Implement seekability for file descriptors (#6)

* Implement seekability for file descriptors

app/build.gradle

@@ -1,12 +1,12 @@
 apply plugin: 'com.android.application'
 
 android {
-    compileSdkVersion 25
+    compileSdkVersion 26
     buildToolsVersion "25.0.2"
     defaultConfig {
         applicationId "com.google.android.sambadocumentsprovider"
         minSdkVersion 21
-        targetSdkVersion 25
+        targetSdkVersion 26
         versionCode 102
         versionName "1.0"
         testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"

app/src/main/cpp/jni_helper/JniHelper.cc

@@ -527,6 +527,46 @@ Java_com_google_android_sambadocumentsprovider_nativefacade_NativeSambaFacade_op
   return fd;
 }
 
+jobject Java_com_google_android_sambadocumentsprovider_nativefacade_SambaFile_fstat(
+        JNIEnv *env,
+        jobject instance,
+        jlong pointer,
+        jint fd) {
+  SambaClient::SambaClient *client =
+          reinterpret_cast<SambaClient::SambaClient*>(pointer);
+
+  jobject stat = NULL;
+
+  struct stat st;
+
+  int result = client->Fstat(fd, &st);
+  if (result < 0) {
+    throw_new_errno_exception(env, "stat", -result);
+  }
+
+  return create_structstat(env, st);
+}
+
+jlong Java_com_google_android_sambadocumentsprovider_nativefacade_SambaFile_seek(
+    JNIEnv *env,
+    jobject instance,
+    jlong pointer,
+    jint fd,
+    jlong offset,
+    jint whence) {
+  SambaClient::SambaClient *client =
+          reinterpret_cast<SambaClient::SambaClient*>(pointer);
+
+  jlong result = client->SeekFile(fd, offset, whence);
+  if (result < 0) {
+    throw_new_errno_exception(env, "seek", static_cast<int>(-result));
+  }
+
+  return result;
+}
+
+
+
 jlong Java_com_google_android_sambadocumentsprovider_nativefacade_SambaFile_read(
     JNIEnv *env,
     jobject instance,

app/src/main/cpp/jni_helper/JniHelper.h

@@ -68,6 +68,14 @@ JNIEXPORT jlong JNICALL
     Java_com_google_android_sambadocumentsprovider_nativefacade_SambaFile_read(
     JNIEnv *env, jobject instance, jlong pointer, jint fd, jobject buffer, jint maxlen);
 
+JNIEXPORT jlong JNICALL
+    Java_com_google_android_sambadocumentsprovider_nativefacade_SambaFile_seek(
+    JNIEnv *env, jobject instance, jlong pointer, jint fd, jlong offset, jint whence);
+
+JNIEXPORT jobject JNICALL
+    Java_com_google_android_sambadocumentsprovider_nativefacade_SambaFile_fstat(
+        JNIEnv *env, jobject instance, jlong pointer, jint fd);
+
 JNIEXPORT jlong JNICALL
     Java_com_google_android_sambadocumentsprovider_nativefacade_SambaFile_write(
     JNIEnv *env, jobject instance, jlong pointer, jint fd, jobject buffer, jint length);

app/src/main/cpp/samba_client/SambaClient.cc

@@ -160,6 +160,19 @@ SambaClient::ReadDir(
   return 0;
 }
 
+int
+SambaClient::Fstat(const int fd, struct stat * const st) {
+  LOGD(TAG, "Getting stat for %x.", fd);
+  int result = smbc_fstat(fd, st);
+  if (result < 0) {
+    int err = errno;
+    LOGE(TAG, "Failed to obtain stat for %x. Errno: %x.", fd, err);
+    return -err;
+  }
+  LOGV(TAG, "Got stat for %x.", fd);
+  return 0;
+}
+
 int
 SambaClient::Stat(const char *url, struct stat * const st) {
   LOGD(TAG, "Getting stat for %s.", url);
@@ -251,6 +264,20 @@ int SambaClient::OpenFile(const char *url, const int flag, const mode_t mode) {
   return fd;
 }
 
