luni/src/main/java/libcore/net/http/HttpResponseCache.java - platform/libcore - Git at Google

 /*
  * Copyright (C) 2010 The Android Open Source Project
  *
  * 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 libcore.net.http;

 import java.io.BufferedWriter;
 import java.io.ByteArrayInputStream;
 import java.io.File;
 import java.io.FilterInputStream;
 import java.io.FilterOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
 import java.io.OutputStreamWriter;
 import java.io.Writer;
 import java.net.CacheRequest;
 import java.net.CacheResponse;
 import java.net.ExtendedResponseCache;
 import java.net.HttpURLConnection;
 import java.net.ResponseCache;
 import java.net.ResponseSource;
 import java.net.SecureCacheResponse;
 import java.net.URI;
 import java.net.URLConnection;
 import java.nio.charset.Charsets;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
 import java.security.Principal;
 import java.security.cert.Certificate;
 import java.security.cert.CertificateEncodingException;
 import java.security.cert.CertificateException;
 import java.security.cert.CertificateFactory;
 import java.security.cert.X509Certificate;
 import java.util.Arrays;
 import java.util.List;
 import java.util.Map;
 import javax.net.ssl.HttpsURLConnection;
 import javax.net.ssl.SSLPeerUnverifiedException;
 import libcore.io.Base64;
 import libcore.io.DiskLruCache;
 import libcore.io.IoUtils;
 import libcore.io.StrictLineReader;

 /**
  * Cache responses in a directory on the file system. Most clients should use
  * {@code android.net.HttpResponseCache}, the stable, documented front end for
  * this.
  */
 public final class HttpResponseCache extends ResponseCache implements ExtendedResponseCache {
     // TODO: add APIs to iterate the cache?
     private static final int VERSION = 201105;
     private static final int ENTRY_METADATA = 0;
     private static final int ENTRY_BODY = 1;
     private static final int ENTRY_COUNT = 2;

     private final DiskLruCache cache;

     /* read and write statistics, all guarded by 'this' */
     private int writeSuccessCount;
     private int writeAbortCount;
     private int networkCount;
     private int hitCount;
     private int requestCount;

     public HttpResponseCache(File directory, long maxSize) throws IOException {
         cache = DiskLruCache.open(directory, VERSION, ENTRY_COUNT, maxSize);
     }

     private String uriToKey(URI uri) {
         try {
             MessageDigest messageDigest = MessageDigest.getInstance("MD5");
             byte[] md5bytes = messageDigest.digest(uri.toString().getBytes(Charsets.UTF_8));
             return IntegralToString.bytesToHexString(md5bytes, false);
         } catch (NoSuchAlgorithmException e) {
             throw new AssertionError(e);
         }
     }

     @Override public CacheResponse get(URI uri, String requestMethod,
             Map<String, List<String>> requestHeaders) {
         String key = uriToKey(uri);
         DiskLruCache.Snapshot snapshot;
         Entry entry;
         try {
             snapshot = cache.get(key);
             if (snapshot == null) {
                 return null;
             }
             entry = new Entry(snapshot.getInputStream(ENTRY_METADATA));
         } catch (IOException e) {
             // Give up because the cache cannot be read.
             return null;
         }

         if (!entry.matches(uri, requestMethod, requestHeaders)) {
             snapshot.close();
             return null;
         }

         return entry.isHttps()
                 ? new EntrySecureCacheResponse(entry, snapshot)
                 : new EntryCacheResponse(entry, snapshot);
     }

     @Override public CacheRequest put(URI uri, URLConnection urlConnection) throws IOException {
         if (!(urlConnection instanceof HttpURLConnection)) {
             return null;
         }

         HttpURLConnection httpConnection = (HttpURLConnection) urlConnection;
         String requestMethod = httpConnection.getRequestMethod();
         String key = uriToKey(uri);

         if (requestMethod.equals(HttpEngine.POST)
                 || requestMethod.equals(HttpEngine.PUT)
                 || requestMethod.equals(HttpEngine.DELETE)) {
             try {
                 cache.remove(key);
             } catch (IOException ignored) {
                 // The cache cannot be written.
             }
             return null;
         } else if (!requestMethod.equals(HttpEngine.GET)) {
             /*
              * Don't cache non-GET responses. We're technically allowed to cache
              * HEAD requests and some POST requests, but the complexity of doing
              * so is high and the benefit is low.
              */
             return null;
         }

         HttpEngine httpEngine = getHttpEngine(httpConnection);
         if (httpEngine == null) {
             // Don't cache unless the HTTP implementation is ours.
             return null;
         }

         ResponseHeaders response = httpEngine.getResponseHeaders();
         if (response.hasVaryAll()) {
             return null;
         }

