Some XMPP features must be offered by the server itself, or can't be available, that's the case of Personal Eventing Protocol (XEP-0163) [2] 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.
Additionaly, a method to do generic treatments (independent of server) on stanza is also provided.
This XEP is complementary to Privileged Entity (XEP-0356) [3] (and works in a similar way), although they can be used together or separately.
Here are some use cases of namespace delegation:
Namespace delegation can be used in two modes:
In admin 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.
In client 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.
Namespaces delegations are granted in the server configuration. Only <iq/> stanza namespaces can be delegated.
A feature is delegated using:
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 'urn:xmpp:delegation:1' 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.
<message from='capulet.lit' to='pubub.capulet.lit' id='12345'>
<delegation xmlns='urn:xmpp:delegation:1'>
<delegated namespace='urn:xmpp:mam:0'>
<attribute name='node' />
</delegated>
<delegated namespace='http://jabber.org/protocol/pubsub'/>
</delegation>
</message>
Here pubsub.capulet.lit will received all stanzas of pubsub namespace sent to capulet.lit. It will also receive MAM stanzas, but only if the 'node' attribute is present in <query/>.
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 domainpart is a domain handled by the server where delegation is activated), it MUST forwards it to the managing entity:
<iq from='juliet@capulet.lit/balcony'
id='pep1'
type='set'>
<pubsub xmlns='http://jabber.org/protocol/pubsub'>
<publish node='http://jabber.org/protocol/mood'>
<item>
<mood xmlns='http://jabber.org/protocol/mood'>
<annoyed/>
<text>curse my nurse!</text>
</mood>
</item>
</publish>
</pubsub>
</iq>
The server gets this stanza, sees that this namespace is delegated to pubsub.capulet.lit, so it forwards it.
To forward, an <iq/> stanza of type "set" is used which contain a <delegation/> element (with namespace 'urn:xmpp:delegation:1') which in turn contain a <forwarded/> element encapsulating the initial stanza, according to Stanza Forwarding (XEP-0297) [1]:
<iq from='capulet.lit'
to='pubsub.capulet.lit'
id='delegate1'
type='set'>
<delegation xmlns='urn:xmpp:delegation:1'>
<forwarded xmlns='urn:xmpp:forward:0'>
<iq from='juliet@capulet.lit/balcony'
id='pep1'
type='set'
xmlns='jabber:client'>
<pubsub xmlns='http://jabber.org/protocol/pubsub'>
<publish node='http://jabber.org/protocol/mood'>
<item>
<mood xmlns='http://jabber.org/protocol/mood'>
<annoyed/>
<text>curse my nurse!</text>
</mood>
</item>
</publish>
</pubsub>
</iq>
</forwarded>
</delegation>
</iq>
The managing entity replies to the stanza by encapsulating its <iq/> result in the same way:
<iq from='pubsub.capulet.lit'
to='capulet.lit'
id='delegate1'
type='result'>
<delegation xmlns='urn:xmpp:delegation:1'>
<forwarded xmlns='urn:xmpp:forward:0'>
<iq to='juliet@capulet.lit/balcony'
id='pep1'
type='result'
xmlns='jabber:client'>
<pubsub xmlns='http://jabber.org/protocol/pubsub' />
</iq>
</forwarded>
</delegation>
</iq>
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.
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.
<iq to='juliet@capulet.lit/balcony'
id='pep1'
type='result'>
<pubsub xmlns='http://jabber.org/protocol/pubsub' />
</iq>
The workflow is fully transparent for Juliet.
N.B.₁: 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/>
N.B.₂: 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/>
N.B.₃: 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
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 Namespace Delegation (XEP-0355) [4] and Privileged Entity (XEP-0356) [3]).
In the following examples, juliet@capulet.lit has its "jabber:iq:roster" namespace delegated to filter.capulet.lit. filter.capulet.lit is a server agnostic component which filters allowed entities (which can be added to a roster), and sort them in enforced groups.
