Proyectos de Subversion Moodle

<?php

// This file is part of Moodle - http://moodle.org/

//

// Moodle is free software: you can redistribute it and/or modify

// it under the terms of the GNU General Public License as published by

// the Free Software Foundation, either version 3 of the License, or

// (at your option) any later version.

//

// Moodle is distributed in the hope that it will be useful,

// but WITHOUT ANY WARRANTY; without even the implied warranty of

// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

// GNU General Public License for more details.

//

// You should have received a copy of the GNU General Public License

// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.

/**

 * Redis Cache Store - Main library

 *

 * @package   cachestore_redis

 * @copyright 2013 Adam Durana

 * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later

 */

defined('MOODLE_INTERNAL') || die();

/**

 * Redis Cache Store

 *

 * To allow separation of definitions in Moodle and faster purging, each cache

 * is implemented as a Redis hash.  That is a trade-off between having functionality of TTL

 * and being able to manage many caches in a single redis instance.  Given the recommendation

 * not to use TTL if at all possible and the benefits of having many stores in Redis using the

 * hash configuration, the hash implementation has been used.

 *

 * @copyright   2013 Adam Durana

 * @license     http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later

 */

class cachestore_redis extends cache_store implements cache_is_key_aware, cache_is_lockable,

        cache_is_configurable, cache_is_searchable {

    /**

     * Compressor: none.

     */

    const COMPRESSOR_NONE = 0;

    /**

     * Compressor: PHP GZip.

     */

    const COMPRESSOR_PHP_GZIP = 1;

    /**

     * Compressor: PHP Zstandard.

     */

    const COMPRESSOR_PHP_ZSTD = 2;

    /**

     * @var string Suffix used on key name (for hash) to store the TTL sorted list

     */

    const TTL_SUFFIX = '_ttl';

    /**

     * @var int Number of items to delete from cache in one batch when expiring old TTL data.

     */

    const TTL_EXPIRE_BATCH = 10000;

    /**

     * Name of this store.

     *

     * @var string

     */

    protected $name;

    /**

     * The definition hash, used for hash key

     *

     * @var string

     */

    protected $hash;

    /**

     * Flag for readiness!

     *

     * @var boolean

     */

    protected $isready = false;

    /**

     * Cache definition for this store.

     *

     * @var cache_definition

     */

    protected $definition = null;

    /**

     * Connection to Redis for this store.

     *

     * @var Redis|RedisCluster

     */

    protected $redis;

    /**

     * Serializer for this store.

     *

     * @var int

     */

    protected $serializer = Redis::SERIALIZER_PHP;

    /**

     * Compressor for this store.

     *

     * @var int

     */

    protected $compressor = self::COMPRESSOR_NONE;

    /**

     * Bytes read or written by last call to set()/get() or set_many()/get_many().

     *

     * @var int

     */

    protected $lastiobytes = 0;

    /** @var int Maximum number of seconds to wait for a lock before giving up. */

    protected $lockwait = 60;

    /** @var int Timeout before lock is automatically released (in case of crashes) */

    protected $locktimeout = 600;

    /** @var ?array Array of current locks, or null if we haven't registered shutdown function */

    protected $currentlocks = null;

    /**

     * Determines if the requirements for this type of store are met.

     *

     * @return bool

     */

    public static function are_requirements_met() {

        return class_exists('Redis');

    }

    /**

     * Determines if this type of store supports a given mode.

     *

     * @param int $mode

     * @return bool

     */

    public static function is_supported_mode($mode) {

        return ($mode === self::MODE_APPLICATION || $mode === self::MODE_SESSION);

    }

    /**

     * Get the features of this type of cache store.

     *

     * @param array $configuration

     * @return int

     */

    public static function get_supported_features(array $configuration = array()) {

        // Although this plugin now supports TTL I did not add SUPPORTS_NATIVE_TTL here, because

        // doing so would cause Moodle to stop adding a 'TTL wrapper' to data items which enforces

        // the precise specified TTL. Unless the scheduled task is set to run rather frequently,

        // this could cause change in behaviour. Maybe later this should be reconsidered...

        return self::SUPPORTS_DATA_GUARANTEE + self::DEREFERENCES_OBJECTS + self::IS_SEARCHABLE;

    }

    /**

     * Get the supported modes of this type of cache store.