+off_t
+SambaClient::SeekFile(const int fd, const off_t offset, const int whence) {
+  LOGV(TAG, "Set offset to %x for file with fd %x", offset, fd);
+
+  off_t result = smbc_lseek(fd, offset, whence);
+  if (result < 0) {
+    int err = errno;
+    LOGE(TAG, "Failed to seek in file %x. Errno: %x", fd, err);
+    return -err;
+  }
+
+  return result;
+}
+
 ssize_t
 SambaClient::ReadFile(const int fd, void *buffer, const size_t maxlen) {
   LOGV(TAG, "Reading max %lu bytes from file with fd %x", maxlen, fd);

app/src/main/cpp/samba_client/SambaClient.h

@@ -18,10 +18,11 @@
 #ifndef SAMBADOCUMENTSPROVIDER_SAMBAPROVIDER_H
 #define SAMBADOCUMENTSPROVIDER_SAMBAPROVIDER_H
 
+#include "samba_includes/libsmbclient.h"
 #include "base/Callback.h"
 #include "jni_helper/JniHelper.h"
-#include "samba_includes/libsmbclient.h"
 
+#include <sys/types.h>
 #include <vector>
 
 namespace SambaClient {
@@ -38,6 +39,8 @@ class SambaClient {
 
   int Stat(const char *url, struct stat *st);
 
+  int Fstat(const int fd, struct stat * const st);
+
   int CreateFile(const char *url);
 
   int Mkdir(const char *url);
@@ -54,6 +57,8 @@ class SambaClient {
 
   ssize_t WriteFile(const int fd, void *buffer, const size_t length);
 
+  off_t SeekFile(const int fd, const off_t offset, const int whence);
+
   int CloseFile(const int fd);
  private:
   ::SMBCCTX *sambaContext = NULL;

app/src/main/java/com/google/android/sambadocumentsprovider/SambaProviderApplication.java

@@ -24,17 +24,18 @@ import android.net.ConnectivityManager.NetworkCallback;
 import android.net.Network;
 import android.net.NetworkCapabilities;
 import android.net.NetworkRequest;
+
 import com.google.android.sambadocumentsprovider.SambaConfiguration.OnConfigurationChangedListener;
 import com.google.android.sambadocumentsprovider.cache.DocumentCache;
 import com.google.android.sambadocumentsprovider.nativefacade.CredentialCache;
 import com.google.android.sambadocumentsprovider.nativefacade.SambaMessageLooper;
-import com.google.android.sambadocumentsprovider.nativefacade.SmbClient;
+import com.google.android.sambadocumentsprovider.nativefacade.SmbFacade;
 
 public class SambaProviderApplication extends Application {
 
   private final DocumentCache mCache = new DocumentCache();
   private final TaskManager mTaskManager = new TaskManager();
-  private final SmbClient mSambaClient;
+  private final SmbFacade mSambaClient;
   private final CredentialCache mCredentialCache;
 
   private SambaConfiguration mSambaConf;
@@ -94,7 +95,7 @@ public class SambaProviderApplication extends Application {
     }
   }
 
-  public static SmbClient getSambaClient(Context context) {
+  public static SmbFacade getSambaClient(Context context) {
     return getApplication(context).mSambaClient;
   }
 

app/src/main/java/com/google/android/sambadocumentsprovider/nativefacade/NativeSambaFacade.java

@@ -17,6 +17,9 @@
 
 package com.google.android.sambadocumentsprovider.nativefacade;
 
+import android.os.ParcelFileDescriptor;
+import android.os.ProxyFileDescriptorCallback;
+import android.os.storage.StorageManager;
 import android.system.ErrnoException;
 import android.system.StructStat;
 import com.google.android.sambadocumentsprovider.BuildConfig;

app/src/main/java/com/google/android/sambadocumentsprovider/nativefacade/SambaFacadeClient.java

@@ -18,17 +18,25 @@
 package com.google.android.sambadocumentsprovider.nativefacade;
 
 import android.os.Bundle;
+import android.os.CancellationSignal;
 import android.os.Looper;
 import android.os.Message;
+import android.os.ParcelFileDescriptor;
+import android.os.storage.StorageManager;
 import android.support.annotation.IntDef;
 import android.system.StructStat;
+
 import com.google.android.sambadocumentsprovider.base.DirectoryEntry;
+import com.google.android.sambadocumentsprovider.provider.ByteBufferPool;
+import com.google.android.sambadocumentsprovider.provider.SambaProxyFileCallback;
+
 import java.io.IOException;
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
+import java.nio.ByteBuffer;
 import java.util.List;
 
