From f6a8f275018797c39003975a931be41d2cb9715e Mon Sep 17 00:00:00 2001
From: Jonathan G Rennison <j.g.rennison@gmail.com>
Date: Mon, 23 Nov 2015 19:47:59 +0000
Subject: [PATCH] Make server and all clients run desync checks if a client
 desyncs.

---
 src/command.cpp                |  4 ++++
 src/command_type.h             |  2 ++
 src/network/network_client.cpp |  3 +++
 src/network/network_server.cpp |  5 +++++
 src/openttd.cpp                | 32 ++++++++++++++++++++++++++------
 5 files changed, 40 insertions(+), 6 deletions(-)

diff --git a/src/command.cpp b/src/command.cpp
index 6575fc34aa..660a9c0f37 100644
--- a/src/command.cpp
+++ b/src/command.cpp
@@ -212,6 +212,8 @@ CommandProc CmdRemovePlan;
 CommandProc CmdRemovePlanLine;
 CommandProc CmdChangePlanVisibility;
 
+CommandProc CmdDesyncCheck;
+
 #define DEF_CMD(proc, flags, type) {proc, #proc, (CommandFlags)flags, type}
 
 /**
@@ -382,6 +384,8 @@ static const Command _command_proc_table[] = {
 	DEF_CMD(CmdRemovePlan,                                     0, CMDT_OTHER_MANAGEMENT      ), // CMD_REMOVE_PLAN
 	DEF_CMD(CmdRemovePlanLine,                                 0, CMDT_OTHER_MANAGEMENT      ), // CMD_REMOVE_PLAN_LINE
 	DEF_CMD(CmdChangePlanVisibility,                           0, CMDT_OTHER_MANAGEMENT      ), // CMD_CHANGE_PLAN_VISIBILITY
+
+	DEF_CMD(CmdDesyncCheck,                           CMD_SERVER, CMDT_SERVER_SETTING        ), // CMD_DESYNC_CHECK
 };
 
 /*!
diff --git a/src/command_type.h b/src/command_type.h
index 6736c29892..4351086ae1 100644
--- a/src/command_type.h
+++ b/src/command_type.h
@@ -343,6 +343,8 @@ enum Commands {
 	CMD_REMOVE_PLAN_LINE,
 	CMD_CHANGE_PLAN_VISIBILITY,
 
+	CMD_DESYNC_CHECK,                 ///< Force desync checks to be run
+
 	CMD_END,                          ///< Must ALWAYS be on the end of this list!! (period)
 };
 
diff --git a/src/network/network_client.cpp b/src/network/network_client.cpp
index f84cfb912b..a9a707d5f0 100644
--- a/src/network/network_client.cpp
+++ b/src/network/network_client.cpp
@@ -256,6 +256,9 @@ void ClientNetworkGameSocketHandler::ClientError(NetworkRecvStatus res)
 				DEBUG(desync, 1, "sync_err: %08x; %02x; %02X", _date, _date_fract, _tick_skip_counter);
 				DEBUG(net, 0, "Sync error detected!");
 				my_client->ClientError(NETWORK_RECV_STATUS_DESYNC);
+
+				extern void CheckCaches(bool force_check);
+				CheckCaches(true);
 				return false;
 			}
 
diff --git a/src/network/network_server.cpp b/src/network/network_server.cpp
index ed9ae4d140..6fbbed6f20 100644
--- a/src/network/network_server.cpp
+++ b/src/network/network_server.cpp
@@ -1179,6 +1179,11 @@ NetworkRecvStatus ServerNetworkGameSocketHandler::Receive_CLIENT_ERROR(Packet *p
 
 	NetworkAdminClientError(this->client_id, errorno);
 
+	if (errorno == NETWORK_ERROR_DESYNC) {
+		// have the server and all clients run some sanity checks
+		NetworkSendCommand(0, 0, 0, CMD_DESYNC_CHECK, NULL, NULL, _local_company, 0);
+	}
+
 	return this->CloseConnection(NETWORK_RECV_STATUS_CONN_LOST);
 }
 
diff --git a/src/openttd.cpp b/src/openttd.cpp
index 2f401793bf..cb33f8b748 100644
--- a/src/openttd.cpp
+++ b/src/openttd.cpp
@@ -1232,13 +1232,15 @@ void SwitchToMode(SwitchMode new_mode)
  * the cached value and what the value would
  * be when calculated from the 'base' data.
  */
-static void CheckCaches()
+void CheckCaches(bool force_check)
 {
-	/* Return here so it is easy to add checks that are run
-	 * always to aid testing of caches. */
-	if (_debug_desync_level < 1) return;
+	if (!force_check) {
+		/* Return here so it is easy to add checks that are run
+		 * always to aid testing of caches. */
+		if (_debug_desync_level < 1) return;
 
-	if (_debug_desync_level == 1 && CURRENT_SCALED_TICKS % 500 != 0) return;
+		if (_debug_desync_level == 1 && CURRENT_SCALED_TICKS % 500 != 0) return;
+	}
 
 	/* Check the town caches. */
 	SmallVector<TownCache, 4> old_town_caches;
@@ -1432,6 +1434,24 @@ static void CheckCaches()
 	}
 }
 
+/**
+ * Network-safe forced desync check.
+ * @param tile unused
+ * @param flags operation to perform
+ * @param p1 unused
+ * @param p2 unused
+ * @param text unused
+ * @return the cost of this operation or an error
+ */
+CommandCost CmdDesyncCheck(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32 p2, const char *text)
+{
+	if (flags & DC_EXEC) {
+		CheckCaches(true);
+	}
+
+	return CommandCost();
+}
+
 /**
  * State controlling game loop.
  * The state must not be changed from anywhere but here.
@@ -1475,7 +1495,7 @@ void StateGameLoop()
 			SaveOrLoad(name, SL_SAVE, AUTOSAVE_DIR, false);
 		}
 
-		CheckCaches();
+		CheckCaches(false);
 
 		/* All these actions has to be done from OWNER_NONE
 		 *  for multiplayer compatibility */