QoS 1 behavior
Ernesto Garcia
I was reading mqtt-s specification.
It says:
"At any point in time a client may have only one QoS level 1 or 2 PUBLISH message outstanding, i.e. it has to
wait for the termination of this PUBLISH message exchange before it could start a new level 1 or 2 transaction."
I understand client refers to publisher node. What happen if the client is working on QoS 1 and it generates a new event to publish , but it has not received the PUBACK of the previous PUBLISH message ?. In the default behavior, i think it discards the new one until it receives the PUBACK.
Is it correct ?
Thanks for your help and suggestions.
--
Ernesto
Nicholas O'Leary
as the spec says, an MQTT-S client may only have one qos1/2 publish in
flight at any one time. A client implementation needs to honour that
requirement so it has the following choices:
1. the easiest thing for a client to do is to discard any newly
submitted publishes until the flow completes - leave it to the
application to deal with resubmitting if it needs to,
2. the client could block the call to submit the publish until the
outstanding flow completes - but it may not be appropriate to block
the application like this,
3. thie client could queue the publishes up internally and send it
when the flow completes - but it means the application won't know
if/when the message is eventually sent.
There is not a default behaviour; it is up to the implementation to
decide which approach to take. Each of which has advantages and
disadvantages.
Regards,
Nick
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