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381 lines
20 KiB
XML
381 lines
20 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>Message Archive Management</title>
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<abstract>This document defines a protocol to query and control and archive of messages stored on a server.</abstract>
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&LEGALNOTICE;
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<number>0313</number>
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<status>Experimental</status>
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<type>Standards Track</type>
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<sig>Standards</sig>
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<dependencies>
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<spec>XMPP Core</spec>
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<spec>XEP-0030</spec>
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<spec>XEP-0059</spec>
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<spec>XEP-0297</spec>
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</dependencies>
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<supersedes/>
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<supersededby/>
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<shortname>mam</shortname>
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<schemaloc>
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<url>http://www.xmpp.org/schemas/archive-management.xsd</url>
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</schemaloc>
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<author>
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<firstname>Matthew</firstname>
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<surname>Wild</surname>
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<email>me@matthewwild.co.uk</email>
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<jid>me@matthewwild.co.uk</jid>
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</author>
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<revision>
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<version>0.1</version>
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<date>2012-04-18</date>
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<initials>mw</initials>
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<remark><p>Initial version, to much rejoicing.</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>It is a common desire for a user using XMPP for IM to want to store their messages in a central archive
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on their server. This feature allows them to record conversations that take place on clients that do not
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support local history storage, and also to synchronise their conversation history seamlessly between
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multiple clients.</p>
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</section1>
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<section1 topic='Requirements'>
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<p>As this extension aims to make things easy for client developers, some research was made into the
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way clients handle history today. The resulting protocol was designed to allow for the following primary
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usage scenarios:</p>
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<ul>
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<li>Automatic history synchronization between multiple clients.</li>
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<li>Calendar-based on-demand display of historic messages in a client that doesn't keep local history.</li>
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<li>So-called 'infinite' scrollback, whereby a client automatically fetches and displays historic messages
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naturally in the message log as the user scrolls back in time.</li>
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</ul>
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<p>Another extension for archiving already exists in XMPP, &xep0136;). However implementation experience has
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shown that the protocol defined therein supports rather more functionality than is typically needed for the
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above uses, and is significantly more effort to implement.</p>
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<p>This specification aims to define a much simpler and modular protocol for working with a server-side
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message store. Through this it is hoped to boost implementation and deployment of archiving in XMPP. It
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should be noted that (although not required) a server is free to implement XEP-0136 alongside this
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protocol if it so chooses, though a mapping between both protocols is beyond the scope of this specification.</p>
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<p>Notable functionality in XEP-0136 that is intentionally not defined by this specification for simplicity:</p>
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<ul>
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<li>Support for 'collections'. Few clients even support this concept for local history storage, and
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it is possible to apply the logic for splitting a stream of messages into conversations on the
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client-side, thus greatly simplifying the protocol.</li>
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<li>Support for uploading to the archive. On the assumption that a server automatically archives
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messages to and from the client, it is typically rare for a client to end up with messages that are
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not already in the archive. Uploading could be useful for bootstrapping an empty archive however, and
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may be defined in a future specification if there is demand for such functionality.</li>
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<li>Support for 'off the record' chats (OTR; not to be confused with the encryption algorithm of
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the same name). This allowed complex negotiation for either the user or contact to command specific
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conversations to bypass the archive. In reality the archiving behaviour of a contact's server cannot
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be enforced (they could ignore the OTR request and archive the messages anyway without your consent)
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so this specification does not try and regulate that. Equivalent functionality can be implemented with
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server logic for not including encrypted or specially-tagged messages in the archive (out of scope for
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this specification).</li>
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<li>Support per-session configuration. This feature was deemed unnecessary for the majority of
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implementations, and hence the configuration protocol in this specification is much simplified,
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which allows for a simple user interface in clients. Advanced configuration however may be performed
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through ad-hoc commands depending on the server implementation.</li>
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</ul>
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</section1>
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<section1 topic='Message archives'>
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<p>An archive is a collection of messages stored on a user's server. Messages sent to or from a
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user's account are generally automatically added to a user's archive by the server. The collection
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is ordered chronologically by the time each message was sent/received.</p>
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<p>Exactly which messages a server archives is left up to implementation and deployment policy,
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but as a minimum servers SHOULD NOT archive messages that do not have a <body/> child tag.</p>
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<p>At a minimum, a stored message consists of the following pieces of information:</p>
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<ul>
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<li>A timestamp of when the message was sent (for an outgoing message) or received (for
