convert will message in mqtt options from string to buffer

[JeffreyThijs]

Motivation:

The payload of the will message now requires to be stored in the MqttClientOptions as a String and is afterwards converted to byte[] assuming UTF-8 in the MqttClientImpl when connecting. This is different from the publish methods where a Buffer is required. Additionally, when the will message payload is binary (e.g. in SparkplugB) converting this to a string feels wrong and might lead to unnecessary conversion issues.

[tsegismont]

Thanks for sharing this. Can you post some more details (e.g. snippet) about the problem?

[JeffreyThijs]

Thanks for sharing this. Can you post some more details (e.g. snippet) about the problem?

Here is a reproducer:

https://github.com/JeffreyThijs/vertx-mqtt-reproducer/blob/master/src/test/kotlin/jthijs/TestMqttWillMessage.kt

[JeffreyThijs]

@tsegismont, i think i made all changes you suggested.

[tsegismont]

@JeffreyThijs @ppatierno I've made some updates and merged the PR

Thank you both!

[tsegismont]

I will take care of backporting to 4.x