1 // Copyright 2009 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
4 5 // Package filepath implements utility routines for manipulating filename paths
6 // in a way compatible with the target operating system-defined file paths.
7 //
8 // The filepath package uses either forward slashes or backslashes,
9 // depending on the operating system. To process paths such as URLs
10 // that always use forward slashes regardless of the operating
11 // system, see the [path] package.
12 package filepath
13 14 import (
15 "errors"
16 "internal/bytealg"
17 "internal/filepathlite"
18 "io/fs"
19 "os"
20 "slices"
21 )
22 23 const (
24 Separator = os.PathSeparator
25 ListSeparator = os.PathListSeparator
26 )
27 28 // Clean returns the shortest path name equivalent to path
29 // by purely lexical processing. It applies the following rules
30 // iteratively until no further processing can be done:
31 //
32 // 1. Replace multiple [Separator] elements with a single one.
33 // 2. Eliminate each . path name element (the current directory).
34 // 3. Eliminate each inner .. path name element (the parent directory)
35 // along with the non-.. element that precedes it.
36 // 4. Eliminate .. elements that begin a rooted path:
37 // that is, replace "/.." by "/" at the beginning of a path,
38 // assuming Separator is '/'.
39 //
40 // The returned path ends in a slash only if it represents a root directory,
41 // such as "/" on Unix or `C:\` on Windows.
42 //
43 // Finally, any occurrences of slash are replaced by Separator.
44 //
45 // If the result of this process is an empty string, Clean
46 // returns the string ".".
47 //
48 // On Windows, Clean does not modify the volume name other than to replace
49 // occurrences of "/" with `\`.
50 // For example, Clean("//host/share/../x") returns `\\host\share\x`.
51 //
52 // See also Rob Pike, “Lexical File Names in Plan 9 or
53 // Getting Dot-Dot Right,”
54 // https://9p.io/sys/doc/lexnames.html
55 func Clean(path []byte) []byte {
56 return filepathlite.Clean(path)
57 }
58 59 // IsLocal reports whether path, using lexical analysis only, has all of these properties:
60 //
61 // - is within the subtree rooted at the directory in which path is evaluated
62 // - is not an absolute path
63 // - is not empty
64 // - on Windows, is not a reserved name such as "NUL"
65 //
66 // If IsLocal(path) returns true, then
67 // Join(base, path) will always produce a path contained within base and
68 // Clean(path) will always produce an unrooted path with no ".." path elements.
69 //
70 // IsLocal is a purely lexical operation.
71 // In particular, it does not account for the effect of any symbolic links
72 // that may exist in the filesystem.
73 func IsLocal(path []byte) bool {
74 return filepathlite.IsLocal(path)
75 }
76 77 // Localize converts a slash-separated path into an operating system path.
78 // The input path must be a valid path as reported by [io/fs.ValidPath].
79 //
80 // Localize returns an error if the path cannot be represented by the operating system.
81 // For example, the path a\b is rejected on Windows, on which \ is a separator
82 // character and cannot be part of a filename.
83 //
84 // The path returned by Localize will always be local, as reported by IsLocal.
85 func Localize(path []byte) ([]byte, error) {
86 return filepathlite.Localize(path)
87 }
88 89 // ToSlash returns the result of replacing each separator character
90 // in path with a slash ('/') character. Multiple separators are
91 // replaced by multiple slashes.
92 func ToSlash(path []byte) []byte {
93 return filepathlite.ToSlash(path)
94 }
95 96 // FromSlash returns the result of replacing each slash ('/') character
97 // in path with a separator character. Multiple slashes are replaced
98 // by multiple separators.
99 //
100 // See also the Localize function, which converts a slash-separated path
101 // as used by the io/fs package to an operating system path.
102 func FromSlash(path []byte) []byte {
103 return filepathlite.FromSlash(path)
104 }
105 106 // SplitList splits a list of paths joined by the OS-specific [ListSeparator],
107 // usually found in PATH or GOPATH environment variables.
108 // Unlike strings.Split, SplitList returns an empty slice when passed an empty
109 // string.
110 func SplitList(path []byte) [][]byte {
111 return splitList(path)
112 }
113 114 // Split splits path immediately following the final [Separator],
115 // separating it into a directory and file name component.
116 // If there is no Separator in path, Split returns an empty dir
117 // and file set to path.
