Switch to retained publication for MQTT target #2
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Signed-off-by: Andy Piper <andypiper@users.noreply.github.com>
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Aug 18, 2022
Per [the change I suggested to the Pico-based Enviro code](pimoroni/enviro#2), with this change, the MQTT messages will be published with the retain flag set, so that if a consumer is not subscribed, the most recent set of readings can still be read by a future subscriber later. This supports the [homebridge-enviroplus plugin](mhawkshaw/homebridge-enviroplus#2 (comment)) better, so that a publication is more likely to exist on the topic even if the Pi with Enviroplus / this example code is not running at the time. Additional update to consider would be to align the message data formats between this sample and the newer Enviro product line.
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Propose changing the MQTT publication to retained by default, this makes it easier to see the last reading published from an Enviro sensor if the viewer / consumer / subscriber joins later. There is already a timestamp in the publication message so should be no risk of being confused at whether that reflects the current, or past, status of the Enviro. Added comments to indicate how to switch this back to False if preferred.
As an aside, I'm now comparing the format of these messages to those published by the MQTT sample shipped with the classic Enviro+ HAT, and will probably send a PR for the latter to get the data formats more aligned if possible.
Signed-off-by: Andy Piper andypiper@users.noreply.github.com