         RawHeaders varyHeaders = httpEngine.getRequestHeaders().getHeaders().getAll(
                 response.getVaryFields());
         Entry entry = new Entry(uri, varyHeaders, httpConnection);
         DiskLruCache.Editor editor = null;
         try {
             editor = cache.edit(key);
             if (editor == null) {
                 return null;
             }
             entry.writeTo(editor);
             return new CacheRequestImpl(editor);
         } catch (IOException e) {
             abortQuietly(editor);
             return null;
         }
     }

     /**
      * Handles a conditional request hit by updating the stored cache response
      * with the headers from {@code httpConnection}. The cached response body is
      * not updated. If the stored response has changed since {@code
      * conditionalCacheHit} was returned, this does nothing.
      */
     public void update(CacheResponse conditionalCacheHit, HttpURLConnection httpConnection) {
         HttpEngine httpEngine = getHttpEngine(httpConnection);
         URI uri = httpEngine.getUri();
         ResponseHeaders response = httpEngine.getResponseHeaders();
         RawHeaders varyHeaders = httpEngine.getRequestHeaders().getHeaders()
                 .getAll(response.getVaryFields());
         Entry entry = new Entry(uri, varyHeaders, httpConnection);
         DiskLruCache.Snapshot snapshot = (conditionalCacheHit instanceof EntryCacheResponse)
                 ? ((EntryCacheResponse) conditionalCacheHit).snapshot
                 : ((EntrySecureCacheResponse) conditionalCacheHit).snapshot;
         DiskLruCache.Editor editor = null;
         try {
             editor = snapshot.edit(); // returns null if snapshot is not current
             if (editor != null) {
                 entry.writeTo(editor);
                 editor.commit();
             }
         } catch (IOException e) {
             abortQuietly(editor);
         }
     }

     private void abortQuietly(DiskLruCache.Editor editor) {
         // Give up because the cache cannot be written.
         try {
             if (editor != null) {
                 editor.abort();
             }
         } catch (IOException ignored) {
         }
     }

     private HttpEngine getHttpEngine(HttpURLConnection httpConnection) {
         if (httpConnection instanceof HttpURLConnectionImpl) {
             return ((HttpURLConnectionImpl) httpConnection).getHttpEngine();
         } else if (httpConnection instanceof HttpsURLConnectionImpl) {
             return ((HttpsURLConnectionImpl) httpConnection).getHttpEngine();
         } else {
             return null;
         }
     }

     public DiskLruCache getCache() {
         return cache;
     }

     public synchronized int getWriteAbortCount() {
         return writeAbortCount;
     }

     public synchronized int getWriteSuccessCount() {
         return writeSuccessCount;
     }

     public synchronized void trackResponse(ResponseSource source) {
         requestCount++;

         switch (source) {
         case CACHE:
             hitCount++;
             break;
         case CONDITIONAL_CACHE:
         case NETWORK:
             networkCount++;
             break;
         }
     }

     public synchronized void trackConditionalCacheHit() {
         hitCount++;
     }

     public synchronized int getNetworkCount() {
         return networkCount;
     }

     public synchronized int getHitCount() {
         return hitCount;
     }

     public synchronized int getRequestCount() {
         return requestCount;
     }

     private final class CacheRequestImpl extends CacheRequest {
         private final DiskLruCache.Editor editor;
         private OutputStream cacheOut;
         private boolean done;
         private OutputStream body;

         public CacheRequestImpl(final DiskLruCache.Editor editor) throws IOException {
             this.editor = editor;
             this.cacheOut = editor.newOutputStream(ENTRY_BODY);
             this.body = new FilterOutputStream(cacheOut) {
                 @Override public void close() throws IOException {
                     synchronized (HttpResponseCache.this) {
                         if (done) {
                             return;
                         }
                         done = true;
                         writeSuccessCount++;
                     }
                     super.close();
                     editor.commit();
                 }

                 @Override
                 public void write(byte[] buffer, int offset, int length) throws IOException {
                     // Since we don't override "write(int oneByte)", we can write directly to "out"
                     // and avoid the inefficient implementation from the FilterOutputStream.
                     out.write(buffer, offset, length);
                 }
             };
         }

         @Override public void abort() {
             synchronized (HttpResponseCache.this) {
                 if (done) {
                     return;
                 }
                 done = true;
                 writeAbortCount++;
             }
             IoUtils.closeQuietly(cacheOut);
             try {
                 editor.abort();
             } catch (IOException ignored) {
             }
         }

         @Override public OutputStream getBody() throws IOException {
             return body;
         }
     }

     private static final class Entry {
         private final String uri;
         private final RawHeaders varyHeaders;
         private final String requestMethod;
         private final RawHeaders responseHeaders;
         private final String cipherSuite;
         private final Certificate[] peerCertificates;
         private final Certificate[] localCertificates;

