[mosquitto-dev] last will from mosquitto_pub - how to get it sent out?

[Markus Maier <maier.m@xxxxxx>]

Hi all,

I'm trying to figure out how last will messages work with mosquitto_pub 
and when it will be sent. I did not find any useful example on this. As 
far as I understand, the connection will be properly closed immediately 
after publishing a message from the command line using mosquitto_pub and 
therefore the last will message will never be sent.

In my scenario, I'm publishing values to a broker and would like to 
inform the subscribers when the publishing device goes down. So I have 
tried something like

mosquitto_pub -h test.mosquitto.org -r -t testbench/willTest -m 
"stillAlive" -k 5 --will-topic testbench/willTest --will-payload "died" 
--will-retain

The will payload is never being sent out to the subscribers. Not even 
after I shut down the publishing device. This might even be expected 
behaviour, but how will this last will of mosquitto_pub be of any use 
then? Or am I missing out a point here?

If so, is there any other way to inform the broker that the publishing 
device has gone down than to also subscribe to some topic from the 
publishing device and giving a last will to mosquitto_sub? This would 
add additional complexity (and traffic) since I would have to monitor 
the state of the subscription.

Thanks
Markus