XEP-Remarks/XEP-0045: Multi-User Chat
Stable Message IDs
As of 2018, server implementations are required to keep the message ID when reflecting client messages. This can be determined by the presence of the 'http://jabber.org/protocol/muc#stable_id' feature on the MUC JID or MUC domain.
Introduces 'ofrom' Extended Stanza Addressing (XEP-33) type
in http://xmpp.org/extensions/xep-0045.html#enter-history, which is not found in XEP-33 (nor XEP-33s schema).
Matching Your Reflected Message
So you sent a message to a MUC and want to immediately display it as "on the way" (good UX). Some time later (usually within some seconds) you receive a message from the MUC which might or might not be your sent message.
Find out if a relfection is your actual message, in six easy steps! The message is your reflection if:
- you recently sent a message to the MUC, AND
- the received message is from your participant JID, AND
- the XEP-0359 origin ID matches (probably not a transport) OR
- the message ID matches (a nice MUC, but not required by the XEP) OR
- the message body matches (not conclusive, some MUCs auto-pastebin) OR
- the received message is the first line of the sent message (transports like IRC split multi-line messages into one-liners) OR
- the sent message is very long (>400 bytes) and the received message is a prefix of it (IRC transpors split very long one-liners too!)
(this mechanism doesn't cover MUCs which don't reflect the message ID and do autopastebin. Screw them!)
Mediated MUC Invitations
The default mechanism to invite somebody into a MUC is §7.8.2 Mediated Invitation, where the MUC service will invite your friend on your behalf.
- Some MUC services will not invite a JID that is already a MUC member, thus breaking the invitation UX.
- With Mediated Invites, a malicious MUC can send an invite in the name of a user's contact, tricking the user's client into auto-joining.
- XEP-0249: Direct MUC Invitations is a potential solution to those issues.
Am I still there?
Current MUC / server implementations do not send offline-presence packets to participants on service restart. Therefore, a client will think it is still joined to a MUC indefinitely, only seeing silence.
There is no portable/reliable mechanism to check if the client is still joined, and no clean way to re-sync the state if it is not joined. Sending a "silent" message or presence update to the MUC will lead to O(N²) complexity (if every client does so), killing all our batteries.
This is solved by XEP-0410: MUC Self-Ping
MUC double join
This has been fixed in revision 1.29 of XEP-0045:
It's not specified what should happen if an entity sends an initial presence when it's already joined. Server implementations should behave towards the joining entity like it successfully joined. That means, if a presence update containing an <x> element is received from a participant, the server should send back the full presence list, the requested amount of history and the room subject.