Add AppCacheResourceTransformer

This change adds a new ResourceTransformer that helps handling resources
within HTML5 AppCache manifests for HTML5 offline application.

This transformer:
* modifies links to match the public URL paths
* appends a comment in the manifest, containing a Hash (e.g. "# Hash:
9de0f09ed7caf84e885f1f0f11c7e326")

See http://www.whatwg.org/specs/web-apps/current-work/multipage/offline.html#offline
for more details on HTML5 offline apps and appcache manifests.

Here is a WebConfig example:

  @Override
  public void addResourceHandlers(ResourceHandlerRegistry registry) {

    AppCacheResourceTransformer appCacheTransformer =
          new AppCacheResourceTransformer();

      registry.addResourceHandler("/**")
          .addResourceLocations("classpath:static/")
          .setResourceResolvers(...)
          .setResourceTransformers(..., appCacheTransformer);
  }

Issue: SPR-11964

spring-webmvc/src/test/java/org/springframework/web/servlet/resource/AppCacheResourceTransformerTests.java

@@ -0,0 +1,113 @@
+/*
+ * Copyright 2002-2014 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.web.servlet.resource;
+
+import static org.junit.Assert.*;
+import static org.mockito.Mockito.*;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+import javax.servlet.http.HttpServletRequest;
+
+import org.hamcrest.Matchers;
+import org.junit.Before;
+import org.junit.Test;
+
+import org.springframework.core.io.ClassPathResource;
+import org.springframework.core.io.Resource;
+import org.springframework.util.FileCopyUtils;
+
+/**
+ * Unit tests for
+ * {@link org.springframework.web.servlet.resource.AppCacheResourceTransformer}.
+ *
+ * @author Brian Clozel
+ */
+public class AppCacheResourceTransformerTests {
+
+	private AppCacheResourceTransformer transformer;
+
+	private ResourceTransformerChain chain;
+
+	private HttpServletRequest request;
+
+	@Before
+	public void setup() {
+		this.transformer = new AppCacheResourceTransformer();
+		this.chain = mock(ResourceTransformerChain.class);
+		this.request = mock(HttpServletRequest.class);
+	}
+
+	@Test
+	public void noTransformIfExtensionNoMatch() throws Exception {
+		Resource resource = mock(Resource.class);
+		when(resource.getFilename()).thenReturn("foobar.file");
+		when(this.chain.transform(this.request, resource)).thenReturn(resource);
+
+		Resource result = this.transformer.transform(this.request, resource, this.chain);
+		assertEquals(resource, result);
+	}
+
+	@Test
+	public void syntaxErrorInManifest() throws Exception {
+		Resource resource = new ClassPathResource("test/error.manifest", getClass());
+		when(this.chain.transform(this.request, resource)).thenReturn(resource);
+
+		Resource result = this.transformer.transform(this.request, resource, this.chain);
+		assertEquals(resource, result);
+	}
+
+	@Test
+	public void transformManifest() throws Exception {
+
+		VersionResourceResolver versionResourceResolver = new VersionResourceResolver();
+		versionResourceResolver
+				.setVersionStrategyMap(Collections.singletonMap("/**", new ContentBasedVersionStrategy()));
+
+		List<ResourceResolver> resolvers = new ArrayList<ResourceResolver>();
+		resolvers.add(versionResourceResolver);
+		resolvers.add(new PathResourceResolver());
+		ResourceResolverChain resolverChain = new DefaultResourceResolverChain(resolvers);
+
+		List<ResourceTransformer> transformers = new ArrayList<>();
+		transformers.add(new CssLinkResourceTransformer());
+		this.chain = new DefaultResourceTransformerChain(resolverChain, transformers);
+
+		Resource resource = new ClassPathResource("test/appcache.manifest", getClass());
+		Resource result = this.transformer.transform(this.request, resource, this.chain);
+		byte[] bytes = FileCopyUtils.copyToByteArray(result.getInputStream());
+		String content = new String(bytes, "UTF-8");
+
+		assertThat("should rewrite resource links", content,
+				Matchers.containsString("foo-e36d2e05253c6c7085a91522ce43a0b4.css"));
+		assertThat("should rewrite resource links", content,
+				Matchers.containsString("bar-11e16cf79faee7ac698c805cf28248d2.css"));
+		assertThat("should rewrite resource links", content,
+				Matchers.containsString("js/bar-bd508c62235b832d960298ca6c0b7645.js"));
+
+		assertThat("should not rewrite external resources", content,
+				Matchers.containsString("//example.org/style.css"));
+		assertThat("should not rewrite external resources", content,
+				Matchers.containsString("http://example.org/image.png"));
+
+		assertThat("should generate fingerprint", content,
+				Matchers.containsString("# Hash: 4bf0338bcbeb0a5b3a4ec9ed8864107d"));
+	}
+
+}