xeps/xep-0424.xml

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE xep SYSTEM 'xep.dtd' [
  <!ENTITY % ents SYSTEM 'xep.ent'>
%ents;
]>
<?xml-stylesheet type='text/xsl' href='xep.xsl'?>
<xep>
<header>
  <title>Message Retraction</title>
  <abstract>This specification defines a method for indicating that a message should be retracted.</abstract>
  &LEGALNOTICE;
  <number>0424</number>
  <status>Proposed</status>
  <lastcall>2022-01-04</lastcall>
  <type>Standards Track</type>
  <sig>Standards</sig>
  <approver>Council</approver>
  <dependencies>
    <spec>XMPP Core</spec>
    <spec>XMPP IM</spec>
    <spec>XEP-0313</spec>
    <spec>XEP-0421</spec>
  </dependencies>
  <supersedes/>
  <supersededby/>
  <shortname>message-retract</shortname>
  &lance;
  &jcbrand;
  <revision>
    <version>0.4.0</version>
    <date>2023-02-19</date>
    <initials>jcb</initials>
    <remark>
        <ul>
          <li>Remove the dependency on XEP-0422 Message Fastening.</li>
          <li>Use 'id' attribute on 'retracted' element instead of a child element.</li>
          <li>Clarify business rlies regarding which 'id' to use to refer to the retracted message.</li>
        </ul>
    </remark>
  </revision>
  <revision>
    <version>0.3.0</version>
    <date>2020-05-17</date>
    <initials>jcb</initials>
    <remark>
        <ul>
            <li>Clarify when a service must advertise support via disco.</li>
            <li>Add another service discovery URN for tombstones.</li>
        </ul>
    </remark>
  </revision>
  <revision>
    <version>0.2.1</version>
    <date>2020-03-25</date>
    <initials>jcb</initials>
    <remark>Recommend XEP-0428 fallback body and XEP-0334 store hint</remark>
  </revision>
  <revision>
    <version>0.2.0</version>
    <date>2019-11-11</date>
    <initials>jcb</initials>
    <remark>Replace the message contents with a tombstone (instead of the message itself) and require an origin-id in tombstone</remark>
  </revision>
  <revision>
    <version>0.1.0</version>
    <date>2019-11-01</date>
    <initials>XEP Editor (jcb)</initials>
    <remark>Accepted by vote of Council on 2019-10-23.</remark>
  </revision>
   <revision>
    <version>0.0.4</version>
    <date>2019-09-25</date>
    <initials>jcb</initials>
    <remark><p>Remove MUC moderation use-case which will go into a separate XEP</p></remark>
  </revision>
   <revision>
    <version>0.0.3</version>
    <date>2016-10-19</date>
    <initials>ljts</initials>
    <remark><p>Fix the XEP title to be Message Retraction.</p></remark>
  </revision>
  <revision>
    <version>0.0.2</version>
    <date>2016-10-12</date>
    <initials>ljts</initials>
    <remark><p>Use the term 'retraction' instead of 'deletion'. Added tombstone marker.</p></remark>
  </revision>
  <revision>
    <version>0.0.1</version>
    <date>2015-07-07</date>
    <initials>ljts</initials>
    <remark><p>First draft.</p></remark>
  </revision>
</header>
<section1 topic='Introduction' anchor='intro'>
  <p>A chat participant might want to retract a message which they've already sent out, for example if they've mistakenly sent it to the wrong recipient or groupchat.</p>
  <p>Due to the federated and extensible nature of XMPP it's not possible to remove a message with full certainty and a retraction can only be considered an <strong>unenforceable request</strong> for such removal. Clients which don't support message retraction are not obligated to enforce the request and people could have seen or copied the message contents already.</p>
</section1>
<section1 topic='Discovering support' anchor='disco'>
  <p>If a client implements message retractions, it MUST specify the 'urn:xmpp:message-retract:1' feature in its service discovery information features as specified in &xep0030; and the Entity Capabilities profile specified in &xep0115;.</p>
  <p>Similarly, a server that is aware of message retractions and will therefore ensure that they're archived for later retrieval (e.g.via &xep0313;), MUST also advertise the 'urn:xmpp:message-retract:1' feature.</p>
    <example caption='Client requests information about a chat partner&apos;s client'><![CDATA[
<iq type='get'
    from='romeo@montague.example/orchard'
    to='juliet@capulet.example/balcony'
    id='info1'>
  <query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>]]></example>
    <example caption='Partner&apos;s client advertises support for retraction'><![CDATA[
<iq type='result'
    to='romeo@montague.example/orchard'
    from='juliet@capulet.example/balcony'
    id='info1'>
  <query xmlns='http://jabber.org/protocol/disco#info'>
...
    <feature var='urn:xmpp:message-retract:1'/>
...
  </query>
</iq>]]></example>
</section1>
<section1 topic='Use Case' anchor='usecase'>
  <p>Consider a situation where a user sends a message to the wrong recipient: </p>
  <example caption="The user's client sends a message to the wrong recipient"><![CDATA[
<message type='chat' to='lord@capulet.example' id='wrong-recipient-1'>
  <body>Have not saints lips, and holy palmers too?</body>
  <origin-id xmlns='urn:xmpp:sid:0' id='origin-id-1'/>
</message>]]></example>

