mirror of
https://github.com/moparisthebest/xeps
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232 lines
11 KiB
XML
232 lines
11 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>MUC presence versioning</title>
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<abstract>This specification defines a versioning mechanism which reduces the amount of presence traffic in a XEP-0045 MUC</abstract>
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&LEGALNOTICE;
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<number>0436</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>XMPP IM</spec>
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<spec>XEP-0045</spec>
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</dependencies>
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<supersedes/>
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<supersededby/>
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<shortname>omnipresent-muc-affiliates</shortname>
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&jcbrand;
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&mwild;
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<revision>
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<version>0.2.0</version>
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<date>2020-05-10</date>
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<initials>jcb</initials>
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<remark>
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<p>Incorporate feedback from the standards list</p>
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<ul>
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<li>Create a separate tag for sending the version number.</li>
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<li>Include a reset token.</li>
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<li>Remove the "Additional measures" section and merge parts into "Requirements".</li>
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<li>Mandate that presences are always sent for affiliated users.</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>0.1.0</version>
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<date>2020-05-05</date>
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<initials>XEP Editor (jsc)</initials>
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<remark>Accepted by vote of Council on 2020-04-01.</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>2020-03-30</date>
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<initials>jcb</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>
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Many modern-day non-XMPP groupchat implementations have discarded the metaphor of physical presence inside a room that a user must enter and exit, as implemented by &xep0045;.
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The newer &xep0369; has therefore made presence subscriptions optional.
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</p>
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<p>
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Often it no longer makes sense for a chat service to require that a user is "present" in order for them to be addressed by other occupants or to receive messages,
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especially if the chat implementation will inform you out-of-band, for example via push notifications or email.
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The notion of "room presence" is therefore less relevant than before, and in some cases can be done away with entirely.
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</p>
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<p>
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Broadcasting all XEP-0045 MUC participants' presences to one another scales quadratically (O(n^2)) and can greatly increase the amount of network traffic,
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for potentially negligable gain.
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</p>
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<p>
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Even though the metaphorical concept of presence inside a room might no longer be relevant for a groupchat implementation,
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<presence/> stanzas might still contain useful metadata, such as the user's affiliation or &xep0317;.
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</p>
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<p>
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This XEP defines a versioning mechanism (similar to roster versioning in &rfc6121;) whereby the amount of presence traffic in a MUC may be greatly reduced.
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</p>
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</section1>
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<section1 topic="How it works">
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<p>
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A client that supports MUC presence versioning needs to keep track and store the presence states of all MUC occupants, across multiple MUC sessions.
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Similarly, a MUC service which supports presence versioning will also need to maintain a changelog of version numbers and corresponding presence states.
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</p>
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<p>
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Before the client enters a MUC, it SHOULD use service discovery to check whether presence versioning is supported
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(see <link url="#disco">determining support</link> below.).
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If MUC presence versioning is supported, the client MAY include a <version> tag with a 'ver' attribute set to the last known version
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inside the <{http://jabber.org/protocol/muc#user}x> tag of the <presence/> stanza, which it sends to join the MUC.
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</p>
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<p>
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If MUC presence versioning is not supported by the server, the client MUST NOT include a 'ver' attribute.
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</p>
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<example caption='User specifies the last known version when seeking to enter a MUC'><![CDATA[
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<presence
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from='hag66@shakespeare.lit/pda'
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id='n13mt3l'
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to='coven@chat.shakespeare.lit/thirdwitch'>
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<x xmlns='http://jabber.org/protocol/muc#user'>
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<version xmlns='urn:xmpp:muc-presence-versioning:0' ver='ver16' />
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</x>
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</presence>
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]]></example>
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<p>
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The MUC will return only those presences that have changed since the version indicated by the client, and in the self-presence of the joining user it will add a
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<version> tag with a 'ver' attribute set to the latest version number inside the <{http://jabber.org/protocol/muc#user}x> tag.
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The client must save the version number (and continuously update with never versions as they're received) and use that next time it joins the MUC.
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</p>
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<example caption="Service Sends New Occupant's Presence to New Occupant"><![CDATA[
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<presence
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from='coven@chat.shakespeare.lit/thirdwitch'
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id='n13mt3l'
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to='hag66@shakespeare.lit/pda'>
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<x xmlns='http://jabber.org/protocol/muc#user'>
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<version xmlns='urn:xmpp:muc-presence-versioning:0' ver='ver17' />
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<item affiliation='member' role='participant'/>
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<status code='110'/>
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</x>
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</presence>
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]]></example>
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<p>
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When presence versioning is enabled, every subsequent <presence/> stanza sent by the server MUST include a new version number,
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which replaces the existing one saved by the client.