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an incoming message).</li>
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<li>The remote JID that the stanza is to (for an outgoing message) or from (for an
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incoming message).</li>
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<li>A server-assigned UID that MUST be unique within the archive.</li>
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<li>The message stanza itself. The entire original stanza SHOULD be stored, but at a
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minimum only the <body/> tag MUST be preserved (ie. the server might, at its
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discretion, strip certain extensions from messages before storage).</li>
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</ul>
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<p>A server MAY impose limits on the size of a user's archive. For example a server might begin
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to discard old messages once the archive reaches a certain size, or only keep messages until they
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reach a certain age. The UIDs of deleted messages MUST NOT be reused for new messages.</p>
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<p>Finally, there is no restriction on where an archive may be hosted. Servers that archive
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messages on behalf of local users SHOULD expose archives to the user on their bare JID, while a
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MUC service might allow MAM queries to be sent to the room's bare JID.</p>
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</section1>
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<section1 topic='Querying the archive'>
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<p>A client is able to query the archive for all messages within a certain timespan, optionally
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restricting results to those to/from a particular JID. To allow limiting the results or paging
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through them a client may use &xep0059;, which MUST be supported by servers.</p>
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<p>A query consists of an <iq/> stanza addressed to the account or server entity hosting
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the archive, with a 'query' payload. On receiving the query, the server pushes to the client a
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series of messages from the archive that match the client's given criteria, and finally returns
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the <iq/> result.</p>
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<example caption='Querying the archive for messages'><![CDATA[
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<iq type='get' id='juliet1'>
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<query xmlns='urn:xmpp:mam:tmp' queryid='f27' />
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</iq>
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[... server sends matching messages ...]
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<iq type='result' id='juliet1'/>
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]]></example>
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<p>To ensure that the client knows when the results are complete, the server MUST delay the result
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<iq/> until after it has pushed all the results to the client. An optional 'queryid' attribute
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allows the client to match results to a certain query.</p>
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<section2 topic="Filtering results">
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<p>The query can contain any combination of three filtering tags - <with/>, <start/>
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and <end/>. By default all messages match a query, the filters are used to request a subset
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of the archived messages.</p>
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<section3 topic="Filtering by contact">
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<p>If a <with/> element is present in the <query/>, it contains a JID against which
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to match messages. The server MUST only return messages if they match the supplied JID.</p>
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<p>If <with/> is omitted, the server SHOULD return all messages in the selected timespan,
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regardless of the to/from addresses on each message.</p>
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<example caption='Querying for all messages to/from a particular JID'><![CDATA[
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<iq type='get' id='juliet1'>
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<query xmlns='urn:xmpp:mam:tmp'>
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<with>juliet@capulet.com</with>
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</query>
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</iq>
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]]></example>
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<p>If (and only if) the supplied JID is a bare JID (i.e. no resource is present), then
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the server SHOULD return messages if their bare to/from address would match it. For example,
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if the client supplies with='juliet@capulet.com' this filter would also match messages to
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or from "juliet@capulet.com/balcony" and "juliet@capulet.com/chamber".</p>
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</section3>
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<section3 topic="Filtering by time received">
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<p>The <start/> and <end/> elements, if provided, MUST contain timestamps
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formatted according to the DateTime profile defined in &xep0082;</p>
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<p>The <start/> element is used to filter out messages before a certain date/time.
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If specified, a server MUST only return messages whose timestamp is equal to or later
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than the given timestamp.</p>
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<p>If omitted, the server SHOULD assume the value of <start/> to be equal to the
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date/time of the earliest message stored in the archive.</p>
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<p>Conversely, the <end/> element is used to exclude from the results messages
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after a certain point in time. If specified, a server MUST only return messages whose
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timestamp is equal to or earlier than the timestamp given in the <end/> element.</p>
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<p>If omitted, the server SHOULD assume the value of <end/> to be equal to the
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date/time of the most recent message stored in the archive.</p>
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<example caption='Querying the archive for all messages in a certain timespan'><![CDATA[
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<iq type='get' id='juliet1'>
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<query xmlns='urn:xmpp:mam:tmp'>
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<start>2010-06-07T00:00:00Z</start>
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<end>2010-07-07T13:23:54Z</end>
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</query>
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</iq>
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]]></example>
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<example caption='Querying the archive for all messages after a certain time'><![CDATA[
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<iq type='get' id='juliet1'>
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<query xmlns='urn:xmpp:mam:tmp'>
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<start>2010-08-07T00:00:00Z</start>
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</query>
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</iq>
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]]></example>
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</section3>
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<section3 topic='Limiting results'>
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<p>Finally, in order for the client or server to limit the number of results transmitted at
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a time a server MUST support &xep0059; and SHOULD support the paging mechanism defined therein.
