add storage java internal reader

/*

 * Copyright (C) 2024 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.aconfig.storage;

public class StorageInternalReader {

    private static final String MAP_PATH = "/metadata/aconfig/maps/";

    private static final String BOOT_PATH = "/metadata/aconfig/boot/";

    private PackageTable mPackageTable;

    private FlagValueList mFlagValueList;

    private int mPackageBooleanStartOffset;

    public StorageInternalReader(String container, String packageName) {

        this(container, packageName, MAP_PATH, BOOT_PATH);

    }

    public StorageInternalReader(

            String container, String packageName, String mapPath, String bootPath) {

        String packageMapFile = mapPath + container + ".package.map";

        String flagValueFile = bootPath + container + ".val";

        mPackageTable = PackageTable.fromBytes(mapStorageFile(packageMapFile));

        mFlagValueList = FlagValueList.fromBytes(mapStorageFile(flagValueFile));

        mPackageBooleanStartOffset = getPackageBooleanStartOffset(packageName);

    }

    public boolean getBooleanFlagValue(int index) {

        index += mPackageBooleanStartOffset;

        if (index >= mFlagValueList.size()) {

            throw new AconfigStorageException("Fail to get boolean flag value");

        }

        return mFlagValueList.get(index);

    }

    private int getPackageBooleanStartOffset(String packageName) {

        PackageTable.Node pNode = mPackageTable.get(packageName);

        if (pNode == null) {

            PackageTable.Header header = mPackageTable.getHeader();

            throw new AconfigStorageException(

                    String.format(

                            "Fail to get package %s from container %s",

                            packageName, header.getContainer()));

        }

        return pNode.getBooleanStartIndex();

    }

    // Map a storage file given file path

    private static MappedByteBuffer mapStorageFile(String file) {

        try {

            FileInputStream stream = new FileInputStream(file);

            FileChannel channel = stream.getChannel();

            return channel.map(FileChannel.MapMode.READ_ONLY, 0, channel.size());

        } catch (IOException e) {

            throw new AconfigStorageException(

                    String.format("Fail to mmap storage file %s", file), e);

        }

    }

}