VC FTP服务器程序分析（三）

　　CControlSocket类的分析，CControlSocket类的内容比较多，为什么呢。因为通信控制命令的传输全部在这里，通信协议的多样也导致了协议解析的多样。

　　1、OnReceive  其大致说明：本函数由框架调用，通知套接字缓冲中有数据，可以调用Receive函数取出。

 void CControlSocket::OnReceive(int nErrorCode)
 {
     try
     {
         TCHAR buff[BUFFER_SIZE+];

         int nRead = Receive(buff, BUFFER_SIZE);
         switch (nRead)
         {
             case :
                 Close();
                 break;

             case SOCKET_ERROR:
                 if (GetLastError() != WSAEWOULDBLOCK)
                 {
                     TCHAR szError[];
                     wsprintf(szError, "OnReceive error: %d", GetLastError());
                     AfxMessageBox (szError);
                 }
                 break;

             default:
                 if ((m_RxBuffer.GetLength() + nRead) > BUFFER_OVERFLOW)
                 {
                     ((CClientThread *)m_pThread)->PostStatusMessage("Buffer overflow: DOS attack?");

                     // buffer overflow (DOS attack ?)
                     AfxGetThread()->PostThreadMessage(WM_QUIT,,);
                 }
                 else
                 if (nRead != SOCKET_ERROR && nRead != )
                 {
                     // terminate the string
                     buff[nRead] = ;
                     m_RxBuffer += CString(buff);

                     GetCommandLine();
                 }
                 break;
         }
     }
     catch(...)
     {
         // something bad happened... (DOS attack?)
         ((CClientThread *)m_pThread)->PostStatusMessage("Exception occurred in CSocket::OnReceive()!");
         // close the connection.
         AfxGetThread()->PostThreadMessage(WM_QUIT,,);
     }
     CSocket::OnReceive(nErrorCode);
 }

　　这个函数就是读控制命令套接字及相应的错误处理。接收到的数据，保存在了m_RxBuffer中。接下来GetCommandLine函数解析接收到的数据。

　　2、GetCommandLine函数 解析命令数据

 void CControlSocket::GetCommandLine()
 {
     CString strTemp;
     int nIndex;

     while(!m_RxBuffer.IsEmpty())                //有接收到的数据待处理
     {
         nIndex = m_RxBuffer.Find("\r\n");       //找一条完整的命令的结束符
         if (nIndex != -)
         {
             strTemp = m_RxBuffer.Left(nIndex);  //将这条命令提取出来
             m_RxBuffer = m_RxBuffer.Mid(nIndex + ); //更新m_RxBuffer 去掉已经提取出来的命令
             if (!strTemp.IsEmpty())
             {
                 m_strCommands.AddTail(strTemp); //可能while循环中提取出多条命令，这里增加一个队列
                 // parse and execute command
                 ProcessCommand();               //去处理这些命令,如果直接处理命令的话，就没有上面m_strCommandsz这个队列缓冲了
             }
         }
         else
             break;
     }
 }

　　该有的解释已经在上面了。CString::Mid的函数与我记忆中的可能有些差别，特意查询下。CString CString ::Mid(int nFirst) const

　　返回值：返回一个包含指定范围字符的拷贝的CString对象。nFirst 此CString对象中的要被提取的子串的第一个字符的从零开始的索引。

　　4、ProcessCmd 解释这些命令，这个函数比较长，值得学习的也有很多。

 void CControlSocket::ProcessCommand()
 {
     CString strCommand, strArgs;

     // get command
     CString strBuff = m_strCommands.RemoveHead();   //得到第一条待解析的命令
     int nIndex = strBuff.Find(" ");                 //查找空格
     if (nIndex == -)
     {
         strCommand = strBuff;
     }
     else
     {
         strCommand = strBuff.Left(nIndex);          //这几行代码就是去掉命令语句里开始的空格（如果有）
         strArgs= strBuff.Mid(nIndex+);             //并将命令关键字和参数分离开来
     }
     strCommand.MakeUpper();                         //命令关键字全部转大写

     // log command
     ((CClientThread *)m_pThread)->PostStatusMessage(strCommand + " " + strArgs);   //在界面上打印收到的命令及参数

     if ((m_nStatus == STATUS_LOGIN) && (strCommand != "USER" && strCommand != "PASS"))  //这句话后面应该有错
     {                                                                              //应该是strArgs != "PASS"
         SendResponse("530 Please login with USER and PASS.");
         return;
     }

     // specify username
     if (strCommand == "USER")  //是USER命令
     {
         // only accept anonymous account
         if (strArgs.CompareNoCase(AfxGetApp()->GetProfileString("Settings", "userName", "sunrise")) == )
         {
             SendResponse("331 User name ok, need password.");
             m_strUserName = strArgs;   //保存登陆上来的用户名
         }
         else
             SendResponse("530 Not logged in. No such account.");
     }
     else
     // specify password
     if (strCommand == "PASS")  //是PASS命令
     {
         if (m_strUserName.IsEmpty())   //要先USER命令
         {
             SendResponse("503 Login with USER first.");
             return;
         }

