[Standards] XEP-0280 Carbon Rules for MUC-PMs

Kim Alvefur zash at zash.se
Tue Jan 31 21:11:49 UTC 2017

On Fri, Jan 27, 2017 at 02:36:56PM +0100, Georg Lukas wrote:
> To fix outgoing PMs, these need to be carbon-copied only to the other
> clients of the user which are joined under the same nickname. This is a
> HARD problem. Possible solutions are:
> a) Require carbon-enabled clients to tag outgoing MUC-PMs with <x/>,
> carbon-copy the 'sent' MUC-PM to all clients, require carbon-enabled
> clients to check for <x/> tag and to drop if they are not joined. This
> is a 90% solution (it will still display outgoing PMs if you are
> joined to the same MUC under different nicknames, as the other client
> doesn't know which nickname the 'sent' message came from).

I believe at least two implementations do this already.

> b) Require the user's server to track MUC joins, including nickname, and
> make the carbons logic depend on that. This is a 100% solution, at least
> once everybody has updated their servers, and it might add a significant
> burden on the server (at least comparable to tracking directed
> presence). Does not conflict with (a) so it might be a long-term
> improvement for the last 10%.

This has the nice property that a service administrator can fix the
problems for their own users in one upgrade, as opposed to having to
wait for all remote MUC services beyond their control.

> c) Let the MUC generate 'sent' carbons to other MSN clients. This is a
> security nightmare waiting to happen. I'm not going to go this route,
> and I only mention it for sake of completeness.

Yeah. No. Let's not. However it would be an interesting experiment to
re-invent groupchat using carbons.

> My favorite is to mandate (a) now and possibly follow up with (b),
> depending on server implementer feedback.

Kim "Zash" Alvefur

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