core/java/android/app/backup/WallpaperBackupHelper.java

/*
 * Copyright (C) 2010 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.app.WallpaperManager;
import android.content.Context;
import android.graphics.BitmapFactory;
import android.graphics.Point;
import android.os.Environment;
import android.os.ParcelFileDescriptor;
import android.os.UserHandle;
import android.util.Slog;
import android.view.Display;
import android.view.WindowManager;

import java.io.File;

/**
 * Helper for backing up / restoring wallpapers.  Basically an AbsoluteFileBackupHelper,
 * but with logic for deciding what to do with restored wallpaper images.
 *
 * @hide
 */
public class WallpaperBackupHelper extends FileBackupHelperBase implements BackupHelper {
    private static final String TAG = "WallpaperBackupHelper";
    private static final boolean DEBUG = false;

    // If 'true', then apply an acceptable-size heuristic at restore time, dropping back
    // to the factory default wallpaper if the restored one differs "too much" from the
    // device's preferred wallpaper image dimensions.
    private static final boolean REJECT_OUTSIZED_RESTORE = true;

    // When outsized restore rejection is enabled, this is the maximum ratio between the
    // source and target image heights that will be permitted.  The ratio is checked both
    // ways (i.e. >= MAX, or <= 1/MAX) to validate restores from both largeer-than-target
    // and smaller-than-target sources.
    private static final double MAX_HEIGHT_RATIO = 1.35;

    // The height ratio check when applying larger images on smaller screens is separate;
    // in current policy we accept any such restore regardless of the relative dimensions.
    private static final double MIN_HEIGHT_RATIO = 0;

    // This path must match what the WallpaperManagerService uses
    // TODO: Will need to change if backing up non-primary user's wallpaper
    // http://b/22388012
    public static final String WALLPAPER_IMAGE =
            new File(Environment.getUserSystemDirectory(UserHandle.USER_SYSTEM),
                    "wallpaper").getAbsolutePath();
    public static final String WALLPAPER_INFO =
            new File(Environment.getUserSystemDirectory(UserHandle.USER_SYSTEM),
                    "wallpaper_info.xml").getAbsolutePath();
    // Use old keys to keep legacy data compatibility and avoid writing two wallpapers
    public static final String WALLPAPER_IMAGE_KEY =
            "/data/data/com.android.settings/files/wallpaper";
    public static final String WALLPAPER_INFO_KEY = "/data/system/wallpaper_info.xml";

    // Stage file - should be adjacent to the WALLPAPER_IMAGE location.  The wallpapers
    // will be saved to this file from the restore stream, then renamed to the proper
    // location if it's deemed suitable.
    // TODO: Will need to change if backing up non-primary user's wallpaper
    // http://b/22388012
    private static final String STAGE_FILE =
            new File(Environment.getUserSystemDirectory(UserHandle.USER_SYSTEM),
                    "wallpaper-tmp").getAbsolutePath();

    Context mContext;
    String[] mFiles;
    String[] mKeys;
    double mDesiredMinWidth;
    double mDesiredMinHeight;

    /**
     * Construct a helper for backing up / restoring the files at the given absolute locations
     * within the file system.
     *
     * @param context
     * @param files
     */
    public WallpaperBackupHelper(Context context, String[] files, String[] keys) {
        super(context);

        mContext = context;
        mFiles = files;
        mKeys = keys;

        final WindowManager wm =
                (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
        final WallpaperManager wpm =
                (WallpaperManager) context.getSystemService(Context.WALLPAPER_SERVICE);
        final Display d = wm.getDefaultDisplay();
        final Point size = new Point();
        d.getSize(size);
        mDesiredMinWidth = Math.min(size.x, size.y);
        mDesiredMinHeight = (double) wpm.getDesiredMinimumHeight();
        if (mDesiredMinHeight <= 0) {
            mDesiredMinHeight = size.y;
        }

        if (DEBUG) {
            Slog.d(TAG, "dmW=" + mDesiredMinWidth + " dmH=" + mDesiredMinHeight);
        }
    }

    /**
     * Based on oldState, determine which of the files from the application's data directory
     * need to be backed up, write them to the data stream, and fill in newState with the
     * state as it exists now.
     */
    @Override
    public void performBackup(ParcelFileDescriptor oldState, BackupDataOutput data,
            ParcelFileDescriptor newState) {
        performBackup_checked(oldState, data, newState, mFiles, mKeys);
    }

    /**
     * Restore one absolute file entity from the restore stream.  If we're restoring the
     * magic wallpaper file, take specific action to determine whether it is suitable for
     * the current device.
     */
    @Override
    public void restoreEntity(BackupDataInputStream data) {
        final String key = data.getKey();
        if (isKeyInList(key, mKeys)) {
            if (key.equals(WALLPAPER_IMAGE_KEY)) {
                // restore the file to the stage for inspection
                File f = new File(STAGE_FILE);
                if (writeFile(f, data)) {

                    // Preflight the restored image's dimensions without loading it
                    BitmapFactory.Options options = new BitmapFactory.Options();
                    options.inJustDecodeBounds = true;
                    BitmapFactory.decodeFile(STAGE_FILE, options);

                    if (DEBUG) Slog.d(TAG, "Restoring wallpaper image w=" + options.outWidth
                            + " h=" + options.outHeight);

                    if (REJECT_OUTSIZED_RESTORE) {
                        // We accept any wallpaper that is at least as wide as our preference
                        // (i.e. wide enough to fill the screen), and is within a comfortable
                        // factor of the target height, to avoid significant clipping/scaling/
                        // letterboxing.  At this point we know that mDesiredMinWidth is the
                        // smallest dimension, regardless of current orientation, so we can
                        // safely require that the candidate's width and height both exceed
                        // that hard minimum.
                        final double heightRatio = mDesiredMinHeight / options.outHeight;
                        if (options.outWidth < mDesiredMinWidth
                                || options.outHeight < mDesiredMinWidth
                                || heightRatio >= MAX_HEIGHT_RATIO
                                || heightRatio <= MIN_HEIGHT_RATIO) {
                            // Not wide enough for the screen, or too short/tall to be a good fit
                            // for the height of the screen, broken image file, or the system's
                            // desires for wallpaper size are in a bad state.  Probably one of the
                            // first two.
                            Slog.i(TAG, "Restored image dimensions (w="
                                    + options.outWidth + ", h=" + options.outHeight
                                    + ") too far off target (tw="
                                    + mDesiredMinWidth + ", th=" + mDesiredMinHeight
                                    + "); falling back to default wallpaper.");
                            f.delete();
                            return;
                        }
                    }

                    // We passed the acceptable-dimensions test (if any), so we're going to
                    // use the restored image.  That comes last, when we are done restoring
                    // both the pixels and the metadata.
                }
            } else if (key.equals(WALLPAPER_INFO_KEY)) {
                // XML file containing wallpaper info
                File f = new File(WALLPAPER_INFO);
                writeFile(f, data);
            }
        }
    }

    /**
     * Hook for the agent to call this helper upon completion of the restore.  We do this
     * upon completion so that we know both the imagery and the wallpaper info have
     * been emplaced without requiring either or relying on ordering.
     */
    public void onRestoreFinished() {
        final File f = new File(STAGE_FILE);
        if (f.exists()) {
            // TODO: spin a service to copy the restored image to sd/usb storage,
            // since it does not exist anywhere other than the private wallpaper
            // file.
            Slog.d(TAG, "Applying restored wallpaper image.");
            f.renameTo(new File(WALLPAPER_IMAGE));
        }
    }
}