C# TCP Server combining received data

Question

I'm working on a rough TCP Server/Client. It works like this: Client sends message to server > Server sends all user data to each client. I have this in a loop as I'm going to use this transfer of data for multiplayer in a game. However, for some reason my server will combine incoming data into one string instead of reading it line by line. For example, it should read something like john:0|0 for user data, but instead it reads like john:0|0john:0|0john:0|0john:0|0 I've tried setting a delay on sending and receiving, but it only seems to work if I delay more than 100ms.

Server

class Program
{

    private static Socket _serverSocket;
    private static readonly List<Socket> _clientSockets = new List<Socket>();
    private const int _BUFFER_SIZE = 2048;
    private const int _PORT = 100;
    private static readonly byte[] _buffer = new byte[_BUFFER_SIZE];
    public static bool clientConnected = false;
    public static Socket current;
    public static int delay = 100; //65
    public static string username = "";

    public static int dataSent = 0;
    public static int dataReceived = 0;

    public static List<Player> players = new List<Player>();

    static void Main()
    {

        Console.Title = "Server";
        SetupServer();
        Console.ReadLine(); // When we press enter close everything
        CloseAllSockets();

    }

    private static void SetupServer()
    {
        Console.WriteLine("Setting up server...");
        _serverSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
        _serverSocket.Bind(new IPEndPoint(IPAddress.Any, _PORT));
        _serverSocket.Listen(5);
        _serverSocket.BeginAccept(AcceptCallback, null);
        Console.WriteLine("Server setup complete");
        Console.WriteLine("Listening on port: " + _PORT);
    }

    private static void CloseAllSockets()
    {

        foreach (Socket socket in _clientSockets)
        {
            socket.Shutdown(SocketShutdown.Both);
            socket.Close();
        }

        _serverSocket.Close();
    }

    private static void AcceptCallback(IAsyncResult AR)
    {
        Socket socket;

        try
        {
            socket = _serverSocket.EndAccept(AR);
        }
        catch (ObjectDisposedException) // I cannot seem to avoid this (on exit when properly closing sockets)
        {
            return;
        }

        _clientSockets.Add(socket);
        socket.BeginReceive(_buffer, 0, _BUFFER_SIZE, SocketFlags.None, ReceiveCallback, socket);
        Console.WriteLine("Client connected: " + socket.RemoteEndPoint);
        _serverSocket.BeginAccept(AcceptCallback, null);
        clientConnected = true;

    }

    private static void ReceiveCallback(IAsyncResult AR)
    {


        current = (Socket)AR.AsyncState;
        int received = 0;

        try
        {
            received = current.EndReceive(AR);
        }
        catch (SocketException)
        {
            Console.WriteLine("Client forcefully disconnected");
            current.Close(); // Dont shutdown because the socket may be disposed and its disconnected anyway
            _clientSockets.Remove(current);
            return;
        }

        byte[] recBuf = new byte[received];
        Array.Copy(_buffer, recBuf, received);
        string text = Encoding.ASCII.GetString(recBuf);



        if (text.Contains("newuser:"))
        {
            string newuser = text.Replace("newuser:", "");
            Player newPlayer = new Player(newuser, current.RemoteEndPoint.ToString());
            players.Add(newPlayer);
            SendString("newuser:" + newuser);
            Console.WriteLine(newuser + " has joined the game.");
        }
        else
        {
             Console.WriteLine(text);  //This is where the client text gets mashed together

        }


        current.BeginReceive(_buffer, 0, _BUFFER_SIZE, SocketFlags.None, ReceiveCallback, current);

    }

    public static void SendString(string message)
    {
        try
        {
            byte[] data = Encoding.ASCII.GetBytes(message.ToString());
            current.Send(data);
            //current.BeginReceive(_buffer, 0, _BUFFER_SIZE, SocketFlags.None, ReceiveCallback, current);
            dataSent++;
        }
        catch (Exception ex)
        {
            Console.WriteLine("Client disconnected!" + ex.Message);
        }
        Console.WriteLine(dataSent);
    }
}

Client.cs

public static class Client
{
    public static string Username = "null";
    public static int delay = 85;
    public static bool hasLoggedin = false;
    public static int dataSent = 0;

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

    private const int port = 100;

    public static void Init()
    {
        Console.Title = "Client";
        ConnectToServer();
        Exit();
    }

    private static void ConnectToServer()
    {
        int attempts = 0;

        while (!_clientSocket.Connected)
        {
            try
            {
                attempts++;
                Console.Write("Username: ");
                //Username = Console.ReadLine();
                Username = "Matt";
                LocalPlayer.username = Username;
                Console.Write("IP: ");
                string ip = "192.168.0.2";
                Console.WriteLine("Port[default]: " + port);
                Console.WriteLine("Connection attempt to " + ip + ": " + attempts + " attempts");
                IPAddress ipAd = IPAddress.Parse(ip);
                _clientSocket.Connect(ipAd, port);


