} |
                          #sctp_paddr_change{addr :: term(),
                                             state :: term(),
                                             error :: term(),
                                             assoc_id :: term()} |
                          #sctp_adaptation_event{adaptation_ind :: term(), assoc_id :: term()},
                      Reason ::
                          inet:posix() |
                          #sctp_send_failed{flags :: term(),
                                            error :: term(),
                                            info :: term(),
                                            assoc_id :: term(),
                                            data :: term()} |
                          #sctp_paddr_change{addr :: term(),
                                             state :: term(),
                                             error :: term(),
                                             assoc_id :: term()} |
                          #sctp_pdapi_event{indication :: term(), assoc_id :: term()} |
                          #sctp_remote_error{error :: term(), assoc_id :: term(), data :: term()} |
                          #sctp_shutdown_event{assoc_id :: term()}.

Receive a `Data` message.

Receives the `Data` message from any association of the socket. If the receive times out, `{error,timeout}` is returned. The default time-out is `infinity`. `FromIP` and `FromPort` indicate the address of the sender.

`AncData` is a list of ancillary data items received with the main `Data`. This list can be empty, or contain a single `#sctp_sndrcvinfo{}` record, if receiving ancillary data is enabled (see option `sctp_events`). Per default, it is enabled, as such ancillary data provides an easy way to determine the association and stream over which the message was received. (An alternative way is to get the association ID from `FromIP` and `FromPort` using socket option `sctp_get_peer_addr_info`, but this does still not give the stream number).

`AncData` may also contain ancillary data from the socket options `recvtos`, `recvtclass` or `recvttl`, if that is supported for the socket by the platform.

The `Data` received can, depending on the socket mode be a `binary/0` or a `list/0` of bytes (integers in the range `0` through `255`), or it can be an SCTP event.

### Possible SCTP events

- `#sctp_sndrcvinfo{}`

- `#sctp_assoc_change{}`

-     #sctp_paddr_change{
            addr      = {ip_address(),port()},
            state     = atom(),
            error     = integer(),
            assoc_id  = assoc_id()
      }

  Indicates change of the status of the IP address of the peer specified by `addr` within association `assoc_id`. Possible values of `state` (mostly self-explanatory) include:

  - `addr_unreachable`

  - `addr_available`

  - `addr_removed`

  - `addr_added`

  - `addr_made_prim`

  - `addr_confirmed`

  In case of an error (for example, `addr_unreachable`), the field `error` provides more diagnostics. In such cases, event `#sctp_paddr_change{}` is automatically converted into an `error` term returned by `recv`. The `error` field value can be converted into a string using `error_string/1`.

-     #sctp_send_failed{
            flags     = true | false,
            error     = integer(),
            info      = #sctp_sndrcvinfo{},
            assoc_id  = assoc_id()
            data      = binary()
      }

  The sender can receive this event if a send operation fails.

  - `flags` - A Boolean specifying if the data has been transmitted over the wire.

  - `error` - Provides extended diagnostics, use `error_string/1`.

  - `info` - The original `#sctp_sndrcvinfo{}` record used in the failed `send/*`.

  - `data` - The whole original data chunk attempted to be sent.

  In the current implementation of the Erlang/SCTP binding, this event is internally converted into an `error` term returned by `recv/*`.

-     #sctp_adaptation_event{
            adaptation_ind = integer(),
            assoc_id       = assoc_id()
      }

  Delivered when a peer sends an adaptation layer indication parameter (configured through option `sctp_adaptation_layer`). Notie that with the current implementation of the Erlang/SCTP binding, this event is disabled by default.

-     #sctp_pdapi_event{
            indication = sctp_partial_delivery_aborted,
            assoc_id   = assoc_id()
      }

  A partial delivery failure. In the current implementation of the Erlang/SCTP binding, this event is internally converted into an `error` term returned by `recv/*`.

# send(Socket, SndRcvInfo, Data)

    -spec send(Socket, SndRcvInfo, Data) -> ok | {error, Reason}
                  when
                      Socket :: sctp_socket(),
                      SndRcvInfo ::
                          #sctp_sndrcvinfo{stream :: term(),
                                           ssn :: term(),
                                           flags :: term(),
                                           ppid :: term(),
                                           context :: term(),
                                           timetolive :: term(),
                                           tsn :: term(),
                                           cumtsn :: term(),
                                           assoc_id :: term()},
                      Data :: binary() | iolist(),
                      Reason :: term().

Send a `Data` message, full-featured.

Sends the `Data` message with all sending parameters from a `#sctp_sndrcvinfo{}` record. This way, the user can specify the PPID (passed to the remote end) and context (passed to the local SCTP layer), which can be used, for example, for error identification. However, such a fine grained user control is rarely required. The function `send/4` is sufficient for most applications.

#### Note

Send is normally blocking, but if the socket option `non_block_send` is set to true, the function will return with e.g. {error, eagain} in the case when the function would otherwise block. It is then up to the user to try again later.

# send(Socket, Assoc, Stream, Data)

    -spec send(Socket, Assoc, Stream, Data) -> ok | {error, Reason}
                  when
                      Socket :: sctp_socket(),
                      Assoc ::
                          #sctp_assoc_change{state :: term(),
                                             error :: term(),
                                             outbound_streams :: term(),
                                             inbound_streams :: term(),
                                             assoc_id :: term()} |
                          assoc_id(),
                      Stream :: integer(),
                      Data :: binary() | iolist(),
                      Reason :: term().

Send a data message.

Sends a `Data` message on the association `Assoc` and `Stream`.

`Assoc` can be specified with a `#sctp_assoc_change{}` record from an association establishment, or as the `assoc_id/0` `integer/0` field value.

#### Note

Send is normally blocking, but if the socket option `non_block_send` is set to true, the function will return with e.g. {error, eagain} in the case when the function would otherwise block. It is then up to the user to try again later.