time: find correct zone abbreviations even on non-English windows systems

Fixes #5783

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/10956043

src/pkg/time/zoneinfo_windows.go

@@ -8,6 +8,7 @@ import (
 	"errors"
 	"runtime"
 	"syscall"
+	"unsafe"
 )
 
 // TODO(rsc): Fall back to copy of zoneinfo files.
@@ -17,6 +18,78 @@ import (
 // The implementation assumes that this year's rules for daylight savings
 // time apply to all previous and future years as well.
 
+// getKeyValue retrieves the string value kname associated with the open registry key kh.
+func getKeyValue(kh syscall.Handle, kname string) (string, error) {
+	var buf [50]uint16 // buf needs to be large enough to fit zone descriptions
+	var typ uint32
+	n := uint32(len(buf) * 2) // RegQueryValueEx's signature expects array of bytes, not uint16
+	p, _ := syscall.UTF16PtrFromString(kname)
+	if err := syscall.RegQueryValueEx(kh, p, nil, &typ, (*byte)(unsafe.Pointer(&buf[0])), &n); err != nil {
+		return "", err
+	}
+	if typ != syscall.REG_SZ { // null terminated strings only
+		return "", errors.New("Key is not string")
+	}
+	return syscall.UTF16ToString(buf[:]), nil
+}
+
+// matchZoneKey checks if stdname and dstname match the corresponding "Std"
+// and "Dlt" key values in the kname key stored under the open registry key zones.
+func matchZoneKey(zones syscall.Handle, kname string, stdname, dstname string) (matched bool, err2 error) {
+	var h syscall.Handle
+	p, _ := syscall.UTF16PtrFromString(kname)
+	if err := syscall.RegOpenKeyEx(zones, p, 0, syscall.KEY_READ, &h); err != nil {
+		return false, err
+	}
+	defer syscall.RegCloseKey(h)
+
+	s, err := getKeyValue(h, "Std")
+	if err != nil {
+		return false, err
+	}
+	if s != stdname {
+		return false, nil
+	}
+	s, err = getKeyValue(h, "Dlt")
+	if err != nil {
+		return false, err
+	}
+	if s != dstname {
+		return false, nil
+	}
+	return true, nil
+}
+
+// toEnglishName searches the registry for an English name of a time zone
+// whose zone names are stdname and dstname and returns the English name.
+func toEnglishName(stdname, dstname string) (string, error) {
+	var zones syscall.Handle
+	p, _ := syscall.UTF16PtrFromString(`SOFTWARE\Microsoft\Windows NT\CurrentVersion\Time Zones`)
+	if err := syscall.RegOpenKeyEx(syscall.HKEY_LOCAL_MACHINE, p, 0, syscall.KEY_READ, &zones); err != nil {
+		return "", err
+	}
+	defer syscall.RegCloseKey(zones)
+
+	var count uint32
+	if err := syscall.RegQueryInfoKey(zones, nil, nil, nil, &count, nil, nil, nil, nil, nil, nil, nil); err != nil {
+		return "", err
+	}
+
+	var buf [50]uint16 // buf needs to be large enough to fit zone descriptions
+	for i := uint32(0); i < count; i++ {
+		n := uint32(len(buf))
+		if syscall.RegEnumKeyEx(zones, i, &buf[0], &n, nil, nil, nil, nil) != nil {
+			continue
+		}
+		kname := syscall.UTF16ToString(buf[:])
+		matched, err := matchZoneKey(zones, kname, stdname, dstname)
+		if err == nil && matched {
+			return kname, nil
+		}
+	}
+	return "", errors.New(`English name for time zone "` + stdname + `" not found in registry`)
+}
+
 // extractCAPS exracts capital letters from description desc.
 func extractCAPS(desc string) string {
 	var short []rune
@@ -33,8 +106,16 @@ func abbrev(z *syscall.Timezoneinformation) (std, dst string) {
 	stdName := syscall.UTF16ToString(z.StandardName[:])
 	a, ok := abbrs[stdName]
 	if !ok {
-		// fallback to using capital letters
 		dstName := syscall.UTF16ToString(z.DaylightName[:])
+		// Perhaps stdName is not English. Try to convert it.
+		englishName, err := toEnglishName(stdName, dstName)
+		if err == nil {
+			a, ok = abbrs[englishName]
+			if ok {
+				return a.std, a.dst
+			}
+		}
+		// fallback to using capital letters
 		return extractCAPS(stdName), extractCAPS(dstName)
 	}
 	return a.std, a.dst