Pass client errors back to client.

By setting failOnClientError(false).

fixes gh-42

spring-cloud-gateway-core/src/main/java/org/springframework/cloud/gateway/filter/NettyRoutingFilter.java

@@ -76,6 +76,7 @@ public class NettyRoutingFilter implements GlobalFilter, Ordered {
 
 		return this.httpClient.request(method, url, req -> {
 			final HttpClientRequest proxyRequest = req.options(NettyPipeline.SendOptions::flushOnEach)
+					.failOnClientError(false)
 					.headers(httpHeaders);
 
 			if (MediaType.APPLICATION_FORM_URLENCODED.includes(request.getHeaders().getContentType())) {

spring-cloud-gateway-core/src/test/java/org/springframework/cloud/gateway/test/BaseWebClientTests.java

@@ -37,6 +37,8 @@ import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.core.annotation.Order;
 import org.springframework.http.MediaType;
+import org.springframework.http.ResponseEntity;
+import org.springframework.http.codec.multipart.Part;
 import org.springframework.web.bind.annotation.PathVariable;
 import org.springframework.web.bind.annotation.RequestBody;
 import org.springframework.web.bind.annotation.RequestMapping;
@@ -130,7 +132,7 @@ public class BaseWebClientTests {
 
 		@RequestMapping(value = "/post", consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
 		public Mono<Map<String, Object>> postFormData(//ServerWebExchange exchange,
-													  // @RequestParam Map<String, Part> parts
+													  @RequestParam Map<String, Part> parts
 											  /*@RequestBody(required = false) String body*/) {
 			HashMap<String, Object> ret = new HashMap<>();
 			// HashMap<String, Object> files = parseMultipart(exchange, null);
@@ -162,6 +164,11 @@ public class BaseWebClientTests {
 			});
 		}
 
+		@RequestMapping("/status/{status}")
+		public ResponseEntity<String> status(@PathVariable int status) {
+			return ResponseEntity.status(status).body("Failed with "+status);
+		}
+
 		@Bean
 		@Order(500)
 		public GlobalFilter modifyResponseFilter() {

spring-cloud-gateway-core/src/test/java/org/springframework/cloud/gateway/test/HttpStatusTests.java

@@ -0,0 +1,63 @@
+/*
+ * Copyright 2013-2017 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.cloud.gateway.test;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.boot.SpringBootConfiguration;
+import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.context.annotation.Import;
+import org.springframework.http.HttpStatus;
+import org.springframework.test.annotation.DirtiesContext;
+import org.springframework.test.context.junit4.SpringRunner;
+import org.springframework.web.reactive.function.client.ClientResponse;
+
+import static org.springframework.boot.test.context.SpringBootTest.WebEnvironment.RANDOM_PORT;
+import static org.springframework.cloud.gateway.test.TestUtils.assertStatus;
+
+import reactor.core.publisher.Mono;
+import reactor.test.StepVerifier;
+
+@RunWith(SpringRunner.class)
+@SpringBootTest(webEnvironment = RANDOM_PORT)
+@DirtiesContext
+@SuppressWarnings("unchecked")
+public class HttpStatusTests extends BaseWebClientTests {
+
+	@Test
+	public void notFoundResponseWorks() {
+		Mono<ClientResponse> result = webClient.get()
+				.uri("/status/404")
+				.exchange();
+
+		StepVerifier.create(result)
+				.consumeNextWith(
+						response -> {
+							assertStatus(response, HttpStatus.NOT_FOUND);
+						})
+				.expectComplete()
+				.verify(DURATION);
+	}
+
+	@EnableAutoConfiguration
+	@SpringBootConfiguration
+	@Import(DefaultTestConfig.class)
+	public static class TestConfig { }
+
+}