src/com/android/browser/BrowserBackupAgent.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 com.android.browser;

import java.io.IOException;

import android.app.backup.BackupAgent;
import android.app.backup.BackupDataInput;
import android.app.backup.BackupDataOutput;
import android.database.Cursor;
import android.os.ParcelFileDescriptor;
import android.provider.Browser;
import android.provider.Browser.BookmarkColumns;
import android.util.Log;

import java.io.ByteArrayOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.EOFException;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.util.ArrayList;
import java.util.zip.CRC32;

/**
 * Settings backup agent for the Android browser.  Currently the only thing
 * stored is the set of bookmarks.  It's okay if I/O exceptions are thrown
 * out of the agent; the calling code handles it and the backup operation
 * simply fails.
 *
 * @hide
 */
public class BrowserBackupAgent extends BackupAgent {
    static final String TAG = "BrowserBackupAgent";
    static final boolean DEBUG = false;

    static final String BOOKMARK_KEY = "_bookmarks_";
    /** this version num MUST be incremented if the flattened-file schema ever changes */
    static final int BACKUP_AGENT_VERSION = 0;

    /**
     * In order to determine whether the bookmark set has changed since the
     * last time we did a backup, we store the following bits of info in the
     * state file after a backup:
     *
     * 1. the size of the flattened bookmark file
     * 2. the CRC32 of that file
     * 3. the agent version number [relevant following an OTA]
     *
     * After we flatten the bookmarks file here in onBackup, we compare its
     * metrics with the values from the saved state.  If they match, it means
     * the bookmarks didn't really change and we don't need to send the data.
     * (If they don't match, of course, then they've changed and we do indeed
     * send the new flattened file to be backed up.)
     */
    @Override
    public void onBackup(ParcelFileDescriptor oldState, BackupDataOutput data,
            ParcelFileDescriptor newState) throws IOException {
        long savedFileSize = -1;
        long savedCrc = -1;
        int savedVersion = -1;

        // Extract the previous bookmark file size & CRC from the saved state
        DataInputStream in = new DataInputStream(
                new FileInputStream(oldState.getFileDescriptor()));
        try {
            savedFileSize = in.readLong();
            savedCrc = in.readLong();
            savedVersion = in.readInt();
        } catch (EOFException e) {
            // It means we had no previous state; that's fine
        }

        // Build a flattened representation of the bookmarks table
        File tmpfile = File.createTempFile("bkp", null, getCacheDir());
        try {
            FileOutputStream outfstream = new FileOutputStream(tmpfile);
            long newCrc = buildBookmarkFile(outfstream);
            outfstream.close();

            // Any changes since the last backup?
            if ((savedVersion != BACKUP_AGENT_VERSION)
                    || (newCrc != savedCrc)
                    || (tmpfile.length() != savedFileSize)) {
                // Different checksum or different size, so we need to back it up
                copyFileToBackup(BOOKMARK_KEY, tmpfile, data);
            }

            // Record our backup state and we're done
            writeBackupState(tmpfile.length(), newCrc, newState);
        } finally {
            // Make sure to tidy up when we're done
            tmpfile.delete();
        }
    }

    /**
     * Restore from backup -- reads in the flattened bookmark file as supplied from
     * the backup service, parses that out, and rebuilds the bookmarks table in the
     * browser database from it.
     */
    @Override
    public void onRestore(BackupDataInput data, int appVersionCode,
            ParcelFileDescriptor newState) throws IOException {
        long crc = -1;
        File tmpfile = File.createTempFile("rst", null, getFilesDir());
        try {
            while (data.readNextHeader()) {
                if (BOOKMARK_KEY.equals(data.getKey())) {
                    // Read the flattened bookmark data into a temp file
                    crc = copyBackupToFile(data, tmpfile, data.getDataSize());

                    FileInputStream infstream = new FileInputStream(tmpfile);
                    DataInputStream in = new DataInputStream(infstream);

                    try {
                        int count = in.readInt();
                        ArrayList<Bookmark> bookmarks = new ArrayList<Bookmark>(count);

                        // Read all the bookmarks, then process later -- if we can't read
                        // all the data successfully, we don't touch the bookmarks table
                        for (int i = 0; i < count; i++) {
                            Bookmark mark = new Bookmark();
                            mark.url = in.readUTF();
                            mark.visits = in.readInt();
                            mark.date = in.readLong();
                            mark.created = in.readLong();
                            mark.title = in.readUTF();
                            bookmarks.add(mark);
                        }

                        // Okay, we have all the bookmarks -- now see if we need to add
                        // them to the browser's database
                        int N = bookmarks.size();
                        int nUnique = 0;
                        if (DEBUG) Log.v(TAG, "Restoring " + N + " bookmarks");
                        String[] urlCol = new String[] { BookmarkColumns.URL };
                        for (int i = 0; i < N; i++) {
                            Bookmark mark = bookmarks.get(i);