-class SambaFacadeClient extends BaseClient implements SmbClient {
+class SambaFacadeClient extends BaseClient implements SmbFacade {
 
   @IntDef({ RESET, READ_DIR, STAT, MKDIR, RENAME, UNLINK, RMDIR, OPEN_FILE })
   @Retention(RetentionPolicy.SOURCE)
@@ -134,14 +142,37 @@ class SambaFacadeClient extends BaseClient implements SmbClient {
 
   @Override
   public SmbFile openFile(String uri, String mode) throws IOException {
+    return new SambaFileClient(mHandler.getLooper(), openFileRaw(uri, mode));
+  }
+
+  @Override
+  public ParcelFileDescriptor openProxyFile(
+          String uri,
+          String mode,
+          StorageManager storageManager,
+          ByteBufferPool bufferPool,
+         CancellationSignal signal) throws IOException {
+    SambaFile file = openFileRaw(uri, mode);
+    return storageManager.openProxyFileDescriptor(
+            ParcelFileDescriptor.parseMode(mode),
+            new SambaProxyFileCallback(file, bufferPool, signal),
+            mHandler);
+  }
+
+  private SambaFile openFileRaw(String uri, String mode) throws IOException {
     try (final MessageValues<SambaFile> messageValues = MessageValues.obtain()) {
-      final Message msg = obtainMessage(OPEN_FILE, messageValues, uri);
+      enqueue(obtainMessageForOpenFile(uri, mode, messageValues));
-      msg.peekData().putString(MODE, mode);
+      return messageValues.getObj();
-      enqueue(msg);
-      return new SambaFileClient(mHandler.getLooper(), messageValues.getObj());
     }
   }
 
+  private Message obtainMessageForOpenFile(String uri, String mode,
+                                           MessageValues<SambaFile> messageValues) {
+    final Message msg = obtainMessage(OPEN_FILE, messageValues, uri);
+    msg.peekData().putString(MODE, mode);
+    return msg;
+  }
+
   private static class SambaServiceHandler extends BaseHandler {
 
     private final SmbClient mClientImpl;

app/src/main/java/com/google/android/sambadocumentsprovider/nativefacade/SambaFile.java

@@ -18,6 +18,9 @@
 package com.google.android.sambadocumentsprovider.nativefacade;
 
 import android.system.ErrnoException;
+import android.system.StructStat;
+import android.util.Log;
+
 import java.io.IOException;
 import java.nio.ByteBuffer;
 
@@ -46,6 +49,23 @@ class SambaFile implements SmbFile {
     }
   }
 
+  public long seek(long offset) throws IOException {
+    try {
+      return seek(mNativeHandler, mNativeFd, offset, 0);
+    } catch (ErrnoException e) {
+      throw new IOException("Failed to move to offset in file. Fd: " + mNativeFd, e);
+    }
+  }
+
+  @Override
+  public StructStat fstat() throws IOException {
+    try {
+      return fstat(mNativeHandler, mNativeFd);
+    } catch (ErrnoException e) {
+      throw new IOException("Failed to get stat of " + mNativeFd, e);
+    }
+  }
+
   @Override
   public void close() throws IOException {
     try {
@@ -63,5 +83,10 @@ class SambaFile implements SmbFile {
   private native int write(long handler, int fd, ByteBuffer buffer, int length)
       throws ErrnoException;
 
+  private native long seek(long handler, int fd, long offset, int whence)
+      throws ErrnoException;
+
+  private native StructStat fstat(long handler, int fd) throws ErrnoException;
+
   private native void close(long handler, int fd) throws ErrnoException;
 }

app/src/main/java/com/google/android/sambadocumentsprovider/nativefacade/SambaFileClient.java

@@ -17,9 +17,12 @@
 
 package com.google.android.sambadocumentsprovider.nativefacade;
 
+import android.os.Bundle;
 import android.os.Looper;
 import android.os.Message;
 import android.support.annotation.IntDef;
+import android.system.StructStat;
+
 import java.io.IOException;
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
@@ -33,6 +36,10 @@ class SambaFileClient extends BaseClient implements SmbFile {
   private static final int READ = 1;
   private static final int WRITE = 2;
   private static final int CLOSE = 3;
+  private static final int SEEK = 4;
+  private static final int FSTAT = 5;
+
+  private static final String OFFSET = "offset";
 