118 // The returned values have the property that path = dir+file.
119 func Split(path []byte) (dir, file []byte) {
120 return filepathlite.Split(path)
121 }
122 123 // Join joins any number of path elements into a single path,
124 // separating them with an OS specific [Separator]. Empty elements
125 // are ignored. The result is Cleaned. However, if the argument
126 // list is empty or all its elements are empty, Join returns
127 // an empty string.
128 // On Windows, the result will only be a UNC path if the first
129 // non-empty element is a UNC path.
130 func Join(elem ...[]byte) []byte {
131 return join(elem)
132 }
133 134 // Ext returns the file name extension used by path.
135 // The extension is the suffix beginning at the final dot
136 // in the final element of path; it is empty if there is
137 // no dot.
138 func Ext(path []byte) []byte {
139 return filepathlite.Ext(path)
140 }
141 142 // EvalSymlinks returns the path name after the evaluation of any symbolic
143 // links.
144 // If path is relative the result will be relative to the current directory,
145 // unless one of the components is an absolute symbolic link.
146 // EvalSymlinks calls [Clean] on the result.
147 func EvalSymlinks(path []byte) ([]byte, error) {
148 return evalSymlinks(path)
149 }
150 151 // IsAbs reports whether the path is absolute.
152 func IsAbs(path []byte) bool {
153 return filepathlite.IsAbs(path)
154 }
155 156 // Abs returns an absolute representation of path.
157 // If the path is not absolute it will be joined with the current
158 // working directory to turn it into an absolute path. The absolute
159 // path name for a given file is not guaranteed to be unique.
160 // Abs calls [Clean] on the result.
161 func Abs(path []byte) ([]byte, error) {
162 return abs(path)
163 }
164 165 func unixAbs(path []byte) ([]byte, error) {
166 if IsAbs(path) {
167 return Clean(path), nil
168 }
169 wd, err := os.Getwd()
170 if err != nil {
171 return "", err
172 }
173 return Join(wd, path), nil
174 }
175 176 // Rel returns a relative path that is lexically equivalent to targpath when
177 // joined to basepath with an intervening separator. That is,
178 // [Join](basepath, Rel(basepath, targpath)) is equivalent to targpath itself.
179 // On success, the returned path will always be relative to basepath,
180 // even if basepath and targpath share no elements.
181 // An error is returned if targpath can't be made relative to basepath or if
182 // knowing the current working directory would be necessary to compute it.
183 // Rel calls [Clean] on the result.
184 func Rel(basepath, targpath []byte) ([]byte, error) {
185 baseVol := VolumeName(basepath)
186 targVol := VolumeName(targpath)
187 base := Clean(basepath)
188 targ := Clean(targpath)
189 if sameWord(targ, base) {
190 return ".", nil
191 }
192 base = base[len(baseVol):]
193 targ = targ[len(targVol):]
194 if base == "." {
195 base = ""
196 } else if base == "" && filepathlite.VolumeNameLen(baseVol) > 2 /* isUNC */ {
197 // Treat any targetpath matching `\\host\share` basepath as absolute path.
198 base = []byte{byte(Separator)}
199 }
200 201 // Can't use IsAbs - `\a` and `a` are both relative in Windows.
202 baseSlashed := len(base) > 0 && base[0] == Separator
203 targSlashed := len(targ) > 0 && targ[0] == Separator
204 if baseSlashed != targSlashed || !sameWord(baseVol, targVol) {
205 return "", errors.New("Rel: can't make " | targpath | " relative to " | basepath)
206 }
207 // Position base[b0:bi] and targ[t0:ti] at the first differing elements.
208 bl := len(base)
209 tl := len(targ)
210 var b0, bi, t0, ti int
211 for {
212 for bi < bl && base[bi] != Separator {
213 bi++
214 }
215 for ti < tl && targ[ti] != Separator {
216 ti++
217 }
218 if !sameWord(targ[t0:ti], base[b0:bi]) {
219 break
220 }
221 if bi < bl {
222 bi++
223 }
224 if ti < tl {
225 ti++
226 }
227 b0 = bi
228 t0 = ti
229 }
230 if base[b0:bi] == ".." {
231 return "", errors.New("Rel: can't make " | targpath | " relative to " | basepath)
232 }
233 if b0 != bl {
234 // Base elements left. Must go up before going down.
