<p>Some XMPP features must be offered by the server itself, or can't be available, that's the case of &xep0163; which is used in several places (e.g. bookmarks storage). But it can be desirable to use an external entity to manage some of these features, because it implements things that the server don't, or because it uses a special implementation useful in a particular case. Some people may also want to decentralize a feature on an entity under their control. This XEP try to solve these cases.<br/>Additionaly, a method to do generic treatments (independent of server) on stanza is also provided.</p>
<p>Here are some use cases of namespace delegation:</p>
<ul>
<li>use an external component for a PEP service because the server doesn't implement it or lacks some features</li>
<li>decentralize a server feature to an entity under client control</li>
<li>make a component which react on new user registration, independent of server implementation</li>
<li>server agnostic roster filtering</li>
</ul>
</section1>
<section1topic='Requirements'anchor='reqs'>
<p>Namespace delegation can be used in two modes:</p>
<ul>
<li><strong>admin</strong> mode, where delegation is specified by the server administrator.</li>
<li><strong>client</strong> mode, where it can be requested by any user.</li>
</ul>
<p>In <em>admin</em> mode, the managing entity manages stanza of the delegated namespace for all users registered on the server. The namespace delegation MUST be totally transparent for the managed entities.</p>
<p>In <em>client</em> mode, a managing entity MUST have an explicit authorization for any namespace he wants to use. Client SHOULD be able to check and revoke granted permissions, and if it's not possible, permissions MUST be revoked after a disconnection.</p>
</section1>
<section1topic='Glossary'anchor='glossary'>
<ul>
<li><strong>Delegated namespace</strong> — the namespace being managed by an external entity.</li>
<p>Once the managing entity is authenticated and stream is started, the server send it a &MESSAGE; stanza with a <delegation/> elements which MUST have the <strong>'urn:xmpp:delegation:2'</strong> namespace. This element contains <delegated/> elements which MUST contain a 'namespace' attribute indicating the delegated namespace. If there is additional attribute filtering, the <delegated/> can have children <attribute/> elements which MUST contain a 'name' attribute with the name of the filtering attribute.</p>
<p>Here <em>pubsub.capulet.lit</em> will received all stanzas of pubsub namespace sent to <em>capulet.lit</em>. It will also receive MAM stanzas, but only if the 'node' attribute is present in &QUERY;.</p>
<p>When a server receives a stanza for a delegated namespace which is either directed to him (no 'to' attribute, or 'to' attribute with its own JID), or directed to any bare jid (and only bare jid) that it manages (i.e. the <em>domainpart</em> is a domain handled by the server where delegation is activated), it MUST forwards it to the managing entity:</p>
<p>To forward, an &IQ; stanza of type "set" is used which contain a <delegation/> element (with namespace <em>'urn:xmpp:delegation:2'</em>) which in turn contain a <forwarded/> element encapsulating the initial stanza, according to &xep0297;:</p>
<p>Then the server MUST decapsulate the &IQ; result, MUST insure that the 'to' and the 'from' attribute corresponds to respectively the 'from' and the 'to' attributes of the initial stanza, MUST insure that the 'id' attribute of the decapsulated stanza is the same as the initial 'id' attribute and that 'type' is "result". If everything is alright, it can send the decapsulated stanza to Juliet.</p>
<p>If the forwarded result from managing entity is bad (i.e. wrong 'to', 'from', 'id' or 'result' attributes), the server MUST send an &IQ; error with condition <service-unavailable/> to managed entity, and MAY close the connexion with managing entity.</p>
<p><strong>N.B.₁:</strong> If the server encounter a delegated namespace and the managing entity is not available, it MUST return an &IQ; stanza of type "error" with an error condition of <service-unavailable/></p>
<p><strong>N.B.₂:</strong> Similarly, if the managing entity return an &IQ; stanza of type "error", the server must return itself an &IQ; stanza of type "error" with an error condition of <service-unavailable/></p>
<p><strong>N.B.₃:</strong> If the server encounter a delegated namespace but the filtering attribute does not match, it MUST follow its normal behaviour, i.e. it must follow the same behaviour it would have had if the namespace was not delegated at all</p>
<p>If a stanza is sent by the managing entity on a managed namespace, the server MUST NOT forward it. This way, the managing entity can use privileged entity to do specific treatments, a kind of universal plugin (i.e. working with all servers implementing &xep0355; and &xep0356;).</p>
<p>In the following examples, <em>juliet@capulet.lit</em> has its "<em>jabber:iq:roster</em>" namespace delegated to <em>filter.capulet.lit</em>. <em>filter.capulet.lit</em> is a server agnostic component which filters allowed entities (which can be added to a roster), and sort them in enforced groups.</p>
<examplecaption='Juliet adds Romeo to her roster'><![CDATA[
<iqfrom='juliet@capulet.lit/balcony'
id='roster1'
type='set'>
<queryxmlns='jabber:iq:roster'>
<itemjid='romeo@montaigu.lit'
name='My Romeo'>
</item>
</query>
</iq>
]]></example>
<examplecaption='server forwards stanza to managing entity'><