Socket Programming C# Chat Service

Question

I know this is probably too general of a question, but what is the concept behind socket programming in C#? I was able to send/receive data with myself using the code below:

//client side?
using System;
using System.Text;
using System.Net;
using System.Net.Sockets;

namespace client1 
{
    class Program
    {

        private static Socket _clientSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);

        static void Main(string[] args)
        {
            Console.Title = "Client";
            LoopConnect();
            SendLoop();
        }

        private static void SendLoop()
        {
            while (true)
            {
                Console.Write("Enter a request: ");
                string req = Console.ReadLine();
                byte[] buffer = Encoding.ASCII.GetBytes(req);
                _clientSocket.Send(buffer);

                byte[] receivedBuf = new byte[1024];
                int rec = _clientSocket.Receive(receivedBuf);
                byte[] data = new byte[rec];
                Array.Copy(receivedBuf, data, rec);
                Console.WriteLine("Received: " + Encoding.ASCII.GetString(data));
            }
        }

        private static void LoopConnect()
        {

            int attempts = 0;

            while (!_clientSocket.Connected)
            {
                try
                {
                    attempts++;

                    _clientSocket.Connect(IPAddress.Loopback, 100);
                }
                catch (SocketException)
                {
                    Console.Clear();
                    Console.WriteLine("Connection attempts: " + attempts.ToString());
                }
            }

            Console.Clear();
            Console.WriteLine("Connected");
        }
    }
}


//server side?
using System;
using System.Collections.Generic;
using System.Text;
using System.Net.Sockets;
using System.Net;

namespace server1
{
    class Program
    {
        private static List<Socket> _clientSockets = new List<Socket>();
        private static Socket _serverSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
        private static byte[] _buffer = new byte[1024];

        static void Main(string[] args)
        {
            Console.Title = "Server";
            SetupServer();
            Console.ReadLine();
        }

        private static void SetupServer()
        {
            Console.WriteLine("Setting up server...");
            _serverSocket.Bind(new IPEndPoint(IPAddress.Any, 100));
            _serverSocket.Listen(5);
            _serverSocket.BeginAccept(new AsyncCallback(AcceptCallback), null);
        }

        private static void AcceptCallback(IAsyncResult AR)
        {
            Socket socket = _serverSocket.EndAccept(AR);
            _clientSockets.Add(socket);
            Console.WriteLine("Client connected...");
            socket.BeginReceive(_buffer, 0, _buffer.Length, SocketFlags.None, new AsyncCallback(ReceiveCallback), socket);
            _serverSocket.BeginAccept(new AsyncCallback(AcceptCallback), null);
        }

        private static void ReceiveCallback(IAsyncResult AR)
        {
            Socket socket = (Socket)AR.AsyncState;
            int received = socket.EndReceive(AR);

            byte[] dataBuf = new byte[received];
            Array.Copy(_buffer, dataBuf, received);

            string text = Encoding.ASCII.GetString(dataBuf);
            Console.WriteLine("Text received: " + text);

            string response = string.Empty;

            if (text.ToLower() != "get time")
            {
                response = "Invalid Request";
            } else
            {
                response = DateTime.Now.ToLongDateString();
            }

            //if (text.ToLower() == "get time")
            //{
                //SendText(DateTime.Now.ToLongTimeString());
                //byte[] data = Encoding.ASCII.GetBytes(DateTime.Now.ToLongTimeString());
                //socket.BeginSend(data, 0, data.Length, SocketFlags.None, new AsyncCallback(SendCallback), socket);
            //}

            byte[] data = Encoding.ASCII.GetBytes(DateTime.Now.ToLongTimeString());
            socket.BeginSend(data, 0, data.Length, SocketFlags.None, new AsyncCallback(SendCallback), socket);
            socket.BeginReceive(_buffer, 0, _buffer.Length, SocketFlags.None, new AsyncCallback(ReceiveCallback), socket);
        }

        private static void SendCallback(IAsyncResult AR)
        {
            Socket socket = (Socket)AR.AsyncState;
            socket.EndSend(AR);
        }
    }
}

However, when I gave the client.exe to my friend who is on the same network while I was running the server.exe, he was not able to connect to me. Does anyone have any suggestions as to what I'm doing wrong?

Answer 1

Based on the current code in your question, the client tries to connect to the loopback (127.0.0.1), so it doesn't work if the server is installed on a different machine.

If that was a typo and you've correctly configured the IP address, please double check that no firewall is blocking the requests.