                            // Does this URL exist in the bookmark table?
                            Cursor cursor = getContentResolver().query(Browser.BOOKMARKS_URI,
                                    urlCol,  BookmarkColumns.URL + " == '" + mark.url + "' AND " +
                                    BookmarkColumns.BOOKMARK + " == 1 ", null, null);
                            // if not, insert it
                            if (cursor.getCount() <= 0) {
                                if (DEBUG) Log.v(TAG, "Did not see url: " + mark.url);
                                // Right now we do not reconstruct the db entry in its
                                // entirety; we just add a new bookmark with the same data
                                Bookmarks.addBookmark(null, getContentResolver(),
                                        mark.url, mark.title, null, false);
                                nUnique++;
                            } else {
                                if (DEBUG) Log.v(TAG, "Skipping extant url: " + mark.url);
                            }
                            cursor.close();
                        }
                        Log.i(TAG, "Restored " + nUnique + " of " + N + " bookmarks");
                    } catch (IOException ioe) {
                        Log.w(TAG, "Bad backup data; not restoring");
                        crc = -1;
                    }
                }

                // Last, write the state we just restored from so we can discern
                // changes whenever we get invoked for backup in the future
                writeBackupState(tmpfile.length(), crc, newState);
            }
        } finally {
            // Whatever happens, delete the temp file
            tmpfile.delete();
        }
    }

    class Bookmark {
        public String url;
        public int visits;
        public long date;
        public long created;
        public String title;
    }
    /*
     * Utility functions
     */

    // Flatten the bookmarks table into the given file, calculating its CRC in the process
    private long buildBookmarkFile(FileOutputStream outfstream) throws IOException {
        CRC32 crc = new CRC32();
        ByteArrayOutputStream bufstream = new ByteArrayOutputStream(512);
        DataOutputStream bout = new DataOutputStream(bufstream);

        Cursor cursor = getContentResolver().query(Browser.BOOKMARKS_URI,
                new String[] { BookmarkColumns.URL, BookmarkColumns.VISITS,
                BookmarkColumns.DATE, BookmarkColumns.CREATED,
                BookmarkColumns.TITLE },
                BookmarkColumns.BOOKMARK + " == 1 ", null, null);

        // The first thing in the file is the row count...
        int count = cursor.getCount();
        if (DEBUG) Log.v(TAG, "Backing up " + count + " bookmarks");
        bout.writeInt(count);
        byte[] record = bufstream.toByteArray();
        crc.update(record);
        outfstream.write(record);

        // ... followed by the data for each row
        for (int i = 0; i < count; i++) {
            cursor.moveToNext();

            String url = cursor.getString(0);
            int visits = cursor.getInt(1);
            long date = cursor.getLong(2);
            long created = cursor.getLong(3);
            String title = cursor.getString(4);

            // construct the flattened record in a byte array
            bufstream.reset();
            bout.writeUTF(url);
            bout.writeInt(visits);
            bout.writeLong(date);
            bout.writeLong(created);
            bout.writeUTF(title);

            // Update the CRC and write the record to the temp file
            record = bufstream.toByteArray();
            crc.update(record);
            outfstream.write(record);

            if (DEBUG) Log.v(TAG, "   wrote url " + url);
        }

        cursor.close();
        return crc.getValue();
    }

    // Write the file to backup as a single record under the given key
    private void copyFileToBackup(String key, File file, BackupDataOutput data)
            throws IOException {
        final int CHUNK = 8192;
        byte[] buf = new byte[CHUNK];

        int toCopy = (int) file.length();
        data.writeEntityHeader(key, toCopy);

        FileInputStream in = new FileInputStream(file);
        int nRead;
        while (toCopy > 0) {
            nRead = in.read(buf, 0, CHUNK);
            data.writeEntityData(buf, nRead);
            toCopy -= nRead;
        }
        in.close();
    }

    // Read the given file from backup to a file, calculating a CRC32 along the way
    private long copyBackupToFile(BackupDataInput data, File file, int toRead)
            throws IOException {
        final int CHUNK = 8192;
        byte[] buf = new byte[CHUNK];
        CRC32 crc = new CRC32();
        FileOutputStream out = new FileOutputStream(file);

        while (toRead > 0) {
            int numRead = data.readEntityData(buf, 0, CHUNK);
            crc.update(buf, 0, numRead);
            out.write(buf, 0, numRead);
            toRead -= numRead;
        }

        out.close();
        return crc.getValue();
    }

    // Write the given metrics to the new state file
    private void writeBackupState(long fileSize, long crc, ParcelFileDescriptor stateFile)
            throws IOException {
        DataOutputStream out = new DataOutputStream(
                new FileOutputStream(stateFile.getFileDescriptor()));
        out.writeLong(fileSize);
        out.writeLong(crc);
        out.writeInt(BACKUP_AGENT_VERSION);
    }
}