     *

     * @param array $configuration

     * @return int

     */

    public static function get_supported_modes(array $configuration = array()) {

        return self::MODE_APPLICATION + self::MODE_SESSION;

    }

    /**

     * Constructs an instance of this type of store.

     *

     * @param string $name

     * @param array $configuration

     */

    public function __construct(

        $name,

        array $configuration = [],

    ) {

        $this->name = $name;

        if (!array_key_exists('server', $configuration) || empty($configuration['server'])) {

            return;

        }

        if (array_key_exists('serializer', $configuration)) {

            $this->serializer = (int)$configuration['serializer'];

        }

        if (array_key_exists('compressor', $configuration)) {

            $this->compressor = (int)$configuration['compressor'];

        }

        if (array_key_exists('lockwait', $configuration)) {

            $this->lockwait = (int)$configuration['lockwait'];

        }

        if (array_key_exists('locktimeout', $configuration)) {

            $this->locktimeout = (int)$configuration['locktimeout'];

        }

        $this->redis = $this->new_redis($configuration);

    }

    /**

     * Create a new Redis or RedisCluster instance and connect to the server.

     *

     * @param array $configuration The redis instance configuration.

     * @return Redis|RedisCluster|null

     */

    protected function new_redis(array $configuration): Redis|RedisCluster|null {

        $encrypt = (bool) ($configuration['encryption'] ?? false);

        $clustermode = (bool) ($configuration['clustermode'] ?? false);

        $password = !empty($configuration['password']) ? $configuration['password'] : '';

        // Set Redis server(s).

        $servers = explode("\n", $configuration['server']);

        $trimmedservers = [];

        foreach ($servers as $server) {

            $server = strtolower(trim($server));

            if (!empty($server)) {

                if ($server[0] === '/' || str_starts_with($server, 'unix://')) {

                    $port = 0;

                    $trimmedservers[] = $server;

                } else {

                    $port = 6379; // No Unix socket so set default port.

                    if (strpos($server, ':')) { // Check for custom port.

                        list($server, $port) = explode(':', $server);

                    }

                    if (!$clustermode && $encrypt) {

                        $server = 'tls://' . $server;

                    }

                    $trimmedservers[] = $server.':'.$port;

                }

                // We only need the first record for the single redis.

                if (!$clustermode) {

                    // Handle the case when the server is not a Unix domain socket.

                    if ($port !== 0) {

                        // We only need the first record for the single redis.

                        $serverchunks = explode(':', $trimmedservers[0]);

                        // Get the last chunk as the port.

                        $port = array_pop($serverchunks);

                        // Combine the rest of the chunks back into a string as the server.

                        $server = implode(':', $serverchunks);

                    }

                    break;

                }

            }

        }

        // TLS/SSL Configuration.

        $exceptionclass = $clustermode ? 'RedisClusterException' : 'RedisException';

        $opts = [];

        if ($encrypt) {

            $opts = empty($configuration['cafile']) ?

                ['verify_peer' => false, 'verify_peer_name' => false] :

                ['cafile' => $configuration['cafile']];

            // For a single (non-cluster) Redis, the TLS/SSL config must be added to the 'stream' key.

            if (!$clustermode) {

                $opts['stream'] = $opts;

            }

        }

        // Connect to redis.

        $redis = null;

        try {

            // Create a $redis object of a RedisCluster or Redis class.

            if ($clustermode) {

                $redis = new RedisCluster(null, $trimmedservers, 1, 1, true, $password, !empty($opts) ? $opts : null);

            } else {

                $redis = new Redis();

                $redis->connect($server, $port, 1, null, 100, 1, $opts);

                if (!empty($password)) {

                    $redis->auth($password);

                }

            }

            // In case of a TLS connection,

            // if phpredis client does not communicate immediately with the server the connection hangs.