<iq from='juliet@capulet.lit/balcony'
id='roster1'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@montaigu.lit'
name='My Romeo'>
</item>
</query>
</iq>
<iq from='capulet.lit'
to='pubsub.capulet.lit'
id='delegate1'
type='set'>
<delegation xmlns='urn:xmpp:delegation:1'>
<forwarded xmlns='urn:xmpp:forward:0'>
<iq from='juliet@capulet.lit/balcony'
id='roster1'
type='set'
xmlns='jabber:client'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@montaigu.lit'
name='My Romeo'>
</item>
</query>
</iq>
</forwarded>
</delegation>
</iq>
filter.capulet.lit accepts to add Romeo, but all JIDs with a montaigu.lit must be in a "Rivals" group, so it first returns a success result (Romeo is accepted).
<iq from='pubsub.capulet.lit'
to='capulet.lit'
id='delegate1'
type='result'>
<delegation xmlns='urn:xmpp:delegation:1'>
<forwarded xmlns='urn:xmpp:forward:0'>
<iq to='juliet@capulet.lit/balcony'
id='roster1'
type='result'
xmlns='jabber:client' />
</forwarded>
</delegation>
</iq>
<iq to='juliet@capulet.lit/balcony'
id='roster1'
type='result' />
At this stade, the entity is accepted, but not added to the roster. filter.capulet.lit is also a privileged entity which can manage "jabber:iq:roster", so it uses this ability to add Romeo in the enforced group:
<iq to='juliet@capulet.lit'
from='filter.capulet.lit'
id='roster2'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@montaigu.lit'
name='My Romeo'>
<group>Rivals</group>
</item>
</query>
</iq>
The namespace is delegated, but as the stanza is from the managing entity, the server manages it normally. The entity is also privileged, so it can change the stanza of Juliet, the server accepts:
<iq to='filter.capulet.lit'
from='juliet@capulet.lit'
id='roster2'
type='result'/>
The server will then send the roster pushes (with the enforced group) normally.
In client mode, the managing entity is not certified by the server administrator, so the delegation MUST be explicitly allowed by the managed entity. This is initiated by the managing entity (it can be after an interaction with a managed entity, like a subscription).
To request delegation for a particular entity, the managing entity MUST have an <iq/> stanza with 'urn:xmpp:delegation:1' namespace. The <query/> element MUST have a 'to' attribute which specify the entity it wants to manage.
Namespace delegations are asked with a <delegate/> element, which MUST contain a 'namespace' attribute set to the requested namespace.
If an entity want to manage PEP service for Juliet, it can ask the delegation like this:
<iq from='pubsub.montaigu.lit' to='capulet.lit' type='get' id='delegation1'>
<query xmlns='urn:xmpp:delegation:1'
to='juliet@capulet.lit'>
<delegate namespace='http://jabber.org/protocol/pubsub'/>
</query>
</iq>
Once received the delegation request, the server ask to the client if it grants access to the requested namespace using Data Forms (XEP-0004) [5]. The server use a challenge which it MUST have generated itself.
<message from='capulet.lit' to='juliet@capulet.lit/balcony'>
<body>
pubsub.montaigu.lit wants to manage a feature normally managed by the server.
Do you allow it to manage the following features?
Be careful! According management to an entity is a serious thing,
think twice that you can trust the entity before doing this.
</body>
<x xmlns='jabber:x:data' type='form'>
<title>Delegation request</title>
<instructions>pubsub.montaigu.lit wants to manage the following features:
Do you allow it?</instructions>
<field type='hidden' var='challenge'><value>5439123</value></field>
<field type='hidden' var='FORM_TYPE'>
<value>urn:xmpp:delegation:1</value>
</field>
<field type='list-single'
label='Manage PubSub (http://jabber.org/protocol/pubsub)'
var='http://jabber.org/protocol/pubsub'>
<value>0</value>
<option label='No'><value>0</value></option>
<option label='Yes'><value>1</value></option>
</field>
</x>
</message>
The server SHOULD include a warning message, SHOULD translate the namespace to human friendly names (and MAY keep the original namespace in addition) and MUST set the default value to '0' (permission refused). The server MUST use namespaces as field var, so a client can use them to have a customized display.
The client can then answer to the form:
<message from='juliet@capulet.lit/balcony' to='capulet.lit'>
<x xmlns='jabber:x:data' type='submit'>
<field var='FORM_TYPE'>
<value></value>
</field>
<field var='challenge'><value>5439123</value></field>
<field var='http://jabber.org/protocol/pubsub'><value>1</value></field>
</x>
</message>
Here Juliet allows pubsub.montaigu.lit to manage the PubSub (and then PEP) service.
