windows: add GUID handling functions

Virtually every project that works with x/sys/window's GUIDs winds up
rolling their own version of this in one way or another. So let's add
the correct win32 wrappers for it, so that these are always generated,
parsed, and converted in the uniform correct way.

Change-Id: I35f4b4ab5fc681d3e16fc5bbaf2cb20031eb3f12
Reviewed-on: https://go-review.googlesource.com/c/sys/+/180938
Run-TryBot: Jason Donenfeld <Jason@zx2c4.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

windows/syscall_windows.go

@@ -286,6 +286,9 @@ func NewCallbackCDecl(fn interface{}) uintptr {
 //sys	SetVolumeLabel(rootPathName *uint16, volumeName *uint16) (err error) = SetVolumeLabelW
 //sys	SetVolumeMountPoint(volumeMountPoint *uint16, volumeName *uint16) (err error) = SetVolumeMountPointW
 //sys	MessageBox(hwnd Handle, text *uint16, caption *uint16, boxtype uint32) (ret int32, err error) [failretval==0] = user32.MessageBoxW
+//sys	clsidFromString(lpsz *uint16, pclsid *GUID) (err error) [failretval!=0] = ole32.CLSIDFromString
+//sys	stringFromGUID2(rguid *GUID, lpsz *uint16, cchMax int) (chars int) = ole32.StringFromGUID2
+//sys	coCreateGuid(pguid *GUID) (ret error) = ole32.CoCreateGuid
 
 // syscall interface implementation for other packages
 
@@ -1241,3 +1244,39 @@ func Readlink(path string, buf []byte) (n int, err error) {
 
 	return n, nil
 }
+
+// GUIDFromString parses a string in the form of
+// "{XXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX}" into a GUID.
+func GUIDFromString(str string) (GUID, error) {
+	guid := GUID{}
+	str16, err := syscall.UTF16PtrFromString(str)
+	if err != nil {
+		return guid, err
+	}
+	err = clsidFromString(str16, &guid)
+	if err != nil {
+		return guid, err
+	}
+	return guid, nil
+}
+
+// GenerateGUID creates a new random GUID.
+func GenerateGUID() (GUID, error) {
+	guid := GUID{}
+	err := coCreateGuid(&guid)
+	if err != nil {
+		return guid, err
+	}
+	return guid, nil
+}
+
+// String returns the canonical string form of the GUID,
+// in the form of "{XXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX}".
+func (guid GUID) String() string {
+	var str [100]uint16
+	chars := stringFromGUID2(&guid, &str[0], len(str))
+	if chars <= 1 {
+		return ""
+	}
+	return string(utf16.Decode(str[:chars-1]))
+}

windows/syscall_windows_test.go

@@ -5,6 +5,7 @@
 package windows_test
 
 import (
+	"fmt"
 	"io/ioutil"
 	"os"
 	"path/filepath"
@@ -169,3 +170,25 @@ func TestPseudoTokens(t *testing.T) {
 		t.Fatal("The real process token does not have the same as the pseudo thread token after impersonating self")
 	}
 }
+
+func TestGUID(t *testing.T) {
+	guid, err := windows.GenerateGUID()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if guid.Data1 == 0 && guid.Data2 == 0 && guid.Data3 == 0 && guid.Data4 == [8]byte{} {
+		t.Fatal("Got an all zero GUID, which is overwhelmingly unlikely")
+	}
+	want := fmt.Sprintf("{%08X-%04X-%04X-%04X-%012X}", guid.Data1, guid.Data2, guid.Data3, guid.Data4[:2], guid.Data4[2:])
+	got := guid.String()
+	if got != want {
+		t.Fatalf("String = %q; want %q", got, want)
+	}
+	guid2, err := windows.GUIDFromString(got)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if guid2 != guid {
+		t.Fatalf("Did not parse string back to original GUID = %q; want %q", guid2, guid)
+	}
+}

windows/zsyscall_windows.go

@@ -42,6 +42,7 @@ var (
 	modmswsock  = NewLazySystemDLL("mswsock.dll")
 	modcrypt32  = NewLazySystemDLL("crypt32.dll")
 	moduser32   = NewLazySystemDLL("user32.dll")
+	modole32    = NewLazySystemDLL("ole32.dll")
 	modws2_32   = NewLazySystemDLL("ws2_32.dll")
 	moddnsapi   = NewLazySystemDLL("dnsapi.dll")
 	modiphlpapi = NewLazySystemDLL("iphlpapi.dll")
@@ -221,6 +222,9 @@ var (
 	procSetVolumeLabelW                    = modkernel32.NewProc("SetVolumeLabelW")
 	procSetVolumeMountPointW               = modkernel32.NewProc("SetVolumeMountPointW")
 	procMessageBoxW                        = moduser32.NewProc("MessageBoxW")
+	procCLSIDFromString                    = modole32.NewProc("CLSIDFromString")
+	procStringFromGUID2                    = modole32.NewProc("StringFromGUID2")
+	procCoCreateGuid                       = modole32.NewProc("CoCreateGuid")
 	procWSAStartup                         = modws2_32.NewProc("WSAStartup")
 	procWSACleanup                         = modws2_32.NewProc("WSACleanup")
 	procWSAIoctl                           = modws2_32.NewProc("WSAIoctl")
@@ -2406,6 +2410,32 @@ func MessageBox(hwnd Handle, text *uint16, caption *uint16, boxtype uint32) (ret
 	return
 }
 
+func clsidFromString(lpsz *uint16, pclsid *GUID) (err error) {
+	r1, _, e1 := syscall.Syscall(procCLSIDFromString.Addr(), 2, uintptr(unsafe.Pointer(lpsz)), uintptr(unsafe.Pointer(pclsid)), 0)
+	if r1 != 0 {
+		if e1 != 0 {
+			err = errnoErr(e1)
+		} else {
+			err = syscall.EINVAL
+		}
+	}
+	return
+}
+
+func stringFromGUID2(rguid *GUID, lpsz *uint16, cchMax int) (chars int) {
+	r0, _, _ := syscall.Syscall(procStringFromGUID2.Addr(), 3, uintptr(unsafe.Pointer(rguid)), uintptr(unsafe.Pointer(lpsz)), uintptr(cchMax))
+	chars = int(r0)
+	return
+}
+
+func coCreateGuid(pguid *GUID) (ret error) {
+	r0, _, _ := syscall.Syscall(procCoCreateGuid.Addr(), 1, uintptr(unsafe.Pointer(pguid)), 0, 0)
+	if r0 != 0 {
+		ret = syscall.Errno(r0)
+	}
+	return
+}
+
 func WSAStartup(verreq uint32, data *WSAData) (sockerr error) {
 	r0, _, _ := syscall.Syscall(procWSAStartup.Addr(), 2, uintptr(verreq), uintptr(unsafe.Pointer(data)), 0)
 	if r0 != 0 {