aboutsummaryrefslogtreecommitdiffhomepage
path: root/src/main/java/com/google/devtools/build/lib/vfs/FileSystemUtils.java
blob: 999c470c8bce8215cd7fefdd2d406164f23e4825 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
// Copyright 2014 The Bazel Authors. All rights reserved.
//
// 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.google.devtools.build.lib.vfs;

import static java.nio.charset.StandardCharsets.ISO_8859_1;

import com.google.common.base.Preconditions;
import com.google.common.base.Predicate;
import com.google.common.io.ByteSink;
import com.google.common.io.ByteSource;
import com.google.common.io.ByteStreams;
import com.google.devtools.build.lib.concurrent.ThreadSafety.ConditionallyThreadSafe;
import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadSafe;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.nio.charset.Charset;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.List;

/**
 * Helper functions that implement often-used complex operations on file
 * systems.
 */
@ConditionallyThreadSafe // ThreadSafe except for deleteTree.
public class FileSystemUtils {

  private FileSystemUtils() {}

  /****************************************************************************
   * Path and PathFragment functions.
   */

  /**
   * Throws exceptions if {@code baseName} is not a valid base name. A valid
   * base name:
   * <ul>
   * <li>Is not null
   * <li>Is not an empty string
   * <li>Is not "." or ".."
   * <li>Does not contain a slash
   * </ul>
   */
  @ThreadSafe
  public static void checkBaseName(String baseName) {
    if (baseName.length() == 0) {
      throw new IllegalArgumentException("Child must not be empty string ('')");
    }
    if (baseName.equals(".") || baseName.equals("..")) {
      throw new IllegalArgumentException("baseName must not be '" + baseName + "'");
    }
    if (baseName.indexOf('/') != -1) {
      throw new IllegalArgumentException("baseName must not contain a slash: '" + baseName + "'");
    }
  }

  /**
   * Returns the common ancestor between two paths, or null if none (including
   * if they are on different filesystems).
   */
  public static Path commonAncestor(Path a, Path b) {
    while (a != null && !b.startsWith(a)) {
      a = a.getParentDirectory();  // returns null at root
    }
    return a;
  }

  /**
   * Returns the longest common ancestor of the two path fragments, or either "/" or "" (depending
   * on whether {@code a} is absolute or relative) if there is none.
   */
  public static PathFragment commonAncestor(PathFragment a, PathFragment b) {
    while (a != null && !b.startsWith(a)) {
      a = a.getParentDirectory();
    }

    return a;
  }

  /**
   * Returns a path fragment from a given from-dir to a given to-path.
   */
  public static PathFragment relativePath(PathFragment fromDir, PathFragment to) {
    if (to.equals(fromDir)) {
      return PathFragment.EMPTY_FRAGMENT;
    }
    if (to.startsWith(fromDir)) {
      return to.relativeTo(fromDir);  // easy case--it's a descendant
    }
    PathFragment ancestor = commonAncestor(fromDir, to);
    if (ancestor == null) {
      return to;  // no common ancestor, use 'to'
    }
    int levels = fromDir.relativeTo(ancestor).segmentCount();
    StringBuilder dotdots = new StringBuilder();
    for (int i = 0; i < levels; i++) {
      dotdots.append("../");
    }
    return PathFragment.create(dotdots.toString()).getRelative(to.relativeTo(ancestor));
  }

  /**
   * Removes the shortest suffix beginning with '.' from the basename of the
   * filename string. If the basename contains no '.', the filename is returned
   * unchanged.
   *
   * <p>e.g. "foo/bar.x" -> "foo/bar"
   *
   * <p>Note that if the filename is composed entirely of ".", this method will return the string
   * with one fewer ".", which may have surprising effects.
   */
  @ThreadSafe
  public static String removeExtension(String filename) {
    int lastDotIndex = filename.lastIndexOf('.');
    if (lastDotIndex == -1) { return filename; }
    int lastSlashIndex = filename.lastIndexOf('/');
    if (lastSlashIndex > lastDotIndex) {
      return filename;
    }
    return filename.substring(0, lastDotIndex);
  }

  /**
   * Removes the shortest suffix beginning with '.' from the basename of the
   * PathFragment. If the basename contains no '.', the filename is returned
   * unchanged.
   *
   * <p>e.g. "foo/bar.x" -> "foo/bar"
   *
   * <p>Note that if the base filename is composed entirely of ".", this method will return the
   * filename with one fewer "." in the base filename, which may have surprising effects.
   */
  @ThreadSafe
  public static PathFragment removeExtension(PathFragment path) {
    return path.replaceName(removeExtension(path.getBaseName()));
  }

  /**
   * Removes the shortest suffix beginning with '.' from the basename of the
   * Path. If the basename contains no '.', the filename is returned
   * unchanged.
   *
   * <p>e.g. "foo/bar.x" -> "foo/bar"
   *
   * <p>Note that if the base filename is composed entirely of ".", this method will return the
   * filename with one fewer "." in the base filename, which may have surprising effects.
   */
  @ThreadSafe
  public static Path removeExtension(Path path) {
    return path.getFileSystem().getPath(removeExtension(path.asFragment()));
  }

  /**
   * Returns a new {@code PathFragment} formed by replacing the extension of the
   * last path segment of {@code path} with {@code newExtension}. Null is
   * returned iff {@code path} has zero segments.
   */
  public static PathFragment replaceExtension(PathFragment path, String newExtension) {
    return path.replaceName(removeExtension(path.getBaseName()) + newExtension);
  }

  /**
   * Returns a new {@code PathFragment} formed by replacing the extension of the
   * last path segment of {@code path} with {@code newExtension}. Null is
   * returned iff {@code path} has zero segments or it doesn't end with {@code oldExtension}.
   */
  public static PathFragment replaceExtension(PathFragment path, String newExtension,
      String oldExtension) {
    String base = path.getBaseName();
    if (!base.endsWith(oldExtension)) {
      return null;
    }
    String newBase = base.substring(0, base.length() - oldExtension.length()) + newExtension;
    return path.replaceName(newBase);
  }

  /**
   * Returns a new {@code Path} formed by replacing the extension of the
   * last path segment of {@code path} with {@code newExtension}. Null is
   * returned iff {@code path} has zero segments.
   */
  public static Path replaceExtension(Path path, String newExtension) {
    PathFragment fragment = replaceExtension(path.asFragment(), newExtension);
    return fragment == null ? null : path.getFileSystem().getPath(fragment);
  }

  /**
   * Returns a new {@code PathFragment} formed by adding the extension to the last path segment of
   * {@code path}. Null is returned if {@code path} has zero segments.
   */
  public static PathFragment appendExtension(PathFragment path, String newExtension) {
    return path.replaceName(path.getBaseName() + newExtension);
  }

  /**
   * Returns a new {@code PathFragment} formed by appending the given string to the last path
   * segment of {@code path} without removing the extension.  Returns null if {@code path}
   * has zero segments.
   */
  public static PathFragment appendWithoutExtension(PathFragment path, String toAppend) {
    return path.replaceName(appendWithoutExtension(path.getBaseName(), toAppend));
  }

  /**
   * Given a string that represents a file with an extension separated by a '.' and a string
   * to append, return a string in which {@code toAppend} has been appended to {@code name}
   * before the last '.' character.  If {@code name} does not include a '.', appends {@code
   * toAppend} at the end.
   *
   * <p>For example,
   * ("libfoo.jar", "-src") ==> "libfoo-src.jar"
   * ("libfoo", "-src") ==> "libfoo-src"
   */
  private static String appendWithoutExtension(String name, String toAppend) {
    int dotIndex = name.lastIndexOf('.');
    if (dotIndex > 0) {
      String baseName = name.substring(0, dotIndex);
      String extension = name.substring(dotIndex);
      return baseName + toAppend + extension;
    } else {
      return name + toAppend;
    }
  }