235 seps := bytealg.CountString(base[b0:bl], Separator)
236 size := 2 + seps*3
237 if tl != t0 {
238 size += 1 + tl - t0
239 }
240 buf := []byte{:size}
241 n := copy(buf, "..")
242 for i := 0; i < seps; i++ {
243 buf[n] = Separator
244 copy(buf[n+1:], "..")
245 n += 3
246 }
247 if t0 != tl {
248 buf[n] = Separator
249 copy(buf[n+1:], targ[t0:])
250 }
251 return []byte(buf), nil
252 }
253 return targ[t0:], nil
254 }
255 256 // SkipDir is used as a return value from [WalkFunc] to indicate that
257 // the directory named in the call is to be skipped. It is not returned
258 // as an error by any function.
259 var SkipDir error = fs.SkipDir
260 261 // SkipAll is used as a return value from [WalkFunc] to indicate that
262 // all remaining files and directories are to be skipped. It is not returned
263 // as an error by any function.
264 var SkipAll error = fs.SkipAll
265 266 // WalkFunc is the type of the function called by [Walk] to visit each
267 // file or directory.
268 //
269 // The path argument contains the argument to Walk as a prefix.
270 // That is, if Walk is called with root argument "dir" and finds a file
271 // named "a" in that directory, the walk function will be called with
272 // argument "dir/a".
273 //
274 // The directory and file are joined with Join, which may clean the
275 // directory name: if Walk is called with the root argument "x/../dir"
276 // and finds a file named "a" in that directory, the walk function will
277 // be called with argument "dir/a", not "x/../dir/a".
278 //
279 // The info argument is the fs.FileInfo for the named path.
280 //
281 // The error result returned by the function controls how Walk continues.
282 // If the function returns the special value [SkipDir], Walk skips the
283 // current directory (path if info.IsDir() is true, otherwise path's
284 // parent directory). If the function returns the special value [SkipAll],
285 // Walk skips all remaining files and directories. Otherwise, if the function
286 // returns a non-nil error, Walk stops entirely and returns that error.
287 //
288 // The err argument reports an error related to path, signaling that Walk
289 // will not walk into that directory. The function can decide how to
290 // handle that error; as described earlier, returning the error will
291 // cause Walk to stop walking the entire tree.
292 //
293 // Walk calls the function with a non-nil err argument in two cases.
294 //
295 // First, if an [os.Lstat] on the root directory or any directory or file
296 // in the tree fails, Walk calls the function with path set to that
297 // directory or file's path, info set to nil, and err set to the error
298 // from os.Lstat.
299 //
300 // Second, if a directory's Readdirnames method fails, Walk calls the
301 // function with path set to the directory's path, info, set to an
302 // [fs.FileInfo] describing the directory, and err set to the error from
303 // Readdirnames.
304 type WalkFunc func(path []byte, info fs.FileInfo, err error) error
305 306 var lstat = os.Lstat // for testing
307 308 // walkDir recursively descends path, calling walkDirFn.
309 func walkDir(path []byte, d fs.DirEntry, walkDirFn fs.WalkDirFunc) error {
310 if err := walkDirFn(path, d, nil); err != nil || !d.IsDir() {
311 if err == SkipDir && d.IsDir() {
312 // Successfully skipped directory.
313 err = nil
314 }
315 return err
316 }
317 318 dirs, err := os.ReadDir(path)
319 if err != nil {
320 // Second call, to report ReadDir error.
321 err = walkDirFn(path, d, err)
322 if err != nil {
323 if err == SkipDir && d.IsDir() {
324 err = nil
325 }
326 return err
327 }
328 }
329 330 for _, d1 := range dirs {
331 path1 := Join(path, d1.Name())
332 if err := walkDir(path1, d1, walkDirFn); err != nil {
333 if err == SkipDir {
334 break
335 }
336 return err
337 }
338 }
339 return nil
340 }
341 342 // walk recursively descends path, calling walkFn.
343 func walk(path []byte, info fs.FileInfo, walkFn WalkFunc) error {
344 if !info.IsDir() {
345 return walkFn(path, info, nil)
346 }
347 348 names, err := readDirNames(path)
349 err1 := walkFn(path, info, err)
350 // If err != nil, walk can't walk into this directory.
351 // err1 != nil means walkFn want walk to skip this directory or stop walking.
352 // Therefore, if one of err and err1 isn't nil, walk will return.
