Armeria With Reactive Java (JDK 11/17)

[dkoval3]

I am migrating code from Spring to Armeria and have a few questions

1. I need a decorator that can reactively chain and not have a serve method with return type of HttpResponse, it must be Single<HttpResponse> or something equivalent
2. When I am exposing an API with return type of Single<T>, I am having issues while with Flowable<T> it works seamlessly. I had to write a ResponseConverter with a block code and perhaps I am missing something how to expose Single<T>
3. It seems that there currently is not a way to return Flowable<HttpReponse> since there's no built-in ResponseCovnerter. What would be the alternative solution?

Any sample code would be helpful. Thanks

[minwoox]

I am missing something how to expose Single

If you add armeria-rxjava3 depdencies, ObservableResponseConverterFunction will be used to convert a Single instance.

armeria/rxjava3/src/main/java/com/linecorp/armeria/server/rxjava3/ObservableResponseConverterFunction.java

Lines 119 to 123 in 4edff55

	if (result instanceof Single) {
	@SuppressWarnings("unchecked")
	final CompletionStage<Object> future = ((Single<Object>) result).toCompletionStage();
	return HttpResponse.of(future.handle(handleResult(ctx, headers, trailers)));
	}

What would be the alternative solution?

Could you return HttpResponse or CompletableFuture<HttpReponse> instead?

I need a decorator that can reactively chain and not have a serve method with return type of HttpResponse, it must be Single or something equivalent

I'm not sure what you really want. 😓 Could you show me an example?

[smahad786]

I think this is what Dane is thinking about. We are able to send the request back to the API caller via CompletableFuture and/or Flowable. However, when we expose a Single we have to add a ResponseConverter, forcing a blockingGet(). Is it possible to avoid this blockingGet(), still return a Single as a return value in our Controllers, without using a ResponseConverter to HttpResponse?

public HttpResponse convertResponse(ServiceRequestContext ctx,
ResponseHeaders headers, @nullable Object result, HttpHeaders trailers) throws Exception {

if (result instanceof Single) {
  return HttpResponse.of(
      HttpStatus.OK,
      Objects.requireNonNull(headers.contentType()),
      mapper.writeValueAsString(((Single) result).blockingGet()));
}
// To the next response converter.
return ResponseConverterFunction.fallthrough();

}

Also, we were thinking of writing an external call to OKTA via a decorator and since this is an external call, we want to keep it async. As long as the conveters are simple, just checking the headers or doing some data format conversions, it is seamless. When we have to make an external call, the converter/decorator chaining requires blocking code. Perhaps the purpose is not to make an external calls from decorator/converter, we need this clarification.

[minwoox]

is it possible to avoid this blockingGet(),

We need to do something like this:

return HttpResponse.of(single.toCompletionStage().thenApply(content -> {
    return HttpResponse.of(HttpStatus.OK,
                           Objects.requireNonNull(headers.contentType()),
                           mapper.writeValueAsString(content));
}));

However, you don't have to do this by yourself. All you need to do is adding this dependency:
https://mvnrepository.com/artifact/com.linecorp.armeria/armeria-rxjava3/1.28.4
then, ObservableResponseConverterFunction will automatically handle it.

doing some data format conversions,

Do you also need the request body from the request to call the outside server?

[smahad786]

@minwoox I added the https://mvnrepository.com/artifact/com.linecorp.armeria/armeria-rxjava3/1.28.4 dependency and returning Single did not work. For some reason, only when I expose Flowable, it works. I did not add any additional code to implement the ResponseConverterFunction. I understand that there is a default Implementation that will handle it and I did not see that behavior. If there is a sample code in GitHub returning Single as the return value in the ReST endpoint, it will be helpful. The Mono works with SpringBoot, only I see some issue with Armeria and it is something I am missing

[ikhoon]

dependency and returning Single did not work.

Could you provide a minimal reproducible example? Some LINE internal users have been using RxJava for a long time. If there were some issues in our implementations, we would get a report from them.

[smahad786]

Thanks @minwoox I will further look into it. I also have a follow up question. Let us test this first and then come back