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<!DOCTYPE erlref SYSTEM "erlref.dtd" [
  <!ENTITY message '<seealso marker="#message">message()</seealso>'>
  <!ENTITY MESSAGES '<seealso marker="#MESSAGES">MESSAGES</seealso>'>
  <!ENTITY start '<seealso marker="#Mod:start-3">start/3</seealso>'>
  <!ENTITY ip_address
  '<seealso marker="kernel:inet#type-ip_address">inet:ip_address()</seealso>'>
  <!ENTITY % also SYSTEM "seealso.ent" >
  <!ENTITY % here SYSTEM "seehere.ent" >
  %also;
  %here;
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<erlref>
<header>
<copyright>
<year>2011</year>
<year>2019</year>
<holder>Ericsson AB. All Rights Reserved.</holder>
</copyright>
<legalnotice>
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
 
    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.

</legalnotice>

<title>diameter_transport(3)</title>
<prepared>Anders Svensson</prepared>
<responsible></responsible>
<docno></docno>
<approved></approved>
<checked></checked>
<date></date>
<rev></rev>
<file>diameter_transport.xml</file>
</header>

<module since="OTP R14B03">diameter_transport</module>
<modulesummary>Diameter transport interface.</modulesummary>

<description>

<p>
A module specified as a <c>transport_module</c> to &mod_add_transport;
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).</p>

</description>

<!-- ===================================================================== -->

<section>
<title>DATA TYPES</title>

<taglist>

<tag>
<marker id="message"/><c>message() = binary() | &codec_packet;</c></tag>
<item>
<p>
A Diameter message as passed over the transport interface.</p>

<p>
For an inbound message from a transport process, a &codec_packet; must
contain the received message in its <c>bin</c> field.
In the case of an inbound request, any value set in the
<c>transport_data</c> field will passed back to the transport module
in the corresponding answer message, unless the sender supplies
another value.</p>

<p>
For an outbound message to a transport process, a &codec_packet; has a
value other than <c>undefined</c> in its <c>transport_data</c> field
and has the binary() to send in its <c>bin</c> field.</p>
</item>

</taglist>

</section>

<!-- ===================================================================== -->

<funcs>

<func>
<name since="OTP R14B03">Mod:start({Type, Ref}, Svc, Config)
         -> {ok, Pid}
          | {ok, Pid, LAddrs}
          | {error, Reason}</name>
<fsummary>Start a transport process.</fsummary>
<type>
<v>Type = connect | accept</v>
<v>Ref = &mod_transport_ref;</v>
<v>Svc = #diameter_service{}</v>
<v>Config = term()</v>
<v>Pid = pid()</v>
<v>LAddrs = [&ip_address;]</v>
<v>Reason = term()</v>
</type>
<desc>
<p>
Start a transport process.
Called by diameter as a consequence of a call to &mod_add_transport; in
order to establish or accept a transport connection respectively.
A transport process maintains a connection with a single remote peer.</p>

<p>
<c>Type</c> indicates whether the transport process in question
is being started for a connecting (<c>Type=connect</c>) or listening
(<c>Type=accept</c>) transport.
In the latter case, transport processes are started as required to
accept connections from multiple peers.</p>

<p>
Ref is the value that was returned from the call to &mod_add_transport;
that has lead to starting of a transport process.</p>

<p>
<c>Svc</c> contains capabilities passed to &mod_start_service; and
&mod_add_transport;, values passed to the latter overriding those
passed to the former.</p>

<p>
<c>Config</c> is as passed in <c>transport_config</c> tuple in the
&mod_transport_opt; list passed to &mod_add_transport;.</p>

<p>
The start function should use the <c>Host-IP-Address</c> list in
<c>Svc</c> and/or <c>Config</c> 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 <c>connected</c> message (see &MESSAGES; below)
following connection establishment.
In either case, the local address list is used to populate
<c>Host-IP-Address</c> AVPs in outgoing capabilities exchange
messages if <c>Host-IP-Address</c> is unspecified.</p>

