I ran across an article on "How to build a simple caching system, with PHP"
on PHPit today. Overall, it's a fairly decent article, and uses some good
principles (using the output buffer to capture content, using a callback to
grab the captured content). There are a few minor improvements I'd make, however.
There are some definite areas I'd change. First off, die() doesn't make
sense to me as a way to abort execution if content is found. exit(0) makes
more sense -- it indicates that execution was successful.
Also, it's often useful to have the ability to clear the cache for a given
page. Adding a check for a $_GET or $SERVER['PATH_INFO'] element could
accomodate that.
The article says to include the file with the caching functions on every
page. I have a couple issues with that:
- Too easy to forget to include it.
- Namespacing -- using function in the global area could conflict with
other user defined functions.
To solve (1), use an auto_prepend_file directive. You can do this in a
.htaccess file ('php_value "auto_prepend_file" "/path/to/cache.php"), in the
httpd.conf, or directly in your php.ini; in either case, it only needs to be
defined once, and you never have to worry about it in your scripts. If there
are scripts you never want to cache, you can override the value in
individual .htaccess directives, or setup a hash-lookup in the caching
routines to skip such scripts.
To solve (2), wrap the functions into a class. You could still call items
statically (Cache::get_url(), etc.). This would also allow you to define the
hash lookup as noted above -- simply place it in a static property.
Finally, this has all been done before. PEAR::Cache_Lite
offers all of this functionality (minus the routines to create unique
identifiers per page), and a little more -- efficiently, even. The only
difference I've seen in practice is that when using PEAR::Cache_Lite, I had
to do an auto_append_file as well to stop the output buffering.
Overall, a nice article and introduction to page caching.
