1 files changed, 464 insertions, 0 deletions
diff --git a/src/path/filepath/path.go b/src/path/filepath/path.go
new file mode 100644
index 000000000..d37fc9dfc
--- /dev/null
+++ b/src/path/filepath/path.go
@@ -0,0 +1,464 @@
+// 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.
+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.html
+func 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.
+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.
+func Join(elem ...string) string {
+	for i, e := range elem {
+		if e != "" {
+			return Clean(strings.Join(elem[i:], string(Separator)))
+		}
+	}
+	return ""
+}
+
+// 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 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 || baseVol != targVol {
+		return "", errors.New("Rel: can't make " + targ + " relative to " + base)
+	}
+	// 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 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 " + targ + " relative to " + base)
+	}
+	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 that if path
+// is a directory and the function returns the special value SkipDir, the
+// contents of the directory are skipped and processing continues as usual on
+// the next file.
+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:" under windows.
+// Given "\\host\share\foo" it returns "\\host\share".
+// On other platforms it returns "".
+func VolumeName(path string) (v string) {
+	return path[:volumeNameLen(path)]
+}