Set replyPostProcessor default value from the message container factory

[anassder]

Expected Behavior
Use default value (bean name or class) for @RabbitListener annotation's attribute replyPostProcessor using message container factory like we do for AfterReceivePostProcessors and BeforeSendReplyPostProcessors.

Current Behavior
We can set replyPostProcessor value only from @RabbitListener annotation.
Example :

@RabbitListener(queues = "test.header", group = "testGroup", replyPostProcessor = "echoCustomHeader")
public String capitalizeWithHeader(String in) {
    return in.toUpperCase();
}

@Bean
public ReplyPostProcessor echoCustomHeader() {
    return (req, resp) -> {
        resp.getMessageProperties().setHeader("myHeader", req.getMessageProperties().getHeader("myHeader"));
        return resp;
    };
}

Context
Currently we need to add a custom header (that we get from inbound request) to our responses, and we can't do that using AfterReceivePostProcessors or BeforeSendReplyPostProcessors because MessagePostProcessor.postProcessMessage give only the current message as parameter.
The best solution for this probleme is to use replyPostProcessor, but we can't change all @RabbitListener annotations to add this attribute.
That's why I suggest to add new method to the container factory to make changing default replyPostProcessor value possible. (like for setAfterReceivePostProcessors and setBeforeSendReplyPostProcessors)

[artembilan]

Agreed.
This is really a valid requirement.
We have a logic like this already:

JavaUtils.INSTANCE // NOSONAR
					.acceptIfNotNull(this.beforeSendReplyPostProcessors,
							messageListener::setBeforeSendReplyPostProcessors)

where the mentioned replyPostProcessor is really a property of the same messageListener.
So, that BaseRabbitListenerContainerFactory can really have such a new replyPostProcessor option exposed.

Feel free to come back to us with a contribution: https://github.com/spring-projects/spring-amqp/blob/main/CONTRIBUTING.adoc

Thank you!

[garyrussell]

It's actually this code that sets the RPP...

spring-amqp/spring-rabbit/src/main/java/org/springframework/amqp/rabbit/config/BaseRabbitListenerContainerFactory.java

Lines 124 to 125 in a3aedc6

	JavaUtils.INSTANCE
	.acceptIfNotNull(endpoint.getReplyPostProcessor(), messageListener::setReplyPostProcessor)

Not the setBeforeSendReplyPostProcessors.

In the meantime, you can use this...

@Bean
public ReplyPostProcessor echoCustomHeader(AbstractRabbitListenerContainerFactory<?> factory) {
	ReplyPostProcessor rpp = (req, resp) -> {
		resp.getMessageProperties().setHeader("myHeader", req.getMessageProperties().getHeader("myHeader"));
		return resp;
	};
	factory.setContainerCustomizer(container -> {
		MessagingMessageListenerAdapter listener = ((MessagingMessageListenerAdapter) container
				.getMessageListener());
		listener.setReplyPostProcessor(rpp);
	});
	return rpp;
}

[artembilan]

Yes, but it also could be done by the BaseRabbitListenerContainerFactory as a common place for such a property.
The @RabbitListener one can override, of course.

[garyrussell]

Original SO question: https://stackoverflow.com/questions/71149751/configure-spring-amqp-to-use-default-bean-for-rabblitlisteners-replypostproces/71159878#71159878