  <p>The message author notices that the message was sent to the wrong recipient and indicates to their client that the message should be retracted.</p>
  <p>The client sends out a retraction message and uses the &xep0359; origin ID to refer to the original message that should be removed.</p>
  <p>In the case of a group chat message, for example &xep0045;, instead of the origin ID, the XEP-0359 stanza ID that was assigned by the group chat SHOULD be used.</p>

  <example caption="The client sends out a retraction message"><![CDATA[
<message type='chat' to='lord@capulet.example' id='retract-message-1'>
  <retract id="origin-id-1" xmlns='urn:xmpp:message-retract:1'/>
  <fallback xmlns="urn:xmpp:fallback:0"/>
  <body>This person attempted to retract a previous message, but it's unsupported by your client.</body>
  <store xmlns="urn:xmpp:hints"/>
</message>]]></example>

<p>It's RECOMMENDED that you include a &xep0428; tag with fallback text in the &lt;body/&gt;, so that older clients can still indicate the intent to retract and so that older servers will archive the retraction. Additionally, you MAY include a &xep0334; &lt;store/&gt; hint, to indicate that the stanza needs to be archived.</p>

</section1>

<section1 topic='Tombstones' anchor='tombstones'>
  <p>It might be desirable to remove the retracted message from a &xep0313; service, while still recording the fact that it once existed, in order to aid clients in synchronizing their archives. To do this, the archiving service MAY replace the retracted message contents with a 'tombstone'.</p>

  <p>A service which supports tombstones MUST advertise the 'urn:xmpp:message-retract:1#tombstone' feature in its Service Discovery responses.</p>

    <example caption='Client requests service discovery information from the server'><![CDATA[
<iq type='get'
    from='romeo@montague.example/orchard'
    to='romeo@montague.example'
    id='info1'>
  <query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>]]></example>
    <example caption='The server advertises support for tombstone retraction'><![CDATA[
<iq type='result'
    to='romeo@montague.example/orchard'
    from='romeo@montague.example'
    id='info1'>
  <query xmlns='http://jabber.org/protocol/disco#info'>
...
    <feature var='urn:xmpp:message-retract:1#tombstone'/>
...
  </query>
</iq>]]></example>

  <p>
      When replacing the original message with a tombstone, the original contents
      (i.e. the &lt;body/&gt; and any related elements which might leak information about the original message)
      get replaced with a &lt;retracted/&gt; element which MUST include an 'id' attribute referring to the
      original message as detailed in the section on <link url='#business-id'>using the correct ID</link>,
      so that clients can match it to the subsequent retraction
      (which MUST also be stored in the archive).
  </p>
  <p>The &lt;retracted/&gt; element SHOULD also include a 'stamp' attribute indicating the time at which the retraction took place.</p>
  <p>As with other XEP-0313 archived messages, the &xep0203; &lt;delay/&gt; element is used to indicate when the original message was received.</p>

  <example caption='Retracted message tombstone in a MAM result'><![CDATA[
<message id='aeb213' to='lord@capulet.example/chamber'>
  <result xmlns='urn:xmpp:mam:2' queryid='f27' id='stanza-id-1'>
    <forwarded xmlns='urn:xmpp:forward:0'>
      <delay xmlns='urn:xmpp:delay' stamp='2019-09-20T23:08:25Z'/>
      <message type="groupchat" from="romeo@montague.example" to="lord@capulet.example" id="wrong-recipient-1">
        <retracted stamp='2019-09-20T23:09:32Z' xmlns='urn:xmpp:message-retract:1' id='origin-id-1'/>
      </message>
  </forwarded>
</result>
</message>]]></example>
</section1>

