MQTT client livecycle is broken and connection is silently dropped

[alexbarcelo]

The dataclay.contrib.mqtt.MQTTMixin class instantiates a client the first time send_to_mqtt is called, but the client loop is not properly instantiated. That means that this connection tends to be dropped after a while of inactivity and then the client is broken and send_to_mqtt ceases to work (silently, with no error).

Steps to reproduce

1. Start dataClay and start a MQTT server (order does not matter).
   • Make sure that MQTT_HOST and MQTT_PORT are correctly set. If running on localhost, 127.0.0.1 seems correct. If using a docker-compose, use the container name.
2. Register a class with the mixin, e.g.

   class SomeClass(DataClayObject, MQTTMixin):
   ...

3. Create a instance of the class, make it persistent, try to call the send_to_mqtt method.
   • The call will work, you will see the message if you listen to the server.
4. Wait for an arbitrary amount of time without sending any messages (brew a coffe and wait 5 minutes).
5. Try to call again the send_to_mqtt. The call will silently fail, no messages will be published.

Possible solutions

Use the network loop that the paho-mqtt library provides.

I am not sure on the proper way of doing that. Trying to call reconnect might also work. I recall finding something along is_connected in the client interface, but I also recall it behaving funny and not being reliable. Maybe in addition to the loop we also need a reconnect callback: the system should be able to "survive" a restart of the server (which needs not only a network loop management but also reconnect semantics).

Desired state

• 10 minutes of idle time should not break the connection. (Send + wait 10 minutes + send again: both send operations should work).
• Restarting the MQTT server should work (Send + restart MQTT server + send again: the second send should correctly send to the new server... it may be slow to reconect, but it should reconnect (it can be minutes, but it cannot be hours).

[marcmonfort]

Solved in commit 8481b50c2fe7825266dcbf9a693e5ebe1917743d