1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one
3 * or more contributor license agreements. See the NOTICE file
4 * distributed with this work for additional information
5 * regarding copyright ownership. The ASF licenses this file
6 * to you under the Apache License, Version 2.0 (the
7 * "License"); you may not use this file except in compliance
8 * with the License. You may obtain a copy of the License at
9 *
10 * http://www.apache.org/licenses/LICENSE-2.0
11 *
12 * Unless required by applicable law or agreed to in writing,
13 * software distributed under the License is distributed on an
14 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
15 * KIND, either express or implied. See the License for the
16 * specific language governing permissions and limitations
17 * under the License.
18 */
19 package org.eclipse.aether.util;
20
21 import java.io.Closeable;
22 import java.io.IOException;
23 import java.io.InputStream;
24 import java.io.OutputStream;
25 import java.nio.ByteBuffer;
26 import java.nio.channels.FileChannel;
27 import java.nio.file.Files;
28 import java.nio.file.Path;
29 import java.nio.file.StandardCopyOption;
30 import java.nio.file.StandardOpenOption;
31 import java.util.concurrent.ThreadLocalRandom;
32 import java.util.concurrent.atomic.AtomicBoolean;
33
34 import static java.util.Objects.requireNonNull;
35
36 /**
37 * A utility class to write files.
38 *
39 * @since 1.9.0
40 */
41 public final class FileUtils {
42 // Logic borrowed from Commons-Lang3: we really need only this, to decide do we fsync on directories or not
43 private static final boolean IS_WINDOWS =
44 System.getProperty("os.name", "unknown").startsWith("Windows");
45
46 private FileUtils() {
47 // hide constructor
48 }
49
50 /**
51 * A temporary file, that is removed when closed.
52 */
53 public interface TempFile extends Closeable {
54 /**
55 * Returns the path of the created temp file.
56 */
57 Path getPath();
58 }
59
60 /**
61 * A collocated temporary file, that resides next to a "target" file, and is removed when closed.
62 */
63 public interface CollocatedTempFile extends TempFile {
64 /**
65 * Upon close, atomically moves temp file to target file it is collocated with overwriting target (if exists).
66 * Invocation of this method merely signals that caller ultimately wants temp file to replace the target
67 * file, but when this method returns, the move operation did not yet happen, it will happen when this
68 * instance is closed.
69 */
70 void move() throws IOException;
71 }
72
73 /**
74 * Creates a {@link TempFile} instance and backing temporary file on file system. It will be located in the default
75 * temporary-file directory. Returned instance should be handled in try-with-resource construct and created
76 * temp file is removed (if exists) when returned instance is closed.
77 * <p>
78 * This method uses {@link Files#createTempFile(String, String, java.nio.file.attribute.FileAttribute[])} to create
79 * the temporary file on file system.
80 */
81 public static TempFile newTempFile() throws IOException {
82 Path tempFile = Files.createTempFile("resolver", "tmp");
83 return new TempFile() {
84 @Override
85 public Path getPath() {
86 return tempFile;
87 }
88
89 @Override
90 public void close() throws IOException {
91 Files.deleteIfExists(tempFile);
92 }
93 };
94 }
95
96 /**
97 * Creates a {@link CollocatedTempFile} instance for given file without backing file. The path will be located in
98 * same directory where given file is, and will reuse its name for generated (randomized) name. Returned instance
99 * should be handled in try-with-resource and created temp path is removed (if exists) when returned instance is
100 * closed. The {@link CollocatedTempFile#move()} makes possible to atomically replace passed in file with the
101 * processed content written into a file backing the {@link CollocatedTempFile} instance.
102 * <p>
103 * The {@code file} nor it's parent directories have to exist. The parent directories are created if needed.
104 * <p>
105 * This method uses {@link Path#resolve(String)} to create the temporary file path in passed in file parent
106 * directory, but it does NOT create backing file on file system.
