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.
21 // A lazybuf is a lazily constructed path buffer.
22 // It supports append, reading previously appended bytes,
23 // and retrieving the final string. It does not allocate a buffer
24 // to hold the output until that output diverges from s.
33 func (b *lazybuf) index(i int) byte {
40 func (b *lazybuf) append(c byte) {
42 if b.w < len(b.path) && b.path[b.w] == c {
46 b.buf = make([]byte, len(b.path))
47 copy(b.buf, b.path[:b.w])
53 func (b *lazybuf) string() string {
55 return b.volAndPath[:b.volLen+b.w]
57 return b.volAndPath[:b.volLen] + string(b.buf[:b.w])
61 Separator = os.PathSeparator
62 ListSeparator = os.PathListSeparator
65 // Clean returns the shortest path name equivalent to path
66 // by purely lexical processing. It applies the following rules
67 // iteratively until no further processing can be done:
69 // 1. Replace multiple Separator elements with a single one.
70 // 2. Eliminate each . path name element (the current directory).
71 // 3. Eliminate each inner .. path name element (the parent directory)
72 // along with the non-.. element that precedes it.
73 // 4. Eliminate .. elements that begin a rooted path:
74 // that is, replace "/.." by "/" at the beginning of a path,
75 // assuming Separator is '/'.
77 // The returned path ends in a slash only if it represents a root directory,
78 // such as "/" on Unix or `C:\` on Windows.
80 // Finally, any occurrences of slash are replaced by Separator.
82 // If the result of this process is an empty string, Clean
83 // returns the string ".".
85 // See also Rob Pike, ``Lexical File Names in Plan 9 or
86 // Getting Dot-Dot Right,''
87 // https://9p.io/sys/doc/lexnames.html
88 func Clean(path string) string {
90 volLen := volumeNameLen(path)
93 if volLen > 1 && originalPath[1] != ':' {
95 return FromSlash(originalPath)
97 return originalPath + "."
101 if volLen > 2 && n == 1 && os.IsPathSeparator(path[0]) {
102 // UNC volume name with trailing slash.
103 return FromSlash(originalPath[:volLen])
105 rooted := os.IsPathSeparator(path[0])
108 // reading from path; r is index of next byte to process.
109 // writing to out; w is index of next byte to write.
110 // dotdot is index in out where .. must stop, either because
111 // it is the leading slash or it is a leading ../../.. prefix.
112 out := lazybuf{path: path, volAndPath: originalPath, volLen: volLen}
115 out.append(Separator)
121 case os.IsPathSeparator(path[r]):
122 // empty path element
124 case path[r] == '.' && (r+1 == n || os.IsPathSeparator(path[r+1])):
127 case path[r] == '.' && path[r+1] == '.' && (r+2 == n || os.IsPathSeparator(path[r+2])):
128 // .. element: remove to last separator
134 for out.w > dotdot && !os.IsPathSeparator(out.index(out.w)) {
138 // cannot backtrack, but not rooted, so append .. element.
140 out.append(Separator)
147 // real path element.
148 // add slash if needed
149 if rooted && out.w != 1 || !rooted && out.w != 0 {
150 out.append(Separator)
153 for ; r < n && !os.IsPathSeparator(path[r]); r++ {
159 // Turn empty string into "."
164 return FromSlash(out.string())
167 // ToSlash returns the result of replacing each separator character
168 // in path with a slash ('/') character. Multiple separators are
169 // replaced by multiple slashes.
170 func ToSlash(path string) string {
171 if Separator == '/' {
174 return strings.ReplaceAll(path, string(Separator), "/")
177 // FromSlash returns the result of replacing each slash ('/') character
178 // in path with a separator character. Multiple slashes are replaced
179 // by multiple separators.
180 func FromSlash(path string) string {
181 if Separator == '/' {
184 return strings.ReplaceAll(path, "/", string(Separator))
187 // SplitList splits a list of paths joined by the OS-specific ListSeparator,
188 // usually found in PATH or GOPATH environment variables.
189 // Unlike strings.Split, SplitList returns an empty slice when passed an empty
191 func SplitList(path string) []string {
192 return splitList(path)
195 // Split splits path immediately following the final Separator,
196 // separating it into a directory and file name component.
