Added the option to purge cache files directly without ngx_cache_purge

[bcole808]

The issue

I needed to be able to purge cache files without using the ngx_cache_purge module.

Solution

This pull request adds an option to the "Purge Options" area to allow the site admin to choose how cache files should be purged. The default option is to use a GET request to the /purge version of the URL, as required by ngx_cache_purge. The second option lets the plugin directly remove the cache files from the server.

Screenshot of new option:

How it works

I followed information from this article to compute the correct cache file to delete. The URL to delete is hashed with md5 and then given a specific folder and file name based on that hash.

Caveats

In order for the "delete local files" option to work, the following must all be true:

• Cache is stored on the same server and * RT_WP_NGINX_HELPER_CACHE_PATH* is defined.
• Default nginx cache level must be used; levels=1:2
• Cache key must be: fastcgi_cache_key "$scheme$request_method$host$request_uri"

Testing

So far it seems to work on my staging server tests. If someone else can help double check that everything is working great that would be much appreciated.

[rahul286]

Thanks for amazing PR, both in terms of functionality and documentation. :-)

[ghost]

Very nice indeed, thanks!

[cromulus]

Just a note: could we allow RT_WP_NGINX_HELPER_CACHE_PATH to be defined in the user interface? Or print it's current value?

I love this PR! Great job!