Merge change 2845 into donut

/*

 * 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.database.sqlite;

import android.content.res.AssetFileDescriptor;

import android.database.Cursor;

import android.os.MemoryFile;

import java.io.FileNotFoundException;

import java.io.IOException;

/**

 * Some helper functions for using SQLite database to implement content providers.

 *

 * @hide

 */

public class SQLiteContentHelper {

    /**

     * Runs an SQLite query and returns an AssetFileDescriptor for the

     * blob in column 0 of the first row. If the first column does

     * not contain a blob, an unspecified exception is thrown.

     *

     * @param db Handle to a readable database.

     * @param sql SQL query, possibly with query arguments.

     * @param selectionArgs Query argument values, or {@code null} for no argument.

     * @return If no exception is thrown, a non-null AssetFileDescriptor is returned.

     * @throws FileNotFoundException If the query returns no results or the

     *         value of column 0 is NULL, or if there is an error creating the

     *         asset file descriptor.

     */

    public static AssetFileDescriptor getBlobColumnAsAssetFile(SQLiteDatabase db, String sql,

            String[] selectionArgs) throws FileNotFoundException {

        try {

            MemoryFile file = simpleQueryForBlobMemoryFile(db, sql, selectionArgs);

            if (file == null) {

                throw new FileNotFoundException("No results.");

            }

            return AssetFileDescriptor.fromMemoryFile(file);

        } catch (IOException ex) {

            throw new FileNotFoundException(ex.toString());

        }

    }

    /**

     * Runs an SQLite query and returns a MemoryFile for the

     * blob in column 0 of the first row. If the first column does

     * not contain a blob, an unspecified exception is thrown.

     *

     * @return A memory file, or {@code null} if the query returns no results

     *         or the value column 0 is NULL.

     * @throws IOException If there is an error creating the memory file.

     */

    // TODO: make this native and use the SQLite blob API to reduce copying

    private static MemoryFile simpleQueryForBlobMemoryFile(SQLiteDatabase db, String sql,

            String[] selectionArgs) throws IOException {

        Cursor cursor = db.rawQuery(sql, selectionArgs);

        if (cursor == null) {

            return null;

        }

        try {

            if (!cursor.moveToFirst()) {

                return null;

            }

            byte[] bytes = cursor.getBlob(0);

            if (bytes == null) {

                return null;

            }

            MemoryFile file = new MemoryFile(null, bytes.length);

            file.writeBytes(bytes, 0, 0, bytes.length);

            file.deactivate();

            return file;

        } finally {

            cursor.close();

        }

    }

}