Add Kotlin Coroutine support

[davidb-e4s]

Improvement

Please can you add Kotlin Coroutine support so we can use the suspend keyword on @RabbitListener functions. Currently it errors.

[artembilan]

We need to investigate that feature: don't have experience with Kotlin Coroutines.
We have support for Reactor Mono, so probably should be something similar for suspend: https://docs.spring.io/spring-amqp/docs/2.2.7.RELEASE/reference/html/

Feel free to provide a Pull Request on the matter if you see how that could be implemented.
Thanks

[garyrussell]

It's not clear what you are trying to achieve here.

My understanding is suspend functions can only be called from a coroutine; since @RabbitListener methods are called by the framework, not user code, we'd have to add a shim between the framework and the listener - but exactly how would that perform any useful function?

[garyrussell]

Closing due to inactivity.

[eduanb]

Can we reopen this? Ran into a weird JSON serialisation issue which was really hard to debug because of this. Spring webflux supports coroutines and spring-amqp already supports reactive so it is confusing to the user.
@garyrussell

[artembilan]

Hi @eduanb !

We are fully open for contribution.
Not sure how JSON is relevant and why you use suspend on the @RabbitListener, but if you open Pull Request for possible fix, we are good to review it ASAP.

Thank you!

[verissimor]

It would be very helpful to have support for coroutines/suspend method on the @RabbitListener.

[artembilan]

In Spring Integration we have a special wrapper:

public class IntegrationInvocableHandlerMethod extends InvocableHandlerMethod {

	public IntegrationInvocableHandlerMethod(Object bean, Method method) {
		super(bean, method);
	}

	@Override
	protected Object doInvoke(Object... args) throws Exception {
		Method method = getBridgedMethod();
		if (KotlinDetector.isSuspendingFunction(method)) {
			return CoroutinesUtils.invokeSuspendingFunction(method, getBean(), args);
		}
		else {
			return super.doInvoke(args);
		}
	}

}

Which we set into a IntegrationMessageHandlerMethodFactory.
That one returns a Mono for suspend functions which we have already support for in the AbstractAdaptableMessageListener:

else if (monoPresent && MonoHandler.isMono(resultArg.getReturnValue())) {

Looks like RabbitListenerAnnotationBeanPostProcessor can give us similar custom factory in its private MessageHandlerMethodFactory createDefaultMessageHandlerMethodFactory() {.

@garyrussell ,

if that is OK to explore, let's reopen this issue!

[garyrussell]

Sure, sounds good.