PHP: read and present a PDF file to download via PHP is generating corrupted files in some cases

I am using the following to read and present a PDF file to the user:

$file='file.pdf';
$filepath="/path-to-download-folder/$file";
if(!is_file($filepath)) die('Ops!');
$f=fopen($filepath,'r');
if($f){
    header('Cache-Control: no-store, no-cache, must-revalidate');
    header('Content-Type: '.mime_content_type($filepath));
    header('Content-Length: '.filesize($filepath));
    header('Content-Disposition: attachment; filename="'.$file.'"');
    fpassthru($f);
}else die("Ops!");
fclose($f);

However some folks are reporting that the PDF file is corrupted when they try to open it.

Am I doing something wrong or forgetting some important header? Is there a better way to achieve the same?

UPDATE:

I sent the PDF file via email and the users got to open the file. So it must be something with the way PHP and Nginx are serving the file.

So I turned off gzip on Nginx but the error continues.

I also applied the tips bellow so the code is now like this:

$file='file.pdf';
$filepath="/path-to-download-folder/$file";

if(!file_exists($filepath)){
  header('HTTP/1.1 404 Not Found');
  exit;
}elseif(!is_file($filepath) or !is_readable($filepath)){
  header('HTTP/1.1 403 Forbidden');
  exit;
}else{
    header('Cache-Control: no-store, no-cache, must-revalidate');
    header('Content-Type: '.mime_content_type($filepath));
    header('Content-Length: '.filesize($filepath));
    header('Content-Disposition: attachment; filename="'.$file.'"');

    set_time_limit(0); // Big files/slow connections may result in incomplete downloads
    readfile($filepath);
    die;
}

However I still am receiving this error: http://mlkshk.com/r/8FGS

UPDATE:

I made a diff among the files:

compare -verbose -debug coder Dicas1.pdf Dicas1A.pdf -compose src OUT.tmp

With this output:

"gs" -q -dQUIET -dPARAN开发者_开发百科OIDSAFER -dBATCH -dNOPAUSE -dNOPROMPT -dMaxBitmap=500000000 -dAlignToPixels=0 -dGridFitTT=0 "-sDEVICE=pnmraw" -dTextAlphaBits=4 -dGraphicsAlphaBits=4 "-r72x72"  "-sOutputFile=/tmp/magick-XXuCqreY" "-f/tmp/magick-XXNkQbcr" "-f/tmp/magick-XXoICX9T"
   **** Warning: File has some garbage before %PDF- .
   **** Error: Cannot find a %%EOF marker anywhere in the file.
   **** Warning:  An error occurred while reading an XREF table.
   **** The file has been damaged.  This may have been caused
   **** by a problem while converting or transfering the file.
   **** Ghostscript will attempt to recover the data.

So I opened it in Leafpad:

Original file:

%PDF-1.5
%Çì¢
1 0 obj
<<
/Type /Catalog
/Outlines 3 0 R
/Pages 4 0 R
/Dests 5 0 R
/AcroForm 6 0 R
/Names 7 0 R
/Threads 8 0 R
/PageLayout /SinglePage
/ViewerPreferences
<<
/PageDirection /L2R
 >>
>>
endobj
2 0 obj
<<
/Creator (Scribus 1.5.0.svn)
/Producer (Scribus PDF Library 1.5.0.svn)
/Title <>
/Author <>
/Subject <>
/Keywords <>
/CreationDate (D:20111016162546Z)
/ModDate (D:20111016162546Z)
/Trapped /False
>>
endobj
9 0 obj
<<
/Length 154566
/Length1 275572
/Filter /FlateDecode
>>
stream

File served by PHP and Nginx:

6Wm931Ja.G46X5WID+1K9G93F.3FD.2IXCWm<br>%PDF-1.5
%Çì¢
1 0 obj
<<
/Type /Catalog
/Outlines 3 0 R
/Pages 4 0 R
/Dests 5 0 R
/AcroForm 6 0 R
/Names 7 0 R
/Threads 8 0 R
/PageLayout /SinglePage
/ViewerPreferences
<<
/PageDirection /L2R
 >>
>>
endobj
2 0 obj
<<
/Creator (Scribus 1.5.0.svn)
/Producer (Scribus PDF Library 1.5.0.svn)
/Title <>
/Author <>
/Subject <>
/Keywords <>
/CreationDate (D:20111016162546Z)
/ModDate (D:20111016162546Z)
/Trapped /False
>>
endobj
9 0 obj
<<
/Length 154566
/Length1 275572
/Filter /FlateDecode
>>
stream

So this is the garbage PHP is puting in the begining of the file:

6Wm931Ja.G46X5WID+1K9G93F.3FD.2IXCWm<br>

And I found that a session value was being echoed in another part of the code and that was the real problem since the beginning.

Thanks.

---

By far and away the most common cause of problems like this is leading/trailing whitespace before/after the <?php ?> tags. Note that you probably don't need a ?> tag, which helps avoid this problem.

Next most common cause is forgetting to call exit/die after outputting the file.

Please check both of the above points.

EDIT

Here is how I would write that code:

$file = 'file.pdf';
$filepath = "/path-to-download-folder/$file";

if (!file_exists($filepath)) {
  header('HTTP/1.1 404 Not Found');
  exit;
} else if (!is_file($filepath) || !is_readable($filepath)) {
  header('HTTP/1.1 403 Forbidden');
  exit;
}

header('Cache-Control: no-store, no-cache, must-revalidate');
header('Content-Type: '.mime_content_type($filepath));
header('Content-Length: '.filesize($filepath));
header('Content-Disposition: attachment; filename="'.$file.'"');

set_time_limit(0); // Big files/slow connections may result in incomplete downloads
readfile($filepath);

exit;

---

Also, you should open the PDF file in binary mode:

$f = fopen($filepath, 'rb');

(Or you could just use readfile().)