Fix a bug where the response cache could be corrupted.

When streaming a response, we copy data from our buffer to the cached file
on disk. Unfortunately we were copying N bytes from the front of the buffer
when we wanted N bytes from the back of the buffer.

Typically these are the same, but certain access patterns can cause them
to be different, corrpting the cached file on disk.

This was uncovered by migrating the cache tests from operating on
HttpURLConnection's API to our new API.

okhttp-tests/src/test/java/com/squareup/okhttp/OkHttpClientTest.java

@@ -21,11 +21,17 @@
 import com.squareup.okhttp.internal.tls.OkHostnameVerifier;
 import java.io.IOException;
 import java.net.Authenticator;
+import java.net.CacheRequest;
+import java.net.CacheResponse;
 import java.net.CookieHandler;
 import java.net.CookieManager;
 import java.net.ProxySelector;
 import java.net.ResponseCache;
+import java.net.URI;
+import java.net.URLConnection;
 import java.util.Arrays;
+import java.util.List;
+import java.util.Map;
 import javax.net.SocketFactory;
 import org.junit.After;
 import org.junit.Test;
@@ -95,9 +101,17 @@ public final class OkHttpClientTest {
     assertNull(client.getCache());
   }
 
-  @Test public void copyWithDefaultsDoesNotHonorGlobalResponseCache() throws Exception {
-    ResponseCache responseCache = new AbstractResponseCache();
-    ResponseCache.setDefault(responseCache);
+  @Test public void copyWithDefaultsDoesNotHonorGlobalResponseCache() {
+    ResponseCache.setDefault(new ResponseCache() {
+      @Override public CacheResponse get(URI uri, String requestMethod,
+          Map<String, List<String>> requestHeaders) throws IOException {
+        throw new AssertionError();
+      }
+
+      @Override public CacheRequest put(URI uri, URLConnection connection) {
+        throw new AssertionError();
+      }
+    });
 
     OkHttpClient client = new OkHttpClient().copyWithDefaults();
     assertNull(client.internalCache());

okhttp-tests/src/test/java/com/squareup/okhttp/internal/http/URLConnectionTest.java

@@ -16,7 +16,6 @@
 
 package com.squareup.okhttp.internal.http;
 
-import com.squareup.okhttp.AbstractResponseCache;
 import com.squareup.okhttp.Cache;
 import com.squareup.okhttp.Challenge;
 import com.squareup.okhttp.ConnectionConfiguration;
@@ -33,7 +32,6 @@
 import com.squareup.okhttp.internal.SingleInetAddressNetwork;
 import com.squareup.okhttp.internal.SslContextBuilder;
 import com.squareup.okhttp.internal.Util;
-import com.squareup.okhttp.internal.huc.CacheAdapter;
 import com.squareup.okhttp.mockwebserver.MockResponse;
 import com.squareup.okhttp.mockwebserver.MockWebServer;
 import com.squareup.okhttp.mockwebserver.RecordedRequest;
@@ -43,7 +41,6 @@
 import java.io.InputStream;
 import java.io.OutputStream;
 import java.net.Authenticator;
-import java.net.CacheRequest;
 import java.net.ConnectException;
 import java.net.HttpRetryException;
 import java.net.HttpURLConnection;
@@ -70,7 +67,6 @@
 import java.util.Set;
 import java.util.UUID;
 import java.util.concurrent.TimeUnit;
-import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.zip.GZIPInputStream;
 import javax.net.SocketFactory;
 import javax.net.ssl.HttpsURLConnection;
@@ -2004,8 +2000,7 @@ private void testResponseRedirectedWithPost(int redirectCode, TransferKind trans
   }
 
   @Test public void redirectedPostStripsRequestBodyHeaders() throws Exception {
-    server.enqueue(new MockResponse()
-        .setResponseCode(HttpURLConnection.HTTP_MOVED_TEMP)
+    server.enqueue(new MockResponse().setResponseCode(HttpURLConnection.HTTP_MOVED_TEMP)
         .addHeader("Location: /page2"));
     server.enqueue(new MockResponse().setBody("Page 2"));
     server.play();
@@ -2430,33 +2425,6 @@ private void testFlushAfterStreamTransmitted(TransferKind transferKind) throws I
     }
   }
 
-  /** Don't explode if the cache returns a null body. http://b/3373699 */
-  @Test public void responseCacheReturnsNullOutputStream() throws Exception {
-    final AtomicBoolean aborted = new AtomicBoolean();
-    Internal.instance.setCache(client.client(), new CacheAdapter(new AbstractResponseCache() {
-      @Override public CacheRequest put(URI uri, URLConnection connection) throws IOException {
-        return new CacheRequest() {
-          @Override public void abort() {
-            aborted.set(true);
-          }
-
-          @Override public OutputStream getBody() throws IOException {
-            return null;
-          }
-        };
-      }
-    }));
-
-    server.enqueue(new MockResponse().setBody("abcdef"));
-    server.play();
-
-    HttpURLConnection connection = client.open(server.getUrl("/"));
-    InputStream in = connection.getInputStream();
-    assertEquals("abc", readAscii(in, 3));
-    in.close();
-    assertFalse(aborted.get()); // The best behavior is ambiguous, but RI 6 doesn't abort here
-  }
-
   /** http://code.google.com/p/android/issues/detail?id=14562 */
   @Test public void readAfterLastByte() throws Exception {
     server.enqueue(new MockResponse().setBody("ABC")