/*
* Copyright 2002-2016 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 java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.StringWriter;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Scanner;
import javax.servlet.http.HttpServletRequest;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.core.io.Resource;
import org.springframework.util.DigestUtils;
import org.springframework.util.FileCopyUtils;
import org.springframework.util.StringUtils;
/**
* A {@link ResourceTransformer} implementation that helps handling resources
* within HTML5 AppCache manifests for HTML5 offline applications.
*
* <p>This transformer:
* <ul>
* <li>modifies links to match the public URL paths that should be exposed to clients,
* using configured {@code ResourceResolver} strategies
* <li>appends a comment in the manifest, containing a Hash (e.g. "# Hash: 9de0f09ed7caf84e885f1f0f11c7e326"),
* thus changing the content of the manifest in order to trigger an appcache reload in the browser.
* </ul>
*
* <p>All files that have the ".appcache" file extension, or the extension given in the constructor,
* will be transformed by this class. This hash is computed using the content of the appcache manifest
* and the content of the linked resources; so changing a resource linked in the manifest
* or the manifest itself should invalidate the browser cache.
*
* <p>In order to serve manifest files with the proper {@code "text/manifest"} content type,
* it is required to configure it with
* {@code contentNegotiationConfigurer.mediaType("appcache", MediaType.valueOf("text/manifest")}
* in a {@code WebMvcConfigurer}.
*
* @author Brian Clozel
* @since 4.1
* @see <a href="https://html.spec.whatwg.org/multipage/browsers.html#offline">HTML5 offline applications spec</a>
*/
public class AppCacheManifestTransformer extends ResourceTransformerSupport {
private static final Collection<String> MANIFEST_SECTION_HEADERS =
Arrays.asList("CACHE MANIFEST", "NETWORK:", "FALLBACK:", "CACHE:");
private static final String MANIFEST_HEADER = "CACHE MANIFEST";
private static final String CACHE_HEADER = "CACHE:";
private static final Charset DEFAULT_CHARSET = StandardCharsets.UTF_8;
private static final Log logger = LogFactory.getLog(AppCacheManifestTransformer.class);
private final String fileExtension;
/**
* Create an AppCacheResourceTransformer that transforms files with extension ".appcache".
*/
public AppCacheManifestTransformer() {
this("appcache");
}
/**
* Create an AppCacheResourceTransformer that transforms files with the extension
* given as a parameter.
*/
public AppCacheManifestTransformer(String fileExtension) {
this.fileExtension = fileExtension;
}
@Override
public Resource transform(HttpServletRequest request, Resource resource,
ResourceTransformerChain chain) throws IOException {
resource = chain.transform(request, resource);
if (!this.fileExtension.equals(StringUtils.getFilenameExtension(resource.getFilename()))) {
return resource;
}
byte[] bytes = FileCopyUtils.copyToByteArray(resource.getInputStream());
String content = new String(bytes, DEFAULT_CHARSET);
if (!content.startsWith(MANIFEST_HEADER)) {
if (logger.isTraceEnabled()) {
logger.trace("Manifest should start with 'CACHE MANIFEST', skip: " + resource);
}
return resource;
}
if (logger.isTraceEnabled()) {
logger.trace("Transforming resource: " + resource);
}
Scanner scanner = new Scanner(content);
LineInfo previous = null;
LineAggregator aggregator = new LineAggregator(resource, content);
while (scanner.hasNext()) {
String line = scanner.nextLine();
LineInfo current = new LineInfo(line, previous);
LineOutput lineOutput = processLine(current, request, resource, chain);
aggregator.add(lineOutput);
previous = current;
}
return aggregator.createResource();
}
private static byte[] getResourceBytes(Resource resource) throws IOException {
return FileCopyUtils.copyToByteArray(resource.getInputStream());
}
private LineOutput processLine(LineInfo info, HttpServletRequest request,
Resource resource, ResourceTransformerChain transformerChain) {
if (!info.isLink()) {
return new LineOutput(info.getLine(), null);
}
Resource appCacheResource = transformerChain.getResolverChain()
.resolveResource(null, info.getLine(), Collections.singletonList(resource));
String path = resolveUrlPath(toAbsolutePath(info.getLine(), request), request, resource, transformerChain);
if (logger.isTraceEnabled()) {
logger.trace("Link modified: " + path + " (original: " + info.getLine() + ")");
}
return new LineOutput(path, appCacheResource);
}
private static class LineInfo {
private final String line;
private final boolean cacheSection;
private final boolean link;
public LineInfo(String line, LineInfo previous) {
this.line = line;
this.cacheSection = initCacheSectionFlag(line, previous);
this.link = iniLinkFlag(line, this.cacheSection);
}
private static boolean initCacheSectionFlag(String line, LineInfo previousLine) {
if (MANIFEST_SECTION_HEADERS.contains(line.trim())) {
return line.trim().equals(CACHE_HEADER);
}
else if (previousLine != null) {
return previousLine.isCacheSection();
}
throw new IllegalStateException(
"Manifest does not start with " + MANIFEST_HEADER + ": " + line);
}
private static boolean iniLinkFlag(String line, boolean isCacheSection) {
return (isCacheSection && StringUtils.hasText(line) && !line.startsWith("#")
&& !line.startsWith("//") && !hasScheme(line));
}
private static boolean hasScheme(String line) {
int index = line.indexOf(":");
return (line.startsWith("//") || (index > 0 && !line.substring(0, index).contains("/")));
}
public String getLine() {
return this.line;
}
public boolean isCacheSection() {
return this.cacheSection;
}
public boolean isLink() {
return this.link;
}
}
private static class LineOutput {
private final String line;
private final Resource resource;
public LineOutput(String line, Resource resource) {
this.line = line;
this.resource = resource;
}
public String getLine() {
return this.line;
}
public Resource getResource() {
return this.resource;
}
}
private static class LineAggregator {
private final StringWriter writer = new StringWriter();
private final ByteArrayOutputStream baos;
private final Resource resource;
public LineAggregator(Resource resource, String content) {
this.resource = resource;
this.baos = new ByteArrayOutputStream(content.length());
}
public void add(LineOutput lineOutput) throws IOException {
this.writer.write(lineOutput.getLine() + "\n");
byte[] bytes = (lineOutput.getResource() != null ?
DigestUtils.md5Digest(getResourceBytes(lineOutput.getResource())) :
lineOutput.getLine().getBytes(DEFAULT_CHARSET));
this.baos.write(bytes);
}
public TransformedResource createResource() {
String hash = DigestUtils.md5DigestAsHex(this.baos.toByteArray());
this.writer.write("\n" + "# Hash: " + hash);
if (logger.isTraceEnabled()) {
logger.trace("AppCache file: [" + resource.getFilename()+ "] hash: [" + hash + "]");
}
byte[] bytes = this.writer.toString().getBytes(DEFAULT_CHARSET);
return new TransformedResource(this.resource, bytes);
}
}
}