Caching of JS and CSS files – Apache mod_headers doesn’t take effect

Question

As suggested by an answer on SO, I'm trying using a version number on my JS and CSS files so that the browser will only make a request when the JS or CSS version number is changed in my PHP file. To facilitate this, I have a rewrite in my httpd.conf which transforms a requested file like myscript--20140904.js to myscript.js. Since I'm doing things this way, I want the browser to cache the file for a long time, since it will see a request for a "different" file when that version number is updated.

According to an answer on Webmasters.SE, I can use FilesMatch along with Header set Cache-Control to only cache the CSS/JS files with the version number on them.

And according to an answer on SO, only Cache-Control is necessary, since it takes precedence over Expires anyway.

But this is not working. The Cache-Control header field is missing from the response.

Here's my Apache configuration:

RewriteEngine on
RewriteRule ^(.*)\-\-.+\.(css|js)$ $1.$2

<IfModule mod_headers.c>
    <FilesMatch "^(.*)\-\-.+\.(js|css)$">
        Header set Cache-Control "max-age=15552000"
        Header unset ETag
        Header unset Last-Modified
    </FilesMatch>
</IfModule>

# <IfModule mod_expires.c>
#     <FilesMatch "\.(js|css)$">
#         ExpiresActive On
#         ExpiresByType text/javascript "access plus 6 months"
#         ExpiresByType text/css "access plus 6 months"
#     </FilesMatch>
# </IfModule>

Here's a request for one of the JS files:

http://localhost/[url]/common.js

GET [url]/common.js HTTP/1.1
Host: localhost
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:31.0) Gecko/20100101 Firefox/31.0
Accept: */*
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Referer: http://localhost/[refererUrl]
Cookie: PHPSESSID=[cookie]
Connection: keep-alive
Pragma: no-cache
Cache-Control: no-cache

HTTP/1.1 200 OK
Date: Thu, 04 Sep 2014 19:45:32 GMT
Server: Apache
Last-Modified: Wed, 03 Sep 2014 22:55:57 GMT
Etag: [etag]
Accept-Ranges: bytes
Content-Length: 5167
Keep-Alive: timeout=5, max=100
Connection: Keep-Alive
Content-Type: application/javascript

Answer 1

<FilesMatch "^(.*)\-\-.+\.(js|css)$">

FilesMatch takes a filename and matches against the file system, not the URL. The underlying file is still called "myscript.js", so this pattern should be something like: \.(js|css)$

(Aside... your example request appears to be for common.js - which wouldn't have matched your pattern anyway - shouldn't this be for common--20140904.js?)