// 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 ( ) // 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 ( *lazybuf) ( int) byte { if .buf != nil { return .buf[] } return .path[] } func ( *lazybuf) ( byte) { if .buf == nil { if .w < len(.path) && .path[.w] == { .w++ return } .buf = make([]byte, len(.path)) copy(.buf, .path[:.w]) } .buf[.w] = .w++ } func ( *lazybuf) () string { if .buf == nil { return .volAndPath[:.volLen+.w] } return .volAndPath[:.volLen] + string(.buf[:.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 ".". // // See also Rob Pike, ``Lexical File Names in Plan 9 or // Getting Dot-Dot Right,'' // https://9p.io/sys/doc/lexnames.html func ( string) string { := := volumeNameLen() = [:] if == "" { if > 1 && [1] != ':' { // should be UNC return FromSlash() } return + "." } := os.IsPathSeparator([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. := len() := lazybuf{path: , volAndPath: , volLen: } , := 0, 0 if { .append(Separator) , = 1, 1 } for < { switch { case os.IsPathSeparator([]): // empty path element ++ case [] == '.' && (+1 == || os.IsPathSeparator([+1])): // . element ++ case [] == '.' && [+1] == '.' && (+2 == || os.IsPathSeparator([+2])): // .. element: remove to last separator += 2 switch { case .w > : // can backtrack .w-- for .w > && !os.IsPathSeparator(.index(.w)) { .w-- } case !: // cannot backtrack, but not rooted, so append .. element. if .w > 0 { .append(Separator) } .append('.') .append('.') = .w } default: // real path element. // add slash if needed if && .w != 1 || ! && .w != 0 { .append(Separator) } // copy element for ; < && !os.IsPathSeparator([]); ++ { .append([]) } } } // Turn empty string into "." if .w == 0 { .append('.') } return FromSlash(.string()) } // ToSlash returns the result of replacing each separator character // in path with a slash ('/') character. Multiple separators are // replaced by multiple slashes. func ( string) string { if Separator == '/' { return } return strings.ReplaceAll(, 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 ( string) string { if Separator == '/' { return } return strings.ReplaceAll(, "/", 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 ( string) []string { return splitList() } // 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 ( string) (, string) { := VolumeName() := len() - 1 for >= len() && !os.IsPathSeparator([]) { -- } return [:+1], [+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 ( ...string) string { return join() } // 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 ( string) string { for := len() - 1; >= 0 && !os.IsPathSeparator([]); -- { if [] == '.' { return [:] } } 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 ( string) (string, error) { return evalSymlinks() } // 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 ( string) (string, error) { return abs() } func unixAbs( string) (string, error) { if IsAbs() { return Clean(), nil } , := os.Getwd() if != nil { return "", } return Join(, ), 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 (, string) (string, error) { := VolumeName() := VolumeName() := Clean() := Clean() if sameWord(, ) { return ".", nil } = [len():] = [len():] if == "." { = "" } // Can't use IsAbs - `\a` and `a` are both relative in Windows. := len() > 0 && [0] == Separator := len() > 0 && [0] == Separator if != || !sameWord(, ) { return "", errors.New("Rel: can't make " + + " relative to " + ) } // Position base[b0:bi] and targ[t0:ti] at the first differing elements. := len() := len() var , , , int for { for < && [] != Separator { ++ } for < && [] != Separator { ++ } if !sameWord([:], [:]) { break } if < { ++ } if < { ++ } = = } if [:] == ".." { return "", errors.New("Rel: can't make " + + " relative to " + ) } if != { // Base elements left. Must go up before going down. := strings.Count([:], string(Separator)) := 2 + *3 if != { += 1 + - } := make([]byte, ) := copy(, "..") for := 0; < ; ++ { [] = Separator copy([+1:], "..") += 3 } if != { [] = Separator copy([+1:], [:]) } return string(), nil } return [:], nil } // SkipDir is used as a return value from WalkFuncs 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 // WalkFunc is the type of the function called by Walk to visit each 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). 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( string, fs.DirEntry, fs.WalkDirFunc) error { if := (, , nil); != nil || !.IsDir() { if == SkipDir && .IsDir() { // Successfully skipped directory. = nil } return } , := readDir() if != nil { // Second call, to report ReadDir error. = (, , ) if != nil { return } } for , := range { := Join(, .Name()) if := (, , ); != nil { if == SkipDir { break } return } } return nil } // walk recursively descends path, calling walkFn. func walk( string, fs.FileInfo, WalkFunc) error { if !.IsDir() { return (, , nil) } , := readDirNames() := (, , ) // 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 != nil || != 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, it will be handled by the caller. // So walk should return whatever walkFn returns. return } for , := range { := Join(, ) , := lstat() if != nil { if := (, , ); != nil && != SkipDir { return } } else { = (, , ) if != nil { if !.IsDir() || != SkipDir { return } } } } 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. func ( string, fs.WalkDirFunc) error { , := os.Lstat() if != nil { = (, nil, ) } else { = walkDir(, &statDirEntry{}, ) } if == SkipDir { return nil } return } type statDirEntry struct { info fs.FileInfo } func ( *statDirEntry) () string { return .info.Name() } func ( *statDirEntry) () bool { return .info.IsDir() } func ( *statDirEntry) () fs.FileMode { return .info.Mode().Type() } func ( *statDirEntry) () (fs.FileInfo, error) { return .info, nil } // 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 ( string, WalkFunc) error { , := os.Lstat() if != nil { = (, nil, ) } else { = walk(, , ) } if == SkipDir { return nil } return } // readDir reads the directory named by dirname and returns // a sorted list of directory entries. func readDir( string) ([]fs.DirEntry, error) { , := os.Open() if != nil { return nil, } , := .ReadDir(-1) .Close() if != nil { return nil, } sort.Slice(, func(, int) bool { return [].Name() < [].Name() }) return , nil } // readDirNames reads the directory named by dirname and returns // a sorted list of directory entry names. func readDirNames( string) ([]string, error) { , := os.Open() if != nil { return nil, } , := .Readdirnames(-1) .Close() if != nil { return nil, } sort.Strings() return , 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 ( string) string { if == "" { return "." } // Strip trailing slashes. for len() > 0 && os.IsPathSeparator([len()-1]) { = [0 : len()-1] } // Throw away volume name = [len(VolumeName()):] // Find the last element := len() - 1 for >= 0 && !os.IsPathSeparator([]) { -- } if >= 0 { = [+1:] } // If empty now, it had only slashes. if == "" { return string(Separator) } return } // 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 ( string) string { := VolumeName() := len() - 1 for >= len() && !os.IsPathSeparator([]) { -- } := Clean([len() : +1]) if == "." && len() > 2 { // must be UNC return } return + } // 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 ( string) string { return [:volumeNameLen()] }