如何构造自定义二进制协议TCP请求

Question

I'm working on a code challenge which, in short, provides a server that encodes/decodes the data sent in the request. It is a TCP/IP server with the following custom binary request/response structures:

I need to create a desktop client that will send requests and receive responses, and display data accordingly. I'm having trouble understanding how the request would be formed, and how I would send the request to the TCP/IP server (using C#). Could someone provide perhaps an example of what this might look like?

Answer 1

not sure about your checksum, but constructing a packet would look something like

        byte[] CreatePacket(string s, Operation op)
        {
            var packet = new List<byte>();
            packet.AddRange(BitConverter.GetBytes((UInt16) 0x1092));
            packet.Add(1);
            var data = Encoding.ASCII.GetBytes(s);
            packet.AddRange(BitConverter.GetBytes((UInt32) (9 + data.Length)));
            packet.Add((byte) (op == Operation.Encode ? 1 : 2));
            packet.AddRange(data);
            packet.Add(CheckSum(packet));
            return packet.ToArray();
        }

given

    enum Operation
    {
        Encode,
        Decode,
    }

and

server.Send(CreatePacket("test string", Operation.Encode))

Also with the checksum spec...

        byte CheckSum(List<byte> packet)
        {
            return (byte)(packet.Select((b, i) => (value: b, index: i))
                .Sum(o => (o.value & (1 << (o.index % 8))) > 0 ? 1 :0) % 256);
        }