001/*
002 * Configurate
003 * Copyright (C) zml and Configurate contributors
004 *
005 * Licensed under the Apache License, Version 2.0 (the "License");
006 * you may not use this file except in compliance with the License.
007 * You may obtain a copy of the License at
008 *
009 *    http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package ninja.leaping.configurate.loader;
018
019import org.checkerframework.checker.nullness.qual.NonNull;
020
021import java.io.BufferedWriter;
022import java.io.FilterWriter;
023import java.io.IOException;
024import java.io.Writer;
025import java.nio.charset.Charset;
026import java.nio.file.Files;
027import java.nio.file.Path;
028import java.nio.file.StandardCopyOption;
029import java.util.concurrent.Callable;
030import java.util.concurrent.ThreadLocalRandom;
031
032import static java.util.Objects.requireNonNull;
033
034/**
035 * A utility for creating "atomic" file writers.
036 *
037 * <p>An atomic writer copies any existing file at the given path to a temporary location, then
038 * writes to the same temporary location, before moving the file back to the desired output path
039 * once the write is fully complete.</p>
040 */
041public final class AtomicFiles {
042    private AtomicFiles() {}
043
044    /**
045     * Creates and returns an "atomic" writer factory for the given path.
046     *
047     * @param path The path
048     * @param charset The charset to be used by the writer
049     * @return The writer factory
050     */
051    @NonNull
052    public static Callable<BufferedWriter> createAtomicWriterFactory(@NonNull Path path, @NonNull Charset charset) {
053        requireNonNull(path, "path");
054        return () -> createAtomicBufferedWriter(path, charset);
055    }
056
057    /**
058     * Creates and returns an "atomic" writer for the given path.
059     *
060     * @param path The path
061     * @param charset The charset to be used by the writer
062     * @return The writer factory
063     * @throws IOException For any underlying filesystem errors
064     */
065    @NonNull
066    public static BufferedWriter createAtomicBufferedWriter(@NonNull Path path, @NonNull Charset charset) throws IOException {
067        path = path.toAbsolutePath();
068
069        Path writePath = getTemporaryPath(path.getParent(), path.getFileName().toString());
070        if (Files.exists(path)) {
071            Files.copy(path, writePath, StandardCopyOption.COPY_ATTRIBUTES, StandardCopyOption.REPLACE_EXISTING);
072        }
073
074        BufferedWriter output = Files.newBufferedWriter(writePath, charset);
075        return new BufferedWriter(new AtomicFileWriter(writePath, path, output));
076    }
077
078    @NonNull
079    private static Path getTemporaryPath(@NonNull Path parent, @NonNull String key) {
080        String fileName = System.nanoTime() + ThreadLocalRandom.current().nextInt() + requireNonNull(key, "key").replaceAll("\\\\|/|:",
081                "-") + ".tmp";
082        return parent.resolve(fileName);
083    }
084
085    private static class AtomicFileWriter extends FilterWriter {
086        private final Path targetPath, writePath;
087
088        protected AtomicFileWriter(Path writePath, Path targetPath, Writer wrapping) {
089            super(wrapping);
090            this.writePath = writePath;
091            this.targetPath = targetPath;
092        }
093
094        @Override
095        public void close() throws IOException {
096            super.close();
097            Files.createDirectories(targetPath.getParent());
098            Files.move(writePath, targetPath, StandardCopyOption.ATOMIC_MOVE, StandardCopyOption.REPLACE_EXISTING);
099        }
100    }
101}