Network protocol error for subscriptions is raised (after publishing)

[Oliver-Piorun]

Describe the bug

A network protocol error for ongoing subscriptions is raised after publishing a message to the server. The error cancels the subscriptions.

Platform:

• Windows 10
• Version: 21H2
• Build: 19044.1348

Client:

• Download: https://mosquitto.org/download/
• Version: 2.0.14

Server:

• Download: https://github.com/chkr1011/MQTTnet/tree/master/Tests/MQTTnet.TestApp.AspNetCore2
• Version: 5e5818d7df78de6a0a1342c9dca692346f70ad97 (latest master)

Important: This issue is not only related to the test app. We also experience it in our server app.

Which project is your bug related to?

• MQTTnet.Server standalone

To Reproduce

Steps to reproduce the behavior:

1. Navigate to the MQTTnet.TestApp.AspNetCore2 project directory
2. Remove the lines 88-92 in Program.cs (to make the app build and run)
3. Run the app via dotnet run --framework net5.0
4. Subscribe via ./mosquitto_sub -h localhost -p 1883 -t '#' -q 1
5. Publish via ./mosquitto_pub -h localhost -p 1883 -t "test/foo" -m "message"

Expected behavior

We expect no network protocol error to occur (which cancels the subscription).

Screenshots

Subscription:

Publish:

Additional context / logging

We found a couple of workarounds for this problem. The following commands avoid a network protocol error:

• ./mosquitto_sub -h localhost -p 1883 -t '#' -q 1 -i "client id" or
• ./mosquitto_sub -h localhost -p 1883 -t '#' -q 1 -V 31 or
• ./mosquitto_pub -h localhost -p 1883 -t "test/foo" -m "message" -V 31

So specifying a client id or the protocol version 31 helps. The protocol versions 311 (default) and 5 are faulty. Using the MQTTnet client does also work btw.

Greetings!

[chkr1011]

Please test with latest version 4.0 and reopen the ticket if the issue persists.