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<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE xep SYSTEM 'xep.dtd' [
<!ENTITY % ents SYSTEM 'xep.ent'>
<?xml-stylesheet type='text/xsl' href='xep.xsl'?>
<title>Best Practices for Resource Locking</title>
<abstract>This document specifies best practices to be followed by Jabber/XMPP clients about when to lock into, and unlock away from, resources.</abstract>
<copyright>This XMPP Extension Protocol is copyright (c) 1999 - 2010 by the XMPP Standards Foundation (XSF).</copyright>
<permissions>Permission is hereby granted, free of charge, to any person obtaining a copy of this specification (the &quot;Specification&quot;), to make use of the Specification without restriction, including without limitation the rights to implement the Specification in a software program, deploy the Specification in a network service, and copy, modify, merge, publish, translate, distribute, sublicense, or sell copies of the Specification, and to permit persons to whom the Specification is furnished to do so, subject to the condition that the foregoing copyright notice and this permission notice shall be included in all copies or substantial portions of the Specification. Unless separate permission is granted, modified works that are redistributed shall not contain misleading information regarding the authors, title, number, or publisher of the Specification, and shall not claim endorsement of the modified works by the authors, any organization or project to which the authors belong, or the XMPP Standards Foundation.</permissions>
<warranty>## NOTE WELL: This Specification is provided on an &quot;AS IS&quot; BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, express or implied, including, without limitation, any warranties or conditions of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A PARTICULAR PURPOSE. In no event shall the XMPP Standards Foundation or the authors of this Specification be liable for any claim, damages, or other liability, whether in an action of contract, tort, or otherwise, arising from, out of, or in connection with the Specification or the implementation, deployment, or other use of the Specification. ##</warranty>
<liability>In no event and under no legal theory, whether in tort (including negligence), contract, or otherwise, unless required by applicable law (such as deliberate and grossly negligent acts) or agreed to in writing, shall the XMPP Standards Foundation or any author of this Specification be liable for damages, including any direct, indirect, special, incidental, or consequential damages of any character arising out of the use or inability to use the Specification (including but not limited to damages for loss of goodwill, work stoppage, computer failure or malfunction, or any and all other commercial damages or losses), even if the XMPP Standards Foundation or such author has been advised of the possibility of such damages.</liability>
<conformance>This XMPP Extension Protocol has been contributed in full conformance with the XSF's Intellectual Property Rights Policy (a copy of which may be found at &lt;<link url='http://www.xmpp.org/extensions/ipr-policy.shtml'>http://www.xmpp.org/extensions/ipr-policy.shtml</link>&gt; or obtained by writing to XSF, P.O. Box 1641, Denver, CO 80201 USA).</conformance>
<spec>XMPP Core</spec>
<spec>XMPP IM</spec>
<firstname>Matthew </firstname>
<remark><p>Initial draft</p></remark>
<section1 topic='Introduction' anchor='intro'>
<p>Section 5.1 of &rfc3921bis; defines the concept of a "one-to-one chat session" and recommends that clients support the behavior described there, including:</p>
<li>Send the first message in a chat session to the bare JID &LOCALBARE; of the intended recipient</li>
<li>Send messages to the full JID &LOCALFULL; only after receiving a reply from the recipient (this is called "locking" into that full JID).</li>
<li>Send messages to the bare JID again if the presence of the recipient changes in any way (this is called "unlocking" from the full JID).</li>
<p>This specification reinforces the recommendations from XMPP-IM and provides additional implementation guidance to developers of XMPP clients. It is hoped that wider deployment of clients that adhere to the advice provided here will result in an improved user experience.</p>
<section1 topic='General Rules' anchor='general'>
<!-- <p>TODO: simple state chart</p> -->
<section2 topic='Initial Conversation State' anchor='general-nolock'>
<p>A client MUST start conversations in the unlocked state. In this state, a client MUST send &MESSAGE;s to a conversee's bare JID.</p>
<section2 topic='Locking a Conversation' anchor='general-lock'>
<p>Once a client receives a chat &MESSAGE; from the conversee, whether or not this client initiated the conversation, it MUST lock the conversation. The client MUST remember the conversee's full JID and send further correspondence to this full JID until one of the unlocking conditions are met.</p>
<section2 topic='Unlocking a Conversation' anchor='general-unlock'>
<p>A client MUST unlock a chat session from a resource when one of the following conditions is met:</p>
<li>A &MESSAGE; from the same bare JID, but a different resource, is received. In this case, the client MAY lock to the new resource; or the client MAY revert to the initial state, sending any following correspondence to the conversee's bare JID.</li>
<li>A &MESSAGE; with a &lt;gone xmlns='http://jabber.org/protocol/chatstates'/&gt; chat state. In this case, the client MUST consider the conversation ended. Any further correspondence MUST be sent with a new threadID and to the bare JID.</li>
<li>any &PRESENCE; update from any resource for the conversee's bare JID, including &lt;presence type='unavailable'/&gt;. The client SHOULD revert to the initial state, sending any following correspondence to the conversee's bare JID.</li>
<section1 topic='User Agent Implementation Notes' anchor='impl'>
<p>This section is non-normative, but provides additional guidelines for clients that interact directly with users.</p>
<section2 topic='User Experience Considerations' anchor='experience'>
<p>To further improve the user experience, clients are strongly encouraged to implement &xep0085; and adhere to the recommendations from &xep0201;.</p>
<section2 topic='Idle Conversations' anchor='idle-chat'>
<p>A client MAY take into account the lack of activity of a conversation. Exactly how much inactivity constitutes an idle conversation is left to implementations to determine.</p>
<section2 topic='Overall Inactivity' anchor='idle-user'>
<p>A client MAY take into account the overall lack of activity of a user, in which case it is RECOMMENDED the client send a &PRESENCE; update to trigger any conversations to unlock. The exact conditions and &PRESENCE; information conveyed is left to implementations to determine.</p>
<!-- <section2 topic='Mobile Considerations' anchor='mobile'>
<p>TODO: notes on mobile clients (aggressiveness of unlocking, interactions with &xep0273;?)</p>
</section2> -->
<section1 topic='Business Rules' anchor='rules'>
<section1 topic='Accessibility Considerations' anchor='access'>
<section1 topic='Internationalization Considerations' anchor='i18n'>
<section1 topic='Security Considerations' anchor='security'>
<section1 topic='IANA Considerations' anchor='iana'>
<section1 topic='XMPP Registrar Considerations' anchor='registrar'>
<section1 topic='XML Schema' anchor='schema'>
<p>REQUIRED for protocol specifications.</p>