C# why TCPListener load CPU

Question

I found TCPListener code from here. In MainWindow class Im starting server.
Then opening websocket from html page

let socket = new WebSocket("ws://192.168.1.149:1112");

Right after this CPU loads to 25% even if nothing sent to server. Further data sending to server going normal. What to do to prevent CPU load? Please help.

class TcpServer
{
    public string ip;
    public int port;
    private Thread bgThread;

    public void StartListen()
    {
        bgThread = new Thread(new ThreadStart(Start))
        {
            IsBackground = true
        };
        bgThread.Start();

    }

    public void Start()
    {
        TcpListener server = new TcpListener(IPAddress.Parse(ip), port);
        server.Start();

        TcpClient client = server.AcceptTcpClient();
        NetworkStream stream = client.GetStream();

        while (true)
        {
            while (!stream.DataAvailable) ;
            while (client.Available < 3) ; // match against "get"

            byte[] bytes = new byte[client.Available];
            stream.Read(bytes, 0, client.Available);
            string strbytes = Encoding.UTF8.GetString(bytes);

            if(strbytes.StartsWith("GET"))
            {
                Console.WriteLine("=====Handshaking from client=====\n{0}", strbytes);

                string swk = Regex.Match(strbytes, "Sec-WebSocket-Key: (.*)").Groups[1].Value.Trim();
                string swka = swk + "258EAFA5-E914-47DA-95CA-C5AB0DC85B11";
                byte[] swkaSha1 = System.Security.Cryptography.SHA1.Create().ComputeHash(Encoding.UTF8.GetBytes(swka));
                string swkaSha1Base64 = Convert.ToBase64String(swkaSha1);

                // HTTP/1.1 defines the sequence CR LF as the end-of-line marker
                byte[] response = Encoding.UTF8.GetBytes(
                    "HTTP/1.1 101 Switching Protocols\r\n" +
                    "Connection: Upgrade\r\n" +
                    "Upgrade: websocket\r\n" +
                    "Sec-WebSocket-Accept: " + swkaSha1Base64 + "\r\n\r\n");

                stream.Write(response, 0, response.Length);
            }
            else
            {
                bool mask = (bytes[1] & 0b10000000) != 0; 

                int msglen = bytes[1] - 128, 
                offset = 2;

                if (msglen == 126)
                {
                    msglen = BitConverter.ToUInt16(new byte[] { bytes[3], bytes[2] }, 0);
                    offset = 4;
                }
                else if (msglen == 127)
                {
                    Console.WriteLine("TODO: msglen == 127, needs qword to store msglen");
                }

                if (msglen == 0)
                    Console.WriteLine("msglen == 0");
                else if (mask)
                {
                    try
                    {
                        byte[] decoded = new byte[msglen];
                        byte[] masks = new byte[4] { bytes[offset], bytes[offset + 1], bytes[offset + 2], bytes[offset + 3] };
                        offset += 4;

                        for (int i = 0; i < msglen; ++i)
                            decoded[i] = (byte)(bytes[offset + i] ^ masks[i % 4]);

                        string text = Encoding.UTF8.GetString(decoded);
                        
                        // other code
                        
                    }
                    catch(Exception exc)
                    {
                        Console.WriteLine(exc.Message + "\n--------\n" + exc.StackTrace);
                    }
                    
                }
                else
                    Console.WriteLine("mask bit not set");

            }
        }
    }
}

private void startServer()
{
    tcpserver = new TcpServer
    {
        ip = ipbox.Text,
        port = 1112
    };
    tcpserver.StartListen();
}



startServer();

P.S: I have not to say anymore but SO says "It looks like your post is mostly code; please add some more details.". So: some words