            }
            catch (SocketException e)
            {
                Console.Clear();
                Console.WriteLine(e.Message);
                Console.ReadLine();
            }
        }

        Console.WriteLine("Connected!");
        SendLoginPacket();
    }

    public static void SendLoginPacket()
    {
        if (hasLoggedin == false)
        {
            SendString("newuser:" + Username);
            Thread.Sleep(delay);
            hasLoggedin = true;
        }

        RequestLoop();

    }
    private static void RequestLoop()
    {
        while (true)
        {
            //SendData();
            ReceiveResponse();
        }
    }

    private static void Exit()
    {
        _clientSocket.Shutdown(SocketShutdown.Both);
        _clientSocket.Close();
        Environment.Exit(0);
    }

    public static void SendData()
    {
        string data = LocalPlayer.username + ":" + LocalPlayer.velocity.X + "|" + LocalPlayer.velocity.Y;
        SendString(data);
    }

    private static void SendString(string text)
    {
        byte[] buffer = Encoding.ASCII.GetBytes(text);
        Console.WriteLine("Sent: " + text);
        _clientSocket.Send(buffer, 0, buffer.Length, SocketFlags.None);
        dataSent++;
        Thread.Sleep(delay);
        Console.WriteLine(dataSent);
    }

    private static void ReceiveResponse()
    {

        var buffer = new byte[2048];
        int received = _clientSocket.Receive(buffer, SocketFlags.None);
        if (received == 0) return;
        var data = new byte[received];
        Array.Copy(buffer, data, received);
        string text = Encoding.ASCII.GetString(data);

        if (text.Contains("newuser:"))
        {
            string str = text.Replace("newuser:", "");
            if (!(str == LocalPlayer.username))
            {
                Player player = new Player(str, Globals.Content);
                Globals.players.Add(player);
                Console.WriteLine(str + " has joined the game.");
            }
        }

        Console.WriteLine("Clients connected: " + Globals.players.Count());
    }


}

How can I change the server so it reads incoming data one at a time, instead of mashing it into one big string?

EDIT: Note the LocalPlayer class is sending it's movement position using the Client class.

Answer 1

This is because the TCP/IP protocol provides the stream of the data (bytes). If the strings are not separated explicitly, they are "concatenated" because of "streaming".

It is required to "join" the messages using the "separator" when sending and "split" the messages using the "separator" when receiving. One of the following alternatives could be considered to implement the "separator" concept:

• Introduce the "end-of-the-message" marker.
• Introduce the message header which contains the length of the message.

The small article, TCP/IP client-server application: exchange with string messages , may be useful to understand the mentioned alternatives.

Update

I would like to recommend implementing the "messaging" appropriately.

Although it seems there is no the reason to compare the source code because it of its principal flaw (lack of "messaging" mechanism), the source code I have used to test the Client and the Server is attached.

Client

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

internal sealed class Program
{
    private const int Port = 100;
    private readonly Socket clientSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
    private bool hasLoggedin;
    private int dataSent;

    public static void Main()
    {
        var client = new Program();
        client.ConnectToServer();
        client.Exit();
    }

    private void ConnectToServer()
    {
        int attempts = 0;

        while (!clientSocket.Connected)
        {
            try
            {
                attempts++;
                string ip = "127.0.0.1";
                Console.WriteLine("Port[default]: " + Port);
                Console.WriteLine("Connection attempt to " + ip + ": " + attempts + " attempts");
                var address = IPAddress.Parse(ip);
                clientSocket.Connect(address, Port);
            }
            catch (SocketException e)
            {
                Console.Clear();
                Console.WriteLine(e.Message);
                Console.ReadLine();
            }
        }

        Console.WriteLine("Connected!");
        SendLoginPacket();
    }

    private void SendLoginPacket()
    {
        if (hasLoggedin == false)
        {
            SendString("newuser:" + Guid.NewGuid());
            hasLoggedin = true;
        }