         /*
          * Reads an entry from an input stream. A typical entry looks like this:
          *   http://google.com/foo
          *   GET
          *   2
          *   Accept-Language: fr-CA
          *   Accept-Charset: UTF-8
          *   HTTP/1.1 200 OK
          *   3
          *   Content-Type: image/png
          *   Content-Length: 100
          *   Cache-Control: max-age=600
          *
          * A typical HTTPS file looks like this:
          *   https://google.com/foo
          *   GET
          *   2
          *   Accept-Language: fr-CA
          *   Accept-Charset: UTF-8
          *   HTTP/1.1 200 OK
          *   3
          *   Content-Type: image/png
          *   Content-Length: 100
          *   Cache-Control: max-age=600
          *
          *   AES_256_WITH_MD5
          *   2
          *   base64-encoded peerCertificate[0]
          *   base64-encoded peerCertificate[1]
          *   -1
          *
          * The file is newline separated. The first two lines are the URL and
          * the request method. Next is the number of HTTP Vary request header
          * lines, followed by those lines.
          *
          * Next is the response status line, followed by the number of HTTP
          * response header lines, followed by those lines.
          *
          * HTTPS responses also contain SSL session information. This begins
          * with a blank line, and then a line containing the cipher suite. Next
          * is the length of the peer certificate chain. These certificates are
          * base64-encoded and appear each on their own line. The next line
          * contains the length of the local certificate chain. These
          * certificates are also base64-encoded and appear each on their own
          * line. A length of -1 is used to encode a null array.
          */
         public Entry(InputStream in) throws IOException {
             try {
                 StrictLineReader reader = new StrictLineReader(in, Charsets.US_ASCII);
                 uri = reader.readLine();
                 requestMethod = reader.readLine();
                 varyHeaders = new RawHeaders();
                 int varyRequestHeaderLineCount = reader.readInt();
                 for (int i = 0; i < varyRequestHeaderLineCount; i++) {
                     varyHeaders.addLine(reader.readLine());
                 }

                 responseHeaders = new RawHeaders();
                 responseHeaders.setStatusLine(reader.readLine());
                 int responseHeaderLineCount = reader.readInt();
                 for (int i = 0; i < responseHeaderLineCount; i++) {
                     responseHeaders.addLine(reader.readLine());
                 }

                 if (isHttps()) {
                     String blank = reader.readLine();
                     if (!blank.isEmpty()) {
                         throw new IOException("expected \"\" but was \"" + blank + "\"");
                     }
                     cipherSuite = reader.readLine();
                     peerCertificates = readCertArray(reader);
                     localCertificates = readCertArray(reader);
                 } else {
                     cipherSuite = null;
                     peerCertificates = null;
                     localCertificates = null;
                 }
             } finally {
                 in.close();
             }
         }

         public Entry(URI uri, RawHeaders varyHeaders, HttpURLConnection httpConnection) {
             this.uri = uri.toString();
             this.varyHeaders = varyHeaders;
             this.requestMethod = httpConnection.getRequestMethod();
             this.responseHeaders = RawHeaders.fromMultimap(httpConnection.getHeaderFields());

             if (isHttps()) {
                 HttpsURLConnection httpsConnection = (HttpsURLConnection) httpConnection;
                 cipherSuite = httpsConnection.getCipherSuite();
                 Certificate[] peerCertificatesNonFinal = null;
                 try {
                     peerCertificatesNonFinal = httpsConnection.getServerCertificates();
                 } catch (SSLPeerUnverifiedException ignored) {
                 }
                 peerCertificates = peerCertificatesNonFinal;
                 localCertificates = httpsConnection.getLocalCertificates();
             } else {
                 cipherSuite = null;
                 peerCertificates = null;
                 localCertificates = null;
             }
         }

         public void writeTo(DiskLruCache.Editor editor) throws IOException {
             OutputStream out = editor.newOutputStream(ENTRY_METADATA);
             Writer writer = new BufferedWriter(new OutputStreamWriter(out, Charsets.UTF_8));

             writer.write(uri + '\n');
             writer.write(requestMethod + '\n');
             writer.write(Integer.toString(varyHeaders.length()) + '\n');
             for (int i = 0; i < varyHeaders.length(); i++) {
                 writer.write(varyHeaders.getFieldName(i) + ": "
                         + varyHeaders.getValue(i) + '\n');
             }

