XEP-0316: MUC Eventing Protocol

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 Publish-Subscribe (XEP-0060) [2]. 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:

<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.

<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 Entity Capabilities (XEP-0115) [6], 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.

<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):

<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.

5. Recommended Defaults¶

A MEP service MUST:

• Support the node discovery, node creation, node deletion, publish item, subscribe, unsubscribe, and item retrieval use cases specified in Publish-Subscribe (XEP-0060) [2].
• Support the "auto-create", "auto-subscribe", and "filtered-notifications" features.
• Support the "owner" and "subscriber" affiliations.
• Support the "presence" access model and set it to the default.
• Treat the room JID and each occupant JID as a collection node (i.e., as the root collection node for the virtual pubsub service associated with the chatroom or with each occupant JID).
• Default the 'deliver_notifications' configuration option to true (i.e., deliver payloads by default).
• Default the 'send_last_published_item' configuration option to on_sub_and_presence (i.e., send the last published item on subscription and on receipt of presence), treating the receipt of directed presence as equivalent to a subscription.

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:

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

<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¶

<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 Publish-Subscribe (XEP-0060) [2], 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

Deferred

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@stpeter.im

JabberID

stpeter@jabber.org

URI

https://stpeter.im/

Appendix C: Legal Notices¶

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 <https://xmpp.org/community/> 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¶

Appendix H: Revision History¶

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

1. Version 0.1 (2013-01-03)¶

   Initial published version approved for publication by the XMPP Council.

   psa
2. Version 0.0.2 (2012-12-09)¶

   Added description of occupant publishing.

   psa
3. Version 0.0.1 (2012-12-06)¶

   First draft.

   psa

Appendix I: Bib(La)TeX Entry

@report{saint-andre2012mep,
  title = {MUC Eventing Protocol},
  author = {Saint-Andre, Peter},
  type = {XEP},
  number = {0316},
  version = {0.1},
  institution = {XMPP Standards Foundation},
  url = {https://xmpp.org/extensions/xep-0316.html},
  date = {2012-12-06/2013-01-03},
}

END