// 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.//// Functions in this package replace any occurrences of the slash ('/') character// with os.PathSeparator when returning paths unless otherwise specified.package filepath import (	"errors"	"os"	"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) 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.//// 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,''// http://plan9.bell-labs.com/sys/doc/lexnames.htmlfunc Clean(path string) string {	originalPath := path	volLen := volumeNameLen(path)	path = path[volLen:]	if path == "" {		if volLen > 1 && 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('.')	} 	return FromSlash(out.string())} // 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.Replace(path, string(Separator), "/", -1)} // 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.Replace(path, "/", string(Separator), -1)} // 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. SplitList does not replace slash characters in the returned paths.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, adding// a Separator if necessary. The result is Cleaned, in particular// all empty strings are ignored.// On Windows, the result is a UNC path if and only if the first path// 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.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.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.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 = ""	}	// 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 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 = errors.New("skip this directory") // WalkFunc is the type of the function called for each file or directory// visited by Walk. The path argument contains the argument to Walk as a// prefix; that is, if Walk is called with "dir", which is a directory// containing the file "a", the walk function will be called with argument// "dir/a". The info argument is the os.FileInfo for the named path.//// If there was a problem walking to the file or directory named by path, the// incoming error will describe the problem and the function can decide how// to handle that error (and Walk will not descend into that directory). If// an error is returned, processing stops. The sole exception is when the function// returns the special value SkipDir. If the function returns SkipDir when invoked// on a directory, Walk skips the directory's contents entirely.// If the function returns SkipDir when invoked on a non-directory file,// Walk skips the remaining files in the containing directory.type WalkFunc func(path string, info os.FileInfo, err error) error var lstat = os.Lstat // for testing // walk recursively descends path, calling w.func walk(path string, info os.FileInfo, walkFn WalkFunc) error {	err := walkFn(path, info, nil)	if err != nil {		if info.IsDir() && err == SkipDir {			return nil		}		return err	} 	if !info.IsDir() {		return nil	} 	names, err := readDirNames(path)	if err != nil {		return walkFn(path, info, err)	} 	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} // Walk walks the file tree rooted at root, calling walkFn for each file or// directory in the tree, including root. All errors that arise visiting files// and directories are filtered by walkFn. The files are walked in lexical// order, which makes the output deterministic but means that for very// large directories Walk can be inefficient.// Walk does not follow symbolic links.func Walk(root string, walkFn WalkFunc) error {	info, err := os.Lstat(root)	if err != nil {		return walkFn(root, nil, err)	}	return walk(root, info, walkFn)} // readDirNames reads the directory named by dirname and returns// a sorted list of directory entries.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, the path is Cleaned 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])	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 path[:volumeNameLen(path)]}