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A client MAY include a <set/> element in its query.</p>
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<p>For the purposes of this protocol, the UIDs used by RSM correspond with the UIDs of the
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stanzas stored in the archive.</p>
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<example caption='A query using Result Set Management'><![CDATA[
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<iq type='get' id='q29302'>
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<query xmlns='urn:xmpp:mam:tmp'>
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<start>2010-08-07T00:00:00Z</start>
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<set xmlns='http://jabber.org/protocol/rsm'>
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<limit>10</limit>
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</set>
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</query>
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</iq>
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]]></example>
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<p>To conserve resources, a server MAY place a reasonable limit on how many stanzas may be
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pushed to a client in one request. If a query returns a number of stanzas greater than this
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limit and either the client did not specify a limit using RSM then the server should return
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a policy-violation error to the client. If the query did include a <set/> element then
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the server SHOULD simply return its limited results and adjust the <before/> and <after/>
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in its reply to allow the client to page through them by timestamp.</p>
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<example caption='Client without RSM requests too many results'><![CDATA[
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<iq type='error' id='q29302'>
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<error type='modify'>
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<policy-violation xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
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<text>Too many results</text>
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</error>
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</iq>
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]]></example>
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</section3>
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</section2>
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<section2 topic="Query results">
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<p>The server responds to the archive query by transmitting to the client all the messages
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that match the criteria the client requested. The results are sent as individual stanzas,
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with the original message encapsulated in a <forwarded/> element as described in &xep0297;.
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</p>
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<p>The result messages MUST contain a <result/> element with an 'id' attribute that gives
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the current message's UID. If the client gave a 'queryid' attribute in its initial query, the
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server MUST also include that in this result element.</p>
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<p>The <forwarded/> element SHOULD contain the original message as it was received, and
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SHOULD also contain a <delay/> element qualified by the 'urn:xmpp:delay' namespace
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specified in &xep0203;. The value of the 'stamp' attribute MUST be the time the message was
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originally received by the forwarding entity.
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</p>
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<example caption='Server returns two matching messages'><![CDATA[
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<message id='aeb213' to='juliet@capulet.com/chamber'>
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<result xmlns='urn:xmpp:mam:tmp' queryid='f27' id='28482-98726-73623' />
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<forwarded xmlns='urn:xmpp:forward:0'>
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<delay xmlns='urn:xmpp:delay' stamp='2010-07-10T23:08:25Z'/>
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<message to='juliet@capulet.com/balcony'
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from='romeo@montague.net/orchard'
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type='chat'>
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<body>Call me but love, and I'll be new baptized; Henceforth I never will be Romeo.</body>
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</message>
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</forwarded>
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</message>
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<message id='aeb214' to='juliet@capulet.com/chamber'>
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<result xmlns='urn:xmpp:mam:tmp' queryid='f27' id='5d398-28273-f7382'/>
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<forwarded xmlns='urn:xmpp:forward:0'>
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<delay xmlns='urn:xmpp:delay' stamp='2010-07-10T23:09:32Z'/>
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<message to='romeo@montague.net/orchard'
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from='juliet@capulet.com/balcony'
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type='chat' id='8a54s'>
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<body>What man art thou that thus bescreen'd in night so stumblest on my counsel?</body>
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</message>
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</forwarded>
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</message>
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]]></example>
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</section2>
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</section1>
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<section1 topic="Archiving Preferences">
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<p>Depending on implementation and deployment policies, a server MAY allow the user to have control
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over the server's archiving behaviour. This specification defines a basic protocol for this, and
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also allows a server to offer more advanced configuration to a user.</p>
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<section2 topic='Simple configuration'>
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<p>If the server supports and allows configuration then it SHOULD implement the protocol defined
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in this section. This allows the user to configure the following preferences:</p>
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<ul>
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<li>A list of JIDs that should always have messages to/from archived in the user's store.</li>
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<li>A list of JIDs that should never have messages to/from archived in the user's store.</li>
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<li>The default archiving behaviour (for JIDs in neither of the above lists).</li>
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</ul>
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<example caption='Updating archiving preferences'><![CDATA[
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<iq type='set' id='juliet2'>
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<prefs xmlns='urn:xmpp:mam:tmp' default="roster">
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<always>
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<jid>romeo@montague.net</jid>
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</always>
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<never>
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<jid>montague@montague.net</jid>
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</never>
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</prefs>
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</iq>
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]]></example>
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<p>The server then replies with the applied preferences (note that due to server policies these
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MAY be different to the preferences sent by the client):</p>
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<example caption='Server responds with updated preferences'><![CDATA[
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<iq type='result' id='juliet1'>
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<prefs xmlns='urn:xmpp:mam:tmp' default="roster">
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<always>
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<jid>romeo@montague.net</jid>
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</always>
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<never>
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<jid>montague@montague.net</jid>
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</never>
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</prefs>
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</iq>
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]]></example>
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<section3 topic='Default behaviour'>
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<p>If a JID is in neither the 'always archive' nor the 'never archive' list then whether it
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is archived depends on this setting, the default.
