Network Development Kit

Environment: VC6 SP2, Windows 98 and NT

Introduction

Network Development Kit is a set of simple classes for a client-server architecture.  It contains 3 main classes : CServerObj, CClientObj and CMessage.  With just few method overrides, you have a complete robust client-server application.  This architecture is based on CSocket from MFC.  You don't have to know how the TCP/IP protocol is implemented to build a client-server application with this NDK.  Because the NDK is based on the TCP/IP protocol, your client-server can run on a local network or on the Internet without any change.  I provide a simple example of a client-server chat, also you can find another freeware based on the NDK at Net Blitz Homepage (a multiplayer chess program that supports Bughouse).

NDK classes

CServerObj : Server side of client-server architecture.

Public interface

• CServerObj() - Construction.
• virtual ~CServerObj() - Destruction.
• BOOL Init(int port) - Initializes the port on which the server will listen.
• BOOL StartListening() - Effectively start the server.
• void Reset() - Resets the server and disconnect any user that might still be connected.
• void DisconnectUser(ID user) - Forces the disconnection of a user, given its ID.
• BOOL SendMessage(ID user, CMessage &msg) - Sends a message to particular user.
• BOOL SendMessageToAll(CMessage &msg) - Sends a message to every connected user.
• void DisconnectAll() - Disconnects every connected user.
• int GetPort() const - Returns the port
• int GetNbUsers() const - Returns the number of users connected

Protected interface

• virtual BOOL CanConnect() = 0 - Callback method that is called when a user tries to connect to the server.
• virtual void OnConnect(ID user) = 0 - Callback method that is called when a user starts a connection to the server.
• virtual void OnMessage(ID user, CMessage &msg) = 0 - Callback that is called whenever any user sends a message to the server.
• virtual void OnDisconnect(ID user) = 0 - Callback that gets called whenever a user is disconnected for an external reason.

CClientObj : Client side of client-server architecture.

Public interface

• CClientObj() - Construction.
• virtual ~CClientObj() - Destruction.
• BOOL OpenConnection(const CIp &ip, int port) - Opens a connection to the server, given its IP address and the port number.
• void CloseConnection() - Closes an established connection with the server.
• BOOL GetIpAndPort(CIp &ip, UINT &port) const - Retreives the IP address and port number of the client.
• BOOL SendMessage(CMessage &msg) - Sends a message through the network.

Protected interface

• virtual void OnMessage(CMessage &msg) = 0 - Callback method that gets called when a message is received.
• virtual void OnDisconnect(EDisconnectionType reason) = 0 - Callback method that gets called whenever an unexpected disconnection occurs.

CMessage : Data sent and received between CServerObj and CClientObj.

Public interface

• CMessage() - Construction.
• CMessage(int identifier) - Construction with a unique identifier.
• virtual ~CMessage() - Destruction.
• void SetIdentifier(int identifier) - Assigns a unique identifier to each message.
• int GetIdentifier() const - Obtains the identifier of this message.
• int GetNbElements() const - Returns the number of elements in the array of this message.
• void SetElementAt(int index, *Type value*) - Sets a basic element.
• void GetElementAt(int index, *Type &value*) const - Gets a basic element.

Sample usage

// Client side

void CChatClientDlg::OnSendButton() 
{
   // Retreive the text typed by the user
   CString text;
   m_inputEdit.GetWindowText(text);
   m_inputEdit.SetWindowText("");

   // Pack a message with the text to send
   CMessage msg(MSG_SEND_TEXT);
   msg.SetElementAt(0, text);

   // Send the message
   ((CChatClientApp*)AfxGetApp())->SendMessage(msg);
}

void CChatClientApp::OnMessage(CMessage &msg)
{
   switch (msg.GetIdentifier())
   {
      case MSG_RECEIVE_TEXT:
      {
         CString text;

         // Unpack message elements to retreive the text
         msg.GetElementAt(0, text);

         ((CChatClientDlg*)m_pMainWnd)->AddMessage(text);
      }
      break;
   }
}

// Server side

void CChatServerApp::OnMessage(ID user, CMessage &msg)
{
   switch (msg.GetIdentifier())
   {
      case MSG_SEND_TEXT:
      {
         CString text;
         CString result;

         // Unpack message elements to retreive the text
         msg.GetElementAt(0, text);

         // Format the text to suit our needs
         result.Format("[User#%d] %s", user, text);

         // Send a text message to everyone
         CMessage msgToAll(MSG_RECEIVE_TEXT);
         msgToAll.SetElementAt(0, result);
         SendMessageToAll(msgToAll);
      }
      break;
   }
}

I hope that this NDK will help you in programming your client-server application.

Downloads

Download demo project - 50 Kb
Download source - 15 Kb