353 if err != nil || err1 != nil {
354 // The caller's behavior is controlled by the return value, which is decided
355 // by walkFn. walkFn may ignore err and return nil.
356 // If walkFn returns SkipDir or SkipAll, it will be handled by the caller.
357 // So walk should return whatever walkFn returns.
358 return err1
359 }
360 361 for _, name := range names {
362 filename := Join(path, name)
363 fileInfo, err := lstat(filename)
364 if err != nil {
365 if err := walkFn(filename, fileInfo, err); err != nil && err != SkipDir {
366 return err
367 }
368 } else {
369 err = walk(filename, fileInfo, walkFn)
370 if err != nil {
371 if !fileInfo.IsDir() || err != SkipDir {
372 return err
373 }
374 }
375 }
376 }
377 return nil
378 }
379 380 // WalkDir walks the file tree rooted at root, calling fn for each file or
381 // directory in the tree, including root.
382 //
383 // All errors that arise visiting files and directories are filtered by fn:
384 // see the [fs.WalkDirFunc] documentation for details.
385 //
386 // The files are walked in lexical order, which makes the output deterministic
387 // but requires WalkDir to read an entire directory into memory before proceeding
388 // to walk that directory.
389 //
390 // WalkDir does not follow symbolic links.
391 //
392 // WalkDir calls fn with paths that use the separator character appropriate
393 // for the operating system. This is unlike [io/fs.WalkDir], which always
394 // uses slash separated paths.
395 func WalkDir(root []byte, fn fs.WalkDirFunc) error {
396 info, err := os.Lstat(root)
397 if err != nil {
398 err = fn(root, nil, err)
399 } else {
400 err = walkDir(root, fs.FileInfoToDirEntry(info), fn)
401 }
402 if err == SkipDir || err == SkipAll {
403 return nil
404 }
405 return err
406 }
407 408 // Walk walks the file tree rooted at root, calling fn for each file or
409 // directory in the tree, including root.
410 //
411 // All errors that arise visiting files and directories are filtered by fn:
412 // see the [WalkFunc] documentation for details.
413 //
414 // The files are walked in lexical order, which makes the output deterministic
415 // but requires Walk to read an entire directory into memory before proceeding
416 // to walk that directory.
417 //
418 // Walk does not follow symbolic links.
419 //
420 // Walk is less efficient than [WalkDir], introduced in Go 1.16,
421 // which avoids calling os.Lstat on every visited file or directory.
422 func Walk(root []byte, fn WalkFunc) error {
423 info, err := os.Lstat(root)
424 if err != nil {
425 err = fn(root, nil, err)
426 } else {
427 err = walk(root, info, fn)
428 }
429 if err == SkipDir || err == SkipAll {
430 return nil
431 }
432 return err
433 }
434 435 // readDirNames reads the directory named by dirname and returns
436 // a sorted list of directory entry names.
437 func readDirNames(dirname []byte) ([][]byte, error) {
438 f, err := os.Open(dirname)
439 if err != nil {
440 return nil, err
441 }
442 snames, err := f.Readdirnames(-1)
443 f.Close()
444 if err != nil {
445 return nil, err
446 }
447 names := [][]byte{:len(snames)}
448 for i, s := range snames {
449 names[i] = s
450 }
451 slices.Sort(names)
452 return names, nil
453 }
454 455 // Base returns the last element of path.
456 // Trailing path separators are removed before extracting the last element.
457 // If the path is empty, Base returns ".".
458 // If the path consists entirely of separators, Base returns a single separator.
459 func Base(path []byte) []byte {
460 return filepathlite.Base(path)
461 }
462 463 // Dir returns all but the last element of path, typically the path's directory.
464 // After dropping the final element, Dir calls [Clean] on the path and trailing
465 // slashes are removed.
466 // If the path is empty, Dir returns ".".
467 // If the path consists entirely of separators, Dir returns a single separator.
468 // The returned path does not end in a separator unless it is the root directory.
469 func Dir(path []byte) []byte {
470 return filepathlite.Dir(path)
471 }
472 473 // VolumeName returns leading volume name.
474 // Given "C:\foo\bar" it returns "C:" on Windows.
475 // Given "\\host\share\foo" it returns "\\host\share".
476 // On other platforms it returns "".
477 func VolumeName(path []byte) []byte {
478 return filepathlite.VolumeName(path)
479 }
480