[Standards] XEP-0369 (MIX): Early stages of a clients connection

Jonas Wielicki jonas at wielicki.name
Thu May 18 15:09:41 UTC 2017

Dear Steve and others,

In the xsf@ MUC, we were discussion the interaction of MIX and roster, and the 
question what happens with roster versioning and MIX entries came up.

The key scenario which is unclear is the following: Assuming a server and 
client both support and use roster versioning, what happens when the client 
gains MIX capability in an update? The client connects to the server and posts 
its roster version X to the server. How does the server reply? Of course, the 
server can "overlay" the addition of MIX (from the point of view of the 
client) ontop of the changes accumulated since version X.

I think this should at least be discussed in the MIX XEP.

A somewhat related point brought up by Dave was *how* does the server find out 
whether a client supports MIX when asked for the roster? The theory was that 
the server would know, because of XEP-0115 Entity Capabilities or similar 
mechanisms. However, at the point the roster is requested, the client may 
easily not have sent presence yet. 

So the server might need to make a disco#info request while letting the client 
wait for the roster response. An extra round-trip, which is not even obvious 
to the client.

Steve and others on the list, opinions?

kind regards,

P.S.: It also seems underspecified in the MIX XEP whether a client needs to 
send available presence to receive MIX messages and whether a client which 
sent available presence, but with negative priority, receives MIX messages. 
But I think Steve already took note of that in the xsf@ MUC. Only including it 
here for completeness.

P.P.S.: None of these issues were found by me (the first was found by Georg, 
the second and third by Dave); I am just re-laying those to the list since we 
don’t have logs currently and I think those are worth discussing.
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