mirror of
https://github.com/moparisthebest/xeps
synced 2024-11-15 22:05:01 -05:00
112 lines
4.7 KiB
XML
112 lines
4.7 KiB
XML
<?xml version='1.0' encoding='UTF-8'?>
|
|
<!DOCTYPE xep SYSTEM 'xep.dtd' [
|
|
<!ENTITY % ents SYSTEM 'xep.ent'>
|
|
%ents;
|
|
<!ENTITY ns "urn:xmpp:fallback:0">
|
|
]>
|
|
<?xml-stylesheet type='text/xsl' href='xep.xsl'?>
|
|
<xep>
|
|
<header>
|
|
<title>Fallback Indication</title>
|
|
<abstract>This specification proposes a mechanism by which message bodies can be marked as being purely for fallback
|
|
purposes, and therefore to be ignored by intermediaries and anything that understands the remainder of the message.</abstract>
|
|
&LEGALNOTICE;
|
|
<number>XXXX</number>
|
|
<status>ProtoXEP</status>
|
|
<type>Standards Track</type>
|
|
<sig>Standards</sig>
|
|
<dependencies>
|
|
<spec>XMPP Core</spec>
|
|
</dependencies>
|
|
<supersedes/>
|
|
<supersededby/>
|
|
<shortname>fallback</shortname>
|
|
&dcridland;
|
|
<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>A common and convenient practise for new extensions is to supply a fallback body. This provides immediate backwards
|
|
compatibility for naive clients, since - not understanding the new protocol - they will gracefully degrade to displaying
|
|
the body as an instant message.</p>
|
|
<p>By way of example, a recent Reactions proposal suggested including the emoji as a <tt><body/></tt> element, so
|
|
that existing clients would simply display it as a normal message.</p>
|
|
<p>The downside of this approach is that servers and other intermediaries treat the presence of a <tt><body/></tt>
|
|
as being an indicator that a message is indeed an instant message. They will then treat it this way for archival
|
|
purposes, etc, which might not be appropriate.</p>
|
|
<p>This specification tackles the problem by providing an element to be used as a hint that the supplied
|
|
<tt><body/></tt> and <tt><subject</tt> elements are only for fallback purposes, and the message SHOULD be
|
|
treated as if they were not present for most purposes.</p>
|
|
</section1>
|
|
|
|
<section1 topic='Overview' anchor="overview">
|
|
<section2 topic="Discovering Support" anchor="feature">
|
|
<p>Support for this protocol MAY be advertised by the Service Discovery protocol defined in &xep0030; using a feature
|
|
of <tt>&ns;</tt>. Note that lack of support will result in the desired fallback behaviour.</p>
|
|
</section2>
|
|
<section2 topic="Fallback Indicator">
|
|
<p>The fallback indicator is an element <tt><fallback/></tt> qualified by the <tt>&ns;</tt> namespace. It has no
|
|
attributes, content, or child elements.</p>
|
|
<example><![CDATA[
|
|
<message from="alice@example.org" to="bob@example.net" type="chat">
|
|
<fallback xmlns="]]>&ns;<![CDATA["/>
|
|
<encrypted xmlns="urn:example:crypto">Abobql jvyy rire qrpelcg bhe fhcre-frperg zrffntr!</encrypted>
|
|
<body>This message is encrypted.</body>
|
|
</message>
|
|
]]></example>
|
|
<p>Receiving the above message, a naive client will naturally display only the <tt><body/></tt> element text, but
|
|
a client or server which supports this specification will know this is merely a fallback placeholder, and to ignore
|
|
(and not display) the content therein.</p>
|
|
</section2>
|
|
<section2 topic="Alternatives">
|
|
<ul>
|
|
<li>&xep0334; was considered, and would probably be ideal - servers often examine these elements and alter
|
|
behaviour accordingly, but the specification was rejected by Council.</li>
|
|
<li>Placing fallback elements within the <tt><fallback/></tt> element would shift the onus from server to
|
|
client, but this is likely to be less useful.</li>
|
|
</ul>
|
|
</section2>
|
|
</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="fallback">
|
|
<xs:complexType/>
|
|
</xs:element>
|
|
</xs:schema>
|
|
]]>
|
|
</code>
|
|
</section1>
|
|
|
|
<section1 topic='Security Considerations' anchor='security'>
|
|
<p>This specification allows messages with a body (and real message content therein) to be treated by a server as
|
|
if that body text does not exist. Servers MAY, particularly in a secure setting, wish to archive copies of the message
|
|
even if they ordinarily would not archive a message with no body.</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 author wishes to share any credit with many members of the community.</p>
|
|
</section1>
|
|
|
|
</xep>
|