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NAME

       gen_sctp - The gen_sctp module provides functions for communicating with sockets using the
       SCTP protocol.

DESCRIPTION

       The gen_sctp module provides functions for  communicating  with  sockets  using  the  SCTP
       protocol.  The  implementation  assumes that the OS kernel supports SCTP (RFC2960) 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), and on 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, and later on 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, and later also on 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 the gen_sctp 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.

CONTENTS

         * DATA TYPES

         * EXPORTS

         * SCTP SOCKET OPTIONS

         * SCTP EXAMPLES

         * SEE ALSO

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".

       option() = {active, true | false | once}
                | {buffer, integer() >= 0}
                | {dontroute, boolean()}
                | {high_msgq_watermark, integer() >= 1}
                | {linger, {boolean(), integer() >= 0}}
                | {low_msgq_watermark, integer() >= 1}
                | {mode, list | binary}
                | list
                | binary
                | {priority, integer() >= 0}
                | {recbuf, integer() >= 0}
                | {reuseaddr, boolean()}
                | {ipv6_v6only, boolean()}
                | {sctp_adaptation_layer, #sctp_setadaptation{}}
                | {sctp_associnfo, #sctp_assocparams{}}
                | {sctp_autoclose, integer() >= 0}
                | {sctp_default_send_param, #sctp_sndrcvinfo{}}
                | {sctp_delayed_ack_time, #sctp_assoc_value{}}
                | {sctp_disable_fragments, boolean()}
                | {sctp_events, #sctp_event_subscribe{}}
                | {sctp_get_peer_addr_info, #sctp_paddrinfo{}}
                | {sctp_i_want_mapped_v4_addr, boolean()}
                | {sctp_initmsg, #sctp_initmsg{}}
                | {sctp_maxseg, integer() >= 0}
                | {sctp_nodelay, boolean()}
                | {sctp_peer_addr_params, #sctp_paddrparams{}}
                | {sctp_primary_addr, #sctp_prim{}}
                | {sctp_rtoinfo, #sctp_rtoinfo{}}
                | {sctp_set_peer_primary_addr, #sctp_setpeerprim{}}
                | {sctp_status, #sctp_status{}}
                | {sndbuf, integer() >= 0}
                | {tos, integer() >= 0}

              One of the SCTP Socket Options.

       option_name() = active
                     | buffer
                     | dontroute
                     | high_msgq_watermark
                     | linger
                     | low_msgq_watermark
                     | mode
                     | priority
                     | recbuf
                     | reuseaddr
                     | ipv6_v6only
                     | sctp_adaptation_layer
                     | sctp_associnfo
                     | sctp_autoclose
                     | sctp_default_send_param
                     | sctp_delayed_ack_time
                     | sctp_disable_fragments
                     | sctp_events
                     | sctp_get_peer_addr_info
                     | sctp_i_want_mapped_v4_addr
                     | sctp_initmsg
                     | sctp_maxseg
                     | sctp_nodelay
                     | sctp_peer_addr_params
                     | sctp_primary_addr
                     | sctp_rtoinfo
                     | sctp_set_peer_primary_addr
                     | sctp_status
                     | sndbuf
                     | tos

       sctp_socket()

              Socket identifier returned from open/*.

EXPORTS

       abort(Socket, Assoc) -> ok | {error, inet:posix()}

              Types:

                 Socket = sctp_socket()
                 Assoc = #sctp_assoc_change{}

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

       close(Socket) -> ok | {error, inet:posix()}

              Types:

                 Socket = sctp_socket()

              Completely closes the socket and all associations on it. The unsent data is flushed
              as in eof/2. The close/1 call is blocking or otherwise depending of  the  value  of
              the  linger  socket option. If close does not linger or linger timeout expires, the
              call returns and the data is flushed in the background.

       connect(Socket, Addr, Port, Opts) ->
                  {ok, Assoc} | {error, inet:posix()}

              Types:

                 Socket = sctp_socket()
                 Addr = inet:ip_address() | inet:hostname()
                 Port = inet:port_number()
                 Opts = [Opt :: option()]
                 Assoc = #sctp_assoc_change{}

              Same as connect(Socket, Addr, Port, Opts, infinity).

       connect(Socket, Addr, Port, Opts, Timeout) ->
                  {ok, Assoc} | {error, inet:posix()}

              Types:

                 Socket = sctp_socket()
                 Addr = inet:ip_address() | inet:hostname()
                 Port = inet:port_number()
                 Opts = [Opt :: option()]
                 Timeout = timeout()
                 Assoc = #sctp_assoc_change{}

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

              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 (i.e. source address and port)
              since the  controlling  process  blocks  until  connect/*  returns.  connect_init/*
              provides an alternative not subject to this limitation.

