使用套接字编写的 POP3 客户端

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引言

本文提供了一个关于如何从任何服务器检索邮件的简单思路。

背景

POP3协议用于允许工作站检索服务器为其保存的邮件。最初，服务器主机通过监听TCP端口110启动POP3服务。当客户端主机希望使用该服务时，它与服务器主机建立TCP连接。连接建立后，POP3服务器发送问候语。

使用代码

代码的工作方式如下：一旦与服务器建立连接，服务器就会验证用户名和密码，然后检索邮件。POP3协议有一些命令，用于身份验证和检索邮件。以下是使用各种命令检索邮件的函数。 1.CONNECT 用于连接到服务器。 2.USER 用于验证用户名。 3.PASS 用于验证密码。 4.STAT 用于获取消息数量。 5.QUIT 用于断开与服务器的连接。

void Tapp::ProcessPop3Commands(enum eCommands pCommand,HWND pHwnd) 
{ 
    switch(pCommand) { 
    
    case CONNECT: 
 
        char* address;               ///<CONTAINS span server.< the of address> 
        char* portno;                ///<CONTAINS span server.< the of no port> 
 
        //handles the submission of the details into the list box on clicking submit  
        address=vWin.RetrieveText(GetDlgItem(pHwnd,IDC_EDITBOX3)); 
        portno=vWin.RetrieveText(GetDlgItem(pHwnd,IDC_EDITBOX4)); 
 
        if(vPop.MakeConnection(address,portno)==TRUE){    
 
 
            //frees the memory allocated for address. 
            free(address); 
 
            //frees the memory allocated for portno. 
            free(portno); 
 
            //retrieves the information from the server. 
            vPop.RecvInfoFromServer();  
 
            //ADD THE RETRIEVED TEXT TO THE LIST BOX  
            MessageBox(pHwnd, vPop.Getresponse(), "Message",MB_OK); 
            //sets the command as USER. 
            pCommand=USER; 
        }else{ 
 
            //frees the memory allocated for address. 
            free(address); 
            //frees the memory allocated for portno. 
            free(portno); 
 
            break; 
        } 
 
    case USER: 
 
        { 
              char   *username;            ///<CONTAINS span the of user< name> 
 
               username=vWin.RetrieveText(GetDlgItem(pHwnd,IDC_EDITBOX1)); 
               if(vPop.SendInformation("USER",username,pHwnd)==TRUE){ 
 
                //frees the memory allocated for username. 
                free(username); 
                //sets the command as PASS. 
                pCommand=PASS; 
            }else{ 
                 
                //frees the memory allocated for username. 
                free(username); 
                //sets the command as QUIT 
                pCommand=QUIT; 
            } 
        } 
 
    case PASS: 
 
        { 
               char   *password;            ///<CONTAINS span the password. 
 
            password=vWin.RetrieveText(GetDlgItem(pHwnd,IDC_EDITBOX2)); 
 
            if(vPop.SendInformation("PASS",password,pHwnd)==TRUE){ 
 
                //frees the memory allocated for password. 
                free(password); 
                //sets the command as STAT. 
                pCommand=STAT; 
            }else{ 
 
                //frees the memory allocated for password. 
                free(password); 
                //sets the command as QUIT. 
                pCommand=QUIT; 
            } 
        } 
 
    case STAT: 
 
        if(vPop.SendInformation("STAT"," ",pHwnd)==TRUE){ 
             
            break; 
        }else{ 
            //sets the command as QUIT. 
            pCommand=QUIT; 
 
        } 
   
    case QUIT: 
 
        if(MessageBox(pHwnd,vPop.Getresponse(), "Message",MB_OK)==IDOK){ 
            vPop.CloseSocket(); 
        } 
        break; 
   
        } 
     
    }