Suppose, the MQTT protocol has another command - UNSUBALL. When the broker receives this command, it interprets it as multiple UNSUBSCRIBE command for every topic the given client has subscribed to. And, so in response, the broker sends those many UNSUBACK responses. Or, perhaps, one UNSUBALL with reason codes as 0 (all un-subscribed), 1 (total failure), 2 (partially un-subscribed) and topic strings that were unsubscribed.
When developing a MQTT client, one can maintain a local store of the topics subscribed and then issue UNSUBSCRIBE to all these in a loop. However, with this command the overhead of maintaining such a store would be removed. A UNSUBALL allows an easy way for 'factory reset'.
Can such a command be added ?
Nagesh