        RequestLoop();
    }

    private void RequestLoop()
    {
        while (true)
        {
            SendData();
            ReceiveResponse();
        }
    }

    private void Exit()
    {
        clientSocket.Shutdown(SocketShutdown.Both);
        clientSocket.Close();
    }

    private void SendData()
    {
        const string Data = "username:100|200";
        SendString(Data);
    }

    private void SendString(string text)
    {
        byte[] buffer = Encoding.ASCII.GetBytes(text);
        Console.WriteLine("Sent: " + text);
        clientSocket.Send(buffer, 0, buffer.Length, SocketFlags.None);
        dataSent++;
        Console.WriteLine(dataSent);
    }

    private void ReceiveResponse()
    {
        var buffer = new byte[2048];
        int received = clientSocket.Receive(buffer, SocketFlags.None);
        if (received == 0)
        {
            return;
        }

        var data = new byte[received];
        Array.Copy(buffer, data, received);
        string text = Encoding.ASCII.GetString(data);

        if (text.Contains("newuser:"))
        {
            string str = text.Replace("newuser:", string.Empty);
            Console.WriteLine(str + " has joined the game.");
        }

        Console.WriteLine("Clients connected.");
    }
}

Server

using System;
using System.Collections.Generic;
using System.Net;
using System.Net.Sockets;
using System.Text;

internal sealed class Program
{
    private const int BufferSize = 2048;
    private const int Port = 100;
    private readonly List<Socket> clientSockets = new List<Socket>();
    private readonly byte[] buffer = new byte[BufferSize];
    private readonly List<Player> players = new List<Player>();
    private Socket serverSocket;
    private Socket current;
    private int dataSent;

    public static void Main()
    {
        var program = new Program();
        program.SetupServer();
        Console.ReadLine();
        program.CloseAllSockets();
    }

    private void SetupServer()
    {
        Console.WriteLine("Setting up server...");
        serverSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
        serverSocket.Bind(new IPEndPoint(IPAddress.Any, Port));
        serverSocket.Listen(5);
        serverSocket.BeginAccept(AcceptCallback, null);
        Console.WriteLine("Server setup complete");
        Console.WriteLine("Listening on port: " + Port);
    }

    private void CloseAllSockets()
    {
        foreach (Socket socket in clientSockets)
        {
            socket.Shutdown(SocketShutdown.Both);
            socket.Close();
        }

        serverSocket.Close();
    }

    private void AcceptCallback(IAsyncResult AR)
    {
        Socket socket;

        try
        {
            socket = serverSocket.EndAccept(AR);
        }
        catch (ObjectDisposedException) // I cannot seem to avoid this (on exit when properly closing sockets)
        {
            return;
        }

        clientSockets.Add(socket);
        socket.BeginReceive(buffer, 0, BufferSize, SocketFlags.None, ReceiveCallback, socket);
        Console.WriteLine("Client connected: " + socket.RemoteEndPoint);
        serverSocket.BeginAccept(AcceptCallback, null);
    }

    private void ReceiveCallback(IAsyncResult AR)
    {
        current = (Socket)AR.AsyncState;
        int received = 0;

        try
        {
            received = current.EndReceive(AR);
        }
        catch (SocketException)
        {
            Console.WriteLine("Client forcefully disconnected");
            current.Close(); // Dont shutdown because the socket may be disposed and its disconnected anyway
            clientSockets.Remove(current);
            return;
        }

        byte[] recBuf = new byte[received];
        Array.Copy(buffer, recBuf, received);
        string text = Encoding.ASCII.GetString(recBuf);

        if (text.Contains("newuser:"))
        {
            string newuser = text.Replace("newuser:", string.Empty);
            Player newPlayer = new Player(newuser, current.RemoteEndPoint.ToString());
            players.Add(newPlayer);
            SendString("newuser:" + newuser);
            Console.WriteLine(newuser + " has joined the game.");
        }
        else
        {
            // This is where the client text gets mashed together.
            Console.WriteLine(text);
        }

        current.BeginReceive(buffer, 0, BufferSize, SocketFlags.None, ReceiveCallback, current);
    }

    private void SendString(string message)
    {
        try
        {
            byte[] data = Encoding.ASCII.GetBytes(message.ToString());
            current.Send(data);
            // current.BeginReceive(buffer, 0, BufferSize, SocketFlags.None, ReceiveCallback, current);
            dataSent++;
        }
        catch (Exception ex)
        {
            Console.WriteLine("Client disconnected!" + ex.Message);
        }
        Console.WriteLine(dataSent);
    }
}

internal sealed class Player
{
    public Player(string newuser, string toString)
    {
    }
}

Client output

Port[default]: 100
Connection attempt to 127.0.0.1: 1 attempts
Connected!
Sent: newuser:6b06f0a6-bdb0-4471-ac58-fa9c490b7555
1
Sent: username:100|200
2
6b06f0a6-bdb0-4471-ac58-fa9c490b7555username:100|200 has joined the game.
Clients connected.
Sent: username:100|200
3

Server output

Setting up server...
Server setup complete
Listening on port: 100
Client connected: 127.0.0.1:1082
1
6b06f0a6-bdb0-4471-ac58-fa9c490b7555username:100|200 has joined the game.
username:100|200