Subscription issues with vernemq

[kbredemeier]

Hello,

First thanks for the great library!

I have some rather strange issues with vernemq 1.8.0. From time to time it looks like tortoise (v0.9.4) is loosing its subscriptions. I can't reproduce this issue locally but I suspect that this happens after vernemq is restarted. The Connection is still present (can see the process in the Tortoise.Supervisor) but somehow the client is not receiving any messages.

I also noticed that the handler's subscription/2 callback is not called if the client reconnects to vernemq. I created a small repository to illustrate the issue: https://github.com/kbredemeier/tortoise_sub_error

The repository comes with a docker-compose.yml that starts a vernemq and a mosquitto container. The application starts a client for each broker and logs the subscription events. If I stop the containers and start them again I can see the subscription logs for mosquitto but not for vernemq. The subscriptions are still active though.

I tested the same thing with a much older version of vernemq (1.3.0) and got a slightly different behaviour. On the first reconnect I get the expected log messages but on any subsequent disconnect the subscription/2 callback is not invoked anymore.

Maybe the two issues are related to each other. I would love to jump in to fix this issue but don't have an idea where to start. Help with this would be much appreciated :)

[gausby]

I know I keep saying this; but I hope I can make some time to focus on the MQTT 5 branch of this project, such that I can get it out the gates—that branch will make significant changes to the structure of the code, so merging changes from master into the mqtt5 branch is kinda troublesome.

I hope you understand. I don't know if it is a Tortoise issue, or a VerneMQ issue. Hopefully I will make a deep dive into tortoise and get it updated, and communicate the architecture such that more people than me can work on it :)