C# Socket keep receiving empty message

Question

I'm trying to train myself and i'm currently building a small Tcp server / client.

I have for the moment 3 small classes that connect, listen for clients and listen to messages. Here are the 3 classes :

public class ServersLauncher
{

    #region Main
    public static void Main(string[] args)
    {
        ServersLauncher sl = new ServersLauncher();
        Console.ReadLine();
        sl._udpServer?.Dispose();
        sl._tcpServer?.Dispose();
    }
    #endregion Main

    private UdpServer _udpServer;
    private TcpServer _tcpServer;

    private ServersLauncher()
    {
        _tcpServer = new TcpServer();
        Socket sc = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
        IPEndPoint localEndPoint = new IPEndPoint(IPAddress.Parse("127.0.0.1"), 25004);
        sc.Bind(localEndPoint);
        IPEndPoint distantEndPoint = new IPEndPoint(IPAddress.Parse("127.0.0.1"), 25000);
        sc.Connect(distantEndPoint);
        while (!sc.Connected)
            Thread.Sleep(1000);
        byte[] buffer = Utility.ConvertMessage("Hell world !");
        sc.Send(buffer, buffer.Length, SocketFlags.None);
        sc.Close();
    }

}

On top is the server launcher, it launches the server, create the client and send a message.

public class TcpServer : IDisposable
{

    private readonly int _portTcp = 25000;
    private Socket _socket;
    private Thread _connectionsThread;
    private List<TcpClient> _clients;

    public TcpServer()
    {
        _clients = new List<TcpClient>();

        _socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
        IPEndPoint endPoint = new IPEndPoint(IPAddress.Parse("127.0.0.1"), _portTcp);
        _socket.Bind(endPoint);
        _connectionsThread = new Thread(new ThreadStart(ListenConnections));
        _connectionsThread.Start();
    }

    public void Dispose()
    {
        _connectionsThread.Abort();
        for(int i = 0; i < _clients.Count; i++)
        {
            _clients[i].Dispose();
        }
        _socket.Close();
    }

    private void ListenConnections()
    {
        _socket.Listen(100);
        while (true)
        {
            Socket clientSocket = _socket.Accept();
            _clients.Add(new TcpClient(clientSocket));
        }
    }

}

On top is the TcpServer that listen to the connections and create a client interface when one client connect.

public class TcpClient : IDisposable
{

    private Socket _client;
    private Thread _receiverThread;

    public TcpClient(Socket client)
    {
        _client = client;
        _receiverThread = new Thread(ReceiveMessage);
        _receiverThread.Start();
    }

    public void Dispose()
    {
        _receiverThread.Abort();
    }

    private void ReceiveMessage()
    {
        while (true)
        {
            byte[] buffer = new byte[1024];
            _client.Receive(buffer);
            Utility.DisplayThread("A message has been received : " + Encoding.ASCII.GetString(buffer).Trim());
        }
    }

}

And here is the TcpClient that store the socket client and listen for messages. Nothing that complicated but i have an issue with the reading of the message. Right now, if i launch the program, the client connect but then... non stop messages ! I receive one "Hell world" then empty messages. I read the documentation of the Receive method for the Socket and it seems that it should block and wait for a message to pursue is routine. Do i do something wrong somewhere ? Do i need to flush the stream from the client before disconnecting ? Thanks for helping !

Answer 1

Reason for receiving empty messages is that your client socket remains connected.

You can wait to receive more messages with your client, if that is what you want try this:

 private void ReceiveMessage()
        {
            while (true) {
                if(_client.Available > 0) {
                    byte[] buffer = new byte[1024];
                    _client.Receive(buffer);
                    Console.WriteLine("A message has been received : " + Encoding.ASCII.GetString(buffer));
                }
            }
        }

if(_client.Available > 0) checks if there are any number of bytes of data received from the network and available to be read.

Update me on how it goes;

Good luck;

Answer 2

Hmm, I'm not sure what behaviour you expect to see.

You create a new ServerLauncher and then when doing so, you do the following:

sc.Connect(distantEndPoint);
while (!sc.Connected)
   Thread.Sleep(1000);
byte[] buffer = Utility.ConvertMessage("Hell world !");
sc.Send(buffer, buffer.Length, SocketFlags.None);
sc.Close();

This connects, waits until connected, sends a message and then closes.

Your main method then calls Console.ReadLine();...

If your server is closed, no more messages will come through. Remove the sc.Close(); line (or only call it when some flag is called like X)

Perhaps you should create a loop and send message from the loop, or better, pass messages from the commandline.