-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()}
         when Ref :: diameter:transport_ref().

start({Type, Ref}, Svc, [Opt]) -> {ok, Pid} | {ok, Pid, [LAddr]} | {error, Reason}

The start function required by diameter_transport.

Options raddr and rport specify the remote address and port for a connecting transport and are not valid for a listening transport.

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 connection 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 ssl_options must be specified for a transport that should support TLS: a value of true results in a TLS handshake immediately upon connection establishment while list/0 specifies options to be passed to ssl:connect/2 or ssl:handshake/2 after capabilities exchange if TLS is negotiated.

Option fragment_timer specifies the timeout, in milliseconds, of a timer used to flush messages from the incoming byte stream even if the number of bytes indicated in the Message Length field of its Diameter Header have not yet been accumulated: such a message is received over the transport interface after two successive timeouts without the reception of additional bytes. Defaults to 1000.

Option sender specifies whether or not to use a dedicated process for sending outgoing messages, which avoids the possibility of send blocking reception. Defaults to false. If set to true then a message_cb that avoids the possibility of messages being queued in the sender process without bound should be configured.

Option message_cb specifies a callback that is invoked on incoming and outgoing messages, that can be used to implement flow control. It is applied to two arguments: an atom indicating the reason for the callback (send, recv, or ack after a completed send), and the message in question (binary() on recv, binary() or diameterpacket record on send or ack, or false on ack when an incoming request has been discarded). It should return a list of actions and a new callback as tail; eg. [fun cb/3, State]. Valid actions are the atoms send or recv, to cause a following message-valued action to be sent/received, a message to send/receive (binary() or diameter_packet record), or a boolean() to enable/disable reading on the socket. More than one send/recv/message sequence can be returned from the same callback, and an initial send/recv can be omitted if the same as the value passed as the callback's first argument. Reading is initially enabled, and returning false does not imply there cannot be subsequent recv callbacks since messages may already have been read. An empty tail is equivalent to the prevailing callback. Defaults to a callback equivalent to `fun(ack, ) -> []; (_, Msg) -> [Msg] end`.

Remaining options are any accepted by ssl:connect/3 or gen_tcp:connect/3 for a connecting transport, or ssl:listen/2 or gen_tcp:listen/2 for a listening transport, depending on whether or not {ssl_options, true} has been specified. Options binary, packet and active cannot be specified. Also, option port can be specified for a listening transport to specify the local listening port, the default being the standardized 3868. Note that the option ip specifies the local address.

An ssl_options list must be specified if and only if the transport in question has set Inband-Security-Id to 1 (TLS), as specified to either diameter:start_service/2 or diameter:add_transport/2, so that the transport process will receive notification of whether or not to commence with a TLS handshake following capabilities exchange. Failing to specify an options list on a TLS-capable transport for which TLS is negotiated will cause TLS handshake to fail. Failing to specify TLS capability when ssl_options has been specified will cause the transport process to wait for a notification that will not be forthcoming, which will eventually cause the RFC 3539 watchdog to take down the connection.

The first element of a non-empty Host-IP-Address list in Svc provides the local IP address if an ip option is not specified. The local address is either returned fromstart/3 or passed in a connected message over the transport interface.