            // See https://github.com/phpredis/phpredis/issues/2332.

            if ($encrypt && !$redis->ping('Ping')) {

                throw new $exceptionclass("Ping failed");

            }

            // If using compressor, serialisation will be done at cachestore level, not php-redis.

            if ($this->compressor === self::COMPRESSOR_NONE) {

                $redis->setOption(Redis::OPT_SERIALIZER, $this->serializer);

            }

            // Set the prefix.

            $prefix = !empty($configuration['prefix']) ? $configuration['prefix'] : '';

            if (!empty($prefix)) {

                $redis->setOption(Redis::OPT_PREFIX, $prefix);

            }

            $this->isready = true;

        } catch (RedisException | RedisClusterException $e) {

            $server = $clustermode ? implode(',', $trimmedservers) : $server.':'.$port;

            debugging("Failed to connect to Redis at {$server}, the error returned was: {$e->getMessage()}");

            $this->isready = false;

        }

        return $redis;

    }

    /**

     * See if we can ping Redis server

     *

     * @param RedisCluster|Redis $redis

     * @return bool

     */

    protected function ping(RedisCluster|Redis $redis): bool {

        try {

            if ($redis->ping() === false) {

                return false;

            }

        } catch (Exception $e) {

            return false;

        }

        return true;

    }

    /**

     * Get the name of the store.

     *

     * @return string

     */

    public function my_name() {

        return $this->name;

    }

    /**

     * Initialize the store.

     *

     * @param cache_definition $definition

     * @return bool

     */

    public function initialise(cache_definition $definition) {

        $this->definition = $definition;

        $this->hash       = $definition->generate_definition_hash();

        return true;

    }

    /**

     * Determine if the store is initialized.

     *

     * @return bool

     */

    public function is_initialised() {

        return ($this->definition !== null);

    }

    /**

     * Determine if the store is ready for use.

     *

     * @return bool

     */

    public function is_ready() {

        return $this->isready;

    }

    /**

     * Get the value associated with a given key.

     *

     * @param string $key The key to get the value of.

     * @return mixed The value of the key, or false if there is no value associated with the key.

     */

    public function get($key) {

        $value = $this->redis->hGet($this->hash, $key);

        if ($this->compressor == self::COMPRESSOR_NONE) {

            return $value;

        }

        // When using compression, values are always strings, so strlen will work.

        $this->lastiobytes = strlen($value);

        return $this->uncompress($value);

    }

    /**

     * Get the values associated with a list of keys.

     *

     * @param array $keys The keys to get the values of.

     * @return array An array of the values of the given keys.

     */

    public function get_many($keys) {

        $values = $this->redis->hMGet($this->hash, $keys) ?: [];

        if ($this->compressor == self::COMPRESSOR_NONE) {

            return $values;

        }

        $this->lastiobytes = 0;

        foreach ($values as &$value) {

            $this->lastiobytes += strlen($value);

            $value = $this->uncompress($value);

        }

        return $values;

    }

    /**

     * Gets the number of bytes read from or written to cache as a result of the last action.

     *

     * If compression is not enabled, this function always returns IO_BYTES_NOT_SUPPORTED. The reason is that

     * when compression is not enabled, data sent to the cache is not serialized, and we would

     * need to serialize it to compute the size, which would have a significant performance cost.

     *

     * @return int Bytes read or written

     * @since Moodle 4.0

     */

    public function get_last_io_bytes(): int {

        if ($this->compressor != self::COMPRESSOR_NONE) {

            return $this->lastiobytes;

        } else {

            // Not supported unless compression is on.

            return parent::get_last_io_bytes();

        }

    }

    /**

     * Set the value of a key.

     *

     * @param string $key The key to set the value of.

     * @param mixed $value The value.

     * @return bool True if the operation succeeded, false otherwise.

     */

    public function set($key, $value) {

        if ($this->compressor != self::COMPRESSOR_NONE) {

            $value = $this->compress($value);

            $this->lastiobytes = strlen($value);

        }

        if ($this->redis->hSet($this->hash, $key, $value) === false) {

            return false;

        }

        if ($this->definition->get_ttl()) {

            // When TTL is enabled, we also store the key name in a list sorted by the current time.