   SambaFileClient(Looper looper, SmbFile smbFileImpl) {
     mHandler = new SambaFileHandler(looper, smbFileImpl);
@@ -59,6 +66,30 @@ class SambaFileClient extends BaseClient implements SmbFile {
     }
   }
 
+  @Override
+  public long seek(long offset) throws IOException {
+    try (final MessageValues messageValues = MessageValues.obtain()) {
+      final Message msg = mHandler.obtainMessage(SEEK, messageValues);
+
+      Bundle data = new Bundle();
+      data.putLong(OFFSET, offset);
+
+      msg.setData(data);
+
+      enqueue(msg);
+      return msg.peekData().getLong(OFFSET);
+    }
+  }
+
+  @Override
+  public StructStat fstat() throws IOException {
+    try (final MessageValues<StructStat> messageValues = MessageValues.obtain()) {
+      final Message msg = mHandler.obtainMessage(FSTAT, messageValues);
+      enqueue(msg);
+      return messageValues.getObj();
+    }
+  }
+
   @Override
   public void close() throws IOException {
     try (final MessageValues messageValues = MessageValues.obtain()) {
@@ -81,22 +112,28 @@ class SambaFileClient extends BaseClient implements SmbFile {
     @Override
     @SuppressWarnings("unchecked")
     public void processMessage(Message msg) {
-      final MessageValues<ByteBuffer> messageValues = (MessageValues<ByteBuffer>) msg.obj;
+      final MessageValues messageValues = (MessageValues) msg.obj;
       try {
-        final ByteBuffer buffer = messageValues.getObj();
-
         switch (msg.what) {
           case READ:
-            messageValues.setInt(mSmbFileImpl.read(buffer));
+            final ByteBuffer readBuffer = (ByteBuffer) messageValues.getObj();
+            messageValues.setInt(mSmbFileImpl.read(readBuffer));
             break;
           case WRITE: {
+            final ByteBuffer writeBuffer = (ByteBuffer) messageValues.getObj();
             final int length = msg.arg1;
-            messageValues.setInt(mSmbFileImpl.write(buffer, length));
+            messageValues.setInt(mSmbFileImpl.write(writeBuffer, length));
             break;
           }
           case CLOSE:
             mSmbFileImpl.close();
             break;
+          case SEEK:
+            long offset = mSmbFileImpl.seek(msg.peekData().getLong(OFFSET));
+            msg.peekData().putLong(OFFSET, offset);
+          case FSTAT:
+            messageValues.setObj(mSmbFileImpl.fstat());
+            break;
           default:
             throw new UnsupportedOperationException("Unknown operation " + msg.what);
         }

app/src/main/java/com/google/android/sambadocumentsprovider/nativefacade/SambaMessageLooper.java

@@ -18,6 +18,7 @@
 package com.google.android.sambadocumentsprovider.nativefacade;
 
 import android.os.Looper;
+
 import java.util.concurrent.CountDownLatch;
 
 public class SambaMessageLooper {
@@ -41,7 +42,7 @@ public class SambaMessageLooper {
     init();
   }
 
-  public SmbClient getClient() {
+  public SmbFacade getClient() {
     return mServiceClient;
   }
 
@@ -55,6 +56,7 @@ public class SambaMessageLooper {
       mLatch.await();
 
       mCredentialCacheClient = new CredentialCacheClient(mLooper, mCredentialCacheImpl);
+
       mServiceClient = new SambaFacadeClient(mLooper, mClientImpl);
     } catch(InterruptedException e) {
       // Should never happen

app/src/main/java/com/google/android/sambadocumentsprovider/nativefacade/SmbFacade.java

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2017 Google Inc.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.google.android.sambadocumentsprovider.nativefacade;
+
+import android.os.CancellationSignal;
+import android.os.ParcelFileDescriptor;
+import android.os.storage.StorageManager;
+
+import com.google.android.sambadocumentsprovider.provider.ByteBufferPool;
+
+import java.io.IOException;
+import java.nio.ByteBuffer;
+
+public interface SmbFacade extends SmbClient {
+  ParcelFileDescriptor openProxyFile(
+          String uri,
+          String mode,
+          StorageManager storageManager,
+          ByteBufferPool bufferPool,
+          CancellationSignal signal) throws IOException;
+}

app/src/main/java/com/google/android/sambadocumentsprovider/nativefacade/SmbFile.java

