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Posted 4 Jun 2006


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A Simple Multi-Threaded Server Client Instant Messenger Application

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4.32/5 (26 votes)
4 Jun 2006CPOL2 min read
A Simple Multi-Threaded Server Client Instant Messenger Application that uses TCP Listener and TCP Client. Allows Personal message and Conference communication between Clients and with the Server
Sample Image - maximum width is 600 pixels

The Library Project

I created a ChatLibrary that will contain the valid commands and a Message that will contain the parsing.

public enum Command
   Login = 0,
   PersonalMessage = 1,    
   ClientList = 2,        
   Conference = 3,
   Logout = 4        

public class Message
string strSender;
string strReceiver;
Command cmdMessageCommand;
string strMessageDetail;
public Message ()
public Message (byte [] rawMessage)
  string strRawStringMessage = System.Text.Encoding.ASCII.GetString (rawMessage);   
  string [] strRawStringMessageArray = strRawStringMessage.Split(new char []{'|'});
  this.strSender = strRawStringMessageArray[1];
  this.strReceiver = strRawStringMessageArray[2];
  this.cmdMessageCommand = (Command) Convert.ToInt32(strRawStringMessageArray[3]);
  this.MessageDetail = strRawStringMessageArray[4];

public byte [] GetRawMessage ()
   System.Text.StringBuilder sbMessage = new System.Text.StringBuilder ("John");
   return System.Text.Encoding.ASCII.GetBytes(sbMessage.ToString());

The Server Project

I created a SocketServer that calls the TCPListener.Start() method:

IPEndPoint endPoint = new IPEndPoint (ipaAddress, iPort);
listener = new TcpListener (endPoint);

Upon calling Listen, a new thread will be created that will listen for incoming clients:

thrListenForClients = new Thread(new ThreadStart(ListenForClients));

The ListenForClients method will wait for connections and will assign the incoming socket to a new Client instance:

Client acceptClient = new Client();
acceptClient.Socket = listener.AcceptTcpClient();
listenForMessageDelegate = new ListenForMessageDelegate (ListenForMessages);
    (acceptClient, new AsyncCallback(ListenForMessagesCallback), "Completed");

The Client, by the way is a class that contains a TCPClient, so we can keep track of our connections:

public class Client {
   string strName;
   TcpClient tcpClient;
   public Client()
   public string Name 
    get{return strName;}
    set{ this.strName = value;}            
   public TcpClient Socket
    get{return tcpClient;}
    set{ this.tcpClient = value;}
   public void SendMessage (Message sendMessage)
    NetworkStream stream = tcpClient.GetStream();
    stream.Write(sendMessage.GetRawMessage() , 0, sendMessage.GetRawMessage().Length);            

Our server is now ready to listen for incoming messages. To do this, we pass the client socket that we received, then make a loop. We use a NetworkStream to read the message:

NetworkStream stream = client.Socket.GetStream();
byte [] bytAcceptMessage = new byte [1024];
stream.Read(bytAcceptMessage, 0, bytAcceptMessage.Length);
Message message = new ChatLibrary.Message(bytAcceptMessage);

Once we receive the message, we can do anything that we want:

txtStatus.Text += "\r\n" + strDisplayMessageType + 
    strWriteText.TrimStart(new char[]{'\r','\n'});

My SocketServer makes use of a few events that make coding a little easier:

public event ClientConnectedEventHandler ClientConnected;
public event ClientDisconnectingEventHandler ClientDisconnecting;
public event MessageReceivedEventHandler MessageReceived;

In my ServerForm code, what I did was I kept a copy of each connected Client in a ClientCollection that inherits from System.Collections.CollectionBase. With this, I can iterate through the Clients.

The Client Project

The Client does basically the same thing. I created a ClientSocket that will create a TCPListener and call Connect():

IPEndPoint serverEndpoint = new IPEndPoint (ipaAddress , iPort);
tcpClient = new TcpClient ();
thrListenForMessages = new Thread (new ThreadStart(ListenForMessages));

What ListenForMessages will do is loop with NetworkStream.Read():

stream = tcpClient.GetStream();
byte [] bytRawMessage = new byte [1024];
stream.Read(bytRawMessage, 0, bytRawMessage.Length);
ChatMessage receivedMessage = new ChatLibrary.Message (bytRawMessage);

Then we do the same process, create a Message using the received bytes.

Again, my goal is to create a YM/MSN - looking Instant Messenger, so I made two UI forms. The MessengerForm and the ClientWindow. The MessengerForm is the class that instantiates the ClientSocket and receives the messages. Upon receiving a message, it calls the MessengerWindow that should display the text.