         //密码是meng
         if (strArgs.CompareNoCase(AfxGetApp()->GetProfileString("Settings", "password", "meng")) != )
         {
             SendResponse("503 password is wrong.");
             return;
         }
         // login client
         m_strHomeDir = ((CServerDlg *)AfxGetApp()->m_pMainWnd)->m_strHomeDirectory;  //设置主目录
         m_strCurrentDir = m_strHomeDir;  //设置当前目录

         SendResponse("230 User logged in."); //回复登陆成功
         m_nStatus = STATUS_IDLE;         //修改状态
     }
     else
     // close connection
     if (strCommand == "QUIT")            //QUIT命令
     {
         // send goodbye message to client
         SendResponse("220 Goodbye.");

         Close();

         // tell our thread we have been closed
         AfxGetThread()->PostThreadMessage(WM_QUIT,,);
     }
     else
     // change transfer type
     if (strCommand == "TYPE")
     {
         SendResponse("200 Type set to %s.", strArgs);
     }
     else
     // print current directory
     if ((strCommand == "PWD") || (strCommand == "XPWD"))
     {
         CString strRelativePath;
         GetRelativePath(m_strCurrentDir, strRelativePath);  //获取当前目录
         SendResponse("257 \"%s\" is current directory.", strRelativePath);
     }
     else
     // change working directory
     if (strCommand == "CWD")
     {
         DoChangeDirectory(strArgs);  //更改路径
     }
     else
     // change to parent directory
     if (strCommand == "CDUP")
     {
         DoChangeDirectory("..");
     }
     else
     // specify IP and port (PORT a1,a2,a3,a4,p1,p2) -> IP address a1.a2.a3.a4, port p1*256+p2.
     if (strCommand == "PORT")       //在这里指定端口
     {
         CString strSub;
         int nCount=;

         while (AfxExtractSubString(strSub, strArgs, nCount++, ','))  //这里又提取了参数，这个命令是在干嘛
         {
             switch(nCount)
             {
                 case :    // a1
                     m_strRemoteHost = strSub;
                     m_strRemoteHost += ".";
                     break;
                 case :    // a2
                     m_strRemoteHost += strSub;
                     m_strRemoteHost += ".";
                     break;
                 case :    // a3
                     m_strRemoteHost += strSub;
                     m_strRemoteHost += ".";
                     break;
                 case :    // a4
                     m_strRemoteHost += strSub;
                     break;
                 case :    // p1
                     m_nRemotePort = *atoi(strSub);
                     break;
                 case :    // p2
                     m_nRemotePort += atoi(strSub);
                     break;
             }
         }
         SendResponse("200 Port command successful.");
     }
     else
     // list current directory (or a specified file/directory)
     if ((strCommand == "LIST") ||
         (strCommand == "NLST"))
     {
         StripParameters(strArgs);

         CString strResult;
         if (!GetDirectoryList(strArgs, strResult))
         {
             return;
         }

         SendResponse("150 Opening ASCII mode data connection for directory list."); 

         // create data connection with client
         if (CreateDataConnection())   //在这里就创建了数据套接字连接了
         {
             if (strResult.IsEmpty())
             {
                 // close data connection with client
                 DestroyDataConnection();

                 SendResponse("226 Transfer complete.");
                 m_nStatus = STATUS_IDLE;
                 return;
             }
         }
         else
         {
             // close data connection with client
             DestroyDataConnection();  //不成功则销毁
             return;
         }

         m_nStatus = STATUS_LIST;      //

         m_pDataSocket->AsyncSelect();        

         // send the listing
         m_pDataSocket->SendData(strResult);
     }
     else
     // retrieve file
     if (strCommand == "RETR")
     {
         if (((CServerDlg *)AfxGetApp()->m_pMainWnd)->m_bAllowDownload)
         {
             DoRetrieveFile(strArgs);
         }
         else
         {
             SendResponse("550 Permission denied.");
         }
     }
     else
     // client wants to upload file
     if (strCommand == "STOR")
     {
         if (((CServerDlg *)AfxGetApp()->m_pMainWnd)->m_bAllowUpload)
         {
             DoStoreFile(strArgs);
         }
         else
         {
             SendResponse("550 Permission denied.");
         }
     }
     else
     // delete file
     if (strCommand == "DELE")
     {
         if (((CServerDlg *)AfxGetApp()->m_pMainWnd)->m_bAllowDelete)
         {
             DoDeleteFile(strArgs);
         }
         else
         {
             SendResponse("550 Permission denied.");
         }
     }
     else
     // remove directory
     if ((strCommand == "RMD") || (strCommand == "XRMD"))
     {
         if (((CServerDlg *)AfxGetApp()->m_pMainWnd)->m_bAllowDelete)
         {
             DoDeleteDirectory(strArgs);
         }
         else
         {
             SendResponse("550 Permission denied.");
         }
     }
     else
     // create directory
     if ((strCommand == "MKD") || (strCommand == "XMKD"))
     {
         if (((CServerDlg *)AfxGetApp()->m_pMainWnd)->m_bAllowCreateDirectory)
         {
             DoCreateDirectory(strArgs);
         }
         else
         {
             SendResponse("550 Permission denied.");
         }
     }
     else
     // rename file or directory (part 1)
     if (strCommand == "RNFR")
     {
         if (((CServerDlg *)AfxGetApp()->m_pMainWnd)->m_bAllowRename)
         {
             DoRenameFrom(strArgs);
         }
         else
         {
             SendResponse("550 Permission denied.");
         }
     }
     else
     // rename file or directory (part 2)
     if (strCommand == "RNTO")
     {
         if (((CServerDlg *)AfxGetApp()->m_pMainWnd)->m_bAllowRename)
         {
             DoRenameTo(strArgs);
         }
         else
         {
             SendResponse("550 Permission denied.");
         }
     }
     else
     // restart transfer from 'x'
     if (strCommand == "REST")
     {
         m_dwRestartOffset = atol(strArgs);
         SendResponse("350 Restarting at %d.", m_dwRestartOffset);
     }
     else
     // get file size
     if (strCommand == "SIZE")
     {
         CString strLocalPath;
         GetLocalPath(strArgs, strLocalPath);

