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// 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"
"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.
//
// 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 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.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, adding
// a Separator if necessary. Join calls Clean on the result; 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.
// 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 = ""
}
// 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). In the
// case of an error, the info argument will be nil. 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 walkFn.
func walk(path string, info os.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, 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
}
// 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 {
err = walkFn(root, nil, err)
} else {
err = walk(root, info, walkFn)
}
if err == SkipDir {
return nil
}
return err
}
// 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, 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 path[:volumeNameLen(path)]
}
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