197 // If there is no Separator in path, Split returns an empty dir
198 // and file set to path.
199 // The returned values have the property that path = dir+file.
200 func Split(path string) (dir, file string) {
201 vol := VolumeName(path)
203 for i >= len(vol) && !os.IsPathSeparator(path[i]) {
206 return path[:i+1], path[i+1:]
209 // Join joins any number of path elements into a single path, adding
210 // a Separator if necessary. Join calls Clean on the result; in particular,
211 // all empty strings are ignored.
212 // On Windows, the result is a UNC path if and only if the first path
213 // element is a UNC path.
214 func Join(elem ...string) string {
218 // Ext returns the file name extension used by path.
219 // The extension is the suffix beginning at the final dot
220 // in the final element of path; it is empty if there is
222 func Ext(path string) string {
223 for i := len(path) - 1; i >= 0 && !os.IsPathSeparator(path[i]); i-- {
231 // EvalSymlinks returns the path name after the evaluation of any symbolic
233 // If path is relative the result will be relative to the current directory,
234 // unless one of the components is an absolute symbolic link.
235 // EvalSymlinks calls Clean on the result.
236 func EvalSymlinks(path string) (string, error) {
237 return evalSymlinks(path)
240 // Abs returns an absolute representation of path.
241 // If the path is not absolute it will be joined with the current
242 // working directory to turn it into an absolute path. The absolute
243 // path name for a given file is not guaranteed to be unique.
244 // Abs calls Clean on the result.
245 func Abs(path string) (string, error) {
249 func unixAbs(path string) (string, error) {
251 return Clean(path), nil
253 wd, err := os.Getwd()
257 return Join(wd, path), nil
260 // Rel returns a relative path that is lexically equivalent to targpath when
261 // joined to basepath with an intervening separator. That is,
262 // Join(basepath, Rel(basepath, targpath)) is equivalent to targpath itself.
263 // On success, the returned path will always be relative to basepath,
264 // even if basepath and targpath share no elements.
265 // An error is returned if targpath can't be made relative to basepath or if
266 // knowing the current working directory would be necessary to compute it.
267 // Rel calls Clean on the result.
268 func Rel(basepath, targpath string) (string, error) {
269 baseVol := VolumeName(basepath)
270 targVol := VolumeName(targpath)
271 base := Clean(basepath)
272 targ := Clean(targpath)
273 if sameWord(targ, base) {
276 base = base[len(baseVol):]
277 targ = targ[len(targVol):]
281 // Can't use IsAbs - `\a` and `a` are both relative in Windows.
282 baseSlashed := len(base) > 0 && base[0] == Separator
283 targSlashed := len(targ) > 0 && targ[0] == Separator
284 if baseSlashed != targSlashed || !sameWord(baseVol, targVol) {
285 return "", errors.New("Rel: can't make " + targpath + " relative to " + basepath)
287 // Position base[b0:bi] and targ[t0:ti] at the first differing elements.
290 var b0, bi, t0, ti int
292 for bi < bl && base[bi] != Separator {
295 for ti < tl && targ[ti] != Separator {
298 if !sameWord(targ[t0:ti], base[b0:bi]) {
310 if base[b0:bi] == ".." {
311 return "", errors.New("Rel: can't make " + targpath + " relative to " + basepath)
314 // Base elements left. Must go up before going down.
315 seps := strings.Count(base[b0:bl], string(Separator))
320 buf := make([]byte, size)
322 for i := 0; i < seps; i++ {
324 copy(buf[n+1:], "..")
329 copy(buf[n+1:], targ[t0:])
331 return string(buf), nil
333 return targ[t0:], nil
336 // SkipDir is used as a return value from WalkFuncs to indicate that
337 // the directory named in the call is to be skipped. It is not returned
338 // as an error by any function.
339 var SkipDir = errors.New("skip this directory")
341 // WalkFunc is the type of the function called for each file or directory
342 // visited by Walk. The path argument contains the argument to Walk as a
343 // prefix; that is, if Walk is called with "dir", which is a directory
344 // containing the file "a", the walk function will be called with argument
345 // "dir/a". The info argument is the os.FileInfo for the named path.
