1 files changed, 123 insertions, 0 deletions
diff --git a/src/os/getwd.go b/src/os/getwd.go
new file mode 100644
index 000000000..d5da53b34
--- /dev/null
+++ b/src/os/getwd.go
@@ -0,0 +1,123 @@
+// 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 (
+	"runtime"
+	"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() (dir string, err error) {
+	if runtime.GOOS == "windows" {
+		return syscall.Getwd()
+	}
+
+	// Clumsy but widespread kludge:
+	// if $PWD is set and matches ".", use it.
+	dot, err := Stat(".")
+	if err != nil {
+		return "", err
+	}
+	dir = Getenv("PWD")
+	if len(dir) > 0 && dir[0] == '/' {
+		d, err := Stat(dir)
+		if err == nil && SameFile(dot, d) {
+			return dir, nil
+		}
+	}
+
+	// If the operating system provides a Getwd call, use it.
+	// Otherwise, we're trying to find our way back to ".".
+	if syscall.ImplementsGetwd {
+		s, e := syscall.Getwd()
+		if useSyscallwd(e) {
+			return s, NewSyscallError("getwd", e)
+		}
+	}
+
+	// Apply same kludge but to cached dir instead of $PWD.
+	getwdCache.Lock()
+	dir = getwdCache.dir
+	getwdCache.Unlock()
+	if len(dir) > 0 {
+		d, err := Stat(dir)
+		if err == nil && SameFile(dot, d) {
+			return dir, 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 dir.
+	dir = ""
+	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) {
+					dir = "/" + name + dir
+					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 = dir
+	getwdCache.Unlock()
+
+	return dir, nil
+}