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    筆者在編寫一個上網(wǎng)計費(fèi)軟件時，涉及到如何對局域網(wǎng)中各工作站上網(wǎng)計費(fèi)問題。一般來講，這些工作站通過代理服務(wù)器上網(wǎng)，而采用現(xiàn)成的代理服務(wù)器軟件時，由于代理服務(wù)器軟件是封閉的系統(tǒng)，很難編寫程序獲取實時的上網(wǎng)計時信息。因此，考慮是否能編寫自己的代理服務(wù)器，一方面解決群體上網(wǎng)，另一方面又解決上網(wǎng)的計費(fèi)問題呢？
    經(jīng)過實驗性編程，終于圓滿地解決了該問題。現(xiàn)寫出來，與各位同行分享。

1、思路
當(dāng)前流行的瀏覽器的系統(tǒng)選項中有一個參數(shù)，即“通過代理服務(wù)器連接”，經(jīng)過編程測
試，當(dāng)局域網(wǎng)中一臺工作站指定了該屬性，再發(fā)出Internet請求時，請求數(shù)據(jù)將發(fā)送到所指定的代理服務(wù)器上，以下為請求數(shù)據(jù)包示例：
                 GET http://home.microsoft.com/intl/cn/ HTTP/1.0
                 Accept: */*
                 Accept-Language: zh-cn
                 Accept-Encoding: gzip, deflate
                 User-Agent: Mozilla/4.0 (compatible; MSIE 5.0; Windows NT)
                 Host: home.microsoft.com
                 Proxy-Connection: Keep-Alive
其中第一行為目標(biāo)URL及相關(guān)方法、協(xié)議，“Host”行指定了目標(biāo)主機(jī)的地址。
由此知道了代理服務(wù)的過程：接收被代理端的請求、連接真正的主機(jī)、接收主機(jī)返回的數(shù)據(jù)、將接收數(shù)據(jù)發(fā)送到被代理端。
為此可編寫一個簡單的程序，完成上述網(wǎng)絡(luò)通信重定向問題。
用Delphi設(shè)計時，選用ServerSocket作為與被代理工作站通信的套接字控件，選用ClientSocket動態(tài)數(shù)組作為與遠(yuǎn)程主機(jī)通信的套接字控件。
編程時應(yīng)解決的一個重要問題是多重連接處理問題，為了加快代理服務(wù)的速度和被代理端的響應(yīng)速度，套接字控件的屬性應(yīng)設(shè)為非阻塞型；各通信會話與套接字動態(tài)綁定，用套接字的SocketHandle屬性值確定屬于哪一個會話。
通信的銜接過程如下圖所示：

                                  代理服務(wù)器

                                  Serversocket
                        (1)          接  收
         被代理端                   發(fā)  送                        遠(yuǎn)程主機(jī)
                        (6)        (2)      (5)
         Browser                  ClientSocket       (4)            Web Server
                                    接  收
                                    發(fā)  送          (3)

（1）、被代理端瀏覽器發(fā)出Web請求，代理服務(wù)器的Serversocket接收到請求。
（2）、代理服務(wù)器程序自動創(chuàng)建一個ClientSocket，并設(shè)置主機(jī)地址、端口等屬性，然后連接遠(yuǎn)程主機(jī)。
（3）、遠(yuǎn)程連通后激發(fā)發(fā)送事件，將Serversocket接收到的Web請求數(shù)據(jù)包發(fā)送到遠(yuǎn)程主機(jī)。
（4）、當(dāng)遠(yuǎn)程主機(jī)返回頁面數(shù)據(jù)時，激發(fā)ClientSocket的讀事件，讀取頁面數(shù)據(jù)。
（5）、代理服務(wù)器程序根據(jù)綁定信息確定屬于ServerSocket控件中的哪一個Socket應(yīng)該將從主機(jī)接收的頁面信息發(fā)送到被代理端。
（6）、ServerSocket中的對應(yīng)Socket將頁面數(shù)據(jù)發(fā)送到被代理端。