            $this->redis->zAdd($this->hash . self::TTL_SUFFIX, [], self::get_time(), $key);

            // The return value to the zAdd function never indicates whether the operation succeeded

            // (it returns zero when there was no error if the item is already in the list) so we

            // ignore it.

        }

        return true;

    }

    /**

     * Set the values of many keys.

     *

     * @param array $keyvaluearray An array of key/value pairs. Each item in the array is an associative array

     *      with two keys, 'key' and 'value'.

     * @return int The number of key/value pairs successfuly set.

     */

    public function set_many(array $keyvaluearray) {

        $pairs = [];

        $usettl = false;

        if ($this->definition->get_ttl()) {

            $usettl = true;

            $ttlparams = [];

            $now = self::get_time();

        }

        $this->lastiobytes = 0;

        foreach ($keyvaluearray as $pair) {

            $key = $pair['key'];

            if ($this->compressor != self::COMPRESSOR_NONE) {

                $pairs[$key] = $this->compress($pair['value']);

                $this->lastiobytes += strlen($pairs[$key]);

            } else {

                $pairs[$key] = $pair['value'];

            }

            if ($usettl) {

                // When TTL is enabled, we also store the key names in a list sorted by the current

                // time.

                $ttlparams[] = $now;

                $ttlparams[] = $key;

            }

        }

        if ($usettl && count($ttlparams) > 0) {

            // Store all the key values with current time.

            $this->redis->zAdd($this->hash . self::TTL_SUFFIX, [], ...$ttlparams);

            // The return value to the zAdd function never indicates whether the operation succeeded

            // (it returns zero when there was no error if the item is already in the list) so we

            // ignore it.

        }

        if ($this->redis->hMSet($this->hash, $pairs)) {

            return count($pairs);

        }

        return 0;

    }

    /**

     * Delete the given key.

     *

     * @param string $key The key to delete.

     * @return bool True if the delete operation succeeds, false otherwise.

     */

    public function delete($key) {

        $ok = true;

        if (!$this->redis->hDel($this->hash, $key)) {

            $ok = false;

        }

        if ($this->definition->get_ttl()) {

            // When TTL is enabled, also remove the key from the TTL list.

            $this->redis->zRem($this->hash . self::TTL_SUFFIX, $key);

        }

        return $ok;

    }

    /**

     * Delete many keys.

     *

     * @param array $keys The keys to delete.

     * @return int The number of keys successfully deleted.

     */

    public function delete_many(array $keys) {

        // If there are no keys to delete, do nothing.

        if (!$keys) {

            return 0;

        }

        $count = $this->redis->hDel($this->hash, ...$keys);

        if ($this->definition->get_ttl()) {

            // When TTL is enabled, also remove the keys from the TTL list.

            $this->redis->zRem($this->hash . self::TTL_SUFFIX, ...$keys);

        }

        return $count;

    }

    /**

     * Purges all keys from the store.

     *

     * @return bool

     */

    public function purge() {

        if ($this->definition->get_ttl()) {

            // Purge the TTL list as well.

            $this->redis->del($this->hash . self::TTL_SUFFIX);

            // According to documentation, there is no error return for the 'del' command (it

            // only returns the number of keys deleted, which could be 0 or 1 in this case) so we

            // do not need to check the return value.

        }

        return ($this->redis->del($this->hash) !== false);

    }

    /**

     * Cleans up after an instance of the store.

     */

    public function instance_deleted() {

        $this->redis->close();

        unset($this->redis);

    }

    /**

     * Determines if the store has a given key.

     *

     * @see cache_is_key_aware

     * @param string $key The key to check for.

     * @return bool True if the key exists, false if it does not.

     */

    public function has($key) {

        return !empty($this->redis->hExists($this->hash, $key));

    }

    /**

     * Determines if the store has any of the keys in a list.

     *

     * @see cache_is_key_aware

     * @param array $keys The keys to check for.

     * @return bool True if any of the keys are found, false none of the keys are found.

     */

    public function has_any(array $keys) {

        foreach ($keys as $key) {

            if ($this->has($key)) {

                return true;

            }

        }

        return false;

    }

    /**

     * Determines if the store has all of the keys in a list.

     *

     * @see cache_is_key_aware

     * @param array $keys The keys to check for.

