[Mono-dev] Listening in on a port (was the daemon thingy a week or so back)

PFJ pjohnson1 at uclan.ac.uk
Tue Jan 12 08:08:02 EST 2010


I'm making some progress with my daemon in C# to listen in on port 80 and
monitor how much time my son is spending on line, but I've hit a snag.

Currently, my code looks like this 

  class Server
    private TcpListener tcpListener;
    private Thread listenThread;

    public Server()
      this.tcpListener = new TcpListener(IPAddress.Any, 80);
      this.listenThread = new Thread(new ThreadStart(ListenForClients));

private void ListenForClients()

  while (true)
    //blocks until a client has connected to the server
    TcpClient client = this.tcpListener.AcceptTcpClient();

    //create a thread to handle communication
    //with connected client
    Thread clientThread = new Thread(new

private void HandleClientComm(object client)
  TcpClient tcpClient = (TcpClient)client;
  NetworkStream clientStream = tcpClient.GetStream();

  byte[] message = new byte[4096];
  int bytesRead;

  while (true)
    bytesRead = 0;

      //blocks until a client sends a message
      bytesRead = clientStream.Read(message, 0, 4096);
      //a socket error has occured

    if (bytesRead == 0)
      //the client has disconnected from the server

    //message has successfully been received
    ASCIIEncoding encoder = new ASCIIEncoding();
    System.Diagnostics.Debug.WriteLine(encoder.GetString(message, 0,


public static void Main()
	Server s = new Server();

Works fine until I start a browser. Then it aborts with

System.Net.Sockets.SocketException: Only one usage of each socket address
(protocol/network address/port) is normally permitted
   at System.Net.Sockets.Socket.DoBind
   at System.Net.Sockets.Socket.Bind
   at System.Net.Sockets.TcpListener.Start
   at System.Net.Sockets.TcpListener.Start
   at TCPServerTutorial.Server.ListenForClients in
Projects\tcpmonitor\tcpmonitor\Program.cs:line 34
   at System.Threading.ThreadHelper.ThreadStart_Context
   at System.Threading.ExecutionContext.Run
   at System.Threading.ThreadHelper.ThreadStart

which looks to me like two apps can't be listening in on port at the same
time. I guess I'm doing something wrong here, but can't see what it is - I'm
guessing that I've coded a server instead of a client, but then I'm not sure
if the software should be a client rather than a server! I'll admit now that
this is the first time I've done anything in C# with networking ports.

The idea is that once I get this running, the trivial matter of timing
(using either a thread timer or System.Timer) will be easy to put in and all
will be good with the world.

Any help on this would be good.


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