The MQTT protocol doesn't allow an empty topic value nor for publisihng neither for subscribing

[qq2429979710]

In what version(s) of Spring Integration are you seeing this issue?

For example:

6.0.7

Describe the bug

A clear and concise description of what the bug is.

To Reproduce

AbstractMqttMessageDrivenChannelAdapter#initTopics
The initTopics method of the AbstractMqttMessageDrivenChannelAdapter class does not check if the topic is an empty string

if empty string

MqttPahoMessageDrivenChannelAdapter#subscribe
The subscription part in the subscribe method in the MqttPahoMessageDrivenChannelAdapter class will report an error
IMqttToken subscribeToken = this.client.subscribe(topics, requestedQos, listeners);

Expected behavior

A verification mechanism should be added

Sample

IMqttToken subscribeToken = this.client.subscribe(topics, requestedQos, listeners);
Will report an error

[artembilan]

Confirmed.
It fails like this:

Caused by: java.lang.IllegalArgumentException: Invalid topic length, should be in range[1, 65535]!
	at org.eclipse.paho.mqttv5.common.util.MqttTopicValidator.validate(MqttTopicValidator.java:69)
	at org.eclipse.paho.mqttv5.client.MqttAsyncClient.subscribe(MqttAsyncClient.java:1239)
	at org.springframework.integration.mqtt.inbound.Mqttv5PahoMessageDrivenChannelAdapter.subscribe(Mqttv5PahoMessageDrivenChannelAdapter.java:411)
	at org.springframework.integration.mqtt.inbound.Mqttv5PahoMessageDrivenChannelAdapter.doStart(Mqttv5PahoMessageDrivenChannelAdapter.java:196)

for this config:

new Mqttv5PahoMessageDrivenChannelAdapter(mqttv5ClientManager, "")