<?php
namespace Automattic\WooCommerce\Caching;
/**
* Base class for caching objects (or associative arrays) that have a unique identifier.
* At the very least, derived classes need to implement the 'get_object_type' method,
* but usually it will be convenient to override some of the other protected members.
*
* The actual caching is delegated to an instance of CacheEngine. By default WpCacheEngine is used,
* but a different engine can be used by either overriding the get_cache_engine_instance method
* or capturing the wc_object_cache_get_engine filter.
*
* Objects are identified by ids that are either integers or strings. The actual cache keys passed
* to the cache engine will be prefixed with the object type and a random string. The 'flush' operation
* just forces the generation a new prefix and lets the old cached objects expire.
*/
abstract class ObjectCache {
private const CACHE_PREFIX_OPTION_NAME = 'wp_object_cache_key_prefix_';
/**
* Expiration value to be passed to 'set' to use the value of $default_expiration.
*/
public const DEFAULT_EXPIRATION = -1;
/**
* Maximum expiration time value, in seconds, that can be passed to 'set'.
*/
public const MAX_EXPIRATION = MONTH_IN_SECONDS;
/**
* This needs to be set in each derived class.
*
* @var string
*/
private $object_type;
/**
* Default value for the duration of the objects in the cache, in seconds
* (may not be used depending on the cache engine used WordPress cache implementation).
*
* @var int
*/
protected $default_expiration = HOUR_IN_SECONDS;
/**
* Temporarily used when retrieving data in 'get'.
*
* @var array
*/
private $last_cached_data;
/**
* The cache engine to use.
*
* @var CacheEngine
*/
private $cache_engine = null;
/**
* The prefix to use for cache keys to pass to the cache engine.
*
* @var string
*/
private $cache_key_prefix = null;
/**
* The name of the option used to store the cache prefix.
*
* @var string
*/
private $cache_key_prefix_option_name;
/**
* Gets an identifier for the types of objects cached by this class.
* This identifier will be used to compose the keys passed to the cache engine,
* to the name of the option that stores the cache prefix, and the names of the hooks used.
* It must be unique for each class inheriting from ObjectCache.
*
* @return string
*/
abstract public function get_object_type(): string;
/**
* Creates a new instance of the class.
*
* @throws CacheException If get_object_type returns null or an empty string.
*/
public function __construct() {
$this->object_type = $this->get_object_type();
if ( empty( $this->object_type ) ) {
throw new CacheException( 'Class ' . get_class( $this ) . ' returns an empty value for get_object_type', $this );
}
$this->cache_key_prefix_option_name = self::CACHE_PREFIX_OPTION_NAME . $this->object_type;
}
/**
* Get the default expiration time for cached objects, in seconds.
*
* @return int
*/
public function get_default_expiration_value(): int {
return $this->default_expiration;
}
/**
* Get the cache engine to use and cache it internally.
*
* @return CacheEngine
*/
private function get_cache_engine(): CacheEngine {
if ( null === $this->cache_engine ) {
$engine = $this->get_cache_engine_instance();
/**
* Filters the underlying cache engine to be used by an instance of ObjectCache.
*
* @since 6.8.0
*
* @param CacheEngine $engine The cache engine to be used by default.
* @param ObjectCache $cache_instance The instance of ObjectCache that will use the cache engine.
* @returns CacheEngine The actual cache engine that will be used.
*/
$this->cache_engine = apply_filters( 'wc_object_cache_get_engine', $engine, $this );
}
return $this->cache_engine;
}
/**
* Get the current cache prefix to use, generating one if none is in use yet.
*
* @return string
*/
private function get_cache_key_prefix(): string {
$value = $this->cache_key_prefix;
if ( ! $value ) {
$value = get_option( $this->cache_key_prefix_option_name );
if ( ! $value ) {
$value = $this->create_cache_key_prefix();
}
$this->cache_key_prefix = $value;
}
return $value;
}
/**
* Generate a prefix for the cache keys to use, containing the object type and a random string,
* and store it persistently using an option.
*
* @return string The generated prefix.
* @throws CacheException Can't store the generated prefix.