2、程序編寫
使用Delphi設(shè)計以上通信過程非常簡單，主要是ServerSocket、ClientSocket的相關(guān)事
件驅(qū)動程序的程序編寫。下面給出作者編寫的實驗用代理服務(wù)器界面與源程序清單，內(nèi)含簡要功能說明：

unit main;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  ExtCtrls, ScktComp, TrayIcon, Menus, StdCtrls;

type
   session_record=record
      Used: boolean;                       {會話記錄是否可用}
      SS_Handle: integer;                  {代理服務(wù)器套接字句柄}
      CSocket: TClientSocket;              {用于連接遠(yuǎn)程的套接字}
      Lookingup: boolean;                  {是否正在查找服務(wù)器}
      LookupTime: integer;                 {查找服務(wù)器時間}
      Request: boolean;                    {是否有請求}
      request_str: string;                 {請求數(shù)據(jù)塊}
      client_connected: boolean;           {客戶機(jī)聯(lián)機(jī)標(biāo)志}
      remote_connected: boolean;           {遠(yuǎn)程服務(wù)器連接標(biāo)志}
end;

type
  TForm1 = class(TForm)
    ServerSocket1: TServerSocket;
    ClientSocket1: TClientSocket;
    Timer2: TTimer;
    TrayIcon1: TTrayIcon;
    PopupMenu1: TPopupMenu;
    N11: TMenuItem;
    N21: TMenuItem;
    N1: TMenuItem;
    N01: TMenuItem;
    Memo1: TMemo;
    Edit1: TEdit;
    Label1: TLabel;
    Timer1: TTimer;
    procedure Timer2Timer(Sender: TObject);
    procedure N11Click(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure FormClose(Sender: TObject; var Action: TCloseAction);
    procedure N21Click(Sender: TObject);
    procedure N01Click(Sender: TObject);
    procedure ServerSocket1ClientConnect(Sender: TObject;
      Socket: TCustomWinSocket);
    procedure ServerSocket1ClientDisconnect(Sender: TObject;
      Socket: TCustomWinSocket);
    procedure ServerSocket1ClientError(Sender: TObject;
      Socket: TCustomWinSocket; ErrorEvent: TErrorEvent;
      var ErrorCode: Integer);
    procedure ServerSocket1ClientRead(Sender: TObject;
      Socket: TCustomWinSocket);
    procedure ClientSocket1Connect(Sender: TObject;
      Socket: TCustomWinSocket);
    procedure ClientSocket1Disconnect(Sender: TObject;
      Socket: TCustomWinSocket);
    procedure ClientSocket1Error(Sender: TObject; Socket: TCustomWinSocket;
      ErrorEvent: TErrorEvent; var ErrorCode: Integer);
    procedure ClientSocket1Write(Sender: TObject;
      Socket: TCustomWinSocket);
    procedure ClientSocket1Read(Sender: TObject; Socket: TCustomWinSocket);
    procedure ServerSocket1Listen(Sender: TObject;
      Socket: TCustomWinSocket);
    procedure AppException(Sender: TObject; E: Exception);
    procedure Timer1Timer(Sender: TObject);
  private
    { Private declarations }
  public
    Service_Enabled: boolean;           {代理服務(wù)是否開啟}
    session: array of session_record;      {會話數(shù)組}
    sessions: integer;                  {會話數(shù)}
    LookUpTimeOut: integer;           {連接超時值}
    InvalidRequests: integer;            {無效請求數(shù)}
  end;

var
  Form1: TForm1;

