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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 path implements utility routines for manipulating slash-separated
// paths.
//
// The path package should only be used for paths separated by forward
// slashes, such as the paths in URLs. This package does not deal with
// Windows paths with drive letters or backslashes; to manipulate
// operating system paths, use the [path/filepath] package.
package path
import "internal/bytealg"
// 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 {
s string
buf []byte
w int
}
func (b *lazybuf) index(i int) byte {
if b.buf != nil {
return b.buf[i]
}
return b.s[i]
}
func (b *lazybuf) append(c byte) {
if b.buf == nil {
if b.w < len(b.s) && b.s[b.w] == c {
b.w++
return
}
b.buf = make([]byte, len(b.s))
copy(b.buf, b.s[:b.w])
}
b.buf[b.w] = c
b.w++
}
func (b *lazybuf) string() string {
if b.buf == nil {
return b.s[:b.w]
}
return string(b.buf[:b.w])
}
// 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 slashes with a single slash.
// 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.
//
// The returned path ends in a slash only if it is the root "/".
//
// 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 {
if path == "" {
return "."
}
rooted := path[0] == '/'
n := len(path)
// 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.
out := lazybuf{s: path}
r, dotdot := 0, 0
if rooted {
out.append('/')
r, dotdot = 1, 1
}
for r < n {
switch {
case path[r] == '/':
// empty path element
r++
case path[r] == '.' && (r+1 == n || path[r+1] == '/'):
// . element
r++
case path[r] == '.' && path[r+1] == '.' && (r+2 == n || path[r+2] == '/'):
// .. element: remove to last /
r += 2
switch {
case out.w > dotdot:
// can backtrack
out.w--
for out.w > dotdot && out.index(out.w) != '/' {
out.w--
}
case !rooted:
// cannot backtrack, but not rooted, so append .. element.
if out.w > 0 {
out.append('/')
}
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('/')
}
// copy element
for ; r < n && path[r] != '/'; r++ {
out.append(path[r])
}
}
}
// Turn empty string into "."
if out.w == 0 {
return "."
}
return out.string()
}
// Split splits path immediately following the final slash,
// separating it into a directory and file name component.
// If there is no slash 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) {
i := bytealg.LastIndexByteString(path, '/')
return path[:i+1], path[i+1:]
}
// Join joins any number of path elements into a single path,
// separating them with slashes. 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.
func Join(elem ...string) string {
size := 0
for _, e := range elem {
size += len(e)
}
if size == 0 {
return ""
}
buf := make([]byte, 0, size+len(elem)-1)
for _, e := range elem {
if len(buf) > 0 || e != "" {
if len(buf) > 0 {
buf = append(buf, '/')
}
buf = append(buf, e...)
}
}
return Clean(string(buf))
}
// Ext returns the file name extension used by path.
// The extension is the suffix beginning at the final dot
// in the final slash-separated element of path;
// it is empty if there is no dot.
func Ext(path string) string {
for i := len(path) - 1; i >= 0 && path[i] != '/'; i-- {
if path[i] == '.' {
return path[i:]
}
}
return ""
}
// Base returns the last element of path.
// Trailing slashes are removed before extracting the last element.
// If the path is empty, Base returns ".".
// If the path consists entirely of slashes, Base returns "/".
func Base(path string) string {
if path == "" {
return "."
}
// Strip trailing slashes.
for len(path) > 0 && path[len(path)-1] == '/' {
path = path[0 : len(path)-1]
}
// Find the last element
if i := bytealg.LastIndexByteString(path, '/'); i >= 0 {
path = path[i+1:]
}
// If empty now, it had only slashes.
if path == "" {
return "/"
}
return path
}
// IsAbs reports whether the path is absolute.
func IsAbs(path string) bool {
return len(path) > 0 && path[0] == '/'
}
// Dir returns all but the last element of path, typically the path's directory.
// After dropping the final element using [Split], the path is Cleaned and trailing
// slashes are removed.
// If the path is empty, Dir returns ".".
// If the path consists entirely of slashes followed by non-slash bytes, Dir
// returns a single slash. In any other case, the returned path does not end in a
// slash.
func Dir(path string) string {
dir, _ := Split(path)
return Clean(dir)
}
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