             writer.write(responseHeaders.getStatusLine() + '\n');
             writer.write(Integer.toString(responseHeaders.length()) + '\n');
             for (int i = 0; i < responseHeaders.length(); i++) {
                 writer.write(responseHeaders.getFieldName(i) + ": "
                         + responseHeaders.getValue(i) + '\n');
             }

             if (isHttps()) {
                 writer.write('\n');
                 writer.write(cipherSuite + '\n');
                 writeCertArray(writer, peerCertificates);
                 writeCertArray(writer, localCertificates);
             }
             writer.close();
         }

         private boolean isHttps() {
             return uri.startsWith("https://");
         }

         private Certificate[] readCertArray(StrictLineReader reader) throws IOException {
             int length = reader.readInt();
             if (length == -1) {
                 return null;
             }
             try {
                 CertificateFactory certificateFactory = CertificateFactory.getInstance("X.509");
                 Certificate[] result = new Certificate[length];
                 for (int i = 0; i < result.length; i++) {
                     String line = reader.readLine();
                     byte[] bytes = Base64.decode(line.getBytes(Charsets.US_ASCII));
                     result[i] = certificateFactory.generateCertificate(
                             new ByteArrayInputStream(bytes));
                 }
                 return result;
             } catch (CertificateException e) {
                 throw new IOException(e);
             }
         }

         private void writeCertArray(Writer writer, Certificate[] certificates) throws IOException {
             if (certificates == null) {
                 writer.write("-1\n");
                 return;
             }
             try {
                 writer.write(Integer.toString(certificates.length) + '\n');
                 for (Certificate certificate : certificates) {
                     byte[] bytes = certificate.getEncoded();
                     String line = Base64.encode(bytes);
                     writer.write(line + '\n');
                 }
             } catch (CertificateEncodingException e) {
                 throw new IOException(e);
             }
         }

         public boolean matches(URI uri, String requestMethod,
                 Map<String, List<String>> requestHeaders) {
             return this.uri.equals(uri.toString())
                     && this.requestMethod.equals(requestMethod)
                     && new ResponseHeaders(uri, responseHeaders)
                             .varyMatches(varyHeaders.toMultimap(), requestHeaders);
         }
     }

     /**
      * Returns an input stream that reads the body of a snapshot, closing the
      * snapshot when the stream is closed.
      */
     private static InputStream newBodyInputStream(final DiskLruCache.Snapshot snapshot) {
         return new FilterInputStream(snapshot.getInputStream(ENTRY_BODY)) {
             @Override public void close() throws IOException {
                 snapshot.close();
                 super.close();
             }
         };
     }

     static class EntryCacheResponse extends CacheResponse {
         private final Entry entry;
         private final DiskLruCache.Snapshot snapshot;
         private final InputStream in;

         public EntryCacheResponse(Entry entry, DiskLruCache.Snapshot snapshot) {
             this.entry = entry;
             this.snapshot = snapshot;
             this.in = newBodyInputStream(snapshot);
         }

         @Override public Map<String, List<String>> getHeaders() {
             return entry.responseHeaders.toMultimap();
         }

         @Override public InputStream getBody() {
             return in;
         }
     }

     static class EntrySecureCacheResponse extends SecureCacheResponse {
         private final Entry entry;
         private final DiskLruCache.Snapshot snapshot;
         private final InputStream in;

         public EntrySecureCacheResponse(Entry entry, DiskLruCache.Snapshot snapshot) {
             this.entry = entry;
             this.snapshot = snapshot;
             this.in = newBodyInputStream(snapshot);
         }

         @Override public Map<String, List<String>> getHeaders() {
             return entry.responseHeaders.toMultimap();
         }

         @Override public InputStream getBody() {
             return in;
         }

         @Override public String getCipherSuite() {
             return entry.cipherSuite;
         }

         @Override public List<Certificate> getServerCertificateChain()
                 throws SSLPeerUnverifiedException {
             if (entry.peerCertificates == null || entry.peerCertificates.length == 0) {
                 throw new SSLPeerUnverifiedException(null);
             }
             return Arrays.asList(entry.peerCertificates.clone());
         }

         @Override public Principal getPeerPrincipal() throws SSLPeerUnverifiedException {
             if (entry.peerCertificates == null || entry.peerCertificates.length == 0) {
                 throw new SSLPeerUnverifiedException(null);
             }
             return ((X509Certificate) entry.peerCertificates[0]).getSubjectX500Principal();
         }

         @Override public List<Certificate> getLocalCertificateChain() {
             if (entry.localCertificates == null || entry.localCertificates.length == 0) {
                 return null;
             }
             return Arrays.asList(entry.localCertificates.clone());
         }

