mirror of
https://github.com/moparisthebest/xeps
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379 lines
16 KiB
XML
379 lines
16 KiB
XML
<?xml version='1.0' encoding='UTF-8'?>
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<!DOCTYPE xep SYSTEM 'xep.dtd' [
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<!ENTITY % ents SYSTEM 'xep.ent'>
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%ents;
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]>
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<?xml-stylesheet type='text/xsl' href='xep.xsl'?>
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<xep>
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<header>
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<title>PubSub Queueing</title>
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<abstract>This specification defines an extension to XMPP publish-subscribe for queueing information at a node.</abstract>
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&LEGALNOTICE;
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<number>0254</number>
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<status>Deferred</status>
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<type>Standards Track</type>
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<sig>Standards</sig>
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<approver>Council</approver>
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<dependencies>
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<spec>XMPP Core</spec>
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<spec>XEP-0060</spec>
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</dependencies>
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<supersedes/>
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<supersededby/>
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<shortname>NOT_YET_ASSIGNED</shortname>
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&hildjj;
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&stpeter;
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<revision>
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<version>0.1</version>
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<date>2008-11-13</date>
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<initials>psa</initials>
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<remark><p>Initial published version.</p></remark>
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</revision>
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<revision>
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<version>0.0.3</version>
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<date>2008-10-07</date>
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<initials>jjh/psa</initials>
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<remark><p>Added more detailed error flows; added additional implementation notes.</p></remark>
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</revision>
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<revision>
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<version>0.0.2</version>
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<date>2008-10-07</date>
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<initials>jjh/psa</initials>
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<remark>
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<ul>
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<li>Specified that notifications are sent to only one subscriber at a time.</li>
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<li>Specified that notifications include payloads.</li>
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<li>Added protocol extension for unlock feature.</li>
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<li>Modified namespace to incorporate namespace versioning.</li>
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</ul>
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</remark>
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</revision>
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<revision>
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<version>0.0.1</version>
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<date>2008-08-14</date>
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<initials>psa/jjh</initials>
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<remark><p>First draft.</p></remark>
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</revision>
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</header>
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<section1 topic='Introduction' anchor='intro'>
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<p>The &xep0060; extension to XMPP provides a comprehensive technology for alerts, notifications, data syndication, rich presence, and other real-time messaging use cases. In terms of traditional publish-subscribe systems like Java Message Service (JMS), the core XMPP PubSub specification covers the Observer design pattern only; however, traditional publish-subscribe systems often include support for a second design pattern, usually called the "point-to-point" or "queueing" pattern. <note>See for instance <<link url='http://en.wikipedia.org/wiki/Java_Message_Service'>http://en.wikipedia.org/wiki/Java_Message_Service</link>>.</note> This specification defines a few small extensions to XMPP PubSub that enable support for a queueing mode in XMPP. The queueing mode is an add-on feature that a service can support, and that a node owner can enable if supported by the service. The feature name is "urn:xmpp:pubsub:queueing:0".</p>
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</section1>
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<section1 topic='How It Works' anchor='howitworks'>
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<section2 topic='Subscribing' anchor='subscribe'>
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<p>If a node has enabled support for the queueing mode, in response to a subscription request without configuration options it MUST return an IQ-error containing a subscription options form; this form MUST include the "queue_requests" field (which specifies the number of parallel requests a subscriber is willing to process).</p>
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<example caption='Service indicates that subscription configuration is required'><![CDATA[
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<iq from='workflows.shakespeare.lit'
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id='sub1'
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to='workerbee237@shakespeare.lit/foo'
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type='error'>
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<pubsub xmlns='http://jabber.org/protocol/pubsub'>
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<subscribe
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jid='workerbee237@shakespeare.lit'
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node='a290fjsl29j19kjb'/>
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<options
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jid='workerbee237@shakespeare.lit'
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node='a290fjsl29j19kjb'>
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<x xmlns='jabber:x:data' type='form'>
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<field var='FORM_TYPE' type='hidden'>
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<value>http://jabber.org/protocol/pubsub#subscribe_options</value>
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</field>
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<field type='text-single' var='pubsub#queue_requests'>
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<required/>
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</field>
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</x>
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</options>
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</pubsub>
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<error type='modify'>
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<not-acceptable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
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<configuration-required xmlns='http://jabber.org/protocol/pubsub#errors'/>
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</error>
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</iq>
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]]></example>
