VC FTP服务器程序分析（四）

　　下面是数据传输的重点-CDataSocket类，函数不多，都比较重要。

　　1、OnAccept  数据tcp服务器被连接的虚函数，由框架调用。

 void CDataSocket::OnAccept(int nErrorCode)
 {
     // Accept the connection using a temp CSocket object.
     CAsyncSocket tmpSocket;
     Accept(tmpSocket);

     SOCKET socket = tmpSocket.Detach();
     Close();

     Attach(socket);

     m_bConnected = TRUE;

     CAsyncSocket::OnAccept(nErrorCode);
 }

　　第7行 得到套接字描述符socket。第8行关闭监听的这个套接字，第11行关联socket与本对象，第12行，标记连接标志。这种处理方法少写一个类。因为tcp监听得一个socket，而连接上来的客户端也需要一个socket来与之通信。这样做适合只有一个客户端的情况。

　　2、OnReceive  数据接收处理函数

 int CDataSocket::Receive()
 {
     TRACE("OnReceive\n");
     int nRead = ;

     if (m_pControlSocket->m_nStatus == STATUS_UPLOAD)
     {
         if (m_File.m_hFile == NULL)
             return ;

         byte data[PACKET_SIZE];
         nRead = CAsyncSocket::Receive(data, PACKET_SIZE);

         switch(nRead)
         {
             case :
             {
                 m_File.Close();
                 m_File.m_hFile = NULL;
                 Close();
                 // tell the client the transfer is complete.
                 m_pControlSocket->SendResponse("226 Transfer complete");
                 // destroy this socket
                 AfxGetThread()->PostThreadMessage(WM_DESTROYDATACONNECTION, , );
                 break;
             }
             case SOCKET_ERROR:
             {
                 if (GetLastError() != WSAEWOULDBLOCK)
                 {
                     m_File.Close();
                     m_File.m_hFile = NULL;
                     Close();
                     m_pControlSocket->SendResponse("426 Connection closed; transfer aborted.");
                     // destroy this socket
                     AfxGetThread()->PostThreadMessage(WM_DESTROYDATACONNECTION, , );
                 }
                 break;
             }
             default:
             {
                 TRY
                 {
                     m_File.Write(data, nRead);
                 }
                 CATCH_ALL(e)
                 {
                     m_File.Close();
                     m_File.m_hFile = NULL;
                     Close();
                     m_pControlSocket->SendResponse("450 Can't access file.");
                     // destroy this socket
                     AfxGetThread()->PostThreadMessage(WM_DESTROYDATACONNECTION, , );
                     return ;
                 }
                 END_CATCH_ALL;
                 break;
             }
         }
     }
     return nRead;
 }

　　如果处于上传状态，那么将接收到的数据写入文件。

　　3、PreSendFile 与发送文件有关的函数

 BOOL CDataSocket::PrepareSendFile(LPCTSTR lpszFilename)
 {
     // close file if it's already open
     if (m_File.m_hFile != NULL)
     {
         m_File.Close();
     }

     // open source file
     if (!m_File.Open(lpszFilename, CFile::modeRead | CFile::typeBinary))
     {
         return FALSE;
     }
     m_nTotalBytesSend = m_File.GetLength();

     if (m_pControlSocket->m_dwRestartOffset < m_nTotalBytesSend)
     {
         m_nTotalBytesTransfered = m_pControlSocket->m_dwRestartOffset;
     }
     else
     {
         m_nTotalBytesTransfered = ;
     }
     return TRUE;
 }

　初始化文件描述符m_File，m_nTotalBytesSend,m_nTotalBytesTransfered。

　4、 SendFile函数  调用PrepareSendFile，调用OnSend发送文件。

 void CDataSocket::SendFile(LPCTSTR lpszFilename)
 {
     if (!PrepareSendFile(lpszFilename))
     {
         // change status
         m_pControlSocket->m_nStatus = STATUS_IDLE;

         m_pControlSocket->SendResponse("426 Connection closed; transfer aborted.");

         // destroy this socket
         AfxGetThread()->PostThreadMessage(WM_DESTROYDATACONNECTION, , );
         return;
     }
     OnSend();
 }

