Query for the most recent data on a topic

[pakerfeldt]

Is is possible to get carconnectivity-mqtt to emit the most recent value for a certain topic? In my use case the mqtt client is re-used, and one internal consumer might join in late and never gets to see the value. Would help a lot if it was possible to send a message that would trigger the server to re-send the latest value.

[pakerfeldt]

Or even simpler, get the server to emit values regularly, even if they have not changed.

[pakerfeldt]

Normally the client should get all values when it connects because the topics are published with the retain flag. If you really want the values always you can set the config option republish_on_update to true this will publish everytime something is read from the server. Not just on changes. But take care, this will cause a lot more MQTT traffic in your network.

But like I said, I share the same client internally, so there is no new mqtt client connecting (I'm using Node-RED).
Is it possible to mute topics? I'm only interested in 2 topics and would be fine getting those 2 every 5 minutes. Everything else is just noise on the wire unfortunately.

[tillsteinbach]

That is a bit difficult to implement. What if there would be a topic that you can write to and that would trigger resending all values?

[pakerfeldt]

Yeah, or for me it would be even better per-topic.
E.g. carconnectivity/0/garage/xxxxx/drives/primary/level_read would trigger the latest known value back on
carconnectivity/0/garage/xxxxx/drives/primary/level

[pakerfeldt]

Anyway, it's not critical as I can work around it for now. Take it as a feature suggestion.

[tillsteinbach]

With MQTT 5 you could also just resubscribe to the topic you are interested in with retain handling 0. that would just send the message again.