add a backup agent.

backup only, restore path is just debugging/verification.
todo: restore path
todo: additional asset backup for widgets and launcher items

Bug: 10778984
Change-Id: I01aed4794a02f03daf21bca28f99cfbea90e4967

5 files changed, 784 insertions, 6 deletions

diff --git a/Android.mk b/Android.mk
index 016d151a9..10c9f2447 100644
--- a/Android.mk
+++ b/Android.mk
@@ -21,7 +21,13 @@ LOCAL_MODULE_TAGS := optional
 
 LOCAL_STATIC_JAVA_LIBRARIES := android-support-v13
 
-LOCAL_SRC_FILES := $(call all-java-files-under, src) $(call all-renderscript-files-under, src)
+LOCAL_SRC_FILES := $(call all-java-files-under, src) $(call all-renderscript-files-under, src) \
+    $(call all-proto-files-under, protos)
+
+LOCAL_PROTOC_OPTIMIZE_TYPE := nano
+
+LOCAL_PROTOC_FLAGS := --proto_path=$(LOCAL_PATH)/protos
+
 LOCAL_SDK_VERSION := 17
 
 LOCAL_PACKAGE_NAME := Launcher3
diff --git a/protos/backup.proto b/protos/backup.proto
new file mode 100644
index 000000000..3780bc583
--- /dev/null
+++ b/protos/backup.proto
@@ -0,0 +1,76 @@
+/*
+ * Copyright (C) 2013 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 launcher_backup;
+
+option java_package = "com.android.launcher3.backup";
+option java_outer_classname = "BackupProtos";
+
+message Key {
+  enum Type {
+    FAVORITE = 1;
+    SCREEN = 2;
+    IMAGE = 3;
+  }
+  required Type type = 1;
+  optional string name = 2;  // keep this short
+  optional int64 id = 3;
+  optional int64 checksum = 4;
+}
+
+message CheckedMessage {
+  required bytes payload = 1;
+  required int64 checksum = 2;
+}
+
+message Journal {
+  required int32 app_version = 1;
+  required int64 t = 2;
+  optional int64 bytes = 3;
+  optional int32 rows = 4;
+  repeated Key key = 5;
+}
+
+message Favorite {
+  required int64 id = 1;
+  required int32 itemType = 2;
+  optional string title = 3;
+  optional int32 container = 4;
+  optional int32 screen = 5;
+  optional int32 cellX = 6;
+  optional int32 cellY = 7;
+  optional int32 spanX = 8;
+  optional int32 spanY = 9;
+  optional int32 displayMode = 10;
+  optional int32 appWidgetId = 11;
+  optional string appWidgetProvider = 12;
+  optional string intent = 13;
+  optional string uri = 14;
+  optional int32 iconType = 15;
+  optional string iconPackage = 16;
+  optional string iconResource = 17;
+  optional bytes icon = 18;
+ }
+
+message Screen {
+  required int64 id = 1;
+  optional int32 rank = 2;
+ }
+
+message Resource {
+  required int32 dpi = 2;
+  required bytes data = 3;
+ }
diff --git a/src/com/android/launcher3/LauncherBackupAgent.java b/src/com/android/launcher3/LauncherBackupAgent.java
new file mode 100644
index 000000000..bb15ca184
--- /dev/null
+++ b/src/com/android/launcher3/LauncherBackupAgent.java
@@ -0,0 +1,655 @@
+/*
+ * Copyright (C) 2013 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 com.android.launcher3;
+
+import com.google.protobuf.nano.InvalidProtocolBufferNanoException;
+import com.google.protobuf.nano.MessageNano;
+
+import com.android.launcher3.LauncherSettings.ChangeLogColumns;
+import com.android.launcher3.LauncherSettings.Favorites;
+import com.android.launcher3.LauncherSettings.WorkspaceScreens;
+import com.android.launcher3.backup.BackupProtos;
+import com.android.launcher3.backup.BackupProtos.CheckedMessage;
+import com.android.launcher3.backup.BackupProtos.Favorite;
+import com.android.launcher3.backup.BackupProtos.Journal;
+import com.android.launcher3.backup.BackupProtos.Key;
+import com.android.launcher3.backup.BackupProtos.Screen;
+
+import android.app.backup.BackupAgent;
+import android.app.backup.BackupDataInput;
+import android.app.backup.BackupDataOutput;
+import android.app.backup.BackupManager;
+import android.content.ContentResolver;
+import android.content.Context;
+import android.database.Cursor;
+import android.os.ParcelFileDescriptor;
+import android.provider.BaseColumns;
+import android.text.TextUtils;
+import android.util.Base64;
+import android.util.Log;
+
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.Set;
+import java.util.zip.CRC32;
+
+/**
+ * Persist the launcher home state across calamities.
+ */
+public class LauncherBackupAgent extends BackupAgent {
+
+    private static final String TAG = "LauncherBackupAgent";
+    private static final boolean DEBUG = false;
+
+    private static final int MAX_JOURNAL_SIZE = 1000000;
+
+    private static BackupManager sBackupManager;
+
+    private static final String[] FAVORITE_PROJECTION = {
+            Favorites._ID,                     // 0
+            Favorites.APPWIDGET_ID,            // 1
+            Favorites.APPWIDGET_PROVIDER,      // 2
+            Favorites.CELLX,                   // 3
+            Favorites.CELLY,                   // 4