         @Override public Principal getLocalPrincipal() {
             if (entry.localCertificates == null || entry.localCertificates.length == 0) {
                 return null;
             }
             return ((X509Certificate) entry.localCertificates[0]).getSubjectX500Principal();
         }
     }
 }
	/*
	* Copyright (C) 2010 The Android Open Source Project
	*
	* 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 libcore.net.http;

	import java.io.BufferedWriter;
	import java.io.ByteArrayInputStream;
	import java.io.File;
	import java.io.FilterInputStream;
	import java.io.FilterOutputStream;
	import java.io.IOException;
	import java.io.InputStream;
	import java.io.OutputStream;
	import java.io.OutputStreamWriter;
	import java.io.Writer;
	import java.net.CacheRequest;
	import java.net.CacheResponse;
	import java.net.ExtendedResponseCache;
	import java.net.HttpURLConnection;
	import java.net.ResponseCache;
	import java.net.ResponseSource;
	import java.net.SecureCacheResponse;
	import java.net.URI;
	import java.net.URLConnection;
	import java.nio.charset.Charsets;
	import java.security.MessageDigest;
	import java.security.NoSuchAlgorithmException;
	import java.security.Principal;
	import java.security.cert.Certificate;
	import java.security.cert.CertificateEncodingException;
	import java.security.cert.CertificateException;
	import java.security.cert.CertificateFactory;
	import java.security.cert.X509Certificate;
	import java.util.Arrays;
	import java.util.List;
	import java.util.Map;
	import javax.net.ssl.HttpsURLConnection;
	import javax.net.ssl.SSLPeerUnverifiedException;
	import libcore.io.Base64;
	import libcore.io.DiskLruCache;
	import libcore.io.IoUtils;
	import libcore.io.StrictLineReader;

	/**
	* Cache responses in a directory on the file system. Most clients should use
	* {@code android.net.HttpResponseCache}, the stable, documented front end for
	* this.
	*/
	public final class HttpResponseCache extends ResponseCache implements ExtendedResponseCache {
	// TODO: add APIs to iterate the cache?
	private static final int VERSION = 201105;
	private static final int ENTRY_METADATA = 0;
	private static final int ENTRY_BODY = 1;
	private static final int ENTRY_COUNT = 2;

	private final DiskLruCache cache;

	/* read and write statistics, all guarded by 'this' */
	private int writeSuccessCount;
	private int writeAbortCount;
	private int networkCount;
	private int hitCount;
	private int requestCount;

	public HttpResponseCache(File directory, long maxSize) throws IOException {
	cache = DiskLruCache.open(directory, VERSION, ENTRY_COUNT, maxSize);
	}

	private String uriToKey(URI uri) {
	try {
	MessageDigest messageDigest = MessageDigest.getInstance("MD5");
	byte[] md5bytes = messageDigest.digest(uri.toString().getBytes(Charsets.UTF_8));
	return IntegralToString.bytesToHexString(md5bytes, false);
	} catch (NoSuchAlgorithmException e) {
	throw new AssertionError(e);
	}
	}

	@Override public CacheResponse get(URI uri, String requestMethod,
	Map<String, List<String>> requestHeaders) {
	String key = uriToKey(uri);
	DiskLruCache.Snapshot snapshot;
	Entry entry;
	try {
	snapshot = cache.get(key);
	if (snapshot == null) {
	return null;
	}
	entry = new Entry(snapshot.getInputStream(ENTRY_METADATA));
	} catch (IOException e) {
	// Give up because the cache cannot be read.
	return null;
	}

	if (!entry.matches(uri, requestMethod, requestHeaders)) {
	snapshot.close();
	return null;
	}

	return entry.isHttps()
	? new EntrySecureCacheResponse(entry, snapshot)
	: new EntryCacheResponse(entry, snapshot);
	}

	@Override public CacheRequest put(URI uri, URLConnection urlConnection) throws IOException {
	if (!(urlConnection instanceof HttpURLConnection)) {
	return null;
	}

	HttpURLConnection httpConnection = (HttpURLConnection) urlConnection;
	String requestMethod = httpConnection.getRequestMethod();
	String key = uriToKey(uri);

	if (requestMethod.equals(HttpEngine.POST)
	\|\| requestMethod.equals(HttpEngine.PUT)
	\|\| requestMethod.equals(HttpEngine.DELETE)) {
	try {
	cache.remove(key);
	} catch (IOException ignored) {
	// The cache cannot be written.
	}
	return null;
	} else if (!requestMethod.equals(HttpEngine.GET)) {
	/*
	* Don't cache non-GET responses. We're technically allowed to cache
	* HEAD requests and some POST requests, but the complexity of doing
	* so is high and the benefit is low.
	*/
	return null;
	}

	HttpEngine httpEngine = getHttpEngine(httpConnection);
	if (httpEngine == null) {
	// Don't cache unless the HTTP implementation is ours.
	return null;
	}

