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<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE xep SYSTEM 'xep.dtd' [
<!ENTITY % ents SYSTEM 'xep.ent'>
%ents;
<!ENTITY ns "urn:xmpp:json-msg:0">
<!ENTITY nsx "urn:example:">
]>
<?xml-stylesheet type='text/xsl' href='xep.xsl'?>
<xep>
<header>
<title>Simple JSON Messaging</title>
<abstract>This specification proposes a simple mechanism by which applications can transfer data safely, without
needing additional protocol design work. It is intended to provide a protocol that is trivial to implement and can
be driven with a simple API.</abstract>
&LEGALNOTICE;
<number>0432</number>
<status>Deferred</status>
<type>Standards Track</type>
<sig>Standards</sig>
<dependencies>
<spec>XMPP Core</spec>
</dependencies>
<supersedes/>
<supersededby/>
<shortname>udt</shortname>
&dcridland;
<revision>
<version>0.1.0</version>
<date>2020-02-25</date>
<initials>XEP Editor (jsc)</initials>
<remark>Accepted by vote of Council on 2020-02-19.</remark>
</revision>
<revision>
<version>0.0.2</version>
<date>2020-02-13</date>
<initials>dwd</initials>
<remark>
<p>Have another crack at getting this through Council.</p>
<ul>
<li>Rename to a more obvious name</li>
<li>Remove IQ</li>
<li>Remove API, instead describe API requirements</li>
</ul>
</remark>
</revision>
<revision>
<version>0.0.1</version>
<date>2019-12-30</date>
<initials>dwd</initials>
<remark>
<ul>
<li>Initial Revision</li>
</ul>
</remark>
</revision>
</header>
<section1 topic='Introduction' anchor='intro'>
<p>Applications written on top of XMPP often need to exchange data that has no existing standard. Such applications are
often written by developers unfamiliar with best practise in designing new extensions for XMPP, making it hard to achieve
this simple design goal without causing longer term problems.</p>
<p>This leads to "solutions" such as stuffing JSON directly in the &lt;body/> element, for example, and recognising
this at the receiver either by heuristics or by a special &lt;subject/>. While this works, it is difficult to then
migrate to something else, and enforces that custom clients are always used.</p>
<p>Therefore this document proposes a very simple (and simplistic) framework for sending such data which - while
very light on features - nevertheless conforms to best practice, and yields an interoperable protocol. Unusually, this
specification SHOULD NOT be used as a base upon which to build other standards.</p>
<section2 topic="Terminology">
<p>Data transferred using this specification is encoded using JSON. The type of the data is given by a URI under
the same rules as an XML namespace, and this specification refers to this as the datatype.</p>
<p>Because this document defines mechanisms for sending essentially arbitrary data, no real-world examples are
given.</p>
<p>Instead, example namespaces are used within an XML namespace prefixed by <tt>&nsx;</tt></p>
</section2>
</section1>
<section1 topic='Overview' anchor="overview">
<section2 topic="Discovering Support" anchor="feature">
<p>Support for this protocol is advertised by the Service Discovery protocol defined in &xep0030; using a feature
of <tt>&ns;</tt>.</p>
<p>Support for a particular datatype is given by concatenating the <tt>&ns;</tt> feature with a hash character
('<tt>#</tt>') and the datatype, for example <tt>&ns;#&nsx;foo</tt>.</p>
</section2>
<section2 topic="Data Transfers">
<p>Simple JSON Messaging payloads may also be placed within a &lt;message/> stanza. &lt;message/> stanzas MAY contain multiple UDT
payloads, but typical usage is expected to be that there will be only one. The JSON Messaging payload may be ancillary data
to another message, or a standalone message in its own right.</p>
<section3 topic="Protocol Syntax">
<p>A Simple JSON Messaging payload consists of a single element, <tt>&lt;payload/></tt>, qualified by the XML namespace
<tt>&ns;</tt>. It has a single, mandatory attribute of <tt>datatype</tt>, which MUST contain a string conformant
to the requirements for XML namespaces (typically a URI under the control of the application developer).</p>
<p>As with XML namespaces, this URI is never expected to be resolved, and is used solely as an identifier.
Different strings are considered entirely different datatypes, and common prefixes etc MUST be considered
irrelevant for the purposes of interpreting the data. There are no common or standard datatypes.</p>
<p>The <tt>&lt;payload</tt> element contains exactly one mandatory child element, the <tt>&lt;json/></tt> element
defined in &xep0335;. This in turns contains the JSON data.</p>
<example><![CDATA[
<message from="gamer@game-company.example"
to="match-maker.game-company.example"
id="12345">
<payload xmlns="]]>&ns;<![CDATA[" datatype="]]>&nsx;foo<![CDATA[">
<json xmlns="urn:xmpp:json:0">
{
"annoying-teenager-level": 11
}
</json>
</payload>
</message>
]]></example>
</section3>
</section2>
</section1>
<section1 topic="API Requirements">
<p>In order to satisfy the goals of this protocol, client library developers are encouraged to provide a simple to use API for this protocol. Developers are encouraged to use terms such as "JSON Message" in their API calls and documentation.</p>
<p>Support for a particular datatype SHOULD be advertised automatically when listening for custom messages of that type if possible.</p>
</section1>
<section1 topic="Schema">
<code>
<![CDATA[
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema attributeFormDefault="unqualified" elementFormDefault="qualified" targetNamespace="]]>&ns;<![CDATA[" xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xs:element name="payload" type="udt:payloadType" xmlns:udt="]]>&ns;<![CDATA["/>
<xs:complexType name="payloadType">
<xs:sequence>
<xs:any minOccurs="1" maxOccurs="1"/>
<!-- Always a XEP-0335 json element, but I can't figure that out. -->
</xs:sequence>
<xs:attribute type="xs:string" name="datatype"/>
</xs:complexType>
</xs:schema>
]]>
</code>
</section1>
<section1 topic='Security Considerations' anchor='security'>
<p>All security implications herein are those of the payload.</p>
</section1>
<section1 topic='IANA Considerations' anchor='iana'>
<p>This XEP requires no interaction with &IANA;. </p>
</section1>
<section1 topic='XMPP Registrar Considerations' anchor='registrar'>
<p>None.</p>
</section1>
<section1 topic='Acknowledgements' anchor='ack'>
<p>The authors wish to share any credit with many members of the community, including Florian Schmaus, Daniel Gultsch, Georg Lukas, and others.</p>
</section1>
</xep>