Split Protocol version into Handshake vs Orders.

Handshake is kept at 7.
Orders is incremented to 8 to reflect immediate order changes.

OpenRA.Game/Network/Connection.cs

@@ -167,12 +167,12 @@ namespace OpenRA.Network
 			{
 				var networkStream = (NetworkStream)networkStreamObject;
 				var reader = new BinaryReader(networkStream);
-				var serverProtocol = reader.ReadInt32();
+				var handshakeProtocol = reader.ReadInt32();
 
-				if (serverProtocol != ProtocolVersion.Version)
+				if (handshakeProtocol != ProtocolVersion.Handshake)
 					throw new InvalidOperationException(
-						"Protocol version mismatch. Server={0} Client={1}"
+						"Handshake protocol version mismatch. Server={0} Client={1}"
-							.F(serverProtocol, ProtocolVersion.Version));
+							.F(handshakeProtocol, ProtocolVersion.Handshake));
 
 				clientId = reader.ReadInt32();
 				connectionState = ConnectionState.Connected;

OpenRA.Game/Network/Handshake.cs

@@ -41,6 +41,10 @@ namespace OpenRA.Network
 		public string Version;
 		public string Password;
 
+		// Default value is hardcoded to 7 so that newer servers
+		// (which define OrdersProtocol > 7) can detect older clients
+		public int OrdersProtocol = 7;
+
 		// For player authentication
 		public string Fingerprint;
 		public string AuthSignature;
@@ -74,7 +78,7 @@ namespace OpenRA.Network
 		{
 			var data = new List<MiniYamlNode>();
 			data.Add(new MiniYamlNode("Handshake", null,
-				new string[] { "Mod", "Version", "Password", "Fingerprint", "AuthSignature" }.Select(p => FieldSaver.SaveField(this, p)).ToList()));
+				new[] { "Mod", "Version", "Password", "Fingerprint", "AuthSignature", "OrdersProtocol" }.Select(p => FieldSaver.SaveField(this, p)).ToList()));
 			data.Add(new MiniYamlNode("Client", FieldSaver.Save(Client)));
 
 			return data.WriteToString();

OpenRA.Game/Network/UnitOrders.cs

@@ -227,7 +227,8 @@ namespace OpenRA.Network
 							Mod = mod.Id,
 							Version = mod.Metadata.Version,
 							Password = orderManager.Password,
-							Fingerprint = localProfile.Fingerprint
+							Fingerprint = localProfile.Fingerprint,
+							OrdersProtocol = ProtocolVersion.Orders
 						};
 
 						if (request.AuthToken != null && response.Fingerprint != null)

OpenRA.Game/Server/ProtocolVersion.cs

@@ -13,7 +13,13 @@ namespace OpenRA.Server
 {
 	public static class ProtocolVersion
 	{
-		// you *must* increment this whenever you make an incompatible protocol change
+		// The protocol for the initial handshake request and response
-		public static readonly int Version = 7;
+		// Backwards incompatible changes will break runtime mod switching, so only change as a last resort!
+		public const int Handshake = 7;
+
+		// The protocol for server and world orders
+		// This applies after the handshake has completed, and is provided to support
+		// alternative server implementations that wish to support multiple versions in parallel
+		public const int Orders = 8;
 	}
 }

OpenRA.Game/Server/Server.cs

@@ -278,7 +278,7 @@ namespace OpenRA.Server
 
 				// Send handshake and client index.
 				var ms = new MemoryStream(8);
-				ms.WriteArray(BitConverter.GetBytes(ProtocolVersion.Version));
+				ms.WriteArray(BitConverter.GetBytes(ProtocolVersion.Handshake));
 				ms.WriteArray(BitConverter.GetBytes(newConn.PlayerIndex));
 				SendData(newConn.Socket, ms.ToArray());
 
@@ -363,6 +363,16 @@ namespace OpenRA.Server
 					return;
 				}
 
+				if (handshake.OrdersProtocol != ProtocolVersion.Orders)
+				{
+					Log.Write("server", "Rejected connection from {0}; incompatible Orders protocol version {1}.",
+						newConn.Socket.RemoteEndPoint, handshake.OrdersProtocol);
+
+					SendOrderTo(newConn, "ServerError", "Server is running an incompatible protocol");
+					DropClient(newConn);
+					return;
+				}
+
 				// Check if IP is banned
 				var bans = Settings.Ban.Union(TempBans);
 				if (bans.Contains(client.IpAddress))