Clear Netty channel attribute

Closes gh-36158

spring-web/src/main/java/org/springframework/http/client/reactive/ReactorClientHttpConnector.java

@@ -21,12 +21,15 @@ import java.util.Map;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Function;
 
+import io.netty.channel.Channel;
+import io.netty.util.Attribute;
 import io.netty.util.AttributeKey;
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 import org.jspecify.annotations.Nullable;
 import reactor.core.publisher.Mono;
 import reactor.netty.NettyOutbound;
+import reactor.netty.channel.ChannelOperations;
 import reactor.netty.http.client.HttpClient;
 import reactor.netty.http.client.HttpClientRequest;
 import reactor.netty.resources.ConnectionProvider;
@@ -160,10 +163,14 @@ public class ReactorClientHttpConnector implements ClientHttpConnector, SmartLif
 				.request(io.netty.handler.codec.http.HttpMethod.valueOf(method.name()));
 
 		requestSender = setUri(requestSender, uri);
+		AtomicReference<Channel> channelRef = new AtomicReference<>();
 		AtomicReference<ReactorClientHttpResponse> responseRef = new AtomicReference<>();
 
 		return requestSender
-				.send((request, outbound) -> requestCallback.apply(adaptRequest(method, uri, request, outbound)))
+				.send((request, outbound) -> {
+					channelRef.set(((ChannelOperations<?, ?>) request).channel());
+					return requestCallback.apply(adaptRequest(method, uri, request, outbound));
+				})
 				.responseConnection((response, connection) -> {
 					ReactorClientHttpResponse clientResponse = new ReactorClientHttpResponse(response, connection);
 					responseRef.set(clientResponse);
@@ -175,6 +182,15 @@ public class ReactorClientHttpConnector implements ClientHttpConnector, SmartLif
 					if (response != null) {
 						response.releaseAfterCancel(method);
 					}
+				})
+				.doOnTerminate(() -> {
+					Channel channel = channelRef.get();
+					if (channel != null) {
+						Attribute<Map<String, Object>> attribute = channel.attr(ATTRIBUTES_KEY);
+						if (attribute != null) {
+							attribute.set(null);
+						}
+					}
 				});
 	}
 

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

@@ -39,6 +39,7 @@ import java.util.function.Function;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
+import io.netty.channel.Channel;
 import io.netty.util.Attribute;
 import mockwebserver3.MockResponse;
 import mockwebserver3.MockWebServer;
@@ -54,6 +55,7 @@ import reactor.core.publisher.Mono;
 import reactor.core.publisher.Sinks;
 import reactor.netty.channel.ChannelOperations;
 import reactor.netty.http.client.HttpClient;
+import reactor.netty.http.client.HttpClientRequest;
 import reactor.netty.resources.ConnectionProvider;
 import reactor.test.StepVerifier;
 
@@ -1320,6 +1322,28 @@ class WebClientIntegrationTests {
 				.verify(Duration.ofSeconds(3));
 	}
 
+	@Test // gh-36158
+	void reactorNettyAttributes() throws IOException {
+		startServer(new ReactorClientHttpConnector());
+
+		prepareResponse(builder ->
+				builder.setHeader("Content-Type", "text/plain").body("Hello Spring!"));
+
+		AtomicReference<Channel> channelRef = new AtomicReference<>();
+
+		Mono<String> result = this.webClient.get().uri("/greeting")
+				.httpRequest(request -> {
+					HttpClientRequest reactorRequest = request.getNativeRequest();
+					channelRef.set(((ChannelOperations<?, ?>) reactorRequest).channel());
+				})
+				.retrieve()
+				.bodyToMono(String.class);
+
+		StepVerifier.create(result).expectNext("Hello Spring!").expectComplete().verify(Duration.ofSeconds(3));
+
+		assertThat(channelRef.get().attr(ReactorClientHttpConnector.ATTRIBUTES_KEY).get()).isNull();
+	}
+
 	private <T> Mono<T> doMalformedChunkedResponseTest(
 			ClientHttpConnector connector, Function<ResponseSpec, Mono<T>> handler) {