     * @return bool True if all of the keys are found, false otherwise.

     */

    public function has_all(array $keys) {

        foreach ($keys as $key) {

            if (!$this->has($key)) {

                return false;

            }

        }

        return true;

    }

    /**

     * Tries to acquire a lock with a given name.

     *

     * @see cache_is_lockable

     * @param string $key Name of the lock to acquire.

     * @param string $ownerid Information to identify owner of lock if acquired.

     * @return bool True if the lock was acquired, false if it was not.

     */

    public function acquire_lock($key, $ownerid) {

        $timelimit = time() + $this->lockwait;

        do {

            // If the key doesn't already exist, grab it and return true.

            if ($this->redis->setnx($key, $ownerid)) {

                // Ensure Redis deletes the key after a bit in case something goes wrong.

                $this->redis->expire($key, $this->locktimeout);

                // If we haven't got it already, better register a shutdown function.

                if ($this->currentlocks === null) {

                    core_shutdown_manager::register_function([$this, 'shutdown_release_locks']);

                    $this->currentlocks = [];

                }

                $this->currentlocks[$key] = $ownerid;

                return true;

            }

            // Wait 1 second then retry.

            sleep(1);

        } while (time() < $timelimit);

        return false;

    }

    /**

     * Releases any locks when the system shuts down, in case there is a crash or somebody forgets

     * to use 'try-finally'.

     *

     * Do not call this function manually (except from unit test).

     */

    public function shutdown_release_locks() {

        foreach ($this->currentlocks as $key => $ownerid) {

            debugging('Automatically releasing Redis cache lock: ' . $key . ' (' . $ownerid .

                    ') - did somebody forget to call release_lock()?', DEBUG_DEVELOPER);

            $this->release_lock($key, $ownerid);

        }

    }

    /**

     * Checks a lock with a given name and owner information.

     *

     * @see cache_is_lockable

     * @param string $key Name of the lock to check.

     * @param string $ownerid Owner information to check existing lock against.

     * @return mixed True if the lock exists and the owner information matches, null if the lock does not

     *      exist, and false otherwise.

     */

    public function check_lock_state($key, $ownerid) {

        $result = $this->redis->get($key);

        if ($result === (string)$ownerid) {

            return true;

        }

        if ($result === false) {

            return null;

        }

        return false;

    }

    /**

     * Finds all of the keys being used by this cache store instance.

     *

     * @return array of all keys in the hash as a numbered array.

     */

    public function find_all() {

        return $this->redis->hKeys($this->hash);

    }

    /**

     * Finds all of the keys whose keys start with the given prefix.

     *

     * @param string $prefix

     *

     * @return array List of keys that match this prefix.

     */

    public function find_by_prefix($prefix) {

        $return = [];

        foreach ($this->find_all() as $key) {

            if (strpos($key, $prefix) === 0) {

                $return[] = $key;

            }

        }

        return $return;

    }

    /**

     * Releases a given lock if the owner information matches.

     *

     * @see cache_is_lockable

     * @param string $key Name of the lock to release.

     * @param string $ownerid Owner information to use.

     * @return bool True if the lock is released, false if it is not.

     */

    public function release_lock($key, $ownerid) {

        if ($this->check_lock_state($key, $ownerid)) {

            unset($this->currentlocks[$key]);

            return ($this->redis->del($key) !== false);

        }

        return false;

    }

    /**

     * Runs TTL expiry process for this cache.

     *

     * This is not part of the standard cache API and is intended for use by the scheduled task

     * \cachestore_redis\ttl.

