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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.eclipse.aether.util;

import java.io.Closeable;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.nio.ByteBuffer;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.StandardCopyOption;
import java.util.concurrent.ThreadLocalRandom;
import java.util.concurrent.atomic.AtomicBoolean;

import static java.util.Objects.requireNonNull;

/**
 * A utility class to write files.
 *
 * @since 1.9.0
 */
public final class FileUtils {
    // Logic borrowed from Commons-Lang3: we really need only this, to decide do we "atomic move" or not
    private static final boolean IS_WINDOWS =
            System.getProperty("os.name", "unknown").startsWith("Windows");

    private FileUtils() {
        // hide constructor
    }

    /**
     * A temporary file, that is removed when closed.
     */
    public interface TempFile extends Closeable {
        /**
         * Returns the path of the created temp file.
         */
        Path getPath();
    }

    /**
     * A collocated temporary file, that resides next to a "target" file, and is removed when closed.
     */
    public interface CollocatedTempFile extends TempFile {
        /**
         * Upon close, atomically moves temp file to target file it is collocated with overwriting target (if exists).
         * Invocation of this method merely signals that caller ultimately wants temp file to replace the target
         * file, but when this method returns, the move operation did not yet happen, it will happen when this
         * instance is closed.
         * 

* Invoking this method without writing to temp file {@link #getPath()} (thus, not creating a temp * file to be moved) is considered a bug, a mistake of the caller. Caller of this method should ensure * that this method is invoked ONLY when the temp file is created and moving it to its final place is * required. */ void move() throws IOException; } /** * Creates a {@link TempFile} instance and backing temporary file on file system. It will be located in the default * temporary-file directory. Returned instance should be handled in try-with-resource construct and created * temp file is removed (if exists) when returned instance is closed. *

* This method uses {@link Files#createTempFile(String, String, java.nio.file.attribute.FileAttribute[])} to create * the temporary file on file system. */ public static TempFile newTempFile() throws IOException { Path tempFile = Files.createTempFile("resolver", "tmp"); return new TempFile() { @Override public Path getPath() { return tempFile; } @Override public void close() throws IOException { Files.deleteIfExists(tempFile); } }; } /** * Creates a {@link CollocatedTempFile} instance for given file without backing file. The path will be located in * same directory where given file is, and will reuse its name for generated (randomized) name. Returned instance * should be handled in try-with-resource and created temp path is removed (if exists) when returned instance is * closed. The {@link CollocatedTempFile#move()} makes possible to atomically replace passed in file with the * processed content written into a file backing the {@link CollocatedTempFile} instance. *

* The {@code file} nor it's parent directories have to exist. The parent directories are created if needed. *

* This method uses {@link Path#resolve(String)} to create the temporary file path in passed in file parent * directory, but it does NOT create backing file on file system. */ public static CollocatedTempFile newTempFile(Path file) throws IOException { Path parent = requireNonNull(file.getParent(), "file must have parent"); Files.createDirectories(parent); Path tempFile = parent.resolve(file.getFileName() + "." + Long.toUnsignedString(ThreadLocalRandom.current().nextLong()) + ".tmp"); return new CollocatedTempFile() { private final AtomicBoolean wantsMove = new AtomicBoolean(false); @Override public Path getPath() { return tempFile; } @Override public void move() { wantsMove.set(true); } @Override public void close() throws IOException { if (wantsMove.get()) { if (IS_WINDOWS) { copy(tempFile, file); } else { Files.move(tempFile, file, StandardCopyOption.ATOMIC_MOVE); } } Files.deleteIfExists(tempFile); } }; } /** * On Windows we use pre-NIO2 way to copy files, as for some reason it works. Beat me why. */ private static void copy(Path source, Path target) throws IOException { ByteBuffer buffer = ByteBuffer.allocate(1024 * 32); byte[] array = buffer.array(); try (InputStream is = Files.newInputStream(source); OutputStream os = Files.newOutputStream(target)) { while (true) { int bytes = is.read(array); if (bytes < 0) { break; } os.write(array, 0, bytes); } } } /** * A file writer, that accepts a {@link Path} to write some content to. Note: the file denoted by path may exist, * hence implementation have to ensure it is able to achieve its goal ("replace existing" option or equivalent * should be used). */ @FunctionalInterface public interface FileWriter { void write(Path path) throws IOException; } /** * Writes file without backup. * * @param target that is the target file (must be file, the path must have parent). * @param writer the writer that will accept a {@link Path} to write content to. * @throws IOException if at any step IO problem occurs. */ public static void writeFile(Path target, FileWriter writer) throws IOException { writeFile(target, writer, false); } /** * Writes file with backup copy (appends ".bak" extension). * * @param target that is the target file (must be file, the path must have parent). * @param writer the writer that will accept a {@link Path} to write content to. * @throws IOException if at any step IO problem occurs. */ public static void writeFileWithBackup(Path target, FileWriter writer) throws IOException { writeFile(target, writer, true); } /** * Utility method to write out file to disk in "atomic" manner, with optional backups (".bak") if needed. This * ensures that no other thread or process will be able to read not fully written files. Finally, this methos * may create the needed parent directories, if the passed in target parents does not exist. * * @param target that is the target file (must be an existing or non-existing file, the path must have parent). * @param writer the writer that will accept a {@link Path} to write content to. * @param doBackup if {@code true}, and target file is about to be overwritten, a ".bak" file with old contents will * be created/overwritten. * @throws IOException if at any step IO problem occurs. */ private static void writeFile(Path target, FileWriter writer, boolean doBackup) throws IOException { requireNonNull(target, "target is null"); requireNonNull(writer, "writer is null"); Path parent = requireNonNull(target.getParent(), "target must have parent"); try (CollocatedTempFile tempFile = newTempFile(target)) { writer.write(tempFile.getPath()); if (doBackup && Files.isRegularFile(target)) { Files.copy(target, parent.resolve(target.getFileName() + ".bak"), StandardCopyOption.REPLACE_EXISTING); } tempFile.move(); } } }





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