  /****************************************************************************
   * FileSystem property functions.
   */

  /**
   * Return the current working directory as expressed by the System property
   * 'user.dir'.
   */
  public static Path getWorkingDirectory(FileSystem fs) {
    return fs.getPath(getWorkingDirectory());
  }

  /**
   * Returns the current working directory as expressed by the System property
   * 'user.dir'. This version does not require a {@link FileSystem}.
   */
  public static PathFragment getWorkingDirectory() {
    return PathFragment.create(System.getProperty("user.dir", "/"));
  }

  /****************************************************************************
   * Path FileSystem mutating operations.
   */

  /**
   * "Touches" the file or directory specified by the path, following symbolic
   * links. If it does not exist, it is created as an empty file; otherwise, the
   * time of last access is updated to the current time.
   *
   * @throws IOException if there was an error while touching the file
   */
  @ThreadSafe
  public static void touchFile(Path path) throws IOException {
    if (path.exists()) {
      // -1L means "use the current time", and is ultimately implemented by
      // utime(path, null), thereby using the kernel's clock, not the JVM's.
      // (A previous implementation based on the JVM clock was found to be
      // skewy.)
      path.setLastModifiedTime(-1L);
    } else {
      createEmptyFile(path);
    }
  }

  /**
   * Creates an empty regular file with the name of the current path, following
   * symbolic links.
   *
   * @throws IOException if the file could not be created for any reason
   *         (including that there was already a file at that location)
   */
  public static void createEmptyFile(Path path) throws IOException {
    path.getOutputStream().close();
  }

  /**
   * Creates or updates a symbolic link from 'link' to 'target'. Replaces
   * existing symbolic links with target, and skips the link creation if it is
   * already present. Will also create any missing ancestor directories of the
   * link. This method is non-atomic
   *
   * <p>Note: this method will throw an IOException if there is an unequal
   * non-symlink at link.
   *
   * @throws IOException if the creation of the symbolic link was unsuccessful
   *         for any reason.
   */
  @ThreadSafe  // but not atomic
  public static void ensureSymbolicLink(Path link, Path target) throws IOException {
    ensureSymbolicLink(link, target.asFragment());
  }

  /**
   * Creates or updates a symbolic link from 'link' to 'target'. Replaces
   * existing symbolic links with target, and skips the link creation if it is
   * already present. Will also create any missing ancestor directories of the
   * link. This method is non-atomic
   *
   * <p>Note: this method will throw an IOException if there is an unequal
   * non-symlink at link.
   *
   * @throws IOException if the creation of the symbolic link was unsuccessful
   *         for any reason.
   */
  @ThreadSafe  // but not atomic
  public static void ensureSymbolicLink(Path link, String target) throws IOException {
    ensureSymbolicLink(link, PathFragment.create(target));
  }

  /**
   * Creates or updates a symbolic link from 'link' to 'target'. Replaces
   * existing symbolic links with target, and skips the link creation if it is
   * already present. Will also create any missing ancestor directories of the
   * link. This method is non-atomic
   *
   * <p>Note: this method will throw an IOException if there is an unequal
   * non-symlink at link.
   *
   * @throws IOException if the creation of the symbolic link was unsuccessful
   *         for any reason.
   */
  @ThreadSafe  // but not atomic
  public static void ensureSymbolicLink(Path link, PathFragment target) throws IOException {
    // TODO(bazel-team): (2009) consider adding the logic for recovering from the case when
    // we have already created a parent directory symlink earlier.
    try {
      if (link.readSymbolicLink().equals(target)) {
        return;  // Do nothing if the link is already there.
      }
    } catch (IOException e) { // link missing or broken
      /* fallthru and do the work below */
    }
    if (link.isSymbolicLink()) {
      link.delete();  // Remove the symlink since it is pointing somewhere else.
    } else {
      createDirectoryAndParents(link.getParentDirectory());
    }
    try {
      link.createSymbolicLink(target);
    } catch (IOException e) {
      // Only pass on exceptions caused by a true link creation failure.
      if (!link.isSymbolicLink() ||
          !link.resolveSymbolicLinks().equals(link.getRelative(target))) {
        throw e;
      }
    }
  }