　5、SendData 发送数据 是为了LIST命令而准备，发送文件目录列表。

　6、OnSend 主要区分了list命令的情况和download的情况。

 void CDataSocket::OnSend(int nErrorCode)
 {
     CAsyncSocket::OnSend(nErrorCode);
     switch(m_pControlSocket->m_nStatus)
     {
         case STATUS_LIST:
         {
             while (m_nTotalBytesTransfered < m_nTotalBytesSend)
             {
                 DWORD dwRead;
                 int dwBytes;

                 CString strDataBlock;

                 dwRead = m_strData.GetLength();

                 if (dwRead <= PACKET_SIZE)
                 {
                     strDataBlock = m_strData;
                 }
                 else
                 {
                     strDataBlock = m_strData.Left(PACKET_SIZE);
                     dwRead = strDataBlock.GetLength();
                 }

                 if ((dwBytes = Send(strDataBlock, dwRead)) == SOCKET_ERROR)
                 {
                     if (GetLastError() == WSAEWOULDBLOCK)
                     {
                         Sleep();
                         return;
                     }
                     else
                     {
                         TCHAR szError[];
                         wsprintf(szError, "Server Socket failed to send: %d", GetLastError());

                         // close the data connection.
                         Close();

                         m_nTotalBytesSend = ;
                         m_nTotalBytesTransfered = ;

                         // change status
                         m_pControlSocket->m_nStatus = STATUS_IDLE;

                         m_pControlSocket->SendResponse("426 Connection closed; transfer aborted.");

                         // destroy this socket
                         AfxGetThread()->PostThreadMessage(WM_DESTROYDATACONNECTION, , );
                     }
                 }
                 else
                 {
                     m_nTotalBytesTransfered += dwBytes;
                     m_strData = m_strData.Mid(dwBytes);
                 }
             }
             if (m_nTotalBytesTransfered == m_nTotalBytesSend)
             {
                 // close the data connection.
                 Close();

                 m_nTotalBytesSend = ;
                 m_nTotalBytesTransfered = ;

                 // change status
                 m_pControlSocket->m_nStatus = STATUS_IDLE;

                 // tell the client the transfer is complete.
                 m_pControlSocket->SendResponse("226 Transfer complete");
                 // destroy this socket
                 AfxGetThread()->PostThreadMessage(WM_DESTROYDATACONNECTION, , );
             }
             break;
         }
         case STATUS_DOWNLOAD:
         {
             while (m_nTotalBytesTransfered < m_nTotalBytesSend)
             {
                 // allocate space to store data
                 byte data[PACKET_SIZE];

                 m_File.Seek(m_nTotalBytesTransfered, CFile::begin);

                 DWORD dwRead = m_File.Read(data, PACKET_SIZE);

                 int dwBytes;

                 if ((dwBytes = Send(data, dwRead)) == SOCKET_ERROR)
                 {
                     if (GetLastError() == WSAEWOULDBLOCK)
                     {
                         Sleep();
                         break;
                     }
                     else
                     {
                         TCHAR szError[];
                         wsprintf(szError, "Server Socket failed to send: %d", GetLastError());

                         // close file.
                         m_File.Close();
                         m_File.m_hFile = NULL;

                         // close the data connection.
                         Close();

                         m_nTotalBytesSend = ;
                         m_nTotalBytesTransfered = ;

                         // change status
                         m_pControlSocket->m_nStatus = STATUS_IDLE;

                         m_pControlSocket->SendResponse("426 Connection closed; transfer aborted.");

                         // destroy this socket
                         AfxGetThread()->PostThreadMessage(WM_DESTROYDATACONNECTION, , );
                     }
                 }
                 else
                 {
                     m_nTotalBytesTransfered += dwBytes;
                 }
             }
             if (m_nTotalBytesTransfered == m_nTotalBytesSend)
             {
                 // close file.
                 m_File.Close();
                 m_File.m_hFile = NULL;

                 // close the data connection.
                 Close();

                 m_nTotalBytesSend = ;
                 m_nTotalBytesTransfered = ;

                 // change status
                 m_pControlSocket->m_nStatus = STATUS_IDLE;

                 // tell the client the transfer is complete.
                 m_pControlSocket->SendResponse("226 Transfer complete");
                 // destroy this socket
                 AfxGetThread()->PostThreadMessage(WM_DESTROYDATACONNECTION, , );
             }
             break;
         }
     }
 }

　　7、OnConnect函数  tcp连接成功时被框架调用的虚函数。

　　8、OnClose函数 当数据发送完成或者接收完成后被框架调用的虚函数。主要做清理工作。

　　9、