implementation

{$R *.DFM}

file://系統(tǒng)啟動定時器，啟動窗顯示完成后，縮小到System Tray…
procedure TForm1.Timer2Timer(Sender: TObject);
begin
   timer2.Enabled:=false;     {關(guān)閉定時器}
   sessions:=0;               {會話數(shù)=0}
   Application.OnException := AppException;     {為了屏蔽代理服務(wù)器出現(xiàn)的異常}
   invalidRequests:=0;           {0錯誤}
   LookUpTimeOut:=60000;      {超時值=1分鐘}
   timer1.Enabled:=true;         {打開定時器}
   n11.Enabled:=false;           {開啟服務(wù)菜單項失效}
   n21.Enabled:=true;           {關(guān)閉服務(wù)菜單項有效}
   serversocket1.Port:=988;      {代理服務(wù)器端口=988}
   serversocket1.Active:=true;    {開啟服務(wù)}
   form1.hide;                 {隱藏界面，縮小到System Tray上}
end;

file://開啟服務(wù)菜單項…
procedure TForm1.N11Click(Sender: TObject);
begin
   serversocket1.Active:=true;    {開啟服務(wù)}
end;

file://停止服務(wù)菜單項…
procedure TForm1.N21Click(Sender: TObject);
begin
   serversocket1.Active:=false;      {停止服務(wù)}
   N11.Enabled:=True;
   N21.Enabled:=False;
   Service_Enabled:=false;           {標(biāo)志清零}
end;

file://主窗口建立…
procedure TForm1.FormCreate(Sender: TObject);
begin
   Service_Enabled:=false;
   timer2.Enabled:=true;        {窗口建立時，打開定時器}
end;

file://窗口關(guān)閉時…
procedure TForm1.FormClose(Sender: TObject; var Action: TCloseAction);
begin
   timer1.Enabled:=false;          {關(guān)閉定時器}
   if Service_Enabled then
      serversocket1.Active:=false;   {退出程序時關(guān)閉服務(wù)}
end;

file://退出程序按鈕…
procedure TForm1.N01Click(Sender: TObject);
begin
   form1.Close;                     {退出程序}
end;

file://開啟代理服務(wù)后…
procedure TForm1.ServerSocket1Listen(Sender: TObject;
  Socket: TCustomWinSocket);
begin
   Service_Enabled:=true;            {置正在服務(wù)標(biāo)志}
   N11.Enabled:=false;
   N21.Enabled:=true;
end;

file://被代理端連接到代理服務(wù)器后，建立一個會話，并與套接字綁定…
procedure TForm1.ServerSocket1ClientConnect(Sender: TObject;
  Socket: TCustomWinSocket);
var
i,j: integer;
begin
   j:=-1;
   for i:=1 to sessions do               {查找是否有空白項}
      if not session[i-1].Used and not session[i-1].CSocket.active then
         begin
            j:=i-1;                      {有，分配它}
            session[j].Used:=true;       {置為在用}
            break;
         end
      else
         if not session[i-1].Used and session[i-1].CSocket.active then
               session[i-1].CSocket.active:=false;
   if j=-1 then
      begin                              {無，新增一個}
         j:=sessions;
         inc(sessions);
         setlength(session,sessions);
         session[j].Used:=true;                        {置為在用}
         session[j].CSocket:=TClientSocket.Create(nil);
         session[j].CSocket.OnConnect:=ClientSocket1Connect;
         session[j].CSocket.OnDisconnect:=ClientSocket1Disconnect;
         session[j].CSocket.OnError:=ClientSocket1Error;
         session[j].CSocket.OnRead:=ClientSocket1Read;
         session[j].CSocket.OnWrite:=ClientSocket1Write;
         session[j].Lookingup:=false;
      end;
   session[j].SS_Handle:=socket.socketHandle;    {保存句柄，實現(xiàn)綁定}
   session[j].Request:=false;                    {無請求}
   session[j].client_connected:=true;            {客戶機(jī)已連接}
   session[j].remote_connected:=false;           {遠(yuǎn)程未連接}
   edit1.text:=inttostr(sessions);
end;

