1 files changed, 201 insertions, 0 deletions
diff --git a/mobile/android/exoplayer2/src/main/java/org/mozilla/thirdparty/com/google/android/exoplayer2/util/AtomicFile.java b/mobile/android/exoplayer2/src/main/java/org/mozilla/thirdparty/com/google/android/exoplayer2/util/AtomicFile.java
new file mode 100644
index 0000000000..d868a7d22a
--- /dev/null
+++ b/mobile/android/exoplayer2/src/main/java/org/mozilla/thirdparty/com/google/android/exoplayer2/util/AtomicFile.java
@@ -0,0 +1,201 @@
+/*
+ * Copyright (C) 2016 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 org.mozilla.thirdparty.com.google.android.exoplayer2.util;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileNotFoundException;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+
+/**
+ * A helper class for performing atomic operations on a file by creating a backup file until a write
+ * has successfully completed.
+ *
+ * <p>Atomic file guarantees file integrity by ensuring that a file has been completely written and
+ * synced to disk before removing its backup. As long as the backup file exists, the original file
+ * is considered to be invalid (left over from a previous attempt to write the file).
+ *
+ * <p>Atomic file does not confer any file locking semantics. Do not use this class when the file
+ * may be accessed or modified concurrently by multiple threads or processes. The caller is
+ * responsible for ensuring appropriate mutual exclusion invariants whenever it accesses the file.
+ */
+public final class AtomicFile {
+
+  private static final String TAG = "AtomicFile";
+
+  private final File baseName;
+  private final File backupName;
+
+  /**
+   * Create a new AtomicFile for a file located at the given File path. The secondary backup file
+   * will be the same file path with ".bak" appended.
+   */
+  public AtomicFile(File baseName) {
+    this.baseName = baseName;
+    backupName = new File(baseName.getPath() + ".bak");
+  }
+
+  /** Returns whether the file or its backup exists. */
+  public boolean exists() {
+    return baseName.exists() || backupName.exists();
+  }
+
+  /** Delete the atomic file. This deletes both the base and backup files. */
+  public void delete() {
+    baseName.delete();
+    backupName.delete();
+  }
+
+  /**
+   * Start a new write operation on the file. This returns an {@link OutputStream} to which you can
+   * write the new file data. If the whole data is written successfully you <em>must</em> call
+   * {@link #endWrite(OutputStream)}. On failure you should call {@link OutputStream#close()}
+   * only to free up resources used by it.
+   *
+   * <p>Example usage:
+   *
+   * <pre>
+   *   DataOutputStream dataOutput = null;
+   *   try {
+   *     OutputStream outputStream = atomicFile.startWrite();
+   *     dataOutput = new DataOutputStream(outputStream); // Wrapper stream
+   *     dataOutput.write(data1);
+   *     dataOutput.write(data2);
+   *     atomicFile.endWrite(dataOutput); // Pass wrapper stream
+   *   } finally{
+   *     if (dataOutput != null) {
+   *       dataOutput.close();
+   *     }
+   *   }
+   * </pre>
+   *
+   * <p>Note that if another thread is currently performing a write, this will simply replace
+   * whatever that thread is writing with the new file being written by this thread, and when the
+   * other thread finishes the write the new write operation will no longer be safe (or will be
+   * lost). You must do your own threading protection for access to AtomicFile.
+   */
+  public OutputStream startWrite() throws IOException {
+    // Rename the current file so it may be used as a backup during the next read
+    if (baseName.exists()) {
+      if (!backupName.exists()) {
+        if (!baseName.renameTo(backupName)) {
+          Log.w(TAG, "Couldn't rename file " + baseName + " to backup file " + backupName);
+        }
+      } else {
+        baseName.delete();
+      }
+    }
+    OutputStream str;
+    try {
+      str = new AtomicFileOutputStream(baseName);
+    } catch (FileNotFoundException e) {
+      File parent = baseName.getParentFile();
+      if (parent == null || !parent.mkdirs()) {
+        throw new IOException("Couldn't create " + baseName, e);
+      }
+      // Try again now that we've created the parent directory.
+      try {
+        str = new AtomicFileOutputStream(baseName);
+      } catch (FileNotFoundException e2) {
+        throw new IOException("Couldn't create " + baseName, e2);
+      }
+    }
+    return str;
+  }
+
+  /**
+   * Call when you have successfully finished writing to the stream returned by {@link
+   * #startWrite()}. This will close, sync, and commit the new data. The next attempt to read the
+   * atomic file will return the new file stream.
+   *
+   * @param str Outer-most wrapper OutputStream used to write to the stream returned by {@link
+   *     #startWrite()}.
+   * @see #startWrite()
+   */
+  public void endWrite(OutputStream str) throws IOException {
+    str.close();
+    // If close() throws exception, the next line is skipped.
+    backupName.delete();
+  }
+
+  /**
+   * Open the atomic file for reading. If there previously was an incomplete write, this will roll
+   * back to the last good data before opening for read.
+   *
+   * <p>Note that if another thread is currently performing a write, this will incorrectly consider
+   * it to be in the state of a bad write and roll back, causing the new data currently being
+   * written to be dropped. You must do your own threading protection for access to AtomicFile.
+   */
+  public InputStream openRead() throws FileNotFoundException {
+    restoreBackup();
+    return new FileInputStream(baseName);
+  }
+
+  private void restoreBackup() {
+    if (backupName.exists()) {
+      baseName.delete();
+      backupName.renameTo(baseName);
+    }
+  }
+
+  private static final class AtomicFileOutputStream extends OutputStream {
+
+    private final FileOutputStream fileOutputStream;
+    private boolean closed = false;
+
+    public AtomicFileOutputStream(File file) throws FileNotFoundException {
+      fileOutputStream = new FileOutputStream(file);
+    }
+
+    @Override
+    public void close() throws IOException {
+      if (closed) {
+        return;
+      }
+      closed = true;
+      flush();
+      try {
+        fileOutputStream.getFD().sync();
+      } catch (IOException e) {
+        Log.w(TAG, "Failed to sync file descriptor:", e);
+      }
+      fileOutputStream.close();
+    }
+
+    @Override
+    public void flush() throws IOException {
+      fileOutputStream.flush();
+    }
+
+    @Override
+    public void write(int b) throws IOException {
+      fileOutputStream.write(b);
+    }
+
+    @Override
+    public void write(byte[] b) throws IOException {
+      fileOutputStream.write(b);
+    }
+
+    @Override
+    public void write(byte[] b, int off, int len) throws IOException {
+      fileOutputStream.write(b, off, len);
+    }
+  }
+}