The Relayed connection setup is optimistic. It does not have any confirmation of an established end-to-end connection. Peers start sending WireGuard handshake packets immediately after the successful offer-answer handshake.
Meanwhile, for successful P2P connection negotiation, we change the WireGuard endpoint address, but this change does not trigger new handshake initiation. Because the peer switched from Relayed connection to P2P, the packets from the Relay server are dropped and must wait for the next WireGuard handshake via P2P.
To avoid this scenario, the relayed WireGuard proxy no longer drops the packets. Instead, it rewrites the source address to the new P2P endpoint and continues forwarding the packets.
We still have one corner case: if the Relayed server negotiation chooses a server that has not been used before. In this case, one side of the peer connection will be slower to reach the Relay server, and the Relay server will drop the handshake packet.
If everything goes well we should see exactly 5 seconds improvements between the WireGuard configuration time and the handshake time.
In the case of user space WireGuard mode, use in-memory proxy between the TURN/Relay connection and the WireGuard Bind. We keep the UDP proxy and eBPF proxy for kernel mode.
The key change is the new wgproxy/bind and the iface/bind/ice_bind changes. Everything else is just to fulfill the dependencies.
