C# Client-Server: Only one client receives data

Question

I'm trying to debug this but it's getting super messy in my head, I really need a little help over here. I'm doing the classic Chat Application program with multiple clients and a server. What I have so far :

• Clients connect to the server;
• The server stores each client in a list;
• When a client sends a message, it is then sent to all the clients in the list;

My problem is about this third step, on my server side, my program outputs the step correctly. For example, if my user is Hugo and he sends Hey:

Sending hugo: hey
 to System.Net.Sockets.TcpClient0

Sending hugo: hey

 to System.Net.Sockets.TcpClient1

The message is redirected to all the Users connected to my server. Now the problem is on the Client Side, for some reasons, the message are displayed only on the LAST connected user. Considering the previous example, the message "Hey" would be displayed two times on TcpClient1 , and never on TcpClient0

Server code

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Net.Sockets;
using System.Net;
using System.Threading;
using System.IO;
using System.Runtime.Serialization.Formatters.Binary;
using System.Collections;
using ConsoleApp1;

namespace ServerSide
{

    class Server
    {
        private int port;
        private byte[] buffer = new byte[1024];
        public delegate void DisplayInvoker(string t);
        private StringBuilder msgclient = new StringBuilder();
        private TcpListener client;
        static IPHostEntry host = Dns.GetHostEntry(Dns.GetHostName());
        private IPAddress ipAddress = host.AddressList[0];
        private TcpClient myclient;
        private List<TcpClient> usersConnected = new List<TcpClient>();



        public Server(int port)
        {
            this.port = port;


        }

        public void startServer()
        {
            client = new TcpListener(ipAddress, port);
            client.Start();
            SERV a = new SERV();
            a.Visible = true;
            a.textBox1.AppendText("Waiting for a new connection...");


            while (true)
            {
                myclient = client.AcceptTcpClient();
                usersConnected.Add(myclient);
                a.textBox1.AppendText("New User connected @" + myclient.ToString() );
                myclient.GetStream().BeginRead(buffer, 0, 1024, Receive, null);
                a.textBox1.AppendText("Size of List " + usersConnected.Count);

            }
        }

        private void Receive(IAsyncResult ar)
        {
            int intCount;

            try
            {
                lock (myclient.GetStream())
                    intCount = myclient.GetStream().EndRead(ar);
                if (intCount < 1)
                {

                    return;
                }
                Console.WriteLine("MESSAGE RECEIVED " + intCount);
                BuildString(buffer, 0, intCount);

                lock (myclient.GetStream())
                    myclient.GetStream().BeginRead(buffer, 0, 1024, Receive, null);
            }
            catch (Exception e)
            {
                return;
            }
        }
        public void Send(string Data)
        {
            lock (myclient.GetStream())
            {
                System.IO.StreamWriter w = new System.IO.StreamWriter(myclient.GetStream());
                w.Write(Data);
                w.Flush();
            }
        }
        private void BuildString(byte[] buffer, int offset, int count)
        {
            int intIndex;
            for (intIndex = offset; intIndex <= (offset + (count - 1)); intIndex++)
            {
                    msgclient.Append((char)buffer[intIndex]);
            }


            OnLineReceived(msgclient.ToString());
            msgclient.Length = 0;

        }
        private void OnLineReceived(string Data)
        {
            int i = 0;

            foreach (TcpClient objClient in usersConnected)
            {
                Console.WriteLine("Sending " + Data + " to " + objClient + i);
                Send(Data);
                i++;
            }
        }



    }
}

Client code

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;
using System.Threading;

namespace WindowsFormsApp2
{
    public partial class Form2 : Form
    {

        private delegate void DisplayInvoker(string t);
        private string currentTopic = null;
        private StringBuilder msg = new StringBuilder();
        static public string MyUser { get; set; }
        static private byte[] buffer = new byte[1024];
        static IPHostEntry host = Dns.GetHostEntry(Dns.GetHostName());
        static IPAddress ipAddress = host.AddressList[0];
        static Client user = new Client(MyUser, ipAddress, 136);
        public Form2(string User) // when a user is logged in , directly connect him to the server
        {

