Reply to WebSocket ping frames

[jasoncodes]

This fixes WebSocket connections to Mosquitto brokers disconnecting every 5 minutes due to the server not receiving any response to WebSocket ping frames. Mosquitto uses libwebsockets which defaults to sending a ping frame every 5 minutes with a 10 second timeout.

[sroebert]

Ah, I figured this was not needed as MQTT has its own ping mechanism to keep the connection alive. Thanks for the contribution.

[jasoncodes]

Yeah, it surprised me a little too. I expected WebSocket pings to not be invoked on a connection which is not idling (due to the MQTT pings) but libwebsockets seems to always ping regardless, right on 5 minutes.

I debugged this issue and tested the fix using websocat in verbose mode as a proxy as that made it easy to enable and configure pings (over recompiling Mosquitto with a custom config).

I looked around for where to add test coverage but didn’t find anywhere suitable. Happy to add some coverage if you see the need and you can point me in the right direction.

[sroebert]

I think for now that it is fine, I still have to find some time to add tests for MQTT pings as well, will try to make this part of that as well at that point.