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<p>The subscriber would then send a new subscription request, this time with options.</p>
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<example caption='Subscribing with options'><![CDATA[
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<iq from='workerbee237@shakespeare.lit/foo'
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id='sub2'
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to='workflows.shakespeare.lit'
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type='set'>
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<pubsub xmlns='http://jabber.org/protocol/pubsub'>
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<subscribe
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jid='workerbee237@shakespeare.lit'
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node='a290fjsl29j19kjb'/>
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<options
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jid='workerbee237@shakespeare.lit'
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node='a290fjsl29j19kjb'>
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<x xmlns='jabber:x:data' type='submit'>
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<field var='FORM_TYPE' type='hidden'>
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<value>http://jabber.org/protocol/pubsub#subscribe_options</value>
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</field>
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<field var='pubsub#queue_requests'>
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<value>5</value>
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</field>
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</x>
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</options>
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</pubsub>
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</iq>
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]]></example>
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<p>If the subscription request can be processed successfully, the service returns an IQ-result and includes the configuration options established during the negotiation.</p>
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<example caption='Service replies with success (including configuration options)'><![CDATA[
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<iq from='workflows.shakespeare.lit'
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id='sub2'
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to='workerbee237@shakespeare.lit/foo'
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type='result'>
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<pubsub xmlns='http://jabber.org/protocol/pubsub'>
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<subscription
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jid='workerbee237@shakespeare.lit'
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node='a290fjsl29j19kjb'
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subid='ba49252aaa4f5d320c24d3766f0bdcade78c78d3'
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subscription='subscribed'/>
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<options>
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<x xmlns='jabber:x:data' type='result'>
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<field var='FORM_TYPE' type='hidden'>
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<value>http://jabber.org/protocol/pubsub#subscribe_options</value>
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</field>
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<field var='pubsub#queue_requests'>
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<value>5</value>
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</field>
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</x>
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</options>
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</pubsub>
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</iq>
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]]></example>
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</section2>
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<section2 topic='Assigning an Item' anchor='assign'>
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<p>At any time, a publisher can push an item to the queue node.</p>
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<example caption='Publisher publishes an item'><![CDATA[
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<iq from='engine.shakespeare.lit'
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id='pub1'
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to='workflow.shakespeare.lit'
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type='set'>
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<pubsub xmlns='http://jabber.org/protocol/pubsub'>
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<publish node='a290fjsl29j19kjb'>
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<item id='ae890ac52d0df67ed7cfdf51b644e901'>
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<example xmlns='urn:xmpp:example'>payload</example>
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</item>
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</publish>
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</pubsub>
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</iq>
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]]></example>
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<p>The item is published to <em>one</em> of the subscribers.</p>
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<example caption='One subscriber receives a notification'><![CDATA[
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<message from='workflow.shakespeare.lit'
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id='foo'
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to='workerbee237@shakespeare.lit'>
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<event xmlns='http://jabber.org/protocol/pubsub#event'>
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<items node='a290fjsl29j19kjb'>
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<item id='ae890ac52d0df67ed7cfdf51b644e901'>
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<example xmlns='urn:xmpp:example'>payload</example>
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</item>
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</items>
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</event>
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</message>
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]]></example>
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</section2>
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<section2 topic='Deleting an Item from the Queue' anchor='delete'>
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<p>When the subscriber that received the item has successfully processed it (whatever that means in the context of the queue), the subscriber deletes the item from the queue.</p>
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<example caption='Entity deletes an item from a node'><![CDATA[
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<iq from='workerbee237@shakespeare.lit/foo'
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id='delete1'
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to='workflows.shakespeare.lit'
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type='get'>
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<pubsub xmlns='http://jabber.org/protocol/pubsub'>
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<retract node='a290fjsl29j19kjb'>
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<item id='ae890ac52d0df67ed7cfdf51b644e901'/>
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</retract>
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</pubsub>
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</iq>
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]]></example>
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<p>In the context of a queue node, the service MUST treat a delete request from a subscriber that received the item as if the sender were a publisher; i.e., it MUST delete the item from the queue and notify only this subscriber that the item has been deleted.</p>
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<example caption='Subscriber receives delete notification'><![CDATA[
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<message from='workflow.shakespeare.lit'
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id='bar'