+            Favorites.CONTAINER,               // 5
+            Favorites.ICON,                    // 6
+            Favorites.ICON_PACKAGE,            // 7
+            Favorites.ICON_RESOURCE,           // 8
+            Favorites.ICON_TYPE,               // 9
+            Favorites.ITEM_TYPE,               // 10
+            Favorites.INTENT,                  // 11
+            Favorites.SCREEN,                  // 12
+            Favorites.SPANX,                   // 13
+            Favorites.SPANY,                   // 14
+            Favorites.TITLE,                   // 15
+    };
+
+    private static final int ID_INDEX = 0;
+    private static final int APPWIDGET_ID_INDEX = 1;
+    private static final int APPWIDGET_PROVIDER_INDEX = 2;
+    private static final int CELLX_INDEX = 3;
+    private static final int CELLY_INDEX = 4;
+    private static final int CONTAINER_INDEX = 5;
+    private static final int ICON_INDEX = 6;
+    private static final int ICON_PACKAGE_INDEX = 7;
+    private static final int ICON_RESOURCE_INDEX = 8;
+    private static final int ICON_TYPE_INDEX = 9;
+    private static final int ITEM_TYPE_INDEX = 10;
+    private static final int INTENT_INDEX = 11;
+    private static final int SCREEN_INDEX = 12;
+    private static final int SPANX_INDEX = 13 ;
+    private static final int SPANY_INDEX = 14;
+    private static final int TITLE_INDEX = 15;
+
+    private static final String[] SCREEN_PROJECTION = {
+            WorkspaceScreens._ID,              // 0
+            WorkspaceScreens.SCREEN_RANK       // 1
+    };
+
+    private static final int SCREEN_RANK_INDEX = 1;
+
+    private static final String[] ID_ONLY_PROJECTION = {
+            BaseColumns._ID
+    };
+
+
+    /**
+     * Notify the backup manager that out database is dirty.
+     *
+     * <P>This does not force an immediate backup.
+     *
+     * @param context application context
+     */
+    public static void dataChanged(Context context) {
+        if (sBackupManager == null) {
+            sBackupManager = new BackupManager(context);
+        }
+        sBackupManager.dataChanged();
+    }
+
+    /**
+     * Back up launcher data so we can restore the user's state on a new device.
+     *
+     * <P>The journal is a timestamp and a list of keys that were saved as of that time.
+     *
+     * <P>Keys may come back in any order, so each key/value is one complete row of the database.
+     *
+     * @param oldState notes from the last backup
+     * @param data incremental key/value pairs to persist off-device
+     * @param newState notes for the next backup
+     * @throws IOException
+     */
+    @Override
+    public void onBackup(ParcelFileDescriptor oldState, BackupDataOutput data,
+            ParcelFileDescriptor newState)
+            throws IOException {
+        Log.v(TAG, "onBackup");
+
+        Journal in = readJournal(oldState);
+        Journal out = new Journal();
+
+        long lastBackupTime = in.t;
+        out.t = System.currentTimeMillis();
+        out.rows = 0;
+        out.bytes = 0;
+
+        Log.v(TAG, "lastBackupTime=" + lastBackupTime);
+
+        ArrayList<Key> keys = new ArrayList<Key>();
+        backupFavorites(in, data, out, keys);
+        backupScreens(in, data, out, keys);
+
+        out.key = keys.toArray(BackupProtos.Key.EMPTY_ARRAY);
+        writeJournal(newState, out);
+        Log.v(TAG, "onBackup: wrote " + out.bytes + "b in " + out.rows + " rows.");
+
+        Log.v(TAG, "onBackup: finished");
+    }
+
+    /**
+     * Restore home screen from the restored data stream.
+     *
+     * <P>Keys may arrive in any order.
+     *
+     * @param data the key/value pairs from the server
+     * @param versionCode the version of the app that generated the data
+     * @param newState notes for the next backup
+     * @throws IOException
+     */
+    @Override
+    public void onRestore(BackupDataInput data, int versionCode, ParcelFileDescriptor newState)
+            throws IOException {
+        Log.v(TAG, "onRestore");
+        int numRows = 0;
+        Journal out = new Journal();
+
+        ArrayList<Key> keys = new ArrayList<Key>();
+        byte[] buffer = new byte[512];
+        while (data.readNextHeader()) {
+            numRows++;
+            String backupKey = data.getKey();
+            int dataSize = data.getDataSize();
+            if (buffer.length < dataSize) {
+                buffer = new byte[dataSize];
+            }
+            Key key = null;
+            int bytesRead = data.readEntityData(buffer, 0, dataSize);
+            if (DEBUG) {
+                Log.d(TAG, "read " + bytesRead + " of " + dataSize + " available");
+            }
+            try {
+                key = backupKeyToKey(backupKey);
