allow enabling of the paho mqtt client logging

[JohnRoesler]

The logs from the paho mqtt client can be very useful in debugging connectivity issues between the bridge and the mqtt broker.

[brocaar]

Hi @JohnRoesler, thanks, I wasn't aware about this log option. I have been playing with it a bit. What do you think about enabling this by default, without requiring any additional configuration?

I made some modifications and ended up with:

type pahoLogWrapper struct {
    ln func(...interface{})
    f  func(string, ...interface{})
}

func (d pahoLogWrapper) Println(v ...interface{}) {
    d.ln(v...)
}

func (d pahoLogWrapper) Printf(format string, v ...interface{}) {
    d.f(format, v...)
}

func enableClientLogging() {
    l := log.WithField("module", "mqtt")
    paho.DEBUG = pahoLogWrapper{l.Debugln, l.Debugf}
    paho.ERROR = pahoLogWrapper{l.Errorln, l.Errorf}
    paho.WARN = pahoLogWrapper{l.Warningln, l.Warningf}
    paho.CRITICAL = pahoLogWrapper{l.Errorln, l.Errorf}
}

For example, the above could be added to the main.go, like I did for the gRPC logging (https://github.com/brocaar/chirpstack-network-server/blob/master/cmd/chirpstack-network-server/main.go).

Then the paho.<LEVEL> = .... lines could be added to an init() function.

I added the l := log.WithField("module", "mqtt") line to make it easier to understand where the log items are coming from. Maybe over time, this could be considered for all log items in general :)

What do you think?

[JohnRoesler]

I do like your implementation. The logs from the paho client were quite noisy, so that would be the only thing I would want to check with this implementation and having them on by default.

[brocaar]

The logs from the paho client were quite noisy

I suppose that is only when you enable debug log level? Or did you find the ERROR, WARN and CRITICAL logs also noisy?

[JohnRoesler]

@brocaar yes - realized since i was logging all levels to debug, of course it was noisy. I'll update this PR

[brocaar]

Thanks @JohnRoesler :+1: