allow_zero_length_clientid appears to be false when using per_listener_settings

[dustin]

I have two instances of mosquitto running, and have MQTT v5 clients talking to both. I noticed my client wasn't working on one of my instances when I didn't send a client ID, but did on the other.

Then I noticed the following on the one that was failing:

mosquitto_pub -t tmp/test -m testing

worked, but

mosquitto_pub -t tmp/test -m testing -V 5

failed with Connection error: Unspecified error

It did work when I sent a -i, so I checked the manual and found

allow_zero_length_clientid [ true | false ]
MQTT 3.1.1 and MQTT 5 allow clients to connect with a zero length client id and have the broker generate a client id for them. Use this option to allow/disallow this behaviour. Defaults to true.

I'm also using per_listener_settings on the system that isn't working (it has a TLS listener), so I tried explicitly setting allow_zero_length_clientid true in each section and it started allowing empty client IDs.

[ralight]

You're right, thanks. I've written a big test that goes through a lot of variations of this and have fixed a few places where it wasn't behaving properly.