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