+                switch (key.type) {
+                    case Key.FAVORITE:
+                        restoreFavorite(key, buffer, dataSize, keys);
+                        break;
+
+                    case Key.SCREEN:
+                        restoreScreen(key, buffer, dataSize, keys);
+                        break;
+
+                    default:
+                        Log.w(TAG, "unknown restore entity type: " + key.type);
+                        break;
+                }
+            } catch (KeyParsingException e) {
+                Log.w(TAG, "ignoring unparsable backup key: " + backupKey);
+            }
+        }
+
+        // clear the output journal time, to force a full backup to
+        // will catch any changes the restore process might have made
+        out.t = 0;
+        out.key = keys.toArray(BackupProtos.Key.EMPTY_ARRAY);
+        writeJournal(newState, out);
+        Log.v(TAG, "onRestore: read " + numRows + " rows");
+    }
+
+    /**
+     * Write all modified favorites to the data stream.
+     *
+     *
+     * @param in notes from last backup
+     * @param data output stream for key/value pairs
+     * @param out notes about this backup
+     * @param keys keys to mark as clean in the notes for next backup
+     * @throws IOException
+     */
+    private void backupFavorites(Journal in, BackupDataOutput data, Journal out,
+            ArrayList<Key> keys)
+            throws IOException {
+        // read the old ID set
+        Set<String> savedIds = new HashSet<String>();
+        for(int i = 0; i < in.key.length; i++) {
+            Key key = in.key[i];
+            if (key.type == Key.FAVORITE) {
+                savedIds.add(keyToBackupKey(key));
+            }
+        }
+        if (DEBUG) Log.d(TAG, "favorite savedIds.size()=" + savedIds.size());
+
+        // persist things that have changed since the last backup
+        ContentResolver cr = getContentResolver();
+        String where = ChangeLogColumns.MODIFIED + " > ?";
+        String[] args = {Long.toString(in.t)};
+        String updateOrder = ChangeLogColumns.MODIFIED;
+        Cursor updated = cr.query(Favorites.CONTENT_URI, FAVORITE_PROJECTION,
+                where, args, updateOrder);
+        if (DEBUG) Log.d(TAG, "favorite updated.getCount()=" + updated.getCount());
+        try {
+            updated.moveToPosition(-1);
+            while(updated.moveToNext()) {
+                final long id = updated.getLong(ID_INDEX);
+                Key key = getKey(Key.FAVORITE, id);
+                byte[] blob = packFavorite(updated);
+                String backupKey = keyToBackupKey(key);
+                data.writeEntityHeader(backupKey, blob.length);
+                data.writeEntityData(blob, blob.length);
+                out.rows++;
+                out.bytes += blob.length;
+                Log.v(TAG, "saving favorite " + backupKey + ": " + id + "/" + blob.length);
+                if(DEBUG) Log.d(TAG, "wrote " +
+                        Base64.encodeToString(blob, 0, blob.length, Base64.NO_WRAP));
+                // remember that is was a new column, so we don't delete it.
+                savedIds.add(backupKey);
+            }
+        } finally {
+            updated.close();
+        }
+        if (DEBUG) Log.d(TAG, "favorite savedIds.size()=" + savedIds.size());
+
+        // build the current ID set
+        String idOrder = BaseColumns._ID;
+        Cursor idCursor = cr.query(Favorites.CONTENT_URI, ID_ONLY_PROJECTION,
+                null, null, idOrder);
+        Set<String> currentIds = new HashSet<String>(idCursor.getCount());
+        try {
+            idCursor.moveToPosition(-1);
+            while(idCursor.moveToNext()) {
+                Key key = getKey(Key.FAVORITE, idCursor.getLong(ID_INDEX));
+                currentIds.add(keyToBackupKey(key));
+                // save the IDs for next time
+                keys.add(key);
+            }
+        } finally {
+            idCursor.close();
+        }
+        if (DEBUG) Log.d(TAG, "favorite currentIds.size()=" + currentIds.size());
+
+        // these IDs must have been deleted
+        savedIds.removeAll(currentIds);
+        for (String deleted : savedIds) {
+            Log.v(TAG, "dropping favorite " + deleted);
+            data.writeEntityHeader(deleted, -1);
+            out.rows++;
+        }
+    }
+
+    /**
+     * Read a favorite from the stream.
+     *
+     * <P>Keys arrive in any order, so screens and containers may not exist yet.
+     *
+     * @param key identifier for the row
+     * @param buffer the serialized proto from the stream, may be larger than dataSize
+     * @param dataSize the size of the proto from the stream