Note that I didn't do a regular instantiation. I called Invoke to be able to make my controls thread safe:

this.Invoke(createNewClientDelegate, new object []{receivedMessage});


  • 4th June 2006: Initial version


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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Comments and Discussions

QuestionIn 10 : error in connecting client to server ! Pin
Dariush Ajami11-Jun-17 23:55
MemberDariush Ajami11-Jun-17 23:55 
GeneralCross threading issue in Visual Studio 2013... Pin
Arslan Tariq22-May-14 9:20
MemberArslan Tariq22-May-14 9:20 
Generalthis code can not send bytes>1024 Pin
daodetianzun19-Sep-08 4:09
Memberdaodetianzun19-Sep-08 4:09 
GeneralGreat but there are some errors to modify Pin
Sugathe0427-Aug-08 18:43
MemberSugathe0427-Aug-08 18:43 
GeneralHelp Please: If I kick a client, or client click disconnect, the server raises a error of "Server has stopped working" Pin
JameYoon2-Jul-08 17:35
MemberJameYoon2-Jul-08 17:35 
GeneralPlease Help :) If I stop the Server(even if there is no client connected), it arises an error. [modified] Pin
JameYoon1-Jul-08 18:18
MemberJameYoon1-Jul-08 18:18 
QuestionNot sure how to use!!! Pin
Lecram21-Jun-08 20:34
MemberLecram21-Jun-08 20:34 
GeneralCross-thread operation not valid: Control 'txtStatus' accessed from a thread other than the thread it was created on. Pin
Shawn12814-Jun-08 22:42
MemberShawn12814-Jun-08 22:42 
AnswerRe: Cross-thread operation not valid: Control 'txtStatus' accessed from a thread other than the thread it was created on. Pin
Jason Barry25-Jun-08 2:57
professionalJason Barry25-Jun-08 2:57 
You can't access an object that wasn't created on the thread you're calling from. So there is a work around using delegates. The code below is how you would accomplish this in your case:

private delegate void AddStatusTextDelegate(string text);

private void AddStatusText(string text)
    if (this.txtStatus.InvokeRequired)
        // This is a worker thread so delegate the task.
        this.txtStatus.Invoke(new AddStatusTextDelegate(this.AddStatusText), text);
        // This is the UI thread so perform the task.
        this.txtStatus.Text += text;

GeneralRe: Cross-thread operation not valid: Control 'txtStatus' accessed from a thread other than the thread it was created on. Pin
Member 87892936-Apr-12 10:16
MemberMember 87892936-Apr-12 10:16 
QuestionClient IP-Address problem Pin
Husti5-Apr-08 9:03
MemberHusti5-Apr-08 9:03 
GeneralSystem.ObjectDisposedException after disconnect Pin
Gaara [BTK]15-Aug-07 14:22
MemberGaara [BTK]15-Aug-07 14:22 
GeneralRe: System.ObjectDisposedException after disconnect Pin
Antbu1325-Oct-07 20:41
MemberAntbu1325-Oct-07 20:41 
GeneralRe: System.ObjectDisposedException after disconnect Pin
Eagle196520-May-09 10:43
MemberEagle196520-May-09 10:43 
Generalproblem in running this application [modified] Pin
vrani12-Jul-07 19:38
Membervrani12-Jul-07 19:38 
GeneralMulti-threading error fix Pin
stormist10-Jun-07 13:43
Memberstormist10-Jun-07 13:43 
Generaltextbox Pin
dark_magician_65-May-07 4:50
Memberdark_magician_65-May-07 4:50 
Questionnot working on lan plz help me Pin
Member 37941123-Mar-07 0:26
MemberMember 37941123-Mar-07 0:26 
Questionit is working in LAN but what do i need to do for WAN ? Pin
evalenzuela2-Feb-07 11:57
Memberevalenzuela2-Feb-07 11:57 
GeneralError Pin
Christian Siebmanns7-Oct-06 5:04
MemberChristian Siebmanns7-Oct-06 5:04 
GeneralRe: Error Pin
bubbler_below9-Oct-06 17:09
Memberbubbler_below9-Oct-06 17:09 
GeneralRe: Error Pin
bubbler_below10-Oct-06 22:25
Memberbubbler_below10-Oct-06 22:25 
GeneralRe: Error Pin
Christian Siebmanns21-Oct-06 5:24
MemberChristian Siebmanns21-Oct-06 5:24 
AnswerRe: Error PinPopular
duffer_0113-Apr-07 10:30
Memberduffer_0113-Apr-07 10:30 
AnswerRe: Error Pin
Jim Weiler13-Aug-07 10:06
MemberJim Weiler13-Aug-07 10:06 

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