RewriteRule checking file in rewriten file path exists - apache

Question

How can you use ModRewrite to check if a cache file exists, and if it does, rewrite to the cache file and otherwise rewrite to a dynamic file.
For example I have the following folder structure:
pages.php
cache/
pages/
1.html
2.html
textToo.html
etc.
How would you setup the RewriteRules for this so request can be send like this:
example.com/pages/1
And if the cache file exists rewrite tot the cache file, and if the cache file does not exists, rewrite to pages.php?p=1
It should be something like this: (note that this does not work, otherwise I would not have asked this)
RewriteRule ^pages/([^/\.]+) cache/pages/$1.html [NC,QSA]
RewriteCond %{REQUEST_FILENAME} -f [NC,OR]
RewriteCond %{REQUEST_FILENAME} -d [NC]
RewriteRule cache/pages/([^/\.]+).html pages.php?p=$1 [NC,QSA,L]
I can off coarse do this using PHP but I thought it had to be possible using mod_rewrite.

Answer 1

RewriteRule ^pages/([^/\.]+) cache/pages/$1.html [NC,QSA]
# At this point, we would have already re-written pages/4 to cache/pages/4.html
RewriteCond %{REQUEST_FILENAME} !-f
# If the above RewriteCond succeeded, we don't have a cache, so rewrite to
# the pages.php URI, otherwise we fall off the end and go with the
# cache/pages/4.html
RewriteRule ^cache/pages/([^/\.]+).html pages.php?p=$1 [NC,QSA,L]
Turning off MultiViews is crucial (if you have them enabled) as well.
Options -MultiViews
Otherwise the initial request (/pages/...) will get automatically converted to /pages.php before mod_rewrite kicks in. You can also just rename pages.php to something else (and update the last rewrite rule as well) to avoid the MultiViews conflict.
Edit: I initially included RewriteCond ... !-d but it is extraneous.

Answer 2

Another approach would be to first look if there is a chached representation available:
RewriteCond %{DOCUMENT_ROOT}/cache/$0 -f
RewriteRule ^pages/[^/\.]+$ cache/$0.html [L,QSA]
RewriteRule ^pages/([^/\.]+)$ pages.php?p=$1 [L,QSA]

Answer 3

To generalize the question: insert this above the rule that should not be matched if the file exists.
RewriteCond %{REQUEST_FILENAME} !-f
Sean Bright's answer provides a nice worked example for the caching question, but this line works more broadly. In my case, I have a link shortener where people can choose custom URLs and I didn't want it to be able to override existing files such as favicon.ico. Adding this line before the rewriterule fixed that issue.