<section1 topic='Business Rules' anchor='rules'>
  <p>A receiving client can choose to remove the retracted message from whatever display is used for messages, from any stored history, or choose to display the fact that a message has been retracted in another way.</p>
  <p>A MUC or other service that supports message retraction SHOULD prevent further distribution of the message by the service (e.g., by not replaying the message to new occupants joining the room, omitting the message from history archive requests where possible, or replacing the original message with a 'tombstone').</p>
  <p>Some clients may have been offline while the retraction was issued. The archiving service therefore MUST store the retraction message, regardless of whether the original message is deleted or replaced with a tombstone. These clients will then become aware of the retraction as soon as they catch up with the archive.</p>
  <p>A client MAY inform the user that a no-longer displayed message did previously exist and has been removed.</p>
  <p>Clients SHOULD add the &xep0359; &lt;origin-id&gt; on sent one-on-one "chat" messages to make them suitable for message retraction.</p>
  <p>The Sender MUST NOT send a retraction request for a message with non-messaging payloads. For example, a sender MUST NOT send a retraction for a roster item exchange request or a file transfer part.</p>
  <p>A retraction (that's not part of a &xep0425; operation) MUST only be processed when both the original message and the retraction request are received from the same bare-JID (in a one-on-one conversation) or full-JID (in a non-anonymous MUC from &xep0045;).</p>
  <p>When used in a semi-anonymous MUC, the recipient client MUST check that a message retraction was sent by the author of the retracted message by checking the occupant id from &xep0421;.</p>

  <section2 topic='Using the correct ID' anchor='business-id'>
    <p>
      For messages of type 'groupchat', the stanza's &xep0359; 'origin ID' MUST NOT be
      used for retractions. Instead, in group chat situations, the ID assigned to
      the stanza by the group chat itself must be used. This is discovered in a
      &lt;stanza-id&gt; element with a 'by' attribute that matches the bare JID
      of the group chat, as defined in &xep0359;.
    </p>
    <p>
      This implies that group chat messages without a &xep0359; stanza ID cannot be retracted.
    </p>
    <p>
      For other message types the sender should use the 'id' from a &xep0359;
      &lt;origin-id&gt; if present, or the value of the 'id' attribute on the
      &lt;message&gt; otherwise.
    </p>
  </section2>
</section1>
<section1 topic='Security Considerations' anchor='security'>
  <p>There can never be a guarantee that a retracted message was never seen or otherwise distributed, and it is encouraged for clients and services when possible to inform users that no such guarantee exists.</p>
  <p>To prevent message spoofing, it's very important that the JID or occupant id of message retractions are checked (as explained in the  <link url='#rules'>Business Rules</link> section).</p>
</section1>
<section1 topic='IANA Considerations' anchor='iana'>
  <p>None.</p>
</section1>
<section1 topic='XMPP Registrar Considerations' anchor='registrar'>
  <section2 topic='Protocol Namespaces' anchor='ns'>
    <p>The &REGISTRAR; includes 'urn:xmpp:message-retract:1' in its registry of protocol namespaces (see &NAMESPACES;).</p>
    <ul>
      <li>urn:xmpp:message-retract:1</li>
    </ul>
  </section2>
  <section2 topic='Protocol Versioning' anchor='registrar-versioning'>
    &NSVER;
  </section2>
</section1>
<section1 topic='XML Schema' anchor='schema'>
  <code><![CDATA[
<?xml version='1.0' encoding='UTF-8'?>

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='urn:xmpp:message-retract:1'
    xmlns='urn:xmpp:message-retract:1'
    elementFormDefault='qualified'>

  <xs:element name='retract'>
    <xs:attribute name='id' type='xs:string' use='required'/>
  </xs:element>

  <xs:element name='retracted'>
    <xs:complexType>
      <xs:simpleContent>
        <xs:extension base='xs:string'>
          <xs:attribute name='by' type='xs:string' use='required'/>
          <xs:attribute name='from' type='xs:string' use='optional'/>
          <xs:attribute name='stamp' type='xs:dateTime' use='required'/>
        </xs:extension>
      </xs:simpleContent>
    </xs:complexType>
  </xs:element>

</xs:schema>
    ]]></code>
</section1>
</xep>