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.
5 // Package filepath implements utility routines for manipulating filename paths
6 // in a way compatible with the target operating system-defined file paths.
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.
22 // A lazybuf is a lazily constructed path buffer.
23 // It supports append, reading previously appended bytes,
24 // and retrieving the final string. It does not allocate a buffer
25 // to hold the output until that output diverges from s.
34 func (b *lazybuf) index(i int) byte {
41 func (b *lazybuf) append(c byte) {
43 if b.w < len(b.path) && b.path[b.w] == c {
47 b.buf = make([]byte, len(b.path))
48 copy(b.buf, b.path[:b.w])
54 func (b *lazybuf) string() string {
56 return b.volAndPath[:b.volLen+b.w]
58 return b.volAndPath[:b.volLen] + string(b.buf[:b.w])
62 Separator = os.PathSeparator
63 ListSeparator = os.PathListSeparator
66 // Clean returns the shortest path name equivalent to path
67 // by purely lexical processing. It applies the following rules
68 // iteratively until no further processing can be done:
70 // 1. Replace multiple Separator elements with a single one.
71 // 2. Eliminate each . path name element (the current directory).
72 // 3. Eliminate each inner .. path name element (the parent directory)
73 // along with the non-.. element that precedes it.
74 // 4. Eliminate .. elements that begin a rooted path:
75 // that is, replace "/.." by "/" at the beginning of a path,
76 // assuming Separator is '/'.
78 // The returned path ends in a slash only if it represents a root directory,
79 // such as "/" on Unix or `C:\` on Windows.
81 // Finally, any occurrences of slash are replaced by Separator.
83 // If the result of this process is an empty string, Clean
84 // returns the string ".".
86 // See also Rob Pike, ``Lexical File Names in Plan 9 or
87 // Getting Dot-Dot Right,''
88 // https://9p.io/sys/doc/lexnames.html
89 func Clean(path string) string {
91 volLen := volumeNameLen(path)
94 if volLen > 1 && originalPath[1] != ':' {
96 return FromSlash(originalPath)
98 return originalPath + "."
100 rooted := os.IsPathSeparator(path[0])
103 // reading from path; r is index of next byte to process.
104 // writing to buf; w is index of next byte to write.
105 // dotdot is index in buf where .. must stop, either because
106 // it is the leading slash or it is a leading ../../.. prefix.
108 out := lazybuf{path: path, volAndPath: originalPath, volLen: volLen}
111 out.append(Separator)
117 case os.IsPathSeparator(path[r]):
118 // empty path element
120 case path[r] == '.' && (r+1 == n || os.IsPathSeparator(path[r+1])):
123 case path[r] == '.' && path[r+1] == '.' && (r+2 == n || os.IsPathSeparator(path[r+2])):
124 // .. element: remove to last separator
130 for out.w > dotdot && !os.IsPathSeparator(out.index(out.w)) {
134 // cannot backtrack, but not rooted, so append .. element.
136 out.append(Separator)
143 // real path element.
144 // add slash if needed
145 if rooted && out.w != 1 || !rooted && out.w != 0 {
146 out.append(Separator)
149 for ; r < n && !os.IsPathSeparator(path[r]); r++ {
155 // Turn empty string into "."
160 return FromSlash(out.string())
163 // ToSlash returns the result of replacing each separator character
164 // in path with a slash ('/') character. Multiple separators are
165 // replaced by multiple slashes.
166 func ToSlash(path string) string {
167 if Separator == '/' {
170 return strings.ReplaceAll(path, string(Separator), "/")
173 // FromSlash returns the result of replacing each slash ('/') character
174 // in path with a separator character. Multiple slashes are replaced
175 // by multiple separators.
176 func FromSlash(path string) string {
177 if Separator == '/' {
180 return strings.ReplaceAll(path, "/", string(Separator))
183 // SplitList splits a list of paths joined by the OS-specific ListSeparator,
184 // usually found in PATH or GOPATH environment variables.
185 // Unlike strings.Split, SplitList returns an empty slice when passed an empty
187 func SplitList(path string) []string {
188 return splitList(path)
191 // Split splits path immediately following the final Separator,
192 // separating it into a directory and file name component.
