XEP-0316: MUC Eventing Protocol

Abstract:This specification defines semantics for using the XMPP publish-subscribe protocol to broadcast state change events associated with a Multi-User Chat (MUC) room. This profile of pubsub therefore enables a chatroom to function as a virtual pubsub service, easing the discovery of syndicated data and event notifications associated with such a room.
Author:Peter Saint-Andre
Copyright:© 1999 - 2014 XMPP Standards Foundation. SEE LEGAL NOTICES.
Status:Experimental
Type:Standards Track
Version:0.1
Last Updated:2013-01-03

WARNING: This Standards-Track document is Experimental. Publication as an XMPP Extension Protocol does not imply approval of this proposal by the XMPP Standards Foundation. Implementation of the protocol described herein is encouraged in exploratory implementations, but production systems are advised to carefully consider whether it is appropriate to deploy implementations of this protocol before it advances to a status of Draft.


Table of Contents


1. Introduction
2. Room Notifications
3. Occupant Notifications
4. Concepts and Approach
    4.1. Every Room JID and Occupant JID a Pubsub Service
    4.2. One Publisher Per Node
    4.3. Use Presence
    4.4. Filtered Notifications
    4.5. Smart Defaults
5. Recommended Defaults
6. Determining Support
7. Security Considerations
8. IANA Considerations
9. XMPP Registrar Considerations
    9.1. Service Discovery Category/Type
10. XML Schema
11. Acknowledgements

Appendices
    A: Document Information
    B: Author Information
    C: Legal Notices
    D: Relation to XMPP
    E: Discussion Venue
    F: Requirements Conformance
    G: Notes
    H: Revision History


1. Introduction

Just as Personal Eventing Protocol (XEP-0163) [1] defines a profile of Publish-Subscribe (XEP-0060) [2] that enables an instant messaging user to send updates or "events" to other users, this specification defines a profile that enables a room occupant or the chatroom itself to send notifications in the context of Multi-User Chat (XEP-0045) [3] chatroom.

Note: Any use cases, error flows, and other protocols details not described herein are described in XEP-0060. This document merely defines a "subset" or "profile" of XMPP publish-subscribe.

2. Room Notifications

Using the chatroom example from XEP-0045, imagine that the room itself wants to notify the occupants of the coven@chat.shakespeare.lit chatroom about events of interest to the group (say, notifications about multimedia aspects of the multi-user session, such as described in Delivering Conference Information to Jingle Participants (Coin) (XEP-0298) [4]).

When new information is available about the multimedia session (say, calling into a conference "bridge" or starting a Jingle (XEP-0166) [5] session to add a video feed), a multimedia engine might capture that event and inform the chatroom by means of a backend API. The chatroom itself then generates an event notification. That is, a chatroom does not publish events, instead it simply generates them based on data of interest. As a result, everyone in the room who is interested in that kind of data will receive a notification about the event:

Example 1. Interested occupants receive event notification

<message from='coven@chat.shakespeare.lit'
         to='crone1@shakespeare.lit/desktop'
         type='headline'
         id='zns61f38'>
  <event xmlns='http://jabber.org/protocol/pubsub#event'>
    <items node='urn:ietf:params:xml:ns:conference-info'>
      <item id='ehs51f40'>
        <conference-info 
            xmlns='urn:ietf:params:xml:ns:conference-info'>
          <conference-description>
            <available-media label='4'>
              <type>video</type>
              <status>sendonly</status>
            </available-media>
          </conference-description>
        </conference-info>
      </item>
    </items>
  </event>
</message>

<message from='coven@chat.shakespeare.lit'
         to='wiccarocks@shakespeare.lit/laptop'
         type='headline'
         id='uh4gs519'>
  <event xmlns='http://jabber.org/protocol/pubsub#event'>
    <items node='urn:ietf:params:xml:ns:conference-info'>
      <item id='ehs51f40'>
        <conference-info 
            xmlns='urn:ietf:params:xml:ns:conference-info'>
          <conference-description>
            <available-media label='4'>
              <type>video</type>
              <status>sendonly</status>
            </available-media>
          </conference-description>
        </conference-info>
      </item>
    </items>
  </event>
</message>
  

But how do the occupants tell the room that they are interested in knowing what about conference-info events? Whereas generic pubsub services require an explicit subscription to a conference-info node, MEP services support the "filtered-notification" feature from XEP-0060 and obviously share presence (since MUC is based on directed presence in the room) so the "auto-subscribe" feature also applies.

