The ~60Hz entity update records now ride UDP in relay mode, so a lost/late
datagram is dropped (dead reckoning absorbs the gap) instead of head-of-line-
blocking the reliable TCP stream -- the fix for internet rubber-banding.
Reliable traffic (make/damage/death/control/egg/launch) stays on TCP.
This RESTORES the authentic 1995 NETNUB split, it doesn't invent one:
Receiver::Message defaults messageFlags=ReliableFlag; the update path clears
it (flags=0, ENTITY.cpp:590); Mode(UnreliableMode) fires at LoadingMission
(APP.cpp:704 -- the 2007 port's Mode() was a no-op, now it STORES the mode).
Routing gate = (mode==UnreliableMode && !(flags & ReliableFlag)) -- flag AND
mode, so the map-stream creation messages (also flags=0 but flowing during the
still-Reliable CreatingMission window) ride TCP for free.
Client (L4NET):
- Mode() stores currentNetworkMode (was ignored).
- ConnectRelayUdp: UDP socket connect()ed to the relay game port; HELLO
(outbound punch-through, relay learns our endpoint); udpUp on HELLO-ACK.
BT_RELAY_TCP_ONLY=1 disables the channel (UDP-blocked nets degrade to the
pure-TCP checkpoint automatically -- no ACK => everything stays on TCP).
- RelayUdpSendFrame: {route, fromHost, seq} envelope + frame, best-effort.
- RelayUdpKeepalive: ~15s NAT-hold + ~1s HELLO retry until acked.
- CheckRelayUdp: HELLO-ACK sets udpUp; per-sender seq gate drops stale/
out-of-order datagrams; frames handed up envelope-stripped like TCP.
- Send / ExclusiveBroadcast: route unreliable-window traffic to UDP, else TCP.
- CheckBuffers polls the UDP channel first, then TCP; keepalive tick.
(The relay-side UDP forwarder + endpoint learning + --udp-drop hook landed in
phase 1.)
Verified 2-node localhost relay: during a drive the update stream flows on UDP
(relay udp tx 2->190+, TCP frozen at 53) and the peer's replicant tracks the
master to sub-2u; 15% forced drop (--udp-drop 15) stays coherent (tracked to
0.1u); TCP-only fallback confirmed (udp-known drops the TCP-only pod); no
crashes; mesh mode un-regressed. KB: context/multiplayer.md gains the D1
RELAY MODE section.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
