From a4267990b868b2a15865361371c66bd5814aa42a Mon Sep 17 00:00:00 2001
From: zsilencer <zsilencergame@gmail.com>
Date: Thu, 30 Jul 2015 08:34:17 -0600
Subject: [PATCH] detect desyncs

---
 src/network/network.cpp      | 25 +++++++++++++++++++++++--
 src/network/network.h        |  3 +++
 src/windows/network_status.c |  4 ++--
 3 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/src/network/network.cpp b/src/network/network.cpp
index 9770721cba..1df19ad80b 100644
--- a/src/network/network.cpp
+++ b/src/network/network.cpp
@@ -470,6 +470,17 @@ void Network::SendPacketToClients(NetworkPacket& packet)
 	}
 }
 
+bool Network::CheckSRAND(uint32 tick, uint32 srand0)
+{
+	if (tick == server_srand0_tick) {
+		server_srand0_tick = 0;
+		if (srand0 != server_srand0) {
+			return false;
+		}
+	}
+	return true;
+}
+
 void Network::Client_Send_AUTH(const char* gameversion, const char* name, const char* password)
 {
 	std::unique_ptr<NetworkPacket> packet = std::move(NetworkPacket::Allocate());
@@ -532,7 +543,7 @@ void Network::Server_Send_GAMECMD(uint32 eax, uint32 ebx, uint32 ecx, uint32 edx
 void Network::Server_Send_TICK()
 {
 	std::unique_ptr<NetworkPacket> packet = std::move(NetworkPacket::Allocate());
-	*packet << (uint32)NETWORK_COMMAND_TICK << (uint32)RCT2_GLOBAL(RCT2_ADDRESS_CURRENT_TICKS, uint32);
+	*packet << (uint32)NETWORK_COMMAND_TICK << (uint32)RCT2_GLOBAL(RCT2_ADDRESS_CURRENT_TICKS, uint32) << (uint32)RCT2_GLOBAL(RCT2_ADDRESS_SCENARIO_SRAND_0, uint32);
 	SendPacketToClients(*packet);
 }
 
@@ -769,6 +780,7 @@ int Network::Client_Handle_MAP(NetworkConnection& connection, NetworkPacket& pac
 					pause_toggle();
 				game_command_queue.clear();
 				server_tick = RCT2_GLOBAL(RCT2_ADDRESS_CURRENT_TICKS, uint32);
+				server_srand0_tick = 0;
 				window_network_status_open("Loaded new map from network");
 			}
 			SDL_RWclose(rw);
@@ -826,7 +838,12 @@ int Network::Server_Handle_GAMECMD(NetworkConnection& connection, NetworkPacket&
 
 int Network::Client_Handle_TICK(NetworkConnection& connection, NetworkPacket& packet)
 {
-	packet >> server_tick;
+	uint32 srand0;
+	packet >> server_tick >> srand0;
+	if (server_srand0_tick == 0) {
+		server_srand0 = srand0;
+		server_srand0_tick = server_tick;
+	}
 	return 1;
 }
 
@@ -905,6 +922,10 @@ int network_begin_server(int port)
 void network_update()
 {
 	gNetwork.Update();
+	if (!gNetwork.CheckSRAND(RCT2_GLOBAL(RCT2_ADDRESS_CURRENT_TICKS, uint32), RCT2_GLOBAL(RCT2_ADDRESS_SCENARIO_SRAND_0, uint32))) {
+		window_network_status_open("Network desync detected");
+		gNetwork.Close();
+	}
 }
 
 int network_get_mode()
diff --git a/src/network/network.h b/src/network/network.h
index 286d725b39..392e8ecff1 100644
--- a/src/network/network.h
+++ b/src/network/network.h
@@ -135,6 +135,7 @@ public:
 	NetworkPlayer* GetPlayerByID(int id);
 	const char* FormatChat(NetworkPlayer* fromplayer, const char* text);
 	void SendPacketToClients(NetworkPacket& packet);
+	bool CheckSRAND(uint32 tick, uint32 srand0);
 
 	void Client_Send_AUTH(const char* gameversion, const char* name, const char* password);
 	void Server_Send_MAP();
@@ -179,6 +180,8 @@ private:
 	uint32 last_tick_sent_time;
 	uint32 last_ping_sent_time;
 	uint32 server_tick;
+	uint32 server_srand0;
+	uint32 server_srand0_tick;
 	uint8 player_id;
 	std::list<std::unique_ptr<NetworkConnection>> client_connection_list;
 	std::multiset<GameCommand> game_command_queue;
diff --git a/src/windows/network_status.c b/src/windows/network_status.c
index 441d93ebce..e0c5af29a0 100644
--- a/src/windows/network_status.c
+++ b/src/windows/network_status.c
@@ -79,6 +79,8 @@ void window_network_status_open(const char* text)
 {
 	rct_window* window;
 
+	strncpy(window_network_status_text, text, sizeof(window_network_status_text));
+
 	// Check if window is already open
 	window = window_bring_to_front_by_class(WC_NETWORK_STATUS);
 	if (window != NULL)
@@ -86,8 +88,6 @@ void window_network_status_open(const char* text)
 
 	window = window_create_centred(320, 90, &window_network_status_events, WC_NETWORK_STATUS, WF_10 | WF_TRANSPARENT);
 
-	strncpy(window_network_status_text, text, sizeof(window_network_status_text));
-
 	window->widgets = window_network_status_widgets;
 	window->enabled_widgets = 1 << WIDX_CLOSE;
 	window_init_scroll_widgets(window);