Add 'Transfer-Encoding' header to the list of filtered headers

Resolves #1220

spring-cloud-function-web/pom.xml

@@ -66,6 +66,11 @@
 			<artifactId>awaitility</artifactId>
 			<scope>test</scope>
 		</dependency>
+		<dependency>
+			<groupId>org.apache.httpcomponents.client5</groupId>
+			<artifactId>httpclient5</artifactId>
+			<scope>test</scope>
+		</dependency>
 	</dependencies>
 
 	<build>

spring-cloud-function-web/src/main/java/org/springframework/cloud/function/web/util/HeaderUtils.java

@@ -45,6 +45,7 @@ public final class HeaderUtils {
 	static {
 		IGNORED.add(MessageHeaders.ID, "");
 		IGNORED.add(HttpHeaders.CONTENT_LENGTH, "0");
+		IGNORED.add(HttpHeaders.TRANSFER_ENCODING, "*");
 		// Headers that would typically be added by a downstream client
 		REQUEST_ONLY.add(HttpHeaders.ACCEPT, "");
 		REQUEST_ONLY.add(HttpHeaders.CONTENT_LENGTH, "");

spring-cloud-function-web/src/test/java/org/springframework/cloud/function/web/function/HeadersResponseMappingTests.java

@@ -0,0 +1,61 @@
+/*
+ * Copyright 2024-2024 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.function.web.function;
+
+
+import java.net.URI;
+import java.util.Locale;
+import java.util.function.Function;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.boot.test.web.client.TestRestTemplate;
+import org.springframework.context.ConfigurableApplicationContext;
+import org.springframework.context.annotation.Bean;
+import org.springframework.http.ResponseEntity;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class HeadersResponseMappingTests {
+
+	// see https://github.com/spring-cloud/spring-cloud-function/issues/1220
+	@Test
+	public void test_1220() throws Exception {
+		ConfigurableApplicationContext context = SpringApplication.run(ApplicationConfiguration.class,
+				"--server.port=0");
+		TestRestTemplate testRestTemplate = new TestRestTemplate();
+		String port = context.getEnvironment().getProperty("local.server.port");
+		ResponseEntity<String> response = testRestTemplate.postForEntity(
+				new URI("http://localhost:" + port + "/uppercase"), new Person("John", "Doe"), String.class);
+		assertThat(response.getBody()).isEqualTo("JOHN");
+	}
+
+	static record Person(String firstName, String lastName) {
+	}
+
+	@SpringBootApplication
+	protected static class ApplicationConfiguration {
+
+		@Bean
+		public Function<Person, String> uppercase() {
+			return s -> s.firstName().toUpperCase(Locale.ROOT);
+		}
+
+	}
+}