content: /*
   * Copyright (C) 2009 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 android.app.backup;
  
  import android.os.ParcelFileDescriptor;
  
  /**
   * Defines the calling interface that {@link BackupAgentHelper} uses
   * when dispatching backup and restore operations to the installed helpers.
   * Applications can define and install their own helpers as well as using those
   * provided as part of the Android framework.
   * <p>
   * Although multiple helper objects may be installed simultaneously, each helper
   * is responsible only for handling its own data, and will not see entities
   * created by other components within the backup system.  Invocations of multiple
   * helpers are performed sequentially by the {@link BackupAgentHelper}, with each
   * helper given a chance to access its own saved state from within the state record
   * produced during the previous backup operation.
   *
   * @see BackupAgentHelper
   * @see FileBackupHelper
   * @see SharedPreferencesBackupHelper
   */
  public interface BackupHelper {
      /**
       * Based on <code>oldState</code>, determine what application content
       * needs to be backed up, write it to <code>data</code>, and fill in
       * <code>newState</code> with the complete state as it exists now.
       * <p>
       * Implementing this method is much like implementing
       * {@link BackupAgent#onBackup(ParcelFileDescriptor, BackupDataOutput, ParcelFileDescriptor)
       * onBackup()} &mdash; the method parameters are the same.  When this method is invoked the
       * {@code oldState} descriptor points to the beginning of the state data
       * written during this helper's previous backup operation, and the {@code newState}
       * descriptor points to the file location at which the helper should write its
       * new state after performing the backup operation.
       * <p class="note">
       * <strong>Note:</strong> The helper should not close or seek either the {@code oldState} or
       * the {@code newState} file descriptors.  It is essential that when reading the helper's
       * saved state from the {@code oldState} file, no extra content is consumed beyond
       * what was stored by this helper.  If more old state data is read, even accidentally,
       * it will make it impossible for additional helpers that may be invoked after this one
       * to properly reconstruct their prior state.</p>
       *
       * @param oldState An open, read-only {@link android.os.ParcelFileDescriptor} pointing to the
       *            last backup state provided by the application. May be
       *            <code>null</code>, in which case no prior state is being
       *            provided and the application should perform a full backup.
       * @param data An open, read/write {@link BackupDataOutput}
       *            pointing to the backup data destination.
       *            Typically the application will use backup helper classes to
       *            write to this file.
       * @param newState An open, read/write {@link android.os.ParcelFileDescriptor} pointing to an
       *            empty file. The application should record the final backup
       *            state here after writing the requested data to the <code>data</code>
       *            output stream.
       */
      public void performBackup(ParcelFileDescriptor oldState, BackupDataOutput data,
              ParcelFileDescriptor newState);
  
      /**
       * Called by {@link android.app.backup.BackupAgentHelper BackupAgentHelper}
       * to restore a single entity from the restore data set.  This method will be
       * called for each entity in the data set that belongs to this handler.
       * <p class="note">
       * <strong>Note:</strong> Do not close the <code>data</code> stream.  Do not read more than
       * {@link android.app.backup.BackupDataInputStream#size() size()} bytes from
       * <code>data</code>.</p>
       *
       * @param data An open {@link BackupDataInputStream} from which the backup data can be read.
       */
      public void restoreEntity(BackupDataInputStream data);
  
      /**
       * Called by {@link android.app.backup.BackupAgentHelper BackupAgentHelper}
       * after a restore operation to write the backup state file corresponding to
       * the data as processed by the helper.  The data written here will be
       * available to the helper during the next call to its
       * {@link #performBackup(ParcelFileDescriptor, BackupDataOutput, ParcelFileDescriptor)
       * performBackup()} method.
       * <p>
       * This method will be called even if the handler's
       * {@link #restoreEntity(BackupDataInputStream) restoreEntity()} method was never invoked during
       * the restore operation.
       * <p class="note">
       * <strong>Note:</strong> The helper should not close or seek the {@code newState}
       * file descriptor.</p>
       *
       * @param newState A {@link android.os.ParcelFileDescriptor} to which the new state will be
       * written.
       */
      public void writeNewStateDescription(ParcelFileDescriptor newState);
  }
  
  