gen_sctp(3)

NAME
gen_sctp - Interface to SCTP sockets.

DESCRIPTION

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 aborts 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);
            {sctp_error, S, _Peer, _Port, {_Anc, Error}} ->
                io:format("SCTP error: ~p~n", [Error]),
                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

DATA TYPES

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".
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() :: 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.
option() :: elementary_option() | record_option().

    SCTP Socket Option name and value, to set.
option_name() :: elementary_option_name() | record_option() | ro_option().

    SCTP Socket Option name, to get.
option_value() :: elementary_option() | record_option() | ro_option().

    SCTP Socket Option name and value, what you get.
record_option() :: {sctp_adaptation_layer, #sctp_setadaptation{}} | {sctp_associnfo, #sctp_assocparams{}} | {sctp_default_send_param, #sctp_sndrcvinfo{}} | {sctp_delayed_ack_time, #sctp_assoc_value{}} | {sctp_events, #sctp_event_subscribe{}} | {sctp_initmsg, #sctp_initmsg{}} | {sctp_peer_addr_params, #sctp_paddrparams{}} | {sctp_primary_addr, #sctp_prim{}} | {sctp_rtoinfo, #sctp_rtoinfo{}} | {sctp_set_peer_primary_addr, #sctp_setpeerprim{}}.
ro_option() :: {sctp_get_peer_addr_info, #sctp_paddrinfo{}} | {sctp_status, #sctp_status{}}.
sctp_socket() :: port().

    Socket identifier returned from open/*.

FUNCTIONS

abort(Socket, Assoc) -> ok | {error, inet:posix()} when Socket :: sctp_socket(), Assoc :: #sctp_assoc_change{}.

    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) -> 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, Timeout) -> {ok, #sctp_assoc_change{state :: comm_up}} | {error, #sctp_assoc_change{state :: cant_assoc}} | {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, #sctp_assoc_change{state :: cant_assoc}} | {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) -> {ok, #sctp_assoc_change{state :: comm_up}} | {error, #sctp_assoc_change{state :: cant_assoc}} | {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, 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) -> 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) -> {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, 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) -> 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) -> ok | {error, Reason} when Socket :: sctp_socket(), Assoc :: #sctp_assoc_change{}, 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) -> 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(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 argumentIsServer 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(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 toopen([{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, received data is delivered to the controlling process as messages:

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

    Error-related events - such as #sctp_send_failed{}, #sctp_pdapi_event{}, and #sctp_remote_error{} - are also delivered to the controlling process as messages, but use a different tuple tag:

        {sctp_error, 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.
peeloff(Socket, Assoc) -> {ok, NewSocket} | {error, Reason} when Socket :: sctp_socket(), Assoc :: #sctp_assoc_change{} | 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, 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{} | inet:ancillary_data()], Data :: binary() | string() | #sctp_sndrcvinfo{} | #sctp_assoc_change{} | #sctp_paddr_change{} | #sctp_adaptation_event{}, Reason :: inet:posix() | #sctp_send_failed{} | #sctp_paddr_change{} | #sctp_pdapi_event{} | #sctp_remote_error{} | #sctp_shutdown_event{}.

    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) -> ok | {error, Reason} when Socket :: sctp_socket(), SndRcvInfo :: #sctp_sndrcvinfo{}, 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) -> ok | {error, Reason} when Socket :: sctp_socket(), Assoc :: #sctp_assoc_change{} | 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.