Implement MQTT QoS 2 support

[harism]

Has it been considered should Hono support MQTT QoS level 2 also? Something like requiring predefined Kafka ack message (or error) for every send adapters make, which, timeouts after a certain period of time or mandates the response for clients?

As the most strict case I believe it should be possible that all adapters could work on this QoS level internally and disregard all it what the client is expecting.

[sophokles73]

I am not sure if I understand correctly. Are you talking about the telemetry or the command & control direction, or both?
In any case, we deliberately chose to not support exactly once delivery semantics simply because we have never seen it work in real deployments ;-)

[harism]

Good question I was thinking about telemetry and event messages actually.

And to keep things simple keep optional too - like add MQTT endpoint in each adapter which the server side clients can choose or not to use.

Ps. as a totally unrelated point I'd like to introduce you to my long time favorite song originating from Germany, and quite obviously hope you enjoy this too.