Overhaul player disconnect notifications.

OpenRA.Game/Network/Connection.cs

@@ -300,8 +300,8 @@ namespace OpenRA.Network
 			while (receivedPackets.TryDequeue(out var p))
 			{
 				var record = true;
-				if (OrderIO.TryParseDisconnect(p.Data, out var disconnectClient))
-					orderManager.ReceiveDisconnect(disconnectClient);
+				if (OrderIO.TryParseDisconnect(p, out var disconnect))
+					orderManager.ReceiveDisconnect(disconnect.ClientId, disconnect.Frame);
 				else if (OrderIO.TryParseSync(p.Data, out var sync))
 					orderManager.ReceiveSync(sync);
 				else if (OrderIO.TryParseAck(p, out var ackFrame))

OpenRA.Game/Network/OrderIO.cs

@@ -79,16 +79,19 @@ namespace OpenRA.Network
 			return ms.GetBuffer();
 		}
 
-		public static bool TryParseDisconnect(byte[] packet, out int clientId)
+		public static bool TryParseDisconnect((int FromClient, byte[] Data) packet, out (int Frame, int ClientId) disconnect)
 		{
-			if (packet.Length == Order.DisconnectOrderLength + 4 && packet[4] == (byte)OrderType.Disconnect)
+			// Valid Disconnect packets are only ever generated by the server
+			if (packet.FromClient != 0 || packet.Data.Length != Order.DisconnectOrderLength + 4 || packet.Data[4] != (byte)OrderType.Disconnect)
 			{
-				clientId = BitConverter.ToInt32(packet, 5);
-				return true;
+				disconnect = (0, 0);
+				return false;
 			}
 
-			clientId = 0;
-			return false;
+			var frame = BitConverter.ToInt32(packet.Data, 0);
+			var clientId = BitConverter.ToInt32(packet.Data, 5);
+			disconnect = (frame, clientId);
+			return true;
 		}
 
 		public static bool TryParseSync(byte[] packet, out (int Frame, int SyncHash, ulong DefeatState) data)

OpenRA.Game/Network/OrderManager.cs

@@ -20,6 +20,8 @@ namespace OpenRA.Network
 {
 	public sealed class OrderManager : IDisposable
 	{
+		const OrderPacket ClientDisconnected = null;
+
 		readonly SyncReport syncReport;
 		readonly Dictionary<int, Queue<(int Frame, OrderPacket Orders)>> pendingOrders = new Dictionary<int, Queue<(int, OrderPacket)>>();
 		readonly Dictionary<int, (int SyncHash, ulong DefeatState)> syncForFrame = new Dictionary<int, (int, ulong)>();
@@ -45,6 +47,9 @@ namespace OpenRA.Network
 		readonly List<Order> localOrders = new List<Order>();
 		readonly List<Order> localImmediateOrders = new List<Order>();
 
+		readonly List<ClientOrder> processClientOrders = new List<ClientOrder>();
+		readonly List<int> processClientsToRemove = new List<int>();
+
 		readonly List<TextNotification> notificationsCache = new List<TextNotification>();
 
 		public IReadOnlyList<TextNotification> NotificationsCache => notificationsCache;
@@ -126,9 +131,18 @@ namespace OpenRA.Network
 			localImmediateOrders.Clear();
 		}
 
-		public void ReceiveDisconnect(int clientIndex)
+		public void ReceiveDisconnect(int clientId, int frame)
 		{
-			pendingOrders.Remove(clientIndex);
+			// All clients must process the disconnect on the same world tick to allow synced actions to run deterministically.
+			// The server guarantees that we will not receive any more order packets from this client from this frame, so we
+			// can insert a marker in the orders stream and process the synced disconnect behaviours on the first tick of that frame.
+			if (GameStarted)
+				ReceiveOrders(clientId, (frame, ClientDisconnected));
+
+			// The Client state field is not synced; update it immediately so it can be shown in the UI
+			var client = LobbyInfo.ClientWithIndex(clientId);
+			if (client != null)
+				client.State = Session.ClientState.Disconnected;
 		}
 
 		public void ReceiveSync((int Frame, int SyncHash, ulong DefeatState) sync)
@@ -198,8 +212,6 @@ namespace OpenRA.Network
 
 		void ProcessOrders()
 		{
-			var clientOrders = new List<ClientOrder>();
-
 			foreach (var (clientId, frameOrders) in pendingOrders)
 			{
 				// The IsReadyForNextFrame check above guarantees that all clients have sent a packet
@@ -211,13 +223,24 @@ namespace OpenRA.Network
 				if (frameNumber != NetFrameNumber)
 					throw new InvalidDataException($"Attempted to process orders from client {clientId} for frame {frameNumber} on frame {NetFrameNumber}");
 
