Skeleton backup agent for Browser

This is a skeleton backup agent for the Android Browser, intended to back up and
restore the bookmarks table from browser.db by extracting the bookmarks table
into a flattened file representation on backup, then unflattening and rebuilding
the table during restore.

It compiles but is completely untested, since the db code to read/write the
bookmarks table is not finished.  The backup agent has been declared in the
Browser manifest, however.

1 files changed, 206 insertions, 0 deletions

diff --git a/src/com/android/browser/BrowserBackupAgent.java b/src/com/android/browser/BrowserBackupAgent.java
new file mode 100644
index 00000000..e38ef054
--- /dev/null
+++ b/src/com/android/browser/BrowserBackupAgent.java
@@ -0,0 +1,206 @@
+/*
+ * 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.BackupAgent;
+import android.backup.BackupDataInput;
+import android.backup.BackupDataOutput;
+import android.database.Cursor;
+import android.os.ParcelFileDescriptor;
+import android.provider.Browser;
+import android.provider.Browser.BookmarkColumns;
+
+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.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.
+ */
+public class BrowserBackupAgent extends BackupAgent {
+    static final String BOOKMARK_KEY = "_bookmarks_";
+
+    /**
+     * 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
+     *
+     * 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;
+
+        // 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();
+        } catch (EOFException e) {
+            // It means we had no previous state; that's fine
+        }
+
+        // TODO: BUILD THE FLATTENED BOOKMARK FILE FROM THE DB (into tmpfile)
+        File tmpfile = getFilesDir().createTempFile("bkp", null);
+        CRC32 crc = new CRC32();
+        try {
+            Cursor cursor = getContentResolver().query(Browser.BOOKMARKS_URI,
+                    new String[] { BookmarkColumns.URL, BookmarkColumns.VISITS,
+                    BookmarkColumns.DATE, BookmarkColumns.CREATED,
+                    BookmarkColumns.TITLE },
+                    BookmarkColumns.BOOKMARK + " == 1 ", null, null);
+            int count = cursor.getCount();
+            FileOutputStream out = new FileOutputStream(tmpfile);
+            for (int i = 0; i < count; i++) {
+                StringBuilder sb = new StringBuilder();
+                // URL
+                sb.append("'");
+                sb.append(cursor.getString(0));
+                sb.append("','");
+                // VISITS
+                sb.append(cursor.getInt(1));
+                sb.append("','");
+                // DATE
+                sb.append(cursor.getLong(2));
+                sb.append("','");
+                // CREATED
+                sb.append(cursor.getLong(3));
+                sb.append("','");
+                // TITLE
+                sb.append(cursor.getString(4));
+                sb.append("'");
+                out.write(sb.toString().getBytes());
+            }
+            out.close();
+            /*
+                    android.util.Log.d("s", "backing up data" +
+                            getContentResolver().openFileDescriptor(Browser.BOOKMARKS_URI, "r").toString());
+             */
+            // NOTE: feed the flattened data through the crc engine on the fly
+            // to save re-reading it later just to checksum it
+
+            // Once the file is built, compare its metrics with the saved ones
+            if ((crc.getValue() != savedCrc) || (tmpfile.length() != savedFileSize)) {
+                // Different checksum or different size, so we need to back it up
+                copyFileToBackup(BOOKMARK_KEY, tmpfile, data);
+            }
+
+            // Last, record the metrics of the bookmark file that we just stored
+            writeBackupState(tmpfile.length(), crc.getValue(), 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 = getFilesDir().createTempFile("rst", null);
+        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());
+
+                    // TODO: READ THE FLAT BOOKMARKS FILE 'tmpfile' AND REBUILD THE DB TABLE
+                }
+
+                // 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();
+        }
+    }
+
+    /*
+     * Utility functions
+     */
+
+    // 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();
+
+        while (toRead > 0) {
+            int numRead = data.readEntityData(buf, 0, CHUNK);
+            crc.update(buf, 0, numRead);
+            toRead -= numRead;
+        }
+
+        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);
+    }
+}