Resilience4j rate limiter is not working properly in project reactor? - project-reactor

Question

I'm currently researching the resilience4j library and for some reason the following code doesn't work as expected:
#Test
public void testRateLimiterProjectReactor()
{
// The configuration below will allow 2 requests per second and a "timeout" of 2 seconds.
RateLimiterConfig config = RateLimiterConfig.custom()
.limitForPeriod(2)
.limitRefreshPeriod(Duration.ofSeconds(1))
.timeoutDuration(Duration.ofSeconds(2))
.build();
// Step 2.
// Create a RateLimiter and use it.
RateLimiterRegistry registry = RateLimiterRegistry.of(config);
RateLimiter rateLimiter = registry.rateLimiter("myReactorServiceNameLimiter");
// Step 3.
Flux<Integer> flux = Flux.from(Flux.range(0, 10))
.transformDeferred(RateLimiterOperator.of(rateLimiter))
.log()
;
StepVerifier.create(flux)
.expectNextCount(10)
.expectComplete()
.verify()
;
}
According to the official examples here and here this should be limiting the request() to 2 elements per second. However, the logs show it's fetching all of the elements immediately:
15:08:24.587 [main] DEBUG reactor.util.Loggers - Using Slf4j logging framework
15:08:24.619 [main] INFO reactor.Flux.Defer.1 - onSubscribe(RateLimiterSubscriber)
15:08:24.624 [main] INFO reactor.Flux.Defer.1 - request(unbounded)
15:08:24.626 [main] INFO reactor.Flux.Defer.1 - onNext(0)
15:08:24.626 [main] INFO reactor.Flux.Defer.1 - onNext(1)
15:08:24.626 [main] INFO reactor.Flux.Defer.1 - onNext(2)
15:08:24.626 [main] INFO reactor.Flux.Defer.1 - onNext(3)
15:08:24.626 [main] INFO reactor.Flux.Defer.1 - onNext(4)
15:08:24.626 [main] INFO reactor.Flux.Defer.1 - onNext(5)
15:08:24.626 [main] INFO reactor.Flux.Defer.1 - onNext(6)
15:08:24.626 [main] INFO reactor.Flux.Defer.1 - onNext(7)
15:08:24.626 [main] INFO reactor.Flux.Defer.1 - onNext(8)
15:08:24.626 [main] INFO reactor.Flux.Defer.1 - onNext(9)
15:08:24.626 [main] INFO reactor.Flux.Defer.1 - onComplete()
I don't see what's wrong?

Answer 1

As already answered in comments above RateLimiter tracks the number of subscriptions, not elements. To achieve rate limiting on elements you can use limitRate (and buffer + delayElements).
For example,
Flux.range(1, 100)
.delayElements(Duration.ofMillis(100)) // to imitate a publisher that produces elements at a certain rate
.log()
.limitRate(10) // used to requests up to 10 elements from the publisher
.buffer(10) // groups integers by 10 elements
.delayElements(Duration.ofSeconds(2)) // emits a group of ints every 2 sec
.subscribe(System.out::println);