Example 2. Occupant sends directed presence to join the room, with caps

<presence from='crone1.shakespeare.lit/desktop'
          to='coven@chat.shakespeare.lit/firstwitch'>
  <x xmlns='http://jabber.org/protocol/muc'/>
  <c xmlns='http://jabber.org/protocol/caps' 
     hash='sha-1'
     node='http://jisti.org'
     ver='054H4A7280JuT6+IroVYxgCAjZo='/>
</presence>
  

That chatroom knows to send conference-info notifications to crone1@shakespeare.lig because when the room unpacks the value of the 'ver' attribute ("054H4A7280JuT6+IroVYxgCAjZo=") in accordance with XEP-0115, it discovers that her client advertises a service discovery feature of "urn:ietf:params:xml:ns:conference-info+notify", where the "+notify" suffix indicates interest in receiving notifications related to the protocol that precedes the suffix. The server can verify this support if needed by sending a service discovery request to crone1's full JID (see XEP-0115 for details).

3. Occupant Notifications

The foregoing section described how the room itself can inform the occupants about data of interest. However, in MEP any particular occupant can also publish information. An occupant does so by sending a publish-subscribe publish request to the occupant's Occupant JID <room@service/nick> (similar to the way in which publishing via PEP happens by sending a request to the user's bare JID <user@host>). For instance, the following example shows how a room occupant would inform the other occupants about an event of interest.

Example 3. Occupant Publishes Activity

<iq from='wiccarocks@shakespeare.lit/laptop'
    id='vlk3h264'
    to='coven@chat.shakespeare.lit/secondwitch'
    type='set'>
  <pubsub xmlns='http://jabber.org/protocol/pubsub'>
    <publish node='http://jabber.org/protocol/activity'>
      <item>
        <activity xmlns='http://jabber.org/protocol/activity'>
          <other/>
          <text xml:lang='en'>I'll give thee a wind.</text>
        </activity>
      </item>
    </publish>
  </pubsub>
</iq>
  

Note: Publishing to an occupant's MEP node happens by sending an explicit publish request to the Occupant JID. Publishing to a user's PEP node MUST NOT trigger a MEP publish request, because PEP and MEP are separate pubsub contexts.

As a result, everyone in the room who is interested in that kind of data will receive a notification about the event (note that even the publisher receives the event, if they have advertised interest in the payload type):

Example 4. Interested occupants receive event notification

<message from='coven@chat.shakespeare.lit/secondwitch'
         to='crone1@shakespeare.lit/desktop'
         type='headline'
         id='hs7bx143'>
  <event xmlns='http://jabber.org/protocol/pubsub#event'>
    <items node='http://jabber.org/protocol/activity'>
      <item id='bxg1c27r'>
        <activity xmlns='http://jabber.org/protocol/activity'>
          <other/>
          <text xml:lang='en'>I'll give thee a wind.</text>
        </activity>
      </item>
    </items>
  </event>
</message>

<message from='coven@chat.shakespeare.lit'
         to='wiccarocks@shakespeare.lit/laptop'
         type='headline'
         id='ke2v1c95'>
  <event xmlns='http://jabber.org/protocol/pubsub#event'>
    <items node='http://jabber.org/protocol/activity'>
      <item id='bxg1c27r'>
        <activity xmlns='http://jabber.org/protocol/activity'>
          <other/>
          <text xml:lang='en'>I'll give thee a wind.</text>
        </activity>
      </item>
    </items>
  </event>
</message>
  

4. Concepts and Approach

MUC eventing via pubsub ("MEP") is based on the following principles:

  1. Every room JID and occupant JID a pubsub service.
  2. One publisher per node (the chatroom or occupant itself).
  3. Use presence (implicit in multi-user chat).
  4. Filter notifications based on expressed interest.
  5. Smart defaults.

These principles are described more fully below.

4.1 Every Room JID and Occupant JID a Pubsub Service

Treating every MEP-enabled chatroom as a pubsub service simplifies the task of discovering and subscribing to information of interest in or about the room.

4.2 One Publisher Per Node

There is no need for multiple publishers to a MEP service, since by definition only the chatroom itself or the occupant itself publishes information.

4.3 Use Presence

By definition, a chatroom has presence information about the occupants, because they use directed presence to join the room.

4.4 Filtered Notifications

By default, the use of directed presence is used to establish a MEP subscription to the chatroom's eventing data. In order to filter which notifications are sent by the MEP service, the contact's client includes extended Entity Capabilities (XEP-0115) [6] information in the directed presence notifications it sends to the chatroom. Because the MEP-enabled room supports the "filtered-notifications" feature, it sends only those notifications that match the occupant's expressed notification preferences.

4.5 Smart Defaults

Most pubsub configuration options and metadata are not needed for MUC eventing. Instead, MEP services offer smart defaults to simplify node creation and management.

5. Recommended Defaults

A MEP service MUST:

A PEP service MAY support other use cases, affiliations, access models, and features, but such support is OPTIONAL.