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</p>
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</section1>
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<section1 topic='Determining support' anchor='disco'>
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<p>If a MUC implements presence versioning, it MUST specify the 'urn:xmpp:muc-presence-versioning:0' feature in its service discovery information features,
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as specified in &xep0030;.</p>
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<example caption='Client queries for information about a specific MUC'><![CDATA[
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<iq type='get'
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from='romeo@montague.example/orchard'
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to='room@muc.shakespeare.example'
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id='info1'>
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<query xmlns='http://jabber.org/protocol/disco#info'/>
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</iq>]]></example>
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<example caption='The MUC advertises support for presence versioning'><![CDATA[
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<iq type='result'
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to='romeo@montague.example/home'
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from='room@muc.shakespeare.example'
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id='info1'>
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<query xmlns='http://jabber.org/protocol/disco#info'>
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...
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<feature var='urn:xmpp:muc-presence-versioning:0'/>
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...
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</query>
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</iq>]]></example>
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</section1>
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<section1 topic='Requirements' anchor='requirements'>
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<section2 topic='Always broadcast presence for affiliated users' anchor='affiliate-presence'>
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<p>
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A MUC that supports presence versioning MUST broadcast presence for all affiliated users, including those who are currently 'unavailable'.
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<cite>XEP-0045</cite> documents the status code '102', which is used to indicate that a MUC shows unavailable members.
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</p>
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<p>
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The only exception is when a MUC has been explicitly configured to only broadcast presence from occupants above a certain affiliation,
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(see the <link url='https://xmpp.org/extensions/xep-0045.html#enter-pres'>presence broadcast</link> section of <cite>XEP-0045</cite>).
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</p>
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<p>
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In order for a user to permanently join a room, and therefore become affiliated so that they are included in presence broadcasts,
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they MAY be allowed to register themselves as members in the MUC.
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<cite>XEP-0045</cite> describes in <link url='https://xmpp.org/extensions/xep-0045.html#register'>section 7.10 "Registering with a Room</link>
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how a user may register themselves with a room, thereby receiving the "member" affiliation and having their preferred nickname reserved in that room.
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</p>
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</section2>
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<section2 topic="Include a reset token when the client's version number has expired" anchor='reset-token'>
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<p>
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If a MUC receives a presence version number that's so old, that it no longer has the corresponding state available,
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it MUST include a <reset> token in the first <presence> stanza it sends (regardless of whom in the MUC the presence relates to).
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The first presence stanza MAY be from the MUC itself (as shown in the example below).
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Afterwards, the MUC MUST then send all presences (including 'unavailable' for affiliated users) as if the client is starting from a blank slate.
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</p>
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<example caption="Service Sends a Reset Token"><![CDATA[
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<presence from='coven@chat.shakespeare.lit'
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id='r3s3t-m3'
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to='hag66@shakespeare.lit/pda'>
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<x xmlns='http://jabber.org/protocol/muc#user'>
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<reset xmlns='urn:xmpp:muc-presence-versioning:0' ver='ver36' />
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</x>
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</presence>
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]]></example>
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</section2>
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</section1>
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<section1 topic='Business Rules' anchor='rules'>
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<p>
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Even if the client did not include a <version> tag with a 'ver' attribute in its "join" <presence/> stanza,
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the server SHOULD still return a <version> tag with 'ver' attribute (set to the latest version number)
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on all relevant <presence/> stanzas.
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This allows clients to bootstrap MUC presence versioning without having to do a service discovery query first.
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</p>
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<p>
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If the client has not yet saved a presence version number and the corresponding presence states,
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then it MUST bootstrap presence versioning by sending a 'ver' attribute set to the empty string (i.e., ver="").
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</p>
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<p>
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In some cases, the presence states being kept track of by the MUC service MAY be reduced to a minimum of only two states, 'available' and 'unavailable'.
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This can drastically reduce the number of states the server needs to keep track off, at the cost of not allowing users to provide more fine-grained
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reporting of their level of availability.
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</p>
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</section1>
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<section1 topic="Security Considerations">
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<p>
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The MUC service should strip the <version> tag from the user's <presence> before relaying it to other occupants,
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to avoid leaking information on when last the user joined the MUC.
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</p>
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</section1>
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<section1 topic='IANA Considerations' anchor='iana'>
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<p>None.</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='ns'>
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<p>The ®ISTRAR; includes 'urn:xmpp:muc-presence-versioning:0' in its registry of protocol namespaces (see &NAMESPACES;).</p>
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<ul>
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<li>urn:xmpp:muc-presence-versioning:0</li>
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</ul>
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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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</section1>
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</xep>
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