Spring Webflux 406 errors when ContentType of Method differs from ExceptionHandler

[pluttrell]

I'm using Spring Webflux and seeing 406 errors when both of the following occur:

1. Exceptions are returned from the the Reactive stream instead of the controller method itself.
2. When the controller method produces a different ContentType then the ExceptionHandler.

This is reproducible using SpringBoot v2.0.3 and v2.1.0-BUILD-SNAPSHOT (as of today).

@RestController
@RequiredArgsConstructor
class BinaryTestController {

  private final AccessKeyValidationService accessKeyValidationService;

  @GetMapping(path = "/binary-test", produces = MediaType.APPLICATION_OCTET_STREAM_VALUE)
  Mono<byte[]> test(@RequestParam("apiKey") String apiKey, @RequestParam(name = "failFirst", required = false) boolean failFirst) {

    if (failFirst) { throw new IllegalArgumentException();}

    return Mono.just(apiKey)
        .filterWhen(accessKeyValidationService::isValid)
        .switchIfEmpty(Mono.error(new IllegalAccessException()))
        .then(Mono.just("test".getBytes(StandardCharsets.UTF_8)));
  }

  @ExceptionHandler(IllegalArgumentException.class)
  ResponseEntity<Mono<BadResponse>> handleIllegalArgumentException() {
    HttpHeaders headers = new HttpHeaders();
    headers.setContentType(MediaType.APPLICATION_JSON_UTF8);
    return new ResponseEntity<>(Mono.just(new BadResponse("better luck next time")), headers, HttpStatus.BAD_REQUEST);
  }

  @ExceptionHandler(IllegalAccessException.class)
  ResponseEntity<Mono<BadResponse>> handleIllegalAccessException() {
    HttpHeaders headers = new HttpHeaders();
    headers.setContentType(MediaType.APPLICATION_JSON_UTF8);
    return new ResponseEntity<>(Mono.just(new BadResponse("access denied")), headers, HttpStatus.FORBIDDEN);
  }

  @Data
  class BadResponse {
    private final String developerMessage;
  }

}

The AccessKeyValidationService does a blocking lookup, so naturally needs to return a Mono and thus needs to be part of the Mono returned from the controller:

@Service
class AccessKeyValidationService {

  Mono<Boolean> isValid(String accessKey) {
    return Mono.defer(() -> Mono.just(blockingLookup(accessKey)))
        .subscribeOn(Schedulers.elastic());
  }

  private Boolean blockingLookup(String accessKey) {
    //Some blocking lookup...
    return accessKey.equals("good");
  }
}

A valid apiKey, results in proper binary output:

$ http localhost:8080/binary-test apiKey==good
HTTP/1.1 200 OK
Content-Length: 4
Content-Type: application/octet-stream

test

When I throw an exception before the Reactive Stream, I get the intended JSON output:

$ http localhost:8080/binary-test apiKey==good failFirst==true
HTTP/1.1 400 Bad Request
Content-Length: 44
Content-Type: application/json;charset=UTF-8

{
    "developerMessage": "better luck next time"
}

But when I trigger the steam to error with an IllegalAccessException, I get a 406:

$ http localhost:8080/binary-test apiKey==bad
HTTP/1.1 406 Not Acceptable
Content-Length: 157
Content-Type: application/json;charset=UTF-8

{
    "error": "Not Acceptable",
    "message": "Could not find acceptable representation",
    "path": "/binary-test",
    "status": 406,
    "timestamp": "2018-06-30T05:23:09.820+0000"
}

If I put a breakpoint in the handleIllegalAccessException method, it stops as expected.

If I switch the return type for the controller method to JSON it works as expected.

Is there something else I need to do to switch the response type when erroring out the returned Mono? Or some other way to resolve it?

Here's a repo with a failing unit test reproducing the problem: https://github.com/pluttrell/spring-webflux-binary-response-exception-handling-example

[pluttrell]

@bclozel As requested on Gitter, here's the issue.

[pluttrell]

@bclozel Wondering if you might have any thoughts on this issue. Thanks in advance.

[bclozel]

Thanks for the report @pluttrell !
This is actually an issue in Spring Framework - I've created SPR-17082 to track it.

I'm about to solve it and the fix will ship with Spring Framework 5.0.8 and 5.1.0.RC1, so Spring Boot 2.0.4 and 2.1.0.M1.

I'm marking it as invalid because technically the issue is not in Spring Boot, but it doesn't mean your contribution is not valued.

Thanks!

[pluttrell]

@bclozel When upgrading to 2.1.0.M4, this issue was resolved. However when moving to 2.1.0.RC1, the issue came back. I've reported the potential regression here: https://jira.spring.io/browse/SPR-17415

[bidadh]

@bclozel I have exactly same issue with spring-boot 2.1.1.RELEASE. an I missing something ?

[bclozel]

@bidadh I don't know - could you create a new issue with a sample application that demonstrates the problem?

[bidadh]

@bclozel yes I can. I thought because this is exactly the same issue maybe it's better to add a comment.

I can also add Controller and ExceptionHandler code here

which one easier for you ?

[bclozel]

A new issue with a complete repro app (for example in a github repo of yours). Sometimes those are tied to dependency management or other issues so a complete repro makes things easier and faster to fix.

[bidadh]

Hi @bclozel

I've created this issue

and here is the repository

Could you please have a look ?

Thanks,
Arthur