Expand range of whitelisted extensions by media type

This commit expands the range of whitelisted extensions by checking
if an extension can be resolved to image/*, audio/*, video/*, as well
as any content type that ends with +xml.

Issue: SPR-13643

spring-web/src/main/java/org/springframework/web/accept/AbstractMappingContentNegotiationStrategy.java

@@ -47,7 +47,17 @@ public abstract class AbstractMappingContentNegotiationStrategy extends MappingM
 
 	@Override
 	public List<MediaType> resolveMediaTypes(NativeWebRequest webRequest) throws HttpMediaTypeNotAcceptableException {
-		String key = getMediaTypeKey(webRequest);
+		return resolveMediaTypeKey(webRequest, getMediaTypeKey(webRequest));
+	}
+
+	/**
+	 * An alternative to {@link #resolveMediaTypes(NativeWebRequest)} that accepts
+	 * an already extracted key.
+	 * @since 3.2.16
+	 */
+	public List<MediaType> resolveMediaTypeKey(NativeWebRequest webRequest, String key)
+			throws HttpMediaTypeNotAcceptableException {
+
 		if (StringUtils.hasText(key)) {
 			MediaType mediaType = lookupMediaType(key);
 			if (mediaType != null) {

spring-web/src/main/java/org/springframework/web/accept/ContentNegotiationManager.java

@@ -99,6 +99,14 @@ public class ContentNegotiationManager implements ContentNegotiationStrategy, Me
 	}
 
 
+	/**
+	 * Return the configured content negotiation strategies.
+	 * @since 3.2.16
+	 */
+	public List<ContentNegotiationStrategy> getStrategies() {
+		return this.contentNegotiationStrategies;
+	}
+
 	/**
 	 * Add MediaTypeFileExtensionResolver instances.
 	 * <p>Note that some {@link ContentNegotiationStrategy} implementations also

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

@@ -39,6 +39,8 @@ import org.springframework.util.CollectionUtils;
 import org.springframework.util.StringUtils;
 import org.springframework.web.HttpMediaTypeNotAcceptableException;
 import org.springframework.web.accept.ContentNegotiationManager;
+import org.springframework.web.accept.ContentNegotiationStrategy;
+import org.springframework.web.accept.PathExtensionContentNegotiationStrategy;
 import org.springframework.web.context.request.NativeWebRequest;
 import org.springframework.web.context.request.ServletWebRequest;
 import org.springframework.web.method.support.HandlerMethodReturnValueHandler;
@@ -73,8 +75,14 @@ public abstract class AbstractMessageConverterMethodProcessor extends AbstractMe
 			"json", "xml", "atom", "rss",
 			"png", "jpe", "jpeg", "jpg", "gif", "wbmp", "bmp"));
 
+	private static final Set<String> WHITELISTED_MEDIA_BASE_TYPES = new HashSet<String>(
+			Arrays.asList("audio", "image", "video"));
+
+
 	private final ContentNegotiationManager contentNegotiationManager;
 
+	private final PathExtensionContentNegotiationStrategy pathStrategy;
+
 	private final ResponseBodyAdviceChain adviceChain;
 
 	private final Set<String> safeExtensions = new HashSet<String>();
@@ -94,11 +102,21 @@ public abstract class AbstractMessageConverterMethodProcessor extends AbstractMe
 
 		super(messageConverters);
 		this.contentNegotiationManager = (manager != null ? manager : new ContentNegotiationManager());
+		this.pathStrategy = initPathStrategy(this.contentNegotiationManager);
 		this.adviceChain = new ResponseBodyAdviceChain(responseBodyAdvice);
 		this.safeExtensions.addAll(this.contentNegotiationManager.getAllFileExtensions());
 		this.safeExtensions.addAll(WHITELISTED_EXTENSIONS);
 	}
 
+	private static PathExtensionContentNegotiationStrategy initPathStrategy(ContentNegotiationManager manager) {
+		for (ContentNegotiationStrategy strategy : manager.getStrategies()) {
+			if (strategy instanceof PathExtensionContentNegotiationStrategy) {
+				return (PathExtensionContentNegotiationStrategy) strategy;
+			}
+		}
+		return new PathExtensionContentNegotiationStrategy();
+	}
+
 
 	protected ResponseBodyAdviceChain getAdviceChain() {
 		return this.adviceChain;
@@ -322,7 +340,31 @@ public abstract class AbstractMessageConverterMethodProcessor extends AbstractMe
 				return true;
 			}
 		}
-		return false;
+		return safeMediaTypesForExtension(extension);
+	}
+
+	private boolean safeMediaTypesForExtension(String extension) {
+		List<MediaType> mediaTypes = null;
+		try {
+			mediaTypes = this.pathStrategy.resolveMediaTypeKey(null, extension);
+		}
+		catch (HttpMediaTypeNotAcceptableException e) {
+			// Ignore
+		}
+		if (CollectionUtils.isEmpty(mediaTypes)) {
+			return false;
+		}
+		for (MediaType mediaType : mediaTypes) {
+			if (!safeMediaType(mediaType)) {
+				return false;
+			}
+		}
+		return true;
+	}
+
+	private boolean safeMediaType(MediaType mediaType) {
+		return (WHITELISTED_MEDIA_BASE_TYPES.contains(mediaType.getType()) ||
+				mediaType.getSubtype().endsWith("+xml"));
 	}
 
 }