Finaly, the server notifies the entity of the granted delegation. It do this in the same way as for admin mode, except that the <delegation/> element has an attitional 'to' attribute set to the managed entity bare jid:
<message from='capulet.net' to='pubub.capulet.lit' id='6789'>
<delegation xmlns='urn:xmpp:delegation:1' to='juliet@capulet.lit'>
<delegated namespace='http://jabber.org/protocol/pubsub'/>
</delegation>
</message>
The managing entity can now manage the namespace in a similar way as in admin mode but with different rules:
Server SHOULD provide a way for clients to check already delegated namespaces, and revoke them by using Ad-Hoc Commands (XEP-0050) [6] on the well-defined command node 'urn:xmpp:delegation:1#configure'.
If present, the configuration commands MUST allow at least to check delegations granted to a managing entity, and to revoke them. A server MAY offer an option to keep delegations from one session to an other (see business rules).
If a server or an entity supports the namespace delegation protocol, it MUST report that fact by including a service discovery feature of "urn:xmpp:delegation:1" in response to a Service Discovery (XEP-0030) [7] information request:
<iq from='pubsub.capulet.lit'
id='disco1'
to='capulet.lit'
type='get'>
<query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>
<iq from='capulet.lit'
id='disco1'
to='pubsub.capulet.lit'
type='result'>
<query xmlns='http://jabber.org/protocol/disco#info'>
...
<feature var='urn:xmpp:delegation:1'/>
...
</query>
</iq>
When a server delegates a namespace to a managing entity, the later can have particular features which must be advertised by the former with disco protocol.
This is done by using a disco node, which is built in the following way: if pubsub.capulet.int manages pubsub namespace, it MUST report that fact in discovery feature, and have a 'urn:xmpp:delegation:1::http://jabber.org/protocol/pubsub' node which reports the managed features.
The node name is obtained by concatenating this XEP namespace (urn:xmpp:delegation:1), a '::' separator, and the delegated namespace (here http://jabber.org/protocol/pubsub).
The server MUST advertise the result in its own discovery answer, and MUST ignore features of its internal component (here internal PubSub service).
In the following example, the capulet.int server delegates its internal PEP component to pubsub.capulet.int. capulet.int only supports REQUIRED PubSub features and auto-create, while pubsub.capulet.int supports REQUIRED PubSub features and publish-options, but not auto-create.
juliet@capulet.int asks its server what it is capable of, she is specially interested in PubSub capabilities.
<iq from='juliet@capulet.lit/balcony'
id='disco1'
to='capulet.lit'
type='get'>
<query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>
Server delegates its PubSub namespace to pubsub.capulet.lit, so it asks its available features for this namespace like this:
<iq from='capulet.lit'
id='disco2'
to='pubsub.capulet.lit'
type='get'>
<query xmlns='http://jabber.org/protocol/disco#info'
node='urn:xmpp:delegation:1::http://jabber.org/protocol/pubsub'/>
</iq>
Note that in real situation, server has probably this information already in cache (see Implementation Notes).
pubsub.capulet.lit returns its available features:
<iq from='pubsub.capulet.lit'
id='disco2'
to='capulet.lit'
type='result'>
<query xmlns='http://jabber.org/protocol/disco#info'
node='urn:xmpp:delegation:1::http://jabber.org/protocol/pubsub'>
<feature var='http://jabber.org/protocol/pubsub'/>
<feature var='http://jabber.org/protocol/pubsub#publish'/>
<feature var='http://jabber.org/protocol/pubsub#subscribe'/>
<feature var='http://jabber.org/protocol/pubsub#publish-options'/>
</query>
</iq>
Server include the results in its own discovery info results:
<iq from='capulet.lit'
id='disco1'
to='juliet@capulet.lit/balcony'
type='result'>
<query xmlns='http://jabber.org/protocol/disco#info'>
<feature var='urn:xmpp:delegation:1'/>
...
<feature var='http://jabber.org/protocol/pubsub'/>
<feature var='http://jabber.org/protocol/pubsub#publish'/>
<feature var='http://jabber.org/protocol/pubsub#subscribe'/>
<feature var='http://jabber.org/protocol/pubsub#publish-options'/>
...
</query>
</iq>
Note that 'http://jabber.org/protocol/pubsub#auto-create' is not available.
