From cdb02fa0af08e25a1630a657e60390e10a665094 Mon Sep 17 00:00:00 2001
From: JuiceyDev <me@juicey.dev>
Date: Fri, 6 Mar 2026 12:10:39 +0100
Subject: [PATCH] Fix: Ensure host-local socket streams created before any
 Connection is built

---
 .../Common/Network/GameNetworkManager.cpp     | 11 +++++
 Minecraft.World/Network/Socket.cpp            | 42 +++++++++++++++----
 Minecraft.World/Network/Socket.h              |  1 +
 3 files changed, 46 insertions(+), 8 deletions(-)

diff --git a/Minecraft.Client/Build/Common/Network/GameNetworkManager.cpp b/Minecraft.Client/Build/Common/Network/GameNetworkManager.cpp
index cc977f6f4..1aa62bb41 100644
--- a/Minecraft.Client/Build/Common/Network/GameNetworkManager.cpp
+++ b/Minecraft.Client/Build/Common/Network/GameNetworkManager.cpp
@@ -212,6 +212,17 @@ bool	CGameNetworkManager::StartNetworkGame(Minecraft *minecraft, LPVOID lpParame
 	}
 
 	static __int64 sseed = seed;	// Create static version so this will be valid until next call to this function & whilst thread is running
+
+	// 4J Fix: Ensure host-local socket streams (s_hostInStream / s_hostOutStream) are always
+	// created before any Socket or Connection objects are allocated.  Socket::Initialise normally
+	// runs on the server thread, but on certain builds the main thread can reach ClientConnection
+	// creation before that thread has a chance to execute, leaving the stream arrays NULL.
+	// Calling Initialise(NULL) here (with the server connection unknown yet) will create the
+	// stream objects on the very first call; all subsequent calls only reset the queue state.
+	// The server thread's later Initialise(connection) call will then correctly update
+	// s_serverConnection without touching the already-allocated stream objects.
+	Socket::Initialise(NULL);
+
 	ServerStoppedCreate(false);
 	if( g_NetworkManager.IsHost() )
 	{
diff --git a/Minecraft.World/Network/Socket.cpp b/Minecraft.World/Network/Socket.cpp
index 801c6a61d..c6c16b824 100644
--- a/Minecraft.World/Network/Socket.cpp
+++ b/Minecraft.World/Network/Socket.cpp
@@ -16,14 +16,34 @@ Socket::SocketOutputStreamLocal *Socket::s_hostOutStream[2];
 Socket::SocketInputStreamLocal *Socket::s_hostInStream[2];
 ServerConnection *Socket::s_serverConnection = NULL;
 
+void Socket::EnsureStreamsInitialised()
+{
+	// Thread-safe one-time initialisation via C++11 magic-statics guarantee.
+	// The lambda body runs exactly once no matter how many threads call concurrently.
+	static bool initialized = []() -> bool {
+		for( int i = 0; i < 2; i++ )
+		{
+			InitializeCriticalSection(&Socket::s_hostQueueLock[i]);
+			s_hostOutStream[i] = new SocketOutputStreamLocal(i);
+			s_hostInStream[i]  = new SocketInputStreamLocal(i);
+		}
+		return true;
+	}();
+	(void)initialized;
+}
+
 void Socket::Initialise(ServerConnection *serverConnection)
 {
 	s_serverConnection = serverConnection;
 
+	// Ensure the host-local stream objects exist (idempotent).
+	EnsureStreamsInitialised();
+
 	// Only initialise everything else once - just setting up static data, one time xrnm things, thread for ticking sockets
 	static bool init = false;
 	if( init )
 	{
+		// Streams already exist – just reset queue state and re-open streams.
 		for( int i = 0; i < 2; i++ )
 		{
 			if(TryEnterCriticalSection(&s_hostQueueLock[i]))
@@ -39,13 +59,8 @@ void Socket::Initialise(ServerConnection *serverConnection)
 		return;
 	}
 	init = true;
-
-	for( int i = 0; i < 2; i++ )
-	{
-		InitializeCriticalSection(&Socket::s_hostQueueLock[i]);
-		s_hostOutStream[i] = new SocketOutputStreamLocal(i);
-		s_hostInStream[i] = new SocketInputStreamLocal(i);
-	}
+	// Streams are already guaranteed to exist via EnsureStreamsInitialised() above.
+	// Nothing more to do for the first call.
 }
 
 Socket::Socket(bool response)
@@ -182,6 +197,11 @@ InputStream *Socket::getInputStream(bool isServerConnection)
 	}
 	else
 	{
+		if( s_hostInStream[m_end] == NULL )
+		{
+			app.DebugPrintf("SOCKET: Warning - s_hostInStream[%d] is NULL in getInputStream(); calling EnsureStreamsInitialised()\n", m_end);
+			EnsureStreamsInitialised();
+		}
 		return s_hostInStream[m_end];
 	}
 }
@@ -216,7 +236,13 @@ Socket::SocketOutputStream *Socket::getOutputStream(bool isServerConnection)
 	}
 	else
 	{
-		return s_hostOutStream[ 1 - m_end ];
+		int outIdx = 1 - m_end;
+		if( s_hostOutStream[outIdx] == NULL )
+		{
+			app.DebugPrintf("SOCKET: Warning - s_hostOutStream[%d] is NULL in getOutputStream(); calling EnsureStreamsInitialised()\n", outIdx);
+			EnsureStreamsInitialised();
+		}
+		return s_hostOutStream[outIdx];
 	}
 }
 
diff --git a/Minecraft.World/Network/Socket.h b/Minecraft.World/Network/Socket.h
index b30e83962..a685fd835 100644
--- a/Minecraft.World/Network/Socket.h
+++ b/Minecraft.World/Network/Socket.h
@@ -117,6 +117,7 @@ public:
 	void setPlayer(INetworkPlayer *player);
 
 public:
+	static void EnsureStreamsInitialised();						// 4J Fix: idempotent stream creation; safe to call before Initialise(connection)
 	static void Initialise(ServerConnection *serverConnection);
 	Socket(bool response = false);								// 4J - Create a local socket, for end 0 or 1 of a connection
 	Socket(INetworkPlayer *player, bool response  = false, bool hostLocal = false);		// 4J - Create a socket for an INetworkPlayer