+     * @param keys keys to mark as clean in the notes for next backup
+     */
+    private void restoreFavorite(Key key, byte[] buffer, int dataSize, ArrayList<Key> keys) {
+        Log.v(TAG, "unpacking favorite " + key.id + " (" + dataSize + " bytes)");
+        if (DEBUG) Log.d(TAG, "read (" + buffer.length + "): " +
+                Base64.encodeToString(buffer, 0, dataSize, Base64.NO_WRAP));
+
+        try {
+            Favorite favorite =  unpackFavorite(buffer, 0, dataSize);
+            if (DEBUG) Log.d(TAG, "unpacked " + favorite.itemType);
+        } catch (InvalidProtocolBufferNanoException e) {
+            Log.w(TAG, "failed to decode proto", e);
+        }
+    }
+
+    /**
+     * Write all modified screens to the data stream.
+     *
+     *
+     * @param in notes from last backup
+     * @param data output stream for key/value pairs
+     * @param out notes about this backup
+     * @param keys keys to mark as clean in the notes for next backup  @throws IOException
+     */
+    private void backupScreens(Journal in, BackupDataOutput data, Journal out,
+            ArrayList<Key> keys)
+            throws IOException {
+        // read the old ID set
+        Set<String> savedIds = new HashSet<String>();
+        for(int i = 0; i < in.key.length; i++) {
+            Key key = in.key[i];
+            if (key.type == Key.SCREEN) {
+                savedIds.add(keyToBackupKey(key));
+            }
+        }
+        if (DEBUG) Log.d(TAG, "screens savedIds.size()=" + savedIds.size());
+
+        // persist things that have changed since the last backup
+        ContentResolver cr = getContentResolver();
+        String where = ChangeLogColumns.MODIFIED + " > ?";
+        String[] args = {Long.toString(in.t)};
+        String updateOrder = ChangeLogColumns.MODIFIED;
+        Cursor updated = cr.query(WorkspaceScreens.CONTENT_URI, SCREEN_PROJECTION,
+                where, args, updateOrder);
+        updated.moveToPosition(-1);
+        if (DEBUG) Log.d(TAG, "screens updated.getCount()=" + updated.getCount());
+        try {
+            while(updated.moveToNext()) {
+                final long id = updated.getLong(ID_INDEX);
+                Key key = getKey(Key.SCREEN, id);
+                byte[] blob = packScreen(updated);
+                String backupKey = keyToBackupKey(key);
+                data.writeEntityHeader(backupKey, blob.length);
+                data.writeEntityData(blob, blob.length);
+                out.rows++;
+                out.bytes += blob.length;
+                Log.v(TAG, "saving screen " + backupKey + ": " + id + "/" + blob.length);
+                if(DEBUG) Log.d(TAG, "wrote " +
+                        Base64.encodeToString(blob, 0, blob.length, Base64.NO_WRAP));
+                // remember that is was a new column, so we don't delete it.
+                savedIds.add(backupKey);
+            }
+        } finally {
+            updated.close();
+        }
+        if (DEBUG) Log.d(TAG, "screen savedIds.size()=" + savedIds.size());
+
+        // build the current ID set
+        String idOrder = BaseColumns._ID;
+        Cursor idCursor = cr.query(WorkspaceScreens.CONTENT_URI, ID_ONLY_PROJECTION,
+                null, null, idOrder);
+        idCursor.moveToPosition(-1);
+        Set<String> currentIds = new HashSet<String>(idCursor.getCount());
+        try {
+            while(idCursor.moveToNext()) {
+                Key key = getKey(Key.SCREEN, idCursor.getLong(ID_INDEX));
+                currentIds.add(keyToBackupKey(key));
+                // save the IDs for next time
+                keys.add(key);
+            }
+        } finally {
+            idCursor.close();
+        }
+        if (DEBUG) Log.d(TAG, "screen currentIds.size()=" + currentIds.size());
+
+        // these IDs must have been deleted
+        savedIds.removeAll(currentIds);
+        for(String deleted: savedIds) {
+            Log.v(TAG, "dropping screen " + deleted);
+            data.writeEntityHeader(deleted, -1);
+            out.rows++;
+        }
+    }
+
+    /**
+     * Read a screen from the stream.
+     *
+     * <P>Keys arrive in any order, so children of this screen may already exist.
+     *
+     * @param key identifier for the row
+     * @param buffer the serialized proto from the stream, may be larger than dataSize
+     * @param dataSize the size of the proto from the stream
+     * @param keys keys to mark as clean in the notes for next backup
+     */
+    private void restoreScreen(Key key, byte[] buffer, int dataSize, ArrayList<Key> keys) {
+        Log.v(TAG, "unpacking screen " + key.id);
+        if (DEBUG) Log.d(TAG, "read (" + buffer.length + "): " +
+                Base64.encodeToString(buffer, 0, dataSize, Base64.NO_WRAP));