<p>
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.</p>

</desc>
</func>

</funcs>

<!-- ===================================================================== -->

<section>
<marker id="MESSAGES"/>
<title>MESSAGES</title>

<p>
All messages sent over the transport interface are of the
form <c>{diameter, term()}</c>.</p>

<p>
A transport process can expect messages of the following types from
its parent.</p>

<taglist>

<tag><c>{diameter, {send, &message; | false}}</c></tag>
<item>
<p>
An outbound Diameter message.
The atom <c>false</c> can only be received when request
acknowledgements have been requests: see the <c>ack</c> message
below.</p>
</item>

<tag><c>{diameter, {close, Pid}}</c></tag>
<item>
<p>
A request to terminate the transport process after having received DPA
in response to DPR.
The transport process should exit.
<c>Pid</c> is the pid() of the parent process.</p>
</item>

<tag><c>{diameter, {tls, Ref, Type, Bool}}</c></tag>
<item>
<p>
Indication of whether or not capabilities exchange has selected
inband security using TLS.
<c>Ref</c> is a reference() that must be included in the
<c>{diameter, {tls, Ref}}</c> reply message to the transport's
parent process (see below).
<c>Type</c> is either <c>connect</c> or <c>accept</c> depending on
whether the process has been started for a connecting or listening
transport respectively.
<c>Bool</c> is a boolean() indicating whether or not the transport
connection should be upgraded to TLS.</p>

<p>
If TLS is requested (<c>Bool=true</c>) 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 <c>{diameter, {tls, Ref}}</c>
message to the parent process.
A failed handshake should cause the process to exit.</p>

<p>
This message is only sent to a transport process over whose
<c>Inband-Security-Id</c> configuration has indicated support for
TLS.</p>
</item>

</taglist>

<p>
A transport process should send messages of the following types
to its parent.</p>

<taglist>

<tag><c>{diameter, {self(), connected}}</c></tag>
<item>
<p>
Inform the parent that the transport process with <c>Type=accept</c> has
established a connection with the peer.
Not sent if the transport process has <c>Type=connect</c>.</p>
</item>

<tag><c>{diameter, {self(), connected, Remote}}</c></tag><item/>
<tag><c>{diameter, {self(), connected, Remote, [LocalAddr]}}</c></tag>
<item>
<p>
Inform the parent that the transport process with <c>Type=connect</c>
has established a connection with a peer.
Not sent if the transport process has <c>Type=accept</c>.&nbsp;
<c>Remote</c> is an arbitrary term that uniquely identifies the remote
endpoint to which the transport has connected.
A <c>LocalAddr</c> list has the same semantics as one returned from
&start;.</p>
</item>

<tag><c>{diameter, ack}</c></tag>
<item>
<p>
Request acknowledgements of unanswered requests.
A transport process should send this once before passing incoming
Diameter messages into diameter.
As a result, every Diameter request passed into diameter with a
<c>recv</c> message (below) will be answered with a
<c>send</c> message (above), either a &message; for the transport
process to send or the atom <c>false</c> if the request has been
discarded or otherwise not answered.</p>

<p>
This is to allow a transport process to keep count of the number
of incoming request messages that have not yet been answered or
discarded, to allow it to regulate the amount of incoming traffic.
Both diameter_tcp and diameter_sctp request acknowledgements when a
<c>message_cb</c> is configured, turning send/recv message into
callbacks that can be used to regulate traffic.</p>
</item>

<tag><c>{diameter, {recv, &message;}}</c></tag>
<item>
<p>
An inbound Diameter message.</p>
</item>

<tag><c>{diameter, {tls, Ref}}</c></tag>
<item>
<p>
Acknowledgment of a successful TLS handshake.
<c>Ref</c> is the reference() received in the
<c>{diameter, {tls, Ref, Type, Bool}}</c> message in response
to which the reply is sent.
A transport must exit if a handshake is not successful.</p>
</item>

</taglist>

</section>

<!-- ===================================================================== -->
<!-- ===================================================================== -->

<section>
<title>SEE ALSO</title>

<p>
&man_tcp;, &man_sctp;</p>

</section>

</erlref>
