Passing values between PHP scripts in this particular situation

Question

So in my HTML markup I have an image tag like this one:

<img src="image_generation.php" alt="template" id="image" />

And the 'src' attribute links to a PHP script that generates an image using a couple of variables defined there which are mostly randomly generated.

Now, what I want to be able to do is to access those random variables in the page which includes the image generation script. I suppose I could send cookies and access them after the image tag as they technically should be readily available to the including file. I don't want to send too much information, just a couple (10-20) variables. Not sure if in that case sessions would be a better choice, as I would have to send several cookies. Sessions also pose a problem as the including script gets the old session and I would have to refresh the page to obtain the values of the previously generated image. I suppose I could also set up a DB and access the DB in the including script, but the variables are temporary and I would have to delete them and that seems like a lot of fuss to me.

The image generation script finishes with:

header('Content-type: image/png');
imagepng($image);
imagedestroy($image);

And nothing can be sent to the browser before the header call or else the image won't be displayed. If I use cookies or sessions, the image_generation.php would have to send both the image and set the cookie(s)/session.

None of the options (cookies, sessions or DB) really convince me, as there are problems with each in this particular situation. Can you think of a way to solve this? Thanks.

MAJOR EDIT #1: Including script gets session of previously generated image without refreshing / Setting cookie(s) and/or a session in included script before / after sending image without output buffering does not pose a problem.

Answer 1

You can use a $_SESSION, but to make the session available in the same script that included the <img> tag (which would have executed before the image script), you would need to make AJAX calls via JavaScript. An AJAX handler that runs at window.onload should have access to the $_SESSION created by the image script, since the image should have fully loaded when it executes.

Example PHP handler getsession.php:

header('Content-type: application/json');
// Simply part of the session into JSON
// Obviously you would want to limit this to only the variables 
// that should be sent back, so you don't expose the session on the client side!
echo json_encode(array($_SESSION['var1'],$_SESSION['var2']));
exit();

Example AJAX call (using jQuery since it will be easy to get started with)

// Variable to hold the object returned by PHP
var imgPHPSession;
$(window).load(function() {
  $.ajax({
    url: 'getsession.php',
    dataType: 'json',
    success: function(data) {
      imgPHPSession = data;
    }
  });
});

Update:

It can be done entirely in PHP, but would require changing your design a bit such that the variables necessary to generate the image are created in $_SESSION by the main script. They are then available in $_SESSION to image_generation.php to be used as needed, but are already known to the main script.

Update 2:

Since the image vars contain info about how it was created, if the image is not too large, you can actually create it in the main script and store it to disk. The image_generation.php script can still be used as the <img src>, but its purpose would then be to retrieve the correct image from disk and serve it back to the browser and delete it from disk when no longer needed. The $_SESSION is then available to both the main and image scripts.

Answer 2

You can pass you parameters to src attribute, for example:

<img src="image_generation.php/user/1/name/tom/param1/variable2"

or

<img src="image_generation.php?user=1&name=tom

this solution lets you forget about session, cookies - it's stateless

Php can do smart tricks with buffer by ob_* function, so at the beginning of your script you can call ob_start() to buffer every php output, it lets you avoid all 'Header already send' errors.

Your image_generation.php does not need to send any cookie. This script will receive cookie with sessionid (browser attach cookie information to every request to the server) what makes possible identify user session on php side - after that you have access to every session parameters.