              The  result  of  connect/*  is  an  #sctp_assoc_change{}  event  which contains, in
              particular, the new Association ID.

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

              The number of outbound and inbound streams 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 got undefined field values, the options record is first read from
              the socket for those values. In effect, Opt option records only define field values
              to change before connecting.

              The returned outbound_streams and inbound_streams are the actual stream numbers  on
              the  socket,  which  may  be  different  from  the requested values (OutStreams and
              MaxInStreams respectively) if the peer requires lower values.

              The following values of state are possible:

                * comm_up: association successfully  established.  This  indicates  a  successful
                  completion of connect.

                * cant_assoc: association cannot be established (connect/* failure).

              All  other  states do not normally occur in the output from connect/*. Rather, they
              may occur in #sctp_assoc_change{} events received instead of data in recv/*  calls.
              All  of  them  indicate losing the association due to various error conditions, and
              are listed here for the sake of completeness. The  error  field  may  provide  more
              detailed diagnostics.

                * comm_lost;

                * restart;

                * shutdown_comp.

       connect_init(Socket, Addr, Port, Opts) ->
                       ok | {error, inet:posix()}

              Types:

                 Socket = sctp_socket()
                 Addr = inet:ip_address() | inet:hostname()
                 Port = inet:port_number()
                 Opts = [option()]

              Same as connect_init(Socket, Addr, Port, Opts, infinity).

       connect_init(Socket, Addr, Port, Opts, Timeout) ->
                       ok | {error, inet:posix()}

              Types:

                 Socket = sctp_socket()
                 Addr = inet:ip_address() | inet:hostname()
                 Port = inet:port_number()
                 Opts = [option()]
                 Timeout = timeout()

              Initiates  a  new  association  for  the  socket Socket, with the peer (SCTP server
              socket) given 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 then the
              result of the association establishement is received by the calling process  as  an
              #sctp_assoc_change{}  event.  The calling process must be prepared to receive this,
              or poll for it using recv/* depending on the value of the active option.

              The parameters are as described in connect/*, with the  exception  of  the  Timeout
              value.

              The timer associated with Timeout only supervises IP resolution of Addr

       controlling_process(Socket, Pid) -> ok | {error, Reason}

              Types:

                 Socket = sctp_socket()
                 Pid = pid()
                 Reason = closed | not_owner | inet:posix()

              Assigns   a   new  controlling  process  Pid  to  Socket.  Same  implementation  as
              gen_udp:controlling_process/2.

       eof(Socket, Assoc) -> ok | {error, Reason}

              Types:

                 Socket = sctp_socket()
                 Assoc = #sctp_assoc_change{}
                 Reason = term()

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

       listen(Socket, IsServer) -> ok | {error, Reason}

       listen(Socket, Backlog) -> ok | {error, Reason}

              Types:

                 Socket = sctp_socket()
                 Backlog = integer()
                 Reason = term()

              Sets up a socket to listen on the IP address and port number it is bound to.

              For type seqpacket sockets (the  default)  IsServer  must  be  true  or  false.  In
              contrast  to  TCP,  in SCTP there is no listening queue length. If IsServer is true
              the socket accepts new associations, i.e. it will become an SCTP server socket.

              For type stream sockets Backlog defines the backlog queue length just like in TCP.

       open() -> {ok, Socket} | {error, inet:posix()}

       open(Port) -> {ok, Socket} | {error, inet:posix()}

       open(Opts) -> {ok, Socket} | {error, inet:posix()}

       open(Port, Opts) -> {ok, Socket} | {error, inet:posix()}

              Types:

                 Opts = [Opt]
                 Opt = {ip, IP}
                     | {ifaddr, IP}
                     | inet:address_family()
                     | {port, Port}
                     | {type, SockType}
                     | option()
                 IP = inet:ip_address() | any | loopback
                 Port = inet:port_number()
                 SockType = seqpacket | stream
                 Socket = sctp_socket()

              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
              one free port.

