Ensure client response is drained with onStatus hook

Issue: SPR-17473

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

@@ -436,19 +436,30 @@ class DefaultWebClient implements WebClient {
 
 		private <T extends Publisher<?>> T bodyToPublisher(ClientResponse response,
 				T bodyPublisher, Function<Mono<? extends Throwable>, T> errorFunction) {
+
 			if (HttpStatus.resolve(response.rawStatusCode()) != null) {
-				return this.statusHandlers.stream()
-						.filter(statusHandler -> statusHandler.test(response.statusCode()))
-						.findFirst()
-						.map(statusHandler -> statusHandler.apply(response))
-						.map(errorFunction::apply)
-						.orElse(bodyPublisher);
+				for (StatusHandler handler : this.statusHandlers) {
+					if (handler.test(response.statusCode())) {
+						Mono<? extends Throwable> exMono = handler.apply(response);
+						exMono = exMono.flatMap(ex -> drainBody(response, ex));
+						exMono = exMono.onErrorResume(ex -> drainBody(response, ex));
+						return errorFunction.apply(exMono);
+					}
+				}
+				return bodyPublisher;
 			}
 			else {
 				return errorFunction.apply(createResponseException(response));
 			}
 		}
 
+		@SuppressWarnings("unchecked")
+		private <T> Mono<T> drainBody(ClientResponse response, Throwable ex) {
+			// Ensure the body is drained, even if the StatusHandler didn't consume it,
+			// but ignore errors in case it did consume it.
+			return (Mono<T>) response.bodyToMono(Void.class).onErrorMap(ex2 -> ex).thenReturn(ex);
+		}
+
 		private static Mono<WebClientResponseException> createResponseException(ClientResponse response) {
 			return DataBufferUtils.join(response.body(BodyExtractors.toDataBuffers()))
 					.map(dataBuffer -> {

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

@@ -595,6 +595,9 @@ public interface WebClient {
 		 * {@link WebClientResponseException} when the response status code is 4xx or 5xx.
 		 * @param statusPredicate a predicate that indicates whether {@code exceptionFunction}
 		 * applies
+		 * <p><strong>NOTE:</strong> if the response is expected to have content,
+		 * the exceptionFunction should consume it. If not, the content will be
+		 * automatically drained to ensure resources are released.
 		 * @param exceptionFunction the function that returns the exception
 		 * @return this builder
 		 */

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

@@ -0,0 +1,151 @@
+/*
+ * Copyright 2002-2018 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.web.reactive.function.client;
+
+import java.time.Duration;
+import java.util.function.Function;
+
+import io.netty.buffer.ByteBufAllocator;
+import io.netty.channel.ChannelOption;
+import okhttp3.mockwebserver.MockResponse;
+import okhttp3.mockwebserver.MockWebServer;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+import reactor.core.publisher.Mono;
+import reactor.test.StepVerifier;
+
+import org.springframework.core.io.buffer.AbstractDataBufferAllocatingTestCase;
+import org.springframework.core.io.buffer.NettyDataBufferFactory;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.MediaType;
+import org.springframework.http.client.reactive.ReactorClientHttpConnector;
+import org.springframework.http.client.reactive.ReactorResourceFactory;
+
+import static org.junit.Assert.*;
+
+/**
+ * WebClient integration tests focusing on data buffer management.
+ * @author Rossen Stoyanchev
+ */
+public class WebClientDataBufferAllocatingTests extends AbstractDataBufferAllocatingTestCase {
+
+	private static final Duration DELAY = Duration.ofSeconds(5);
+
+
+	private MockWebServer server;
+
+	private WebClient webClient;
+
+	private ReactorResourceFactory factory;
+
+
+	@Before
+	public void setUp() {
+
+		this.factory = new ReactorResourceFactory();
+		this.factory.afterPropertiesSet();
+
+		this.server = new MockWebServer();
+		this.webClient = WebClient
+				.builder()
+				.clientConnector(initConnector())
+				.baseUrl(this.server.url("/").toString())
+				.build();
+	}
+
+	private ReactorClientHttpConnector initConnector() {
+		if (bufferFactory instanceof NettyDataBufferFactory) {
+			ByteBufAllocator allocator = ((NettyDataBufferFactory) bufferFactory).getByteBufAllocator();
+			return new ReactorClientHttpConnector(this.factory, httpClient ->
+					httpClient.tcpConfiguration(tcpClient -> tcpClient.option(ChannelOption.ALLOCATOR, allocator)));
+		}
+		else {
+			return new ReactorClientHttpConnector();
+		}
+	}
+
+	@After
+	public void shutDown() throws InterruptedException {
+		waitForDataBufferRelease(Duration.ofSeconds(2));
+		this.factory.destroy();
+	}
+
+
+
+	@Test
+	public void bodyToMonoVoid() {
+
+		this.server.enqueue(new MockResponse()
+				.setResponseCode(201)
+				.setHeader("Content-Type", "application/json")
+				.setChunkedBody("{\"foo\" : {\"bar\" : \"123\", \"baz\" : \"456\"}}", 5));
+
+		Mono<Void> mono = this.webClient.get()
+				.uri("/json").accept(MediaType.APPLICATION_JSON)
+				.retrieve()
+				.bodyToMono(Void.class);
+
+		StepVerifier.create(mono).expectComplete().verify(Duration.ofSeconds(3));
+		assertEquals(1, this.server.getRequestCount());
+	}
+
+
+	@Test
+	public void onStatusWithBodyNotConsumed() {
+		RuntimeException ex = new RuntimeException("response error");
+		testOnStatus(ex, response -> Mono.just(ex));
+	}
+
+	@Test
+	public void onStatusWithBodyConsumed() {
+		RuntimeException ex = new RuntimeException("response error");
+		testOnStatus(ex, response -> response.bodyToMono(Void.class).thenReturn(ex));
+	}
+
+	@Test // SPR-17473
+	public void onStatusWithMonoErrorAndBodyNotConsumed() {
+		RuntimeException ex = new RuntimeException("response error");
+		testOnStatus(ex, response -> Mono.error(ex));
+	}
+
+	@Test
+	public void onStatusWithMonoErrorAndBodyConsumed() {
+		RuntimeException ex = new RuntimeException("response error");
+		testOnStatus(ex, response -> response.bodyToMono(Void.class).then(Mono.error(ex)));
+	}
+
+	private void testOnStatus(Throwable expected,
+			Function<ClientResponse, Mono<? extends Throwable>> exceptionFunction) {
+
+		HttpStatus errorStatus = HttpStatus.BAD_GATEWAY;
+
+		this.server.enqueue(new MockResponse()
+				.setResponseCode(errorStatus.value())
+				.setHeader("Content-Type", "application/json")
+				.setChunkedBody("{\"error\" : {\"status\" : 502, \"message\" : \"Bad gateway.\"}}", 5));
+
+		Mono<String> mono = this.webClient.get()
+				.uri("/json").accept(MediaType.APPLICATION_JSON)
+				.retrieve()
+				.onStatus(status -> status.equals(errorStatus), exceptionFunction)
+				.bodyToMono(String.class);
+
+		StepVerifier.create(mono).expectErrorSatisfies(actual -> assertSame(expected, actual)).verify(DELAY);
+		assertEquals(1, this.server.getRequestCount());
+	}
+
+}