CODEWITHSUNDEEP
phphttpcachinghttp-headers
jd.
jd.

Reputation: 4098

304: Not modified and front end caching

I am using a PHP script to serve files. I would like to be able to send back a 304 not modified header in my http response if the file has not changed since the client last downloaded it. This seems to be a feature in Apache (and most other web servers), but I have no clue how this can be implemented through PHP.

I have heard of using $_SERVER['HTTP_IF_MODIFIED_SINCE'], but this variable does not seem to appear in my $_SERVER super array.

My question is not how to return a 304 header, but how to know that one should be returned.

Edit: The problem is that my $_SERVER['HTTP_IF_MODIFIED_SINCE'] is not set. This is the content of my .htaccess file:

ExpiresActive On 
ExpiresByType image/jpeg "modification plus 1 month"
ExpiresByType image/png "modification plus 1 month"
ExpiresByType image/gif "modification plus 1 month"
Header append Cache-Control: "must-revalidate" 


<IfModule mod_rewrite.c>
   RewriteEngine On
   RewriteCond $1 !^(controller\.php)
   RewriteRule (.*\.jpg|.*\.png|.*\.gif) controller.php/$1
</IfModule>

HTTP_IF_MODIFIED_SINCE still does not appear in the $_SERVER super array.

Upvotes: 15

Views: 19578

Answers (6)

Martin Zvar&#237;k
Martin Zvar&#237;k

Reputation: 2479

Note that $_SERVER["HTTP_IF_NONE_MATCH"] can contain quotes and -gzip suffix.

$server_etag = str_replace("-gzip", "", str_replace('"', '', stripslashes($_SERVER['HTTP_IF_NONE_MATCH'])));

if ($server_etag == $etag) ...

Upvotes: 0

Coder
Coder

Reputation: 3103

I had this problem and it turned out to simply be that I had Firebug open. This has an option under the Net tab "Disable Browser Cache" that is ticked by default. There is a similar option in Chrome's developer tools, one of the tick boxes on the bar under the menu bar.

Unticking these options resulted in the browser correctly sending HTTP_IF_MODIFIED_SINCE and everything working fine after all (even with Firebug or Chrome Dev Tools open).

Upvotes: 1

Jack
Jack

Reputation: 302

There are also some others parameters to check .. in my case I didn't had both of those headers :

$_SERVER['HTTP_IF_NONE_MATCH'] && $_SERVER['HTTP_IF_MODIFIED_SINCE']

which are required to return a proper 304 header, as my system clock was a little late, It'll interpret those pages as expiring in the future, then not sending those values at all

Also check that header which is returned by apache, or at least override it to a bigger value

Cache-Control: max-age=3600

As it won't send previous headers if 

Last-Modified previous sent header < ( NOW - 3600 )

So in my case I've set this pretty handy function function lastModified($file){ $x=filemtime($file); while($x>time())$x-=86000;}#reduce by one day if touched in future date $date=gmdate('D, j M Y H:i:s',$x).' GMT'; header('Cache-Control: max-age=86000',1); if($_SERVER['HTTP_IF_NONE_MATCH'] == $x || $_SERVER['HTTP_IF_MODIFIED_SINCE']==$date){ header('HTTP/1.1 304 Not Modified',1,304);die;} header('Etag: '.$x,1);header('Last-Modified: '.$date,1); }

Upvotes: 0

ekhaled
ekhaled

Reputation: 2930

$_SERVER['HTTP_IF_MODIFIED_SINCE'] is usually empty when register_globals is off.

Check whether that's the case, and if so try getenv('HTTP_IF_MODIFIED_SINCE')

Upvotes: 0

c_harm
c_harm

Reputation:

HTTP_IF_MODIFIED_SINCE is the right way to do it. If you aren't getting it, check that Apache has mod_expires and mod_headers enabled and working properly. Borrowed from a comment on PHP.net:

$last_modified_time = filemtime($file); 
$etag = md5_file($file);
// always send headers
header("Last-Modified: ".gmdate("D, d M Y H:i:s", $last_modified_time)." GMT"); 
header("Etag: $etag"); 
// exit if not modified
if (@strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE']) == $last_modified_time || 
    @trim($_SERVER['HTTP_IF_NONE_MATCH']) == $etag) { 
    header("HTTP/1.1 304 Not Modified"); 
    exit; 
}

// output data

Upvotes: 27

John Magnolia
John Magnolia

Reputation: 16793

This article will answer all your questions on caching

I found that adding 

RewriteRule .* - [E=HTTP_IF_MODIFIED_SINCE:%{HTTP:If-Modified-Since}]
RewriteRule .* - [E=HTTP_IF_NONE_MATCH:%{HTTP:If-None-Match}]

To the bottom of my htaccess file (below all rewriterule) worked.

Upvotes: 1

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