WordPress Caching, part 3: Custom Caching Library

When building Elemental (WordPress Theme) I decided to develop my own, very simple, caching plugin to help speed up the theme.

There were a few reasons why I did it but the main ones were:

  1. I was doing things with public apis that have an hourly request limit, so I had to build some sort of data cache.
  2. Whilst wp_super_cache and W3 Total Cache are well known there’s no guarantee people will use it.
  3. I thought it would be interesting to learn how.

My objectives when coding it were simple and follow my personal code desires. I wanted something small, clean, and fast – and hopefully I achieved all three.

BM_Cache Library

I ended up writing a library of functions that get and set cache values – and since I like to share I thought I would open it up. The library is just a series of functions and it can actually be repurposed for any PHP application really easily. Maybe others will find a use for it or, even better, offer improvements.

<pre style="height:500px;"><?php
 * cachePut
 * Save Cache files to cache directory
 * @param string $id cache key - unique string for saving and retrieving cache data
 * @param mixed $data data to save to cache
 * @return boolean
function bm_cachePut ($id = '', $data = NULL) {

	// make sure required values are visible
	if ($id == '' || $data == NULL) {
		return FALSE;
	if ($handle = @fopen(bm_cacheName ($id), 'w')) {
		fwrite($handle, serialize ($data));
		return true;
	} else {
		echo '';
	return false;


 * cacheGet
 * Retreive the cache using the unique key specifying an expiration age so that the cache can be refreshed
 * @param string $id cache key - unique string for saving and retrieving cache data
 * @param integer $expires time in seconds that the cache file can live for before being refreshed
 * @return array
function bm_cacheGet ($id = '', $expires = 0) {

	if ($expires == 0) {
		$expires = BM_CACHE_TIME;
	// add on random 10 percent of the expire time to add some randomness
	// will mean all caches on one page for same time frame do not expire at the same time
	$expires = $expires + ceil (rand (1, ($expires / 10)));
	$filename = bm_cacheName ($id);
	$filenameExists = file_exists ($filename);
	if ($filenameExists) {
		$age = (time() - filemtime ($filename));
		//echo '';
		if ($age

As you can see, it’s very straight forward. There are four functions and they fo the following:

  • bm_cachePut – This saves the specified data to a cache file with the specified key
  • bm_cacheGet – load the data for the specified cache key. Uses a time parameter to set how long the cached data should live for before being reset
  • bm_cacheName – This converts the cache key into the file name for the cached content
  • bm_cacheKill – Delete a cache file based upon it’s key


To make use of the cache library I created another function that “gets” the “content”. This function makes use of the WP_Http class that I wrote about recently.

function bm_getContent ($url, $cacheTime = 60, $prefix = 'getContent') {

	$cachename = $prefix . '_' . md5($url . $cacheTime);
	$content = '';
	if (!$content = bm_cacheGet($cachename, $cacheTime)) {
		$request = new WP_Http;
		$result = $request->request($url);
		if (!isset($result->errors)) {
			$content = $result['body'];
		bm_cachePut ($cachename, $content);
	if ($content != '') {
		return $content;
	} else {
		return FALSE;


To use it all you have to do is use the code below and it will automatically cache the request for 1 minute:

<?php $content = bm_getContent ('url_to_cache'); ?>

A real life example could be with the Yahoo! weather code I wrote about a few months ago.

function bm_getWeather ($code = '', $temp = 'c') {

	$file = 'http://weather.yahooapis.com/forecastrss?p=' . $code . '&u=' . $temp;

	$data = bm_getContent($file);

	$output = array (
		'temperature' => bm_getWeatherProperties('temp', $data),
		'weather' => bm_getWeatherProperties('text', $data),
		'weather_code' => bm_getWeatherProperties('code', $data),
		'class' => 'weatherIcon-' . bm_getWeatherProperties('code', $data),

	return $output;


function bm_getWeatherProperties ($needle, $data) {

	$regex = '<yweather .="" :condition.=""></yweather>';
	preg_match($regex, $data, $matches);

	return $matches[1];


Was it good/ useful/ a load of old rubbish? Let me know on Mastodon, or BlueSky (or Twitter X if you must).

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