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</p>
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<p>The 'default' attribute of the 'prefs' element MUST be one of the following values:</p>
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<ul>
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<li>'always' - all messages are archived by default.</li>
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<li>'never' - messages are never archived by default.</li>
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<li>'roster' - messages are archived only if the contact's bare JID is in the user's roster.</li>
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</ul>
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</section3>
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<section3 topic='Always archive'>
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<p>The <prefs/> element MAY contain an <always/> child element. If present, it
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contains a list of <jid/> elements, each containing a single JID. The server SHOULD
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archive any messages to/from this JID (see 'JID matching').
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</p>
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<p>If missing from the preferences, <always/> SHOULD be assumed by the server to be an
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empty list.
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</p>
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</section3>
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<section3 topic='Never archive'>
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<p>The <prefs/> element MAY contain an <never/> child element. If present, it
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contains a list of <jid/> elements, each containing a single JID. The server SHOULD
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NOT archive any messages to/from this JID (see 'JID matching').
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</p>
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<p>If missing from the preferences, <never/> SHOULD be assumed by the server to be an
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empty list.
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</p>
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</section3>
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</section2>
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<section2 topic='Advanced configuration'>
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<p>In addition to this protocol, a server MAY offer more advanced configuration to the user
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through &xep0050;. Such an interface might, for example, allow the user to configure what
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types of messages to store, or set a limit on how long messages should remain in the
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archive.</p>
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<p>If supported, such a configuration command SHOULD be presented on the well-defined
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command node of "urn:xmpp:mam#configure".</p>
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</section2>
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<section2 topic='JID matching'>
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<section3 topic='General rules'>
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<p>When comparing the message target JID against the user's roster (ie. when the user has
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set default='roster') the comparison MUST use the bare target JID (that is, stripped of
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any resource).
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</p>
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<p>For matching against entries in either the 'allow' or 'never' lists, for each listed
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JID:
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</p>
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<ul>
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<li>If the listed JID contains a resource, compare against the target JID as-is.</li>
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<li>If the listed JID has no resource (it is a bare JID) then first strip any resource
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from the target JID prior to comparison.
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</li>
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</ul>
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</section3>
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<section3 topic='Outgoing messages'>
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<p>For outgoing messages, the server MUST use the value of the 'to' attribute as the target JID.
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</p>
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</section3>
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<section3 topic='Incoming messages'>
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<p>For incoming messages, the server MUST use the value of the 'from' attribute as the target JID.
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</p>
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</section3>
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</section2>
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</section1>
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<section1 topic='Determining support'>
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<p>If a server or other entity hosts archives and supports MAM queries, it MUST advertise that fact
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by including the feature "urn:xmpp:mam:tmp" in response to a &xep0030; request:</p>
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<example caption='Client queries for server features'><![CDATA[
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<iq type='get' id='disco1' to='capulet.lit' from='juliet@capulet.lit/balcony'>
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<query xmlns='http://jabber.org/protocol/disco#info'/>
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</iq>
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]]></example>
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<example caption='Server responds with features'><![CDATA[
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<iq type='result' id='disco1' from='capulet.lit' to='juliet@capulet.lit/balcony'>
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<query xmlns='http://jabber.org/protocol/disco#info'>
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...
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<feature var='urn:xmpp:mam:tmp'/>
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...
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</query>
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</iq>
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]]></example>
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</section1>
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</xep>
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