GH-1219: Fix header mapping for replies (@SendTo)

Resolves https://github.com/spring-projects/spring-amqp/issues/1219

The headers were mapped after message conversion.
This prevented using a `ContentTypeDelegatingMessageConverter` because
the content type was not set.

Add a header to control whether the user or converter gets to set the
content type property in the final message.

**cherry-pick to 2.2.x, 2.1.x, 1.7.x**

# Conflicts:
#	spring-amqp/src/main/java/org/springframework/amqp/support/AmqpHeaders.java
#	spring-amqp/src/main/java/org/springframework/amqp/support/converter/MessagingMessageConverter.java
#	src/reference/asciidoc/amqp.adoc

# Conflicts:
#	src/reference/asciidoc/amqp.adoc

spring-amqp/src/main/java/org/springframework/amqp/support/AmqpHeaders.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -49,6 +49,8 @@ public abstract class AmqpHeaders {
 
 	public static final String CONTENT_TYPE = MessageHeaders.CONTENT_TYPE;
 
+	public static final String CONTENT_TYPE_CONVERTER_WINS = PREFIX + "contentTypeConverterWins";
+
 	public static final String CORRELATION_ID = PREFIX + "correlationId";
 
 	public static final String DELAY = PREFIX + "delay";

spring-amqp/src/main/java/org/springframework/amqp/support/converter/MessagingMessageConverter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2014 the original author or authors.
+ * Copyright 2014-2020 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.
@@ -20,9 +20,11 @@ import java.util.Map;
 
 import org.springframework.amqp.core.MessageProperties;
 import org.springframework.amqp.support.AmqpHeaderMapper;
+import org.springframework.amqp.support.AmqpHeaders;
 import org.springframework.amqp.support.SimpleAmqpHeaderMapper;
 import org.springframework.beans.factory.InitializingBean;
 import org.springframework.messaging.Message;
+import org.springframework.messaging.MessageHeaders;
 import org.springframework.messaging.support.MessageBuilder;
 import org.springframework.util.Assert;
 
@@ -101,10 +103,16 @@ public class MessagingMessageConverter implements MessageConverter, Initializing
 					Message.class.getName() + "] is handled by this converter");
 		}
 		Message<?> input = (Message<?>) object;
+		this.headerMapper.fromHeaders(input.getHeaders(), messageProperties);
 		org.springframework.amqp.core.Message amqpMessage = this.payloadConverter.toMessage(
 				input.getPayload(), messageProperties);
-
-		this.headerMapper.fromHeaders(input.getHeaders(), messageProperties);
+		// Default previous behavior of mapper wins for backwards compatibility.
+		if (!Boolean.TRUE.equals(input.getHeaders().get(AmqpHeaders.CONTENT_TYPE_CONVERTER_WINS))) {
+			String contentType = input.getHeaders().get(MessageHeaders.CONTENT_TYPE, String.class);
+			if (contentType != null) {
+				messageProperties.setContentType(contentType);
+			}
+		}
 		return amqpMessage;
 	}
 

spring-rabbit/src/test/java/org/springframework/amqp/rabbit/annotation/ContentTypeDelegatingMessageConverterIntegrationTests.java