N.B.: In the special case of attribute filtering, the server still display managing entity's features for the whole delegated namespace instead of its own internal ones.
As an entity may ask for discovery information on bare JID, which the server would answer, the managing entity must be able to send this kind of information.
To do so, the mechanism is the same as for server features, but the separator is ':bare:' instead of '::':
<iq from='juliet@capulet.lit/balcony'
id='disco3'
to='juliet@capulet.lit'
type='get'>
<query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>
Server delegate its PubSub namespace to pubsub.capulet.lit, so it ask its available features for this namespace like this:
<iq from='capulet.lit'
id='disco4'
to='pubsub.capulet.lit'
type='get'>
<query xmlns='http://jabber.org/protocol/disco#info'
node='urn:xmpp:delegation:1:bare:http://jabber.org/protocol/pubsub'/>
</iq>
As for general case, server has probably this information already in cache.
pubsub.capulet.lit returns its available features:
<iq from='pubsub.capulet.lit'
id='disco4'
to='capulet.lit'
type='result'>
<query xmlns='http://jabber.org/protocol/disco#info'
node='urn:xmpp:delegation:1:bare:http://jabber.org/protocol/pubsub'>
<identity category='pubsub' type='pep'/>
<feature var='http://jabber.org/protocol/pubsub#access-presence'/>
<feature var='http://jabber.org/protocol/pubsub#auto-create'/>
<feature var='http://jabber.org/protocol/pubsub#auto-subscribe'/>
<feature var='http://jabber.org/protocol/pubsub#config-node'/>
<feature var='http://jabber.org/protocol/pubsub#create-and-configure'/>
<feature var='http://jabber.org/protocol/pubsub#create-nodes'/>
<feature var='http://jabber.org/protocol/pubsub#filtered-notifications'/>
<feature var='http://jabber.org/protocol/pubsub#persistent-items'/>
<feature var='http://jabber.org/protocol/pubsub#publish'/>
<feature var='http://jabber.org/protocol/pubsub#retrieve-items'/>
<feature var='http://jabber.org/protocol/pubsub#subscribe'/>
...
</query>
</iq>
Then the server returns the answer to Juliet, as in general case, with requested bare JID in 'from' field.
<iq from='juliet@capulet.lit'
id='disco3'
to='juliet@capulet.lit/balcony'
type='result'>
<query xmlns='http://jabber.org/protocol/disco#info'>
<identity category='account' type='registered'/>
<identity category='pubsub' type='pep'/>
<feature var='http://jabber.org/protocol/pubsub#access-presence'/>
<feature var='http://jabber.org/protocol/pubsub#auto-create'/>
<feature var='http://jabber.org/protocol/pubsub#auto-subscribe'/>
<feature var='http://jabber.org/protocol/pubsub#config-node'/>
<feature var='http://jabber.org/protocol/pubsub#create-and-configure'/>
<feature var='http://jabber.org/protocol/pubsub#create-nodes'/>
<feature var='http://jabber.org/protocol/pubsub#filtered-notifications'/>
<feature var='http://jabber.org/protocol/pubsub#persistent-items'/>
<feature var='http://jabber.org/protocol/pubsub#publish'/>
<feature var='http://jabber.org/protocol/pubsub#retrieve-items'/>
<feature var='http://jabber.org/protocol/pubsub#subscribe'/>
...
</query>
</iq>
Extensions of Service Discovery as specified in Service Discovery Extensions (XEP-0128) [8] follow the same rules: for the delegated namespace, internal extensions MUST be removed and extensions of managing entity MUST be included instead.
This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [10].
The XMPP Registrar [11] includes 'urn:xmpp:delegation:1' in its registry of protocol namespaces (see <https://xmpp.org/registrar/namespaces.html>).
If the protocol defined in this specification undergoes a revision that is not fully backwards-compatible with an older version, the XMPP Registrar shall increment the protocol version number found at the end of the XML namespaces defined herein, as described in Section 4 of XEP-0053.
