URLDownlloadToFile How to clear Cache First?

If you have a .php (or some other file) that throws the binary file for download put these headers:

<?php
header('Cache-Control: no-cache, no-store, must-revalidate'); //HTTP/1.1
header('Expires: Sun, 01 Jul 2005 00:00:00 GMT');
header('Pragma: no-cache'); //HTTP/1.0
?>

This should force the download from the server and skip the cache.

The flags I am posting do not work with UrlDownloadToFile (router trace shows no difference), but in using UrlDownloadToCacheFile they do work (since v4.01 sp2 of Internet explorer). By passing the flag BINDF_GETNEWESTVERSION you can force the url handling to recheck the site for a newer version, vs reading the data from the cache. More info can be obtained here:

http://support.microsoft.com/kb/q196466/

Below is an example of using the URLDownloadToCacheFile function. The only real difference is that the function gives you the file name instead of you specifying one. (But you could always use CopyFile to move it.). And because you get back the cache file name, you can delete it using DeleteFile, etc if you wanted.

Regards,
Russell


const
  BINDF_ASYNCHRONOUS            = $00000001;
  BINDF_ASYNCSTORAGE            = $00000002;
  BINDF_NOPROGRESSIVERENDERING  = $00000004;
  BINDF_OFFLINEOPERATION        = $00000008;
  BINDF_GETNEWESTVERSION        = $00000010;
  BINDF_NOWRITECACHE            = $00000020;
  BINDF_NEEDFILE                = $00000040;
  BINDF_PULLDATA                = $00000080;
  BINDF_IGNORESECURITYPROBLEM   = $00000100;
  BINDF_RESYNCHRONIZE           = $00000200;
  BINDF_HYPERLINK               = $00000400;
  BINDF_NO_UI                   = $00000800;
  BINDF_SILENTOPERATION         = $00001000;
  BINDF_PRAGMA_NO_CACHE         = $00002000;
  BINDF_GETCLASSOBJECT          = $00004000;
  BINDF_RESERVED_1              = $00008000;
  BINDF_FREE_THREADED           = $00010000;
  BINDF_DIRECT_READ             = $00020000;
  BINDF_FORMS_SUBMIT            = $00040000;
  BINDF_GETFROMCACHE_IF_NET_FAIL= $00080000;
  BINDF_FROMURLMON              = $00100000;
  BINDF_FWD_BACK                = $00200000;
  BINDF_PREFERDEFAULTHANDLER    = $00400000;
  BINDF_RESERVED_3              = $00800000;

procedure TForm1.Button2Click(Sender: TObject);
var  dwMark:        LongWord;
     bSuccess:      Boolean;
     lpszFile:      Array [0..MAX_PATH] of Char;
begin

  dwMark:=GetTickCount;
  try
     // With this version, the file will get pulled from cache
     // bSuccess:=(URLDownloadToCacheFile(nil, 'http://www.yahoo.com', @lpszFile, MAX_PATH, 0, nil) = S_OK);
     //
     // This version re-checks the site for a newer version
     bSuccess:=(URLDownloadToCacheFile(nil, 'http://www.yahoo.com', @lpszFile, MAX_PATH, BINDF_GETNEWESTVERSION, nil) = S_OK);
  finally
     dwMark:=GetTickCount-dwMark;
  end;
  ShowMessage(Format('Download completed with value %d in %d ms', [Ord(bSuccess), dwMark]));
  if bSuccess then
     ShowMessage(Format('Your bits are located in the following file: %s', [lpszFile]));

end;

Hello,

I've tried to use the following:

URLDownloadToFile(nil,
                     'http://www.mysite.com/updates/program.exe',
                     Pchar(ExtractFilePath(application.Exename)+'program.exe'),
                     BINDF_GETNEWESTVERSION , bsc);

should not give the same result?
But the file is not downloaded again :(

any idea?

Hi Ivanov,

but then how do I push the file back to the client? ...

Thx!
Dave

For example like this:

<?php
  header('Cache-Control: no-cache, no-store, must-revalidate'); //HTTP/1.1
  header('Expires: Sun, 01 Jul 2005 00:00:00 GMT');
  header('Pragma: no-cache'); //HTTP/1.0

  // We'll be outputting a PDF
  header('Content-type: application/pdf');

  // It will be called downloaded.pdf
  header('Content-Disposition: attachment; filename="downloaded.pdf"');

  // The PDF source is in original.pdf
  readfile('original.pdf');
?>

What part of this:

>> The flags I am posting do not work with UrlDownloadToFile (router trace shows no difference), but in using UrlDownloadToCacheFile they do work (since v4.01 sp2 of Internet explorer).

did you not understand? Let me rephrase it; you MUST use UrlDownloadToCacheFile because the flags DO NOT WORK with UrlDownloadToFile

Russell

It works! Thank you!