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to='workerbee237@shakespeare.lit'>
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<event xmlns='http://jabber.org/protocol/pubsub#event'>
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<items node='a290fjsl29j19kjb'>
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<retract id='ae890ac52d0df67ed7cfdf51b644e901'/>
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</items>
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</event>
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</message>
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]]></example>
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<p>Note: The subscriber SHOULD NOT commit any pending transactions until it receives the delete notification.</p>
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<p>If the item does not exist, the service MUST return an ¬found; error as described in <cite>XEP-0060</cite>.</p>
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<p>If the entity that attempts to delete the item is not the subscriber that received the item, the service MUST return a &forbidden; error as described in <cite>XEP-0060</cite>.</p>
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<p>If the item is locked by another subscriber, the service MUST return a &conflict; error (this flow is not defined in <cite>XEP-0060</cite>.</p>
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<example caption='Item is locked by another subscriber'><![CDATA[
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<iq from='workflows.shakespeare.lit'
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id='delete1'
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to='workerbee237@shakespeare.lit/foo'
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type='get'>
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<pubsub xmlns='http://jabber.org/protocol/pubsub'>
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<retract node='a290fjsl29j19kjb'>
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<item id='ae890ac52d0df67ed7cfdf51b644e901'/>
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</retract>
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</pubsub>
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<error type='auth'>
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<forbidden xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
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</error>
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</iq>
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]]></example>
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<p>If the subscriber that received the item attempts to delete the item but the item is no longer locked by the subscriber (e.g., because of a race condition or a lost notification), the service MUST return an &unexpected; error (this flow is not defined in <cite>XEP-0060</cite>.</p>
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<example caption='Item is no longer locked by subscriber'><![CDATA[
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<iq from='workflows.shakespeare.lit'
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id='delete1'
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to='workerbee237@shakespeare.lit/foo'
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type='get'>
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<pubsub xmlns='http://jabber.org/protocol/pubsub'>
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<retract node='a290fjsl29j19kjb'>
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<item id='ae890ac52d0df67ed7cfdf51b644e901'/>
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</retract>
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</pubsub>
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<error type='wait'>
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<unexpected-request xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
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</error>
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</iq>
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]]></example>
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</section2>
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<section2 topic='Unlocking an Item' anchor='unlock'>
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<p>The subscriber might determine that it cannot process the item (whatever that means in the context of the queue); if so, the subscriber unlocks the item.</p>
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<example caption='Entity unlocks an item'><![CDATA[
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<iq from='workerbee237@shakespeare.lit/foo'
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id='unlock1'
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to='workflows.shakespeare.lit'
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type='get'>
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<pubsub xmlns='http://jabber.org/protocol/pubsub'>
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<unlock xmlns='urn:xmpp:pubsub:queueing:0'
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node='a290fjsl29j19kjb'>
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<item id='ae890ac52d0df67ed7cfdf51b644e901'/>
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</unlock>
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</pubsub>
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</iq>
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]]></example>
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<p>The service then MUST unlock the item and notify only this subscriber that the item has been unlocked.</p>
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<example caption='Subscriber receives unlock notification'><![CDATA[
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<message from='workflow.shakespeare.lit'
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id='baz'
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to='workerbee237@shakespeare.lit'>
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<event xmlns='http://jabber.org/protocol/pubsub#event'>
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<items node='a290fjsl29j19kjb'>
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<unlock xmlns='urn:xmpp:queueing:0'
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id='ae890ac52d0df67ed7cfdf51b644e901'/>
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</items>
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</event>
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</message>
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]]></example>
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<p>When an item is unlocked, the service would then send a publish notification to another subscriber according to application-specific logic for determining the "next" subscriber.</p>
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<p>If the item does not exist, the service MUST return an ¬found; error.</p>
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<example caption='Item does not exist'><![CDATA[
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<iq from='workflows.shakespeare.lit'
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id='delete1'
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to='workerbee237@shakespeare.lit/foo'
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type='error'>
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<pubsub xmlns='http://jabber.org/protocol/pubsub'>
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<unlock xmlns='urn:xmpp:pubsub:queueing:0'
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node='a290fjsl29j19kjb'>
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<item id='ae890ac52d0df67ed7cfdf51b644e901'/>
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</unlock>
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</pubsub>
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<error type='cancel'>
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<item-not-found xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
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</error>
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</iq>
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]]></example>
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<p>If the entity that attempts to unlock the item is not the subscriber that received the item, the service MUST return a &forbidden; error.</p>
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<example caption='Requesting entity did not receive item'><![CDATA[