+				if (orders == ClientDisconnected)
+				{
+					processClientsToRemove.Add(clientId);
+					World.OnClientDisconnected(clientId);
+
+					continue;
+				}
+
 				foreach (var order in orders.GetOrders(World))
 				{
 					UnitOrders.ProcessOrder(this, World, clientId, order);
-					clientOrders.Add(new ClientOrder { Client = clientId, Order = order });
+					processClientOrders.Add(new ClientOrder { Client = clientId, Order = order });
 				}
 			}
 
+			foreach (var clientId in processClientsToRemove)
+				pendingOrders.Remove(clientId);
+
 			if (NetFrameNumber >= GameSaveLastSyncFrame)
 			{
 				var defeatState = 0UL;
@@ -232,7 +255,10 @@ namespace OpenRA.Network
 
 			if (generateSyncReport)
 				using (new PerfSample("sync_report"))
-					syncReport.UpdateSyncReport(clientOrders);
+					syncReport.UpdateSyncReport(processClientOrders);
+
+			processClientOrders.Clear();
+			processClientsToRemove.Clear();
 
 			++NetFrameNumber;
 		}

OpenRA.Game/Network/ReplayConnection.cs

@@ -147,8 +147,8 @@ namespace OpenRA.Network
 			{
 				foreach (var o in chunks.Dequeue().Packets)
 				{
-					if (OrderIO.TryParseDisconnect(o.Packet, out var disconnectClient))
-						orderManager.ReceiveDisconnect(disconnectClient);
+					if (OrderIO.TryParseDisconnect(o, out var disconnect))
+						orderManager.ReceiveDisconnect(disconnect.ClientId, disconnect.Frame);
 					else if (OrderIO.TryParseSync(o.Packet, out var sync))
 						orderManager.ReceiveSync(sync);
 					else if (OrderIO.TryParseOrderPacket(o.Packet, out var orders))

OpenRA.Game/Network/SyncReport.cs

@@ -51,20 +51,21 @@ namespace OpenRA.Network
 				syncReports[i] = new Report();
 		}
 
-		internal void UpdateSyncReport(List<OrderManager.ClientOrder> orders)
+		internal void UpdateSyncReport(IEnumerable<OrderManager.ClientOrder> orders)
 		{
 			GenerateSyncReport(syncReports[curIndex], orders);
 			curIndex = ++curIndex % NumSyncReports;
 		}
 
-		void GenerateSyncReport(Report report, List<OrderManager.ClientOrder> orders)
+		void GenerateSyncReport(Report report, IEnumerable<OrderManager.ClientOrder> orders)
 		{
 			report.Frame = orderManager.NetFrameNumber;
 			report.SyncedRandom = orderManager.World.SharedRandom.Last;
 			report.TotalCount = orderManager.World.SharedRandom.TotalCount;
 			report.Traits.Clear();
 			report.Effects.Clear();
-			report.Orders = orders;
+			report.Orders.Clear();
+			report.Orders.AddRange(orders);
 
 			foreach (var actor in orderManager.World.ActorsHavingTrait<ISync>())
 			{

OpenRA.Game/Network/UnitOrders.cs

@@ -34,21 +34,6 @@ namespace OpenRA.Network
 					TextNotificationsManager.AddSystemLine(order.TargetString);
 					break;
 
-				// Reports that the target player disconnected
-				case "Disconnected":
-					{
-						var client = orderManager.LobbyInfo.ClientWithIndex(clientId);
-						if (client != null)
-						{
-							client.State = Session.ClientState.Disconnected;
-							var player = world?.FindPlayerByClient(client);
-							if (player != null)
-								world.OnPlayerDisconnected(player);
-						}
-
-						break;
-					}
-
 				case "Chat":
 					{
 						var client = orderManager.LobbyInfo.ClientWithIndex(clientId);