wintun: Use native Win32 API for I/O

Signed-off-by: Simon Rozman <simon@rozman.si>

tun/ztun_windows.go

@@ -0,0 +1,61 @@
+// Code generated by 'go generate'; DO NOT EDIT.
+
+package tun
+
+import (
+	"syscall"
+	"unsafe"
+
+	"golang.org/x/sys/windows"
+)
+
+var _ unsafe.Pointer
+
+// Do the interface allocations only once for common
+// Errno values.
+const (
+	errnoERROR_IO_PENDING = 997
+)
+
+var (
+	errERROR_IO_PENDING error = syscall.Errno(errnoERROR_IO_PENDING)
+)
+
+// errnoErr returns common boxed Errno values, to prevent
+// allocations at runtime.
+func errnoErr(e syscall.Errno) error {
+	switch e {
+	case 0:
+		return nil
+	case errnoERROR_IO_PENDING:
+		return errERROR_IO_PENDING
+	}
+	// TODO: add more here, after collecting data on the common
+	// error values see on Windows. (perhaps when running
+	// all.bat?)
+	return e
+}
+
+var (
+	modkernel32 = windows.NewLazySystemDLL("kernel32.dll")
+
+	procGetOverlappedResult = modkernel32.NewProc("GetOverlappedResult")
+)
+
+func getOverlappedResult(handle windows.Handle, overlapped *windows.Overlapped, done *uint32, wait bool) (err error) {
+	var _p0 uint32
+	if wait {
+		_p0 = 1
+	} else {
+		_p0 = 0
+	}
+	r1, _, e1 := syscall.Syscall6(procGetOverlappedResult.Addr(), 4, uintptr(handle), uintptr(unsafe.Pointer(overlapped)), uintptr(unsafe.Pointer(done)), uintptr(_p0), 0, 0)
+	if r1 == 0 {
+		if e1 != 0 {
+			err = errnoErr(e1)
+		} else {
+			err = syscall.EINVAL
+		}
+	}
+	return
+}