Insomnia headaches on a simple javascript Cache, while If-Modified-Since headers are in place!

Question

Hello fellow earthlings! For some time I'm fantasizing possible solutions, but i'm out of clues for this strange problem. Let me describe the reason, then the problem:

In order to combine the javascripts files to reduce http request, I put them into php, a headache-less simple little yet happy solution that will cache for half a year. (Would life be lot nicer if more things would work like that?) A fire and forget solution. So I tought...

The website works fine and all, except, that when viewing the headers on the php-generated js file, it seems that this showstopper appeared:

An If-Modified-Since conditional request returned the full content unchanged.

What's wrong here in the php generated file combined.js? Any suggestive answers are much appreciated!

below file < allcombined.js >

<?php
header("Content-type: text/javascript; charset=UTF-8");
header("Expires: " . gmdate ("D, d M Y H:i:s", time() + 2419200) . " GMT");
header("Last-Modified: " . gmdate("D, d M Y H:i:s", time() - 604800) . " GMT");

ob_start("compress");

include('script1.js');
include('script2.js');
include('script3.js');

ob_end_flush(); 
?>

Answer 1

To handle "If-Modified-Since" headers, you need to parse that header and compare it to your last modification date. This isn't done automatically unless you have a HTTP cache like Varnish in front of your web server. In PHP, if the date is satisfactory, then do not render a body, instead return a 304 Not Modified response. Here is a good example of this being done. [php.net]

The reason you're getting more requests for your asset than you expect is because you haven't set Cache-Control or Pragma headers. You probably want to do:

header("Cache-Control: public, max-age=2419200");
header("Pragma: public");

You may not want to set a max-age this long if you want the client to check in for updates now and again...