Fix @RequestBody argument processing for null Content-Type

Since the changes introduced in SPR-12778, some `@RequestBody` args
would not be properly processed in some cases:

* requests with an empty body
* no Content-Type header defined

This typically happens when GET requests are mapped on a handler dealing
with POST requests and HTTP bodies.

This change makes sure that the `RequestResponseBodyMethodProcessor` is
only involved for requests that:

* have a Content-Type defined
* OR are HTTP requests eligible for an HTTP body (PUT, POST, PATCH)

Issue: SPR-13176
Fixes spring-projects/spring-boot#3313

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/RequestResponseBodyMethodProcessor.java

@@ -18,6 +18,7 @@ package org.springframework.web.servlet.mvc.method.annotation;
 
 import java.io.IOException;
 import java.lang.reflect.Type;
+import java.util.Arrays;
 import java.util.List;
 
 import javax.servlet.http.HttpServletRequest;
@@ -25,7 +26,7 @@ import javax.servlet.http.HttpServletRequest;
 import org.springframework.core.Conventions;
 import org.springframework.core.MethodParameter;
 import org.springframework.core.annotation.AnnotationUtils;
-import org.springframework.http.HttpInputMessage;
+import org.springframework.http.HttpMethod;
 import org.springframework.http.converter.HttpMessageConverter;
 import org.springframework.http.converter.HttpMessageNotReadableException;
 import org.springframework.http.server.ServletServerHttpRequest;
@@ -58,6 +59,9 @@ import org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolv
  */
 public class RequestResponseBodyMethodProcessor extends AbstractMessageConverterMethodProcessor {
 
+	private static final List<HttpMethod> SUPPORTED_METHODS =
+			Arrays.asList(HttpMethod.POST, HttpMethod.PUT, HttpMethod.PATCH);
+
 	/**
 	 * Basic constructor with converters only. Suitable for resolving
 	 * {@code @RequestBody}. For handling {@code @ResponseBody} consider also
@@ -143,16 +147,19 @@ public class RequestResponseBodyMethodProcessor extends AbstractMessageConverter
 			Type paramType) throws IOException, HttpMediaTypeNotSupportedException {
 
 		HttpServletRequest servletRequest = webRequest.getNativeRequest(HttpServletRequest.class);
-		HttpInputMessage inputMessage = new ServletServerHttpRequest(servletRequest);
-
-		Object arg = readWithMessageConverters(inputMessage, methodParam, paramType);
-		if (arg == null) {
-			if (methodParam.getParameterAnnotation(RequestBody.class).required()) {
-				throw new HttpMessageNotReadableException("Required request body is missing: " +
-						methodParam.getMethod().toGenericString());
+		ServletServerHttpRequest inputMessage = new ServletServerHttpRequest(servletRequest);
+
+		Object arg = null;
+		if (webRequest.getHeader("Content-Type") != null ||
+				SUPPORTED_METHODS.contains(inputMessage.getMethod())) {
+			arg = readWithMessageConverters(inputMessage, methodParam, paramType);
+			if (arg == null) {
+				if (methodParam.getParameterAnnotation(RequestBody.class).required()) {
+					throw new HttpMessageNotReadableException("Required request body is missing: " +
+							methodParam.getMethod().toGenericString());
+				}
 			}
 		}
-
 		return arg;
 	}
 

spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/RequestMappingHandlerAdapterIntegrationTests.java

@@ -212,6 +212,7 @@ public class RequestMappingHandlerAdapterIntegrationTests {
 
 		Class<?>[] parameterTypes = new Class<?>[] { byte[].class };
 
+		request.setMethod("POST");
 		request.addHeader("Content-Type", "text/plain; charset=utf-8");
 		request.setContent("Hello Server".getBytes("UTF-8"));
 

spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/RequestResponseBodyMethodProcessorMockTests.java

@@ -102,6 +102,7 @@ public class RequestResponseBodyMethodProcessorMockTests {
 		mavContainer = new ModelAndViewContainer();
 
 		servletRequest = new MockHttpServletRequest();
+		servletRequest.setMethod("POST");
 		webRequest = new ServletWebRequest(servletRequest, new MockHttpServletResponse());
 	}
 
@@ -178,17 +179,11 @@ public class RequestResponseBodyMethodProcessorMockTests {
 		processor.resolveArgument(paramRequestBodyString, mavContainer, webRequest, null);
 	}
 
-	@Test
+	@Test(expected = HttpMediaTypeNotSupportedException.class)
 	public void resolveArgumentNoContentType() throws Exception {
 		servletRequest.setContent("payload".getBytes(Charset.forName("UTF-8")));
 		given(messageConverter.canRead(String.class, MediaType.APPLICATION_OCTET_STREAM)).willReturn(false);
-		try {
-			processor.resolveArgument(paramRequestBodyString, mavContainer, webRequest, null);
-			fail("Expected exception");
-		}
-		catch (HttpMediaTypeNotSupportedException ex) {
-			// expected
-		}
+		processor.resolveArgument(paramRequestBodyString, mavContainer, webRequest, null);
 	}
 
 	@Test(expected = HttpMediaTypeNotSupportedException.class)
@@ -217,6 +212,14 @@ public class RequestResponseBodyMethodProcessorMockTests {
 		assertNull(processor.resolveArgument(paramStringNotRequired, mavContainer, webRequest, new ValidatingBinderFactory()));
 	}
 
+	@Test
+	public void resolveArgumentNotGetRequests() throws Exception {
+		servletRequest.setMethod("GET");
+		servletRequest.setContent(new byte[0]);
+		given(messageConverter.canRead(String.class, MediaType.APPLICATION_OCTET_STREAM)).willReturn(false);
+		assertNull(processor.resolveArgument(paramStringNotRequired, mavContainer, webRequest, new ValidatingBinderFactory()));
+	}
+
 	@Test
 	public void handleReturnValue() throws Exception {
 		MediaType accepted = MediaType.TEXT_PLAIN;

spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/RequestResponseBodyMethodProcessorTests.java

@@ -112,6 +112,7 @@ public class RequestResponseBodyMethodProcessorTests {
 		mavContainer = new ModelAndViewContainer();
 
 		servletRequest = new MockHttpServletRequest();
+		servletRequest.setMethod("POST");
 		servletResponse = new MockHttpServletResponse();
 		webRequest = new ServletWebRequest(servletRequest, servletResponse);
 
@@ -140,6 +141,7 @@ public class RequestResponseBodyMethodProcessorTests {
 	@Test
 	public void resolveArgumentRawTypeFromParameterizedType() throws Exception {
 		String content = "fruit=apple&vegetable=kale";
+		this.servletRequest.setMethod("GET");
 		this.servletRequest.setContent(content.getBytes("UTF-8"));
 		this.servletRequest.setContentType(MediaType.APPLICATION_FORM_URLENCODED_VALUE);