*/
private function create_cache_key_prefix(): string {
$prefix_variable_part = $this->get_random_string();
$prefix = "woocommerce_object_cache|{$this->object_type}|{$prefix_variable_part}|";
if ( ! update_option( $this->cache_key_prefix_option_name, $prefix ) ) {
throw new CacheException( "Can't store the key prefix option", $this );
}
return $prefix;
}
/**
* Add an object to the cache, or update an already cached object.
*
* @param int|string|null $id Id of the object to be cached, if null, get_object_id will be used to get it.
* @param object|array $object The object to be cached.
* @param int $expiration Expiration of the cached data in seconds from the current time, or DEFAULT_EXPIRATION to use the default value.
* @return bool True on success, false on error.
* @throws CacheException Invalid parameter, or null id was passed and get_object_id returns null too.
*/
public function set( $id = null, $object, int $expiration = self::DEFAULT_EXPIRATION ): bool {
if ( null === $object ) {
throw new CacheException( "Can't cache a null value", $this, $id );
}
if ( ! is_array( $object ) && ! is_object( $object ) ) {
throw new CacheException( "Can't cache a non-object, non-array value", $this, $id );
}
if ( ! is_string( $id ) && ! is_int( $id ) && ! is_null( $id ) ) {
throw new CacheException( "Object id must be an int, a string, or null for 'set'", $this, $id );
}
$this->verify_expiration_value( $expiration );
if ( null === $id ) {
$id = $this->get_object_id( $object );
if ( null === $id ) {
throw new CacheException( "Null id supplied and the cache class doesn't implement get_object_id", $this );
}
}
$errors = $this->validate( $object );
if ( null !== $errors && 1 === count( $errors ) ) {
throw new CacheException( 'Object validation/serialization failed: ' . $errors[0], $this, $id, $errors );
} elseif ( ! empty( $errors ) ) {
throw new CacheException( 'Object validation/serialization failed', $this, $id, $errors );
}
$data = $this->serialize( $object );
/**
* Filters the serialized object that will be passed by an instance of ObjectCache to its cache engine to be cached.
*
* @since 6.8.0
*
* @param array $data The already serialized object data.
* @param array|object $object The object before serialization.
* @returns array The actual serialized object data that will be passed to the cache engine.
*/
$data = apply_filters( "woocommerce_after_serializing_{$this->object_type}_for_caching", $data, $object, $id );
$this->last_cached_data = $data;
return $this->get_cache_engine()->cache_object( $this->get_cache_key_prefix() . $id, $data, self::DEFAULT_EXPIRATION === $expiration ? $this->default_expiration : $expiration );
}
/**
* Check if the given expiration time value is valid, throw an exception if not.
*
* @param int $expiration Expiration time to check.
* @return void
* @throws CacheException Expiration time is negative or higher than MAX_EXPIRATION.
*/
private function verify_expiration_value( int $expiration ): void {
if ( self::DEFAULT_EXPIRATION !== $expiration && ( ( $expiration < 1 ) || ( $expiration > self::MAX_EXPIRATION ) ) ) {
throw new CacheException( 'Invalid expiration value, must be ObjectCache::DEFAULT_EXPIRATION or a value between 1 and ObjectCache::MAX_EXPIRATION', $this );
}
}
/**
* Retrieve a cached object, and if no object is cached with the given id,
* try to get one via get_from_datastore method or by supplying a callback and then cache it.
*
* If you want to provide a callable but still use the default expiration value,
* pass "ObjectCache::DEFAULT_EXPIRATION" as the second parameter.
*
* @param int|string $id The id of the object to retrieve.
* @param int $expiration Expiration of the cached data in seconds from the current time, used if an object is retrieved from datastore and cached.
* @param callable|null $get_from_datastore_callback Optional callback to get the object if it's not cached, it must return an object/array or null.
* @return object|array|null Cached object, or null if it's not cached and can't be retrieved from datastore or via callback.
* @throws CacheException Invalid id parameter.
*/
public function get( $id, int $expiration = self::DEFAULT_EXPIRATION, callable $get_from_datastore_callback = null ) {
if ( ! is_string( $id ) && ! is_int( $id ) ) {
throw new CacheException( "Object id must be an int or a string for 'get'", $this );
}
$this->verify_expiration_value( $expiration );
$data = $this->get_cache_engine()->get_cached_object( $this->get_cache_key_prefix() . $id );
if ( null === $data ) {
if ( $get_from_datastore_callback ) {
$object = $get_from_datastore_callback( $id );
} else {
$object = $this->get_from_datastore( $id );
}
if ( null === $object ) {
return null;
}
$this->set( $id, $object, $expiration );
$data = $this->last_cached_data;
}
$object = $this->deserialize( $data );
/**
* Filters the deserialized object that is retrieved from the cache engine of an instance of ObjectCache and will be returned by 'get'.
