<?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 Processing Hints</title> <abstract>This document defines a way to include hints to entities routing or receiving a message.</abstract> &LEGALNOTICE; <number>0334</number> <status>Proposed</status> <lastcall>2017-02-22</lastcall> <type>Standards Track</type> <sig>Standards</sig> <approver>Council</approver> <dependencies> <spec>XMPP Core</spec> </dependencies> <supersedes/> <supersededby/> <shortname>hints</shortname> &mwild; <revision> <version>0.2</version> <date>2015-09-01</date> <initials>dg</initials> <remark> <p>Fixed the wrong use of no-storage instead of no-store</p> <p>Added a message hint <store/></p> </remark> </revision> <revision> <version>0.1</version> <date>2013-07-11</date> <initials>psa</initials> <remark><p>Initial published version approved by the XMPP Council.</p></remark> </revision> <revision> <version>0.0.1</version> <date>2013-06-18</date> <initials>mw</initials> <remark><p>First draft.</p></remark> </revision> </header> <section1 topic='Introduction' anchor='intro'> <p>Message types ('normal', 'chat', 'headline', etc.) provide an existing framework for determining how an entity should deliver or handle a message. For example &xmppim; defines that messages of type 'headline' should not be stored offline by the server, and that messages of type 'groupchat' must not be directed to other resources.</p> <p>However this framework of rules is quite inflexible, and new extensions are being developed that push at the boundaries of what is capable of. This specification defines a more flexible approach that allows the sender to add finer-grained 'hints' to messages, which can be used as a generic mechanism for XMPP entities to handle messages.</p> <p>A similar but much more extensive framework is defined in &xep0079; for applications that need it.</p> </section1> <section1 topic='Requirements' anchor='reqs'> <p>This specification aims to solve the following common problems, and allow a sender to hint to the recipient:</p> <ul> <li>Whether to store a message (e.g. for archival or as an 'offline message').</li> <li>Whether to copy a message to other resources.</li> <li>Whether to store a message that would not have been stored under normal conditions</li> </ul> </section1> <section1 topic='Use Cases' anchor='usecases'> <section2 topic="Session-based stanzas" anchor='usecases-session'> <p>Suppose that Romeo and Juliet are avoiding the surveillance of Prince Escalus and communicating using a session-based encryption protocol between their laptops. In order to prevent Juliet's tablet computer that uses &xep0280; from receiving copies of the encrypted messages (and not being able to decrypt them), Romeo inserts the <no-copy/> hint into the messages he sends. Since it is also useless for these messages to be archived, he additionally adds the <no-store/> hint:</p> <example caption='Sending a message with no-copy and no-store hints'><![CDATA[ <message from='romeo@montague.lit/laptop' to='juliet@capulet.lit/laptop'> <body>V unir avtug'f pybnx gb uvqr zr sebz gurve fvtug</body> <no-copy xmlns="urn:xmpp:hints"/> <no-store xmlns="urn:xmpp:hints"/> </message> ]]></example> </section2> <section2 topic="Notifications" anchor='usecases-notification'> <p>Some automated notifications may be transient, and there would be no purpose in delaying their delivery. Such messages may be marked with the <no-store/> hint.</p> </section2> <section2 topic="Sensitive messages" anchor='usercases-sensitive'> <p>A sender may want to indicate their preference to have no permanent record of a message (also known as "off the record" messages), but may be happy for it to be stored temporarily as a normal part of delivery (e.g. if the recipient is offline at the time of sending). Such a message can be marked with the <no-permanent-store/> hint. </p> </section2> <section2 topic="Storage-worthy messages" anchor='store-worthy'> <p>Offline storage and &xep0313; can define their own rules on what messages to store and usually only store messages that contain a body element. However a sender may want to indicate that a message is worth storeing even though it might not match those rules (e.g. an encrypted message that carries the payload outside the body element). Such a message can be marked with a <store/> hint.</p> </section2> </section1> <section1 topic="Hints" anchor="hints"> <section2 topic="No permanent store" anchor="no-permanent-store"> <p>The <no-permanent-store/> hint informs entities that they shouldn't store the message in any permanent or semi-permanent public or private archive (such as described in &xep0136; and &xep0313;) or in logs (such as chatroom logs). </p> </section2> <section2 topic="No store" anchor="no-store"> <p>A message containing a <no-store/> hint should not be stored by a server either permanently (as above) or temporarily, e.g. for later delivery to an offline client, or to users not currently present in a chatroom. </p> </section2> <section2 topic="No copies" anchor="no-copy"> <p>Messages with the <no-copy/> hint should not be copied to addresses other than the one to which it is addressed, for example through &xep0280;.</p> <p>This hint MUST only be included on messages addressed to full JIDs and explicitly does not override the behaviour defined in &xmppim; for handling messages to bare JIDs, which may involve copying to multiple resources, or multiple occupants in a &xep0045; room. </p> </section2> <section2 topic="Store"> <p>A message containing the <store/> hint that is not of type 'error' SHOULD be stored by the entity.</p> </section2> </section1> <section1 topic='Business Rules' anchor='rules'> <p>It is important to note that message hints are, as the name implies, just hints. Implementations MUST NOT rely on other entities interpretation of the hints for any particular purpose.</p> </section1> <section1 topic='Security Considerations' anchor='security'> <p>This specification introduces no known security considerations.</p> </section1> <section1 topic='IANA Considerations' anchor='iana'> <p>This document requires no interaction with &IANA;.</p> </section1> <section1 topic='XMPP Registrar Considerations' anchor='registrar'> <p>This document requires no interaction with ®ISTRAR;.</p> </section1> <section1 topic='XML Schema'> <code><![CDATA[ <?xml version='1.0' encoding='UTF-8'?> <xs:schema xmlns:xs='http://www.w3.org/2001/XMLSchema' targetNamespace='urn:xmpp:hints' xmlns='urn:xmpp:hints' elementFormDefault='qualified'> <xs:element name='no-permanent-store' type='empty'/> <xs:element name='no-store' type='empty'/> <xs:element name='no-copy' type='empty'/> <xs:element name='store' type='empty'/> <xs:simpleType name='empty'> <xs:restriction base='xs:string'> <xs:enumeration value=''/> </xs:restriction> </xs:simpleType> </xs:schema> ]]></code> </section1> </xep>