Network Development Kit 2.0

NDK Standard

• Download demo project - 100 Kb
• Download source - 29.2 Kb

NDK in an Extension DLL

• Download demo project - 98.8 Kb
• Download source - 35.6 Kb

Introduction

With the success of NDK 1.0, I decided to improve the functionality. NDK represents Network Development Kit. The NDK is a set of classes that implements a client/server architecture. The NDK hides all the complexity of the connection, sending, and receiving of data over a network. You only have to deal with three classes: CNDKServer, CNDKClient, and CNDKMessage. With just a few methods to override, you obtain a complete robust client/server application. The NDK is based on the class CSocket from MFC, so you can run your application on a local network or on the Internet without any change. To easily understand the integration of the NDK in an application, you'll find at the end of this article a complete chat application.

Classes

CNDKServer: Server side of the client/server architecture

Attributes:

• BOOL IsStarted() const;
• long GetPort() const;
• long GetNbUsers() const;
• void GetUserIds(CLongArray& alIds) const;

Operations:

• BOOL StartListening(long lPort);
• void Stop();
• BOOL SendMessageToUser(long lUserId, CNDKMessage& message);
• BOOL SendMessageToAllUsers(CNDKMessage& message);
• BOOL SendMessageToSomeUsers(const CLongArray& alUserIds, CNDKMessage& message);
• BOOL SendMessageToAllUsersExceptFor(long lUserId, CNDKMessage& message);
• BOOL SendMessageToAllUsersExceptFor(const CLongArray& alUserIds, CNDKMessage& message);
• BOOL DisconnectUser(long lUserId);
• void DisconnectAllUsers();
• BOOL PingUser(long lUserId);
• void PingAllUsers();

Callbacks:

• virtual BOOL OnIsConnectionAccepted() = 0;
• virtual void OnConnect(long lUserId) = 0;
• virtual void OnMessage(long lUserId, CNDKMessage& message) = 0;
• virtual void OnDisconnect(long lUserId, NDKServerDisconnection disconnectionType) = 0;
• virtual void OnPing(long lUserId, long lNbMilliseconds);

CNDKClient: Client side of the client/server architecture

Attributes:

• BOOL IsConnected() const;
• BOOL GetIpAndPort(CString& strIp, long& lPort) const;

Operations:

• BOOL OpenConnection(const CString& strServerIp, long lPort);
• void CloseConnection();
• BOOL SendMessageToServer(CNDKMessage& message);
• BOOL PingServer();

Callbacks:

• virtual void OnMessage(CNDKMessage& message) = 0;
• virtual void OnDisconnect(NDKClientDisconnection disconnectionType) = 0;
• virtual void OnPing(long lNbMilliseconds);

CNDKMessage: Encapsulation of the data that is sent and received by CNDKServer and CNDKClient

Attributes:

• void SetId(long lId);
• long GetId() const;
• int GetNbElements() const;

Operations:

• void Add(TYPE typeData);
• void SetAt(long lIndex, TYPE typeData);
• void GetAt(long lIndex, TYPE& typeData) const;
• void GetNext(TYPE& typeData);

Where TYPE can be a UCHAR, char, USHORT, short, UINT, int, long, float, double, CString, or LPVOID data.

What's new in 2.0

• Hungarian notation is used everywhere
• CNDKServer notifies automatically CNDKClient when it disconnects and vice-versa
• CNDKServer has new methods to send a message to a group of users
• CNDKMessage is easier to use and more robust
• New methods to ping the server or the client
• NDK prefix added to all classes to make sure that all class names are unique in your project
• NDK is standalone or encapsulated in an extension DLL

Client/Server chat

Here are two screenshots of the chat application. Most features of the NDK are shown in both programs.

Sample code from the chat client

void CChatClientDlg::OnButtonSend() 
{
   if (UpdateData(TRUE))
   {
      // Create the message with a unique Id: ChatText
      CNDKMessage message(ChatText);

      // Add the data into the message
      message.Add(m_strChatInput);

      // Send the message to the server      
      SendMessageToServer(message);

      // Update the UI of the dialog
      AddText(m_strChatInput);

      m_strChatInput.Empty();
      UpdateData(FALSE);
   }
}

Sample code from the chat server

void CChatServerDlg::OnMessage(long lUserId, CNDKMessage& message)
{
   switch (message.GetId())
   {
      //...

      case ChatText:
      {
         CString strNickname;

         // Obtain the nickname stored in the map
         m_mapIdsNicknames.Lookup(lUserId, strNickname);

         CString strText;

         // Get the text encapsulated in the message
         message.GetAt(0, strText);

         // Update the UI of the dialog
         AddText(strNickname + _T(": ") + strText);

         // Prepare the message
         message.SetAt(0, strNickname);
         message.SetAt(1, strText);

         // Send the message to all others users
         SendMessageToAllUsersExceptFor(lUserId, message);
      }
      break;

      //...
   }
}

History

• 17 December 2006
  • Fixed a bug in NDKMessage concerning the length parameter of the GetAt and GetNext methods.
• 14 October 2005
  • Telnet connections are now disconnected when a connection sends data to the server. Thanks to Stephan Douglas for the solution.
  • Fixed a bug that resolves socket notification since the NDK uses Visual C++ .NET. After a short time, socket notifications were not send anymore.
  • A verification is now made in the serialization of a CNDKMessage to make sure that the message is really a CNDKMessage.
  • Fixed a bug in the method SendMessageToSomeUsers in the NDKServer.cpp.
  • The project is now converted for Visual C++ .NET.

Fact

In 2002, the NDK was used in two NASA experiments for the Endeavor mission.

Conclusion

You don't have to be a guru of networking to create a client/server application, you only need to understand the above classes.

If you use the NDK in your project, I would really appreciate to receive an E-mail from you. I plan to make a web page of all programs using the NDK.

I would like to thank Yannick Létourneau who helped me in NDK 1.0.

Good Programming!