CircuitBreaker does not prevent execution of upstream Mono if flatMap is used

Expected behavior

Both tests simple, withMap, and withFlatMap behave the same.

Actual behavior

In simple and withMap getNext() is called twice (as expected) and withFlatMap getNext() is called four times.

Log for simple/withMap test

Requested Counter: 1
16:03:19.461 [main] DEBUG io.github.resilience4j.circuitbreaker.internal.CircuitBreakerStateMachine - No Consumers: Event SUCCESS not published
Ctr: 1
Requested Counter: 2
16:03:19.476 [main] DEBUG io.github.resilience4j.circuitbreaker.internal.CircuitBreakerStateMachine - CircuitBreaker 'test' recorded a failure:
java.lang.RuntimeException: Error
	...
16:03:19.477 [main] DEBUG io.github.resilience4j.circuitbreaker.internal.CircuitBreakerStateMachine - No Consumers: Event ERROR not published
16:03:19.494 [main] DEBUG io.github.resilience4j.circuitbreaker.internal.CircuitBreakerStateMachine - No Consumers: Event STATE_TRANSITION not published
RuntimeException
16:03:19.496 [main] DEBUG io.github.resilience4j.circuitbreaker.internal.CircuitBreakerStateMachine - No Consumers: Event NOT_PERMITTED not published
CircuitBreakerOpenException
16:03:19.497 [main] DEBUG io.github.resilience4j.circuitbreaker.internal.CircuitBreakerStateMachine - No Consumers: Event NOT_PERMITTED not published
CircuitBreakerOpenException

Log for withFlatMap test

Requested Counter: 1
16:03:19.601 [main] DEBUG io.github.resilience4j.circuitbreaker.internal.CircuitBreakerStateMachine - No Consumers: Event SUCCESS not published
Ctr: 1
Requested Counter: 2
16:03:19.603 [main] DEBUG io.github.resilience4j.circuitbreaker.internal.CircuitBreakerStateMachine - CircuitBreaker 'test' recorded a failure:
java.lang.RuntimeException: Error
	...
16:03:19.603 [main] DEBUG io.github.resilience4j.circuitbreaker.internal.CircuitBreakerStateMachine - No Consumers: Event ERROR not published
16:03:19.603 [main] DEBUG io.github.resilience4j.circuitbreaker.internal.CircuitBreakerStateMachine - No Consumers: Event STATE_TRANSITION not published
RuntimeException
Requested Counter: 3
16:03:19.603 [main] DEBUG io.github.resilience4j.circuitbreaker.internal.CircuitBreakerStateMachine - No Consumers: Event NOT_PERMITTED not published
CircuitBreakerOpenException
Requested Counter: 4
16:03:19.604 [main] DEBUG io.github.resilience4j.circuitbreaker.internal.CircuitBreakerStateMachine - No Consumers: Event NOT_PERMITTED not published
CircuitBreakerOpenException

Steps to reproduce

public class Resilience4jSimpleTest {
    int counter = 0;

    CircuitBreakerConfig breakerConfig = CircuitBreakerConfig.custom()
            .ringBufferSizeInClosedState(2)
            .build();

    CircuitBreaker circuitBreaker = CircuitBreaker.of("test", breakerConfig);

    @Test
    public void simple() {
        System.out.println(performCall(circuitBreaker));
        System.out.println(performCall(circuitBreaker));
        System.out.println(performCall(circuitBreaker));
        System.out.println(performCall(circuitBreaker));
    }

    @Test
    public void withMap() {
        System.out.println(performCallWithMap(circuitBreaker));
        System.out.println(performCallWithMap(circuitBreaker));
        System.out.println(performCallWithMap(circuitBreaker));
        System.out.println(performCallWithMap(circuitBreaker));
    }

    @Test
    public void withFlatMap() {
        System.out.println(performCallWithFlatMap(circuitBreaker));
        System.out.println(performCallWithFlatMap(circuitBreaker));
        System.out.println(performCallWithFlatMap(circuitBreaker));
        System.out.println(performCallWithFlatMap(circuitBreaker));
    }

    String getNext() {
        counter++;
        System.out.println("Requested Counter: " + counter);
        if (counter % 2 == 0) {
            throw new RuntimeException("Error");
        }
        return "Ctr: " + counter;
    }

    private String performCall(CircuitBreaker circuitBreaker) {
        return Mono.fromCallable(this::getNext)
                .transform(CircuitBreakerOperator.of(circuitBreaker))
                .onErrorResume(Exception.class, (e) -> Mono.just(e.getClass().getSimpleName()))
                .block();
    }

    private String performCallWithMap(CircuitBreaker circuitBreaker) {
        return Mono.fromCallable(this::getNext)
                .map(Function.identity())
                .transform(CircuitBreakerOperator.of(circuitBreaker))
                .onErrorResume(Exception.class, (e) -> Mono.just(e.getClass().getSimpleName()))
                .block();
    }

    private String performCallWithFlatMap(CircuitBreaker circuitBreaker) {
        return Mono.fromCallable(this::getNext)
                .flatMap(Mono::just)
                .transform(CircuitBreakerOperator.of(circuitBreaker))
                .onErrorResume(Exception.class, (e) -> Mono.just(e.getClass().getSimpleName()))
                .block();
    }
}

Versions

• resilience4j 0.13.2
• reactor: 3.2.6.Final

Possible related #334 issue

[RobWin]

This will be fixed in the next release.

[RobWin]

This test is successful now

    @Test
    public void shouldNotSubscribeToMonoFromCallable() {
        given(circuitBreaker.tryAcquirePermission()).willReturn(false);
        given(helloWorldService.returnHelloWorld()).willReturn("Hello World");

        StepVerifier.create(
                Mono.fromCallable(() -> helloWorldService.returnHelloWorld())
                        .flatMap(Mono::just)
                        .compose(CircuitBreakerOperator.of(circuitBreaker)))
                .expectError(CallNotPermittedException.class)
                .verify();

        then(helloWorldService).should(never()).returnHelloWorld();
        verify(circuitBreaker, never()).onSuccess(anyLong());
        verify(circuitBreaker, never()).onError(anyLong(), any(Throwable.class));
    }