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<iq from='workflows.shakespeare.lit'
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id='delete1'
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to='workerbee237@shakespeare.lit/foo'
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type='error'>
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<pubsub xmlns='http://jabber.org/protocol/pubsub'>
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<unlock xmlns='urn:xmpp:pubsub:queueing:0'
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node='a290fjsl29j19kjb'>
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<item id='ae890ac52d0df67ed7cfdf51b644e901'/>
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</unlock>
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</pubsub>
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<error type='auth'>
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<forbidden xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
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</error>
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</iq>
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]]></example>
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<p>If the item is locked by another subscriber, the service MUST return a &conflict; error.</p>
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<example caption='Item is locked by another subscriber'><![CDATA[
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<iq from='workflows.shakespeare.lit'
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id='delete1'
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to='workerbee237@shakespeare.lit/foo'
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type='error'>
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<pubsub xmlns='http://jabber.org/protocol/pubsub'>
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<unlock xmlns='urn:xmpp:pubsub:queueing:0'
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node='a290fjsl29j19kjb'>
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<item id='ae890ac52d0df67ed7cfdf51b644e901'/>
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</unlock>
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</pubsub>
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<error type='cancel'>
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<conflict xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
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</error>
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</iq>
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]]></example>
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<p>If the subscriber that received the item attempts to unlock the item but the item is no longer locked by the subscriber (e.g., because of a race condition or a lost notification), the service MUST return an &unexpected; error.</p>
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<example caption='Item is no longer locked by subscriber'><![CDATA[
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<iq from='workflows.shakespeare.lit'
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id='delete1'
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to='workerbee237@shakespeare.lit/foo'
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type='error'>
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<pubsub xmlns='http://jabber.org/protocol/pubsub'>
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<unlock xmlns='urn:xmpp:pubsub:queueing:0'
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node='a290fjsl29j19kjb'>
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<item id='ae890ac52d0df67ed7cfdf51b644e901'/>
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</unlock>
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</pubsub>
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<error type='wait'>
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<unexpected-request xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
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</error>
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</iq>
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]]></example>
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</section2>
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</section1>
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<section1 topic='Determining Support' anchor='support'>
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<p>If a pubsub service supports the queueing mode, it MUST advertise support for the "urn:xmpp:pubsub:queueing:0" namespace in response to &xep0030; information requests.</p>
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</section1>
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<section1 topic='Implementation Notes' anchor='impl'>
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<p>If the service receives unavailable presence from a subscriber, it SHOULD unlock all outstanding queue items associated with the subscriber and unsubscribe the subscriber to prevent delivery of further publish notifications.</p>
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<p>If a subscriber cannot process queue items because of an unrecoverable error (e.g., disk full), the subscriber SHOULD unsubscribe and then unlock all of its outstanding queue items.</p>
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<p>If the service does not receive a delete or unlock request from a subscriber that received a queue item in a configurable amount of time, it SHOULD timeout the request, send an unlock notification to the subscriber, and send a publish notification to the "next" subscriber.</p>
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</section1>
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<section1 topic='Security Considerations' anchor='security'>
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<p>To follow.</p>
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</section1>
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<section1 topic='IANA Considerations' anchor='iana'>
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<p>This document requires no interaction with &IANA;.</p>
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</section1>
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<section1 topic='XMPP Registrar Considerations' anchor='registrar'>
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<section2 topic='Protocol Namespaces' anchor='registrar-ns'>
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<p>This specification defines the following XML namespace:</p>
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<ul>
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<li>urn:xmpp:pubsub:queueing:0</li>
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</ul>
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<p>Upon advancement of this specification from a status of Experimental to a status of Draft, the ®ISTRAR; shall add the foregoing namespaces to the registry located at &NAMESPACES;, as described in Section 4 of &xep0053;.</p>
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</section2>
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<section2 topic='Protocol Versioning' anchor='registrar-versioning'>
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&NSVER;
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</section2>
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<section2 topic='Service Discovery Features' anchor='registrar-features'>
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<p>The ®ISTRAR; maintains a registry of service discovery features (see &DISCOFEATURES;), which includes a number of features that can be returned by pubsub services. The following registry submission supplements the existing list.</p>
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<code><![CDATA[
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<var>
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<name>urn:xmpp:pubsub:queueing:0</name>
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<desc>The node or service supports the queueing mode.</desc>
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<doc>XEP-xxxx</doc>
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</var>
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]]></code>
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</section2>
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</section1>
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</xep>
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