mirror of
https://github.com/moparisthebest/xeps
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165 lines
8.1 KiB
XML
165 lines
8.1 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 Forwarding</title>
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<abstract>This document defines a protocol to forward a message from one entity to another.</abstract>
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&LEGALNOTICE;
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<number>0297</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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</dependencies>
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<supersedes/>
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<supersededby/>
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<shortname>forwarding</shortname>
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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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&ksmith;
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<revision>
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<version>0.3</version>
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<date>2011-07-11</date>
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<initials>ks</initials>
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<remark><p>Made security considerations more explicit.</p></remark>
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</revision>
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<revision>
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<version>0.2</version>
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<date>2011-07-06</date>
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<initials>psa</initials>
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<remark><p>Corrected XML namespace to reflect official publication.</p></remark>
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</revision>
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<revision>
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<version>0.1</version>
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<date>2011-04-11</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>0.0.1</version>
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<date>2011-03-22</date>
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<initials>mw/ks</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>There are many situations is which an entity needs to forward a previously sent message to another entity, such as forwarding an interesting message to a friend, or a server forwarding stored messages from an archive. Here we specify a simple encapsulation method for such forwarded messages. This format can be used in other specifications requiring the forwarding of messages, or used in isolation for a user to forward a message to another user (rather like email forwards).</p>
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</section1>
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<section1 topic='Requirements' anchor='requirements'>
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<p>Several properties are desirable when forwarding messages:</p>
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<ul>
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<li>The original sender and receiver should be identified.</li>
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<li>Extension payloads should be included (not only a message <body/></li>
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<li>It should be possible to annotate the message (e.g. with a timestamp) without ambiguity as to the original message.</li>
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<li>It should allow features such as encryption or signing of the original message to survive the forwarding.</li>
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</ul>
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</section1>
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<section1 topic='Forwarding a message'>
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<section2 topic='Overview'>
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<p>Let us suppose that a Romeo receives a message from Juliet:</p>
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<example caption='Receiving a message'><![CDATA[
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<message to='romeo@montague.lit' from='juliet@capulet.lit/orchard' type='chat' id='0202197'>
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<body>Yet I should kill thee with much cherishing.</body>
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<mood xmlns='http://jabber.org/protocol/mood'>
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<amorous/>
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</mood>
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</message>
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]]></example>
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<p>To forward this to Mercutio, Romeo would send a new message with a <forwarded/> payload of namespace 'urn:xmpp:forward:0'.</p>
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<example caption='Forwarding a message'><![CDATA[
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<message to='mercutio@verona.lit' from='romeo@montague.lit/orchard' type='chat' id='28gs'>
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<body>A most courteous exposition!</body>
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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='romeo@montague.lit' from='juliet@capulet.lit/orchard' type='chat' id='0202197' xmlns='jabber:client'>
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<body>Yet I should kill thee with much cherishing.</body>
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<mood xmlns='http://jabber.org/protocol/mood'>
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<amorous/>
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</mood>
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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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<section2 topic='Business rules'>
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<ul>
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<li>Forwarded messages SHOULD include all relevant child elements of the original message by default.
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However, an implementation MAY omit elements it deems irrelevant and safe to discard. An example
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would be omitting &xep0085; elements which typically do not make sense outside the context of a
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conversation session. However it should be noted that removing such elements can invalidate any
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digital signature on a stanza. If preserving a signature is important in the context this extension
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is used then child elements SHOULD NOT be removed.</li>
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<li>The forwarding entity SHOULD add a <delay/> child to the <forwarded/> element
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to indicate to the recipient the date/time that the forwarding entity received the original
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message. The format of this element is described in &xep0203;.</li>
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<li>The namespace of the forwarded stanza MUST be preserved (this is typically 'jabber:client').
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If no 'xmlns' is set for the stanza then as per XML namespacing rules it would inherit the
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'urn:xmpp:forward:0' namespace, which is wrong.</li>
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<li>When this extension is employed simply for a user to forward a given message to a contact, the
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outer <message/> SHOULD contain a body (even if empty) and a receiving client should pay
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particular attention to ensure it renders both the sender's text and the forwarded message
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unambiguously.</li>
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</ul>
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</section2>
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</section1>
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<section1 topic='Security Considerations' anchor='security'>
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<p>Forwarding messages can reveal information about the original sender, including possible presence leaks as well as the message payloads themselves. Any extensions using this format must therefore consider the implications of this.</p>
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<p>Forwarding can either be used as-is, or in the context of another specification, with different security considerations:</p>
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<section2 topic='As-is' anchor='as-is-sc'>
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<p>Receipt of a forwarded message from a third-party does not guarantee that the original message was actually received, or that the content has not been modified, by the forwarder. Integrity of the original message can only be determined through digital signing mechanisms such as described in &xep0285; and &xep0290;.</p>
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<p>Considering the above an end-user client should take special care in its rendering of a forwarded message to ensure that the user cannot mistake it for a message received directly from the original sender.</p>
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<p>An entity SHOULD NOT trust that forwards are genuine when receiving them unprovoked (i.e. outside the scope of another specification).</p>
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</section2>
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<section2 topic='Extensions' anchor='extensions-sc'>
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<p>While security considerations are ultimately dependent upon the specifications using the format defined herein, forwarding introduces scope for message forgery such that authors of derivative specifications will need to address security considerations themselves. These need to cover which entities a client should accept forwards from, and which entities those are permitted to forward messages for. For example, a specification may choose to only trust forwards if they are received from the user's client, another client on the bare JID, or the user's server.</p>
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</section2>
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</section1>
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<section1 topic='XML Schema' anchor='schema'>
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<code><![CDATA[
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<?xml version='1.0' encoding='UTF-8'?>
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<xs:schema
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xmlns:xs='http://www.w3.org/2001/XMLSchema'
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targetNamespace='urn:xmpp:forward:0'
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xmlns='urn:xmpp:forward:0'
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elementFormDefault='qualified'>
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<xs:annotation>
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<xs:documentation>
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The protocol documented by this schema is defined in
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XEP-xxxx: http://www.xmpp.org/extensions/inbox/forwarding.html
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</xs:documentation>
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</xs:annotation>
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<xs:element name='forwarded'>
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<xs:complexType>
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<xs:sequence xmlns:delay='urn:xmpp:delay'>
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<xs:element ref='delay:delay' minOccurs='0' maxOccurs='1' />
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<xs:any namespace='##other' minOccurs='1' maxOccurs='1' />
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</xs:sequence>
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</xs:complexType>
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</xs:element>
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</xs:schema>
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]]></code>
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</section1>
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<section1 topic='Acknowledgements' anchor='ack'>
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<p>Thanks to Matt Miller and Florian Zeitz for feedback.</p>
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</section1>
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</xep>
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