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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 os
import (
"sync"
"syscall"
)
var getwdCache struct {
sync.Mutex
dir string
}
// useSyscallwd determines whether to use the return value of
// syscall.Getwd based on its error.
var useSyscallwd = func(error) bool { return true }
// Getwd returns a rooted path name corresponding to the
// current directory. If the current directory can be
// reached via multiple paths (due to symbolic links),
// Getwd may return any one of them.
func Getwd() (pwd string, err error) {
// If the operating system provides a Getwd call, use it.
if syscall.ImplementsGetwd {
s, e := syscall.Getwd()
if useSyscallwd(e) {
return s, NewSyscallError("getwd", e)
}
}
// Otherwise, we're trying to find our way back to ".".
dot, err := Stat(".")
if err != nil {
return "", err
}
// Clumsy but widespread kludge:
// if $PWD is set and matches ".", use it.
pwd = Getenv("PWD")
if len(pwd) > 0 && pwd[0] == '/' {
d, err := Stat(pwd)
if err == nil && SameFile(dot, d) {
return pwd, nil
}
}
// Apply same kludge but to cached dir instead of $PWD.
getwdCache.Lock()
pwd = getwdCache.dir
getwdCache.Unlock()
if len(pwd) > 0 {
d, err := Stat(pwd)
if err == nil && SameFile(dot, d) {
return pwd, nil
}
}
// Root is a special case because it has no parent
// and ends in a slash.
root, err := Stat("/")
if err != nil {
// Can't stat root - no hope.
return "", err
}
if SameFile(root, dot) {
return "/", nil
}
// General algorithm: find name in parent
// and then find name of parent. Each iteration
// adds /name to the beginning of pwd.
pwd = ""
for parent := ".."; ; parent = "../" + parent {
if len(parent) >= 1024 { // Sanity check
return "", syscall.ENAMETOOLONG
}
fd, err := Open(parent)
if err != nil {
return "", err
}
for {
names, err := fd.Readdirnames(100)
if err != nil {
fd.Close()
return "", err
}
for _, name := range names {
d, _ := Lstat(parent + "/" + name)
if SameFile(d, dot) {
pwd = "/" + name + pwd
goto Found
}
}
}
Found:
pd, err := fd.Stat()
if err != nil {
return "", err
}
fd.Close()
if SameFile(pd, root) {
break
}
// Set up for next round.
dot = pd
}
// Save answer as hint to avoid the expensive path next time.
getwdCache.Lock()
getwdCache.dir = pwd
getwdCache.Unlock()
return pwd, nil
}
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