Server

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

using System.Net;
using System.Net.Sockets;

namespace Server3
{
    public partial class Form1 : Form
    {
        private static Socket serverSocket;
        private const int PortNumber = 2000;
        private List<Socket> clientSockets;
        byte[] buffer = new byte[1024];
        public Form1()
        {
            InitializeComponent();
            serverSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
            clientSockets = new List<Socket>();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            StartServer();
        }
        private void StartServer()
        {
            try
            {
                serverSocket.Bind(new IPEndPoint(IPAddress.Any, PortNumber));
                serverSocket.Listen(10);

                AddMessage("Server has been started");

                serverSocket.BeginAccept(new AsyncCallback(AcceptCallback), serverSocket);
            }
            catch (Exception)
            {
                AddMessage("Could not start server");
            }
        }

        private void StopServer()
        {
            foreach (Socket connection in clientSockets) connection.Close();

            ClearMessageList();
            serverSocket.Close();
            AddMessage("Server has been stopped");
        }

        public void AcceptCallback(IAsyncResult asyncResult)
        {
            Socket client = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);

            try
            {
                client = serverSocket.EndAccept(asyncResult);

                clientSockets.Add(client);

                AddMessage("Connected to a new client");

                client.BeginReceive(buffer, 0, 1024, 0, new AsyncCallback(ReceiveCallback), client);
                serverSocket.BeginAccept(new AsyncCallback(AcceptCallback), serverSocket);
            }
            catch (Exception)
            {
                client.Close();
                clientSockets.Remove(client);
            }
        }

        public void ReceiveCallback(IAsyncResult asyncResult)
        {
            Socket client = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);

            try
            {
                client = serverSocket.EndAccept(asyncResult);
                int bytesRead = client.EndReceive(asyncResult);
                string message = Encoding.ASCII.GetString(buffer, 0, bytesRead);
                if (bytesRead > 0)
                {
                    AddMessage(message);
                    foreach (Socket receiverClient in clientSockets) Send(receiverClient, message);
                }
                client.BeginReceive(buffer, 0, 1024, 0, new AsyncCallback(ReceiveCallback), client);
            }
            catch (Exception)
            {
                AddMessage("Disconnected from client");

                client.Close();
                clientSockets.Remove(client);
            }
        }

        private void Send(Socket client, string message)
        {
            byte[] data = Encoding.ASCII.GetBytes(message);

            client.Send(data);
        }

        private void AddMessage(string message)
        {
            messageList.Invoke((MethodInvoker)delegate ()
            {
                messageList.Items.Add(message);
            });
        }

        private void ClearMessageBox()
        {
            messageBox.Invoke((MethodInvoker)delegate ()
            {
                messageBox.Text = String.Empty;
            });
        }
        private void ClearMessageList()
        {
            messageList.Invoke((MethodInvoker)delegate ()
            {
                messageList.Items.Clear();
            });
        }

        private void SendButtonOnClick(object sender, EventArgs e)
        {
            string message = messageBox.Text;
            ClearMessageBox();
            AddMessage(message);

            foreach (Socket client in clientSockets) Send(client, message);
        }
    }
}