  public static ByteSource asByteSource(final Path path) {
    return new ByteSource() {
      @Override public InputStream openStream() throws IOException {
        return path.getInputStream();
      }
    };
  }

  public static ByteSink asByteSink(final Path path, final boolean append) {
    return new ByteSink() {
      @Override public OutputStream openStream() throws IOException {
        return path.getOutputStream(append);
      }
    };
  }

  public static ByteSink asByteSink(final Path path) {
    return asByteSink(path, false);
  }

  /**
   * Copies the file from location "from" to location "to", while overwriting a
   * potentially existing "to". File's last modified time, executable and
   * writable bits are also preserved.
   *
   * <p>If no error occurs, the method returns normally. If a parent directory does
   * not exist, a FileNotFoundException is thrown. An IOException is thrown when
   * other erroneous situations occur. (e.g. read errors)
   */
  @ThreadSafe  // but not atomic
  public static void copyFile(Path from, Path to) throws IOException {
    try {
      to.delete();
    } catch (IOException e) {
      throw new IOException("error copying file: "
          + "couldn't delete destination: " + e.getMessage());
    }
    asByteSource(from).copyTo(asByteSink(to));
    to.setLastModifiedTime(from.getLastModifiedTime()); // Preserve mtime.
    if (!from.isWritable()) {
      to.setWritable(false); // Make file read-only if original was read-only.
    }
    to.setExecutable(from.isExecutable()); // Copy executable bit.
  }

  /**
   * Moves the file from location "from" to location "to", while overwriting a potentially existing
   * "to". If "from" is a regular file, its last modified time, executable and writable bits are
   * also preserved. Symlinks are also supported but not directories or special files.
   *
   * <p>If no error occurs, the method returns normally. If a parent directory does not exist, a
   * FileNotFoundException is thrown. {@link IOException} is thrown when other erroneous situations
   * occur. (e.g. read errors)
   */
  @ThreadSafe // but not atomic
  public static void moveFile(Path from, Path to) throws IOException {
    // We don't try-catch here for better performance.
    to.delete();
    try {
      from.renameTo(to);
    } catch (IOException e) {
      // Fallback to a copy.
      FileStatus stat = from.stat(Symlinks.NOFOLLOW);
      if (stat.isFile()) {
        asByteSource(from).copyTo(asByteSink(to));
        to.setLastModifiedTime(stat.getLastModifiedTime()); // Preserve mtime.
        if (!from.isWritable()) {
          to.setWritable(false); // Make file read-only if original was read-only.
        }
        to.setExecutable(from.isExecutable()); // Copy executable bit.
      } else if (stat.isSymbolicLink()) {
        to.createSymbolicLink(from.readSymbolicLink());
      } else {
        throw new IOException("Don't know how to copy " + from);
      }
      if (!from.delete()) {
        if (!to.delete()) {
          throw new IOException("Unable to delete " + to);
        }
        throw new IOException("Unable to delete " + from);
      }
    }
  }

  /**
   * Copies a tool binary from one path to another, returning the target path.
   * The directory of the target path must already exist. The target copy's time
   * is set to match, as well as its read-only and executable flags. The
   * operation is skipped if the target file has the same time and size as the
   * source.
   */
  public static Path copyTool(Path source, Path target) throws IOException {
    FileStatus sourceStat = null;
    FileStatus targetStat = target.statNullable();
    if (targetStat != null) {
      // stat the source file only if we'll need the stat.
      sourceStat = source.stat(Symlinks.FOLLOW);
    }
    if (targetStat == null ||
        targetStat.getLastModifiedTime() != sourceStat.getLastModifiedTime() ||
        targetStat.getSize() != sourceStat.getSize()) {
      copyFile(source, target);
      target.setWritable(source.isWritable());
      target.setExecutable(source.isExecutable());
      target.setLastModifiedTime(source.getLastModifiedTime());
    }
    return target;
  }

