As I'm close to releasing a "production-ready" version of my GodotInSim library, I went back to the details of the TCP/UDP settings in the ISI packet. Using full TCP or full UDP works just fine (UDPPort = 0 for both protocols), however I am having issues with NLP/MCI packets on mixed TCP/UDP, as well as just UDP but using a different port (basically, any time I set UDPPort to something other than zero).

Using Wireshark, I can see the packets are being sent (with port numbers e.g. 29999 -> 30000, haven't checked their contents), however I can't seem to get any packet in Godot (I already checked the UDP socket is connected on the correct port). Additionally, setting UDPPort to the same port as the TCP one causes LFS to throw errors for each NLP/MCI packet sent:

Quote :

InSim : first packet has unexpected size - should be ISI
InSim : first byte in packet does not represent size

To sum up the possible options:

1. connect using TCP, UDPPort == 0: works fine
   
2. connect using UDP, UDPPort == 0: works fine
   
3. connect using TCP, UDPPort != connection port: cannot get NLP/MCI packets
   
4. connect using TCP, UDPPort == connection port: cannot get NLP/MCI packets, InSim throws errors
   
5. connect using UDP, UDPPort != ISI port: cannot get NLP/MCI packets
   
6. connect using UDP, UDPPort == ISI port: cannot get NLP/MCI packets, InSim throws errors (more of the same error when sending packets)
   

For reference, my implementation has an LFSConnection class/pseudo-interface to handle connect, disconnect, send_packet and get_packet, with LFSConnectionTCP and LFSConnectionUDP implementing those functions. LFSConnectionTCP also creates an instance of LFSConnectionUDP. Both the "main" UDP connection and the child one with TCP exhibit the same issues, and the main UDP connection can still send and receive other packets, only NLP/MCI are missing (though in case 6 above, sending packets causes additional InSim errors).

I will investigate some more on the Godot side and in my code, in case I made a mistake somewhere, but I would appreciate any insight, also the errors do seem to be an issue on LFS's side. I just cannot understand why those packets are not being picked up by Godot, especially in UDP-only mode (cases 5-6 above), as other packets are being sent and received properly.

Okay, so as per usual, it turns out I did make a mistake (though I don't fully understand it): when I refactored my connection code, I changed the PacketPeerUDP socket's bind() method to connect_to_host(); this works perfectly fine for InSim itself, but not for OutGauge, OutSim and the NLP/MCI packets sent via UDP. On the other hand, using bind() triggers an error when connecting InSim (this is the part I don't get), but it works for the others.
I solved this a bit hackily by changing how I connect the socket for InSim and the others, and everything is working so far. Still getting the InSim errors when using the same port, though.

Networking isn't exactly my forte, apologies for the short monologue