+        try {
+            Screen screen = unpackScreen(buffer, 0, dataSize);
+            if (DEBUG) Log.d(TAG, "unpacked " + screen.rank);
+        } catch (InvalidProtocolBufferNanoException e) {
+            Log.w(TAG, "failed to decode proto", e);
+        }
+    }
+
+    /** create a new key object.
+     *
+     * <P> Keys contain their own checksum instead of using
+     * the heavy-weight CheckedMessage wrapper.
+     */
+    private Key getKey(int type, long id) {
+        Key key = new Key();
+        key.type = type;
+        key.id = id;
+        key.checksum = checkKey(key);
+        return key;
+    }
+
+    /** keys need to be strings, serialize and encode. */
+    private String keyToBackupKey(Key key) {
+        return Base64.encodeToString(Key.toByteArray(key), Base64.NO_WRAP | Base64.NO_PADDING);
+    }
+
+    /** keys need to be strings, decode and parse. */
+    private Key backupKeyToKey(String backupKey) throws KeyParsingException {
+        try {
+            Key key = Key.parseFrom(Base64.decode(backupKey, Base64.DEFAULT));
+            if (key.checksum != checkKey(key)) {
+                key = null;
+                throw new KeyParsingException("invalid key read from stream" + backupKey);
+            }
+            return key;
+        } catch (InvalidProtocolBufferNanoException e) {
+            throw new KeyParsingException(e);
+        } catch (IllegalArgumentException e) {
+            throw new KeyParsingException(e);
+        }
+    }
+
+    /** Compute the checksum over the important bits of a key. */
+    private long checkKey(Key key) {
+        CRC32 checksum = new CRC32();
+        checksum.update(key.type);
+        checksum.update((int) (key.id & 0xffff));
+        checksum.update((int) ((key.id >> 32) & 0xffff));
+        if (!TextUtils.isEmpty(key.name)) {
+            checksum.update(key.name.getBytes());
+        }
+        return checksum.getValue();
+    }
+
+    /** Serialize a Favorite for persistence, including a checksum wrapper. */
+    private byte[] packFavorite(Cursor c) {
+        Favorite favorite = new Favorite();
+        favorite.id = c.getLong(ID_INDEX);
+        favorite.screen = c.getInt(SCREEN_INDEX);
+        favorite.container = c.getInt(CONTAINER_INDEX);
+        favorite.cellX = c.getInt(CELLX_INDEX);
+        favorite.cellY = c.getInt(CELLY_INDEX);
+        favorite.spanX = c.getInt(SPANX_INDEX);
+        favorite.spanY = c.getInt(SPANY_INDEX);
+        favorite.iconType = c.getInt(ICON_TYPE_INDEX);
+        if (favorite.iconType == Favorites.ICON_TYPE_RESOURCE) {
+            String iconPackage = c.getString(ICON_PACKAGE_INDEX);
+            if (!TextUtils.isEmpty(iconPackage)) {
+                favorite.iconPackage = iconPackage;
+            }
+            String iconResource = c.getString(ICON_RESOURCE_INDEX);
+            if (!TextUtils.isEmpty(iconResource)) {
+                favorite.iconResource = iconResource;
+            }
+        }
+        if (favorite.iconType == Favorites.ICON_TYPE_BITMAP) {
+            byte[] blob = c.getBlob(ICON_INDEX);
+            if (blob != null && blob.length > 0) {
+                favorite.icon = blob;
+            }
+        }
+        String title = c.getString(TITLE_INDEX);
+        if (!TextUtils.isEmpty(title)) {
+            favorite.title = title;
+        }
+        String intent = c.getString(INTENT_INDEX);
+        if (!TextUtils.isEmpty(intent)) {
+            favorite.intent = intent;
+        }
+        favorite.itemType = c.getInt(ITEM_TYPE_INDEX);
+        if (favorite.itemType == Favorites.ITEM_TYPE_APPWIDGET) {
+            favorite.appWidgetId = c.getInt(APPWIDGET_ID_INDEX);
+            String appWidgetProvider = c.getString(APPWIDGET_PROVIDER_INDEX);
+            if (!TextUtils.isEmpty(appWidgetProvider)) {
+                favorite.appWidgetProvider = appWidgetProvider;
+            }
+        }
+
+        return writeCheckedBytes(favorite);
+    }
+
+    /** Deserialize a Favorite from persistence, after verifying checksum wrapper. */
+    private Favorite unpackFavorite(byte[] buffer, int offset, int dataSize)
+            throws InvalidProtocolBufferNanoException {
+        Favorite favorite = new Favorite();
+        MessageNano.mergeFrom(favorite, readCheckedBytes(buffer, offset, dataSize));
+        return favorite;
+    }
+
+    /** Serialize a Screen for persistence, including a checksum wrapper. */
+    private byte[] packScreen(Cursor c) {
+        Screen screen = new Screen();
+        screen.id = c.getLong(ID_INDEX);
+        screen.rank = c.getInt(SCREEN_RANK_INDEX);
+
+        return writeCheckedBytes(screen);
+    }
+
+    /** Deserialize a Screen from persistence, after verifying checksum wrapper. */
