Handle cross platform close

Former-commit-id: 89932bb736c7f4b3eb9bb2384b0cf6bd27872c1c

olm/olm.go

@@ -8,7 +8,6 @@ import (
 	_ "net/http/pprof"
 	"os"
 	"sync"
-	"syscall"
 	"time"
 
 	"github.com/fosrl/newt/bind"
@@ -576,7 +575,7 @@ func (o *Olm) Close() {
 		// If we never created a device from the FD, close it explicitly
 		// This can happen if tunnel is stopped during registration before handleConnect
 		logger.Debug("Closing unused TUN file descriptor %d", o.tunnelConfig.FileDescriptorTun)
-		if err := syscall.Close(int(o.tunnelConfig.FileDescriptorTun)); err != nil {
+		if err := closeFD(o.tunnelConfig.FileDescriptorTun); err != nil {
 			logger.Error("Failed to close TUN file descriptor: %v", err)
 		} else {
 			logger.Info("Closed unused TUN file descriptor")

olm/olm_unix.go

@@ -0,0 +1,10 @@
+//go:build !windows
+
+package olm
+
+import "syscall"
+
+// closeFD closes a file descriptor in a platform-specific way
+func closeFD(fd uint32) error {
+	return syscall.Close(int(fd))
+}

olm/olm_windows.go

@@ -0,0 +1,10 @@
+//go:build windows
+
+package olm
+
+import "syscall"
+
+// closeFD closes a file descriptor in a platform-specific way
+func closeFD(fd uint32) error {
+	return syscall.Close(syscall.Handle(fd))
+}