[sugar] Tubes message dropping

[Simon McVittie]

On Sat, 21 Jul 2007 at 13:50:27 +0200, J.M. Maurer wrote:
> To the Tube guys:
> 
> Do you drop messages on your XMPP server? An AbiCollab packet that
> contains an image never gets sent over, resulting in documents getting
> out of sync (in fact, the PS seems to disconnect the buddy altogether
> from the Write session).

Without reading the source for Gabble: It's possible that (a) we don't
fragment large Tubes messages into multiple XMPP-level messages, and (b) the
XMPP server we're using fails on large messages. I'd have to check the
source and XEPs to be sure. If this is the case, a workaround would be to
avoid sending very large single messages in user apps, and the correct fix
would be to fragment the D-Bus message into multiple XMPP messages in Gabble.

Guillaume: you touched it last, I think. Are we likely to have this bug?

> What would be the proper way to solve this? I can implement full
> checking of message ordering/dropping in AbiCollab ofcourse, but that
> seems like a solution at the wrong level.

Agreed - D-Bus tubes should either get all the messages through
correctly, or disconnect you.

Please note, however, that we don't guarantee total ordering of messages.
In the master/slave topology you use for AbiCollab this won't be a
problem, since the order in which the master sees messages can be
treated as authoritative, but in a more "socialist" protocol this could lead
to problems unless designed carefully. (I'm told the overhead which would be
involved in guaranteeing total ordering in Salut makes it unreasonable to
do in general.)

	Simon