Extra space at beginning of downloaded image

Question

I'm using custom code to download images, as I need to check permissions and keep a trace of each download (inter alia).

Here's how I decided to go:

• Simple link, triggering an AJAX call of my download page
• As it's an AJAX called page, html--ajax.tpl.php is used
• Same for page--ajax.tpl.php
• My final file force the image download

...and the content of the 3 related files:

html--ajax.tpl.php:

<?php print $page; ?>

page--ajax.tpl.php:

<?php print render($page['content']); ?>

download.ajax.php:

<?php

// ...extra code to populate $path and $filename

header('Content-Description: File Transfer');
header('Content-Type: application/octet-stream'); 
header('Content-Disposition: attachment; filename='.$filename);
header('Expires: 0');
header('Cache-Control: must-revalidate');
header('Pragma: public');
header('Content-Length: ' . filesize($path));
readfile($path);
exit;

My problem is that I've an extra space in my downloaded image bytes

The downloaded image is corrupted, so I decided to compare its bytes with the original image with xxd, and here's the result where you can see an extra 20 byte at the very beginning:

00000000: 20ff d8ff e000 104a 4649 4600 0101 0000   ......JFIF.....
00000010: 0100 0100 00ff fe00 3b43 5245 4154 4f52  ........;CREATOR
00000020: 3a20 6764 2d6a 7065 6720 7631 2e30 2028  : gd-jpeg v1.0 (
00000030: 7573 696e 6720 494a 4720 4a50 4547 2076  using IJG JPEG v
00000040: 3632 292c 2071 7561 6c69 7479 203d 2037  62), quality = 7
00000050: 300a ffdb 0043 000a 0707 0807 060a 0808  0....C..........
00000060: 080b 0a0a 0b0e 1810 0e0d 0d0e 1d15 1611  ................
00000070: 1823 1f25 2422 1f22 2126 2b37 2f26 2934  .#.%$"."!&+7/&)4
00000080: 2921 2230 4131 3439 3b3e 3e3e 252e 4449  )!"0A149;>>>%.DI
00000090: 433c 4837 3d3e 3bff db00 4301 0a0b 0b0e  C<H7=>;...C.....

I used the same approach as the one described in this post to find the origin the the space. The better I could have is to determine that the space appears in page--ajax.tpl.php :

00000000: 5020 44ff d8ff e000 104a 4649 4600 0101  P D......JFIF...

P is printed before the render(), in page--ajax.tpl.php, and D before my readfile().

Any ideas to helps me to find the origin of this space?

Thanks

Answer 1

Vinodkumar's answer didn't solved my issue, but it pointed me in the right direction.

I still haven't found the extra space, but as Drupal already used ob_start() in bootstrap.inc, I can now call ob_clean() to ensure no extra characters are shown:

<?php

// ...extra code to populate $path and $filename

ob_clean();
header('Content-Description: File Transfer');
header('Content-Type: application/octet-stream'); 
header('Content-Disposition: attachment; filename='.$filename);
header('Expires: 0');
header('Cache-Control: must-revalidate');
header('Pragma: public');
header('Content-Length: ' . filesize($path));
readfile($path);
exit;

Answer 2

Remove extra space in the file download.ajax.php at the top. If that didn't work then try to call ob_start() function at the start of the file and check it. It will work.