Can't cache private files after setting correct header

Posted by Jiho on November 18, 2012 at 6:37pm

Hi,

I'm writing a very simple module to allow private files caching.

I have been searching a solution for a long time before posting here.
I'm talking about browser cache.
I work on my dedicated server with root access to apache/drupal settings.
I want to cache images using different styles of and original file.
And I have no problem with caching css/js files or images using public files system.

As you can read here the image_file_download function doesn't set Expires, Cache-Control and ETag headers for images.

// By not explicitly setting them here, this uses normal Drupal
// Expires, Cache-Control and ETag headers to prevent proxy or
// browser caching of private images.

So i use a hook_file_download in this function to define them :

function privatefilescache_file_download($uri){
	$year = 86400 * 365;
	// Getting file info
	$info = image_get_info($uri);
	// For images files
	if(isset($info['mime_type']) && strpos($info['mime_type'], 'image/') === 0){				
		$header = array(
			'Cache-Control' => 'max-age='.$year.', private',
			'Expires' => gmdate('D, d M Y H:i:s', time() + $year) .' GMT',
			'ETag' => strtr(md5($info['file_size']), 0, 10)
		);
		drupal_set_message('<pre>'. print_r($header, TRUE) .'</pre>');
		return $header;
	}
}

In my HTTP Header, i can see that Cache-Control, Expires and ETag are correctly set.
Request and Response parameters are equal but Last-Modified parameter is automatically set to the current date, and I have a 200 instead of 304 status code.

Even if i set Last-Modified to "Mon, 13 Aug 2012 14:35:00 GMT" for example, I still have a 200 status code.

The request :

Cache-Control:max-age=0
If-Modified-Since:Mon, 13 Aug 2012 14:35:00 GMT
If-None-Match:bec86aeee7d11a957751af645155a115

The response :

Cache-Control:max-age=31536000, private
Date:Sun, 18 Nov 2012 18:11:07 GMT
ETag:bec86aeee7d11a957751af645155a115
Expires:Mon, 18 Nov 2013 18:11:07 GMT
Last-Modified:Mon, 13 Aug 2012 14:35:00 GMT

I tried with 'public' instead of 'private' in Cache-Control. Still doesn't work.

Can it be an error in Apache configuration ?
How can I fix my problem?

I'm working on a private image bank, you understand why I have to deal with cache and private files system..

Comments

A suggestion

Posted by goofus on November 18, 2012 at 11:23pm

Hello,
I am not an expert on HTTP 304 messages :) However, I did a quick bit of research.

Here's a link to the W3 web site:
http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html

Here is what is says about 304 messages:

10.3.5 304 Not Modified
If the client has performed a conditional GET request and access is allowed, but the document has not been modified, the server SHOULD respond with this status code. The 304 response MUST NOT contain a message-body, and thus is always terminated by the first empty line after the header fields.

Note the "no body", my emphasis. In your code, aren't you explicitly sending a body with the following statement: drupal_set_message('<pre>'. print_r($header, TRUE) .'</pre>');? Check the doc on drupal_set_message here:
http://api.drupal.org/api/drupal/includes%21bootstrap.inc/function/drupal_set_message/7. Note the source code contains

// Mark this page as being uncacheable.
    drupal_page_is_cacheable(FALSE);

. Thus, could be part of your issue :)

Good Luck :)

Thinking is the best way to travel.

Doesn't work

Posted by Jiho on November 21, 2012 at 3:05pm

Thank you for your message but it doesn't fix the problem.

Glad to have helped

Posted by goofus on November 21, 2012 at 5:23pm

Hello,
Glad to have helped.

Again, I'm not an expert on generating an HTTP 304. However, if the the W3 doc I referenced is current, then you need to explicitly instruct Drupal to finish (write, flush, close) as soon as the headers are written. Not content should be added to the response after the headers.

In addition, you need to make sure the client (web browser) is performing a "conditional get".

My prior point was, issuing the drupal_set_message() is one factor in the failure. Yes, you should remove it, however you have more to do. Again, I'm not an expert, so I'll leave this other folks to help you further.

Good Luck :)

Thinking is the best way to travel.

Hi, I had the same problem...

Posted by krisdigital on December 23, 2012 at 2:23am

Hi,
I had the same problem... No Caching is no option. So here is how it works for me, I adjusted your example, all managed files are cached:

<?php
function privatefilescache_file_download($uri){
if(isset($_SERVER['HTTP_IF_MODIFIED_SINCE'])) {
      $ifs = strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE']);
      
      $file = db_select('file_managed', 'fm')
        ->fields('fm')
        ->condition("uri", $uri)
        ->execute()
        ->fetchAssoc();

    if(!empty($file)) {
      $modified = $file['timestamp'];
      if($modified < $ifs) {
        header('HTTP/1.1 304 Not Modified');
        exit();
      }
    }
    }
    $year = 86400 * 365;
      
        $header = array(
            'Cache-Control' => 'max-age='.$year,
            'Expires' => gmdate('D, d M Y H:i:s', time() + $year) .' GMT',
            'ETag' => strtr(md5($uri), 0, 10)
        ); 

        return $header;
}
?>

krisdigital

http://krisdigital.com