Subscriptions are not renewed when auto-reconnecting

[SeadexWP]

If a connection to a MQTT broker is lost and auto-reconnected, subscriptions to topics are not renewed (not even with cleansession activated).
This is especially bad if the connection was lost due to a broker crash and the broker cannot (or does not want to) restore old sessions.
I was told (I did not confirm this) that the paho Java MQTT client does this correctly.

[ralight]

It was a conscious decision not to do this. It is easy to do at the client level by subscribing in the on_connect() callback.

[SeadexWP]

It was a conscious decision not to do this.

Thanks for the info!

It is easy to do at the client level by subscribing in the on_connect() callback

I used the on_connect() approach in my thin C++ wrapper.
And I agree that it is not a big effort to do this "manually", however I don't quite see the point to push this task onto the client. It's just plumbing that the client has to take care off: No obvious benefit, or is there something I overlook? I can't quite see the secenario in which - after a (unwanted) disconnect with auto-reconnect - I would not want to subscribe the topics I had subscribed before.
Maybe at least an optional auto-resubscribe can be considered for future versions?!

[icraggs]

If you want to retain the subscriptions, then you have the option of connecting with cleansession=false.

I do realize that there are drawbacks to this solution, given the semantics of clean session in MQTT (which should be solved in MQTT v5 incidentally).

The Paho Java client has the same behaviour, so I think your information is wrong in that case.

[icraggs]

I'm going to close this as being the way that the MQTT 3.1.1 clients work. When V5 comes along, the protocol update will fix.