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<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE xep SYSTEM 'xep.dtd' [
<!ENTITY % ents SYSTEM 'xep.ent'>
<!ENTITY xep0285 "<span class='ref'><link url='http://xmpp.org/extensions/xep-0285.html'>Encapsulating Digital Signatures in XMPP</link></span> <note>XEP-0285: Encapsulating Digital Signatures in XMPP &lt;<link url='http://xmpp.org/extensions/xep-0285.html'>http://xmpp.org/extensions/xep-0285.html</link>&gt;.</note>" >
<!ENTITY xep0290 "<span class='ref'><link url='http://xmpp.org/extensions/xep-0290.html'>Encapsulated Digital Signatures in XMPP</link></span> <note>XEP-0290: Encapsulated Digital Signatures in XMPP &lt;<link url='http://xmpp.org/extensions/xep-0290.html'>http://xmpp.org/extensions/xep-0290.html</link>&gt;.</note>" >
%ents;
]>
<?xml-stylesheet type='text/xsl' href='xep.xsl'?>
<xep>
<header>
<title>Message Forwarding</title>
<abstract>This document defines a protocol to forward a message from one entity to another.</abstract>
&LEGALNOTICE;
<number>xxxx</number>
<status>ProtoXEP</status>
<type>Standards Track</type>
<sig>Standards</sig>
<dependencies>
<spec>XMPP Core</spec>
</dependencies>
<supersedes/>
<supersededby/>
<shortname>forwarding</shortname>
<schemaloc>
<url>http://www.xmpp.org/schemas/forwarding.xsd</url>
</schemaloc>
<author>
<firstname>Matthew</firstname>
<surname>Wild</surname>
<email>me@matthewwild.co.uk</email>
<jid>me@matthewwild.co.uk</jid>
</author>
&ksmith;
<revision>
<version>0.0.1</version>
<date>2011-03-22</date>
<initials>mw/ks</initials>
<remark><p>First draft.</p></remark>
</revision>
</header>
<section1 topic='Introduction' anchor='intro'>
<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.</p>
</section1>
<section1 topic='Requirements' anchor='requirements'>
<p>Several properties are desirable when forwarding messages:</p>
<ul>
<li>The original sender and receiver should be identified.</li>
<li>Extension payloads should be included (not only a message &lt;body/&gt;</li>
<li>It should be possible to annotate the message (e.g. with a timestamp) without ambiguity as to the original message.</li>
<li>It should allow features such as encryption or signing of the original message to survive the forwarding.</li>
</ul>
</section1>
<section1 topic='Forwarding a message'>
<section2 topic='Overview'>
<p>Let us suppose that a Romeo receives a message from Juliet:</p>
<example caption='Receiving a message'><![CDATA[
<message to='romeo@montague.lit' from='juliet@capulet.lit/orchard' type='chat' id='0202197'>
<body>Yet I should kill thee with much cherishing.</body>
<mood xmlns='http://jabber.org/protocol/mood'>
<amorous/>
</mood>
</message>
]]></example>
<p>To forward this to Mercutio, Romeo would send a new message with a &lt;forwarded/&gt; payload of namespace 'urn:xmpp:forward:tmp'.</p>
<example caption='Forwarding a message'><![CDATA[
<message to='mercutio@verona.lit' from='romeo@montague.lit/orchard' type='chat' id='28gs'>
<body>A most courteous exposition!</body>
<forwarded xmlns='urn:xmpp:forward:tmp'>
<delay xmlns='urn:xmpp:delay' stamp='2010-07-10T23:08:25Z'/>
<message to='romeo@montague.lit' from='juliet@capulet.lit/orchard' type='chat' id='0202197' xmlns='jabber:client'>
<body>Yet I should kill thee with much cherishing.</body>
<mood xmlns='http://jabber.org/protocol/mood'>
<amorous/>
</mood>
</message>
</forwarded>
</message>
]]></example>
</section2>
<section2 topic='Business rules'>
<ul>
<li>Forwarded messages SHOULD include all relevant child elements of the original message by default.
However, an implementation MAY omit elements it deems irrelevant and safe to discard. An example
would be omitting &xep0085; elements which typically do not make sense outside the context of a
conversation session. However it should be noted that removing such elements can invalidate any
digital signature on a stanza. If preserving a signature is important in the context this extension
is used then child elements SHOULD NOT be removed.</li>
<li>The forwarding entity SHOULD add a &lt;delay/&gt; child to the &lt;forwarded/&gt; element
to indicate to the recipient the date/time that the forwarding entity received the original
message. The format of this element is described in &xep0203;.</li>
<li>The namespace of the forwarded stanza MUST be preserved (this is typically 'jabber:client').
If no 'xmlns' is set for the stanza then as per XML namespacing rules it would inherit the
'urn:xmpp:forward:tmp' namespace, which is wrong.</li>
<li>When this extension is employed simply for a user to forward a given message to a contact, the
outer &lt;message/&gt; SHOULD contain a body (even if empty) and a receiving client should pay
particular attention to ensure it renders both the sender's text and the forwarded message
unambiguously.</li>
</ul>
</section2>
</section1>
<section1 topic='Security Considerations' anchor='security'>
<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>
<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>
<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>
</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:forward:tmp'
xmlns='urn:xmpp:forward:tmp'
elementFormDefault='qualified'>
<xs:annotation>
<xs:documentation>
The protocol documented by this schema is defined in
XEP-xxxx: http://www.xmpp.org/extensions/inbox/forwarding.html
</xs:documentation>
</xs:annotation>
<xs:element name='forwarded'>
<xs:complexType>
<xs:sequence xmlns:delay='urn:xmpp:delay'>
<xs:element ref='delay:delay' minOccurs='0' maxOccurs='1' />
<xs:any namespace='##other' minOccurs='1' maxOccurs='1' />
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:schema>
]]></code>
</section1>
<section1 topic='Acknowledgements' anchor='ack'>
<p>Thanks to Florian Zeitz for feedback.</p>
</section1>
</xep>