*
* @since 6.8.0
*
* @param array|object $object The object after being deserialized.
* @param array $data The serialized object data that was retrieved from the cache engine.
* @returns array|object The actual deserialized object data that will be returned by 'get'.
*/
return apply_filters( "woocommerce_after_deserializing_{$this->object_type}_from_cache", $object, $data, $id );
}
/**
* Remove an object from the cache.
*
* @param int|string $id The id of the object to remove.
* @return bool True if the object is removed from the cache successfully, false otherwise (because the object wasn't cached or for other reason).
*/
public function remove( $id ): bool {
$result = $this->get_cache_engine()->delete_cached_object( $this->get_cache_key_prefix() . $id );
/**
* Action triggered by an instance of ObjectCache after an object is (attempted to be) removed from the cache.
*
* @since 6.8.0
*
* @param int|string $id The id of the object being removed.
* @param bool $result True if the object removal succeeded, false otherwise.
*/
do_action( "woocommerce_after_removing_{$this->object_type}_from_cache", $id, $result );
return $result;
}
/**
* Remove all the objects from the cache.
* This is done by forcing the generation of a new cache key prefix
* and leaving the old cached objects to expire.
*
* @return void
*/
public function flush(): void {
delete_option( $this->cache_key_prefix_option_name );
$this->cache_key_prefix = null;
/**
* Action triggered by an instance of ObjectCache after it flushes all the cached objects.
*
* @since 6.8.0
*
* @param ObjectCache $cache_instance The instance of ObjectCache whose 'flush` method has been called.
* @param CacheEngine $engine The cache engine in use.
*/
do_action( "woocommerce_after_flushing_{$this->object_type}_cache", $this, $this->get_cache_engine() );
}
/**
* Is a given object cached?
*
* @param int|string $id The id of the object to check.
* @return bool True if there's a cached object with the specified id.
*/
public function is_cached( $id ): bool {
return $this->get_cache_engine()->is_cached( $this->get_cache_key_prefix() . $id );
}
/**
* Get the id of an object. This is used by 'set' when a null id is passed.
* If the object id can't be determined the method must return null.
*
* @param array|object $object The object to get the id for.
* @return int|string|null
*/
protected function get_object_id( $object ) {
return null;
}
/**
* Validate an object before it's cached.
*
* @param array|object $object Object to validate.
* @return array|null An array with validation error messages, null or an empty array if there are no errors.
*/
protected function validate( $object ): ?array {
return null;
}
/**
* Convert an object to a serialized form suitable for caching.
* If a class overrides this method it should override 'deserialize' as well.
*
* @param array|object $object The object to serialize.
* @return array The serialized object.
*/
protected function serialize( $object ): array {
return array( 'data' => $object );
}
/**
* Deserializes a set of object data after having been retrieved from the cache.
* If a class overrides this method it should override 'serialize' as well.
*
* @param array $serialized Serialized object data as it was returned by 'validate_and_serialize'.
* @return object|array Deserialized object, ready to be returned by 'get'.
*/
protected function deserialize( array $serialized ) {
return $serialized['data'];
}
/**
* Get an object from an authoritative data store.
* This is used by 'get' if the object isn't cached and no custom object retrieval callback is suupplied.
*
* @param int|string $id The id of the object to get.
* @return array|object|null The retrieved object, or null if it's not possible to retrieve an object by the given id.
*/
protected function get_from_datastore( $id ) {
return null;
}
/**
* Get the instance of the cache engine to use.
*
* @return CacheEngine
*/
protected function get_cache_engine_instance(): CacheEngine {
return wc_get_container()->get( WpCacheEngine::class );
}
/**
* Get a random string to be used to compose the cache key prefix.
* It should return a different string each time.
*
* @return string
*/
protected function get_random_string(): string {
return dechex( microtime( true ) * 1000 ) . bin2hex( random_bytes( 8 ) );
}
}