WebFlux - ignore 'cancel' signal - reactive-programming

Question

Tried to get the answer from other SO q&a, directly from reactor's documentation and spring webflux documentation but somehow I am not sure still, how to achieve this :(
Say I have simple controller as follows:
#RestController
class DemoController {
#GetMapping("/demo/{text}")
public Flux<String> getDemo(#PathVariable String text) {
return Flux.fromArray(text.split(""))
.map(String::toUpperCase)
.delayElements(Duration.ofSeconds(1L))
.doOnNext(s -> System.out.println("S: " + s + " -> " + LocalDateTime.now().getSecond()))
.doOnCancel(() -> System.out.println("Cancelled"));
}
}
and I would like the processing to ignore "cancel" signal, that normally comes when client disconnects. Tried to achieve that via nginx's proxy_ignore_client_abort on; but that does not work properly.
I can .subscribe(...) to a custom subscriber, that in example ignores cancel signals, but than I saw the processing is executed twice - which is quite obvious and not anticipated.
Another option, is that I can extends Flux<T> and just override:
#Override
public void cancel() {
System.out.println("Cancelled / ignored");
}
but that somehow looks more like hacking.
To sum up
Could someone please advise, what is the "proper" way of running some reactive pipeline, triggered via controller, that can ignore cancel signal?

Answer 1

The current webflux behavior is perfect. However your requirement seems to be different that you always want to emit even when the subscriber is no longer is interested in listening to the data. In this case, just make the source HOT.
#RestController
class DemoController {
#GetMapping("/demo/{text}")
public Flux<String> getDemo(#PathVariable String text) {
return Flux.fromArray(text.split(""))
.map(String::toUpperCase)
.delayElements(Duration.ofSeconds(1L))
.doOnNext(s -> System.out.println("S: " + s + " -> " + LocalDateTime.now().getSecond()))
.doOnCancel(() -> System.out.println("Cancelled"))
.cache(); // hot source
}
}