Issue with "retained" MQTT messages

[makkie2002]

I have been using your code for several months now without issues 😄, until today😟.

This is the issue:

• I am feeding in the grid power data (from the Belgian P1 port) through MQTT.
• I have the "retain" flag on for these messages (for some now-unknown reason).
• If now my grid-meter is not updating the MQTT messages anymore, the script restarts after the 60s timeout, it subscribes to the MQTT topic, it receives the (old) retained value and sends it to Victron ...
• In my case the Victron got fully confused and was discharging the battery at full power ....

So maybe to solve this issue we could check if after restarting the service the first received value is ignored, so that we are sure that we are not dealing with retained messages ...

Thanks!

[mr-manuel]

Solving the issue on the root would be the better choice. Do not retain data for values that are not valid anymore after a short amount of time.

[makkie2002]

Solving the issue on the root would be the better choice. Do not retain data for values that are not valid anymore after a short amount of time.

Hmmm, yes and no. I had to dig a bit to find the root cause. Simply turning off the retain flag wasn’t enough because the MQTT server still keeps serving the last "retained" message. Sending an empty message with retain was needed to clear it.

Capturing this edge case could make the service more robust 😃. Having the script forget the first received power message should do the trick.