Micronaut Reactive Streams: Emission rate is not maintained

Question

I'm trying to test streaming a Flux with a delay of 1000 millis for each element.

@Get(value = "/carts/reactive", produces = MediaType.APPLICATION_JSON_STREAM)
public Flux<Cart> getCartsReactive() {
     return Flux.range(1, 10)
            .map(integer -> Cart.builder().name("cart" + integer).build())
            .delayElements(Duration.ofMillis(1000))
            .doOnNext(cart -> log.info("Returning Flux of cart: " +cart));
}

When I hit the service, I don't get a response for 10 seconds and get a blog of response.

curl http://localhost:7070/carts/reactive

{"name":"cart1"}{"name":"cart2"}{"name":"cart3"}{"name":"cart4"}{"name":"cart5"}{"name":"cart6"}{"name":"cart7"}{"name":"cart8"}{"name":"cart9"}{"name":"cart10"}

Is this a bug? Why doesn't it emit 1 cart every second?

Answer 1

There's nothing wrong with your code as you've written it - here's a complete project using micronaut + reactor with exactly that code in a controller:

https://github.com/berry120/micronaut-reactive-demo

It produces the elements one at a time, as expected, with a one second delay:

You can compare that project to your own to see what configuration / code you may be missing that's preventing it from working properly. I haven't done anything particularly special with the above project at all - this was purely created from the Micronaut initializr, with the reactor add-on included.

Note that you should configure the micronaut-reactor module (implementation("io.micronaut.reactor:micronaut-reactor")) rather than just including reactor as a third party dependency, otherwise that may cause issues.