Major The current spec is ambiguous with respect to the acceptable values of the QoS flag for PUBREL, SUBSCRIBE and UNSUBSCRIBE operations.
It could be interpreted that QoS must be set to 1 to force an appropriate ACK. However the ACK behavior is described independently.
do we accept only one value ?
if so, should it be 0, 1 or 2?
Are other values be treated as malformed?
Forcing 0 would change the protocol flow on the wire.
Forcing 1 is consistent with the spirit of the input spec, but we need some clarity. The intended ACK behavior is not really related to QoS.
Agreed Raph. I think it makes sense to define clearly what the client must flow and what the server must reject.
On Behalf of Roger Light:-
Hello,
The mosquitto broker and clients set the fixed header QoS bits to 1
for PUBREL, SUBSCRIBE and UNSUBSCRIBE. On receipt of one of those
messages they don't verify if QoS is set to 1 however, because it's
already clear what needs to be done.
It feels as though specifying the QoS here is more notional/for
completeness than in the PUBLISH case. It doesn't provide any extra
information.
Cheers,
Roger
Ta Roger for the comments.
discussed at scrub call on 08.08.2013. Proposal updated for TC vote on next call
TC approve at TC call 15.08.2013
checked WD12
I'm going to argue there's no one completely right answer. However, for consistency, I'd go with forcing 1. If we leave it 'woolly', then we create difficulties down the road if we ever do want to use any of these values for something else.
Does any one know what current implementations of clients do?