On 12/02/2014 07:49 PM, Alan Conway wrote:
On Tue, 2014-12-02 at 17:57 +0000, Gordon Sim wrote:
On 12/02/2014 05:38 PM, Gordon Sim wrote:
On 12/01/2014 05:41 PM, [email protected] wrote:
Author: aconway
Date: Mon Dec 1 17:41:09 2014
New Revision: 1642720
URL: http://svn.apache.org/r1642720
Log:
QPID-6252: AMQP 1.0 browsing client generates large number of errors
on broker.
The problem was that messages for browsing receivers were being
recorded on the
client SessionContext unacked list. This is incorrect since you don't ack
browsed messages. They remained on the list after the browsing
receiver was
closed, and every subsequent call to acknowledge() on the client would
attempt
to ack these messages for a no-longer-existing link. Fix is to not record
browsed messages.
I don't think this is right.
From the client's perspective, it should still be able to accept and
settle deliveries, regardless of whether the broker will dequeue in
response.
From the protocol perspective, deliveries must always get settled.
Otherwise they need to be tracked (whether within proton or on the
sending peer).
As regards the original error, the spec says:
The disposition performative MAY refer to deliveries on
links that are no longer attached. As long as the links
have not been closed or detached with an error then the
deliveries are still “live” and the updated state MUST
be applied.
It doesn't explicitly say what should happen if the link has been closed
(not just detached), so its probably best to just ignore it on the
broker (change the log level from error to info perhaps).
The client should probably also settle all existing deliveries received
on a link before closing it.
Or perhaps at least remove the deliveries from the unacked list if their
associated link is closed.
The client definitely needs to do something with these deliveries,
otherwise they accumulate on the session and you get longer and longer
lists of bad acknowledgements as time goes on. I don't think anyone on
the user interface side expects that they can/should ack messages from a
browsing session, although I would think doing so should be a no-op not
an error. Are you saying that the protocol requires it?
Yes, proton does also. However we could just settle at the point the
delivery is received and not add to the unacked list at all (as you do
now). As the code stands now that would be sufficient. Ideally I think
acknowledge is compatible with browse, it just serves a different
purpose. Rather than directly causing a message to be dequeued, it
signals to the broker that this subscriber has seen it. A future
implementation on the/a broker could then use that to determine when all
registered subscribers have seen it.
From my reading
the stuff about settlement only applies to "acquired transfers", which I
took to exclude transfers from a link that is in COPY mode.
You could argue that the accept outcome is only relevant to acquired
transfers (in my view it's not that clear in the spec text). However
settlement is distinct from that.
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