// Copyright 2009 The Go Authors. All rights reserved. // Use of this source code is governed by a BSD-style // license that can be found in the LICENSE file. // Package filepath implements utility routines for manipulating filename paths // in a way compatible with the target operating system-defined file paths. // // The filepath package uses either forward slashes or backslashes, // depending on the operating system. To process paths such as URLs // that always use forward slashes regardless of the operating // system, see the [path] package. package filepath import ( "errors" "io/fs" "os" "slices" "sort" "strings" ) // A lazybuf is a lazily constructed path buffer. // It supports append, reading previously appended bytes, // and retrieving the final string. It does not allocate a buffer // to hold the output until that output diverges from s. type lazybuf struct { path string buf []byte w int volAndPath string volLen int } func (b *lazybuf) index(i int) byte { if b.buf != nil { return b.buf[i] } return b.path[i] } func (b *lazybuf) append(c byte) { if b.buf == nil { if b.w < len(b.path) && b.path[b.w] == c { b.w++ return } b.buf = make([]byte, len(b.path)) copy(b.buf, b.path[:b.w]) } b.buf[b.w] = c b.w++ } func (b *lazybuf) prepend(prefix ...byte) { b.buf = slices.Insert(b.buf, 0, prefix...) b.w += len(prefix) } func (b *lazybuf) string() string { if b.buf == nil { return b.volAndPath[:b.volLen+b.w] } return b.volAndPath[:b.volLen] + string(b.buf[:b.w]) } const ( Separator = os.PathSeparator ListSeparator = os.PathListSeparator ) // Clean returns the shortest path name equivalent to path // by purely lexical processing. It applies the following rules // iteratively until no further processing can be done: // // 1. Replace multiple [Separator] elements with a single one. // 2. Eliminate each . path name element (the current directory). // 3. Eliminate each inner .. path name element (the parent directory) // along with the non-.. element that precedes it. // 4. Eliminate .. elements that begin a rooted path: // that is, replace "/.." by "/" at the beginning of a path, // assuming Separator is '/'. // // The returned path ends in a slash only if it represents a root directory, // such as "/" on Unix or `C:\` on Windows. // // Finally, any occurrences of slash are replaced by Separator. // // If the result of this process is an empty string, Clean // returns the string ".". // // On Windows, Clean does not modify the volume name other than to replace // occurrences of "/" with `\`. // For example, Clean("//host/share/../x") returns `\\host\share\x`. // // See also Rob Pike, “Lexical File Names in Plan 9 or // Getting Dot-Dot Right,” // https://9p.io/sys/doc/lexnames.html func Clean(path string) string { originalPath := path volLen := volumeNameLen(path) path = path[volLen:] if path == "" { if volLen > 1 && os.IsPathSeparator(originalPath[0]) && os.IsPathSeparator(originalPath[1]) { // should be UNC return FromSlash(originalPath) } return originalPath + "." } rooted := os.IsPathSeparator(path[0]) // Invariants: // reading from path; r is index of next byte to process. // writing to buf; w is index of next byte to write. // dotdot is index in buf where .. must stop, either because // it is the leading slash or it is a leading ../../.. prefix. n := len(path) out := lazybuf{path: path, volAndPath: originalPath, volLen: volLen} r, dotdot := 0, 0 if rooted { out.append(Separator) r, dotdot = 1, 1 } for r < n { switch { case os.IsPathSeparator(path[r]): // empty path element r++ case path[r] == '.' && (r+1 == n || os.IsPathSeparator(path[r+1])): // . element r++ case path[r] == '.' && path[r+1] == '.' && (r+2 == n || os.IsPathSeparator(path[r+2])): // .. element: remove to last separator r += 2 switch { case out.w > dotdot: // can backtrack out.w-- for out.w > dotdot && !os.IsPathSeparator(out.index(out.w)) { out.w-- } case !rooted: // cannot backtrack, but not rooted, so append .. element. if out.w > 0 { out.append(Separator) } out.append('.') out.append('.') dotdot = out.w } default: // real path element. // add slash if needed if rooted && out.w != 1 || !rooted && out.w != 0 { out.append(Separator) } // copy element for ; r < n && !os.IsPathSeparator(path[r]); r++ { out.append(path[r]) } } } // Turn empty string into "." if out.w == 0 { out.append('.') } postClean(&out) // avoid creating absolute paths on Windows return FromSlash(out.string()) } // IsLocal reports whether path, using lexical analysis only, has all of these properties: // // - is within the subtree rooted at the directory in which path is evaluated // - is not an absolute path // - is not empty // - on Windows, is not a reserved name such as "NUL" // // If IsLocal(path) returns true, then // Join(base, path) will always produce a path contained within base and // Clean(path) will always produce an unrooted path with no ".." path elements. // // IsLocal is a purely lexical operation. // In particular, it does not account for the effect of any symbolic links // that may exist in the filesystem. func IsLocal(path string) bool { return isLocal(path) } func unixIsLocal(path string) bool { if IsAbs(path) || path == "" { return false } hasDots := false for p := path; p != ""; { var part string part, p, _ = strings.Cut(p, "/") if part == "." || part == ".." { hasDots = true break } } if hasDots { path = Clean(path) } if path == ".." || strings.HasPrefix(path, "../") { return false } return true } // ToSlash returns the result of replacing each separator character // in path with a slash ('/') character. Multiple separators are // replaced by multiple slashes. func ToSlash(path string) string { if Separator == '/' { return path } return strings.ReplaceAll(path, string(Separator), "/") } // FromSlash returns the result of replacing each slash ('/') character // in path with a separator character. Multiple slashes are replaced // by multiple separators. func FromSlash(path string) string { if Separator == '/' { return path } return strings.ReplaceAll(path, "/", string(Separator)) } // SplitList splits a list of paths joined by the OS-specific [ListSeparator], // usually found in PATH or GOPATH environment variables. // Unlike strings.Split, SplitList returns an empty slice when passed an empty // string. func SplitList(path string) []string { return splitList(path) } // Split splits path immediately following the final [Separator], // separating it into a directory and file name component. // If there is no Separator in path, Split returns an empty dir // and file set to path. // The returned values have the property that path = dir+file. func Split(path string) (dir, file string) { vol := VolumeName(path) i := len(path) - 1 for i >= len(vol) && !os.IsPathSeparator(path[i]) { i-- } return path[:i+1], path[i+1:] } // Join joins any number of path elements into a single path, // separating them with an OS specific [Separator]. Empty elements // are ignored. The result is Cleaned. However, if the argument // list is empty or all its elements are empty, Join returns // an empty string. // On Windows, the result will only be a UNC path if the first // non-empty element is a UNC path. func Join(elem ...string) string { return join(elem) } // Ext returns the file name extension used by path. // The extension is the suffix beginning at the final dot // in the final element of path; it is empty if there is // no dot. func Ext(path string) string { for i := len(path) - 1; i >= 0 && !os.IsPathSeparator(path[i]); i-- { if path[i] == '.' { return path[i:] } } return "" } // EvalSymlinks returns the path name after the evaluation of any symbolic // links. // If path is relative the result will be relative to the current directory, // unless one of the components is an absolute symbolic link. // EvalSymlinks calls [Clean] on the result. func EvalSymlinks(path string) (string, error) { return evalSymlinks(path) } // Abs returns an absolute representation of path. // If the path is not absolute it will be joined with the current // working directory to turn it into an absolute path. The absolute // path name for a given file is not guaranteed to be unique. // Abs calls [Clean] on the result. func Abs(path string) (string, error) { return abs(path) } func unixAbs(path string) (string, error) { if IsAbs(path) { return Clean(path), nil } wd, err := os.Getwd() if err != nil { return "", err } return Join(wd, path), nil } // Rel returns a relative path that is lexically equivalent to targpath when // joined to basepath with an intervening separator. That is, // [Join](basepath, Rel(basepath, targpath)) is equivalent to targpath itself. // On success, the returned path will always be relative to basepath, // even if basepath and targpath share no elements. // An error is returned if targpath can't be made relative to basepath or if // knowing the current working directory would be necessary to compute it. // Rel calls [Clean] on the result. func Rel(basepath, targpath string) (string, error) { baseVol := VolumeName(basepath) targVol := VolumeName(targpath) base := Clean(basepath) targ := Clean(targpath) if sameWord(targ, base) { return ".", nil } base = base[len(baseVol):] targ = targ[len(targVol):] if base == "." { base = "" } else if base == "" && volumeNameLen(baseVol) > 2 /* isUNC */ { // Treat any targetpath matching `\\host\share` basepath as absolute path. base = string(Separator) } // Can't use IsAbs - `\a` and `a` are both relative in Windows. baseSlashed := len(base) > 0 && base[0] == Separator targSlashed := len(targ) > 0 && targ[0] == Separator if baseSlashed != targSlashed || !sameWord(baseVol, targVol) { return "", errors.New("Rel: can't make " + targpath + " relative to " + basepath) } // Position base[b0:bi] and targ[t0:ti] at the first differing elements. bl := len(base) tl := len(targ) var b0, bi, t0, ti int for { for bi < bl && base[bi] != Separator { bi++ } for ti < tl && targ[ti] != Separator { ti++ } if !sameWord(targ[t0:ti], base[b0:bi]) { break } if bi < bl { bi++ } if ti < tl { ti++ } b0 = bi t0 = ti } if base[b0:bi] == ".." { return "", errors.New("Rel: can't make " + targpath + " relative to " + basepath) } if b0 != bl { // Base elements left. Must go up before going down. seps := strings.Count(base[b0:bl], string(Separator)) size := 2 + seps*3 if tl != t0 { size += 1 + tl - t0 } buf := make([]byte, size) n := copy(buf, "..") for i := 0; i < seps; i++ { buf[n] = Separator copy(buf[n+1:], "..") n += 3 } if t0 != tl { buf[n] = Separator copy(buf[n+1:], targ[t0:]) } return string(buf), nil } return targ[t0:], nil } // SkipDir is used as a return value from [WalkFunc] to indicate that // the directory named in the call is to be skipped. It is not returned // as an error by any function. var SkipDir error = fs.SkipDir // SkipAll is used as a return value from [WalkFunc] to indicate that // all remaining files and directories are to be skipped. It is not returned // as an error by any function. var SkipAll error = fs.SkipAll // WalkFunc is the type of the function called by [Walk] to visit each // file or directory. // // The path argument contains the argument to Walk as a prefix. // That is, if Walk is called with root argument "dir" and finds a file // named "a" in that directory, the walk function will be called with // argument "dir/a". // // The directory and file are joined with Join, which may clean the // directory name: if Walk is called with the root argument "x/../dir" // and finds a file named "a" in that directory, the walk function will // be called with argument "dir/a", not "x/../dir/a". // // The info argument is the fs.FileInfo for the named path. // // The error result returned by the function controls how Walk continues. // If the function returns the special value [SkipDir], Walk skips the // current directory (path if info.IsDir() is true, otherwise path's // parent directory). If the function returns the special value [SkipAll], // Walk skips all remaining files and directories. Otherwise, if the function // returns a non-nil error, Walk stops entirely and returns that error. // // The err argument reports an error related to path, signaling that Walk // will not walk into that directory. The function can decide how to // handle that error; as described earlier, returning the error will // cause Walk to stop walking the entire tree. // // Walk calls the function with a non-nil err argument in two cases. // // First, if an [os.Lstat] on the root directory or any directory or file // in the tree fails, Walk calls the function with path set to that // directory or file's path, info set to nil, and err set to the error // from os.Lstat. // // Second, if a directory's Readdirnames method fails, Walk calls the // function with path set to the directory's path, info, set to an // [fs.FileInfo] describing the directory, and err set to the error from // Readdirnames. type WalkFunc func(path string, info fs.FileInfo, err error) error var lstat = os.Lstat // for testing // walkDir recursively descends path, calling walkDirFn. func walkDir(path string, d fs.DirEntry, walkDirFn fs.WalkDirFunc) error { if err := walkDirFn(path, d, nil); err != nil || !d.IsDir() { if err == SkipDir && d.IsDir() { // Successfully skipped directory. err = nil } return err } dirs, err := os.ReadDir(path) if err != nil { // Second call, to report ReadDir error. err = walkDirFn(path, d, err) if err != nil { if err == SkipDir && d.IsDir() { err = nil } return err } } for _, d1 := range dirs { path1 := Join(path, d1.Name()) if err := walkDir(path1, d1, walkDirFn); err != nil { if err == SkipDir { break } return err } } return nil } // walk recursively descends path, calling walkFn. func walk(path string, info fs.FileInfo, walkFn WalkFunc) error { if !info.IsDir() { return walkFn(path, info, nil) } names, err := readDirNames(path) err1 := walkFn(path, info, err) // If err != nil, walk can't walk into this directory. // err1 != nil means walkFn want walk to skip this directory or stop walking. // Therefore, if one of err and err1 isn't nil, walk will return. if err != nil || err1 != nil { // The caller's behavior is controlled by the return value, which is decided // by walkFn. walkFn may ignore err and return nil. // If walkFn returns SkipDir or SkipAll, it will be handled by the caller. // So walk should return whatever walkFn returns. return err1 } for _, name := range names { filename := Join(path, name) fileInfo, err := lstat(filename) if err != nil { if err := walkFn(filename, fileInfo, err); err != nil && err != SkipDir { return err } } else { err = walk(filename, fileInfo, walkFn) if err != nil { if !fileInfo.IsDir() || err != SkipDir { return err } } } } return nil } // WalkDir walks the file tree rooted at root, calling fn for each file or // directory in the tree, including root. // // All errors that arise visiting files and directories are filtered by fn: // see the [fs.WalkDirFunc] documentation for details. // // The files are walked in lexical order, which makes the output deterministic // but requires WalkDir to read an entire directory into memory before proceeding // to walk that directory. // // WalkDir does not follow symbolic links. // // WalkDir calls fn with paths that use the separator character appropriate // for the operating system. This is unlike [io/fs.WalkDir], which always // uses slash separated paths. func WalkDir(root string, fn fs.WalkDirFunc) error { info, err := os.Lstat(root) if err != nil { err = fn(root, nil, err) } else { err = walkDir(root, fs.FileInfoToDirEntry(info), fn) } if err == SkipDir || err == SkipAll { return nil } return err } // Walk walks the file tree rooted at root, calling fn for each file or // directory in the tree, including root. // // All errors that arise visiting files and directories are filtered by fn: // see the [WalkFunc] documentation for details. // // The files are walked in lexical order, which makes the output deterministic // but requires Walk to read an entire directory into memory before proceeding // to walk that directory. // // Walk does not follow symbolic links. // // Walk is less efficient than [WalkDir], introduced in Go 1.16, // which avoids calling os.Lstat on every visited file or directory. func Walk(root string, fn WalkFunc) error { info, err := os.Lstat(root) if err != nil { err = fn(root, nil, err) } else { err = walk(root, info, fn) } if err == SkipDir || err == SkipAll { return nil } return err } // readDirNames reads the directory named by dirname and returns // a sorted list of directory entry names. func readDirNames(dirname string) ([]string, error) { f, err := os.Open(dirname) if err != nil { return nil, err } names, err := f.Readdirnames(-1) f.Close() if err != nil { return nil, err } sort.Strings(names) return names, nil } // Base returns the last element of path. // Trailing path separators are removed before extracting the last element. // If the path is empty, Base returns ".". // If the path consists entirely of separators, Base returns a single separator. func Base(path string) string { if path == "" { return "." } // Strip trailing slashes. for len(path) > 0 && os.IsPathSeparator(path[len(path)-1]) { path = path[0 : len(path)-1] } // Throw away volume name path = path[len(VolumeName(path)):] // Find the last element i := len(path) - 1 for i >= 0 && !os.IsPathSeparator(path[i]) { i-- } if i >= 0 { path = path[i+1:] } // If empty now, it had only slashes. if path == "" { return string(Separator) } return path } // Dir returns all but the last element of path, typically the path's directory. // After dropping the final element, Dir calls [Clean] on the path and trailing // slashes are removed. // If the path is empty, Dir returns ".". // If the path consists entirely of separators, Dir returns a single separator. // The returned path does not end in a separator unless it is the root directory. func Dir(path string) string { vol := VolumeName(path) i := len(path) - 1 for i >= len(vol) && !os.IsPathSeparator(path[i]) { i-- } dir := Clean(path[len(vol) : i+1]) if dir == "." && len(vol) > 2 { // must be UNC return vol } return vol + dir } // VolumeName returns leading volume name. // Given "C:\foo\bar" it returns "C:" on Windows. // Given "\\host\share\foo" it returns "\\host\share". // On other platforms it returns "". func VolumeName(path string) string { return FromSlash(path[:volumeNameLen(path)]) }