	ResponseHeaders response = httpEngine.getResponseHeaders();
	if (response.hasVaryAll()) {
	return null;
	}

	RawHeaders varyHeaders = httpEngine.getRequestHeaders().getHeaders().getAll(
	response.getVaryFields());
	Entry entry = new Entry(uri, varyHeaders, httpConnection);
	DiskLruCache.Editor editor = null;
	try {
	editor = cache.edit(key);
	if (editor == null) {
	return null;
	}
	entry.writeTo(editor);
	return new CacheRequestImpl(editor);
	} catch (IOException e) {
	abortQuietly(editor);
	return null;
	}
	}

	/**
	* Handles a conditional request hit by updating the stored cache response
	* with the headers from {@code httpConnection}. The cached response body is
	* not updated. If the stored response has changed since {@code
	* conditionalCacheHit} was returned, this does nothing.
	*/
	public void update(CacheResponse conditionalCacheHit, HttpURLConnection httpConnection) {
	HttpEngine httpEngine = getHttpEngine(httpConnection);
	URI uri = httpEngine.getUri();
	ResponseHeaders response = httpEngine.getResponseHeaders();
	RawHeaders varyHeaders = httpEngine.getRequestHeaders().getHeaders()
	.getAll(response.getVaryFields());
	Entry entry = new Entry(uri, varyHeaders, httpConnection);
	DiskLruCache.Snapshot snapshot = (conditionalCacheHit instanceof EntryCacheResponse)
	? ((EntryCacheResponse) conditionalCacheHit).snapshot
	: ((EntrySecureCacheResponse) conditionalCacheHit).snapshot;
	DiskLruCache.Editor editor = null;
	try {
	editor = snapshot.edit(); // returns null if snapshot is not current
	if (editor != null) {
	entry.writeTo(editor);
	editor.commit();
	}
	} catch (IOException e) {
	abortQuietly(editor);
	}
	}

	private void abortQuietly(DiskLruCache.Editor editor) {
	// Give up because the cache cannot be written.
	try {
	if (editor != null) {
	editor.abort();
	}
	} catch (IOException ignored) {
	}
	}

	private HttpEngine getHttpEngine(HttpURLConnection httpConnection) {
	if (httpConnection instanceof HttpURLConnectionImpl) {
	return ((HttpURLConnectionImpl) httpConnection).getHttpEngine();
	} else if (httpConnection instanceof HttpsURLConnectionImpl) {
	return ((HttpsURLConnectionImpl) httpConnection).getHttpEngine();
	} else {
	return null;
	}
	}

	public DiskLruCache getCache() {
	return cache;
	}

	public synchronized int getWriteAbortCount() {
	return writeAbortCount;
	}

	public synchronized int getWriteSuccessCount() {
	return writeSuccessCount;
	}

	public synchronized void trackResponse(ResponseSource source) {
	requestCount++;

	switch (source) {
	case CACHE:
	hitCount++;
	break;
	case CONDITIONAL_CACHE:
	case NETWORK:
	networkCount++;
	break;
	}
	}

	public synchronized void trackConditionalCacheHit() {
	hitCount++;
	}

	public synchronized int getNetworkCount() {
	return networkCount;
	}

	public synchronized int getHitCount() {
	return hitCount;
	}

	public synchronized int getRequestCount() {
	return requestCount;
	}

	private final class CacheRequestImpl extends CacheRequest {
	private final DiskLruCache.Editor editor;
	private OutputStream cacheOut;
	private boolean done;
	private OutputStream body;

	public CacheRequestImpl(final DiskLruCache.Editor editor) throws IOException {
	this.editor = editor;
	this.cacheOut = editor.newOutputStream(ENTRY_BODY);
	this.body = new FilterOutputStream(cacheOut) {
	@Override public void close() throws IOException {
	synchronized (HttpResponseCache.this) {
	if (done) {
	return;
	}
	done = true;
	writeSuccessCount++;
	}
	super.close();
	editor.commit();
	}

	@Override
	public void write(byte[] buffer, int offset, int length) throws IOException {
	// Since we don't override "write(int oneByte)", we can write directly to "out"
	// and avoid the inefficient implementation from the FilterOutputStream.
	out.write(buffer, offset, length);
	}
	};
	}

	@Override public void abort() {
	synchronized (HttpResponseCache.this) {
	if (done) {
	return;
	}
	done = true;
	writeAbortCount++;
	}
	IoUtils.closeQuietly(cacheOut);
	try {
	editor.abort();
	} catch (IOException ignored) {
	}
	}

