Joël Gähwiler

As pointed out in the issue, we would need to first implemented the changes in [lwmqtt](https://github.com/256dpi/lwmqtt).

What does the "my_external_callback" do?

A publish can only fail due to network issues. I don't think the Arduino API specifies temporary errors ATM. Therefore, if that happens, we need to properly close the socket...

There is a "command timeout". However it also depends on the modem and how it implemented timeouts.

This is a known problem. The common Arduino APIs do not yet expose a way to set a connect timeout. Depending on your platform you might find a way to...

The client will not attempt to send a message again after loosing the connection as we do not have a persistent store (session) for messages. You need to arrange for...

Since MQTT is running on TCP a packet cannot just go missing as TCP guarantees a stable stream. Therefore, correct MQTT clients only attempt to resend unacked packets when reconnecting....

Yes this would be nice to get fixed. Possibly we could do this together with #145. In any case this should be first implemented in [lwmqtt](https://github.com/256dpi/lwmqtt).

Hi @dustin, sorry about that! My plan I is still to implement MQTT5 in shiftr.io to have a service to test the implementation with. This should happen soon, but ATM...

Thanks for the PR! I'm 100% for making running an example a frictionless experience for the potentially newcomer users of this library. However, after thinking about it a little more...