  /****************************************************************************
   * Directory tree operations.
   */

  /**
   * Returns a new collection containing all of the paths below a given root
   * path, for which the given predicate is true. Symbolic links are not
   * followed, and may appear in the result.
   *
   * @throws IOException If the root does not denote a directory
   */
  @ThreadSafe
  public static Collection<Path> traverseTree(Path root, Predicate<? super Path> predicate)
      throws IOException {
    List<Path> paths = new ArrayList<>();
    traverseTree(paths, root, predicate);
    return paths;
  }

  /**
   * Populates an existing Path List, adding all of the paths below a given root
   * path for which the given predicate is true. Symbolic links are not
   * followed, and may appear in the result.
   *
   * @throws IOException If the root does not denote a directory
   */
  @ThreadSafe
  public static void traverseTree(Collection<Path> paths, Path root,
      Predicate<? super Path> predicate) throws IOException {
    for (Path p : root.getDirectoryEntries()) {
      if (predicate.apply(p)) {
        paths.add(p);
      }
      if (p.isDirectory(Symlinks.NOFOLLOW)) {
        traverseTree(paths, p, predicate);
      }
    }
  }

  /**
   * Deletes 'p', and everything recursively beneath it if it's a directory.
   * Does not follow any symbolic links.
   *
   * @throws IOException if any file could not be removed.
   */
  @ThreadSafe
  public static void deleteTree(Path p) throws IOException {
    deleteTreesBelow(p);
    p.delete();
  }

  /**
   * Deletes all dir trees recursively beneath 'dir' if it's a directory,
   * nothing otherwise. Does not follow any symbolic links.
   *
   * @throws IOException if any file could not be removed.
   */
  @ThreadSafe
  public static void deleteTreesBelow(Path dir) throws IOException {
    if (dir.isDirectory(Symlinks.NOFOLLOW)) {  // real directories (not symlinks)
      dir.setReadable(true);
      dir.setWritable(true);
      dir.setExecutable(true);
      for (Path child : dir.getDirectoryEntries()) {
        deleteTree(child);
      }
    }
  }

  /**
   * Copies all dir trees under a given 'from' dir to location 'to', while overwriting all files in
   * the potentially existing 'to'. Resolves symbolic links if {@code followSymlinks ==
   * Symlinks#FOLLOW}. Otherwise copies symlinks as-is.
   *
   * <p>The source and the destination must be non-overlapping, otherwise an
   * IllegalArgumentException will be thrown. This method cannot be used to copy a dir tree to a sub
   * tree of itself.
   *
   * <p>If no error occurs, the method returns normally. If the given 'from' does not exist, a
   * FileNotFoundException is thrown. An IOException is thrown when other erroneous situations
   * occur. (e.g. read errors)
   */
  @ThreadSafe
  public static void copyTreesBelow(Path from, Path to, Symlinks followSymlinks)
      throws IOException {
    if (to.startsWith(from)) {
      throw new IllegalArgumentException(to + " is a subdirectory of " + from);
    }

    Collection<Path> entries = from.getDirectoryEntries();
    for (Path entry : entries) {
      Path toPath = to.getChild(entry.getBaseName());
      if (!followSymlinks.toBoolean() && entry.isSymbolicLink()) {
        FileSystemUtils.ensureSymbolicLink(toPath, entry.readSymbolicLink());
      } else if (entry.isFile()) {
        copyFile(entry, toPath);
      } else {
        toPath.createDirectory();
        copyTreesBelow(entry, toPath, followSymlinks);
      }
    }
  }