193 // If there is no Separator in path, Split returns an empty dir
194 // and file set to path.
195 // The returned values have the property that path = dir+file.
196 func Split(path string) (dir, file string) {
197 vol := VolumeName(path)
199 for i >= len(vol) && !os.IsPathSeparator(path[i]) {
202 return path[:i+1], path[i+1:]
205 // Join joins any number of path elements into a single path,
206 // separating them with an OS specific Separator. Empty elements
207 // are ignored. The result is Cleaned. However, if the argument
208 // list is empty or all its elements are empty, Join returns
210 // On Windows, the result will only be a UNC path if the first
211 // non-empty element is a UNC path.
212 func Join(elem ...string) string {
216 // Ext returns the file name extension used by path.
217 // The extension is the suffix beginning at the final dot
218 // in the final element of path; it is empty if there is
220 func Ext(path string) string {
221 for i := len(path) - 1; i >= 0 && !os.IsPathSeparator(path[i]); i-- {
229 // EvalSymlinks returns the path name after the evaluation of any symbolic
231 // If path is relative the result will be relative to the current directory,
232 // unless one of the components is an absolute symbolic link.
233 // EvalSymlinks calls Clean on the result.
234 func EvalSymlinks(path string) (string, error) {
235 return evalSymlinks(path)
238 // Abs returns an absolute representation of path.
239 // If the path is not absolute it will be joined with the current
240 // working directory to turn it into an absolute path. The absolute
241 // path name for a given file is not guaranteed to be unique.
242 // Abs calls Clean on the result.
243 func Abs(path string) (string, error) {
247 func unixAbs(path string) (string, error) {
249 return Clean(path), nil
251 wd, err := os.Getwd()
255 return Join(wd, path), nil
258 // Rel returns a relative path that is lexically equivalent to targpath when
259 // joined to basepath with an intervening separator. That is,
260 // Join(basepath, Rel(basepath, targpath)) is equivalent to targpath itself.
261 // On success, the returned path will always be relative to basepath,
262 // even if basepath and targpath share no elements.
263 // An error is returned if targpath can't be made relative to basepath or if
264 // knowing the current working directory would be necessary to compute it.
265 // Rel calls Clean on the result.
266 func Rel(basepath, targpath string) (string, error) {
267 baseVol := VolumeName(basepath)
268 targVol := VolumeName(targpath)
269 base := Clean(basepath)
270 targ := Clean(targpath)
271 if sameWord(targ, base) {
274 base = base[len(baseVol):]
275 targ = targ[len(targVol):]
279 // Can't use IsAbs - `\a` and `a` are both relative in Windows.
280 baseSlashed := len(base) > 0 && base[0] == Separator
281 targSlashed := len(targ) > 0 && targ[0] == Separator
282 if baseSlashed != targSlashed || !sameWord(baseVol, targVol) {
283 return "", errors.New("Rel: can't make " + targpath + " relative to " + basepath)
285 // Position base[b0:bi] and targ[t0:ti] at the first differing elements.
288 var b0, bi, t0, ti int
290 for bi < bl && base[bi] != Separator {
293 for ti < tl && targ[ti] != Separator {
296 if !sameWord(targ[t0:ti], base[b0:bi]) {
308 if base[b0:bi] == ".." {
309 return "", errors.New("Rel: can't make " + targpath + " relative to " + basepath)
312 // Base elements left. Must go up before going down.
313 seps := strings.Count(base[b0:bl], string(Separator))
318 buf := make([]byte, size)
320 for i := 0; i < seps; i++ {
322 copy(buf[n+1:], "..")
327 copy(buf[n+1:], targ[t0:])
329 return string(buf), nil
331 return targ[t0:], nil
334 // SkipDir is used as a return value from WalkFuncs to indicate that
335 // the directory named in the call is to be skipped. It is not returned
336 // as an error by any function.
337 var SkipDir = errors.New("skip this directory")
339 // WalkFunc is the type of the function called for each file or directory
340 // visited by Walk. The path argument contains the argument to Walk as a
341 // prefix; that is, if Walk is called with "dir", which is a directory
342 // containing the file "a", the walk function will be called with argument
343 // "dir/a". The info argument is the fs.FileInfo for the named path.