     *

     * @return array Various keys with information about how the expiry went

     */

    public function expire_ttl(): array {

        $ttl = $this->definition->get_ttl();

        if (!$ttl) {

            throw new \coding_exception('Cache definition ' . $this->definition->get_id() . ' does not use TTL');

        }

        $limit = self::get_time() - $ttl;

        $count = 0;

        $batches = 0;

        $timebefore = microtime(true);

        $memorybefore = $this->store_total_size();

        do {

            $keys = $this->redis->zRangeByScore($this->hash . self::TTL_SUFFIX, 0, $limit,

                    ['limit' => [0, self::TTL_EXPIRE_BATCH]]);

            $this->delete_many($keys);

            $count += count($keys);

            $batches++;

        } while (count($keys) === self::TTL_EXPIRE_BATCH);

        $memoryafter = $this->store_total_size();

        $timeafter = microtime(true);

        $result = ['keys' => $count, 'batches' => $batches, 'time' => $timeafter - $timebefore];

        if ($memorybefore !== null) {

            $result['memory'] = $memorybefore - $memoryafter;

        }

        return $result;

    }

    /**

     * Gets the current time for TTL functionality. This wrapper makes it easier to unit-test

     * the TTL behaviour.

     *

     * @return int Current time

     */

    protected static function get_time(): int {

        global $CFG;

        if (PHPUNIT_TEST && !empty($CFG->phpunit_cachestore_redis_time)) {

            return $CFG->phpunit_cachestore_redis_time;

        }

        return time();

    }

    /**

     * Sets the current time (within unit test) for TTL functionality.

     *

     * This setting is stored in $CFG so will be automatically reset if you use resetAfterTest.

     *

     * @param int $time Current time (set 0 to start using real time).

     */

    public static function set_phpunit_time(int $time = 0): void {

        global $CFG;

        if (!PHPUNIT_TEST) {

            throw new \coding_exception('Function only available during unit test');

        }

        if ($time) {

            $CFG->phpunit_cachestore_redis_time = $time;

        } else {

            unset($CFG->phpunit_cachestore_redis_time);

        }

    }

    /**

     * Estimates the stored size, taking into account whether compression is turned on.

     *

     * @param mixed $key Key name

     * @param mixed $value Value

     * @return int Approximate stored size

     */

    public function estimate_stored_size($key, $value): int {

        if ($this->compressor == self::COMPRESSOR_NONE) {

            // If uncompressed, use default estimate.

            return parent::estimate_stored_size($key, $value);

        } else {

            // If compressed, compress value.

            return strlen($this->serialize($key)) + strlen($this->compress($value));

        }

    }

    /**

     * Gets Redis reported memory usage.

     *

     * @return int|null Memory used by Redis or null if we don't know

     */

    public function store_total_size(): ?int {

        try {

            $details = $this->redis->info('MEMORY');

        } catch (RedisException $e) {

            return null;

        }

        if (empty($details['used_memory'])) {

            return null;

        } else {

            return (int)$details['used_memory'];

        }

    }

    /**

     * Creates a configuration array from given 'add instance' form data.

     *

     * @see cache_is_configurable

     * @param stdClass $data

     * @return array

     */

    public static function config_get_configuration_array($data) {

        return array(

            'server' => $data->server,

            'prefix' => $data->prefix,

            'password' => $data->password,

            'serializer' => $data->serializer,

            'compressor' => $data->compressor,

            'encryption' => $data->encryption,

            'cafile' => $data->cafile,

            'clustermode' => $data->clustermode,

        );

    }

    /**

     * Sets form data from a configuration array.

     *

     * @see cache_is_configurable

     * @param moodleform $editform

     * @param array $config

     */

    public static function config_set_edit_form_data(moodleform $editform, array $config) {

        $data = array();

        $data['server'] = $config['server'];

        $data['prefix'] = !empty($config['prefix']) ? $config['prefix'] : '';

        $data['password'] = !empty($config['password']) ? $config['password'] : '';

        if (!empty($config['serializer'])) {

            $data['serializer'] = $config['serializer'];

        }

        if (!empty($config['compressor'])) {

            $data['compressor'] = $config['compressor'];

        }

        if (!empty($config['encryption'])) {

            $data['encryption'] = $config['encryption'];

        }

        if (!empty($config['cafile'])) {

            $data['cafile'] = $config['cafile'];

        }

        if (!empty($config['clustermode'])) {

            $data['clustermode'] = $config['clustermode'];

        }

        $editform->set_data($data);

    }

    /**

     * Creates an instance of the store for testing.

     *

     * @param cache_definition $definition

     * @return mixed An instance of the store, or false if an instance cannot be created.

