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<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;
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<number > 0334</number>
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<status > Experimental</status>
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<lastcall > 2017-03-01</lastcall>
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<lastcall > 2017-02-22</lastcall>
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<type > Standards Track</type>
<sig > Standards</sig>
<approver > Council</approver>
<dependencies >
<spec > XMPP Core</spec>
</dependencies>
<supersedes />
<supersededby />
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<shortname > hints</shortname>
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&mwild;
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<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>
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<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>
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<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>
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<li > Whether to store a message that would not have been stored under normal conditions</li>
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</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>
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]]></example>
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</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>
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<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>
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</section1>
<section1 topic= "Hints" anchor= "hints" >
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<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
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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>
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<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)
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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>
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<section2 topic= "Store" >
<p > A message containing the < store/> hint that is not of type 'error' SHOULD be stored by the entity.</p>
</section2>
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</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' />
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<xs:element name= 'store' type= 'empty' />
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<xs:simpleType name= 'empty' >
<xs:restriction base= 'xs:string' >
<xs:enumeration value= '' />
</xs:restriction>
</xs:simpleType>
</xs:schema>
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]]></code>
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</section1>
</xep>
