Fix in MockMultipartHttpServletRequest#getMultipartHeaders

Previously this method returned headers only when a Content-Type part header
was present. Now it is guaranteed to return headers (possibly empty) as long
as there is a MultipartFile or Part with the given name.

Closes gh-26501

spring-test/src/main/java/org/springframework/mock/web/MockMultipartHttpServletRequest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2021 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.
@@ -17,6 +17,7 @@
 package org.springframework.mock.web;
 
 import java.io.IOException;
+import java.util.ArrayList;
 import java.util.Collections;
 import java.util.Enumeration;
 import java.util.Iterator;
@@ -33,6 +34,7 @@ import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
+import org.springframework.web.multipart.MultipartException;
 import org.springframework.web.multipart.MultipartFile;
 import org.springframework.web.multipart.MultipartHttpServletRequest;
 
@@ -155,15 +157,28 @@ public class MockMultipartHttpServletRequest extends MockHttpServletRequest impl
 
 	@Override
 	public HttpHeaders getMultipartHeaders(String paramOrFileName) {
-		String contentType = getMultipartContentType(paramOrFileName);
-		if (contentType != null) {
+		MultipartFile file = getFile(paramOrFileName);
+		if (file != null) {
 			HttpHeaders headers = new HttpHeaders();
-			headers.add(HttpHeaders.CONTENT_TYPE, contentType);
+			if (file.getContentType() != null) {
+				headers.add(HttpHeaders.CONTENT_TYPE, file.getContentType());
+			}
 			return headers;
 		}
-		else {
-			return null;
+		try {
+			Part part = getPart(paramOrFileName);
+			if (part != null) {
+				HttpHeaders headers = new HttpHeaders();
+				for (String headerName : part.getHeaderNames()) {
+					headers.put(headerName, new ArrayList<>(part.getHeaders(headerName)));
+				}
+				return headers;
+			}
 		}
+		catch (Throwable ex) {
+			throw new MultipartException("Could not access multipart servlet request", ex);
+		}
+		return null;
 	}
 
 }

spring-web/src/main/java/org/springframework/web/multipart/MultipartHttpServletRequest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2011 the original author or authors.
+ * Copyright 2002-2021 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.
@@ -60,9 +60,10 @@ public interface MultipartHttpServletRequest extends HttpServletRequest, Multipa
 	HttpHeaders getRequestHeaders();
 
 	/**
-	 * Return the headers associated with the specified part of the multipart request.
-	 * <p>If the underlying implementation supports access to headers, then all headers are returned.
-	 * Otherwise, the returned headers will include a 'Content-Type' header at the very least.
+	 * Return the headers for the specified part of the multipart request.
+	 * <p>If the underlying implementation supports access to part headers,
+	 * then all headers are returned. Otherwise, e.g. for a file upload, the
+	 * returned headers may expose a 'Content-Type' if available.
 	 */
 	@Nullable
 	HttpHeaders getMultipartHeaders(String paramOrFileName);

spring-web/src/testFixtures/java/org/springframework/web/testfixture/servlet/MockMultipartHttpServletRequest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2021 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.
@@ -17,6 +17,7 @@
 package org.springframework.web.testfixture.servlet;
 
 import java.io.IOException;
+import java.util.ArrayList;
 import java.util.Collections;
 import java.util.Enumeration;
 import java.util.Iterator;
@@ -33,6 +34,7 @@ import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
+import org.springframework.web.multipart.MultipartException;
 import org.springframework.web.multipart.MultipartFile;
 import org.springframework.web.multipart.MultipartHttpServletRequest;
 
@@ -155,15 +157,28 @@ public class MockMultipartHttpServletRequest extends MockHttpServletRequest impl
 
 	@Override
 	public HttpHeaders getMultipartHeaders(String paramOrFileName) {
-		String contentType = getMultipartContentType(paramOrFileName);
-		if (contentType != null) {
+		MultipartFile file = getFile(paramOrFileName);
+		if (file != null) {
 			HttpHeaders headers = new HttpHeaders();
-			headers.add(HttpHeaders.CONTENT_TYPE, contentType);
+			if (file.getContentType() != null) {
+				headers.add(HttpHeaders.CONTENT_TYPE, file.getContentType());
+			}
 			return headers;
 		}
-		else {
-			return null;
+		try {
+			Part part = getPart(paramOrFileName);
+			if (part != null) {
+				HttpHeaders headers = new HttpHeaders();
+				for (String headerName : part.getHeaderNames()) {
+					headers.put(headerName, new ArrayList<>(part.getHeaders(headerName)));
+				}
+				return headers;
+			}
 		}
+		catch (Throwable ex) {
+			throw new MultipartException("Could not access multipart servlet request", ex);
+		}
+		return null;
 	}
 
 }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2021 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.
@@ -36,6 +36,7 @@ import org.springframework.core.annotation.SynthesizingMethodParameter;
 import org.springframework.http.HttpInputMessage;
 import org.springframework.http.MediaType;
 import org.springframework.http.converter.HttpMessageConverter;
+import org.springframework.http.converter.StringHttpMessageConverter;
 import org.springframework.lang.Nullable;
 import org.springframework.util.ReflectionUtils;
 import org.springframework.validation.BindingResult;
@@ -51,6 +52,7 @@ import org.springframework.web.method.support.ModelAndViewContainer;
 import org.springframework.web.multipart.MultipartException;
 import org.springframework.web.multipart.MultipartFile;
 import org.springframework.web.multipart.support.MissingServletRequestPartException;
+import org.springframework.web.testfixture.method.ResolvableMethod;
 import org.springframework.web.testfixture.servlet.MockHttpServletRequest;
 import org.springframework.web.testfixture.servlet.MockHttpServletResponse;
 import org.springframework.web.testfixture.servlet.MockMultipartFile;
@@ -311,6 +313,22 @@ public class RequestPartMethodArgumentResolverTests {
 		testResolveArgument(new SimpleBean("foo"), paramValidRequestPart);
 	}
 
+	@Test // gh-26501
+	public void resolveRequestPartWithoutContentType() throws Exception {
+		MockMultipartHttpServletRequest servletRequest = new MockMultipartHttpServletRequest();
+		servletRequest.addPart(new MockPart("requestPartString", "part value".getBytes(StandardCharsets.UTF_8)));
+		ServletWebRequest webRequest = new ServletWebRequest(servletRequest, new MockHttpServletResponse());
+
+		List<HttpMessageConverter<?>> converters = Collections.singletonList(new StringHttpMessageConverter());
+		RequestPartMethodArgumentResolver resolver = new RequestPartMethodArgumentResolver(converters);
+		MethodParameter parameter = ResolvableMethod.on(getClass()).named("handle").build().arg(String.class);
+
+		Object actualValue = resolver.resolveArgument(
+				parameter, new ModelAndViewContainer(), webRequest, new ValidatingBinderFactory());
+
+		assertThat(actualValue).isEqualTo("part value");
+	}
+
 	@Test
 	public void isMultipartRequest() throws Exception {
 		MockHttpServletRequest request = new MockHttpServletRequest();
@@ -606,7 +624,8 @@ public class RequestPartMethodArgumentResolverTests {
 			@RequestPart("requestPart") Optional<List<MultipartFile>> optionalMultipartFileList,
 			Optional<Part> optionalPart,
 			@RequestPart("requestPart") Optional<List<Part>> optionalPartList,
-			@RequestPart("requestPart") Optional<SimpleBean> optionalRequestPart) {
+			@RequestPart("requestPart") Optional<SimpleBean> optionalRequestPart,
+			@RequestPart("requestPartString") String requestPartString) {
 	}
 
 }