Improve recording of cancellation signal in WebClient

With its initial fix in gh-18444, the `WebClient` instrumentation would
record all CANCEL signals, including:

* when a `timeout` expires and the response has not been received
* when the client partially consumes the response body

Since the second use case is arguable intentional, this commit restricts
the instrumentation and thus avoids recording two events for a single
request in that case.

Closes gh-18444

spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/metrics/web/reactive/client/MetricsWebClientFilterFunction.java

@@ -17,6 +17,7 @@
 package org.springframework.boot.actuate.metrics.web.reactive.client;
 
 import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicBoolean;
 
 import io.micrometer.core.instrument.MeterRegistry;
 import io.micrometer.core.instrument.Tag;
@@ -77,13 +78,15 @@ public class MetricsWebClientFilterFunction implements ExchangeFilterFunction {
 	}
 
 	private Mono<ClientResponse> instrumentResponse(ClientRequest request, Mono<ClientResponse> responseMono) {
+		final AtomicBoolean responseReceived = new AtomicBoolean();
 		return Mono.deferWithContext((ctx) -> responseMono.doOnEach((signal) -> {
 			if (signal.isOnNext() || signal.isOnError()) {
+				responseReceived.set(true);
 				Iterable<Tag> tags = this.tagProvider.tags(request, signal.get(), signal.getThrowable());
 				recordTimer(tags, getStartTime(ctx));
 			}
 		}).doFinally((signalType) -> {
-			if (SignalType.CANCEL.equals(signalType)) {
+			if (!responseReceived.get() && SignalType.CANCEL.equals(signalType)) {
 				Iterable<Tag> tags = this.tagProvider.tags(request, null, null);
 				recordTimer(tags, getStartTime(ctx));
 			}

spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/metrics/web/reactive/client/MetricsWebClientFilterFunctionTests.java

@@ -24,6 +24,7 @@ import java.util.concurrent.TimeUnit;
 import io.micrometer.core.instrument.MeterRegistry;
 import io.micrometer.core.instrument.MockClock;
 import io.micrometer.core.instrument.Timer;
+import io.micrometer.core.instrument.search.MeterNotFoundException;
 import io.micrometer.core.instrument.simple.SimpleConfig;
 import io.micrometer.core.instrument.simple.SimpleMeterRegistry;
 import org.junit.jupiter.api.BeforeEach;
@@ -40,6 +41,7 @@ import org.springframework.web.reactive.function.client.ExchangeFunction;
 import org.springframework.web.reactive.function.client.WebClient;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static org.mockito.BDDMockito.given;
 import static org.mockito.Mockito.mock;
 
@@ -124,6 +126,23 @@ class MetricsWebClientFilterFunctionTests {
 		assertThat(this.registry.get("http.client.requests")
 				.tags("method", "GET", "uri", "/projects/spring-boot", "status", "CLIENT_ERROR").timer().count())
 						.isEqualTo(1);
+		assertThatThrownBy(() -> this.registry.get("http.client.requests")
+				.tags("method", "GET", "uri", "/projects/spring-boot", "status", "200").timer())
+						.isInstanceOf(MeterNotFoundException.class);
+	}
+
+	@Test
+	void filterWhenCancelAfterResponseThrownShouldNotRecordTimer() {
+		ClientRequest request = ClientRequest
+				.create(HttpMethod.GET, URI.create("https://example.com/projects/spring-boot")).build();
+		given(this.response.rawStatusCode()).willReturn(HttpStatus.OK.value());
+		Mono<ClientResponse> filter = this.filterFunction.filter(request, this.exchange);
+		StepVerifier.create(filter).expectNextCount(1).thenCancel().verify(Duration.ofSeconds(5));
+		assertThat(this.registry.get("http.client.requests")
+				.tags("method", "GET", "uri", "/projects/spring-boot", "status", "200").timer().count()).isEqualTo(1);
+		assertThatThrownBy(() -> this.registry.get("http.client.requests")
+				.tags("method", "GET", "uri", "/projects/spring-boot", "status", "CLIENT_ERROR").timer())
+						.isInstanceOf(MeterNotFoundException.class);
 	}
 
 	@Test