<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE erlref SYSTEM "erlref.dtd" [
  <!ENTITY records
  '<seealso marker="diameter_dict#MESSAGE_RECORDS">diameter_dict(4)</seealso>'>
  <!ENTITY types
  '<seealso marker="diameter_dict#DATA_TYPES">diameter_dict(4)</seealso>'>
  <!ENTITY decode_format
  '<seealso marker="diameter#decode_format">decode format</seealso>'>

<!ENTITY % also SYSTEM "seealso.ent" >
  <!ENTITY % here SYSTEM "seehere.ent" >
  %also;
  %here;
]>

<erlref>
<header>
<copyright>
<year>2012</year>
<year>2017</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_codec(3)</title>
<prepared>Anders Svensson</prepared>
<responsible></responsible>
<docno></docno>
<approved></approved>
<checked></checked>
<date></date>
<rev></rev>
<file>diameter_codec.xml</file>
</header>

<module since="OTP R15B03">diameter_codec</module>
<modulesummary>Decode and encode of Diameter messages.</modulesummary>

<description>

<p>
Incoming Diameter messages are decoded from binary() before being
communicated to &man_app; callbacks.
Similarly, outgoing Diameter messages are encoded into binary() before
being passed to the appropriate &man_transport; module for
transmission.
The functions documented here implement the default encode/decode.</p>

<warning>
<p>
The diameter user does not need to call functions here explicitly when
sending and receiving messages using &mod_call; and the callback
interface documented in &man_app;: diameter itself provides encode/decode
as a consequence of configuration passed to &mod_start_service;, and
the results may differ from those returned by the functions documented
here, depending on configuration.</p>
</warning>

<p>
The &header; and &packet; records below
are defined in diameter.hrl, which can be included as follows.</p>

<pre>
-include_lib("diameter/include/diameter.hrl").
</pre>

<p>
Application-specific records are defined in the hrl
files resulting from dictionary file compilation.</p>

</description>

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

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

<p></p>

<taglist>

<tag>
<marker id="integers"/><c>uint8()&nbsp; = 0..255</c></tag><item/>
<tag><c>uint24() = 0..16777215</c></tag><item/>
<tag><c>uint32() = 0..4294967295</c></tag>
<item>
<p>
8-bit, 24-bit and 32-bit integers occurring in Diameter and AVP
headers.</p>
</item>

<tag>
<marker id="avp"/><c>avp() = #diameter_avp{}</c></tag>
<item>
<p>
The application-neutral representation of an AVP.
Primarily intended for use by relay applications that need to handle
arbitrary Diameter applications.
A service implementing a specific Diameter application
(for which it configures a dictionary) can manipulate values of type
&message; instead.</p>

<p>
Fields have the following types.</p>

<taglist>

<tag><c>code = uint32()</c></tag><item/>
<tag><c>is_mandatory = boolean()</c></tag><item/>
<tag><c>need_encryption = boolean()</c></tag><item/>
<tag><c>vendor_id = uint32() | undefined</c></tag>
<item>
<p>
Values in the AVP header, corresponding to AVP Code, the M flag, P
flags and Vendor-ID respectively.
A Vendor-ID other than <c>undefined</c> implies a set V flag.</p>
</item>

<tag><c>data = iolist()</c></tag>
<item>
<p>
The data bytes of the AVP.</p>
</item>

<tag><c>name = atom()</c></tag>
<item>
<p>
The name of the AVP as defined in the dictionary file in question, or
<c>undefined</c> if the AVP is unknown to the dictionary file in
question.</p>
</item>

<tag><c>value = term()</c></tag>
<item>
<p>
The decoded value of an AVP.
Will be <c>undefined</c> on decode if the data bytes could
not be decoded, the AVP is unknown, or if the &decode_format; is
<c>none</c>.
The type of a decoded value is as document in &types;.</p>
</item>

<tag><c>type = atom()</c></tag>
<item>
<p>
The type of the AVP as specified in the dictionary file in question
(or one it inherits).
Possible types are <c>undefined</c> and the Diameter types:
<c>OctetString</c>, <c>Integer32</c>, <c>Integer64</c>,
<c>Unsigned32</c>, <c>Unsigned64</c>, <c>Float32</c>, <c>Float64</c>,
<c>Grouped</c>, <c>Enumerated</c>, <c>Address</c>, <c>Time</c>,
<c>UTF8String</c>, <c>DiameterIdentity</c>, <c>DiameterURI</c>,
<c>IPFilterRule</c> and <c>QoSFilterRule</c>.</p>
</item>

</taglist>

</item>

<tag>
<marker id="dictionary"/><c>dictionary() = module()</c></tag>
<item>

<p>
The name of a generated dictionary module as generated by &man_compile;
or &make_codec;.
The interface provided by a dictionary module is an
implementation detail that may change.</p>
</item>

<tag>
<marker id="header"/><c>header() = #diameter_header{}</c></tag>
<item>
<p>
The record representation of the Diameter header.
Values in a &packet; returned by &decode; are as extracted from the
incoming message.
Values set in an &packet; passed to &encode; are preserved in the
encoded binary(), with the exception of <c>length</c>, <c>cmd_code</c>
and <c>application_id</c>, all of which are determined by the
&dictionary; in question.</p>

