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[mosquitto-dev] Trouble with wills and retain, not sure where 
I've been using mosquitto (two instances, bridged) with two Home
Assistants as the main listeners, and a variety of publishers for a long
time with good results.  I'm cleaning up some python code for public
consumption, that polls a UPS (ups-nut) and reports once a minute or
promptly if the data is interesting (e.g. power failure), and this led
me to really look at what's going on.

I'm runing mosquitto 2.0.12 on NetBSD 9 amd64, and py-paho-mqtt 1.6.1 on
python 3.8.

My python program uses py-paho-mqtt and tries to set a will to set a
particular to OFF, and sets that topic to ON on connect (payload values
to align with Home Assistant binary mqtt sensor).

I used to call will_set before connecting, and noticed that if I killed
the program, there was no update (watching with mosquitto_sub on the
same machine as the broker).  So I moved it to the on_connect callback.
I found the docs unclear, that's really a paho question.

My variable topic is "/sensor/foo/ups-bar".

I also noticed that the online message was coming through retain=False,
so I added the middle line for debugging.

        self.client.will_set(topic + "/online", payload="OFF", qos=2, retain=True)
        self.client.publish(topic + "/online", payload="ON", qos=1, retain=False)
        self.client.publish(topic + "/online", payload="ON", qos=2, retain=True)


On connect I get (mix of syslog and mosquitto_sub, minor name
redaction):

Dec 23 12:41:09 mosquitto[836]: 1640281269: New client connected from [ipv6addr-of-ups-box] as ups-bar (p2, c1, k60, u'mqttuser').
{"tst":"2021-12-23T12:41:09.641631Z-0500","topic":"sensor/foo/ups-bar/online","qos":1,"retain":0,"payloadlen":2,"mid":30,"payload":ON}
{"tst":"2021-12-23T12:41:09.798029Z-0500","topic":"sensor/foo/ups-bar/online","qos":2,"retain":0,"payloadlen":2,"mid":31,"payload":ON}

I then see my every-minute json dictionary of UPS info.

On killing the script I get:

Dec 23 12:49:52 mosquitto[836]: 1640281792: Client ups-bar closed its connection.


So:

  I'm seeing retain 0/False on both publishes of online, but qos 1/2
  comes through as expected.

  I am not seeing the will be executed on disconnect.

I have also noticed other sensors failing to have the will work when
they go offline (power, network), but I need to go back and check/update
their (nodemcu) code.

I know wills used to work for me, but I don't remember when.


This is a long way of asking: Is anybody else on 2.0.12 seeing wills be
correctly executed?  Seeing problems?  Any other advice?

(I'll try to look into this harder, of course, but already I'm
suspicious there's a bug not in my code.)

Thanks,
Greg

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