file://被代理端斷開時…
procedure TForm1.ServerSocket1ClientDisconnect(Sender: TObject;
  Socket: TCustomWinSocket);
var
i,j,k: integer;
begin
   for i:=1 to sessions do
      if (session[i-1].SS_Handle=socket.SocketHandle) and session[i-1].Used then
         begin
            session[i-1].client_connected:=false;   {客戶機(jī)未連接}
            if session[i-1].remote_connected then
               session[i-1].CSocket.active:=false   {假如遠(yuǎn)程尚連接，斷開它}
            else
               session[i-1].Used:=false;           {假如兩者都斷開，則置釋放資源標(biāo)志}
            break;
         end;
   j:=sessions;
   k:=0;
   for i:=1 to j do                        {統(tǒng)計會話數(shù)組尾部有幾個未用項}
      begin
         if session[j-i].Used then
            break;
         inc(k);
      end;
   if k>0 then                          {修正會話數(shù)組，釋放尾部未用項}
      begin
         sessions:=sessions-k;
         setlength(session,sessions);
      end;
   edit1.text:=inttostr(sessions);
end;

file://通信錯誤出現(xiàn)時…
procedure TForm1.ServerSocket1ClientError(Sender: TObject;
  Socket: TCustomWinSocket; ErrorEvent: TErrorEvent;
  var ErrorCode: Integer);
var
i,j,k: integer;
begin
   for i:=1 to sessions do
      if (session[i-1].SS_Handle=socket.SocketHandle) and session[i-1].Used then
         begin
            session[i-1].client_connected:=false;   {客戶機(jī)未連接}
            if session[i-1].remote_connected then
               session[i-1].CSocket.active:=false   {假如遠(yuǎn)程尚連接，斷開它}
            else
               session[i-1].Used:=false;           {假如兩者都斷開，則置釋放資源標(biāo)志}
            break;
         end;
   j:=sessions;
   k:=0;
   for i:=1 to j do
      begin
         if session[j-i].Used then
            break;
         inc(k);
      end;
   if k>0 then
      begin
         sessions:=sessions-k;
         setlength(session,sessions);
      end;
   edit1.text:=inttostr(sessions);
   errorcode:=0;
end;

file://被代理端發(fā)送來頁面請求時…
procedure TForm1.ServerSocket1ClientRead(Sender: TObject;
  Socket: TCustomWinSocket);
var
tmp,line,host: string;
i,j,port: integer;
begin
   for i:=1 to sessions do                 {判斷是哪一個會話}
      if session[i-1].Used and (session[i-1].SS_Handle=socket.sockethandle) then
          begin
             session[i-1].request_str:=socket.ReceiveText;  {保存請求數(shù)據(jù)}
             tmp:=session[i-1].request_str;                 {存放到臨時變量}
             memo1.lines.add(tmp);
             j:=pos(char(13)+char(10),tmp);                 {一行標(biāo)志}
             while j>0 do                       {逐行掃描請求文本，查找主機(jī)地址}
                begin
                   line:=copy(tmp,1,j-1);                  {取一行}
                   delete(tmp,1,j+1);                      {刪除一行}
                   j:=pos('Host',line);                    {主機(jī)地址標(biāo)志}
                   if j>0 then
                      begin
                         delete(line,1,j+5);               {刪除前面的無效字符}
                         j:=pos(':',line);
                         if j>0 then
                            begin
                               host:=copy(line,1,j-1);
                               delete(line,1,j);
                               try
                                  port:=strtoint(line);
                               except
                                  port:=80;
                               end;
                            end
                         else
                            begin
                               host:=trim(line);                 {獲取主機(jī)地址}
                               port:=80;
                            end;
                         if not session[i-1].remote_connected then  {假如遠(yuǎn)征尚未連接}
                            begin
                               session[i-1].Request:=true;      {置請求數(shù)據(jù)就緒標(biāo)志}
                               session[i-1].CSocket.host:=host;  {設(shè)置遠(yuǎn)程主機(jī)地址}
                               session[i-1].CSocket.port:=port;     {設(shè)置端口}
                               session[i-1].CSocket.active:=true;   {連接遠(yuǎn)程主機(jī)}
                               session[i-1].Lookingup:=true;        {置標(biāo)志}
                               session[i-1].LookupTime:=0;          {從0開始計時}
                            end
                         else
                            {假如遠(yuǎn)程已連接，直接發(fā)送請求}
                            session[i-1].CSocket.socket.sendtext(session[i-1].request_str);
                         break;                        {停止掃描請求文本}
                      end;
                   j:=pos(char(13)+char(10),tmp);           {指向下一行}
                end;
             break;                    {停止循環(huán)}
          end;
end;

