reactor-core/src/main/java/reactor/core/publisher/Mono.java
public final Mono<T> doOnRequest(final LongConsumer consumer) {
		Objects.requireNonNull(consumer, "consumer");
		return doOnSignal(this, null, null, null, null, consumer, null);
	}
public final Mono<T> doOnRequest(final LongConsumer consumer) {
		Objects.requireNonNull(consumer, "consumer");
		return doOnSignal(this, null, null, null, null, consumer, null);
	}
Add behavior triggering a {@link LongConsumer} when the {@link Mono} receives any request.
<p>
Note that non fatal error raised in the callback will not be propagated and
will simply trigger {@link Operators#onOperatorError(Throwable, Context)}.

<p>
<img class="marble" src="doc-files/marbles/doOnRequestForMono.svg" alt="">

@param consumer the consumer to invoke on each request

@return an observed  {@link Mono}