Merge "Remove internal AtomicFile"

/*

 * 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.internal.os;

import android.annotation.UnsupportedAppUsage;

import android.os.Build;

import android.os.FileUtils;

import android.util.Log;

import java.io.File;

import java.io.FileInputStream;

import java.io.FileNotFoundException;

import java.io.FileOutputStream;

import java.io.IOException;

/**

 * Helper class for performing atomic operations on a file, by creating a

 * backup file until a write has successfully completed.

 * <p>

 * Atomic file guarantees file integrity by ensuring that a file has

 * been completely written and sync'd to disk before removing its backup.

 * As long as the backup file exists, the original file is considered

 * to be invalid (left over from a previous attempt to write the file).

 * </p><p>

 * Atomic file does not confer any file locking semantics.

 * Do not use this class when the file may be accessed or modified concurrently

 * by multiple threads or processes.  The caller is responsible for ensuring

 * appropriate mutual exclusion invariants whenever it accesses the file.

 * </p>

 */

public final class AtomicFile {

    private final File mBaseName;

    private final File mBackupName;

    @UnsupportedAppUsage

    public AtomicFile(File baseName) {

        mBaseName = baseName;

        mBackupName = new File(baseName.getPath() + ".bak");

    }

    @UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.P, trackingBug = 115609023)

    public File getBaseFile() {

        return mBaseName;

    }

    @UnsupportedAppUsage

    public FileOutputStream startWrite() throws IOException {

        // Rename the current file so it may be used as a backup during the next read

        if (mBaseName.exists()) {

            if (!mBackupName.exists()) {

                if (!mBaseName.renameTo(mBackupName)) {

                    Log.w("AtomicFile", "Couldn't rename file " + mBaseName

                            + " to backup file " + mBackupName);

                }

            } else {

                mBaseName.delete();

            }

        }

        FileOutputStream str = null;

        try {

            str = new FileOutputStream(mBaseName);

        } catch (FileNotFoundException e) {

            File parent = mBaseName.getParentFile();

            if (!parent.mkdir()) {

                throw new IOException("Couldn't create directory " + mBaseName);

            }

            FileUtils.setPermissions(

                parent.getPath(),

                FileUtils.S_IRWXU|FileUtils.S_IRWXG|FileUtils.S_IXOTH,

                -1, -1);

            try {

                str = new FileOutputStream(mBaseName);

            } catch (FileNotFoundException e2) {

                throw new IOException("Couldn't create " + mBaseName);

            }

        }

        return str;

    }

    @UnsupportedAppUsage

    public void finishWrite(FileOutputStream str) {

        if (str != null) {

            FileUtils.sync(str);

            try {

                str.close();

                mBackupName.delete();

            } catch (IOException e) {

                Log.w("AtomicFile", "finishWrite: Got exception:", e);

            }

        }

    }

    @UnsupportedAppUsage

    public void failWrite(FileOutputStream str) {

        if (str != null) {

            FileUtils.sync(str);

            try {

                str.close();

                mBaseName.delete();

                mBackupName.renameTo(mBaseName);

            } catch (IOException e) {

                Log.w("AtomicFile", "failWrite: Got exception:", e);

            }

        }

    }

    @UnsupportedAppUsage

    public FileOutputStream openAppend() throws IOException {

        try {

            return new FileOutputStream(mBaseName, true);

        } catch (FileNotFoundException e) {

            throw new IOException("Couldn't append " + mBaseName);

        }

    }

    @UnsupportedAppUsage

    public void truncate() throws IOException {

        try {

            FileOutputStream fos = new FileOutputStream(mBaseName);

            FileUtils.sync(fos);

            fos.close();

        } catch (FileNotFoundException e) {

            throw new IOException("Couldn't append " + mBaseName);

        } catch (IOException e) {

        }

    }

    public boolean exists() {

        return mBaseName.exists() || mBackupName.exists();

    }

    public void delete() {

        mBaseName.delete();

        mBackupName.delete();

    }

    @UnsupportedAppUsage

    public FileInputStream openRead() throws FileNotFoundException {

        if (mBackupName.exists()) {

            mBaseName.delete();

            mBackupName.renameTo(mBaseName);

        }

        return new FileInputStream(mBaseName);

    }

    @UnsupportedAppUsage

    public byte[] readFully() throws IOException {

        FileInputStream stream = openRead();

        try {

            int pos = 0;

            int avail = stream.available();

            byte[] data = new byte[avail];

            while (true) {

                int amt = stream.read(data, pos, data.length-pos);

                //Log.i("foo", "Read " + amt + " bytes at " + pos

                //        + " of avail " + data.length);

                if (amt <= 0) {

                    //Log.i("foo", "**** FINISHED READING: pos=" + pos

                    //        + " len=" + data.length);

                    return data;

                }

                pos += amt;

                avail = stream.available();

                if (avail > data.length-pos) {

                    byte[] newData = new byte[pos+avail];

                    System.arraycopy(data, 0, newData, 0, pos);

                    data = newData;

                }

            }

        } finally {

            stream.close();

        }

    }

}