C# TCP Server Reply Packet Issue

Question

I have been banging my head against my code for the better part of the day, and I am completely stumped. Basically, the source game engine has a documented protocol for its RCON (Remote Console Over Network?) which I am trying to reproduce. There are hundreds of examples, but all of them are from the client side (establishing a connection to the game server's RCON) where as I am trying to actually re-create the server portion to reply to clients.

Here is the information on the RCON Protocol. The problem I am having with the code is, when I receive the Authentication request everything is fine. When I attempt to reply to it and okay the connection, the connection fails. So I am doing something wrong when replying but not sure what.

http://developer.valvesoftware.com/wiki/Source_RCON_Protocol

private void ReadClientPacket(object client)
{
    TcpClient tcpClient = (TcpClient)client;
    NetworkStream clientStream = tcpClient.GetStream();

    while (true)
    {
        try
        {
            int packetsize;

            // Create a new Packet Object and fill out the data from the incoming TCP Packets
            RCONPacket packet = new RCONPacket();

            using (BinaryReader reader = new BinaryReader(clientStream))
            {
                // First Int32 is Packet Size
                packetsize = reader.ReadInt32();

                packet.RequestId = reader.ReadInt32();
                packet.RconDataReceived = (RCONPacket.RCONDATA_rec)reader.ReadInt32();

                Console.WriteLine("Packet Size: {0} RequestID: {1} ServerData: {2}", packetsize, packet.RequestId, packet.RconDataReceived);

                // Read first and second String in the Packet (UTF8 Null Terminated)
                packet.String1 = ReadBytesString(reader);
                packet.String2 = ReadBytesString(reader);

                Console.WriteLine("String1: {0} String2: {1}", packet.String1, packet.String2);

                switch (packet.RconDataReceived)
                {
                    case RCONPacket.RCONDATA_rec.SERVERDATA_AUTH:
                    {
                        ReplyAuthRequest(packet.RequestId, tcpClient);
                        break;
                    }
                    case RCONPacket.RCONDATA_rec.SERVERDATA_EXECCOMMAND:
                    {
                        //ReplyExecCommand(packet.RequestId, tcpClient);
                        break;
                    }
                    default:
                    {
                        break;
                    }
                }
            }

            break;
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.Message);
            break;
        }
    }

    tcpClient.Close();
}

private void ReplyAuthRequest(int RequestID, TcpClient client)
{
    Console.WriteLine("Replying to Auth Request");

    // Authentication Reply
    using (NetworkStream clientStream = client.GetStream())
    using (MemoryStream stream = new MemoryStream())
    using (BinaryWriter writer = new BinaryWriter(stream))
    {
        writer.Write((int)10); // Packet Size
        writer.Write(RequestID); // Mirror RequestID if Authenticated, -1 if Failed
        writer.Write((int)RCONPacket.RCONDATA_sent.SERVERDATA_AUTH_RESPONSE);
        writer.Write(ConvertStringToByteArray("" + char.MinValue));
        writer.Write(ConvertStringToByteArray("" + char.MinValue));
        byte[] buffer = stream.ToArray();
        Console.WriteLine("size of full auth response packet is {0}", buffer.Length);

        clientStream.Write(buffer, 0, buffer.Length);
        clientStream.Flush();
    }
}

Answer 1

Have you been using Wireshark ?

This tool is essential when you try to copy/reverse-engineer existing protocols. Just do a normal authentication with a known-working client and save the log. Then use your own code and try to see where the bits sent on the wire are different from those in the log.

Sometimes its pretty difficult things to see just by looking at the code, like a '\\n' getting inserted at the wrong point, or an extra line after the whole message

Answer 2

I've had a similar problem a while ago

In your Reply function :

using (NetworkStream clientStream = client.GetStream())
(...)

The disposal of the clientStream could be the culprit. In my case the disposal of the stream caused the connection termination, GetStream() doesn't return a new instance of a stream, it returns the Stream that is owned by the TCPClient. See if that helps.