<note>
<p>
It is not necessary to set header fields explicitly in outgoing
messages as diameter itself will set appropriate values.
Setting inappropriate values can be useful for test purposes.</p>
</note>

<p>
Fields have the following types.</p>

<taglist>

<tag><c>version = uint8()</c></tag><item/>
<tag><c>length = uint24()</c></tag><item/>
<tag><c>cmd_code = uint24()</c></tag><item/>
<tag><c>application_id = uint32()</c></tag><item/>
<tag><c>hop_by_hop_id = uint32()</c></tag><item/>
<tag><c>end_to_end_id = uint32()</c></tag>
<item>
<p>
Values of the Version, Message Length, Command-Code, Application-ID,
Hop-by-Hop Identifier and End-to-End Identifier fields of the Diameter
header.</p>
</item>

<tag><c>is_request = boolean()</c></tag><item/>
<tag><c>is_proxiable = boolean()</c></tag><item/>
<tag><c>is_error = boolean()</c></tag><item/>
<tag><c>is_retransmitted = boolean()</c></tag>
<item>
<p>
Values corresponding to the R(equest), P(roxiable), E(rror)
and T(Potentially re-transmitted message) flags of the Diameter
header.</p>
</item>

</taglist>

</item>

<tag>
<marker id="message"/><c>message() = record()
                                   | maybe_improper_list()</c></tag>
<item>
<p>
The representation of a Diameter message as passed to
&mod_call; or returned from a &app_handle_request; callback.
The record representation is as outlined in &records;:
a message as defined in a dictionary file is encoded as a record with
one field for each component AVP.
Equivalently, a message can also be encoded as a list whose head is
the atom-valued message name (as specified in the relevant dictionary
file) and whose tail is either a list of AVP name/values
pairs or a map with values keyed on AVP names.
The format at decode is determined by &mod_decode_format;.
Any of the formats is accepted at encode.</p>

<p>
Another list-valued representation allows a message to be specified
as a list whose head is a &header; and whose tail is an &avp; list.
This representation is used by diameter itself when relaying requests
as directed by the return value of a &app_handle_request; callback.
It differs from the other two in that it bypasses the checks for
messages that do not agree with their definitions in the dictionary in
question: messages are sent exactly as specified.</p>

</item>

<tag>
<marker id="packet"/><c>packet() = #diameter_packet{}</c></tag>
<item>
<p>
A container for incoming and outgoing Diameter messages.
Fields have the following types.</p>

<taglist>

<tag><c>header = &header; | undefined</c></tag>
<item>
<p>
The Diameter header of the message.
Can be (and typically should be) <c>undefined</c> for an outgoing
message in a non-relay application, in which case diameter provides
appropriate values.</p>
</item>

<tag><c>avps = [&avp;] | undefined</c></tag>
<item>
<p>
The AVPs of the message.
Ignored for an outgoing message if the <c>msg</c> field is set to a
value other than <c>undefined</c>.</p>
</item>

<tag><c>msg = &message; | undefined</c></tag>
<item>
<p>
The incoming/outgoing message.
For an incoming message, a term corresponding to the configured
&decode_format; if the message can be decoded in a non-relay
application, <c>undefined</c> otherwise.
For an outgoing message, setting a <c>[&header; | &avp;]</c> list is
equivalent to setting the <c>header</c> and <c>avps</c> fields to the
corresponding values.</p>

<warning>
<p>
A value in the <c>msg</c> field does <em>not</em> imply an absence of
decode errors.
The <c>errors</c> field should also be examined.</p>
</warning>

</item>

<tag><c>bin = binary()</c></tag>
<item>
<p>
The incoming message prior to encode or the outgoing message after
encode.</p>
</item>

<tag><c>errors = [5000..5999 | {5000..5999, avp()}]</c></tag>
<item>
<p>
Errors detected at decode of an incoming message, as identified by
a corresponding 5xxx series Result-Code (Permanent Failures).
For an incoming request, these should be used to formulate an
appropriate answer as documented for the &app_handle_request;
callback in &man_app;.
For an incoming answer, the &mod_application_opt;
<c>answer_errors</c> determines the behaviour.</p>
</item>

<tag><c>transport_data = term()</c></tag>
<item>
<p>
An arbitrary term of meaning only to the transport process in
question, as documented in &man_transport;.</p>
</item>

</taglist>

</item>

</taglist>

</section>

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

<funcs>

<func>
<name since="OTP R15B03">decode(Mod, Bin) -> Pkt</name>
<fsummary>Decode a Diameter message.</fsummary>
<type>
<v>Mod = &dictionary;</v>
<v>Bin = binary()</v>
<v>Pkt = &packet;</v>
</type>
<desc>

<p>
Decode a Diameter message.</p>

</desc>
</func>

<func>
<name since="OTP R15B03">encode(Mod, Msg) -> Pkt</name>
<fsummary>Encode a Diameter message.</fsummary>
<type>
<v>Mod = &dictionary;</v>
<v>Msg = &message; | &packet;</v>
<v>Pkt = &packet;</v>
</type>
<desc>

<p>
Encode a Diameter message.
</p>

</desc>
</func>

</funcs>

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

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

<p>
&man_compile;, &man_app;, &man_dict;, &man_make;</p>

</section>

</erlref>