	@Override public OutputStream getBody() throws IOException {
	return body;
	}
	}

	private static final class Entry {
	private final String uri;
	private final RawHeaders varyHeaders;
	private final String requestMethod;
	private final RawHeaders responseHeaders;
	private final String cipherSuite;
	private final Certificate[] peerCertificates;
	private final Certificate[] localCertificates;

	/*
	* Reads an entry from an input stream. A typical entry looks like this:
	* http://google.com/foo
	* GET
	* 2
	* Accept-Language: fr-CA
	* Accept-Charset: UTF-8
	* HTTP/1.1 200 OK
	* 3
	* Content-Type: image/png
	* Content-Length: 100
	* Cache-Control: max-age=600
	*
	* A typical HTTPS file looks like this:
	* https://google.com/foo
	* GET
	* 2
	* Accept-Language: fr-CA
	* Accept-Charset: UTF-8
	* HTTP/1.1 200 OK
	* 3
	* Content-Type: image/png
	* Content-Length: 100
	* Cache-Control: max-age=600
	*
	* AES_256_WITH_MD5
	* 2
	* base64-encoded peerCertificate[0]
	* base64-encoded peerCertificate[1]
	* -1
	*
	* The file is newline separated. The first two lines are the URL and
	* the request method. Next is the number of HTTP Vary request header
	* lines, followed by those lines.
	*
	* Next is the response status line, followed by the number of HTTP
	* response header lines, followed by those lines.
	*
	* HTTPS responses also contain SSL session information. This begins
	* with a blank line, and then a line containing the cipher suite. Next
	* is the length of the peer certificate chain. These certificates are
	* base64-encoded and appear each on their own line. The next line
	* contains the length of the local certificate chain. These
	* certificates are also base64-encoded and appear each on their own
	* line. A length of -1 is used to encode a null array.
	*/
	public Entry(InputStream in) throws IOException {
	try {
	StrictLineReader reader = new StrictLineReader(in, Charsets.US_ASCII);
	uri = reader.readLine();
	requestMethod = reader.readLine();
	varyHeaders = new RawHeaders();
	int varyRequestHeaderLineCount = reader.readInt();
	for (int i = 0; i < varyRequestHeaderLineCount; i++) {
	varyHeaders.addLine(reader.readLine());
	}

	responseHeaders = new RawHeaders();
	responseHeaders.setStatusLine(reader.readLine());
	int responseHeaderLineCount = reader.readInt();
	for (int i = 0; i < responseHeaderLineCount; i++) {
	responseHeaders.addLine(reader.readLine());
	}

	if (isHttps()) {
	String blank = reader.readLine();
	if (!blank.isEmpty()) {
	throw new IOException("expected \"\" but was \"" + blank + "\"");
	}
	cipherSuite = reader.readLine();
	peerCertificates = readCertArray(reader);
	localCertificates = readCertArray(reader);
	} else {
	cipherSuite = null;
	peerCertificates = null;
	localCertificates = null;
	}
	} finally {
	in.close();
	}
	}

	public Entry(URI uri, RawHeaders varyHeaders, HttpURLConnection httpConnection) {
	this.uri = uri.toString();
	this.varyHeaders = varyHeaders;
	this.requestMethod = httpConnection.getRequestMethod();
	this.responseHeaders = RawHeaders.fromMultimap(httpConnection.getHeaderFields());

	if (isHttps()) {
	HttpsURLConnection httpsConnection = (HttpsURLConnection) httpConnection;
	cipherSuite = httpsConnection.getCipherSuite();
	Certificate[] peerCertificatesNonFinal = null;
	try {
	peerCertificatesNonFinal = httpsConnection.getServerCertificates();
	} catch (SSLPeerUnverifiedException ignored) {
	}
	peerCertificates = peerCertificatesNonFinal;
	localCertificates = httpsConnection.getLocalCertificates();
	} else {
	cipherSuite = null;
	peerCertificates = null;
	localCertificates = null;
	}
	}

	public void writeTo(DiskLruCache.Editor editor) throws IOException {
	OutputStream out = editor.newOutputStream(ENTRY_METADATA);
	Writer writer = new BufferedWriter(new OutputStreamWriter(out, Charsets.UTF_8));

	writer.write(uri + '\n');
	writer.write(requestMethod + '\n');
	writer.write(Integer.toString(varyHeaders.length()) + '\n');
	for (int i = 0; i < varyHeaders.length(); i++) {
	writer.write(varyHeaders.getFieldName(i) + ": "
	+ varyHeaders.getValue(i) + '\n');
	}

	writer.write(responseHeaders.getStatusLine() + '\n');
	writer.write(Integer.toString(responseHeaders.length()) + '\n');
	for (int i = 0; i < responseHeaders.length(); i++) {
	writer.write(responseHeaders.getFieldName(i) + ": "
	+ responseHeaders.getValue(i) + '\n');
	}

