Default interceptor for legacy contentType

Fixes #1057

Enable consumers to convert from originalContentType to contentType in the case of
legacy producers sending messages with originalContentType header.
By default, this conversion will not happen and only be acitvated by setting
`spring.cloud.stream.bindings.input.legacyContentTypeHeaderEnabled` to true.

spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/config/LegacyContentTypeTests.java

@@ -0,0 +1,75 @@
+/*
+ * Copyright 2015-2017 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.stream.config;
+
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.cloud.stream.annotation.EnableBinding;
+import org.springframework.cloud.stream.binder.BinderHeaders;
+import org.springframework.cloud.stream.messaging.Sink;
+import org.springframework.context.annotation.PropertySource;
+import org.springframework.integration.support.MessageBuilder;
+import org.springframework.messaging.Message;
+import org.springframework.messaging.MessageHandler;
+import org.springframework.messaging.MessageHeaders;
+import org.springframework.messaging.MessagingException;
+import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * @author Soby Chacko
+ */
+@RunWith(SpringJUnit4ClassRunner.class)
+@SpringBootTest(classes = { LegacyContentTypeTests.LegacyTestSink.class})
+public class LegacyContentTypeTests {
+
+	@Autowired
+	private Sink testSink;
+
+	@Test
+	public void testOriginalContentTypeIsRetrievedForLegacyContentHeaderType() throws Exception {
+		final CountDownLatch latch = new CountDownLatch(1);
+		MessageHandler messageHandler = new MessageHandler() {
+			@Override
+			public void handleMessage(Message<?> message) throws MessagingException {
+				assertThat(message.getPayload()).isInstanceOf(byte[].class);
+				assertThat(message.getPayload()).isEqualTo("{\"message\":\"Hi\"}".getBytes());
+				assertThat(message.getHeaders().get(MessageHeaders.CONTENT_TYPE)).isEqualTo("application/json");
+				latch.countDown();
+			}
+		};
+		testSink.input().subscribe(messageHandler);
+		testSink.input().send(MessageBuilder.withPayload("{\"message\":\"Hi\"}".getBytes()).setHeader(BinderHeaders.BINDER_ORIGINAL_CONTENT_TYPE, "application/json").build());
+		assertThat(latch.await(10, TimeUnit.SECONDS)).isTrue();
+		testSink.input().unsubscribe(messageHandler);
+	}
+
+	@EnableBinding(Sink.class)
+	@EnableAutoConfiguration
+	@PropertySource("classpath:/org/springframework/cloud/stream/config/channel/legacy-sink-channel-configurers.properties")
+	public static class LegacyTestSink {
+
+	}
+}

spring-cloud-stream-integration-tests/src/test/resources/org/springframework/cloud/stream/config/channel/legacy-sink-channel-configurers.properties

@@ -0,0 +1,4 @@
+spring.cloud.stream.bindings.input.destination=configure1
+spring.cloud.stream.bindings.input.legacyContentTypeHeaderEnabled=true
+spring.cloud.stream.bindings.input.contentType=application/x-spring-tuple
+