Build a Complete FTP Server

Description

This article presents a fully functional implementation of an FTP server. It can handle multiple connections at the same time (multi threaded) and has most of the features you would find in other commercial/shareware FTP servers. The server handles all basic FTP commands and offers easy user account management.

This article describes the most important classes of the application.

CFTPServer

This class is in fact the FTP server and controls all other classes needed for the server to work. Although CFTPServer is part of a dialog based application, it does not rely on an User Interface and can easily be implemented in a service or console application as well.

BOOL Start()

Activates the FTP server. It opens a listening socket (port 21) to accept connections.

void Stop()

Deactivates the server and disconnects all connected clients by terminating the running threads.

BOOL IsActive()

Is FTP server active?

void SetMaxUsers(int nValue)

Set maximum number of users

void SetPort(int nValue)

Set listening port for new connections

void SetTimeout(int nValue)

Set connection timeout (in ms). When a client does not send any commands for nValue ms, the server will close the connection.

void SetWelcomeMessage(LPCTSTR lpszText)
Set the text that will be displayed when the client logs on.

void Initialize(CFTPEventSink *pEventSink)

Set the event sink. The event sink will be the window (or any class) that receives the events generated by the FTP server. See CFTPEventSink description for more info.

CFTPEventSink

To be able to 'send' events from the CFTPServer class to the main application, I used multiple inheritance and virtual functions. The CFTPEventSink is just a helper class that contains nothing other than virtual functions. When you derive your class from CFTPEventSink, these virtual functions become a kind of events. The class CFTPServer has a reference to this class and calls the virtual funtions when it needs to notify the application.

The following 'events' are available:

void OnFTPUserConnected(DWORD nThreadID, LPCTSTR lpszUser, LPCSTR lpszAddress);

A client has successfully connected.

void OnFTPUserDisconnected(DWORD nThreadID, LPCTSTR lpszUser);

A client has disconnected.

void OnFTPStatusChange(int nType, LPCTSTR lpszText);

FTP server status has changed (file downloaded/uploaded).

void OnFTPReceivedBytesChange(int nBytes);

The number of received bytes has changed.

void OnFTPSentBytesChange(int nBytes);

The number of sent bytes received has changed.

void OnFTPStatisticChange(int nType, int nValue);

A statistic has changed; for example, the number of dowloaded or uploaded files.

Other Helper Classes

CUserManager

The class CUserManager handles all user- and file-related stuff. It checks the connected users for their access rights and converts remote to local paths. CUserManager uses Serializing to store and load the user settings.

CListenSocket

This socket is part of CFTPServer and accepts incoming connections. When a clients connects to the server, CListenSocket accepts the connection and creates a new thread (CConnectThread) that will take care of all further communication between the client and the server. After the thread has been created, CListenSocket will return to its waiting state.

CConnectThread

This thread will use CConnectSocket to handle all communication between the client and the server.

CConnectSocket

This socket class will process all incoming FTP commands and send the response back to the client.

CDataSocket

When data needs to be send or received, a CDataSocket will be created by CConnectSocket. The CDataSocket class will transfer this data (such as directory listings and files) on a seperate port.

All the other classes are just UI related and are only included to make it look a little bit fancier.

CFTPServer Usage

To use the class in your application, you need to do the following:

  1. Add the class to your application.
  2. Derive your main class from CFTPEventSink.
  3. Override the virtual functions of CFTPEventSink; these are the events that come from the server.
  4. Initialize the eventsink.
  5. Start the server.
class CMyDlg : public CDialog, CFTPEventSink
{
   ...

   CFTPServer m_FTPSERVER;

   virtual void OnFTPUserConnected(DWORD nThreadID,
                                   LPCTSTR lpszUser,
                                   LPCSTR lpszAddress);
   virtual void OnFTPUserDisconnected(DWORD nThreadID,
                                      LPCTSTR lpszUser);
   virtual void OnFTPStatusChange(int nType, LPCTSTR lpszText);
   virtual void OnFTPReceivedBytesChange(int nBytes);
   virtual void OnFTPSentBytesChange(int nBytes);
   virtual void OnFTPStatisticChange(int nType, int nValue);

   ...
}


BOOL CMyDlg::OnInitDialog()
{
   CDialog::OnInitDialog();

   ...

   // initialize event sink
   m_FTPSERVER.Initialize(this);
   // set maximum users to 10
   m_FTPSERVER.SetMaxUsers(10);
   // accept new connections on port 21
   m_FTPSERVER.SetPort(21);
   // activate server
   m_FTPSERVER.Start();

   return TRUE;
}

Contacting the Author

For any updates to this article, check my site: http://www.pablosoftwaresolutions.com.

Credits

Inspired by FileZilla Server.



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