LockResources.java

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/*
 * Sleuth Kit Data Model
 *
 * Copyright 2024 Basis Technology Corp.
 * Contact: carrier <at> sleuthkit <dot> org
 *
 * 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 org.sleuthkit.datamodel;

import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.channels.FileChannel;
import java.nio.channels.FileLock;
import java.nio.channels.OverlappingFileLockException;

class LockResources implements AutoCloseable {

        private static final String LOCK_FILE_PREFIX = ".lock_";

        private File lockFile = null;
        private RandomAccessFile lockFileRaf = null;
        private FileChannel lockFileChannel = null;
        private FileLock lockFileLock = null;

        LockResources(File lockFile, RandomAccessFile lockFileRaf, FileChannel lockFileChannel, FileLock lockFileLock) {
                this.lockFile = lockFile;
                this.lockFileRaf = lockFileRaf;
                this.lockFileChannel = lockFileChannel;
                this.lockFileLock = lockFileLock;
        }

        static LockResources tryAcquireFileLock(String caseDir, String dbName, String applicationName) throws ConcurrentDbAccessException, IOException, OverlappingFileLockException {
                // get the lock file path
                String lockFileName = LOCK_FILE_PREFIX + (dbName == null ? "tskdb" : dbName);
                File lockFile = new File(caseDir, lockFileName);
                // make directories leading up to that
                lockFile.getParentFile().mkdirs();

                // if the lock file exists
                if (lockFile.isFile() && !lockFile.canWrite()) {
                        // get the random access file as read only
                        RandomAccessFile lockFileRaf = new RandomAccessFile(lockFile, "r");
                        throw ConcurrentDbAccessException.createForFile(lockFile.getAbsolutePath(), lockFileRaf);
                } else {
                        RandomAccessFile lockFileRaf = new RandomAccessFile(lockFile, "rw");
                        FileChannel lockFileChannel = lockFileRaf.getChannel();
                        FileLock lockFileLock = lockFileChannel == null
                                        ? null
                                        : lockFileChannel.tryLock(1024L, 1L, false);

                        if (lockFileLock != null) {
                                lockFileRaf.setLength(0);
                                String limitedAppName = applicationName.length() > 500 ? applicationName.substring(0, 500) : applicationName;
                                lockFileRaf.writeChars(limitedAppName);
                                return new LockResources(lockFile, lockFileRaf, lockFileChannel, lockFileLock);
                        } else {
                                throw ConcurrentDbAccessException.createForFile(lockFile.getAbsolutePath(), lockFileRaf);
                        }
                }
        }

        @Override
        public void close() throws Exception {
                // close lock file resources in reverse acquisition order
                if (this.lockFileLock != null) {
                        this.lockFileLock.close();
                        this.lockFileLock = null;
                }

                if (this.lockFileChannel != null) {
                        this.lockFileChannel.close();
                        this.lockFileChannel = null;
                }

                if (this.lockFileRaf != null) {
                        this.lockFileRaf.close();
                        this.lockFileRaf = null;
                }

                if (this.lockFile != null) {
                        this.lockFile.delete();
                        this.lockFile = null;
                }
        }
}