Downloading Images via PHP

Question

I have a PHP file called generate.php which generates a PNG email based on some parameters I set. The image can be displayed for example by using which will return an image of "myString" text.

I would then like to add a link which allows the user to download the image:

I created a file download.php with the following code:

header('Content-disposition: attachment; filename=string.png');
header('Content-type: image/png');
readfile('generatePicture.php?string=' . $_REQUEST["string"]);

But, while I download a png file, I cannot seem to download. Any suggestions?

Answer 1

When you readfile() a PHP file, its source is displayed. Below I'll show you my way to solve this problem.

Assuming generatePicture.php looks like:

<?php
$im = imagecreatetruecolor($w, $h);
// work with the picture
header('Content-type: image/png');
imagepng($im);
?>

... it could be integrated with download.php this way:

<?php
$im = imagecreatetruecolor($w, $h);
// work with the picture

if(isset($_GET['download']))
    header('Content-disposition: attachment; filename=string.png');

header('Content-type: image/png');
imagepng($im);
?>

Now instead of linking to download.php?string=loremipsum , link to generatePicture.php?string=loremipsum&download=1

Hope it helps.

Answer 2

I've been using this with moderate success for multiple file types. The main thing you need extracted from the file information is the file type, file name, and file size.

  header("Content-Description: PHP Generated Data");
  header("Content-type:".$type);
  header("Content-Disposition: Attachment; Filename=".$name);
  header("Content-length:".$size);
  echo $data;

That might give you something different to try.

Answer 3

Session locking. If you have two scripts that use session_start() the first script opens and locks the session's cache, and the second script must wait for the first to complete before it can open the cache.

If you have a long-running script that you don't want to monopolize a user's session, then either do not call session_start() for that script, or call session_write_close() after you've finished with the session data, but before you begin the long-running operation.

Either that, or use two different browsers to open two separate sessions.