  /**
   * Moves all dir trees under a given 'from' dir to location 'to', while overwriting
   * all files in the potentially existing 'to'. Doesn't resolve symbolic links.
   *
   * <p>The source and the destination must be non-overlapping, otherwise an
   * IllegalArgumentException will be thrown. This method cannot be used to copy
   * a dir tree to a sub tree of itself.
   *
   * <p>If no error occurs, the method returns normally. If the given 'from' does
   * not exist, a FileNotFoundException is thrown. An IOException is thrown when
   * other erroneous situations occur. (e.g. read errors)
   */
  @ThreadSafe
  public static void moveTreesBelow(Path from , Path to) throws IOException {
    if (to.startsWith(from)) {
      throw new IllegalArgumentException(to + " is a subdirectory of " + from);
    }

    Collection<Path> entries = from.getDirectoryEntries();
    for (Path entry : entries) {
      if (entry.isDirectory(Symlinks.NOFOLLOW)) {
        Path subDir = to.getChild(entry.getBaseName());
        subDir.createDirectory();
        moveTreesBelow(entry, subDir);
      } else {
        Path newEntry = to.getChild(entry.getBaseName());
        moveFile(entry, newEntry);
      }
    }
  }

  /**
   * Attempts to create a directory with the name of the given path, creating ancestors as
   * necessary.
   *
   * <p>Deprecated. Prefer to call {@link Path#createDirectoryAndParents()} directly.
   */
  @Deprecated
  @ThreadSafe
  public static void createDirectoryAndParents(Path dir) throws IOException {
    dir.createDirectoryAndParents();
  }

  /**
   * Attempts to remove a relative chain of directories under a given base.
   * Returns {@code true} if the removal was successful, and returns {@code
   * false} if the removal fails because a directory was not empty. An
   * {@link IOException} is thrown for any other errors.
   */
  @ThreadSafe
  public static boolean removeDirectoryAndParents(Path base, PathFragment toRemove) {
    if (toRemove.isAbsolute()) {
      return false;
    }
    try {
      for (; toRemove.segmentCount() > 0; toRemove = toRemove.getParentDirectory()) {
        Path p = base.getRelative(toRemove);
        if (p.exists()) {
          p.delete();
        }
      }
    } catch (IOException e) {
      return false;
    }
    return true;
  }

  /****************************************************************************
   * Whole-file I/O utilities for characters and bytes. These convenience
   * methods are not efficient and should not be used for large amounts of data!
   */

  /**
   * Decodes the given byte array assumed to be encoded with ISO-8859-1 encoding (isolatin1).
   */
  public static char[] convertFromLatin1(byte[] content) {
    char[] latin1 = new char[content.length];
    for (int i = 0; i < latin1.length; i++) { // yeah, latin1 is this easy! :-)
      latin1[i] = (char) (0xff & content[i]);
    }
    return latin1;
  }

  /**
   * Writes lines to file using ISO-8859-1 encoding (isolatin1).
   */
  @ThreadSafe // but not atomic
  public static void writeIsoLatin1(Path file, String... lines) throws IOException {
    writeLinesAs(file, ISO_8859_1, lines);
  }

  /**
   * Append lines to file using ISO-8859-1 encoding (isolatin1).
   */
  @ThreadSafe // but not atomic
  public static void appendIsoLatin1(Path file, String... lines) throws IOException {
    appendLinesAs(file, ISO_8859_1, lines);
  }

  /**
   * Writes the specified String as ISO-8859-1 (latin1) encoded bytes to the
   * file. Follows symbolic links.
   *
   * @throws IOException if there was an error
   */
  public static void writeContentAsLatin1(Path outputFile, String content) throws IOException {
    writeContent(outputFile, ISO_8859_1, content);
  }

  /**
   * Writes the specified String using the specified encoding to the file.
   * Follows symbolic links.
   *
   * @throws IOException if there was an error
   */
  public static void writeContent(Path outputFile, Charset charset, String content)
      throws IOException {
    asByteSink(outputFile).asCharSink(charset).write(content);
  }

