Still emit response if return type is Void

[yawkat]

Before this patch, HttpClient would remove the actual response from the response publisher if the expected body type is Void. I don't see a reason to do this, and it leads to HTTP filters not seeing the response as they should.

However there is an outstanding bug that this uncovered: If there is a declarative client method that is supposed to return Publisher, it instead always returns a Publisher<HttpResponse> (the type returned from HttpClient.exchange). The code here does not convert properly when the returnType is Publisher<Void> and the result is another publisher:

micronaut-core/aop/src/main/java/io/micronaut/aop/internal/intercepted/PublisherInterceptedMethod.java

Lines 112 to 118 in f81ecea

	private Object convertPublisherResult(ReturnType<?> returnType, Object result) {
	if (returnType.getType().isInstance(result)) {
	return result;
	}
	return conversionService.convert(result, returnType.asArgument())
	.orElseThrow(() -> new IllegalStateException("Cannot convert publisher result: " + result + " to '" + returnType.getType().getName() + "'"));
	}

– this causes a class cast exception in HttpGetSpec.test simple get with Publisher<Void> return.

@dstepanov do you have any idea how to fix this?

Fixes #8366

[timyates]

Added it to the 3.8.0 project, and kicked off the Java CI again

The Graal CI is failing as there's no Graal for java 11?

[yawkat]

not sure it'll be ready for 3.8.0

[dstepanov]

What do you mean by removing of the response? Do you mean thr body of the response?

[timyates]

not sure it'll be ready for 3.8.0

Cool, added it to 3.9.0 as well 😎

[yawkat]

Nevermind, I've solved it differently.

Basically, HttpClientIntroductionAdvice has a special path for Void, Publisher<Void>, etc...: It calls .exchange (which returns a Publisher<HttpResponse<O>>) instead of .retrieve (which returns a Publisher<O>). Before this change, this worked fine, because for void bodyType, exchange would always return an empty publisher anyway, so the exact type of the publisher did not matter. Now that exchange correctly returns a publisher with a single HttpResponse<Void>, there was a cast exception because that HttpResponse can't be cast to Void and the conversion (HttpResponse<O> to O) did not run for the Publisher<Void> case.

I've updated HttpClientIntroductionAdvice to use .retrieve for Void as well, and I've altered retrieve to work with Void bodyType (a body that is null is not received well by the code).