(un)subscribed signal does not pass topic any more

[ejvr]

The subscribe signal in QMQTT::Client still has a topic argument, but it will always be an empty string. Apparently the topic is not passed in the SUBACK message (See ClientPrivate::onNetworkReceived). The same goes for the unsubscribed signal.

Personally I do not have problems with this (not using the signals anyway), but I guess it may confuse people. Wouldn't it be better to remove the topic variable from the signals? The Client interface was already changed with pull request #96 which introduced the issue, so it seems OK to change it once more.

[mwallnoefer]

Good catch! I think it would be better to re-introduce the topic, so that we save it in a member variable. Of course it should be done only if it does not complicate our code too much.

@emqtt/qmqtt-team What do you think?

[ejvr]

This could be fixed by introducing a message ID -> topic lookup in the ClientPrivate class. Upon a (un)subscribe we add the message ID/topic combination to the lookup. When the (UN)SUBACK arrives we can recover the topic using the message ID in the message.

This would be a simple fix which would change the ClientPrivate class only. It just tried it and it seemed to work (with mosquitto as the broker). If you want, I can create a pull request with the change.

[mwallnoefer]

@ejvr Yes please, I am eager to accept your marvelous contributions.