Max QoS

[slavslavov]

Is it possible to add a configuration setting to limit the QoS? Something like max_qos in Mosquitto? It will be great if this can be done per listener though.

[halfgaar]

MQTT5 actually supports sending max QoS to clients in the CONNACK, but FlashMQ apparently doesn't to this yet. It should be easy enough to do.

For MQTT5, the behavior is specified as disconnecting the client. For MQTT3 clients, it becomes more fuzzy. I see Mosquitto simply disconnects those clients, but that's kind of harsh, because clients can't know they are not supposed to do that.

[slavslavov]

In my case, users will know that this particular connection supports only QoS 0 so if their devices get disconnected they will know the reason.

[slavslavov]

Will it make sense to have a plugin callback and based on the return value to ignore the message or disconnect the client? This may not be a standard behaviour but is a real use case.

[halfgaar]

In that case, a special return value for the ACL check may be needed.

However, thinking about it, disconnecting the client may be the only good option. If you don't, you have two choices:

• Drop the packet. The client will not get the ack, and therefore will see many in-flight packets.
• Send an ack-deny and drop the packet. This still causes the overhead you'd sought to avoid.

Perhaps an MQTT3 reject action could be configured.