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='urn:xmpp:delegation:1'
xmlns='urn:xmpp:delegation:1'
elementFormDefault='qualified'>
<xs:import namespace='urn:xmpp:forward:0'
schemaLocation='http://xmpp.org/schemas/forward.xsd'/>
<xs:element name='query'>
<xs:complexType>
<xs:attribute name='to' use='required' type='xs:string'/>
</xs:attribute>
<xs:element name='delegate'
maxOccurs='unbounded'>
<xs:complexType>
<xs:attribute name='namespace' use='required' type='xs:string'/>
</xs:complexType>
</xs:element>
</xs:complexType>
</xs:element>
<xs:element name='delegation'>
<xs:complexType>
<xs:element ref='urn:xmpp:forward:0' minOccurs='0' maxOccurs='1' />
<xs:element name='delegated'
minOccurs='0'
maxOccurs='unbounded'>
<xs:complexType>
<xs:attribute name='namespace' use='required' type='xs:string'/>
<xs:element name='attribute'
minOccurs='0'
maxOccurs='unbounded'>
<xs:complexType>
<xs:attribute name='name' use='required' type='xs:string'/>
</xs:complexType>
</xs:element>
</xs:complexType>
</xs:element>
</xs:complexType>
</xs:element>
</xs:schema>
This XEP is linked with Privileged Entity (XEP-0356) [3] and works in a similar way.
The client mode delegation mechanism is inspired from Remote Roster Management (XEP-0321) [12] permission request.
Thanks to Adrien Cossa for his typos/style corrections
Thanks to Philipp Hancke, Dave Cridland, Kurt Zeilenga, Sergey Dobrov and Анна Мухаррам for their feedbacks.
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Permission is hereby granted, free of charge, to any person obtaining a copy of this specification (the "Specification"), 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.
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This XMPP Extension Protocol has been contributed in full conformance with the XSF's Intellectual Property Rights Policy (a copy of which can be found at <https://xmpp.org/about/xsf/ipr-policy> or obtained by writing to XMPP Standards Foundation, P.O. Box 787, Parker, CO 80134 USA).
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The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 6120) and XMPP IM (RFC 6121) specifications contributed by the XMPP Standards Foundation to the Internet Standards Process, which is managed by the Internet Engineering Task Force in accordance with RFC 2026. Any protocol defined in this document has been developed outside the Internet Standards Process and is to be understood as an extension to XMPP rather than as an evolution, development, or modification of XMPP itself.
The primary venue for discussion of XMPP Extension Protocols is the <standards@xmpp.org> discussion list.
Discussion on other xmpp.org discussion lists might also be appropriate; see <http://xmpp.org/about/discuss.shtml> for a complete list.
Errata can be sent to <editor@xmpp.org>.
The following requirements keywords as used in this document are to be interpreted as described in RFC 2119: "MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT"; "SHOULD", "RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY", "OPTIONAL".
1. XEP-0297: Stanza Forwarding <https://xmpp.org/extensions/xep-0297.html>.
2. XEP-0163: Personal Eventing Protocol <https://xmpp.org/extensions/xep-0163.html>.
3. XEP-0356: Privileged Entity <https://xmpp.org/extensions/xep-0356.html>.
4. XEP-0355: Namespace Delegation <https://xmpp.org/extensions/xep-0355.html>.
5. XEP-0004: Data Forms <https://xmpp.org/extensions/xep-0004.html>.
6. XEP-0050: Ad-Hoc Commands <https://xmpp.org/extensions/xep-0050.html>.
7. XEP-0030: Service Discovery <https://xmpp.org/extensions/xep-0030.html>.
8. XEP-0128: Service Discovery Extensions <https://xmpp.org/extensions/xep-0128.html>.
9. RFC 6120: Extensible Messaging and Presence Protocol (XMPP): Core <http://tools.ietf.org/html/rfc6120>.
10. The Internet Assigned Numbers Authority (IANA) is the central coordinator for the assignment of unique parameter values for Internet protocols, such as port numbers and URI schemes. For further information, see <http://www.iana.org/>.
11. The XMPP Registrar maintains a list of reserved protocol namespaces as well as registries of parameters used in the context of XMPP extension protocols approved by the XMPP Standards Foundation. For further information, see <https://xmpp.org/registrar/>.
12. XEP-0321: Remote Roster Management <https://xmpp.org/extensions/xep-0321.html>.
Note: Older versions of this specification might be available at http://xmpp.org/extensions/attic/
Cross-document editorial adjustments for inclusive language.
Corrected examples (Stefan Strigler).
Several updates according to feedbacks:
Initial published version approved by the XMPP Council.
First draft.
END