  /**
   * Writes lines to file using the given encoding, ending every line with a
   * line break '\n' character.
   */
  @ThreadSafe // but not atomic
  public static void writeLinesAs(Path file, Charset charset, String... lines)
      throws IOException {
    writeLinesAs(file, charset, Arrays.asList(lines));
  }

  /**
   * Appends lines to file using the given encoding, ending every line with a
   * line break '\n' character.
   */
  @ThreadSafe // but not atomic
  public static void appendLinesAs(Path file, Charset charset, String... lines)
      throws IOException {
    appendLinesAs(file, charset, Arrays.asList(lines));
  }

  /**
   * Writes lines to file using the given encoding, ending every line with a
   * line break '\n' character.
   */
  @ThreadSafe // but not atomic
  public static void writeLinesAs(Path file, Charset charset, Iterable<String> lines)
      throws IOException {
    createDirectoryAndParents(file.getParentDirectory());
    asByteSink(file).asCharSink(charset).writeLines(lines);
  }

  /**
   * Appends lines to file using the given encoding, ending every line with a
   * line break '\n' character.
   */
  @ThreadSafe // but not atomic
  public static void appendLinesAs(Path file, Charset charset, Iterable<String> lines)
      throws IOException {
    createDirectoryAndParents(file.getParentDirectory());
    asByteSink(file, true).asCharSink(charset).writeLines(lines);
  }

  /**
   * Writes the specified byte array to the output file. Follows symbolic links.
   *
   * @throws IOException if there was an error
   */
  public static void writeContent(Path outputFile, byte[] content) throws IOException {
    asByteSink(outputFile).write(content);
  }

  /**
   * Updates the contents of the output file if they do not match the given array, thus maintaining
   * the mtime and ctime in case of no updates. Follows symbolic links.
   *
   * <p>If the output file already exists but is unreadable, this tries to overwrite it with the new
   * contents. In other words: unreadable or missing files are considered to be non-matching.
   *
   * @throws IOException if there was an error
   */
  public static void maybeUpdateContent(Path outputFile, byte[] newContent) throws IOException {
    byte[] currentContent;
    try {
      currentContent = readContent(outputFile);
    } catch (IOException e) {
      // Ignore error per the rationale given in the docstring. Keep in mind that what we are doing
      // here is for performance reasons only so we should only break if the real action (that is,
      // the write) fails -- not any of the optimization steps.
      currentContent = null;
    }

    if (currentContent == null) {
      writeContent(outputFile, newContent);
    } else {
      if (!Arrays.equals(newContent, currentContent)) {
        if (!outputFile.isWritable()) {
          outputFile.delete();
        }
        writeContent(outputFile, newContent);
      }
    }
  }

  /**
   * Returns the entirety of the specified input stream and returns it as a char
   * array, decoding characters using ISO-8859-1 (Latin1).
   *
   * @throws IOException if there was an error
   */
  public static char[] readContentAsLatin1(InputStream in) throws IOException {
    return convertFromLatin1(ByteStreams.toByteArray(in));
  }

  /**
   * Returns the entirety of the specified file and returns it as a char array,
   * decoding characters using ISO-8859-1 (Latin1).
   *
   * @throws IOException if there was an error
   */
  public static char[] readContentAsLatin1(Path inputFile) throws IOException {
    return convertFromLatin1(readContent(inputFile));
  }

  /**
   * Returns an iterable that allows iterating over ISO-8859-1 (Latin1) text
   * file contents line by line. If the file ends in a line break, the iterator
   * will return an empty string as the last element.
   *
   * @throws IOException if there was an error
   */
  public static Iterable<String> iterateLinesAsLatin1(Path inputFile) throws IOException {
    return readLines(inputFile, ISO_8859_1);
  }

  /**
   * Returns an iterable that allows iterating over text file contents line by line in the given
   * {@link Charset}. If the file ends in a line break, the iterator will return an empty string
   * as the last element.
   *
   * @throws IOException if there was an error
   */
  public static Iterable<String> readLines(Path inputFile, Charset charset) throws IOException {
    return asByteSource(inputFile).asCharSource(charset).readLines();
  }