@@ -17,6 +17,8 @@
 
 package com.google.android.sambadocumentsprovider.nativefacade;
 
+import android.system.StructStat;
+
 import java.io.Closeable;
 import java.io.IOException;
 import java.nio.ByteBuffer;
@@ -25,5 +27,7 @@ public interface SmbFile extends Closeable {
 
   int read(ByteBuffer buffer) throws IOException;
   int write(ByteBuffer buffer, int length) throws IOException;
+  long seek(long offset) throws IOException;
+  StructStat fstat() throws IOException;
 
 }

app/src/main/java/com/google/android/sambadocumentsprovider/provider/ByteBufferPool.java

@@ -20,12 +20,12 @@ package com.google.android.sambadocumentsprovider.provider;
 import android.support.v4.util.Pools;
 import java.nio.ByteBuffer;
 
-class ByteBufferPool {
+public class ByteBufferPool {
 
   private static final int BUFFER_CAPACITY = 128 * 1024;
   private final Pools.Pool<ByteBuffer> mBufferPool = new Pools.SynchronizedPool<>(16);
 
-  ByteBuffer obtainBuffer() {
+  public ByteBuffer obtainBuffer() {
     ByteBuffer buffer = mBufferPool.acquire();
 
     if (buffer == null) {
@@ -35,7 +35,7 @@ class ByteBufferPool {
     return buffer;
   }
 
-  void recycleBuffer(ByteBuffer buffer) {
+  public void recycleBuffer(ByteBuffer buffer) {
     buffer.clear();
     mBufferPool.release(buffer);
   }

app/src/main/java/com/google/android/sambadocumentsprovider/provider/SambaDocumentsProvider.java

@@ -27,9 +27,11 @@ import android.content.Context;
 import android.database.Cursor;
 import android.database.MatrixCursor;
 import android.net.Uri;
+import android.os.Build;
 import android.os.Bundle;
 import android.os.CancellationSignal;
 import android.os.ParcelFileDescriptor;
+import android.os.storage.StorageManager;
 import android.provider.DocumentsContract;
 import android.provider.DocumentsContract.Document;
 import android.provider.DocumentsContract.Root;
@@ -53,6 +55,9 @@ import com.google.android.sambadocumentsprovider.base.OnTaskFinishedCallback;
 import com.google.android.sambadocumentsprovider.document.LoadDocumentTask;
 import com.google.android.sambadocumentsprovider.document.LoadStatTask;
 import com.google.android.sambadocumentsprovider.nativefacade.SmbClient;
+import com.google.android.sambadocumentsprovider.nativefacade.SmbFacade;
+import com.google.android.sambadocumentsprovider.nativefacade.SmbFile;
+
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.util.Collection;
@@ -131,10 +136,11 @@ public class SambaDocumentsProvider extends DocumentsProvider {
   };
 
   private ShareManager mShareManager;
-  private SmbClient mClient;
+  private SmbFacade mClient;
   private ByteBufferPool mBufferPool;
   private DocumentCache mCache;
   private TaskManager mTaskManager;
+  private StorageManager mStorageManager;
 
   @Override
   public boolean onCreate() {
@@ -145,6 +151,7 @@ public class SambaDocumentsProvider extends DocumentsProvider {
     mBufferPool = new ByteBufferPool();
     mShareManager = SambaProviderApplication.getServerManager(context);
     mShareManager.addListener(mShareChangeListener);
+    mStorageManager = (StorageManager) context.getSystemService(Context.STORAGE_SERVICE);
 
     return mClient != null;
   }
@@ -547,12 +554,23 @@ public class SambaDocumentsProvider extends DocumentsProvider {
   public ParcelFileDescriptor openDocument(String documentId, String mode,
       CancellationSignal cancellationSignal) throws FileNotFoundException {
     Log.d(TAG, "Opening document " + documentId + " with mode " + mode);
+
     try {
       if (!"r".equals(mode) && !"w".equals(mode)) {
         throw new UnsupportedOperationException("Mode " + mode + " is not supported");
       }
 
