UPNP support

[ARoese]

When possible, the launcher should attempt to automatically forward a server's ports when it is launched. Use UPNP.

• UPNP support should be generally verifiable without needing to launch a server
  • (low priority) we may want to be able to detect a double-NAT architecture
    • use a tracert to look for two hops on different private subnets?
    • (extremely low priority) use tracert or nmap info to nest UPNP mappings so they work across a double-NAT.
      • This might not be possible and would deserve to be an independent library if it was.
• UPNP packets should not be sent without a user interaction that would reasonably be expected to trigger it.
  • Starting a server meets this requirement
• Whether ports were successfully forwarded automatically should be visible in the GUI of that server
  • We could have a validation endpoint that probes a server's ports to detect if they are forwarded correctly and reports back their status.
    • This endpoint should require the server's key before probing it. We don't want this to be used as an amplifier for DDOS.

Resources:

• mono-upnp
• Open.NAT (newer)
• example project using NATUPNP.DLL which is apparently built into windows

[ARoese]

After trying it out, I concluded that NATUPNP.DLL is an interface not even Microsoft could love. Just don't use it, lmao. It will seemingly randomly return nulls as the StaticPortMappingCollection with no way to see why. (invalid response? no UPNP device found? No network?)

StaticPortMappingCollection.Add() can throw an interop "The resource is in use" exception without any explanation as to what resource is actually in use.

I will be trying mono-upnp next.