gen_sctp

CONTENTS

• DATA TYPES
• EXPORTS
• SCTP SOCKET OPTIONS
• SCTP EXAMPLES
• SEE ALSO
• AUTHORS

DATA TYPES

assoc_id()

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

charlist() = [char()]

iolist() = [char() | binary()]

ip_address()

Represents an address of an SCTP socket. It is a tuple as explained in inet(3).

port_number() = 0 .. 65535

posix()

See inet(3); POSIX Error Codes.

sctp_option()

One of the SCTP Socket Options.

sctp_socket()

Socket identifier returned from open/*.

timeout() = int() | infinity

Timeout used in SCTP connect and receive calls.

SCTP SOCKET OPTIONS

The set of admissible SCTP socket options is by construction orthogonal to the sets of TCP, UDP and generic INET options: only those options which are explicitly listed below are allowed for SCTP sockets. Options can be set on the socket using gen_sctp:open/1,2 or inet:setopts/2, retrieved using inet:getopts/2, and when calling gen_sctp:connect/4,5 options can be changed.

{mode, list|binary}or just list or binary.

Determines the type of data returned from gen_sctp:recv/1,2.

{active, true|false|once}

• If false (passive mode, the default), the caller needs to do an explicit gen_sctp:recv call in order to retrieve the available data from the socket.

• If true (full active mode), the pending data or events are sent to the owning process.

  NB: This can cause the message queue to overflow, as there is no way to throttle the sender in this case (no flow control!).

• If once, only one message is automatically placed in the message queue, after that the mode is automatically re-set to passive. This provides flow control as well as the possibility for the receiver to listen for its incoming SCTP data interleaved with other inter-process messages.

{buffer, int()}

Determines the size of the user-level software buffer used by the SCTP driver. Not to be confused with sndbuf and recbuf options which correspond to the kernel socket buffers. It is recommended to have val(buffer) >= max(val(sndbuf),val(recbuf)). In fact, the val(buffer) is automatically set to the above maximum when sndbuf or recbuf values are set.

{tos, int()}

Sets the Type-Of-Service field on the IP datagrams being sent, to the given value, which effectively determines a prioritization policy for the outbound packets. The acceptable values are system-dependent. TODO: we do not provide symbolic names for these values yet.

{priority, int()}

A protocol-independent equivalent of tos above. Setting priority implies setting tos as well.

{dontroute, true|false}

By default false. If true, the kernel does not send packets via any gateway, only sends them to directly connected hosts.

{reuseaddr, true|false}

By default false. If true, the local binding address {IP,Port} of the socket can be re-used immediately: no waiting in the CLOSE_WAIT state is performed (may be required for high-throughput servers).

{linger, {true|false, int()}

Determines the timeout in seconds for flushing unsent data in the gen_sctp:close/1 socket call. If the 1st component of the value tuple is false, the 2nd one is ignored, which means that gen_sctp:close/1 returns immediately not waiting for data to be flushed. Otherwise, the 2nd component is the flushing time-out in seconds.

{sndbuf, int()}

The size, in bytes, of the *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, int()}

The size, in bytes, of the *kernel* recv 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).

{sctp_rtoinfo, #sctp_rtoinfo{}}

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

Determines re-transmission time-out parameters, in milliseconds, for the association(s) given by assoc_id. If assoc_id = 0 (default) indicates the whole endpoint. See RFC2960 and Sockets API Extensions for SCTP for the exact semantics of the fields values.

{sctp_associnfo, #sctp_assocparams{}}

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

Determines association parameters for the association(s) given 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   = int(),
       max_instreams  = int(),
       max_attempts   = int(),
       max_init_timeo = int()
  }        

Determines the default parameters which this socket attempts to negotiate with its peer while establishing an association with it. Should 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: max number of in-bound streams;

• max_attempts: max re-transmissions while establishing an association;

• max_init_timeo: time-out in milliseconds for establishing an association.

{sctp_autoclose, int()|infinity}

Determines the time (in seconds) after which an idle association is automatically closed.

{sctp_nodelay, true|false}

Turns on|off the Nagle algorithm for merging small packets into larger ones (which improves throughput at the expense of latency).

{sctp_disable_fragments, true|false}

If true, induces an error on an attempt to send a message which is larger than the current PMTU size (which would require fragmentation/re-assembling). Note 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, int()}

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 given by assoc_id, {IP,Port} must be one of the peer's addresses. This option determines that the given address is treated by the local SCTP stack as the peer's primary address.

{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 that it should use {IP, Port} as the primary address of the local endpoint for the association given by assoc_id.

{sctp_adaptation_layer, #sctp_setadaptation{}}

  #sctp_setadaptation{
        adaptation_ind = int()
  }        

When set, requests that the local endpoint uses the value given by adaptation_ind as the Adaptation Indication parameter for establishing new associations. See RFC2960 and Sockets API Extenstions for SCTP for more details.

{sctp_peer_addr_params, #sctp_paddrparams{}}

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

This option determines various per-address parameters for the association given by assoc_id and the peer address address (the SCTP protocol supports multi-homing, so more than 1 address can correspond to a given association).

• hbinterval: heartbeat interval, in milliseconds;

• pathmaxrxt: max 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: enable heartbeat;

  • hb_disable: disable heartbeat;

  • hb_demand: initiate heartbeat immediately;

  • pmtud_enable: enable automatic Path MTU discovery;

  • pmtud_disable: disable automatic Path MTU discovery;

  • sackdelay_enable: enable SAC delay;

  • sackdelay_disable: disable SAC delay.

{sctp_default_send_param, #sctp_sndrcvinfo{}}

  #sctp_sndrcvinfo{
        stream     = int(),
        ssn        = int(),
        flags      = list(),
        ppid       = int(),
        context    = int(),
        timetolive = int(),
        tsn        = int(),
        cumtsn     = int(),
        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 a default values for subsequent gen_sctp:sendcalls on the association given by assoc_id. assoc_id = 0 (default) indicates the whole endpoint. The following fields typically need to 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 gen_sctp:send overwrites the primary peer address;

  • abort: abort the current association without flushing any unsent data;

  • eof: gracefully shut down the current association, with flushing of unsent data.

  Other fields are rarely used. See RFC2960 and Sockets API Extensions for SCTP for full information.

{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 are to be received (via 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 = int()
  }        

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

{sctp_status, #sctp_status{}}

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

This option is read-only. It determines the status of the SCTP association given by assoc_id. Possible values of state follows. The state designations are mostly self-explanatory. state_empty is the default which means that no other state is active:

• sctp_state_empty

• 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

The semantics of other fields is the following:

• sstat_rwnd: the association peer's current receiver window size;

• 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 will occur;

• 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,
        cwnd      = int(),
        srtt      = int(),
        rto       = int(),
        mtu       = int()
  }
  IP = ip_address()
  Port = port_number()        

This option is read-only. It determines the parameters specific to the peer's address given by address within the association given by assoc_id. The address field must 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; see RFC2960 and Sockets API Extensions for SCTP for the semantics of all fields.

SCTP EXAMPLES

• Example of an Erlang SCTP Server which 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([{ip,IP},{port,Port}],[{recbuf,65536}]),
        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 which interacts with the above Server. Note that in this example, the Client creates an association with the Server with 5 outbound streams. For this reason, 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 the corresponding Event being 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 very simple Erlang SCTP Client which 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

inet(3), gen_tcp(3), gen_upd(3), RFC2960 (Stream Control Transmission Protocol), Sockets API Extensions for SCTP.