+    private Screen unpackScreen(byte[] buffer, int offset, int dataSize)
+            throws InvalidProtocolBufferNanoException {
+        Screen screen = new Screen();
+        MessageNano.mergeFrom(screen, readCheckedBytes(buffer, offset, dataSize));
+        return screen;
+    }
+
+    /**
+     * Read the old journal from the input file.
+     *
+     * In the event of any error, just pretend we didn't have a journal,
+     * in that case, do a full backup.
+     *
+     * @param oldState the read-0only file descriptor pointing to the old journal
+     * @return a Journal protocol bugffer
+     */
+    private Journal readJournal(ParcelFileDescriptor oldState) {
+        int fileSize = (int) oldState.getStatSize();
+        int remaining = fileSize;
+        byte[] buffer = null;
+        Journal journal = new Journal();
+        if (remaining < MAX_JOURNAL_SIZE) {
+            FileInputStream inStream = new FileInputStream(oldState.getFileDescriptor());
+            int offset = 0;
+
+            buffer = new byte[remaining];
+            while (remaining > 0) {
+                int bytesRead = 0;
+                try {
+                    bytesRead = inStream.read(buffer, offset, remaining);
+                } catch (IOException e) {
+                    Log.w(TAG, "failed to read the journal", e);
+                    buffer = null;
+                    remaining = 0;
+                }
+                if (bytesRead > 0) {
+                    remaining -= bytesRead;
+                } else {
+                    // act like there is not journal
+                    Log.w(TAG, "failed to read the journal");
+                    buffer = null;
+                    remaining = 0;
+                }
+            }
+
+            if (buffer != null) {
+                try {
+                    MessageNano.mergeFrom(journal, readCheckedBytes(buffer, 0, fileSize));
+                } catch (InvalidProtocolBufferNanoException e) {
+                    Log.d(TAG, "failed to read the journal", e);
+                    journal.clear();
+                }
+            }
+
+            try {
+                inStream.close();
+            } catch (IOException e) {
+                Log.d(TAG, "failed to close the journal", e);
+            }
+        }
+        return journal;
+    }
+
+    /**
+     * Write the new journal to the output file.
+     *
+     * In the event of any error, just pretend we didn't have a journal,
+     * in that case, do a full backup.
+
+     * @param newState the write-only file descriptor pointing to the new journal
+     * @param journal a Journal protocol buffer
+     */
+    private void writeJournal(ParcelFileDescriptor newState, Journal journal) {
+        FileOutputStream outStream = null;
+        try {
+            outStream = new FileOutputStream(newState.getFileDescriptor());
+            outStream.write(writeCheckedBytes(journal));
+            outStream.close();
+        } catch (IOException e) {
+            Log.d(TAG, "failed to write backup journal", e);
+        }
+    }
+
+    /** Wrap a proto in a CheckedMessage and compute the checksum. */
+    private byte[] writeCheckedBytes(MessageNano proto) {
+        CheckedMessage wrapper = new CheckedMessage();
+        wrapper.payload = MessageNano.toByteArray(proto);
+        CRC32 checksum = new CRC32();
+        checksum.update(wrapper.payload);
+        wrapper.checksum = checksum.getValue();
+        return MessageNano.toByteArray(wrapper);
+    }
+
+    /** Unwrap a proto message from a CheckedMessage, verifying the checksum. */
+    private byte[] readCheckedBytes(byte[] buffer, int offset, int dataSize)
+            throws InvalidProtocolBufferNanoException {
+        CheckedMessage wrapper = new CheckedMessage();
+        MessageNano.mergeFrom(wrapper, buffer, offset, dataSize);
+        CRC32 checksum = new CRC32();
+        checksum.update(wrapper.payload);
+        if (wrapper.checksum != checksum.getValue()) {
+            throw new InvalidProtocolBufferNanoException("checksum does not match");
+        }
+        return wrapper.payload;
+    }
+
+    private class KeyParsingException extends Throwable {
+        private KeyParsingException(Throwable cause) {
+            super(cause);
+        }
+
+        public KeyParsingException(String reason) {
+            super(reason);
+        }
+    }
+}
diff --git a/src/com/android/launcher3/LauncherProvider.java b/src/com/android/launcher3/LauncherProvider.java
index fa61b1185..471d2d2fc 100644
--- a/src/com/android/launcher3/LauncherProvider.java
+++ b/src/com/android/launcher3/LauncherProvider.java
@@ -49,6 +49,7 @@ import android.util.AttributeSet;
 import android.util.Log;
 import android.util.Xml;
 
