Ok, here's a tough one:
I have these website with several CSS files that uses cache busting and it worked fine. i was getting 403 Not Modified with every call.
But now Im using this rule in my htaccess to concatenate all my files
<FilesMatch "\.combined\.css$">
Options +Includes
AddOutputFilterByType INCLUDES text/css
SetOutputFilter INCLUDES
</FilesMatch>
Inside script.combined.css you can find this:
<!--#include file="file1.css" -->
<!--#include file="file2.css" -->
The problem comes that even though my file "script.combined.css" uses cache busting. it's always returning "200 Ok". These are the headers of script.combined.css:
Request
URL:http://XXX/css/script.combined.css
Request Method:GET
Status Code:200 OK
Request Headers
Accept:text/css,*/*;q=0.1
Accept-Charset:ISO-8859-1,utf-8;q=0.7,*;q=0.3
Accept-Encoding:gzip,deflate,sdch
Accept-Language:en-US,en;q=0.8
Cache-Control:max-age=0
Connection:keep-alive
Cookie:typo3-login-cookiecheck=true; PHPSESSID=2evc53ngjjobateti38gpahtt7; tx_phpmyadmin=quf4sgevagubd1snd9eoq4g4d0; be_typo_user=0f4c7e291b6d7673310d6f15da687910; Typo3InstallTool=62erpih8fmqbbl3pe75pcenuu0; fe_typo_user=a7e5de71521603161fa598ed523b024b
Host:XXX
Referer:http://XXX/
User-Agent:Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/534.30 (KHTML, like Gecko) Ubuntu/11.04 Chromium/12.0.742.112 Chrome/12.0.742.112 Safari/534.30
Response Headers
Accept-Ranges:bytes
Cache-Control:max-age=31536000, public
Connection:Keep-Alive
Content-Type:text/css
Date:Wed, 17 Aug 2011 13:56:42 GMT
Expires:Thu, 16 Aug 2012 13:56:42 GMT
Keep-Alive:timeout=5, max=99
Server:HTTPD
Transfer-Encoding:chunked
...while these are the headers for another simple css file:
Request URL:http://XXX/css/style.css
Request Method:GET
Status Code:304 Not Modified
Request Headers
Accept:text/css,*/*;q=0.1
Accept-Charset:ISO-8859-1,utf-8;q=0.7,*;q=0.3
Accept-Encoding:gzip,deflate,sdch
Accept-Language:en-US,en;q=0.8
Cache-Control:max-age=0
Connection:keep-alive
Cookie:typo3-login-cookiecheck=true; PHPSESSID=2evc53ngjjobateti38gpahtt7; tx_phpmyadmin=quf4sgevagubd1snd9eoq4g4d0; be_typo_user=0f4c7e291b6d7673310d6f15da687910; Typo3InstallTool=62erpih8fmqbbl3pe75pcenuu0; fe_typo_user=a7e5de71521603161fa598ed523b024b
Host:XXX
If-Modified-Since:Wed, 17 Aug 2011 11:45:17 GMT
Referer:http://XXX/
User-Agent:Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/534.30 (KHTML, like Gecko) Ubuntu/11.04 Chromium/12.0.742.112 Chrome/12.0.742.112 Safari/534.30
Response Headers
Cache-Control:max-age=31536000, public
Connection:Keep-Alive
Date:Wed, 17 Aug 2011 13:56:42 GMT
Expires:Thu, 16 Aug 2012 13:56:42 GMT
Keep-Alive:timeout=5, max=97
Server:HTTPD
I used an extension to measure Page Speed from google and I got this message:
Specify a cache validator
The following resources are missing a cache validator. Resources that do not specify a cache validator cannot be refreshed efficiently. Specify a Last-Modified or ETag header to enable cache validation for the following resources:
What should I do??
According to Apache's documentation for server side includes:
In its default configuration, Apache does not send the last modified date or content length HTTP headers on SSI pages, because these values are difficult to calculate for dynamic content.
http://httpd.apache.org/docs/1.3/howto/ssi.html
So a direct request in your browser to styles.combined.css will never return a 304 Not Modified status.
But if you're setting expires headers, the browser simply pulls the asset from the local cache. The request to check the last-modified date is unnecessary and doesn't get sent.