os: fix Open for empty root directories on windows

Fixes #4601.

R=golang-dev, rsc, bradfitz, kardianos
CC=golang-dev
https://golang.org/cl/7033046

diff --git a/src/pkg/os/file_windows.go b/src/pkg/os/file_windows.go
index 9dff57000ca2fbf190bbaa60d537e7bb256796fe..f11b273f635f1a42c0538c16c15cf2615be21f20 100644 (file)
--- a/src/pkg/os/file_windows.go
+++ b/src/pkg/os/file_windows.go
@@ -11,6 +11,7 @@ import (
        "syscall"
        "unicode/utf16"
        "unicode/utf8"
+       "unsafe"
 )
 
 // File represents an open file descriptor.
@@ -41,12 +42,9 @@ func (file *File) Fd() uintptr {
        return uintptr(file.fd)
 }
 
-// NewFile returns a new File with the given file descriptor and name.
-func NewFile(fd uintptr, name string) *File {
-       h := syscall.Handle(fd)
-       if h == syscall.InvalidHandle {
-               return nil
-       }
+// newFile returns a new File with the given file handle and name.
+// Unlike NewFile, it does not check that h is syscall.InvalidHandle.
+func newFile(h syscall.Handle, name string) *File {
        f := &File{&file{fd: h, name: name}}
        var m uint32
        if syscall.GetConsoleMode(f.fd, &m) == nil {
@@ -56,11 +54,21 @@ func NewFile(fd uintptr, name string) *File {
        return f
 }
 
+// NewFile returns a new File with the given file descriptor and name.
+func NewFile(fd uintptr, name string) *File {
+       h := syscall.Handle(fd)
+       if h == syscall.InvalidHandle {
+               return nil
+       }
+       return newFile(h, name)
+}
+
 // Auxiliary information if the File describes a directory
 type dirInfo struct {
        data     syscall.Win32finddata
        needdata bool
        path     string
+       isempty  bool // set if FindFirstFile returns ERROR_FILE_NOT_FOUND
 }
 
 func epipecheck(file *File, e error) {
@@ -73,7 +81,7 @@ func (f *file) isdir() bool { return f != nil && f.dirinfo != nil }
 func openFile(name string, flag int, perm FileMode) (file *File, err error) {
        r, e := syscall.Open(name, flag|syscall.O_CLOEXEC, syscallMode(perm))
        if e != nil {
-               return nil, &PathError{"open", name, e}
+               return nil, e
        }
        return NewFile(uintptr(r), name), nil
 }
@@ -81,19 +89,37 @@ func openFile(name string, flag int, perm FileMode) (file *File, err error) {
 func openDir(name string) (file *File, err error) {
        maskp, e := syscall.UTF16PtrFromString(name + `\*`)
        if e != nil {
-               return nil, &PathError{"open", name, e}
+               return nil, e
        }
        d := new(dirInfo)
        r, e := syscall.FindFirstFile(maskp, &d.data)
        if e != nil {
-               return nil, &PathError{"open", name, e}
+               // FindFirstFile returns ERROR_FILE_NOT_FOUND when
+               // no matching files can be found. Then, if directory
+               // exists, we should proceed.
+               if e != syscall.ERROR_FILE_NOT_FOUND {
+                       return nil, e
+               }
+               var fa syscall.Win32FileAttributeData
+               namep, e := syscall.UTF16PtrFromString(name)
+               if e != nil {
+                       return nil, e
+               }
+               e = syscall.GetFileAttributesEx(namep, syscall.GetFileExInfoStandard, (*byte)(unsafe.Pointer(&fa)))
+               if e != nil {
+                       return nil, e
+               }
+               if fa.FileAttributes&syscall.FILE_ATTRIBUTE_DIRECTORY == 0 {
+                       return nil, e
+               }
+               d.isempty = true
        }
        d.path = name
        if !isAbs(d.path) {
                cwd, _ := Getwd()
                d.path = cwd + `\` + d.path
        }
-       f := NewFile(uintptr(r), name)
+       f := newFile(r, name)
        f.dirinfo = d
        return f, nil
 }
@@ -120,7 +146,7 @@ func OpenFile(name string, flag int, perm FileMode) (file *File, err error) {
        if e == nil {
                return r, nil
        }
-       return nil, e
+       return nil, &PathError{"open", name, e}
 }
 
 // Close closes the File, rendering it unusable for I/O.
@@ -130,7 +156,14 @@ func (file *File) Close() error {
 }
 
 func (file *file) close() error {
-       if file == nil || file.fd == syscall.InvalidHandle {
+       if file == nil {
+               return syscall.EINVAL
+       }
+       if file.isdir() && file.dirinfo.isempty {
+               // "special" empty directories
+               return nil
+       }
+       if file.fd == syscall.InvalidHandle {
                return syscall.EINVAL
        }
        var e error
@@ -151,12 +184,15 @@ func (file *file) close() error {
 }
 
 func (file *File) readdir(n int) (fi []FileInfo, err error) {
-       if file == nil || file.fd == syscall.InvalidHandle {
+       if file == nil {
                return nil, syscall.EINVAL
        }
        if !file.isdir() {
                return nil, &PathError{"Readdir", file.name, syscall.ENOTDIR}
        }
+       if !file.dirinfo.isempty && file.fd == syscall.InvalidHandle {
+               return nil, syscall.EINVAL
+       }
        wantAll := n <= 0
        size := n
        if wantAll {
@@ -165,7 +201,7 @@ func (file *File) readdir(n int) (fi []FileInfo, err error) {
        }
        fi = make([]FileInfo, 0, size) // Empty with room to grow.
        d := &file.dirinfo.data
-       for n != 0 {
+       for n != 0 && !file.dirinfo.isempty {
                if file.dirinfo.needdata {
                        e := syscall.FindNextFile(syscall.Handle(file.fd), d)
                        if e != nil {