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NAME
diameter_transport - Diameter transport interface.
DESCRIPTION
A module specified as a transport_module to diameter:add_transport/2 must implement the interface
documented here. The interface consists of a function with which diameter starts a transport process and
a message interface with which the transport process communicates with the process that starts it (aka
its parent).
DATA TYPES
message() = binary() | diameter_codec:packet():
A Diameter message as passed over the transport interface.
For an inbound message from a transport process, a diameter_codec:packet() must contain the received
message in its bin field. In the case of an inbound request, any value set in the transport_data
field will passed back to the transport module in the corresponding answer message, unless the sender
supplies another value.
For an outbound message to a transport process, a diameter_codec:packet() has a value other than
undefined in its transport_data field and has the binary() to send in its bin field.
EXPORTS
Mod:start({Type, Ref}, Svc, Config) -> {ok, Pid} | {ok, Pid, LAddrs} | {error, Reason}
Types:
Type = connect | accept
Ref = diameter:transport_ref()
Svc = #diameter_service{}
Config = term()
Pid = pid()
LAddrs = [inet:ip_address()]
Reason = term()
Start a transport process. Called by diameter as a consequence of a call to
diameter:add_transport/2 in order to establish or accept a transport connection respectively. A
transport process maintains a connection with a single remote peer.
Type indicates whether the transport process in question is being started for a connecting
(Type=connect) or listening (Type=accept) transport. In the latter case, transport processes are
started as required to accept connections from multiple peers.
Ref is the value that was returned from the call to diameter:add_transport/2 that has lead to
starting of a transport process.
Svc contains capabilities passed to diameter:start_service/2 and diameter:add_transport/2, values
passed to the latter overriding those passed to the former.
Config is as passed in transport_config tuple in the diameter:transport_opt() list passed to
diameter:add_transport/2.
The start function should use the Host-IP-Address list in Svc and/or Config to select and return
an appropriate list of local IP addresses. In the connecting case, the local address list can
instead be communicated in a connected message (see MESSAGES below) following connection
establishment. In either case, the local address list is used to populate Host-IP-Address AVPs in
outgoing capabilities exchange messages if Host-IP-Address is unspecified.
A transport process must implement the message interface documented below. It should retain the
pid of its parent, monitor the parent and terminate if it dies. It should not link to the parent.
It should exit if its transport connection with its peer is lost.
MESSAGES
All messages sent over the transport interface are of the form {diameter, term()}.
A transport process can expect messages of the following types from its parent.
{diameter, {send, message()}}:
An outbound Diameter message.
{diameter, {close, Pid}}:
A request to terminate the transport process after having received DPA in response to DPR. The
transport process should exit. Pid is the pid() of the parent process.
{diameter, {tls, Ref, Type, Bool}}:
Indication of whether or not capabilities exchange has selected inband security using TLS. Ref is a
reference() that must be included in the {diameter, {tls, Ref}} reply message to the transport's
parent process (see below). Type is either connect or accept depending on whether the process has
been started for a connecting or listening transport respectively. Bool is a boolean() indicating
whether or not the transport connection should be upgraded to TLS.
If TLS is requested (Bool=true) then a connecting process should initiate a TLS handshake with the
peer and an accepting process should prepare to accept a handshake. A successful handshake should be
followed by a {diameter, {tls, Ref}} message to the parent process. A failed handshake should cause
the process to exit.
This message is only sent to a transport process over whose Inband-Security-Id configuration has
indicated support for TLS.
A transport process should send messages of the following types to its parent.
{diameter, {self(), connected}}:
Inform the parent that the transport process with Type=accept has established a connection with the
peer. Not sent if the transport process has Type=connect.
{diameter, {self(), connected, Remote}}:
{diameter, {self(), connected, Remote, [LocalAddr]}}:
Inform the parent that the transport process with Type=connect has established a connection with a
peer. Not sent if the transport process has Type=accept. Remote is an arbitrary term that uniquely
identifies the remote endpoint to which the transport has connected. A LocalAddr list has the same
semantics as one returned from start/3.
{diameter, {recv, message()}}:
An inbound Diameter message.
{diameter, {tls, Ref}}:
Acknowledgment of a successful TLS handshake. Ref is the reference() received in the {diameter, {tls,
Ref, Type, Bool}} message in response to which the reply is sent. A transport must exit if a
handshake is not successful.
SEE ALSO
diameter_tcp(3erl), diameter_sctp(3erl)
Ericsson AB diameter 2.1.3 diameter_transport(3erl)