       final String uri = toUriString(documentId);
+
+      if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
+        return mClient.openProxyFile(
+                uri,
+                mode,
+                mStorageManager,
+                mBufferPool,
+                cancellationSignal);
+      }
+
       ParcelFileDescriptor[] pipe = ParcelFileDescriptor.createReliablePipe();
       switch (mode) {
         case "r": {
@@ -560,7 +578,7 @@ public class SambaDocumentsProvider extends DocumentsProvider {
               uri, mClient, pipe[1], mBufferPool, cancellationSignal);
           mTaskManager.runIoTask(task);
         }
-          return pipe[0];
+        return pipe[0];
         case "w": {
           final WriteFileTask task = new WriteFileTask(uri, mClient, pipe[0], mBufferPool,
               cancellationSignal, mWriteFinishedCallback);

app/src/main/java/com/google/android/sambadocumentsprovider/provider/SambaProxyFileCallback.java

@@ -0,0 +1,117 @@
+/*
+ * Copyright 2017 Google Inc.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.google.android.sambadocumentsprovider.provider;
+
+import android.os.CancellationSignal;
+import android.os.ProxyFileDescriptorCallback;
+import android.system.ErrnoException;
+import android.system.StructStat;
+import android.util.Log;
+
+import com.google.android.sambadocumentsprovider.nativefacade.SmbFile;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.nio.ByteBuffer;
+
+public class SambaProxyFileCallback extends ProxyFileDescriptorCallback {
+    private static final String TAG = "SambaProxyFileCallback";
+
+    private final SmbFile mFile;
+    private final ByteBufferPool mBufferPool;
+    private final ByteBuffer mBuffer;
+    private final CancellationSignal mSignal;
+
+    public SambaProxyFileCallback(SmbFile file, ByteBufferPool bufferPool, CancellationSignal signal) {
+        mFile = file;
+        mBufferPool = bufferPool;
+        mBuffer = mBufferPool.obtainBuffer();
+        mSignal = signal;
+    }
+
+    @Override
+    public long onGetSize() throws ErrnoException {
+        StructStat stat = null;
+        try {
+            stat = mFile.fstat();
+            return stat.st_size;
+        } catch (IOException e) {
+            Log.e(TAG, "Failed to get size for file");
+        }
+
+        return 0;
+    }
+
+    @Override
+    public int onRead(long offset, int size, byte[] data) throws ErrnoException {
+        try (ByteArrayOutputStream os = new ByteArrayOutputStream()) {
+            mFile.seek(offset);
+
+            int readSize;
+            int total = 0;
+            while ((mSignal == null || !mSignal.isCanceled())
+                    && (readSize = mFile.read(mBuffer)) > 0) {
+                mBuffer.get(data, total, Math.min(size - total, readSize));
+                mBuffer.clear();
+                total += Math.min(size - total, readSize);
+                if (total >= size) {
+                    break;
+                }
+            }
+
+            return Math.min(size, total);
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+
+        return 0;
+    }
+
+    @Override
+    public int onWrite(long offset, int size, byte[] data) throws ErrnoException {
+        int written = 0;
+
+        try {
+            mFile.seek(offset);
+
+            while ((mSignal == null || !mSignal.isCanceled())
+                    && written < size) {
+                int willWrite = Math.min(size - written, mBuffer.capacity());
+                mBuffer.put(data, written, willWrite);
+                int res = mFile.write(mBuffer, willWrite);
+                written += res;
+                mBuffer.clear();
+            }
+        } catch (IOException e) {
+            Log.e(TAG, "Failed to write file.", e);
+        }
+
+        return written;
+    }
+
+    @Override
+    public void onRelease() {
+        mBufferPool.recycleBuffer(mBuffer);
+
+        try {
+            mFile.close();
+        } catch (IOException e) {
+            Log.e(TAG, "Failed to close file");
+        }
+    }
+}

build.gradle

@@ -5,7 +5,7 @@ buildscript {
         jcenter()
     }
     dependencies {
-        classpath 'com.android.tools.build:gradle:2.3.1'
+        classpath 'com.android.tools.build:gradle:2.3.3'
     }
 }