path/filepath: normalize output of EvalSymlinks on windows

Current implementation uses GetShortPathName and GetLongPathName
to get a normalized path. That approach sometimes fails because
user can disable short path name anytime. This CL provides
an alternative approach suggested by MSDN.

https://msdn.microsoft.com/en-us/library/windows/desktop/aa364989(v=vs.85).aspx

Fixes #13980

Change-Id: Icf4afe4c9c4b507fc110c1483bf8db2c3f606b0a
Reviewed-on: https://go-review.googlesource.com/20860Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/path/filepath/export_windows_test.go

+// Copyright 2016 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 filepath
+
+var ToNorm = toNorm

src/path/filepath/path_windows_test.go

@@ -279,3 +279,59 @@ func TestEvalSymlinksCanonicalNamesWith8dot3Disabled(t *testing.T) {
 	}
 	TestEvalSymlinksCanonicalNames(t)
 }
+
+func TestToNorm(t *testing.T) {
+	stubBase := func(path string) (string, error) {
+		vol := filepath.VolumeName(path)
+		path = path[len(vol):]
+
+		if strings.Contains(path, "/") {
+			return "", fmt.Errorf("invalid path is given to base: %s", vol+path)
+		}
+
+		if path == "" || path == "." || path == `\` {
+			return "", fmt.Errorf("invalid path is given to base: %s", vol+path)
+		}
+
+		i := strings.LastIndexByte(path, filepath.Separator)
+		if i == len(path)-1 { // trailing '\' is invalid
+			return "", fmt.Errorf("invalid path is given to base: %s", vol+path)
+		}
+		if i == -1 {
+			return strings.ToUpper(path), nil
+		}
+
+		return strings.ToUpper(path[i+1:]), nil
+	}
+
+	// On this test, toNorm should be same as string.ToUpper(filepath.Clean(path)) except empty string.
+	tests := []struct {
+		arg  string
+		want string
+	}{
+		{"", ""},
+		{".", "."},
+		{"./foo/bar", `FOO\BAR`},
+		{"/", `\`},
+		{"/foo/bar", `\FOO\BAR`},
+		{"/foo/bar/baz/qux", `\FOO\BAR\BAZ\QUX`},
+		{"foo/bar", `FOO\BAR`},
+		{"C:/foo/bar", `C:\FOO\BAR`},
+		{"C:foo/bar", `C:FOO\BAR`},
+		{"c:/foo/bar", `C:\FOO\BAR`},
+		{"C:/foo/bar", `C:\FOO\BAR`},
+		{"C:/foo/bar/", `C:\FOO\BAR`},
+		{`C:\foo\bar`, `C:\FOO\BAR`},
+		{`C:\foo/bar\`, `C:\FOO\BAR`},
+		{"C:/ふー/バー", `C:\ふー\バー`},
+	}
+
+	for _, test := range tests {
+		got, err := filepath.ToNorm(test.arg, stubBase)
+		if err != nil {
+			t.Errorf("unexpected toNorm error, arg: %s, err: %v\n", test.arg, err)
+		} else if got != test.want {
+			t.Errorf("toNorm error, arg: %s, want: %s, got: %s\n", test.arg, test.want, got)
+		}
+	}
+}

src/path/filepath/symlink_windows.go

@@ -5,45 +5,82 @@
 package filepath
 
 import (
+	"strings"
 	"syscall"
 )
 
-func toShort(path string) (string, error) {
-	p, err := syscall.UTF16FromString(path)
+// normVolumeName is like VolumeName, but makes drive letter upper case.
+// result of EvalSymlinks must be unique, so we have
+// EvalSymlinks(`c:\a`) == EvalSymlinks(`C:\a`).
+func normVolumeName(path string) string {
+	volume := VolumeName(path)
+
+	if len(volume) > 2 { // isUNC
+		return volume
+	}
+
+	return strings.ToUpper(volume)
+}
+
+// normBase retruns the last element of path.
+func normBase(path string) (string, error) {
+	p, err := syscall.UTF16PtrFromString(path)
 	if err != nil {
 		return "", err
 	}
-	b := p // GetShortPathName says we can reuse buffer
-	n := uint32(len(b))
-	for {
-		n, err = syscall.GetShortPathName(&p[0], &b[0], uint32(len(b)))
-		if err != nil {
-			return "", err
-		}
-		if n <= uint32(len(b)) {
-			return syscall.UTF16ToString(b[:n]), nil
-		}
-		b = make([]uint16, n)
-	}
-}
 
-func toLong(path string) (string, error) {
-	p, err := syscall.UTF16FromString(path)
+	var data syscall.Win32finddata
+
+	h, err := syscall.FindFirstFile(p, &data)
 	if err != nil {
 		return "", err
 	}
-	b := p // GetLongPathName says we can reuse buffer
-	n := uint32(len(b))
+	syscall.FindClose(h)
+
+	return syscall.UTF16ToString(data.FileName[:]), nil
+}
+
+func toNorm(path string, base func(string) (string, error)) (string, error) {
+	if path == "" {
+		return path, nil
+	}
+
+	path = Clean(path)
+
+	volume := normVolumeName(path)
+	path = path[len(volume):]
+
+	// skip special cases
+	if path == "." || path == `\` {
+		return volume + path, nil
+	}
+
+	var normPath string
+
 	for {
-		n, err = syscall.GetLongPathName(&p[0], &b[0], uint32(len(b)))
+		name, err := base(volume + path)
 		if err != nil {
 			return "", err
 		}
-		if n <= uint32(len(b)) {
-			return syscall.UTF16ToString(b[:n]), nil
+
+		normPath = name + `\` + normPath
+
+		i := strings.LastIndexByte(path, Separator)
+		if i == -1 {
+			break
+		}
+		if i == 0 { // `\Go` or `C:\Go`
+			normPath = `\` + normPath
+
+			break
 		}
-		b = make([]uint16, n)
+
+		path = path[:i]
 	}
+
+	normPath = normPath[:len(normPath)-1] // remove trailing '\'
+
+	return volume + normPath, nil
 }
 
 func evalSymlinks(path string) (string, error) {
@@ -51,20 +88,5 @@ func evalSymlinks(path string) (string, error) {
 	if err != nil {
 		return "", err
 	}
-	p, err := toShort(path)
-	if err != nil {
-		return "", err
-	}
-	p, err = toLong(p)
-	if err != nil {
-		return "", err
-	}
-	// syscall.GetLongPathName does not change the case of the drive letter,
-	// but the result of EvalSymlinks must be unique, so we have
-	// EvalSymlinks(`c:\a`) == EvalSymlinks(`C:\a`).
-	// Make drive letter upper case.
-	if len(p) >= 2 && p[1] == ':' && 'a' <= p[0] && p[0] <= 'z' {
-		p = string(p[0]+'A'-'a') + p[1:]
-	}
-	return Clean(p), nil
+	return toNorm(path, normBase)
 }