     */

    public static function initialise_test_instance(cache_definition $definition) {

        if (!self::are_requirements_met()) {

            return false;

        }

        $config = get_config('cachestore_redis');

        if (empty($config->test_server)) {

            return false;

        }

        $configuration = array('server' => $config->test_server);

        if (!empty($config->test_serializer)) {

            $configuration['serializer'] = $config->test_serializer;

        }

        if (!empty($config->test_password)) {

            $configuration['password'] = $config->test_password;

        }

        if (!empty($config->test_encryption)) {

            $configuration['encryption'] = $config->test_encryption;

        }

        if (!empty($config->test_cafile)) {

            $configuration['cafile'] = $config->test_cafile;

        }

        if (!empty($config->test_clustermode)) {

            $configuration['clustermode'] = $config->test_clustermode;

        }

        // Make it possible to test TTL performance by hacking a copy of the cache definition.

        if (!empty($config->test_ttl)) {

            $definition = clone $definition;

            $property = (new ReflectionClass($definition))->getProperty('ttl');

            $property->setValue($definition, 999);

        }

        $cache = new cachestore_redis('Redis test', $configuration);

        $cache->initialise($definition);

        return $cache;

    }

    /**

     * Return configuration to use when unit testing.

     *

     * @return array

     */

    public static function unit_test_configuration() {

        global $DB;

        if (!self::are_requirements_met() || !self::ready_to_be_used_for_testing()) {

            throw new moodle_exception('TEST_CACHESTORE_REDIS_TESTSERVERS not configured, unable to create test configuration');

        }

        return ['server' => TEST_CACHESTORE_REDIS_TESTSERVERS,

                'prefix' => $DB->get_prefix(),

                'encryption' => defined('TEST_CACHESTORE_REDIS_ENCRYPT') && TEST_CACHESTORE_REDIS_ENCRYPT,

        ];

    }

    /**

     * Returns true if this cache store instance is both suitable for testing, and ready for testing.

     *

     * When TEST_CACHESTORE_REDIS_TESTSERVERS is set, then we are ready to be use d for testing.

     *

     * @return bool

     */

    public static function ready_to_be_used_for_testing() {

        return defined('TEST_CACHESTORE_REDIS_TESTSERVERS');

    }

    /**

     * Gets an array of options to use as the serialiser.

     * @return array

     */

    public static function config_get_serializer_options() {

        $options = array(

            Redis::SERIALIZER_PHP => get_string('serializer_php', 'cachestore_redis')

        );

        if (defined('Redis::SERIALIZER_IGBINARY')) {

            $options[Redis::SERIALIZER_IGBINARY] = get_string('serializer_igbinary', 'cachestore_redis');

        }

        return $options;

    }

    /**

     * Gets an array of options to use as the compressor.

     *

     * @return array

     */

    public static function config_get_compressor_options() {

        $arr = [

            self::COMPRESSOR_NONE     => get_string('compressor_none', 'cachestore_redis'),

            self::COMPRESSOR_PHP_GZIP => get_string('compressor_php_gzip', 'cachestore_redis'),

        ];

        // Check if the Zstandard PHP extension is installed.

        if (extension_loaded('zstd')) {

            $arr[self::COMPRESSOR_PHP_ZSTD] = get_string('compressor_php_zstd', 'cachestore_redis');

        }

        return $arr;

    }

    /**

     * Compress the given value, serializing it first.

     *

     * @param mixed $value

     * @return string

     */

    private function compress($value) {

        $value = $this->serialize($value);

        switch ($this->compressor) {

            case self::COMPRESSOR_NONE:

                return $value;

            case self::COMPRESSOR_PHP_GZIP:

                return gzencode($value);

            case self::COMPRESSOR_PHP_ZSTD:

                return zstd_compress($value);

            default:

                debugging("Invalid compressor: {$this->compressor}");

                return $value;

        }

    }

    /**

     * Uncompresses (deflates) the data, unserialising it afterwards.

     *

     * @param string $value

     * @return mixed

     */

    private function uncompress($value) {

        if ($value === false) {

            return false;

        }

        switch ($this->compressor) {

            case self::COMPRESSOR_NONE:

                break;