MQTT-C | A portable MQTT C client for embedded systems and PCs

So I got fixed it.

I don't know where the problem exactly was.

I load a backup of my vm when all was working. Then I updated openjdk-11 to the latest version. After this the error appears again.

So it's really an problem with the update to openjdk-11-jdk 11.0.14.

After deleting openjdk and make a clean reinstall all works fine again.

Maybe this will help someone.

It appears that your question is answered in this issue:

If you set the username and password on the connect call, they will not be stored and reused when the client reconnects (for security reasons).

The following code (from the issue linked above) demonstrates the approach:

MQTT Explorer is built using Node.js and the MQTT library MQTT.js. As per this issue:

Node.js requires the IP address to be in the subjectAltNames for the cert and not in the CN. Maybe MQTT.fx isn't requiring that, but it should.

and:

If your server's certificate says CN=localhost in the Subject field, connect using localhost and not 127.0.0.1 and it should work. If it says CN=127.0.0.1, you have to make a new one because Node.js won't validate the IP address unless it's in the SAN extension. There is a way to work around it in code (I think it's an option called checkServerIdentity), but I would prefer to fix my certificate if I had this problem.

A rationale for the approach taken in Node is set out in this answer which includes the following quote from RFC2818: HTTP Over TLS :

In some cases, the URI is specified as an IP address rather than a hostname. In this case, the iPAddress subjectAltName must be present in the certificate and must exactly match the IP in the URI.

As you are using MQTT over TLS (as opposed to HTTP Over TLS) you could argue that the above does not apply but, given that the main use of the TLS library is for HTTP traffic, it makes sense that it confirms to the RFC by default.

You have a few options including:

• Use a hostname (e.g. localhost) rather then an IP when creating the certificate/connecting.
• Add the IP as a subjectAltName
• Modify the library to use a noop checkServerIdentity (see this answer).
• Use another application for testing (not really recommended as some applications will work and others will not). The issue quoted above mentions that MQTT.fx works.

std::bind returns a callable object, not a function pointer. It works with WiFi.onEvent because there is an overload taking a std::function:

This behaviour has now been fixed by HiveMQ Cloud.

You need to add allow_anonymous true to allow users to connect without supplying a username/password.

This is part of the set of changes introduced in v2.0 to improve the default security posture of mosquitto out of the box.

Here's what was happening: I configured CMakeLists.txt incorrectly to integrate with conan. Since I had paho-mqtt-cpp installed beforehand, the program was linking to installed libraries instead of those provided by conan.

This CMakeLists.txt works for me:

Check the websocket headers API setting you may be sending the wrong headers for your broker.

Have a look at the mqtt_server_client_websocket.dart file in the examples directory, the setting you want is client.websocketProtocols, look at the API for this.

remove the entrypoint from your docker-compose file, it will start by the CMD of dockerfile. You can also set the restart option to always.