Send order queue length in ping responses.

OpenRA.Game/Network/Connection.cs

@@ -304,12 +304,11 @@ namespace OpenRA.Network
 					orderManager.ReceiveDisconnect(disconnect.ClientId, disconnect.Frame);
 				else if (OrderIO.TryParseSync(p.Data, out var sync))
 					orderManager.ReceiveSync(sync);
-				else if (OrderIO.TryParsePing(p.FromClient, p.Data, out var ping))
+				else if (OrderIO.TryParsePingRequest(p, out var timestamp))
 				{
-					// The Ping packet is sent back directly without changes
 					// Note that processing this here, rather than in NetworkConnectionReceive,
 					// so that poor world tick performance can be reflected in the latency measurement
-					Send(ping);
+					Send(OrderIO.SerializePingResponse(timestamp, (byte)orderManager.OrderQueueLength));
 					record = false;
 				}
 				else if (OrderIO.TryParseAck(p, out var ackFrame, out var ackCount))

OpenRA.Game/Network/OrderIO.cs

@@ -93,6 +93,16 @@ namespace OpenRA.Network
 			return ms.GetBuffer();
 		}
 
+		public static byte[] SerializePingResponse(long timestamp, byte queueLength)
+		{
+			var ms = new MemoryStream(14);
+			ms.WriteArray(BitConverter.GetBytes(0));
+			ms.WriteByte((byte)OrderType.Ping);
+			ms.WriteArray(BitConverter.GetBytes(timestamp));
+			ms.WriteByte(queueLength);
+			return ms.GetBuffer();
+		}
+
 		public static bool TryParseDisconnect((int FromClient, byte[] Data) packet, out (int Frame, int ClientId) disconnect)
 		{
 			// Valid Disconnect packets are only ever generated by the server
@@ -123,24 +133,24 @@ namespace OpenRA.Network
 			return true;
 		}
 
-		public static bool TryParsePing(int fromClient, byte[] packet, out byte[] ping)
+		public static bool TryParsePingRequest((int FromClient, byte[] Data) packet, out long timestamp)
 		{
-			// Valid Ping packets are only ever generated by the server
-			if (fromClient != 0 || packet.Length != 13 || packet[4] != (byte)OrderType.Ping)
+			// Valid Ping requests are only ever generated by the server
+			if (packet.FromClient != 0 || packet.Data.Length != 13 || packet.Data[4] != (byte)OrderType.Ping)
 			{
-				ping = null;
+				timestamp = 0;
 				return false;
 			}
 
 			// Valid Ping packets always have frame 0
-			var frame = BitConverter.ToInt32(packet, 0);
+			var frame = BitConverter.ToInt32(packet.Data, 0);
 			if (frame != 0)
 			{
-				ping = null;
+				timestamp = 0;
 				return false;
 			}
 
-			ping = packet;
+			timestamp = BitConverter.ToInt64(packet.Data, 5);
 			return true;
 		}
 

OpenRA.Game/Network/OrderManager.cs

@@ -29,6 +29,7 @@ namespace OpenRA.Network
 		public Session LobbyInfo = new Session();
 		public Session.Client LocalClient => LobbyInfo.ClientWithIndex(Connection.LocalClientId);
 		public World World;
+		public int OrderQueueLength => pendingOrders.Count > 0 ? pendingOrders.Min(q => q.Value.Count) : 0;
 
 		public string ServerError = null;
 		public bool AuthenticationFailed = false;

OpenRA.Game/Server/Connection.cs

@@ -128,13 +128,13 @@ namespace OpenRA.Server
 								{
 									// Ping packets are sent and processed internally within this thread to reduce
 									// server-introduced latencies from polling loops
-									if (expectLength == 9 && bytes[0] == (byte)OrderType.Ping)
+									if (expectLength == 10 && bytes[0] == (byte)OrderType.Ping)
 									{
 										if (pingHistory.Count == MaxPingSamples)
 											pingHistory.Dequeue();
 
 										pingHistory.Enqueue((int)(Game.RunTime - BitConverter.ToInt64(bytes, 1)));
-										server.OnConnectionPing(this, pingHistory.ToArray());
+										server.OnConnectionPing(this, pingHistory.ToArray(), bytes[9]);
 									}
 									else
 										server.OnConnectionPacket(this, frame, bytes);

OpenRA.Game/Server/ProtocolVersion.cs

@@ -41,6 +41,7 @@ namespace OpenRA.Server
 		//   - byte containing the number of sent order packets to apply
 		// - 0x20: Ping
 		//   - Int64 containing the server timestamp when the ping was generated
+		//   - [client -> server only] byte containing the number of frames ready to simulate
 		//
 		// A connection handshake begins when a client opens a connection to the server:
 		// - Server sends:

OpenRA.Game/Server/Server.cs

@@ -323,9 +323,9 @@ namespace OpenRA.Server
 			events.Add(new ConnectionPacketEvent(conn, frame, data));
 		}
 
-		internal void OnConnectionPing(Connection conn, int[] pingHistory)
+		internal void OnConnectionPing(Connection conn, int[] pingHistory, byte queueLength)
 		{
-			events.Add(new ConnectionPingEvent(conn, pingHistory));
+			events.Add(new ConnectionPingEvent(conn, pingHistory, queueLength));
 		}
 
 		internal void OnConnectionDisconnect(Connection conn)
@@ -1021,7 +1021,7 @@ namespace OpenRA.Server
 			}
 		}
 
-		public void ReceivePing(Connection conn, int[] pingHistory)
+		public void ReceivePing(Connection conn, int[] pingHistory, byte queueLength)
 		{
 			// Levels set relative to the default order lag of 3 net ticks (360ms)
 			// TODO: Adjust this once dynamic lag is implemented
@@ -1367,16 +1367,18 @@ namespace OpenRA.Server
 		{
 			readonly Connection connection;
 			readonly int[] pingHistory;
+			readonly byte queueLength;
 
-			public ConnectionPingEvent(Connection connection, int[] pingHistory)
+			public ConnectionPingEvent(Connection connection, int[] pingHistory, byte queueLength)
 			{
 				this.connection = connection;
 				this.pingHistory = pingHistory;
+				this.queueLength = queueLength;
 			}
 
 			void IServerEvent.Invoke(Server server)
 			{
-				server.ReceivePing(connection, pingHistory);
+				server.ReceivePing(connection, pingHistory, queueLength);
 			}
 		}