	if (isHttps()) {
	writer.write('\n');
	writer.write(cipherSuite + '\n');
	writeCertArray(writer, peerCertificates);
	writeCertArray(writer, localCertificates);
	}
	writer.close();
	}

	private boolean isHttps() {
	return uri.startsWith("https://");
	}

	private Certificate[] readCertArray(StrictLineReader reader) throws IOException {
	int length = reader.readInt();
	if (length == -1) {
	return null;
	}
	try {
	CertificateFactory certificateFactory = CertificateFactory.getInstance("X.509");
	Certificate[] result = new Certificate[length];
	for (int i = 0; i < result.length; i++) {
	String line = reader.readLine();
	byte[] bytes = Base64.decode(line.getBytes(Charsets.US_ASCII));
	result[i] = certificateFactory.generateCertificate(
	new ByteArrayInputStream(bytes));
	}
	return result;
	} catch (CertificateException e) {
	throw new IOException(e);
	}
	}

	private void writeCertArray(Writer writer, Certificate[] certificates) throws IOException {
	if (certificates == null) {
	writer.write("-1\n");
	return;
	}
	try {
	writer.write(Integer.toString(certificates.length) + '\n');
	for (Certificate certificate : certificates) {
	byte[] bytes = certificate.getEncoded();
	String line = Base64.encode(bytes);
	writer.write(line + '\n');
	}
	} catch (CertificateEncodingException e) {
	throw new IOException(e);
	}
	}

	public boolean matches(URI uri, String requestMethod,
	Map<String, List<String>> requestHeaders) {
	return this.uri.equals(uri.toString())
	&& this.requestMethod.equals(requestMethod)
	&& new ResponseHeaders(uri, responseHeaders)
	.varyMatches(varyHeaders.toMultimap(), requestHeaders);
	}
	}

	/**
	* Returns an input stream that reads the body of a snapshot, closing the
	* snapshot when the stream is closed.
	*/
	private static InputStream newBodyInputStream(final DiskLruCache.Snapshot snapshot) {
	return new FilterInputStream(snapshot.getInputStream(ENTRY_BODY)) {
	@Override public void close() throws IOException {
	snapshot.close();
	super.close();
	}
	};
	}

	static class EntryCacheResponse extends CacheResponse {
	private final Entry entry;
	private final DiskLruCache.Snapshot snapshot;
	private final InputStream in;

	public EntryCacheResponse(Entry entry, DiskLruCache.Snapshot snapshot) {
	this.entry = entry;
	this.snapshot = snapshot;
	this.in = newBodyInputStream(snapshot);
	}

	@Override public Map<String, List<String>> getHeaders() {
	return entry.responseHeaders.toMultimap();
	}

	@Override public InputStream getBody() {
	return in;
	}
	}

	static class EntrySecureCacheResponse extends SecureCacheResponse {
	private final Entry entry;
	private final DiskLruCache.Snapshot snapshot;
	private final InputStream in;

	public EntrySecureCacheResponse(Entry entry, DiskLruCache.Snapshot snapshot) {
	this.entry = entry;
	this.snapshot = snapshot;
	this.in = newBodyInputStream(snapshot);
	}

	@Override public Map<String, List<String>> getHeaders() {
	return entry.responseHeaders.toMultimap();
	}

	@Override public InputStream getBody() {
	return in;
	}

	@Override public String getCipherSuite() {
	return entry.cipherSuite;
	}

	@Override public List<Certificate> getServerCertificateChain()
	throws SSLPeerUnverifiedException {
	if (entry.peerCertificates == null \|\| entry.peerCertificates.length == 0) {
	throw new SSLPeerUnverifiedException(null);
	}
	return Arrays.asList(entry.peerCertificates.clone());
	}

	@Override public Principal getPeerPrincipal() throws SSLPeerUnverifiedException {
	if (entry.peerCertificates == null \|\| entry.peerCertificates.length == 0) {
	throw new SSLPeerUnverifiedException(null);
	}
	return ((X509Certificate) entry.peerCertificates[0]).getSubjectX500Principal();
	}

	@Override public List<Certificate> getLocalCertificateChain() {
	if (entry.localCertificates == null \|\| entry.localCertificates.length == 0) {
	return null;
	}
	return Arrays.asList(entry.localCertificates.clone());
	}

	@Override public Principal getLocalPrincipal() {
	if (entry.localCertificates == null \|\| entry.localCertificates.length == 0) {
	return null;
	}
	return ((X509Certificate) entry.localCertificates[0]).getSubjectX500Principal();
	}
	}
	}