Simple file-based persistent object cache for WordPress. For testing scenarios only.

object-cache.php

<?php
/**
 * Simple file-based WordPress object cache implementation.
 * 
 * Drop this file in wp-content/ to enable persistent object caching.
 * Each cache group stores its data in a separate file using PHP serialization.
 * Files will go in WP_CONTENT_DIR . '/cache/object-cache', or if
 * no WP_CONTENT_DIR constant is defined, in '/tmp/wp-object-cache'.
 * 
 * This file is provided as-is without warranty of any kind.
 * It's not officially supported by WooCommerce or Automattic.
 *
 * NOT FOR PRODUCTION - For development/testing only.
 */

class WP_Object_Cache {
	/**
	 * Cache directory path.
	 *
	 * @var string
	 */
	private $cache_dir;

	/**
	 * In-memory cache for this request.
	 *
	 * @var array
	 */
	private $cache = array();

	/**
	 * Dirty flags to track which groups need saving.
	 *
	 * @var array
	 */
	private $dirty = array();

	/**
	 * Whether cache directory has been initialized.
	 *
	 * @var bool
	 */
	private $initialized = false;

	/**
	 * Initialize cache directory (lazy initialization).
	 */
	private function init() {
		if ( $this->initialized ) {
			return;
		}

		$this->cache_dir = defined( 'WP_CONTENT_DIR' ) ? WP_CONTENT_DIR . '/cache/object-cache' : '/tmp/wp-object-cache';

		// Create cache directory if it doesn't exist.
		if ( ! is_dir( $this->cache_dir ) ) {
			// Use mkdir instead of wp_mkdir_p which may not be available yet.
			@mkdir( $this->cache_dir, 0755, true );
		}

		$this->initialized = true;
	}

	/**
	 * Get a value from cache.
	 *
	 * @param string $key    Cache key.
	 * @param string $group  Cache group.
	 * @param bool   $force  Not used.
	 * @param bool   &$found Whether the key was found.
	 * @return mixed|false The cached value or false if not found.
	 */
	public function get( $key, $group = 'default', $force = false, &$found = null ) {
		$this->init();
		$group = empty( $group ) ? 'default' : $group;

		// Check in-memory cache first.
		if ( ! isset( $this->cache[ $group ] ) ) {
			$this->load_group( $group );
		}

		if ( isset( $this->cache[ $group ][ $key ] ) ) {
			$entry = $this->cache[ $group ][ $key ];

			// Check if expired.
			if ( $entry['expires'] > 0 && $entry['expires'] < time() ) {
				unset( $this->cache[ $group ][ $key ] );
				$this->dirty[ $group ] = true;
				$found = false;
				return false;
			}

			$found = true;
			return $entry['value'];
		}

		$found = false;
		return false;
	}

	/**
	 * Set a value in cache.
	 *
	 * @param string $key    Cache key.
	 * @param mixed  $value  Value to cache.
	 * @param string $group  Cache group.
	 * @param int    $expire Expiration in seconds (0 = no expiration).
	 * @return bool True on success.
	 */
	public function set( $key, $value, $group = 'default', $expire = 0 ) {
		$this->init();
		$group = empty( $group ) ? 'default' : $group;

		if ( ! isset( $this->cache[ $group ] ) ) {
			$this->cache[ $group ] = array();
		}

		$this->cache[ $group ][ $key ] = array(
			'value'   => $value,
			'expires' => $expire > 0 ? time() + $expire : 0,
		);

		$this->dirty[ $group ] = true;

		return true;
	}

	/**
	 * Delete a value from cache.
	 *
	 * @param string $key   Cache key.
	 * @param string $group Cache group.
	 * @return bool True on success.
	 */
	public function delete( $key, $group = 'default' ) {
		$this->init();
		$group = empty( $group ) ? 'default' : $group;

		if ( isset( $this->cache[ $group ][ $key ] ) ) {
			unset( $this->cache[ $group ][ $key ] );
			$this->dirty[ $group ] = true;
			return true;
		}

		return false;
	}

	/**
	 * Flush all cache.
	 *
	 * @return bool True on success.
	 */
	public function flush() {
		$this->init();
		$this->cache = array();
		$this->dirty = array();

		// Delete all cache files.
		$files = glob( $this->cache_dir . '/*.php' );
		if ( $files ) {
			foreach ( $files as $file ) {
				unlink( $file );
			}
		}

		return true;
	}

	/**
	 * Get cache file path for a group.
	 *
	 * @param string $group Group name.
	 * @return string File path.
	 */
	private function get_cache_file( $group ) {
		// Sanitize group name for filename.
		$safe_group = preg_replace( '/[^a-z0-9_\-]/', '_', strtolower( $group ) );
		return $this->cache_dir . '/' . md5( $group ) . '-' . $safe_group . '.php';
	}

