fix(control): add graceful fallback for UDP port conflicts

- Add graceful fallback when UDP connection creation fails
- Use listening connection directly when address is already in use
- Improve error handling and logging for better debugging
- Maintain backward compatibility with existing functionality

Author: kix

control/udp.go

@@ -55,7 +55,21 @@ func ChooseNatTimeout(data []byte, sniffDns bool) (dmsg *dnsmessage.Msg, timeout
 func sendPkt(log *logrus.Logger, data []byte, from netip.AddrPort, realTo, to netip.AddrPort, lConn *net.UDPConn) (err error) {
 	uConn, _, err := DefaultAnyfromPool.GetOrCreate(from.String(), AnyfromTimeout)
 	if err != nil {
-		return fmt.Errorf("failed to get UDP connection from %s to %s: %w", from, realTo, err)
+		// If we can't create a new connection (e.g., address already in use),
+		// fallback to using the listening connection directly
+		if log.IsLevelEnabled(logrus.DebugLevel) {
+			log.WithError(err).WithFields(logrus.Fields{
+				"from": from.String(),
+				"to":   realTo.String(),
+			}).Debug("failed to create UDP connection, using fallback")
+		}
+
+		// Fallback: send directly through the listening connection
+		_, err = lConn.WriteToUDPAddrPort(data, realTo)
+		if err != nil {
+			return fmt.Errorf("failed to write UDP packet via fallback to %s: %w", realTo, err)
+		}
+		return nil
 	}
 	_, err = uConn.WriteToUDPAddrPort(data, realTo)
 	if err != nil {