Add server url property to MqttIntegrationEvent

[ikarsokolov]

Expected Behavior
MqttIntegrationEvent should have server property or other means to find what MQTT server caused it.

Current Behavior
MqttIntegrationEvent does not have server property.

Context
I have multiple inbound MQTT adapters connected to different servers. Right now it is impossible to find what server caused application event. For example MqttConnectionFailedEvent may not have any mentions of failed server depending on type of the underlying exception.

AbstractMqttMessageDrivenChannelAdapter.getUrl() is protected. Also I am not sure if it is set correctly if urls are configured through MqttConnectOptions. At the very least AbstractMqttMessageDrivenChannelAdapter should log server url on errors.

[artembilan]

The MqttIntegrationEvent is supplied with a source which is essentially a channel adapter caused such an event.
We probably need to introduce something like MqttClientAccessor to implement in all the MQTT channel adapters and give access from there to serverURIs array. We might deprecate that protected String getUrl() since Paho client really operates over the array of uris - an explicit or provided via MqttConnectOptions.getServerURIs().

This way the source of the event could be cast to that type via EventObject.getSource() and you'll get access to that URIs option.

We probably indeed should enhance that

logger.error("Error connecting or subscribing to " + Arrays.toString(topics), e);

to include some connection information as well.

@garyrussell , any thoughts?

[ikarsokolov]

This way the source of the event could be cast to that type via EventObject.getSource() and you'll get access to that URIs option.

May be override MqttIntegrationEvent.getSource() to public MqttClientAccessor getSource() to avoid client-side cast?

[garyrussell]

@garyrussell , any thoughts?

I concur with both suggestions.

Yes, we could narrow the getSource() return type, or add another getter.

[artembilan]

Yes, we could narrow the getSource() return type, or add another getter.

We removed that downcast in the past because of classes tangle...

[garyrussell]

Oh, right, yes, of course; I added the following to KafkaEvent to make it a bit more user friendly...

	/**
	 * Get the container (source) that published the event. This is provided as an
	 * alternative to {@link #getSource()} to avoid the need to cast in user code. The
	 * type is required here to avoid a dependency tangle between the event and listener
	 * packages.
	 * @param type the container type (e.g. {@code MessageListenerContainer.class}).
	 * @param <T> the type.
	 * @return the container.
	 * @see #getContainer(Class)
	 * @see #getSource()
	 * @since 2.2.1
	 */
	@SuppressWarnings("unchecked")
	public <T> T getSource(Class<T> type) {
		Assert.isInstanceOf(type, getSource());
		return (T) getSource();
	}

We could also add

public <T> T getClient() { }

And the compiler can infer the type

MqttClientAccessor accessor = event.getClient();

[artembilan]

Yep! That is possible. We even just don't need that Class<T> type and let the program to fail if wrong type is expected after return!