107 */
108 public static CollocatedTempFile newTempFile(Path file) throws IOException {
109 Path parent = requireNonNull(file.getParent(), "file must have parent");
110 Files.createDirectories(parent);
111 Path tempFile = parent.resolve(file.getFileName() + "."
112 + Long.toUnsignedString(ThreadLocalRandom.current().nextLong()) + ".tmp");
113 return new CollocatedTempFile() {
114 private final AtomicBoolean wantsMove = new AtomicBoolean(false);
115
116 @Override
117 public Path getPath() {
118 return tempFile;
119 }
120
121 @Override
122 public void move() {
123 wantsMove.set(true);
124 }
125
126 @Override
127 public void close() throws IOException {
128 if (wantsMove.get() && Files.isReadable(tempFile)) {
129 if (IS_WINDOWS) {
130 copy(tempFile, file);
131 } else {
132 fsyncFile(tempFile);
133 Files.move(tempFile, file, StandardCopyOption.ATOMIC_MOVE);
134 fsyncParent(tempFile);
135 }
136 }
137 Files.deleteIfExists(tempFile);
138 }
139 };
140 }
141
142 /**
143 * On Windows we use pre-NIO2 way to copy files, as for some reason it works. Beat me why.
144 */
145 private static void copy(Path source, Path target) throws IOException {
146 ByteBuffer buffer = ByteBuffer.allocate(1024 * 32);
147 byte[] array = buffer.array();
148 try (InputStream is = Files.newInputStream(source);
149 OutputStream os = Files.newOutputStream(target)) {
150 while (true) {
151 int bytes = is.read(array);
152 if (bytes < 0) {
153 break;
154 }
155 os.write(array, 0, bytes);
156 }
157 }
158 }
159
160 /**
161 * Performs fsync: makes sure no OS "dirty buffers" exist for given file.
162 *
163 * @param target Path that must not be {@code null}, must exist as plain file.
164 */
165 private static void fsyncFile(Path target) throws IOException {
166 try (FileChannel file = FileChannel.open(target, StandardOpenOption.WRITE)) {
167 file.force(true);
168 }
169 }
170
171 /**
172 * Performs directory fsync: not usable on Windows, but some other OSes may also throw, hence thrown IO exception
173 * is just ignored.
174 *
175 * @param target Path that must not be {@code null}, must exist as plain file, and must have parent.
176 */
177 private static void fsyncParent(Path target) throws IOException {
178 try (FileChannel parent = FileChannel.open(target.getParent(), StandardOpenOption.READ)) {
179 try {
180 parent.force(true);
181 } catch (IOException e) {
182 // ignore
183 }
184 }
185 }
186
187 /**
188 * A file writer, that accepts a {@link Path} to write some content to. Note: the file denoted by path may exist,
189 * hence implementation have to ensure it is able to achieve its goal ("replace existing" option or equivalent
190 * should be used).
191 */
192 @FunctionalInterface
193 public interface FileWriter {
194 void write(Path path) throws IOException;
195 }
196
197 /**
198 * Writes file without backup.
199 *
200 * @param target that is the target file (must be file, the path must have parent).
201 * @param writer the writer that will accept a {@link Path} to write content to.
202 * @throws IOException if at any step IO problem occurs.
203 */
204 public static void writeFile(Path target, FileWriter writer) throws IOException {
205 writeFile(target, writer, false);
206 }
207
208 /**
209 * Writes file with backup copy (appends ".bak" extension).
210 *
211 * @param target that is the target file (must be file, the path must have parent).
212 * @param writer the writer that will accept a {@link Path} to write content to.
213 * @throws IOException if at any step IO problem occurs.
214 */
215 public static void writeFileWithBackup(Path target, FileWriter writer) throws IOException {
216 writeFile(target, writer, true);
217 }
218
219 /**
220 * Utility method to write out file to disk in "atomic" manner, with optional backups (".bak") if needed. This
221 * ensures that no other thread or process will be able to read not fully written files. Finally, this methos
222 * may create the needed parent directories, if the passed in target parents does not exist.
223 *
224 * @param target that is the target file (must be an existing or non-existing file, the path must have parent).
225 * @param writer the writer that will accept a {@link Path} to write content to.
226 * @param doBackup if {@code true}, and target file is about to be overwritten, a ".bak" file with old contents will
227 * be created/overwritten.
228 * @throws IOException if at any step IO problem occurs.
229 */
230 private static void writeFile(Path target, FileWriter writer, boolean doBackup) throws IOException {
231 requireNonNull(target, "target is null");
232 requireNonNull(writer, "writer is null");
233 Path parent = requireNonNull(target.getParent(), "target must have parent");
234
235 try (CollocatedTempFile tempFile = newTempFile(target)) {
236 writer.write(tempFile.getPath());
237 if (doBackup && Files.isRegularFile(target)) {
238 Files.copy(target, parent.resolve(target.getFileName() + ".bak"), StandardCopyOption.REPLACE_EXISTING);
239 }
240 tempFile.move();
241 }
242 }
243 }