	/**
	 * Load a cache group from disk.
	 *
	 * @param string $group Group name.
	 */
	private function load_group( $group ) {
		$file = $this->get_cache_file( $group );

		if ( ! file_exists( $file ) ) {
			$this->cache[ $group ] = array();
			return;
		}

		$contents = file_get_contents( $file );

		// Remove the PHP header if present.
		if ( strpos( $contents, '<?php' ) === 0 ) {
			$contents = substr( $contents, strpos( $contents, "\n" ) + 1 );
		}

		$data = @unserialize( $contents );

		if ( $data !== false && is_array( $data ) ) {
			$this->cache[ $group ] = $data;
		} else {
			$this->cache[ $group ] = array();
		}
	}

	/**
	 * Save a cache group to disk.
	 *
	 * @param string $group Group name.
	 */
	private function save_group( $group ) {
		$file = $this->get_cache_file( $group );
		$data = isset( $this->cache[ $group ] ) ? $this->cache[ $group ] : array();

		// Clean up expired entries before saving.
		$now = time();
		foreach ( $data as $key => $entry ) {
			if ( $entry['expires'] > 0 && $entry['expires'] < $now ) {
				unset( $data[ $key ] );
			}
		}

		if ( empty( $data ) ) {
			// Delete file if group is empty.
			if ( file_exists( $file ) ) {
				unlink( $file );
			}
		} else {
			// Save with PHP header to prevent direct access.
			$serialized = serialize( $data );
			file_put_contents( $file, "<?php exit; ?>\n" . $serialized );
		}

		unset( $this->dirty[ $group ] );
	}

	/**
	 * Save all dirty groups to disk.
	 */
	private function save_dirty_groups() {
		if ( ! $this->initialized ) {
			return;
		}

		foreach ( array_keys( $this->dirty ) as $group ) {
			$this->save_group( $group );
		}
	}

	/**
	 * Destructor - save dirty groups on shutdown.
	 */
	public function __destruct() {
		$this->save_dirty_groups();
	}
}

/**
 * Ensure cache object is initialized.
 */
function wp_cache_init() {
	global $wp_object_cache;

	if ( ! ( $wp_object_cache instanceof WP_Object_Cache ) ) {
		$wp_object_cache = new WP_Object_Cache();
	}
}

// Initialize global cache object.
wp_cache_init();

/**
 * WordPress object cache functions.
 */

function wp_cache_add( $key, $data, $group = '', $expire = 0 ) {
	return wp_cache_set( $key, $data, $group, $expire );
}

function wp_cache_set( $key, $data, $group = '', $expire = 0 ) {
	global $wp_object_cache;

	if ( ! ( $wp_object_cache instanceof WP_Object_Cache ) ) {
		wp_cache_init();
	}

	return $wp_object_cache->set( $key, $data, $group, (int) $expire );
}

function wp_cache_get( $key, $group = '', $force = false, &$found = null ) {
	global $wp_object_cache;

	if ( ! ( $wp_object_cache instanceof WP_Object_Cache ) ) {
		wp_cache_init();
	}

	return $wp_object_cache->get( $key, $group, $force, $found );
}

function wp_cache_delete( $key, $group = '' ) {
	global $wp_object_cache;

	if ( ! ( $wp_object_cache instanceof WP_Object_Cache ) ) {
		wp_cache_init();
	}

	return $wp_object_cache->delete( $key, $group );
}

function wp_cache_replace( $key, $data, $group = '', $expire = 0 ) {
	return wp_cache_set( $key, $data, $group, $expire );
}

function wp_cache_flush() {
	global $wp_object_cache;

	if ( ! ( $wp_object_cache instanceof WP_Object_Cache ) ) {
		wp_cache_init();
	}

	return $wp_object_cache->flush();
}

function wp_cache_incr( $key, $offset = 1, $group = '' ) {
	// Not used by our caches, minimal implementation.
	return false;
}

function wp_cache_decr( $key, $offset = 1, $group = '' ) {
	// Not used by our caches, minimal implementation.
	return false;
}

function wp_cache_switch_to_blog( $blog_id ) {
	// Multisite not needed for basic testing.
	return true;
}

function wp_cache_add_non_persistent_groups( $groups ) {
	// All groups are persistent in this implementation.
	return true;
}

function wp_cache_add_global_groups( $groups ) {
	// Single-site compatibility.
	return true;
}

function wp_cache_close() {
	return true;
}