LiveHttpHeaders: which cache-control info is right

Question

Using LiveHttpHeaders for Firefox 6 I was trying to see if my css, JS files being cached using Headers Module from Apache using htaccess. But I confuse, there are 2 values from the 'Cache-Control' data:

GET /proz/css/global.css HTTP/1.1
Host: localhost
User-Agent: Mozilla/5.0 (Windows NT 5.1; rv:5.0) Gecko/20100101 Firefox/5.0
Accept: text/css,*/*;q=0.1
Accept-Language: en-us,en;q=0.5
Accept-Encoding: gzip, deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Connection: keep-alive
Referer: http://localhost/proz/
Cookie: PHPSESSID=el34de37pe3bnp4rdtbst1kd43
If-Modified-Since: Fri, 16 Sep 2011 21:15:32 GMT
If-None-Match: "400000000b06a-2999-4ad157e5b4583"
Cache-Control: max-age=0

HTTP/1.1 304 Not Modified
Date: Sat, 17 Sep 2011 03:04:50 GMT
Server: Apache/2.2.17 (Win32) PHP/5.2.8
Connection: Keep-Alive
Keep-Alive: timeout=5, max=99
Etag: "400000000b06a-2999-4ad157e5b4583"
Cache-Control: max-age=604800, public
Vary: Accept-Encoding

Which one is the true data, the first Cache-Control data (max-age=0) or the latter one.

I also would like to know how do I make sure that my JS, CSS, HTML files being compress after I use deflate module in htaccess. And yes, both headers and deflate modules are turn on.

Arnaud Le Blanc Arnaud Le Blanc · Accepted Answer · 2011-09-17T12:27:16

There are two parts in this listing:

The part before the blank line is the request, sent by your browser
The part after the blank line is the response, sent by the server

The Cache-Control: max-age=0 sent by the client (your browser) tells the server (or any proxy in the middle) to send the most fresh version of the file. The browser usually sends this when you hit the refresh button.

The Cache-Control: max-age=604800, public sent by the server tells the client (your browser or a proxy) that the file is valid for 604800 seconds and can be cached for that time. (The browser won't even attemps to ask the server if a newer version exists, unless you hit refresh, as you did in this case.)

The server replied 304 Not Modified, this means that your browser already has the most recent version and it doesn't need to download it again (it did not downloaded it again).

The Vary: Accept-Encoding header indicate that the server taken some decisions based on the client's Accent-Encoding header. This may indicate that, if the server didn't replied 304 Not Modified, it would have compressed the file.

To verify this last point, clear your cache, and request the file again, and look at the content of the Content-Encoding header (must be gzip or deflate if the data is compressed).

LiveHttpHeaders: which cache-control info is right

1 Answers