Wordpress Redis plugin (dokku/dokku-alt redis plugin spec compatible)

WP_Redis.php

<?php
/*
 * Plugin Name: WP_Redis
 * Description: Exposes Redis to Wordpress as WP_Redis class. Requires ENV variable REDIS_URL (i.e. redis://localhost:port; dokku / dokku-alt compatible )
 * Author: Aubrey Hewes<aubrey@hewes.org.uk>
 * Version: 1.0
 * License: MIT
 */

/**
 * Class WP_Redis
 *
 * Simple Redis wrapper uses requested theme/plugin name as extra prefix on "wp_".
 *
 * The extra prefixing is only due to usage within a non-containerised environment/development environment; so the
 * value is not possibly broken by other apps.
 *
 * i.e. "wp_[theme]key"
 * i.e. "wp_[plugin]key"
 *
 * @todo hash the prefix based on runtime environment (host); makes sure non-containerised envs can not influence each other.
 *
 */
class WP_Redis {

	/**
	 * @var Redis
	 */
	private $instance;

	/**
	 * @var string
	 */
	private $prefix;

	/**
	 * Create a WordPress Redis Manager
	 *
	 * @param string $host
	 * @param int $port defaults to 6379
	 * @param int $timeout defaults to 0
	 * @param string $prefix defaults to 'wp_'
	 *
	 * @throws \Exception If the Redis module is not available
	 */
	public function __construct($host, $port = 6379, $timeout = 0, $prefix = 'wp_') {
		$this->prefix = $prefix;

		if (!class_exists('Redis')) {
			throw new \Exception('Redis module is not available'); // @todo trigger_error / wp error
		}

		try {
			$this->instance = new Redis();
			$this->instance->connect($host, $port, $timeout);
		} catch (\Exception $ex) {
			// log_error
			// dev: trigger_error
			$this->instance = null;
		}
	}

	/**
	 * Returns a cache key localised to site/theme/plugin
	 *
	 * @TODO test for plugin usage and use plugin as prefix
	 *
	 * @return string
	 */
	private function getKey($key) {
		$prefix = $this->prefix;
		/* @var WP_Theme $theme */
		$theme = wp_get_theme();
		if (!empty($theme->template)) {
			$prefix .= $theme->template;
		}
		return $prefix.$key;
	}

	/**
	 * If Redis is unavailable will return false else the result of the Redis get call (false/mixed)
	 *
	 * @param string $key
	 *
	 * @return bool|mixed
	 */
	public function get($key) {
		if ($this->instance === null) {
			return false;
		}
		return $this->instance->get($this->getKey($key));
	}

	/**
	 * Set a Redis key/value.
	 *
	 * If Redis is unavailable will return false else the result of the Redis set (true/false)
	 *
	 * @param string $key
	 * @param mixed $value
	 *
	 * @return bool
	 */
	public function set($key, $value) {
		if ($this->instance === null) {
			return false;
		}
		return $this->instance->set($this->getKey($key), $value);
	}

	/**
	 * Deletes a Redis key/value
	 *
	 * @param string $key
	 */
	public function delete($key) {
		/*return */$this->instance->delete($this->getKey($key));
	}

}

/**
 * Initialises Redis using the environment variable REDIS_URL (dokku / dokku-alt compatible).
 *
 * REDIS_URL is in the format <code>redis://host:port[/prefix]</code> you can set this in wp-config.php
 *
 * If environment variable REDIS_URL is empty then Redis is not available.
 */
function redis_init() {
	global $redis;

	$REDIS_URL = getenv('REDIS_URL'); // dokku/dokku-alt spec
	if (empty($REDIS_URL)) { // not via dokku/dokku-alt or app not setup for spec
		return;
	}

	$REDIS_URL = parse_url($REDIS_URL); // parse the url parts
	if (empty($REDIS_URL)) { // url is malformed; http://php.net/manual/en/function.parse-url.php
		return;
	}

	// create wp redis wrapper using optional default port
	$redis = new WP_Redis($REDIS_URL['host'], !empty($REDIS_URL['port']) ? $REDIS_URL['port'] : 6379);

}

/**
 * Set a Redis key/value.
 *
 * If Redis is unavailable will return false else the result of the Redis set (true/false)
 *
 * @note Global method for bc/seu usage
 *
 * @param string $key
 * @param mixed $value
 *
 * @return bool If Redis is unavailable will return false else the result of the Redis set call (true/false)
 */
function redis_set($key, $value) {
	global $redis;
	return $redis->set($key, $value);
}

/**
 * Get a Redis value by key.
 *
 * @note Global method for bc/seu usage
 *
 * @param string $key
 *
 * @return bool|mixed If Redis is unavailable will return false else the result of the Redis get call (false/mixed)
 */
function redis_get($key) {
	global $redis;
	return $redis->get($key);
}

/**
 * Delete a Redis value by key
 *
 * @param string $key
 *
 * @return bool If Redis is unavailable will return false else the result of the Redis unset call (true/false)
 */
function redis_del($key) {
	global $redis;
	/*return */$redis->delete($key);
}

// HOOK IT UP TO WORDPRESS
add_action( 'init', 'redis_init' );

// available within wordpress:
// - redis_set(key, value)
// - redis_get(key)
// - redis_del(key)