In XMPP, rosters and presence subscriptions have been used to date only among IM users (see XMPP IM [1]). However, nothing prevents the application of these concepts to other XMPP entities, such as components and servers. Given that a presence subscription typically indicates some level of trust in a peer, server deployments can use the sharing of XMPP presence information as a way to indicate that a given server has a trust relationship with a peer server (informally, we can say that the two servers consider each other "buddies"). The server might then share certain kinds of additional information only with its trusted peers, for example Incident Reporting (XEP-0268) [2] and Entity Reputation (XEP-0275) [3]. The server buddy relationship can also be leveraged for additional functionality, such as Service Directories (XEP-0309) [4]
To establish such a trust relationship with a peer, a server sends a presence subscription request to the peer, just as is done between XMPP users.
<presence from='montague.lit'
to='capulet.lit'
type='subscribe'/>
A server MUST NOT send such a presence subscription request unless explicitly requested to do so by a server administrator (see below).
Upon receiving such a presence subscription request, the XMPP server software running at the peer shall either prompt the server administrator to approve the request or (if explicitly configured to accept subscriptions requests) automatically approve it. (A future version of this specification might define an approval method based on Data Forms (XEP-0004) [5].)
If the request is approved, the peer server then informs the originating server that the request has been approved.
<presence from='capulet.lit'
to='montague.lit'
type='subscribed'/>
The peer SHOULD also send a subscription request to the originating server.
<presence from='capulet.lit'
to='montague.lit'
type='subscribe'/>
The originating server would then approve that subscription request.
<presence from='montague.lit'
to='capulet.lit'
type='subscribed'/>
If an XMPP server implementation supports this usage of presence subscriptions, it MUST keep a list of approved entities, which we denote a "server roster". The implementation MAY use that roster for access control purposes defined in other specifications.
This section defines an Ad-Hoc Commands (XEP-0050) [6] node scoped by the Field Standardization for Data Forms (XEP-0068) [7] FORM_TYPE specified in Service Administration (XEP-0133) [8]. Upon advancement of this specification to Draft, this section ought to be moved to XEP-0133.
The command node for this use case SHOULD be "http://jabber.org/protocol/admin#server-buddy".
A sample protocol flow for this use case is shown below.
<iq from='bard@shakespeare.lit/globe'
id='nrw51vs8'
to='shakespeare.lit'
type='set'
xml:lang='en'>
<command xmlns='http://jabber.org/protocol/commands'
action='execute'
node='http://jabber.org/protocol/admin#server-buddy'/>
</iq>
Unless an error occurs (see the "Error Handling" section of XEP-0133), the service SHOULD return the appropriate form.
<iq from='shakespeare.lit'
id='nrw51vs8'
to='bard@shakespeare.lit/globe'
type='result'
xml:lang='en'>
<command xmlns='http://jabber.org/protocol/commands'
node='http://jabber.org/protocol/admin#server-buddy'
sessionid='server-buddy:20040408T0337Z'
status='executing'>
<x xmlns='jabber:x:data' type='form'>
<title>Subscribing to a Peer Server</title>
<instructions>Fill out this form to subscribe your server to a peer server.</instructions>
<field type='hidden' var='FORM_TYPE'>
<value>http://jabber.org/protocol/admin</value>
</field>
<field label='The domain name of the peer server'
type='jid-single'
var='peerjid'>
<required/>
</field>
</x>
</command>
</iq>
Note: In virtual hosting environments, the server can determine the domain name from which to send the presence subscription based on the 'to' address of the <iq/> stanza.
<iq from='bard@shakespeare.lit/globe'
id='lk2vs82g'
to='shakespeare.lit'
type='set'
xml:lang='en'>
<command xmlns='http://jabber.org/protocol/commands'
node='http://jabber.org/protocol/admin#server-buddy'
sessionid='server-buddy:20040408T0337Z'>
<x xmlns='jabber:x:data' type='submit'>
<field type='hidden' var='FORM_TYPE'>
<value>http://jabber.org/protocol/admin</value>
</field>
<field var='peerjid'>
<value>marlowe.lit</value>
</field>
</x>
</command>
</iq>
<iq from='shakespeare.lit'
id='lk2vs82g'
to='bard@shakespeare.lit/globe'
type='result'
xml:lang='en'>
<command xmlns='http://jabber.org/protocol/commands'
node='http://jabber.org/protocol/admin#server-buddy'
sessionid='server-buddy:20040408T0337Z'
status='completed'/>
</iq>
Notification of completion MAY include the processed data in a data form of type "result".
To advertise its support for the server buddy feature, when replying to service discovery information ("disco#info") requests a server MUST return a URN of "urn:xmpp:server-presence".
<iq from='jabber.org'
id='uw72g176'
to='xmpp.net'
type='get'>
<query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>
<iq from='xmpp.net'
id='uw72g176'
to='jabber.org'
type='result'>
<query xmlns='http://jabber.org/protocol/disco#info'>
<feature var='urn:xmpp:server-presence'/>
</query>
</iq>
Because server "buddies" might be granted greater privileges than unknown peers, care should be taken in sending or approving presence subscription requests. In particular, a server MUST NOT send a presence subscription request unless explicitly requested to do so by a server administrator.
This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [9].
<var> <name>urn:xmpp:server-presence</name> <desc>Support for subscriptions to server presence</desc> <doc>XEP-0267</doc> </var>
Field Standardization for Data Forms (XEP-0068) [7] defines a process for standardizing the fields used within Data Forms scoped by a particular namespace. This registration adds two more reserved fields to the 'http://jabber.org/protocol/admin' namespace defined in XEP-0133.
<form_type>
<name>http://jabber.org/protocol/admin</name>
<field var='peerjid'
type='jid-single'
label='The Jabber ID of a peer server'/>
</form_type>
Thanks to Kim Alvefur, Waqas Hussain, and Tobias Markmann for their feedback.
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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 <https://xmpp.org/community/> 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. RFC 6121: Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence <http://tools.ietf.org/html/rfc6121>.
2. XEP-0268: Incident Reporting <https://xmpp.org/extensions/xep-0268.html>.
3. XEP-0275: Entity Reputation <https://xmpp.org/extensions/xep-0275.html>.
4. XEP-0309: Service Directories <https://xmpp.org/extensions/xep-0309.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-0068: Field Data Standardization for Data Forms <https://xmpp.org/extensions/xep-0068.html>.
8. XEP-0133: Service Administration <https://xmpp.org/extensions/xep-0133.html>.
9. 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/>.
Note: Older versions of this specification might be available at https://xmpp.org/extensions/attic/
Corrected several examples and points in the text.
Noted that sending server can be derived from 'to' address on IQ stanza, so removed serverjid field from FORM_TYPE; defined method for determining support; added further XMPP Registrar Considerations.
Updated ad-hoc command with field for the sending server; added XMPP Registrar Considerations.
Defined ad-hoc command for admin generation of outbound presence subscription; added security considerations.
Initial published version.
First draft, split from the incident reporting proposal.
@report{hefczyc2009xep0267,
title = {Server Buddies},
author = {Hefczyc, Artur and Jensen, Florian and Rémond, Mickaël and Saint-Andre, Peter and Wild, Matthew},
type = {XEP},
number = {0267},
version = {0.5},
institution = {XMPP Standards Foundation},
url = {https://xmpp.org/extensions/xep-0267.html},
date = {2009-04-30/2012-05-29},
}END