// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package os
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import (
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"runtime"
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"sync"
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"syscall"
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)
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var getwdCache struct {
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sync.Mutex
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dir string
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}
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// useSyscallwd determines whether to use the return value of
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// syscall.Getwd based on its error.
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var useSyscallwd = func(error) bool { return true }
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// Getwd returns a rooted path name corresponding to the
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// current directory. If the current directory can be
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// reached via multiple paths (due to symbolic links),
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// Getwd may return any one of them.
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func Getwd() (dir string, err error) {
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if runtime.GOOS == "windows" || runtime.GOOS == "plan9" {
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return syscall.Getwd()
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}
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// Clumsy but widespread kludge:
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// if $PWD is set and matches ".", use it.
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dot, err := statNolog(".")
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if err != nil {
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return "", err
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}
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dir = Getenv("PWD")
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if len(dir) > 0 && dir[0] == '/' {
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d, err := statNolog(dir)
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if err == nil && SameFile(dot, d) {
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return dir, nil
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}
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}
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// If the operating system provides a Getwd call, use it.
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// Otherwise, we're trying to find our way back to ".".
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if syscall.ImplementsGetwd {
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s, e := syscall.Getwd()
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if useSyscallwd(e) {
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return s, NewSyscallError("getwd", e)
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}
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}
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// Apply same kludge but to cached dir instead of $PWD.
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getwdCache.Lock()
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dir = getwdCache.dir
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getwdCache.Unlock()
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if len(dir) > 0 {
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d, err := statNolog(dir)
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if err == nil && SameFile(dot, d) {
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return dir, nil
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}
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}
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// Root is a special case because it has no parent
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// and ends in a slash.
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root, err := statNolog("/")
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if err != nil {
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// Can't stat root - no hope.
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return "", err
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}
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if SameFile(root, dot) {
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return "/", nil
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}
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// General algorithm: find name in parent
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// and then find name of parent. Each iteration
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// adds /name to the beginning of dir.
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dir = ""
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for parent := ".."; ; parent = "../" + parent {
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if len(parent) >= 1024 { // Sanity check
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return "", syscall.ENAMETOOLONG
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}
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fd, err := openFileNolog(parent, O_RDONLY, 0)
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if err != nil {
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return "", err
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}
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for {
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names, err := fd.Readdirnames(100)
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if err != nil {
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fd.Close()
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return "", err
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}
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for _, name := range names {
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d, _ := lstatNolog(parent + "/" + name)
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if SameFile(d, dot) {
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dir = "/" + name + dir
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goto Found
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}
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}
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}
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Found:
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pd, err := fd.Stat()
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if err != nil {
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return "", err
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}
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fd.Close()
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if SameFile(pd, root) {
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break
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}
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// Set up for next round.
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dot = pd
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}
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// Save answer as hint to avoid the expensive path next time.
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getwdCache.Lock()
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getwdCache.dir = dir
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getwdCache.Unlock()
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return dir, nil
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}
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