  /**
   * Returns the entirety of the specified file and returns it as a byte array.
   *
   * @throws IOException if there was an error
   */
  public static byte[] readContent(Path inputFile) throws IOException {
    return asByteSource(inputFile).read();
  }

  /**
   * Reads the entire file using the given charset and returns the contents as a string
   */
  public static String readContent(Path inputFile, Charset charset) throws IOException {
    return asByteSource(inputFile).asCharSource(charset).read();
  }

  /**
   * Reads at most {@code limit} bytes from {@code inputFile} and returns it as a byte array.
   *
   * @throws IOException if there was an error.
   */
  public static byte[] readContentWithLimit(Path inputFile, int limit) throws IOException {
    Preconditions.checkArgument(limit >= 0, "limit needs to be >=0, but it is %s", limit);
    ByteSource byteSource = asByteSource(inputFile);
    byte[] buffer = new byte[limit];
    try (InputStream inputStream = byteSource.openBufferedStream()) {
      int read = ByteStreams.read(inputStream, buffer, 0, limit);
      return read == limit ? buffer : Arrays.copyOf(buffer, read);
    }
  }

  /**
   * Reads the given file {@code path}, assumed to have size {@code fileSize}, and does a sanity
   * check on the number of bytes read.
   *
   * <p>Use this method when you already know the size of the file. The sanity check is intended to
   * catch issues where filesystems incorrectly truncate files.
   *
   * @throws IOException if there was an error, or if fewer than {@code fileSize} bytes were read.
   */
  public static byte[] readWithKnownFileSize(Path path, long fileSize) throws IOException {
    if (fileSize > Integer.MAX_VALUE) {
      throw new IOException("Cannot read file with size larger than 2GB");
    }
    int fileSizeInt = (int) fileSize;
    byte[] bytes = readContentWithLimit(path, fileSizeInt);
    if (fileSizeInt > bytes.length) {
      throw new IOException("Unexpected short read from file '" + path
          + "' (expected " + fileSizeInt + ", got " + bytes.length + " bytes)");
    }
    return bytes;
  }

  /**
   * Returns the type of the file system path belongs to.
   */
  public static String getFileSystem(Path path) {
    return path.getFileSystem().getFileSystemType(path);
  }

  /**
   * Returns whether the given path starts with any of the paths in the given
   * list of prefixes.
   */
  public static boolean startsWithAny(Path path, Iterable<Path> prefixes) {
    for (Path prefix : prefixes) {
      if (path.startsWith(prefix)) {
        return true;
      }
    }
    return false;
  }

  /**
   * Returns whether the given path starts with any of the paths in the given
   * list of prefixes.
   */
  public static boolean startsWithAny(PathFragment path, Iterable<PathFragment> prefixes) {
    for (PathFragment prefix : prefixes) {
      if (path.startsWith(prefix)) {
        return true;
      }
    }
    return false;
  }


  /**
   * Create a new hard link file at "linkPath" for file at "originalPath". If "originalPath" is a
   * directory, then for each entry, create link under "linkPath" recursively.
   *
   * @param linkPath The path of the new link file to be created
   * @param originalPath The path of the original file
   * @throws IOException if there was an error executing {@link Path#createHardLink}
   */
  public static void createHardLink(Path linkPath, Path originalPath) throws IOException {

    // Directory
    if (originalPath.isDirectory()) {
      for (Path originalSubpath : originalPath.getDirectoryEntries()) {
        Path linkSubpath = linkPath.getRelative(originalSubpath.relativeTo(originalPath));
        createHardLink(linkSubpath, originalSubpath);
      }
      // Other types of file
    } else {
      Path parentDir = linkPath.getParentDirectory();
      if (!parentDir.exists()) {
        FileSystemUtils.createDirectoryAndParents(parentDir);
      }
      originalPath.createHardLink(linkPath);
    }
  }
}