Provide access to HTTP headers in resource routing

This commit adds additional overloaded methods that allow for HTTP
header manipulation of served resources.

Closes gh-29985

spring-webflux/src/main/java/org/springframework/web/reactive/function/server/DefaultResourceCacheLookupStrategy.java

@@ -0,0 +1,33 @@
+/*
+ * Copyright 2002-2023 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.web.reactive.function.server;
+
+import org.springframework.core.io.Resource;
+import org.springframework.http.CacheControl;
+
+/**
+ * Default lookup that performs no caching.
+ * @author Jakob Fels
+ */
+public class DefaultResourceCacheLookupStrategy implements ResourceCacheLookupStrategy {
+
+	@Override
+	public CacheControl lookupCacheControl(Resource resource) {
+		return CacheControl.empty();
+	}
+
+}

spring-webflux/src/main/java/org/springframework/web/reactive/function/server/ResourceCacheLookupStrategy.java

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2002-2023 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.web.reactive.function.server;
+
+import org.springframework.core.io.Resource;
+import org.springframework.http.CacheControl;
+
+/**
+ * Strategy interface to allow for looking up cache control for a given resource.
+ *
+ * @author Jakob Fels
+ */
+public interface ResourceCacheLookupStrategy {
+
+
+	static ResourceCacheLookupStrategy noCaching() {
+		return new DefaultResourceCacheLookupStrategy();
+	}
+
+	CacheControl lookupCacheControl(Resource resource);
+
+}

spring-webflux/src/main/java/org/springframework/web/reactive/function/server/ResourceHandlerFunction.java

@@ -27,6 +27,7 @@ import java.util.Set;
 import reactor.core.publisher.Mono;
 
 import org.springframework.core.io.Resource;
+import org.springframework.http.CacheControl;
 import org.springframework.http.HttpMethod;
 import org.springframework.http.HttpStatus;
 import org.springframework.lang.Nullable;
@@ -45,10 +46,18 @@ class ResourceHandlerFunction implements HandlerFunction<ServerResponse> {
 
 
 	private final Resource resource;
+	private final CacheControl cacheControl;
 
 
 	public ResourceHandlerFunction(Resource resource) {
 		this.resource = resource;
+		this.cacheControl = CacheControl.empty();
+	}
+
+
+	public ResourceHandlerFunction(Resource resource, ResourceCacheLookupStrategy strategy) {
+		this.resource = resource;
+		this.cacheControl = strategy.lookupCacheControl(resource);
 	}
 
 
@@ -56,12 +65,16 @@ class ResourceHandlerFunction implements HandlerFunction<ServerResponse> {
 	public Mono<ServerResponse> handle(ServerRequest request) {
 		HttpMethod method = request.method();
 		if (HttpMethod.GET.equals(method)) {
-			return EntityResponse.fromObject(this.resource).build()
+			return EntityResponse.fromObject(this.resource)
+					.cacheControl(this.cacheControl)
+					.build()
 					.map(response -> response);
 		}
 		else if (HttpMethod.HEAD.equals(method)) {
 			Resource headResource = new HeadMethodResource(this.resource);
-			return EntityResponse.fromObject(headResource).build()
+			return EntityResponse.fromObject(headResource)
+					.cacheControl(this.cacheControl)
+					.build()
 					.map(response -> response);
 		}
 		else if (HttpMethod.OPTIONS.equals(method)) {

spring-webflux/src/main/java/org/springframework/web/reactive/function/server/RouterFunctionBuilder.java

@@ -241,11 +241,21 @@ class RouterFunctionBuilder implements RouterFunctions.Builder {
 		return add(RouterFunctions.resources(pattern, location));
 	}
 
+	@Override
+	public RouterFunctions.Builder resources(String pattern, Resource location, ResourceCacheLookupStrategy resourceCacheLookupStrategy) {
+		return add(RouterFunctions.resources(pattern,location,resourceCacheLookupStrategy));
+	}
+
 	@Override
 	public RouterFunctions.Builder resources(Function<ServerRequest, Mono<Resource>> lookupFunction) {
 		return add(RouterFunctions.resources(lookupFunction));
 	}
 
+	@Override
+	public RouterFunctions.Builder resources(Function<ServerRequest, Mono<Resource>> lookupFunction, ResourceCacheLookupStrategy resourceCacheLookupStrategy) {
+		return add(RouterFunctions.resources(lookupFunction,resourceCacheLookupStrategy));
+	}
+
 	@Override
 	public RouterFunctions.Builder nest(RequestPredicate predicate,
 			Consumer<RouterFunctions.Builder> builderConsumer) {

spring-webflux/src/main/java/org/springframework/web/reactive/function/server/RouterFunctions.java