         // check if directory exists
         if (!FileExists(strLocalPath, FALSE))
         {
             SendResponse("550 File not found.");
             return;
         }
         CFileStatus status;
         CFile::GetStatus(strLocalPath, status);
         SendResponse("213 %d", status.m_size);
     }
     else
     // switch to passive mode
     if (strCommand == "PASV")
     {
         // delete existing datasocket
         DestroyDataConnection();

         // create new data socket
         m_pDataSocket = new CDataSocket(this);

         if (!m_pDataSocket->Create(gFixedDataPort))
         {
             DestroyDataConnection();
             SendResponse("421 Failed to create socket.");
             return;
         }
         // start listening
         m_pDataSocket->Listen();
         m_pDataSocket->AsyncSelect();

         CString strIP, strTmp;
         UINT nPort;

         // get our ip address
         GetSockName(strIP, nPort);
         // retrieve port
         m_pDataSocket->GetSockName(strTmp, nPort);
         // replace dots
         strIP.Replace(".", ",");
         // tell the client which address/port to connect to
         SendResponse("227 Entering Passive Mode (%s,%d,%d).", strIP, nPort/, nPort%);
         m_bPassiveMode = TRUE;
     }
     else
     // abort transfer
     if ((strCommand == "ABOR") || (strCommand.Right() == "ABOR"))
     {
         if (m_pDataSocket)
         {
             if (m_nStatus != STATUS_IDLE)
             {
                 SendResponse("426 Data connection closed.");
             }
             // destroy data connection
             m_pThread->PostThreadMessage(WM_DESTROYDATACONNECTION,  ,);
         }
         SendResponse("226 ABOR command successful.");
     }
     else
     // get system info
     if (strCommand == "SYST")
     {
         SendResponse("215 UNIX emulated by Baby FTP Server.");
     }
     else
     // dummy instruction
     if (strCommand == "NOOP")
     {
         SendResponse("200 NOOP command successful.");
     }
     else
     {
         SendResponse("502 Command not implemented.");
     }
 }

　　首先从命令行语句里拆分出命令关键字和参数。这里面的命令要是一个个列出来太长了。主要是要弄清楚FTP通信的流程，也就是这些命令的内在逻辑，等到具体开发某个功能的时候，再一一弄清楚就可以了。

　　 5、m_pDataSocket是CControlSocket中的成员变量，指向的是数据传输socket。在什么地方创建了CDataSocket呢，在LIST/NLIST命令中调用了 CreateDataConnection函数，这里创建了CDataSocket。然后在PASV命令里也创建了CDataSocket。这其实就是文件数据传输时的两种模式，前一种作为tcp客户端，后一种作为tcp服务器。下面是CreateDataConnect函数：

 BOOL CControlSocket::CreateDataConnection()
 {
     if (!m_bPassiveMode)
     {
         m_pDataSocket = new CDataSocket(this);
         if (m_pDataSocket->Create())
         {
             m_pDataSocket->AsyncSelect(FD_CONNECT | FD_CLOSE | FD_ACCEPT);
             // connect to remote site
             if (m_pDataSocket->Connect(m_strRemoteHost, m_nRemotePort) == )
             {
                 if (GetLastError() != WSAEWOULDBLOCK)
                 {
                     SendResponse("425 Can't open data connection.");
                     return FALSE;
                 }
             }
         }
         else
         {
             SendResponse("421 Failed to create data connection socket.");
             return FALSE;
         }
     }

     // wait until we're connected
     DWORD dwTickCount = GetTickCount() + ;
     while (!m_pDataSocket->m_bConnected)
     {
         DoEvents();
         if (dwTickCount < GetTickCount())
         {
             SendResponse("421 Failed to create data connection socket.");
             return FALSE;
         }
     }
     return TRUE;
 }

　　数据传输socket已tcp客户端的形式连接服务器，注意连接的端口和服务器ip。这两个参数都在参数PORT解析时被设置。