6. Determining Support

If a chatroom supports MEP, it MUST advertise that fact in its responses to Service Discovery (XEP-0030) [7] information ("disco#info") requests by returning an identity of "pubsub/mep" and the relevant pubsub features:

Example 5. A disco#info query

<iq type='get' 
    from='hag66@shakespeare.lit/pda'
    to='coven@chat.shakespeare.lit'
    id='k3hs5174'>
  <query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>
  

Example 6. A disco#info response

<iq type='result' 
    from='coven@chat.shakespeare.lit'
    to='hag66@shakespeare.lit/pda'
    id='k3hs5174'>
  <query xmlns='http://jabber.org/protocol/disco#info'>
    <identity category='conference' type='text'/>
    <identity category='pubsub' type='mep'/>
    ...
    <feature var='http://jabber.org/protocol/disco#info'/>
    <feature var='http://jabber.org/protocol/disco#items'/>
    <feature var='http://jabber.org/protocol/muc'/>
    <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'/>
    <feature var='muc_passwordprotected'/>
    <feature var='muc_hidden'/>
    <feature var='muc_temporary'/>
    <feature var='muc_open'/>
    <feature var='muc_unmoderated'/>
    <feature var='muc_nonanonymous'/>
    ...
  </query>
</iq>
  

7. Security Considerations

The security considerations of XEP-0045 and XEP-0163 apply.

8. IANA Considerations

This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [8].

9. XMPP Registrar Considerations

9.1 Service Discovery Category/Type

The XMPP Registrar [9] includes a category of "pubsub" in its registry of Service Discovery identities (see <http://xmpp.org/registrar/disco-categories.html>); as a result of this document, the Registrar includes a type of "pep" to that category.

The registry submission is as follows:

<category>
  <name>pubsub</name>
  <type>
    <name>mep</name>
    <desc>
      A MUC eventing service that supports the 
      publish-subscribe subset defined herein.
    </desc>
    <doc>XEP-0316</doc>
  </type>
</category>
    

10. XML Schema

Because MEP simply reuses the protocol specified in XEP-0060, a separate schema is not needed.

11. Acknowledgements

Thanks to Joe Hildebrand, Matt Miller, and Matthew Wild for their input.


Appendices


Appendix A: Document Information

Series: XEP
Number: 0316
Publisher: XMPP Standards Foundation
Status: Experimental
Type: Standards Track
Version: 0.1
Last Updated: 2013-01-03
Approving Body: XMPP Council
Dependencies: XMPP Core, XMPP IM, XEP-0030, XEP-0045, XEP-0060, XEP-0115
Supersedes: None
Superseded By: None
Short Name: mep
Source Control: HTML
This document in other formats: XML  PDF


Appendix B: Author Information

Peter Saint-Andre

Email: stpeter@jabber.org
JabberID: stpeter@jabber.org
URI: https://stpeter.im/


Appendix C: Legal Notices

Copyright

This XMPP Extension Protocol is copyright © 1999 - 2014 by the XMPP Standards Foundation (XSF).

Permissions

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.

Disclaimer of Warranty

## NOTE WELL: This Specification is provided on an "AS IS" 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. ##

Limitation of 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 from, out of, or in connection with the Specification or the implementation, deployment, or other use of 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.

IPR Conformance

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 <http://xmpp.org/about-xmpp/xsf/xsf-ipr-policy/> or obtained by writing to XMPP Standards Foundation, 1899 Wynkoop Street, Suite 600, Denver, CO 80202 USA).

Appendix D: Relation to XMPP

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.


Appendix E: Discussion Venue

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>.


Appendix F: Requirements Conformance

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".


Appendix G: Notes

1. XEP-0163: Personal Eventing Protocol <http://xmpp.org/extensions/xep-0163.html>.

2. XEP-0060: Publish-Subscribe <http://xmpp.org/extensions/xep-0060.html>.

3. XEP-0045: Multi-User Chat <http://xmpp.org/extensions/xep-0045.html>.

4. XEP-0298: Delivering Conference Information to Jingle Participants (Coin) <http://xmpp.org/extensions/xep-0298.html>.

5. XEP-0166: Jingle <http://xmpp.org/extensions/xep-0166.html>.

6. XEP-0115: Entity Capabilities <http://xmpp.org/extensions/xep-0115.html>.

7. XEP-0030: Service Discovery <http://xmpp.org/extensions/xep-0030.html>.

8. 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/>.

9. 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 <http://xmpp.org/registrar/>.


Appendix H: Revision History

Note: Older versions of this specification might be available at http://xmpp.org/extensions/attic/

Version 0.1 (2013-01-03)

Initial published version approved for publication by the XMPP Council.

(psa)

Version 0.0.2 (2012-12-09)

Added description of occupant publishing.

(psa)

Version 0.0.1 (2012-12-06)

First draft.

(psa)

END