@@ -156,7 +156,10 @@ public abstract class RouterFunctions {
 	 * @see #resourceLookupFunction(String, Resource)
 	 */
 	public static RouterFunction<ServerResponse> resources(String pattern, Resource location) {
-		return resources(resourceLookupFunction(pattern, location));
+		return resources(resourceLookupFunction(pattern, location), ResourceCacheLookupStrategy.noCaching());
+	}
+	public static RouterFunction<ServerResponse> resources(String pattern, Resource location, ResourceCacheLookupStrategy lookupStrategy) {
+		return resources(resourceLookupFunction(pattern, location), lookupStrategy);
 	}
 
 	/**
@@ -186,7 +189,10 @@ public abstract class RouterFunctions {
 	 * @return a router function that routes to resources
 	 */
 	public static RouterFunction<ServerResponse> resources(Function<ServerRequest, Mono<Resource>> lookupFunction) {
-		return new ResourcesRouterFunction(lookupFunction);
+		return new ResourcesRouterFunction(lookupFunction, ResourceCacheLookupStrategy.noCaching());
+	}
+	public static RouterFunction<ServerResponse> resources(Function<ServerRequest, Mono<Resource>> lookupFunction, ResourceCacheLookupStrategy lookupStrategy) {
+		return new ResourcesRouterFunction(lookupFunction, lookupStrategy);
 	}
 
 	/**
@@ -652,6 +658,7 @@ public abstract class RouterFunctions {
 		 * @return this builder
 		 */
 		Builder resources(String pattern, Resource location);
+		Builder resources(String pattern, Resource location, ResourceCacheLookupStrategy resourceCacheLookupStrategy);
 
 		/**
 		 * Route to resources using the provided lookup function. If the lookup function provides a
@@ -661,6 +668,7 @@ public abstract class RouterFunctions {
 		 * @return this builder
 		 */
 		Builder resources(Function<ServerRequest, Mono<Resource>> lookupFunction);
+		Builder resources(Function<ServerRequest, Mono<Resource>> lookupFunction, ResourceCacheLookupStrategy resourceCacheLookupStrategy);
 
 		/**
 		 * Route to the supplied router function if the given request predicate applies. This method
@@ -1142,14 +1150,22 @@ public abstract class RouterFunctions {
 
 		private final Function<ServerRequest, Mono<Resource>> lookupFunction;
 
+		private final ResourceCacheLookupStrategy lookupStrategy;
+
 		public ResourcesRouterFunction(Function<ServerRequest, Mono<Resource>> lookupFunction) {
+			this(lookupFunction, ResourceCacheLookupStrategy.noCaching());
+		}
+
+		public ResourcesRouterFunction(Function<ServerRequest, Mono<Resource>> lookupFunction, ResourceCacheLookupStrategy lookupStrategy) {
 			Assert.notNull(lookupFunction, "Function must not be null");
+			Assert.notNull(lookupStrategy, "Strategy must not be null");
 			this.lookupFunction = lookupFunction;
+			this.lookupStrategy = lookupStrategy;
 		}
 
 		@Override
 		public Mono<HandlerFunction<ServerResponse>> route(ServerRequest request) {
-			return this.lookupFunction.apply(request).map(ResourceHandlerFunction::new);
+			return this.lookupFunction.apply(request).map(resource -> new ResourceHandlerFunction(resource, this.lookupStrategy));
 		}
 
 		@Override

spring-webflux/src/test/java/org/springframework/web/reactive/function/server/RouterFunctionBuilderTests.java

@@ -17,6 +17,7 @@
 package org.springframework.web.reactive.function.server;
 
 import java.io.IOException;
+import java.time.Duration;
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
@@ -28,6 +29,8 @@ import reactor.test.StepVerifier;
 
 import org.springframework.core.io.ClassPathResource;
 import org.springframework.core.io.Resource;
+import org.springframework.http.CacheControl;
+import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.HttpStatusCode;
 import org.springframework.http.MediaType;
@@ -130,6 +133,28 @@ public class RouterFunctionBuilderTests {
 				.verifyComplete();
 	}
 
+	@Test
+	public void resourcesCaching() {
+		Resource resource = new ClassPathResource("/org/springframework/web/reactive/function/server/");
+		assertThat(resource.exists()).isTrue();
+
+		RouterFunction<ServerResponse> route = RouterFunctions.route()
+				.resources("/resources/**", resource, resource1 -> CacheControl.maxAge(Duration.ofSeconds(60)))
+				.build();
+
+		MockServerHttpRequest mockRequest = MockServerHttpRequest.get("https://localhost/resources/response.txt").build();
+		ServerRequest resourceRequest = new DefaultServerRequest(MockServerWebExchange.from(mockRequest), Collections.emptyList());
+
+		Mono<String> responseMono = route.route(resourceRequest)
+				.flatMap(handlerFunction -> handlerFunction.handle(resourceRequest))
+				.map(ServerResponse::headers)
+				.mapNotNull(HttpHeaders::getCacheControl);
+
+		StepVerifier.create(responseMono)
+				.expectNext("max-age=60")
+				.verifyComplete();
+	}
+
 	@Test
 	public void nest() {
 		RouterFunction<?> route = RouterFunctions.route()