[mathgladiator]

MQTT v5 is fine enough until you have to care about reliability at scale. What I have seen happen is that it turns into a slightly better TCP where you have to build your own primitives.

For example, when you SUB, you get a SUBACK if enabled. However, there is nothing like a SUBFIN (subscribe over/finished/closed) to indicate that the subscription is over or failed. In many ways, pub/sub overcommits in many ways. Now, this all depends on what does SUBACK mean? is it durable? tied to a connection?

An interesting foil is something like rsocket. RSocket has a lot of nice things, but it requires an implementation to be damn near perfect. Paradoxically, rsocket lacks the notion of a SUBACK but it has something like a SUBFIN.

A key challenge with a stream is knowing if it is working. With request-response, you can always time out. With a stream, how does one tell the difference between we broken stream and an inactive stream?