file://當(dāng)連接遠(yuǎn)程主機(jī)成功時…
procedure TForm1.ClientSocket1Connect(Sender: TObject;
  Socket: TCustomWinSocket);
var
i: integer;
begin
   for i:=1 to sessions do
      if (session[i-1].CSocket.socket.sockethandle=socket.SocketHandle) and session[i-1].Used then
         begin
            session[i-1].CSocket.tag:=socket.SocketHandle;
            session[i-1].remote_connected:=true;   {置遠(yuǎn)程主機(jī)已連通標(biāo)志}
            session[i-1].Lookingup:=false;         {清標(biāo)志}
            break;
         end;
end;

file://當(dāng)遠(yuǎn)程主機(jī)斷開時…
procedure TForm1.ClientSocket1Disconnect(Sender: TObject;
  Socket: TCustomWinSocket);
var
i,j,k: integer;
begin
   for i:=1 to sessions do
      if (session[i-1].CSocket.tag=socket.SocketHandle) and session[i-1].Used then
         begin
            session[i-1].remote_connected:=false;       {置為未連接}
            if not session[i-1].client_connected then
               session[i-1].Used:=false       {假如客戶機(jī)已斷開，則置釋放資源標(biāo)志}
            else
               for k:=1 to serversocket1.Socket.ActiveConnections do
                  if (serversocket1.Socket.Connections[k-1].SocketHandle=session[i-1].SS_Handle) and session[i-1].used then
                     begin
                        serversocket1.Socket.Connections[k-1].Close;
                        break;
                     end;
            break;
         end;
   j:=sessions;
   k:=0;
   for i:=1 to j do
      begin
         if session[j-i].Used then
            break;
         inc(k);
      end;
   if k>0 then                        {修正會話數(shù)組}
      begin
         sessions:=sessions-k;
         setlength(session,sessions);
      end;
   edit1.text:=inttostr(sessions);
end;

file://當(dāng)與遠(yuǎn)程主機(jī)通信發(fā)生錯誤時…
procedure TForm1.ClientSocket1Error(Sender: TObject;
  Socket: TCustomWinSocket; ErrorEvent: TErrorEvent;
  var ErrorCode: Integer);
var
i,j,k: integer;
begin
   for i:=1 to sessions do
      if (session[i-1].CSocket.tag=socket.SocketHandle) and session[i-1].Used then
         begin
            socket.close;
            session[i-1].remote_connected:=false;       {置為未連接}
            if not session[i-1].client_connected then
               session[i-1].Used:=false        {假如客戶機(jī)已斷開，則置釋放資源標(biāo)志}
            else
               for k:=1 to serversocket1.Socket.ActiveConnections do
                  if (serversocket1.Socket.Connections[k-1].SocketHandle=session[i-1].SS_Handle) and session[i-1].used then
                     begin
                        serversocket1.Socket.Connections[k-1].Close;
                        break;
                     end;
            break;
         end;
   j:=sessions;
   k:=0;
   for i:=1 to j do
      begin
         if session[j-i].Used then
            break;
         inc(k);
      end;
   errorcode:=0;
   if k>0 then                        {修正會話數(shù)組}
      begin
         sessions:=sessions-k;
         setlength(session,sessions);
      end;
   edit1.text:=inttostr(sessions);
end;

