Can somebody explain aedes.subscribe (topic, deliverfunc, callback)

[aqibamir]

I've tried to understand deliverfunc from documentation but I just can not wrap my head around it.

[robertsLando]

• topic is the topic to subscribe to
• deliverFunction is the function called when a message is received matching the sub topic. It has packet, done args, packet is the published packet received and done is the funcction to call once you finish processing the packet. The reason about done is to provide backpressure, in poor words means that until you don't call done aedes will stop processing other packets (stops the incoming stream).
• cb is called when subscription is correctly setup on broker, it's optional BTW, it uses mqemitter: https://github.com/mcollina/mqemitter#emitteron-topic-listener-callback