C# Socket Listen On Specific Port

This is a discussion on C# Socket Listen On Specific Port within the C# Programming forums, part of the General Programming Boards category; I'm trying to create a socket polling server (well that's the first step anyway - end goal is a reverse ...

  1. #1
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    C# Socket Listen On Specific Port

    I'm trying to create a socket polling server (well that's the first step anyway - end goal is a reverse proxy server).

    Anyway, I'm fairly useless with C#, but I can't seem to get it to bind a port to a listening socket... It throws an exception every time I run it on the listenSock.bind(endPoint) call:

    Code:
    System.Net.Sockets.SocketException: An invalid argument was supplied
    at System.Net.Sockets.Socket.DoBind(EndPoint endPointSnapshot, SocketAddress socketAddress)
    at System.Net.Sockets.Socket.Bind(EndPoint localEP)
    at Proxy.Form1..ctor() in Blah:\Form1.cs: line 27
    Code:
    List<Socket> connectedClients = new List<Socket>();
            
            public Form1() {
                InitializeComponent();
    
                IPAddress addr = IPAddress.Parse("127.0.0.1");
                IPEndPoint endPoint = new IPEndPoint(addr, Globals.port);
    
                Socket listenSock =
                    new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.IP);
    
                while (true) {
                    try {
                        listenSock.Bind(endPoint);
                    }
                    catch (Exception e) {
                        MessageBox.Show(e.ToString());
                    }
                    listenSock.Listen(10);
                    if (listenSock.Poll(0, SelectMode.SelectRead))
                        connectedClients.Add(listenSock.Accept());
    
                    foreach (Socket sock in connectedClients) {
                        if (sock.Poll(0, SelectMode.SelectError))
                            connectedClients.Remove(sock);
                        else if (sock.Poll(0, SelectMode.SelectRead))
                            // placeholder
                            ParserFunction(sock);
                    }
                }
    Can anyone let me know what I'm doing wrong? :/ I've done some Google searches and from the Google hits it appears I'm doing it correctly.

    Thanks!
    Thank you, anon. You sure know how to recognize different types of trees from quite a long way away.

  2. #2
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    Hi, I use the TcpListener class built into .net.

    Before I show any examples of how to use TcpListener, can I first point out a big mistake you've made based on the code you've provided. You are running an endless loop in the form's constructor!! This means user inputs to the GUI will never be processed, indeed the GUI might not even appear at all. In my opinion anything involving an endless loop requires it's own thread.

    Anyway, I have edited your code to demonstrate how you could use the TcpListener object in it's own thread.

    Code:
    using System;
    using System.Collections.Generic;
    using System.Windows.Forms;
    using System.Net;
    using System.Threading;
    using System.Net.Sockets;
    
    namespace WindowsFormsApplication1
    {
        public partial class Form1 : Form
        {
            private List<Socket> clients = new List<Socket>();
            private Thread listening_thread;
            private TcpListener listener;
    
            public Form1()
            {
                InitializeComponent();
    
                this.listening_thread = new Thread(new ThreadStart(this.ListeningThread));
                this.listening_thread.Start();
            }
    
            private void ListeningThread() // let's listen in another thread instead!!
            {
                int port = 12345; // change as required
    
                this.listener = new TcpListener(IPAddress.Any, port);
    
                try
                {
                    this.listener.Start();
                }
                catch (Exception e) { MessageBox.Show("couldn't bind to port " + port + " -> " + e.Message); return; }
    
                while (true)
                {
                    if (this.listener.Pending())
                        this.clients.Add(this.listener.AcceptSocket()); // won't block because pending was true
    
                    foreach (Socket sock in this.clients)
                        if (sock.Poll(0, SelectMode.SelectError))
                            clients.Remove(sock);
                        else if (sock.Poll(0, SelectMode.SelectRead))
                            ParserFunction(sock);
    
                    Thread.Sleep(30);
                }
            }
    
            private void ParserFunction(Socket sock)
            {
    
            }
        }
    }
    Hope this helps.

  3. #3
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    Thanks a lot theoobe, appreciated. I'll rework my model around what you've provided.
    Thank you, anon. You sure know how to recognize different types of trees from quite a long way away.

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