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Plugin Description
Adds the ETag, Last-Modified, Expires and Cache-Control headers to HTTP responses generated by WordPress for more efficient caching.
Why is it useful?
Add-Headers gives you control over the ETag, Last-Modified, Expires and Cache-Control HTTP headers
which your WordPress powered website sends back to the clients when dynamic pages are requested.
This results in more efficient caching, reduction of bandwidth consumption and server load.
The aforementioned HTTP headers are sent to the client when visiting the page of a
post, page, attachment, custom post type, the front page (static pages are supported)
or a page of a category, tag, custom taxonomy, author or date based archive (pagination is supported).
All feeds (posts feed, comments feed, post comments feed, archive feeds) are supported.
Search results pages are supported, but no caching is permitted by default.
The value of each header is based on information provided by the post object
in each of the above pages.
In case of archives, the first post is used in order to determine the time
the archive was last modified. It is possible to customize this by utilizing
the addh_archive_post filter (see below). Special consideration has been
taken so that ETags are unique, even if a post appears first in more than one archives.
In case of feeds, the ETag and the Last-Modified headers are generated by
WordPress itself. Add-Headers adds the Expires and Cache-Control headers to
the feeds.
By default, the expiration date of each page is set to one day (86400 seconds)
after the time the client accessed the resource, but this is configurable
(see configuration section).
In addition to the Cache-Control header, the plugin also sets the Pragma
header to cache or no-cache according to the defined max-age of the
Cache-Control header.
Free License and Donations
Add-Headers is released under the terms of the GNU General Public License version 3 and, therefore, is Free Software.
However, a significant amount of time and energy has been put into developing and testing this plugin, so, its production has not been free from cost. If you find this plugin useful and if it has helped your blog pages get cached more efficiently and has saved you bandwidth and CPU load, you can show your appreciation by making a small donation.
Donations in the following crypto currencies are also accepted and welcome. Send coins to the following addresses:
- BitCoin (BTC):
1KkgpmaBKqQVk643VRhFRkL19Bbci4Mwn9
- LiteCoin (LTC):
LS8UF39LfLahzGo49y736ooRYBVT1zZ2Fa
Thank you in advance for donating!
Configuration
The plugin can be configured by filtering the options array. You can add a
filtering function like the following in the functions.php file of your theme:
function addh_custom_options ( $options ) {
// These are the default options.
return array_merge( $options, array(
'add_etag_header' => true,
'generate_weak_etag' => false,
'add_last_modified_header' => true,
'add_expires_header' => true,
'add_cache_control_header' => true,
'cache_max_age_seconds' => 86400,
'cache_max_age_seconds_for_search_results' => 0,
'cache_max_age_seconds_for_authenticated_users' => 0,
) );
}
add_filter( 'addh_options', 'addh_custom_options', 10, 1 );
The settings above demonstrate the default values.
By setting any of the max-age settings to 0, a Cache-Control: no-cache, must-revalidate, max-age=0
header is sent. cache_max_age_seconds_for_search_results only affects search
results. cache_max_age_seconds affects all pages. If you need more customization,
it is possible to filter the headers before they are sent to the client (see Available Filters section).
The rest of the options should be self-explanatory.
Available Filters
The following filters can be used to further customize the HTTP headers.
addh_options
- applied to the plugin options array. The hooked function should accept and return 1 argument: an array of options. See the example in the configuration section above.
addh_cache_control_header_format
- applied to the template that is used to generate the
Cache-Control header’s value. The hooked function should accept and return 1 argument: a string. The default template is “public, max-age=%s“. The template must have one %s placeholder for the max-age seconds.
addh_headers
- applied to all HTTP headers that have been generated by Add-Headers before they are sent to the client. The hooked function should accept and return 1 argument: an array of HTTP headers (strings).
addh_headers_feed
- applied to all HTTP headers that have been generated by Add-Headers for a feed. The hooked function should accept and return 1 argument: an array of HTTP headers (strings).
addh_archive_post
- applied to the post object that is used in order to generate HTTP headers for the whole archive. The hooked function should accept and return 1 argument: a post object.
addh_supported_post_types_singular
- applied to the array of post types that are supported on pages where
is_singular() is true. By default, regular posts, pages, attachments and public custom post types are supported. The hooked function should accept and return 1 argument: an array of post types.
addh_supported_post_types_archive
- applied to the array of post types that are supported on pages where
is_archive() is true. By default, regular posts and public custom post types are supported. The hooked function should accept and return 1 argument: an array of post types.
Testing
You can use curl in order to check the headers.
For example:
curl -I -L http://example.org/sample-page/
curl -I -L -H "Accept-Encoding: gzip,deflate" http://example.org/sample-page/
curl -I -L -H "If-Modified-Since: Mon, 16 Dec 2013 10:10:00 GMT" http://example.org/sample-page/
curl -I -L -H "If-None-Match: "abcdefghijklmn"" http://example.org/sample-page/
Development
The development takes place at:
https://bitbucket.org/gnotaras/wordpress-add-headers
Mirror:
https://github.com/gnotaras/wordpress-add-headers
Pull requests are welcome.
If you use Varnish
If you use Varnish, try the WPVM plugin
to purge pages either automatically as they are updated or on demand.
Screenshots
No screenshots are available at this time.