file://向遠(yuǎn)程主機(jī)發(fā)送頁面請求…
procedure TForm1.ClientSocket1Write(Sender: TObject;
  Socket: TCustomWinSocket);
var
i: integer;
begin
   for i:=1 to sessions do
      if (session[i-1].CSocket.tag=socket.SocketHandle) and session[i-1].Used then
         begin
            if session[i-1].Request then
               begin
                  socket.SendText(session[i-1].request_str);   {假如有請求，發(fā)送}
                  session[i-1].Request:=false;                 {清標(biāo)志}
               end;
            break;
         end;
end;

file://遠(yuǎn)程主機(jī)發(fā)來頁面數(shù)據(jù)時…
procedure TForm1.ClientSocket1Read(Sender: TObject;
  Socket: TCustomWinSocket);
var
i,j: integer;
rec_bytes: integer;                  {傳回的數(shù)據(jù)塊長度}
rec_Buffer: array[0..2047] of char;  {傳回的數(shù)據(jù)塊緩沖區(qū)}
begin
   for i:=1 to sessions do
      if (session[i-1].CSocket.tag=socket.SocketHandle) and session[i-1].Used then
         begin
            rec_bytes:=socket.ReceiveBuf(rec_buffer,2048);    {接收數(shù)據(jù)}
            for j:=1 to serversocket1.Socket.ActiveConnections do
               if serversocket1.Socket.Connections[j-1].SocketHandle=session[i-1].SS_Handle then
                  begin
                     serversocket1.Socket.Connections[j-1].SendBuf(rec_buffer,rec_bytes);  {發(fā)送數(shù)據(jù)}
                     break;
                  end;
            break;
         end;
end;

file://“頁面找不到”等錯誤信息出現(xiàn)時…
procedure TForm1.AppException(Sender: TObject; E: Exception);
begin
  inc(invalidrequests);
end;

file://查找遠(yuǎn)程主機(jī)定時…
procedure TForm1.Timer1Timer(Sender: TObject);
var
i,j: integer;
begin
   for i:=1 to sessions do
      if session[i-1].Used and session[i-1].Lookingup then    {假如正在連接}
         begin
            inc(session[i-1].LookupTime);
            if session[i-1].LookupTime>lookuptimeout then     {假如超時}
               begin
                  session[i-1].Lookingup:=false;
                  session[i-1].CSocket.active:=false;         {停止查找}
                  for j:=1 to serversocket1.Socket.ActiveConnections do
                     if serversocket1.Socket.Connections[j-1].SocketHandle=session[i-1].SS_Handle then
                        begin
                           serversocket1.Socket.Connections[j-1].Close;  {斷開客戶機(jī)}
                           break;
                        end;
               end;
         end;
end;
end.

3、后記
由于這種設(shè)計思路僅僅在被代理端和遠(yuǎn)程主機(jī)之間增加了一個重定向功能，被代理端原
有的緩存技術(shù)等特點均保留，因此效率較高。經(jīng)過測試，利用1個33.6K的Modem上網(wǎng)時，三到十個被代理工作站同時上網(wǎng)，仍有較好的響應(yīng)速度。由于被代理工作站和代理服務(wù)器工作站之間的連接一般通過高速鏈路，因此瓶頸主要出現(xiàn)在代理服務(wù)器的上網(wǎng)方式上。
通過上述方法，作者成功開發(fā)了一套完善的代理服務(wù)器軟件并與機(jī)房計費(fèi)系統(tǒng)完全集
成，實現(xiàn)了利用一臺工作站完成上網(wǎng)代理、上網(wǎng)計費(fèi)、用機(jī)計費(fèi)等功能。有編程經(jīng)驗的朋友完全可以另行增加代理服務(wù)器功能，如設(shè)定禁止訪問站點、統(tǒng)計客戶流量、Web訪問列表等等。

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