Adds RemoveContentLengthRequestHeadersFilter

Removes workaround in RestClientProxyExchange and ClientHttpRequestFactoryProxyExchange

See gh-2949

spring-cloud-gateway-server-mvc/src/main/java/org/springframework/cloud/gateway/server/mvc/GatewayServerMvcAutoConfiguration.java

@@ -31,6 +31,7 @@
 import org.springframework.cloud.gateway.server.mvc.filter.ForwardedRequestHeadersFilter;
 import org.springframework.cloud.gateway.server.mvc.filter.HttpHeadersFilter.RequestHttpHeadersFilter;
 import org.springframework.cloud.gateway.server.mvc.filter.HttpHeadersFilter.ResponseHttpHeadersFilter;
+import org.springframework.cloud.gateway.server.mvc.filter.RemoveContentLengthRequestHeadersFilter;
 import org.springframework.cloud.gateway.server.mvc.filter.RemoveHopByHopRequestHeadersFilter;
 import org.springframework.cloud.gateway.server.mvc.filter.RemoveHopByHopResponseHeadersFilter;
 import org.springframework.cloud.gateway.server.mvc.filter.TransferEncodingNormalizationRequestHeadersFilter;
@@ -116,6 +117,12 @@ public ProxyExchangeHandlerFunction proxyExchangeHandlerFunction(ProxyExchange p
 		return new ProxyExchangeHandlerFunction(proxyExchange, requestHttpHeadersFilters, responseHttpHeadersFilters);
 	}
 
+	@Bean
+	@ConditionalOnMissingBean
+	public RemoveContentLengthRequestHeadersFilter removeContentLengthRequestHeadersFilter() {
+		return new RemoveContentLengthRequestHeadersFilter();
+	}
+
 	@Bean
 	@ConditionalOnMissingBean
 	public RemoveHopByHopRequestHeadersFilter removeHopByHopRequestHeadersFilter() {

spring-cloud-gateway-server-mvc/src/main/java/org/springframework/cloud/gateway/server/mvc/filter/RemoveContentLengthRequestHeadersFilter.java

@@ -0,0 +1,45 @@
+/*
+ * Copyright 2013-2023 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
+ *
+ *      https://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.server.mvc.filter;
+
+import org.springframework.core.Ordered;
+import org.springframework.http.HttpHeaders;
+import org.springframework.web.servlet.function.ServerRequest;
+
+// jdk http clients seem to not like having this copied from the initial request.
+// urlconnection fails with form url encoded
+public class RemoveContentLengthRequestHeadersFilter implements HttpHeadersFilter.RequestHttpHeadersFilter, Ordered {
+
+	@Override
+	public int getOrder() {
+		return 1000;
+	}
+
+	@Override
+	public HttpHeaders apply(HttpHeaders input, ServerRequest request) {
+		if (input.containsKey(HttpHeaders.CONTENT_LENGTH)) {
+
+			HttpHeaders filtered = new HttpHeaders();
+			// avoids read only if input is read only
+			filtered.addAll(input);
+			filtered.remove(HttpHeaders.CONTENT_LENGTH);
+			return filtered;
+		}
+		return input;
+	}
+
+}

spring-cloud-gateway-server-mvc/src/main/java/org/springframework/cloud/gateway/server/mvc/handler/ClientHttpRequestFactoryProxyExchange.java

@@ -38,8 +38,6 @@ public ServerResponse exchange(Request request) {
 		try {
 			ClientHttpRequest clientHttpRequest = requestFactory.createRequest(request.getUri(), request.getMethod());
 			clientHttpRequest.getHeaders().putAll(request.getHeaders());
-			// TODO: why does this help form encoding?
-			clientHttpRequest.getHeaders().remove("content-length");
 			// copy body from request to clientHttpRequest
 			StreamUtils.copy(request.getServerRequest().servletRequest().getInputStream(), clientHttpRequest.getBody());
 			ClientHttpResponse clientHttpResponse = clientHttpRequest.execute();

spring-cloud-gateway-server-mvc/src/main/java/org/springframework/cloud/gateway/server/mvc/handler/RestClientProxyExchange.java

@@ -35,12 +35,8 @@ public RestClientProxyExchange(RestClient restClient) {
 	@Override
 	public ServerResponse exchange(Request request) {
 		return restClient.method(request.getMethod()).uri(request.getUri())
-				.headers(httpHeaders -> request.getHeaders().forEach((header, values) -> {
-					// TODO: why does this help form encoding?
-					if (!header.equalsIgnoreCase("content-length")) {
-						httpHeaders.put(header, values);
-					}
-				})).body(outputStream -> copyBody(request, outputStream))
+				.headers(httpHeaders -> httpHeaders.putAll(request.getHeaders()))
+				.body(outputStream -> copyBody(request, outputStream))
 				.exchange((clientRequest, clientResponse) -> doExchange(request, clientResponse), false);
 	}
 

spring-cloud-gateway-server-mvc/src/test/java/org/springframework/cloud/gateway/server/mvc/ServerMvcIntegrationTests.java

@@ -118,10 +118,16 @@
 import static org.springframework.web.servlet.function.RequestPredicates.path;
 
 @SuppressWarnings("unchecked")
-@SpringBootTest(properties = {}, webEnvironment = WebEnvironment.RANDOM_PORT)
+@SpringBootTest(properties = { "spring.cloud.gateway.mvc.http-client.type=jdk" },
+		webEnvironment = WebEnvironment.RANDOM_PORT)
 @ContextConfiguration(initializers = HttpbinTestcontainers.class)
 public class ServerMvcIntegrationTests {
 
+	static {
+		// if set type to autodetect above
+		System.setProperty("sun.net.http.allowRestrictedHeaders", "true");
+	}
+
 	@LocalServerPort
 	int port;