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// Copyright 2011 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 os
const (
PathSeparator = '\\' // OS-specific path separator
PathListSeparator = ';' // OS-specific path list separator
)
// IsPathSeparator reports whether c is a directory separator character.
func IsPathSeparator(c uint8) bool {
// NOTE: Windows accepts / as path separator.
return c == '\\' || c == '/'
}
// basename removes trailing slashes and the leading
// directory name and drive letter from path name.
func basename(name string) string {
// Remove drive letter
if len(name) == 2 && name[1] == ':' {
name = "."
} else if len(name) > 2 && name[1] == ':' {
name = name[2:]
}
i := len(name) - 1
// Remove trailing slashes
for ; i > 0 && (name[i] == '/' || name[i] == '\\'); i-- {
name = name[:i]
}
// Remove leading directory name
for i--; i >= 0; i-- {
if name[i] == '/' || name[i] == '\\' {
name = name[i+1:]
break
}
}
return name
}
func isAbs(path string) (b bool) {
v := volumeName(path)
if v == "" {
return false
}
path = path[len(v):]
if path == "" {
return false
}
return IsPathSeparator(path[0])
}
func volumeName(path string) (v string) {
if len(path) < 2 {
return ""
}
// with drive letter
c := path[0]
if path[1] == ':' &&
('0' <= c && c <= '9' || 'a' <= c && c <= 'z' ||
'A' <= c && c <= 'Z') {
return path[:2]
}
// is it UNC
if l := len(path); l >= 5 && IsPathSeparator(path[0]) && IsPathSeparator(path[1]) &&
!IsPathSeparator(path[2]) && path[2] != '.' {
// first, leading `\\` and next shouldn't be `\`. its server name.
for n := 3; n < l-1; n++ {
// second, next '\' shouldn't be repeated.
if IsPathSeparator(path[n]) {
n++
// third, following something characters. its share name.
if !IsPathSeparator(path[n]) {
if path[n] == '.' {
break
}
for ; n < l; n++ {
if IsPathSeparator(path[n]) {
break
}
}
return path[:n]
}
break
}
}
}
return ""
}
func fromSlash(path string) string {
// Replace each '/' with '\\' if present
var pathbuf []byte
var lastSlash int
for i, b := range path {
if b == '/' {
if pathbuf == nil {
pathbuf = make([]byte, len(path))
}
copy(pathbuf[lastSlash:], path[lastSlash:i])
pathbuf[i] = '\\'
lastSlash = i + 1
}
}
if pathbuf == nil {
return path
}
copy(pathbuf[lastSlash:], path[lastSlash:])
return string(pathbuf)
}
func dirname(path string) string {
vol := volumeName(path)
i := len(path) - 1
for i >= len(vol) && !IsPathSeparator(path[i]) {
i--
}
dir := path[len(vol) : i+1]
last := len(dir) - 1
if last > 0 && IsPathSeparator(dir[last]) {
dir = dir[:last]
}
if dir == "" {
dir = "."
}
return vol + dir
}
// This is set via go:linkname on runtime.canUseLongPaths, and is true when the OS
// supports opting into proper long path handling without the need for fixups.
var canUseLongPaths bool
// fixLongPath returns the extended-length (\\?\-prefixed) form of
// path when needed, in order to avoid the default 260 character file
// path limit imposed by Windows. If path is not easily converted to
// the extended-length form (for example, if path is a relative path
// or contains .. elements), or is short enough, fixLongPath returns
// path unmodified.
//
// See https://learn.microsoft.com/en-us/windows/win32/fileio/naming-a-file#maximum-path-length-limitation
func fixLongPath(path string) string {
if canUseLongPaths {
return path
}
// Do nothing (and don't allocate) if the path is "short".
// Empirically (at least on the Windows Server 2013 builder),
// the kernel is arbitrarily okay with < 248 bytes. That
// matches what the docs above say:
// "When using an API to create a directory, the specified
// path cannot be so long that you cannot append an 8.3 file
// name (that is, the directory name cannot exceed MAX_PATH
// minus 12)." Since MAX_PATH is 260, 260 - 12 = 248.
//
// The MSDN docs appear to say that a normal path that is 248 bytes long
// will work; empirically the path must be less then 248 bytes long.
if len(path) < 248 {
// Don't fix. (This is how Go 1.7 and earlier worked,
// not automatically generating the \\?\ form)
return path
}
// The extended form begins with \\?\, as in
// \\?\c:\windows\foo.txt or \\?\UNC\server\share\foo.txt.
// The extended form disables evaluation of . and .. path
// elements and disables the interpretation of / as equivalent
// to \. The conversion here rewrites / to \ and elides
// . elements as well as trailing or duplicate separators. For
// simplicity it avoids the conversion entirely for relative
// paths or paths containing .. elements. For now,
// \\server\share paths are not converted to
// \\?\UNC\server\share paths because the rules for doing so
// are less well-specified.
if len(path) >= 2 && path[:2] == `\\` {
// Don't canonicalize UNC paths.
return path
}
if !isAbs(path) {
// Relative path
return path
}
const prefix = `\\?`
pathbuf := make([]byte, len(prefix)+len(path)+len(`\`))
copy(pathbuf, prefix)
n := len(path)
r, w := 0, len(prefix)
for r < n {
switch {
case IsPathSeparator(path[r]):
// empty block
r++
case path[r] == '.' && (r+1 == n || IsPathSeparator(path[r+1])):
// /./
r++
case r+1 < n && path[r] == '.' && path[r+1] == '.' && (r+2 == n || IsPathSeparator(path[r+2])):
// /../ is currently unhandled
return path
default:
pathbuf[w] = '\\'
w++
for ; r < n && !IsPathSeparator(path[r]); r++ {
pathbuf[w] = path[r]
w++
}
}
}
// A drive's root directory needs a trailing \
if w == len(`\\?\c:`) {
pathbuf[w] = '\\'
w++
}
return string(pathbuf[:w])
}
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