            InitializeComponent();
            MyUser = User;        
            user.clientConnection();
            Thread readingg = new Thread(reading);
            readingg.Start();
            user.sendText(MyUser + " joined the chatroom!" +"\n");
            IPAdress.Text = GetLocalIP(host);
            IPAdress.ReadOnly = true;
        }
        public void reading()
        {
            user.getClient().GetStream().BeginRead(buffer, 0, 1024, ReadFlow, null);
            Console.WriteLine("READING FUNCTION TRIGGERED FOR "+MyUser);
        }
        private void DisplayText(string t)
        {
            UserChat.AppendText(t);
            Console.WriteLine("DISPLAY FUNCTION TRIGGERED FOR " + MyUser + "with " +msg.ToString());

        }
        private void BuildString(byte[] buffer,int offset, int count)
        {
            int intIndex;
            for(intIndex = offset; intIndex <= (offset + (count - 1)); intIndex++)
            {
                if (buffer[intIndex] == 10)
                {
                    msg.Append("\n");
                    object[] @params = { msg.ToString() };
                    Console.WriteLine("BUILDSTIRNG FUNCTION TRIGGERED FOR " + MyUser);
                    Invoke(new DisplayInvoker(DisplayText),@params);
                    msg.Length = 0;
                }
                else
                {
                    msg.Append((char)buffer[intIndex]);
                }
            }
        }
        private void ReadFlow(IAsyncResult ar)
        {

            int intCount;

            try
            {

                intCount = user.getClient().GetStream().EndRead(ar);
                Console.WriteLine(intCount);
                if (intCount < 1)
                {
                    return;
                }
                Console.WriteLine(MyUser + "received a message");
                BuildString(buffer, 0, intCount);

                user.getClient().GetStream().BeginRead(buffer, 0, 1024, this.ReadFlow, null);

            }catch(Exception e)
            {
                return;
            }
        }
        private string GetLocalIP(IPHostEntry host)
        {

            foreach (IPAddress ip in host.AddressList)
            {
                if (ip.AddressFamily == AddressFamily.InterNetwork)
                {
                    return ip.ToString();
                }
            }

            return "192.168.1.1";
        } // get your local ip
        private void label1_(object sender, EventArgs e)
        {
            this.Text = "Hello " + MyUser;
        }
        private void listBox1_SelectedIndexChanged(object sender, EventArgs e)
        {

        }
        private void UserMessage_TextChanged(object sender, EventArgs e)
        {

        }
        private void UserMessage_Focus(object sender, EventArgs e)
        {
            UserMessage.Text = "";
        }       
        private void UserMessage_Focus2(object sender, EventArgs e)
        {

        }
        private void button2_Click(object sender, EventArgs e)
        {
            listBox1.Items.Add(addTopic.Text);
            addTopic.Text = "Add Topic";
        }
        private void button2_(object sender, EventArgs e)
        {

        }
        private void addTopic_(object sender, EventArgs e)
        {

        }
        private void addTopic_TextChanged(object sender, EventArgs e)
        {

        }
        private void listBox1_MouseDoubleClick(object sender, MouseEventArgs e)
        {
            string curItem = listBox1.SelectedItem.ToString();
            label1.Text = "Topic "+curItem;
            currentTopic = curItem;
        }
        private void IPAdress_TextChanged(object sender, EventArgs e)
        {

        }
       // send msg to the server
        private void UserChat_TextChanged(object sender, EventArgs e)
        {

        }
        private void Form2_Closing(object sender, System.ComponentModel.CancelEventArgs e)
        {
            //Handle event here
            System.Windows.Forms.Application.Exit();
        }
        private void Send_Click_1(object sender, EventArgs e)
        {
            user.sendText(MyUser + ": " + UserMessage.Text +"\n");
            UserMessage.Text = " ";
        }//send message
    }
}

Answer 1

In OnLineReceived, for each client you call SendData, where you send to myclient. You probably want to pass objClient into SendData, and send to that.

Note that there are also some threading problems there; if someone connects exactly while you are iterating the list, it'll break the iterator, for example.