              Other options are:

                inet6:
                  Set up the socket for IPv6.

                inet:
                  Set 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.

       peeloff(Socket, Assoc) -> {ok, NewSocket} | {error, Reason}

              Types:

                 Socket = sctp_socket()
                 Assoc = #sctp_assoc_change{} | assoc_id()
                 NewSocket = sctp_socket()
                 Reason = term()

              Branch off an existing association Assoc in a socket Socket of type seqpacket (one-
              to-many style) into a new socket NewSocket of type stream (one-to-one style).

              The existing association argument Assoc can  be  either  a   #sctp_assoc_change{}
              record  as returned from e.g recv/*, connect/* or from a listening socket in active
              mode. Or it can be just the field assoc_id integer from such a record.

       recv(Socket) ->
               {ok, {FromIP, FromPort, AncData, Data}} | {error, Reason}

       recv(Socket, Timeout) ->
               {ok, {FromIP, FromPort, AncData, Data}} | {error, Reason}

              Types:

                 Socket = sctp_socket()
                 Timeout = timeout()
                 FromIP = inet:ip_address()
                 FromPort = inet:port_number()
                 AncData = [#sctp_sndrcvinfo{}]
                 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{}

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

              AncData is a list of Ancillary Data items which may be received along with the main
              Data.  This  list  can  be empty, or contain a single #sctp_sndrcvinfo{} record, if
              receiving of such ancillary data is enabled (see option sctp_events). It is enabled
              by  default,  since  such  ancillary  data  provide  an easy way of determining the
              association and stream over which the message has been  received.  (An  alternative
              way  would  be  to  get  the  Association ID from the FromIP and FromPort using the
              sctp_get_peer_addr_info socket option, but this would still not produce the  Stream
              number).

              The  actual  Data  received  may be a binary(), or list() of bytes (integers in the
              range 0 through 255) depending on the socket mode, or an SCTP Event. The  following
              SCTP Events are possible:

                * #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 peer's IP address given by addr within
                  the 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  (e.g.  addr_unreachable),  the  error  field  provides
                  additional diagnostics.  In  such  cases,  the  #sctp_paddr_change{}  Event  is
                  automatically converted into an error term returned by gen_sctp: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 may receive this event if a send operation fails.  The  flags  is  a
                  Boolean  specifying  whether  the  data have actually been transmitted over the
                  wire; error provides extended diagnostics,  use  error_string/1;  info  is  the
                  original  #sctp_sndrcvinfo{}  record used in the failed send/*, and data is 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 the  option  sctp_adaptation_layer).  Note  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}

              Types:

                 Socket = sctp_socket()
                 SndRcvInfo = #sctp_sndrcvinfo{}
                 Data = binary() | iolist()
                 Reason = term()

              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 level of user control is rarely required. The
              send/4 function is sufficient for most applications.

       send(Socket, Assoc, Stream, Data) -> ok | {error, Reason}

              Types:

                 Socket = sctp_socket()
                 Assoc = #sctp_assoc_change{} | assoc_id()
                 Stream = integer()
                 Data = binary() | iolist()
                 Reason = term()

              Sends Data message over an existing association and given stream.

       error_string(ErrorNumber) -> ok | string() | unknown_error

              Types:

                 ErrorNumber = integer()

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

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.

         {tos, integer()}:
           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, integer()}:
           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).

         {sndbuf, integer()}:
           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, integer()}:
           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_module, module()}:
           Override  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   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               = integer(),
                 number_peer_destinations = integer(),
                 peer_rwnd                = integer(),
                 local_rwnd               = integer(),
                 cookie_life              = integer()
           }

           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   = integer(),
                max_instreams  = integer(),
                max_attempts   = integer(),
                max_init_timeo = integer()
           }

           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, 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  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, 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 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 = integer()
           }

           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 = integer(),
                 pathmaxrxt = integer(),
                 pathmtu    = integer(),
                 sackdelay  = integer(),
                 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     = 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 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 = integer()
           }

           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                = 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  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      = 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'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(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 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(3erl),  gen_tcp(3erl), gen_udp(3erl), RFC2960 (Stream Control Transmission Protocol),
       Sockets API Extensions for SCTP.