Global, thread safe, cookies manager with Indy

问题:

My Delphi 2010 app uploads stuff using multi-threading, uploaded data is POSTed to a PHP/web application which requires login, so I need to use a shared/global cookies manager (I'm using Indy10 Revision 4743) since TIdCookieManager is not thread-safe :(

Also, server side, session id is automatically re-generated every 5 minutes, so I must keep both the global & local cookie managers in sync.

My code looks like this:

TUploadThread = class(TThread)
// ...

var
   GlobalCookieManager : TIdCookieManager;

procedure TUploadThread.Upload(FileName : String);
var
   IdHTTP           : TIdHTTP;
   TheSSL           : TIdSSLIOHandlerSocketOpenSSL;
   TheCompressor    : TIdCompressorZLib;
   TheCookieManager : TIdCookieManager;
   AStream          : TIdMultipartFormDataStream;
begin
     ACookieManager := TIdCookieManager.Create(IdHTTP);

     // Automatically sync cookies between local & global Cookie managers
     @TheCookieManager.OnNewCookie := pPointer(Cardinal(pPointer( procedure(ASender : TObject; ACookie : TIdCookie; var VAccept : Boolean)
     begin
          OmniLock.Acquire;
          try
             GlobalCookieManager.CookieCollection.AddCookie(ACookie, TIdHTTP(TIdCookieManager(ASender).Owner).URL{IdHTTP.URL});
          finally
                  OmniLock.Release;
          end;    // try/finally

          VAccept := True;
     end )^ ) + $0C)^;
     // ======================================== //


     IdHTTP         := TIdHTTP.Create(nil);
     with IdHTTP do
     begin
          HTTPOptions     := [hoForceEncodeParams, hoNoParseMetaHTTPEquiv];
          AllowCookies    := True;
          HandleRedirects := True;
          ProtocolVersion := pv1_1;

          IOHandler       := TheSSL;
          Compressor      := TheCompressor;
          CookieManager   := TheCookieManager;
     end;    // with

     OmniLock.Acquire;
     try
        // Load login info/cookies
        TheCookieManager.CookieCollection.AddCookies(GlobalCookieManager.CookieCollection);
     finally
            OmniLock.Release;
     end;    // try/finally

     AStream         := TIdMultipartFormDataStream.Create;

     with Stream.AddFile('file_name', FileName, 'application/octet-stream') do
     begin
          HeaderCharset  := 'utf-8';
          HeaderEncoding := '8';
     end;    // with

     IdHTTP.Post('https://www.domain.com/post.php', AStream);
     AStream.Free;
end;

But it doesn't work! I'm getting this exception when calling AddCookies()

Project MyEXE.exe raised exception class EAccessViolation with message 'Access violation at address 00000000. Read of address 00000000'.

I also tried using assign(), ie.

 TheCookieManager.CookieCollection.Assign(GlobalCookieManager.CookieCollection);

But I still get the same exception, usually here:

 TIdCookieManager.GenerateClientCookies()

Anyone knows how to fix this?

回答1:

Responding to the comment:

Thank you guys, I converted to a normal method, but I'm still getting exceptions in AddCookies(), last one happened in the line that reads FRWLock.BeginWrite; in this procedure TIdCookies.LockCookieList(AAccessType: TIdCookieAccess): TIdCookieList;

If your error is an Access Violation with Read of address 00000000, that's got a very specific meaning. It means you're trying to do something with an object that's nil.

When you get that, break to the debugger. If the error's taking place on the line you said it's happening on, then it's almost certain that either Self or FRWLock is nil at this point. Check both variables and figure out which one hasn't been constructed yet, and that'll point you to the solution.

回答2:

Don't use an anonymous procedure for the OnNewCookie event. Use a normal class method instead:

procedure TUploadThread.NewCookie(ASender: TObject; ACookie : TIdCookie; var VAccept : Boolean);
var
  LCookie: TIdCookie;
begin
  LCookie := TIdCookieClass(ACookie.ClassType).Create;
  LCookie.Assign(ACookie);
  OmniLock.Acquire; 
  try 
    GlobalCookieManager.CookieCollection.AddCookie(LCookie, TIdHTTP(TIdCookieManager(ASender).Owner).URL); 
  finally 
    OmniLock.Release; 
  end;
  VAccept := True;
end;

Or:

procedure TUploadThread.NewCookie(ASender: TObject; ACookie : TIdCookie; var VAccept : Boolean);
begin
  OmniLock.Acquire; 
  try 
    GlobalCookieManager.CookieCollection.AddServerCookie(ACookie.ServerCookie, TIdHTTP(TIdCookieManager(ASender).Owner).URL); 
  finally 
    OmniLock.Release; 
  end;
  VAccept := True;
end;

Then use it like this:

procedure TUploadThread.Upload(FileName : String); 
var 
  IdHTTP           : TIdHTTP; 
  TheSSL           : TIdSSLIOHandlerSocketOpenSSL; 
  TheCompressor    : TIdCompressorZLib; 
  TheCookieManager : TIdCookieManager; 
  TheStream        : TIdMultipartFormDataStream; 
begin 
  IdHTTP := TIdHTTP.Create(nil); 
  try
    ...
    TheCookieManager := TIdCookieManager.Create(IdHTTP); 
    TheCookieManager.OnNewCookie := NewCookie;

    with IdHTTP do 
    begin 
      HTTPOptions     := [hoForceEncodeParams, hoNoParseMetaHTTPEquiv]; 
      AllowCookies    := True; 
      HandleRedirects := True; 
      ProtocolVersion := pv1_1; 

      IOHandler       := TheSSL; 
      Compressor      := TheCompressor; 
      CookieManager   := TheCookieManager; 
    end;    // with 

    OmniLock.Acquire; 
    try 
      // Load login info/cookies 
      TheCookieManager.CookieCollection.AddCookies(GlobalCookieManager.CookieCollection); 
    finally 
      OmniLock.Release; 
    end;

    TheStream := TIdMultipartFormDataStream.Create; 
    try
      with TheStream.AddFile('file_name', FileName, 'application/octet-stream') do 
      begin 
        HeaderCharset  := 'utf-8'; 
        HeaderEncoding := '8'; 
      end;

      IdHTTP.Post('https://www.domain.com/post.php', TheStream); 
    finally
      TheStream.Free; 
    end;
  finally
    IdHTTP.Free;
  end;
end; 

回答3:

If I had to guess, I'd say your problem is in here somewhere:

 // Automatically sync cookies between local & global Cookie managers
 @TheCookieManager.OnNewCookie := pPointer(Cardinal(pPointer( procedure(ASender : TObject; ACookie : TIdCookie; var VAccept : Boolean)
 begin
      OmniLock.Acquire;
      try
         GlobalCookieManager.CookieCollection.AddCookie(ACookie, TIdHTTP(TIdCookieManager(ASender).Owner).URL{IdHTTP.URL});
      finally
              OmniLock.Release;
      end;    // try/finally

      VAccept := True;
 end )^ ) + $0C)^;

I'm not sure what the $0C magic number is there for, but I bet all those casts are there because you had a heck of a time getting the compiler to accept this. It gave you type errors saying you couldn't assign the one thing to the other.

Those type errors are there for a reason! If you hack your way around the type system, things are very likely to break. Try turning that anonymous method into a normal method on TUploadThread and assign it that way, and see if it doesn't work better.