[jdev] Reliable presence

[JD Conley]

> since I saw happen for the first time last night. While I was in jdev
> there
> happened to be a 6 hour ghost due to a server's connection being
broken.
> That was due to an unavailable presence never being sent. The same
could
> happen if one of my contacts was online. He'd still appear online if
his
> server's connection to the outside world vanished.

I see this happen all the time. 

> Justin suggested that
> server's should cache available presences that get routed through it,
and
> if the s2s connection isn't there the server would try to connect
> periodically to make sure the server was still reachable. If it wasn't
> then
> the server would generate unavailable presence stanzas for all JIDs
for
> that server.

I agree that this needs to be a function of each server.  It's also
necessary to make sure both the outgoing and incoming channels work with
the remote server.  Thus, something like the proposed ping protocol
would be required, not just a connection attempt.  I've spent a great
deal of time thinking about how to best fix this issue in our server and
have come to the same conclusions as Justin.  We have some similar
"fix-it" logic around presence subscriptions.

JD