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# diameter_sctp (diameter v2.5.1)

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Diameter transport over SCTP.

This module implements diameter transport over SCTP using `gen_sctp`. It can be specified as the value of a transport_module option to `diameter:add_transport/2` and implements the behaviour documented in `diameter_transport`.

## SEE ALSO

`diameter`, `diameter_transport`, `gen_sctp`, `inet`

# Summary

## Types

connect_option()
listen_option()
match()
option()

## Functions

start(TypeRef, Svc, Options)

The start function required by `diameter_transport`.

# Types

# connect_option()

(since OTP R14B03)

    -type connect_option() :: {raddr, inet:ip_address()} | {rport, inet:port_number()} | option() | term().

# listen_option()

(since OTP R14B03)

    -type listen_option() :: {accept, match()} | option() | term().

# match()

(not exported) (since OTP R14B03)

    -type match() :: inet:ip_address() | string() | [match()].

# option()

(not exported) (since OTP R14B03)

    -type option() ::
              {sender, boolean()} |
              sender |
              {packet, boolean() | raw} |
              {message_cb, false | diameter:eval()}.

# Functions

# start(TypeRef, Svc, Options)

(since OTP R14B03)

    -spec start({accept, Ref},
                #diameter_service{pid :: term(), capabilities :: term(), applications :: term()},
                [listen_option()]) ->
                   {ok, pid(), [inet:ip_address()]}
                   when Ref :: diameter:transport_ref();
               ({connect, Ref},
                #diameter_service{pid :: term(), capabilities :: term(), applications :: term()},
                [connect_option()]) ->
                   {ok, pid(), [inet:ip_address()]}
                   when Ref :: diameter:transport_ref().

The start function required by `diameter_transport`.

Options `raddr` and `rport` specify the remote address and port for a connecting transport and not valid for a listening transport: the former is required while latter defaults to 3868 if unspecified. Multiple `raddr` options can be specified, in which case the connecting transport in question attempts each in sequence until an association is established.

Option `accept` specifies remote addresses for a listening transport and is not valid for a connecting transport. If specified, a remote address that does not match one of the specified addresses causes the association to be aborted. Multiple `accept` options can be specified. A string-valued `Match` that does not parse as an address is interpreted as a regular expression.

Option `unordered` specifies whether or not to use unordered delivery, integer `N` being equivalent to `N =< OS`, where `OS` is the number of outbound streams negotiated on the association in question. Regardless of configuration, sending is ordered on stream 0 until reception of a second incoming message, to ensure that a peer receives capabilities exchange messages before any other. Defaults to `false`.

Option `packet` determines how/if an incoming message is packaged into a diameter_packet record. If `false` then messages are received as binary(). If `true` then as a record with the binary() message in the `bin` field and a `{stream, Id}` tuple in the `transport_data` field, where `Id` is the identifier of the inbound stream the message was received on. If `raw` then as a record with the received ancillary sctp_sndrcvinfo record in the `transport_data` field. Defaults to `true`.

Options `message_cb` and `sender` have semantics identical to those documented in diameter_tcp(3), but with the message argument to a `recv` callback being as directed by the `packet` option.

An `{outstream, Id}` tuple in the `transport_data` field of a outgoing diameter_packet record sets the outbound stream on which the message is sent, modulo the negotiated number of outbound streams. Any other value causes successive such sends to cycle though all outbound streams.

Remaining options are any accepted by `gen_sctp:open/1`, with the exception of options `mode`, `binary`, `list`, `active` and `sctp_events`. Note that options `ip` and `port` specify the local address and port respectively.

Multiple `ip` options can be specified for a multihomed peer. If none are specified then the values of `Host-IP-Address` in the `diameter_service` record are used. Option `port` defaults to 3868 for a listening transport and 0 for a connecting transport.

#### Warning

An small receive buffer may result in a peer having to resend incoming messages: set the `inet` option `recbuf` to increase the buffer size.

An small send buffer may result in outgoing messages being discarded: set the `inet` option `sndbuf` to increase the buffer size.