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Add "Compare-And-Publish PubSub Items" ProtoXEP

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Florian Schmaus 2017-04-20 00:02:46 +02:00
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<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE xep SYSTEM 'xep.dtd' [
<!ENTITY % ents SYSTEM 'xep.ent'>
%ents;
]>
<?xml-stylesheet type='text/xsl' href='xep.xsl'?>
<xep>
<header>
<title>Atomically Compare-And-Publish PubSub Items</title>
<abstract>This specification provides a mechanism to atomically Compare-And-Publish items to a PubSub node.</abstract>
&LEGALNOTICE;
<number>xxxx</number>
<status>ProtoXEP</status>
<type>Standards Track</type>
<sig>Standards</sig>
<approver>Council</approver>
<dependencies>
<spec>XEP-0030</spec>
<spec>XEP-0060</spec>
</dependencies>
<supersedes/>
<supersededby/>
<shortname>cap</shortname>
&flow;
<revision>
<version>0.0.1</version>
<date>2017-04-20</date>
<initials>fs</initials>
<remark><p>First draft.</p></remark>
</revision>
</header>
<section1 topic='Introduction' anchor='intro'>
<p>This specification provides a mechanism to atomically publish
items to a PubSub node depending on the item ID of the node's latest
item. This allows to prevent race conditions and avoids data
loss in certain situations.</p>
</section1>
<section1 topic='Discoverying Support' anchor='disco'>
<p>If an entity supports the Compared-And-Publish feature it MUST
advertise the fact by returning a &lt;feature/&gt; with the 'var'
attribute set to 'urn:xmpp:pubsub:cap:0' in response to a &xep0030;
query for information.</p>
</section1>
<section1 topic='Compare-And-Publish PubSub Items' anchor='cap'>
<p>In order to atomically compare-and-publish an item, a client
sends an &IQ; with a 'pubsub' element qualified by the
'urn:xmpp:pubsub:cap:0' namespace. The element MUST contain the same
attributes and elements as the &lt;publish/&gt; element defined in
&xep0060; <em>and</em> it MUST contain a previd attribute containing
an item ID.</p>
<p>The PubSub service MUST only publish the item if the node's
latest item ID is equal to the ID found in the 'previd'
attribute.</p>
<example caption='Publisher publishes an item using Compare-And-Publish'><![CDATA[
<iq type='set'
from='hamlet@denmark.lit/blogbot'
to='pubsub.shakespeare.lit'
id='compare-and-publish1'>
<pubsub xmlns='urn:xmpp:pubsub:cap:0'>
<compare-and-publish
node='princely_musings'
previd='1'>
<item>
<entry xmlns='http://www.w3.org/2005/Atom'>
<title>Soliloquy</title>
<summary>
To be, or not to be: that is the question:
Whether 'tis nobler in the mind to suffer
The slings and arrows of outrageous fortune,
Or to take arms against a sea of troubles,
And by opposing end them?
</summary>
<link rel='alternate' type='text/html'
href='http://denmark.lit/2003/12/13/atom03'/>
<id>tag:denmark.lit,2003:entry-32397</id>
<published>2003-12-13T18:30:02Z</published>
<updated>2003-12-13T18:30:02Z</updated>
</entry>
</item>
</publish>
</pubsub>
</iq>
]]></example>
<section2 topic='Successfully published an item using Compare-And-Publish'>
<p>If the 'previd' matched the latest item's ID and if the service
was able to successfully process the request then the protocol
continues as defined in <cite>XEP-0060 7.1.2</cite>.</p>
</section2>
<section2 topic='Could not publish because newest item ID did not match'>
<p>In case the Compare-And-Publish operation failed because the
latest node id is not the same as given in the 'previd' attribute
in the request, the server returns an &IQ; result with 'pubsub'
element qualified by the 'urn:xmpp:pubsub:cap:0' namespace which
contains a &lt;compare-and-publish-failed/&gt; element. The
element MUST have a 'id' attribute with the ID of the lastest
item.</p>
<example caption='Service returns IQ response notifying of failed Compare-And-Publish operation'><![CDATA[
<iq type='result'
from='pubsub.shakespeare.lit'
to='hamlet@denmark.lit/blogbot'
id='compare-and-ublish1'>
<pubsub xmlns='urn:xmpp:pubsub:cap:0'>
<compare-and-publish-failed id='2'/>
</pubsub>
</iq>
]]></example>
</section2>
<section2 topic='Error cases'>
<p>All other error cases are handled as specified in
<cite>XEP-0060 § 7.1.3</cite></p>
</section2>
</section1>
<section1 topic='Security Considerations' anchor='security'>
<p>This extension protocol does not add any further security
considerations to the ones mentioned in <cite>XEP-0060 §
14.</cite>.</p>
</section1>
<section1 topic='IANA Considerations' anchor='iana'>
<p>This document requires no interaction with the Internet Assigned
Numbers Authority (IANA).</p>
</section1>
<section1 topic='XMPP Registrar Considerations' anchor='registrar'>
<p>This specification defines the following XML namespaces:</p>
<ul>
<li>urn:xmpp:pubsub:cap:0</li>
</ul>
<code caption='Registry Submission'><![CDATA[
<var>
<name>urn:xmpp:pubsub:cap:0</name>
<desc>Indicates support for Compare-And-Publish</desc>
<doc>XEP-XXXX</doc>
</var>]]></code>
</section1>
<section1 topic='XML Schema' anchor='schema'>
<p>TODO: Add after the XEP leaves the 'experimental' state.</p>
</section1>
</xep>