quick_client.cs

static void Main(string[] args)
{
    Run().GetAwaiter().GetResult();
}

static async Task Run()
{
    TcpClient client = new TcpClient("127.0.0.1", 8080);
    NetworkStream stream = client.GetStream();

    while (true)
    {
        byte[] readBuffer = new byte[128];
        byte[] writeBuffer = new byte[128];
        string input = Console.ReadLine();
        int len =  Encoding.ASCII.GetByteCount(input);
        writeBuffer[0] = 0x41;
        writeBuffer[1] = (byte) len;
        Encoding.ASCII.GetBytes(input, 0, len, writeBuffer,2);
        await stream.WriteAsync(writeBuffer);
        int bytesCount = await stream.ReadAsync(readBuffer);
        Console.WriteLine(Encoding.ASCII.GetString(readBuffer[2..(2 + bytesCount)]));
    }
}