Remove observation context from ClientRequest

Prior to this commit, gh-31609 added the current observation context as
a request attribute for `WebClient` calls. While it was not confirmed as
the main cause, this feature was linked to several reports of memory
leaks. This would indeed attach more memory to the request object graph
at runtime - although it shouldn't prevent its collection by the GC.

This commit removes this feature and instead developers should get the
current observation from the reactor context if they wish to interact
with it.

Closes gh-32198

Author: bclozel

spring-webflux/src/main/java/org/springframework/web/reactive/function/client/ClientRequestObservationContext.java

@@ -16,8 +16,6 @@
 
 package org.springframework.web.reactive.function.client;
 
-import java.util.Optional;
-
 import io.micrometer.observation.transport.RequestReplySenderContext;
 
 import org.springframework.lang.Nullable;
@@ -35,14 +33,6 @@
  */
 public class ClientRequestObservationContext extends RequestReplySenderContext<ClientRequest.Builder, ClientResponse> {
 
-	/**
-	 * Name of the request attribute holding the {@link ClientRequestObservationContext context}
-	 * for the current observation.
-	 * @since 6.0.15
-	 */
-	public static final String CURRENT_OBSERVATION_CONTEXT_ATTRIBUTE = ClientRequestObservationContext.class.getName();
-
-
 	@Nullable
 	private String uriTemplate;
 
@@ -127,15 +117,4 @@ public ClientRequest getRequest() {
 	}
 
 
-	/**
-	 * Get the current {@link ClientRequestObservationContext observation context}
-	 * from the given request, if available.
-	 * @param request the current client request
-	 * @return the current observation context
-	 * @since 6.0.15
-	 */
-	public static Optional<ClientRequestObservationContext> findCurrent(ClientRequest request) {
-		return Optional.ofNullable((ClientRequestObservationContext) request.attributes().get(CURRENT_OBSERVATION_CONTEXT_ATTRIBUTE));
-	}
-
 }

spring-webflux/src/main/java/org/springframework/web/reactive/function/client/DefaultWebClient.java

@@ -450,9 +450,7 @@ public Mono<ClientResponse> exchange() {
 				if (filterFunctions != null) {
 					filterFunction = filterFunctions.andThen(filterFunction);
 				}
-				ClientRequest request = requestBuilder
-						.attribute(ClientRequestObservationContext.CURRENT_OBSERVATION_CONTEXT_ATTRIBUTE, observationContext)
-						.build();
+				ClientRequest request = requestBuilder.build();
 				observationContext.setUriTemplate((String) request.attribute(URI_TEMPLATE_ATTRIBUTE).orElse(null));
 				observationContext.setRequest(request);
 				Mono<ClientResponse> responseMono = filterFunction.apply(exchangeFunction)

spring-webflux/src/test/java/org/springframework/web/reactive/function/client/WebClientObservationTests.java

@@ -148,23 +148,6 @@ void setsCurrentObservationInReactorContext() {
 		verifyAndGetRequest();
 	}
 
-	@Test
-	void setsCurrentObservationContextAsRequestAttribute() {
-		ExchangeFilterFunction assertionFilter = (request, chain) -> {
-			Optional<ClientRequestObservationContext> observationContext = ClientRequestObservationContext.findCurrent(request);
-			assertThat(observationContext).isPresent();
-			return chain.exchange(request).contextWrite(context -> {
-				Observation currentObservation = context.get(ObservationThreadLocalAccessor.KEY);
-				assertThat(currentObservation.getContext()).isEqualTo(observationContext.get());
-				return context;
-			});
-		};
-		this.builder.filter(assertionFilter).build().get().uri("/resource/{id}", 42)
-				.retrieve().bodyToMono(Void.class)
-				.block(Duration.ofSeconds(10));
-		verifyAndGetRequest();
-	}
-
 	@Test
 	void recordsObservationWithResponseDetailsWhenFilterFunctionErrors() {
 		ExchangeFilterFunction errorFunction = (req, next) -> next.exchange(req).then(Mono.error(new IllegalStateException()));