// ...
var client = e.TcpClient;
NetworkStream networkStream = client.GetStream();
while(true) {
    byte[] query = new byte[32];
    networkStream.Read(query, 0, query.Length);

    if(query[1] == 0x0a) {
        byte[] entpass = new byte[] { 0x00 };
        byte[] sizeBuffer = new byte[4];
        networkStream.Read(sizeBuffer, 0, sizeBuffer.Length);
        int size = BitConverter.ToInt32(sizeBuffer, 0);
        byte[] data = new byte[size];
        int bytes = networkStream.Read(data, 0, size);
        // ...
        // Далі йде читання даних з БД
    }
    // ...
}