Question

I’ve got the following in my .conf file used for cache busting js:

<Directory "/www/virtual/site/html/js/">
    RewriteEngine on
    RewriteCond %{REQUEST_FILENAME} !-f
    RewriteCond %{REQUEST_FILENAME} !-d
    RewriteRule ^\d+\/(.+)$ $1 [L]
</Directory>

The idea here is to rewrite site.com/js/123456/script.js to site.com/js/script.js

(The rewriting works just fine)

If I look at the rewrite log the part I’m not understanding is that it is applying the RewriteRule to the script after the interal redirect… Shouldn’t the %{REQUEST_FILENAME} !-f prevent it from processing the RewriteRule since the file exists?

Rewrite Log

[rid#2b607f8f2dc8/initial] (3) [perdir /www/virtual/site2/html/js/] add path info postfix: /www/virtual/site2/html/js/1234 -> /www/virtual/site2/html/js/1234/script.js
[rid#2b607f8f2dc8/initial] (3) [perdir /www/virtual/site2/html/js/] strip per-dir prefix: /www/virtual/site2/html/js/1234/script.js -> 1234/script.js
[rid#2b607f8f2dc8/initial] (3) [perdir /www/virtual/site2/html/js/] applying pattern '^\d+\/(.+)$' to uri '1234/script.js'
[rid#2b607f8f2dc8/initial] (2) [perdir /www/virtual/site2/html/js/] rewrite '1234/script.js' -> 'script.js'
[rid#2b607f8f2dc8/initial] (3) [perdir /www/virtual/site2/html/js/] add per-dir prefix: script.js -> /www/virtual/site2/html/js/script.js
[rid#2b607f8f2dc8/initial] (2) [perdir /www/virtual/site2/html/js/] strip document_root prefix: /www/virtual/site2/html/js/script.js -> /js/script.js
[rid#2b607f8f2dc8/initial] (1) [perdir /www/virtual/site2/html/js/] internal redirect with /js/script.js [INTERNAL REDIRECT]
[rid#2b6073eb14a8/initial/redir#1] (3) [perdir /www/virtual/site2/html/js/] strip per-dir prefix: /www/virtual/site2/html/js/script.js -> script.js
[rid#2b6073eb14a8/initial/redir#1] (3) [perdir /www/virtual/site2/html/js/] applying pattern '^\d+\/(.+)$' to uri 'script.js'
[rid#2b6073eb14a8/initial/redir#1] (1) [perdir /www/virtual/site2/html/js/] pass through /www/virtual/site2/html/js/script.js

Answer 1

mod_rewrite (by design) keeps on applying rewrite-rules, till the url no longer changes.

So the first time it rewrite 1234/script.js to script.js the second time it tries to apply the rule, the pattern regular expression doesn’t match and script.js is ‘passed through’.

This is the way it is supposed to work. It can sometimes be a pain, but it makes mod_rewrite a lot more powerful/useful.

edit

mod_rewite first tests the RewriteRule pattern, before trying to apply the RewriteCond‘s. This is so you can use backreferences $0, $1 etc. in your RewriteCond. After all the RewriteCond’s it will create the substitution string, so it can also use backrefereces %0, %1. etc. See also the diagram below.

So this is why it tried to apply the pattern before testing if the file exists.