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<?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>Deferred</status>
<lastcall>2017-03-01</lastcall>
<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>0.3.0</version>
<date>2018-01-25</date>
<initials>XEP Editor (jwi)</initials>
<remark>Defer due to lack of activity.</remark>
</revision>
<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 &lt;store/&gt;</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 &lt;no-copy/&gt; hint into the
messages he sends. Since it is also useless for these messages to be archived, he additionally adds the &lt;no-store/&gt;
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 &lt;no-store/&gt; 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 &lt;no-permanent-store/&gt; 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 storing 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 &lt;store/&gt; hint.</p>
</section2>
</section1>
<section1 topic="Hints" anchor="hints">
<section2 topic="No permanent store" anchor="no-permanent-store">
<p>The &lt;no-permanent-store/&gt; 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 &lt;no-store/&gt; 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 &lt;no-copy/&gt; 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 &lt;store/&gt; 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 &REGISTRAR;.</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>