MQTTv5 Publish Returns "No Matching Subscribers" Even When Subscribers are Subscribed on 2.0.19

[kent-bowling-bytetrail]

I'm running Mosquitto via Docker on Ubuntu 22.04 using the eclipse-mosquitto image tagged 2.0.19-openssl. Our software pays attention to see if clients are subscribed when doing a PUBLISH, and doesn't PUBLISH additional extra information if nobody is subscribed and listening. Starting with 2.0.19, all PUBLISH's via MQTTv5 are returning 16 (AKA 0x10), which indicates nobody is subscribed (even when other clients are).

This does not happen on the 2.0.18 image and seems to have started for me because I was using "latest".

I have attached a zip file with a Python script (and requirements.txt) and a mosquitto.conf file that together will run the test to show the problem. This does use docker (via Python Docker SDK) and outputs the following. Notice how on 2.0.18 the Published message callback returns a 0 and on 2.0.19 it's a 16 (No matching subscribers). The output also captures all of mosquitto's logging which also shows the same thing via "rc 0" and "rc 16".

*********** 2.0.18-openssl ***********
Subscriber connected with result code Success
test b'Hello World'
Publisher connected with result code Success
Published message with id 1 - rc: 0 (Success)
chown: /mosquitto/config/mosquitto.conf: Read-only file system
1728355348: mosquitto version 2.0.18 starting
1728355348: Config loaded from /mosquitto/config/mosquitto.conf.
1728355348: Opening ipv4 listen socket on port 1883.
1728355348: Opening ipv6 listen socket on port 1883.
1728355348: mosquitto version 2.0.18 running
1728355353: New connection from 172.17.0.1:34966 on port 1883.
1728355353: New client connected from 172.17.0.1:34966 as sub_client (p5, c1, k30).
1728355353: No will message specified.
1728355353: Sending CONNACK to sub_client (0, 0)
1728355353: Received SUBSCRIBE from sub_client
1728355353:     test (QoS 1)
1728355353: sub_client 1 test
1728355353: Sending SUBACK to sub_client
1728355358: New connection from 172.17.0.1:34982 on port 1883.
1728355358: New client connected from 172.17.0.1:34982 as pub_client (p5, c1, k30).
1728355358: No will message specified.
1728355358: Sending CONNACK to pub_client (0, 0)
1728355358: Received PUBLISH from pub_client (d0, q1, r0, m1, 'test', ... (11 bytes))
1728355358: Sending PUBLISH to sub_client (d0, q1, r0, m1, 'test', ... (11 bytes))
1728355358: Sending PUBACK to pub_client (m1, rc0)
1728355358: Received PUBACK from sub_client (Mid: 1, RC:0)
1728355364: Client sub_client closed its connection.
1728355364: Client pub_client closed its connection.

*********** 2.0.19-openssl ***********
Subscriber connected with result code Success
test b'Hello World'
Publisher connected with result code Success
Published message with id 1 - rc: 16 (No matching subscribers)
chown: /mosquitto/config/mosquitto.conf: Read-only file system
1728355365: mosquitto version 2.0.19 starting
1728355365: Config loaded from /mosquitto/config/mosquitto.conf.
1728355365: Opening ipv4 listen socket on port 1883.
1728355365: Opening ipv6 listen socket on port 1883.
1728355365: mosquitto version 2.0.19 running
1728355370: New connection from 172.17.0.1:41458 on port 1883.
1728355370: New client connected from 172.17.0.1:41458 as sub_client (p5, c1, k30).
1728355370: No will message specified.
1728355370: Sending CONNACK to sub_client (0, 0)
1728355370: Received SUBSCRIBE from sub_client
1728355370:     test (QoS 1)
1728355370: sub_client 1 test
1728355370: Sending SUBACK to sub_client
1728355375: New connection from 172.17.0.1:42628 on port 1883.
1728355375: New client connected from 172.17.0.1:42628 as pub_client (p5, c1, k30).
1728355375: No will message specified.
1728355375: Sending CONNACK to pub_client (0, 0)
1728355375: Received PUBLISH from pub_client (d0, q1, r0, m1, 'test', ... (11 bytes))
1728355375: Sending PUBLISH to sub_client (d0, q1, r0, m1, 'test', ... (11 bytes))
1728355375: Sending PUBACK to pub_client (m1, rc16)
1728355375: Received PUBACK from sub_client (Mid: 1, RC:0)
1728355381: Client sub_client closed its connection.
1728355381: Client pub_client closed its connection.

test.zip

[ralight]

Thanks for the report and the script, I've got a fix for it and will be releasing 2.0.20 soon.