moodle redis session handler

redis.php

<?php

/**
 * Redis based session handler.
 *
 * @copyright 2015 Dongsheng Cai {@link http://dongsheng.org}
 * @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */

/**
 *
 * 1. Copy this file to $CFG->dirroot/lib/classes/session/redis.php
 *
 * 2. Add following lines to config.php:
 *
 *     $CFG->session_handler_class = '\core\session\redis';
 *     $CFG->session_redis_save_path = 'tcp://127.0.0.1:6379?prefix=m27sess:';
 *     $CFG->session_redis_acquire_lock_timeout = 120;
 *
 */
namespace core\session;

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

class redis extends handler {
    protected $savepath;
    protected $acquiretimeout = 120;
    protected $servers = array();

    public function __construct() {
        global $CFG;

        if (empty($CFG->session_redis_save_path)) {
            $this->savepath = '';
        } else {
            $this->savepath = $CFG->session_redis_save_path;
        }
        if (!empty($this->savepath)) {
            $this->servers = self::parse_connection_string($this->savepath);
        }

        if (!empty($CFG->session_redis_acquire_lock_timeout)) {
            $this->acquiretimeout = (int)$CFG->session_redis_acquire_lock_timeout;
        } else {
            $this->acquiretimeout = ini_get('max_execution_time');
        }
    }

    public function init() {
        if (!extension_loaded('redis')) {
            throw new exception('sessionhandlerproblem', 'error', '', null,
                    'redis extension is not loaded');
        }
        if (empty($this->savepath)) {
            throw new exception('sessionhandlerproblem', 'error', '', null,
                    '$CFG->session_redis_save_path must be specified in config.php');
        }

        ini_set('session.save_handler', 'redis');
        ini_set('session.save_path', $this->savepath);
    }

    public function start() {
        set_time_limit($this->acquiretimeout);

        $result = parent::start();

        return $result;
    }

    public function session_exists($sid) {
        $result = false;

        foreach ($this->get_redis_servers() as $redis) {
            if ($result === false) {
                if ($redis->exists($sid)) {
                    $result = true;
                }
            }
            $redis->close();
        }

        return $result;
    }

    public function get_redis_servers() {
        $result = array();
        foreach ($this->servers as $server) {
            $redis = new \Redis();

            if ($server->type === 'tcp') {
                $redis->connect($server->host, $server->port, $this->acquiretimeout);
            } else {
                $redis->connect($server->path, null, $this->acquiretimeout);
            }
            if (!empty($server->options)) {
                foreach($server->options as $key=>$value) {
                    if ($key === 'prefix') {
                        $redis->setOption(\Redis::OPT_PREFIX, $value);
                    }
                }
            }

            $result[] = $redis;
        }
        return $result;
    }

    public function kill_all_sessions() {
        global $DB;
        if (!$this->servers) {
            return;
        }

        $redisservers = $this->get_redis_servers();

        $rs = $DB->get_recordset('sessions', array(), 'id DESC', 'id, sid');
        foreach ($rs as $record) {
            foreach ($redisservers as $redis) {
                $redis->delete($record->sid);
            }
        }
        $rs->close();

        foreach ($redisservers as $redis) {
            $redis->close();
        }
    }

    public function kill_session($sid) {
        foreach ($this->get_redis_servers() as $redis) {
            $redis->delete($sid);
            $redis->close();
        }
    }

    public static function parse_connection_string($str) {
        $servers = array();
        $conns = explode(',', $str);
        foreach ($conns as $conn) {
            $conn = trim($conn);
            if (strpos($conn, 'unix') === 0) {
                $conn = preg_replace('/^unix/', 'file', $conn, 1);
            }
            $parts = parse_url($conn);
            $server = new \stdClass;
            $server->type = $parts['scheme'];
            if (!empty($parts['host'])) {
                $server->host = $parts['host'];
            }
            if (!empty($parts['port'])) {
                $server->port = $parts['port'];
            } else {
                $server->port = 6379;
            }
            if (!empty($parts['path'])) {
                $server->path = $parts['path'];
            }

            $query = $parts['query'];
            $options = array();
            parse_str($query, $options);
            $server->options = $options;
            $servers[] = $server;

        }
        return $servers;
    }
}