windows: add (*DLL).FindProcByOrdinal

Change-Id: I0b0ef2c62994fad4d89bf15c8c6c95fa660190c3
GitHub-Last-Rev: 379ab4a0f5
GitHub-Pull-Request: golang/sys#69
Reviewed-on: https://go-review.googlesource.com/c/sys/+/227439
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>

windows/dll_windows.go

@@ -104,6 +104,35 @@ func (d *DLL) MustFindProc(name string) *Proc {
 	return p
 }
 
+// FindProcByOrdinal searches DLL d for procedure by ordinal and returns *Proc
+// if found. It returns an error if search fails.
+func (d *DLL) FindProcByOrdinal(ordinal uintptr) (proc *Proc, err error) {
+	a, e := GetProcAddressByOrdinal(d.Handle, ordinal)
+	name := "#" + itoa(int(ordinal))
+	if e != nil {
+		return nil, &DLLError{
+			Err:     e,
+			ObjName: name,
+			Msg:     "Failed to find " + name + " procedure in " + d.Name + ": " + e.Error(),
+		}
+	}
+	p := &Proc{
+		Dll:  d,
+		Name: name,
+		addr: a,
+	}
+	return p, nil
+}
+
+// MustFindProcByOrdinal is like FindProcByOrdinal but panics if search fails.
+func (d *DLL) MustFindProcByOrdinal(ordinal uintptr) *Proc {
+	p, e := d.FindProcByOrdinal(ordinal)
+	if e != nil {
+		panic(e)
+	}
+	return p
+}
+
 // Release unloads DLL d from memory.
 func (d *DLL) Release() (err error) {
 	return FreeLibrary(d.Handle)

windows/syscall_test.go

@@ -79,3 +79,24 @@ func TestGetWindowsDirectory(t *testing.T) {
 		t.Fatalf("System Windows directory does not end in windows: %s", d2)
 	}
 }
+func TestFindProcByOrdinal(t *testing.T) {
+	// Attempt calling shlwapi.dll:IsOS, resolving it by ordinal, as
+	// suggested in
+	// https://msdn.microsoft.com/en-us/library/windows/desktop/bb773795.aspx
+	dll, err := windows.LoadDLL("shlwapi.dll")
+	if err != nil {
+		t.Fatalf("Failed to load shlwapi.dll: %s", err)
+	}
+	procIsOS, err := dll.FindProcByOrdinal(437)
+	if err != nil {
+		t.Fatalf("Could not find shlwapi.dll:IsOS by ordinal: %s", err)
+	}
+	if procIsOS.Name != "#437" {
+		t.Fatalf("Proc's name is incorrect: %s,expected #437", procIsOS.Name)
+	}
+	const OS_NT = 1
+	r, _, _ := syscall.Syscall(procIsOS.Addr(), 1, OS_NT, 0, 0)
+	if r == 0 {
+		t.Error("shlwapi.dll:IsOS(OS_NT) returned 0, expected non-zero value")
+	}
+}