347 // If there was a problem walking to the file or directory named by path, the
348 // incoming error will describe the problem and the function can decide how
349 // to handle that error (and Walk will not descend into that directory). In the
350 // case of an error, the info argument will be nil. If an error is returned,
351 // processing stops. The sole exception is when the function returns the special
352 // value SkipDir. If the function returns SkipDir when invoked on a directory,
353 // Walk skips the directory's contents entirely. If the function returns SkipDir
354 // when invoked on a non-directory file, Walk skips the remaining files in the
355 // containing directory.
356 type WalkFunc func(path string, info os.FileInfo, err error) error
358 var lstat = os.Lstat // for testing
360 // walk recursively descends path, calling walkFn.
361 func walk(path string, info os.FileInfo, walkFn WalkFunc) error {
363 return walkFn(path, info, nil)
366 names, err := readDirNames(path)
367 err1 := walkFn(path, info, err)
368 // If err != nil, walk can't walk into this directory.
369 // err1 != nil means walkFn want walk to skip this directory or stop walking.
370 // Therefore, if one of err and err1 isn't nil, walk will return.
371 if err != nil || err1 != nil {
372 // The caller's behavior is controlled by the return value, which is decided
373 // by walkFn. walkFn may ignore err and return nil.
374 // If walkFn returns SkipDir, it will be handled by the caller.
375 // So walk should return whatever walkFn returns.
379 for _, name := range names {
380 filename := Join(path, name)
381 fileInfo, err := lstat(filename)
383 if err := walkFn(filename, fileInfo, err); err != nil && err != SkipDir {
387 err = walk(filename, fileInfo, walkFn)
389 if !fileInfo.IsDir() || err != SkipDir {
398 // Walk walks the file tree rooted at root, calling walkFn for each file or
399 // directory in the tree, including root. All errors that arise visiting files
400 // and directories are filtered by walkFn. The files are walked in lexical
401 // order, which makes the output deterministic but means that for very
402 // large directories Walk can be inefficient.
403 // Walk does not follow symbolic links.
404 func Walk(root string, walkFn WalkFunc) error {
405 info, err := os.Lstat(root)
407 err = walkFn(root, nil, err)
409 err = walk(root, info, walkFn)
417 // readDirNames reads the directory named by dirname and returns
418 // a sorted list of directory entries.
419 func readDirNames(dirname string) ([]string, error) {
420 f, err := os.Open(dirname)
424 names, err := f.Readdirnames(-1)
433 // Base returns the last element of path.
434 // Trailing path separators are removed before extracting the last element.
435 // If the path is empty, Base returns ".".
436 // If the path consists entirely of separators, Base returns a single separator.
437 func Base(path string) string {
441 // Strip trailing slashes.
442 for len(path) > 0 && os.IsPathSeparator(path[len(path)-1]) {
443 path = path[0 : len(path)-1]
445 // Throw away volume name
446 path = path[len(VolumeName(path)):]
447 // Find the last element
449 for i >= 0 && !os.IsPathSeparator(path[i]) {
455 // If empty now, it had only slashes.
457 return string(Separator)
462 // Dir returns all but the last element of path, typically the path's directory.
463 // After dropping the final element, Dir calls Clean on the path and trailing
464 // slashes are removed.
465 // If the path is empty, Dir returns ".".
466 // If the path consists entirely of separators, Dir returns a single separator.
467 // The returned path does not end in a separator unless it is the root directory.
468 func Dir(path string) string {
469 vol := VolumeName(path)
471 for i >= len(vol) && !os.IsPathSeparator(path[i]) {
474 dir := Clean(path[len(vol) : i+1])
475 if dir == "." && len(vol) > 2 {
482 // VolumeName returns leading volume name.
483 // Given "C:\foo\bar" it returns "C:" on Windows.
484 // Given "\\host\share\foo" it returns "\\host\share".
485 // On other platforms it returns "".
486 func VolumeName(path string) string {
487 return path[:volumeNameLen(path)]