From 3ec27d115b0a6ff3ac20fe4486239150c3872e25 Mon Sep 17 00:00:00 2001
From: MiTHRAL <mithral@mithral.local>
Date: Fri, 28 Aug 2026 13:28:58 -0400
Subject: [PATCH] netcode-revival: receive timeout on the relay transport
 socket

The Run thread blocked in recvfrom with no SO_RCVTIMEO, so when there was no
inbound game traffic the 4s heartbeat never fired (the relay swept the
silent transport client after ~8s) AND StopLocked()'s join() deadlocked
SetRelay on a room change (hanging the ghost network loop). A 200ms receive
timeout wakes the loop regularly: the heartbeat keeps the transport alive
and shutdown/room-change joins complete promptly.
---
 src/system/xnet_transport.cpp | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/src/system/xnet_transport.cpp b/src/system/xnet_transport.cpp
index 04727da..cc60f6f 100644
--- a/src/system/xnet_transport.cpp
+++ b/src/system/xnet_transport.cpp
@@ -60,6 +60,23 @@ void SocketClose(int64_t s) {
 #endif
 }
 
+// The receive loop must wake regularly so the heartbeat fires even with no
+// inbound traffic (otherwise the relay sweeps a silent transport client
+// after ~8s) and so StopLocked()'s join completes promptly instead of
+// deadlocking SetRelay on a room change.
+void SocketSetRecvTimeout(int64_t s, int timeout_ms) {
+#if REX_PLATFORM_WIN32
+  DWORD tv = DWORD(timeout_ms);
+  ::setsockopt(SOCKET(s), SOL_SOCKET, SO_RCVTIMEO,
+               reinterpret_cast<const char*>(&tv), sizeof(tv));
+#else
+  timeval tv = {};
+  tv.tv_sec = timeout_ms / 1000;
+  tv.tv_usec = (timeout_ms % 1000) * 1000;
+  ::setsockopt(int(s), SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv));
+#endif
+}
+
 bool SocketSendTo(int64_t s, const sockaddr_in* to, const void* buf, int size) {
 #if REX_PLATFORM_WIN32
   const int n = ::sendto(SOCKET(s), reinterpret_cast<const char*>(buf), size, 0,
@@ -176,6 +193,8 @@ void XNetTransport::Reconnect() {
     REXLOG_WARN("xnet transport: cannot open relay socket");
     return;
   }
+  // Wake the receive loop every 200ms (heartbeat + prompt shutdown).
+  SocketSetRecvTimeout(sock_, 200);
   REXLOG_INFO("xnet transport: connecting to relay '{}:{}' room '{}' (vip {}.{}.{}.{})", host_,
               port_, room_.c_str(), (LocalVirtualIp() >> 24) & 0xFF, (LocalVirtualIp() >> 16) & 0xFF,
               (LocalVirtualIp() >> 8) & 0xFF, LocalVirtualIp() & 0xFF);