@@ -0,0 +1,191 @@
+/*
+ * Copyright 2020 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.amqp.rabbit.annotation;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+
+import org.junit.ClassRule;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import org.springframework.amqp.core.AnonymousQueue;
+import org.springframework.amqp.core.Message;
+import org.springframework.amqp.core.MessageProperties;
+import org.springframework.amqp.rabbit.config.SimpleRabbitListenerContainerFactory;
+import org.springframework.amqp.rabbit.connection.CachingConnectionFactory;
+import org.springframework.amqp.rabbit.connection.ConnectionFactory;
+import org.springframework.amqp.rabbit.core.RabbitAdmin;
+import org.springframework.amqp.rabbit.core.RabbitTemplate;
+import org.springframework.amqp.rabbit.junit.BrokerRunning;
+import org.springframework.amqp.support.AmqpHeaders;
+import org.springframework.amqp.support.converter.ContentTypeDelegatingMessageConverter;
+import org.springframework.amqp.support.converter.MessageConversionException;
+import org.springframework.amqp.support.converter.MessageConverter;
+import org.springframework.amqp.support.converter.SimpleMessageConverter;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.messaging.MessageHeaders;
+import org.springframework.messaging.handler.annotation.SendTo;
+import org.springframework.messaging.support.MessageBuilder;
+import org.springframework.test.context.junit4.SpringRunner;
+
+/**
+ * @author Gary Russell
+ * @author Artem Bilan
+ *
+ * @since 1.7.15
+ *
+ */
+@RunWith(SpringRunner.class)
+public class ContentTypeDelegatingMessageConverterIntegrationTests {
+
+	@ClassRule
+	public static final BrokerRunning BROKER_RUNNING = BrokerRunning.isRunning();
+
+	@Autowired
+	private Config config;
+
+	@Autowired
+	private RabbitTemplate template;
+
+	@Autowired
+	private AnonymousQueue queue1;
+
+	@Test
+	public void testReplyContentType() throws InterruptedException {
+		this.template.convertAndSend(this.queue1.getName(), "foo", msg -> {
+			msg.getMessageProperties().setContentType("foo/bar");
+			return msg;
+		});
+		assertTrue(this.config.latch1.await(10, TimeUnit.SECONDS));
+		assertEquals("baz/qux", this.config.replyContentType);
+		assertEquals("baz/qux", this.config.receivedReplyContentType);
+
+		this.template.convertAndSend(this.queue1.getName(), "bar", msg -> {
+			msg.getMessageProperties().setContentType("foo/bar");
+			return msg;
+		});
+		assertTrue(this.config.latch2.await(10, TimeUnit.SECONDS));
+		assertEquals("baz/qux", this.config.replyContentType);
+		assertEquals("foo/bar", this.config.receivedReplyContentType);
+	}
+
+	@Configuration
+	@EnableRabbit
+	public static class Config {
+
+		final CountDownLatch latch1 = new CountDownLatch(1);
+
+		final CountDownLatch latch2 = new CountDownLatch(2);
+
+		volatile String replyContentType;
+
+		volatile String receivedReplyContentType;
+
+		@Bean
+		public ConnectionFactory cf() {
+			return new CachingConnectionFactory(BROKER_RUNNING.getConnectionFactory());
+		}
+
+		@Bean
+		public SimpleRabbitListenerContainerFactory rabbitListenerContainerFactory() {
+			SimpleRabbitListenerContainerFactory factory = new SimpleRabbitListenerContainerFactory();
+			factory.setConnectionFactory(cf());
+			ContentTypeDelegatingMessageConverter converter =
+					new ContentTypeDelegatingMessageConverter(new SimpleMessageConverter());
+			converter.addDelegate("foo/bar", new MessageConverter() {
+
+				@Override
+				public Message toMessage(Object object, MessageProperties messageProperties)
+						throws MessageConversionException {
+
+					return new Message("foo".getBytes(), messageProperties);
+				}
+
+				@Override
+				public Object fromMessage(Message message) throws MessageConversionException {
+					return new String(message.getBody());
+				}
+
+			});
+			converter.addDelegate("baz/qux", new MessageConverter() {
+
+				@Override
+				public Message toMessage(Object object, MessageProperties messageProperties)
+						throws MessageConversionException {
+
+					Config.this.replyContentType = messageProperties.getContentType();
+					messageProperties.setContentType("foo/bar");
+					return new Message("foo".getBytes(), messageProperties);
+				}
+
+				@Override
+				public Object fromMessage(Message message) throws MessageConversionException {
+					return new String(message.getBody());
+				}
+
+			});
+			factory.setMessageConverter(converter);
+			return factory;
+		}
+
+		@Bean
+		public RabbitTemplate template() {
+			return new RabbitTemplate(cf());
+		}
+
+		@Bean
+		public RabbitAdmin admin() {
+			return new RabbitAdmin(cf());
+		}
+
+		@Bean
+		public AnonymousQueue queue1() {
+			return new AnonymousQueue();
+		}
+
+		@Bean
+		public AnonymousQueue queue2() {
+			return new AnonymousQueue();
+		}
+
+		@RabbitListener(queues = "#{@queue1.name}")
+		@SendTo("#{@queue2.name}")
+		public org.springframework.messaging.Message<String> listen1(String in) {
+			MessageBuilder<String> builder = MessageBuilder.withPayload(in)
+					.setHeader(MessageHeaders.CONTENT_TYPE, "baz/qux");
+			if ("bar".equals(in)) {
+				builder.setHeader(AmqpHeaders.CONTENT_TYPE_CONVERTER_WINS, true);
+			}
+			return builder.build();
+		}
+
+		@RabbitListener(queues = "#{@queue2.name}")
+		public void listen2(Message in) {
+			this.receivedReplyContentType = in.getMessageProperties().getContentType();
+			this.latch1.countDown();
+			this.latch2.countDown();
+		}
+
+	}
+
+}

src/reference/asciidoc/amqp.adoc

@@ -1896,7 +1896,7 @@ public Message<OrderStatus> processOrder(Order order) {
 }
 ----
 
-The `@SendTo` value is assumed as a reply `exchange` and `routingKey` pair following the pattern `exchange/routingKey`,
+The `@SendTo` value is assumed as a reply `exchange` and `routingKey` pair that follows the `exchange/routingKey` pattern,
 where one of those parts can be omitted.
 The valid values are:
 
@@ -1968,6 +1968,28 @@ beans are referenced by their names.
 `!{...}` is evaluated at runtime for each message with the root object having the properties above and beans are
 referenced with their names, prefixed by `@`.
 
+====== Reply ContentType
+
+If you are using a sophisticated message converter, such as the `ContentTypeDelegatingMessageConverter`, you can control the content type of the reply by returning a `spring-messaging` `Message<?>`:
+
+====
+[source, java]
+----
+@RabbitListener(queues = "q1")
+@SendTo("q2")
+public Message<String> listen(String in) {
+    ...
+    return MessageBuilder.withPayload(in.toUpperCase())
+            .setHeader(MessageHeaders.CONTENT_TYPE, "application/xml")
+            .build();
+}
+----
+====
+
+This content type will be passed in the `MessageProperties` to the converter.
+By default, for backwards compatibility, any content type property set by the converter will be overwritten by this value after conversion.
+If you wish to override that behavior, also set the `AmqpHeaders.CONTENT_TYPE_CONVERTER_WINS` to `true` and any value set by the converter will be retained.
+
 [[annotation-method-selection]]
 ====== Multi-Method Listeners