345 // If there was a problem walking to the file or directory named by path, the
346 // incoming error will describe the problem and the function can decide how
347 // to handle that error (and Walk will not descend into that directory). In the
348 // case of an error, the info argument will be nil. If an error is returned,
349 // processing stops. The sole exception is when the function returns the special
350 // value SkipDir. If the function returns SkipDir when invoked on a directory,
351 // Walk skips the directory's contents entirely. If the function returns SkipDir
352 // when invoked on a non-directory file, Walk skips the remaining files in the
353 // containing directory.
354 type WalkFunc func(path string, info fs.FileInfo, err error) error
356 var lstat = os.Lstat // for testing
358 // walk recursively descends path, calling walkFn.
359 func walk(path string, info fs.FileInfo, walkFn WalkFunc) error {
361 return walkFn(path, info, nil)
364 names, err := readDirNames(path)
365 err1 := walkFn(path, info, err)
366 // If err != nil, walk can't walk into this directory.
367 // err1 != nil means walkFn want walk to skip this directory or stop walking.
368 // Therefore, if one of err and err1 isn't nil, walk will return.
369 if err != nil || err1 != nil {
370 // The caller's behavior is controlled by the return value, which is decided
371 // by walkFn. walkFn may ignore err and return nil.
372 // If walkFn returns SkipDir, it will be handled by the caller.
373 // So walk should return whatever walkFn returns.
377 for _, name := range names {
378 filename := Join(path, name)
379 fileInfo, err := lstat(filename)
381 if err := walkFn(filename, fileInfo, err); err != nil && err != SkipDir {
385 err = walk(filename, fileInfo, walkFn)
387 if !fileInfo.IsDir() || err != SkipDir {
396 // Walk walks the file tree rooted at root, calling walkFn for each file or
397 // directory in the tree, including root. All errors that arise visiting files
398 // and directories are filtered by walkFn. The files are walked in lexical
399 // order, which makes the output deterministic but means that for very
400 // large directories Walk can be inefficient.
401 // Walk does not follow symbolic links.
402 func Walk(root string, walkFn WalkFunc) error {
403 info, err := os.Lstat(root)
405 err = walkFn(root, nil, err)
407 err = walk(root, info, walkFn)
415 // readDirNames reads the directory named by dirname and returns
416 // a sorted list of directory entries.
417 func readDirNames(dirname string) ([]string, error) {
418 f, err := os.Open(dirname)
422 names, err := f.Readdirnames(-1)
431 // Base returns the last element of path.
432 // Trailing path separators are removed before extracting the last element.
433 // If the path is empty, Base returns ".".
434 // If the path consists entirely of separators, Base returns a single separator.
435 func Base(path string) string {
439 // Strip trailing slashes.
440 for len(path) > 0 && os.IsPathSeparator(path[len(path)-1]) {
441 path = path[0 : len(path)-1]
443 // Throw away volume name
444 path = path[len(VolumeName(path)):]
445 // Find the last element
447 for i >= 0 && !os.IsPathSeparator(path[i]) {
453 // If empty now, it had only slashes.
455 return string(Separator)
460 // Dir returns all but the last element of path, typically the path's directory.
461 // After dropping the final element, Dir calls Clean on the path and trailing
462 // slashes are removed.
463 // If the path is empty, Dir returns ".".
464 // If the path consists entirely of separators, Dir returns a single separator.
465 // The returned path does not end in a separator unless it is the root directory.
466 func Dir(path string) string {
467 vol := VolumeName(path)
469 for i >= len(vol) && !os.IsPathSeparator(path[i]) {
472 dir := Clean(path[len(vol) : i+1])
473 if dir == "." && len(vol) > 2 {
480 // VolumeName returns leading volume name.
481 // Given "C:\foo\bar" it returns "C:" on Windows.
482 // Given "\\host\share\foo" it returns "\\host\share".
483 // On other platforms it returns "".
484 func VolumeName(path string) string {
485 return path[:volumeNameLen(path)]