The Multi-User Chat (XEP-0045) [1] protocol was not designed to handle s2s interruptions or message loss well. Rather often, the restart of a server or a component causes a client to believe that it is still joined to a given chatroom, while the chatroom service does not know of this occupant.
Existing approaches for re-synchronization are either inefficient (presence updates and "silent" messages are reflected to all occupants, totalling to O(N²) stanzas per time unit), or mask message / presence losses (the implicit join performed via the deprecated GC1.0 protocol).
This specification aims to provide the most efficient, albeit not the most elegant, way for clients to periodically check whether they are still joined to a chatroom. However, it can not ensure that a client remains joined to a room without any interruptions.
This specification only makes sense in the context of Multi-User Chat (XEP-0045) [1] chatrooms. It makes use of XMPP Ping (XEP-0199) [2] to perform periodic self-pings.
Server support for this extension is optional, but will significantly improve the reliability with Multi-Session Nicks and mobile clients.
A typical connection between a client and a Multi-User-Chatroom (MUC) goes through the client-to-server link, possibly a server-to-server link and a typically local server-to-component link. If one of the involved servers or the MUC component is restarted, or one of the links is disturbed for some time, this can lead to the removal of some or all occupants from the affected MUCs, without the clients being informed.
To an occupant, this looks like the MUC is silent (there is no chat activity and no presence changes), making it hard to realize that the connection was interrupted.
To prevent the bad usability effect (message loss, lack of reaction from people in a chatroom), a client needs to actively check whether it is still joined to a MUC.
There are multiple alternative approaches for a client to test whether it is still joined to a MUC:
The private IQ is the most robust and traffic-efficient solution, and it does not rely on server support. The XMPP Ping (XEP-0199) [2] protocol is appropriate to use for this use case.
After an adequate amount of silence from a given MUC (e.g. 15 minutes), or from all MUCs from a given service domain, a client should initiate a self-ping. If Juliet is joined as JuliC in the characters@chat.shakespeare.lit MUC, her client will send the following ping IQ:
<iq from='juliet@capulet.lit/client' id='s2c1' type='get'
to='characters@chat.shakespeare.lit/JuliC'>
<ping xmlns='urn:xmpp:ping'/>
</iq>
If Juliet's client is not joined, the MUC service will respond with a <not-acceptable> error. Thus, her client can automatically attempt a rejoin.
<iq from='characters@chat.shakespeare.lit/JuliC' id='s2c1' type='error'
to='juliet@capulet.lit/client' >
<error type="cancel" by="characters@chat.shakespeare.lit">
<not-acceptable xmlns="urn:ietf:params:xml:ns:xmpp-stanzas" />
</error>
</iq>
If her client is joined, the IQ request will be forwarded to any one of Juliet's joined clients.
<iq from='characters@chat.shakespeare.lit/JuliC' id='c0ffee-s2c1' type='get'
to='juliet@capulet.lit/somerandomclient' >
<ping xmlns='urn:xmpp:ping'/>
</iq>
Depending on the other client implementation and its connection status,
the IQ will be responded to eventually, in one of these ways, as
delivered to the "client" resource:
The normal routing rules of the self-ping impose two round-trips: first the initial ping from the client to the MUC, then the reflection of the ping and its response (possibly to another client), and finally the response to the initial IQ. If the other client is experiencing network connectivity issues, which is often the case with mobile devices, the ping request might never be responded to.
Therefore, a MUC service supporting this protocol may directly respond
to a occupant's Ping request to the occupant's own nickname, as
opposed to routing it to any of the occupant's clients. A service
implementing this optimization needs to advertise the
http://jabber.org/protocol/muc#self-ping-optimization feature in the Service Discovery (XEP-0030) [5] disco#info response on
the individual MUC room JIDs, and it MUST respond to a self-ping request
as follows:
<iq from='darkcave@chat.shakespeare.lit'
type='result'>
<query xmlns='http://jabber.org/protocol/disco#info'>
<!-- ... -->
<feature var='http://jabber.org/protocol/muc#self-ping-optimization'/>
</query>
</iq>
In Multi-Session-Nick scenarios, where multiple clients of the same user are joined as the same occupant, it is possible that another client initiates a nickname change while a ping request is pending. In that case, the ping might be responded to with <item-not-found>.
A client should not perform a self-ping after initiating a nickname change, and before receiving the response to the nickname change from the service, as it is not yet clear whether the new nickname will be accepted.
If a client session is in hibernation (Stream Management (XEP-0198) [6]), the client should defer sending of self-ping requests until it is reconnected and re-authenticated.
A MUC service implementation should not allow a non-occupant to obtain information about occupants. This is however true irregardless of implementing this specification.
This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [7].
Include "http://jabber.org/protocol/muc#self-ping-optimization"
as a valid feature in the Registry of Features.
<var> <name>http://jabber.org/protocol/muc#self-ping-optimization</name> <desc>Support for the MUC self-ping optimization</desc> <doc>XEP-0410</doc> </var>
This document does not define any new XML structure requiring a schema.
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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.
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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-0045: Multi-User Chat <https://xmpp.org/extensions/xep-0045.html>.
2. XEP-0199: XMPP Ping <https://xmpp.org/extensions/xep-0199.html>.
3. XEP-0085: Chat State Notifications <https://xmpp.org/extensions/xep-0085.html>.
4. Different service implementations will send different responses to a client that's not joined. The recommended error code is <not-acceptable>, however some servers will respond with <not-allowed> or <bad-request> as well.
5. XEP-0030: Service Discovery <https://xmpp.org/extensions/xep-0030.html>.
6. XEP-0198: Stream Management <https://xmpp.org/extensions/xep-0198.html>.
7. 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 http://xmpp.org/extensions/attic/
Add handling for another corner case, change title to Council’s liking
First draft.
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