BackupAgent.java

/*
 * 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;

import android.app.IBackupAgent;
import android.backup.BackupDataInput;
import android.backup.BackupDataOutput;
import android.content.Context;
import android.content.ContextWrapper;
import android.os.IBinder;
import android.os.ParcelFileDescriptor;
import android.os.RemoteException;
import android.util.Log;

import java.io.IOException;

/**
 * This is the central interface between an application and Android's
 * settings backup mechanism.
 * 
 * @hide pending API solidification
 */
public abstract class BackupAgent extends ContextWrapper {
    private static final String TAG = "BackupAgent";
    private static final boolean DEBUG = false;

    public BackupAgent() {
        super(null);
    }

    public void onCreate() {
    }

    public void onDestroy() {
    }

    /**
     * The application is being asked to write any data changed since the
     * last time it performed a backup operation.  The state data recorded
     * during the last backup pass is provided in the oldState file descriptor.
     * If oldState is null, no old state is available and the application should perform
     * a full backup.  In both cases, a representation of the final backup state after
     * this pass should be written to the file pointed to by the newStateFd file descriptor.
     *
     * @param oldState An open, read-only ParcelFileDescriptor pointing to the last backup
     *                 state provided by the application.  May be null, in which
     *                 case no prior state is being provided and the application should
     *                 perform a full backup.
     * @param data An open, read/write ParcelFileDescriptor 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 ParcelFileDescriptor pointing to an empty
     *                 file.  The application should record the final backup state
     *                 here after writing the requested data to dataFd.
     */
    public abstract void onBackup(ParcelFileDescriptor oldState, BackupDataOutput data,
             ParcelFileDescriptor newState) throws IOException;
    
    /**
     * The application is being restored from backup, and should replace any
     * existing data with the contents of the backup.  The backup data is
     * provided in the file pointed to by the dataFd file descriptor.  Once
     * the restore is finished, the application should write a representation
     * of the final state to the newStateFd file descriptor, 
     *
     * @param data An open, read-only ParcelFileDescriptor pointing to a full snapshot
     *             of the application's data.
     * @param appVersionCode The android:versionCode value of the application that backed
     *        up this particular data set.  This makes it easier for an application's
     *        agent to distinguish among several possible older data versions when
     *        asked to perform the restore operation.
     * @param newState An open, read/write ParcelFileDescriptor pointing to an empty
     *                 file.  The application should record the final backup state
     *                 here after restoring its data from dataFd.
     */
    public abstract void onRestore(BackupDataInput data, int appVersionCode,
            ParcelFileDescriptor newState)
            throws IOException;


    // ----- Core implementation -----
    
    /**
     * Returns the private interface called by the backup system.  Applications will
     * not typically override this.
     */
    public IBinder onBind() {
        return mBinder;
    }

    private final IBinder mBinder = new BackupServiceBinder().asBinder();

    /** @hide */
    public void attach(Context context) {
        attachBaseContext(context);
    }

    // ----- IBackupService binder interface -----
    private class BackupServiceBinder extends IBackupAgent.Stub {
        private static final String TAG = "BackupServiceBinder";

        public void doBackup(ParcelFileDescriptor oldState,
                ParcelFileDescriptor data,
                ParcelFileDescriptor newState) throws RemoteException {
            // !!! TODO - real implementation; for now just invoke the callbacks directly
            if (DEBUG) Log.v(TAG, "doBackup() invoked");
            BackupDataOutput output = new BackupDataOutput(data.getFileDescriptor());
            try {
                BackupAgent.this.onBackup(oldState, output, newState);
            } catch (IOException ex) {
                Log.d(TAG, "onBackup (" + BackupAgent.this.getClass().getName() + ") threw", ex);
                throw new RuntimeException(ex);
            } catch (RuntimeException ex) {
                Log.d(TAG, "onBackup (" + BackupAgent.this.getClass().getName() + ") threw", ex);
                throw ex;
            }
        }

        public void doRestore(ParcelFileDescriptor data, int appVersionCode,
                ParcelFileDescriptor newState) throws RemoteException {
            // !!! TODO - real implementation; for now just invoke the callbacks directly
            if (DEBUG) Log.v(TAG, "doRestore() invoked");
            BackupDataInput input = new BackupDataInput(data.getFileDescriptor());
            try {
                BackupAgent.this.onRestore(input, appVersionCode, newState);
            } catch (IOException ex) {
                Log.d(TAG, "onRestore (" + BackupAgent.this.getClass().getName() + ") threw", ex);
                throw new RuntimeException(ex);
            } catch (RuntimeException ex) {
                Log.d(TAG, "onRestore (" + BackupAgent.this.getClass().getName() + ") threw", ex);
                throw ex;
            }
        }
    }
}