+import com.android.launcher3.LauncherSettings.BaseLauncherColumns;
 import com.android.launcher3.LauncherSettings.Favorites;
 
 import org.xmlpull.v1.XmlPullParser;
@@ -65,7 +66,7 @@ public class LauncherProvider extends ContentProvider {
 
     private static final String DATABASE_NAME = "launcher.db";
 
-    private static final int DATABASE_VERSION = 14;
+    private static final int DATABASE_VERSION = 15;
 
     static final String OLD_AUTHORITY = "com.android.launcher2.settings";
     static final String AUTHORITY = "com.android.launcher3.settings";
@@ -146,6 +147,7 @@ public class LauncherProvider extends ContentProvider {
         SqlArguments args = new SqlArguments(uri);
 
         SQLiteDatabase db = mOpenHelper.getWritableDatabase();
+        addModifiedTime(initialValues);
         final long rowId = dbInsertAndCheck(mOpenHelper, db, args.table, null, initialValues);
         if (rowId <= 0) return null;
 
@@ -164,6 +166,7 @@ public class LauncherProvider extends ContentProvider {
         try {
             int numValues = values.length;
             for (int i = 0; i < numValues; i++) {
+                addModifiedTime(values[i]);
                 if (dbInsertAndCheck(mOpenHelper, db, args.table, null, values[i]) < 0) {
                     return 0;
                 }
@@ -192,6 +195,7 @@ public class LauncherProvider extends ContentProvider {
     public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
         SqlArguments args = new SqlArguments(uri, selection, selectionArgs);
 
+        addModifiedTime(values);
         SQLiteDatabase db = mOpenHelper.getWritableDatabase();
         int count = db.update(args.table, values, args.where, args.args);
         if (count > 0) sendNotify(uri);
@@ -204,6 +208,13 @@ public class LauncherProvider extends ContentProvider {
         if (notify == null || "true".equals(notify)) {
             getContext().getContentResolver().notifyChange(uri, null);
         }
+
+        // always notify the backup agent
+        LauncherBackupAgent.dataChanged(getContext());
+    }
+
+    private void addModifiedTime(ContentValues values) {
+        values.put(LauncherSettings.ChangeLogColumns.MODIFIED, System.currentTimeMillis());
     }
 
     public long generateNewItemId() {
@@ -343,7 +354,8 @@ public class LauncherProvider extends ContentProvider {
                     "icon BLOB," +
                     "uri TEXT," +
                     "displayMode INTEGER," +
-                    "appWidgetProvider TEXT" +
+                    "appWidgetProvider TEXT," +
+                    "modified INTEGER NOT NULL DEFAULT 0" +
                     ");");
             addWorkspacesTable(db);
 
@@ -384,7 +396,8 @@ public class LauncherProvider extends ContentProvider {
         private void addWorkspacesTable(SQLiteDatabase db) {
             db.execSQL("CREATE TABLE " + TABLE_WORKSPACE_SCREENS + " (" +
                     LauncherSettings.WorkspaceScreens._ID + " INTEGER," +
-                    LauncherSettings.WorkspaceScreens.SCREEN_RANK + " INTEGER" +
+                    LauncherSettings.WorkspaceScreens.SCREEN_RANK + " INTEGER," +
+                    LauncherSettings.ChangeLogColumns.MODIFIED + " INTEGER NOT NULL DEFAULT 0" +
                     ");");
         }
 
@@ -643,6 +656,25 @@ public class LauncherProvider extends ContentProvider {
                 }
             }
 
+
+            if (version < 15) {
+                db.beginTransaction();
+                try {
+                    // Insert new column for holding update timestamp
+                    db.execSQL("ALTER TABLE favorites " +
+                            "ADD COLUMN modified INTEGER NOT NULL DEFAULT 0;");
+                    db.execSQL("ALTER TABLE workspaceScreens " +
+                            "ADD COLUMN modified INTEGER NOT NULL DEFAULT 0;");
+                    db.setTransactionSuccessful();
+                    version = 15;
+                } catch (SQLException ex) {
+                    // Old version remains, which means we wipe old data
+                    Log.e(TAG, ex.getMessage(), ex);
+                } finally {
+                    db.endTransaction();
+                }
+            }
+
             if (version != DATABASE_VERSION) {
                 Log.w(TAG, "Destroying all old data.");
                 db.execSQL("DROP TABLE IF EXISTS " + TABLE_FAVORITES);
diff --git a/src/com/android/launcher3/LauncherSettings.java b/src/com/android/launcher3/LauncherSettings.java
index ada09e9b8..988e5efca 100644
--- a/src/com/android/launcher3/LauncherSettings.java
+++ b/src/com/android/launcher3/LauncherSettings.java
@@ -23,7 +23,16 @@ import android.provider.BaseColumns;
  * Settings related utilities.
  */
 class LauncherSettings {
-    static interface BaseLauncherColumns extends BaseColumns {
+    /** Columns required on table staht will be subject to backup and restore. */
+    static interface ChangeLogColumns extends BaseColumns {
+        /**
+         * The time of the last update to this row.
+         * <P>Type: INTEGER</P>
+         */
+        static final String MODIFIED = "modified";
+    }
+
+    static interface BaseLauncherColumns extends ChangeLogColumns {
         /**
          * Descriptive name of the gesture that can be displayed to the user.
          * <P>Type: TEXT</P>
@@ -95,7 +104,7 @@ class LauncherSettings {
      *
      * Tracks the order of workspace screens.
      */
-    static final class WorkspaceScreens implements BaseColumns {
+    static final class WorkspaceScreens implements ChangeLogColumns {
         /**
          * The content:// style URL for this table
          */