MyRedisSessionModule.php

<?php

/* Usage Example
$save_handler = new MyRedisSessionModule();
$save_handler->save_path = "tcp://127.0.0.1:6379?weight=1";
session_set_save_handler($save_handler, true);
*/

class MyRedisSessionModule implements SessionHandlerInterface {
    /**
     * Total of all connection weights, used as divisor in key distribution
     */
    protected $weight = 0;

    /**
     * Map of redis backend servers to use
     *
     * Comes from session.save_path which is a comma delimted list of URIs
     * in the form of:
     *
     *   proto://hostOrPath:optionalPort?key=val&key=val...
     *
     * Where proto is one of: tcp | unix
     *
     * When proto is 'tcp' and no port is given, Redis::DEFAULT_PORT is assumed
     *
     * Key/Value pairs are as follows:
     *  weight(int) - Likelihood of using this backend will be $weight/$total
     *  timeout(int) - Connection timeout in seconds
     *  persistent(int) - 0 or 1 for non-persistent or persistent connections
     *  prefix(string) - String prefix to apply to all session keys in the DB
     *  auth(string) - Password used to authenticate to the DB
     *  database(int) - Database shard to use
     *
     * Defaults can be found in the code below
     */
    protected $paths = [];

    public $save_path = null;

    public function open($save_path, $session_name) {
        if (!$save_path && $this->save_path) {
            $save_path = $this->save_path;
        }

        $this->weight = 0;
        $this->paths  = [];

        $paths = preg_split('/[\s,]+/', $save_path, -1, PREG_SPLIT_NO_EMPTY);

        foreach ($paths as $path) {
            if (!strncmp($path, "unix:", 5)) {
                $path = 'file:' . substr($path, 5);
            }
            $url = parse_url($path);
            $args = [
                'weight' => 1,
                'timeout' => 86400,
                'persistent' => 0,
                'prefix' => 'PHPREDIS_SESSION:',
                'auth' => '',
                'database' => 0
            ];
            if (isset($url['query'])) {
                parse_str($url['query'], $query);
                foreach ($args as $key => &$val) {
                    if (!isset($query[$key])) continue;
                    if (is_string($val)) {
                        $val = $query[$key];
                    } else {
                        $val = (int)$query[$key];
                    }
                }
            }

            if ($args['weight'] === 0) {
                // Disabled target, skip
                continue;
            }
            if ($args['weight'] < 1) {
                error_log("Invalid weight specified for session.save_path(redis), ".
                    "assuming 1", E_USER_WARNING);
                $args['weight'] = 1;
            }

            if ($url['scheme'] == 'file') {
                $args['host'] = "unix://{$url['path']}";
                $args['port'] = null;
            } else {
                $args['host'] = $url['host'];
                $args['port'] = !empty($url['port'])
                    ? $url['port'] : Redis::DEFAULT_PORT;
            }

            $args['connection'] = null;

            $this->weight += $args['weight'];
            $this->paths[] = $args;
        }

        return true;
    }

    protected function &selectWeight($key) {
        if (count($this->paths) === 1) {
            return $this->paths[0];
        }
        $pos  = abs(unpack("I", $key));
        $pos %= $this->weight;
        foreach ($this->paths as $path) {
            $pos -= $path['weight'];
            if ($pos <= 0) {
                return $path;
            }
        }

        throw new RedisException("Ran out of weights selecting redis host ".
            "for session: $key");
    }

    protected function connect($key) {
        $r =& $this->selectWeight($key);
        if (!empty($r['connection'])) {
            return $r['connection'];
        }

        $redis = new Redis;
        $func = ($r['persistent']) ? 'pconnect' : 'connect';
        if (!$redis->{$func}($r['host'], $r['port'], $r['timeout'])) {
            return false;
        }
        if (($r['auth'] !== '') &&
            !$redis->auth($r['auth'])) {
            return false;
        }
        if (($r['database'] !== 0) &&
            !$redis->select($r['database'])) {
            return false;
        }
        if (!$redis->setOption(Redis::OPT_PREFIX, $r['prefix'])) {
            return false;
        }

        $r['connection'] = $redis;
        return $redis;
    }

    public function close() {
        foreach ($this->paths as &$path) {
            $path['connection'] = null;
        }

        return true;
    }

    public function read($key) {
        $redis = $this->connect($key);
        return (string)$redis->get($key);
    }

    public function write($key, $value) {
        $redis = $this->connect($key);
        return $redis->set($key, $value, ini_get('session.gc_maxlifetime'));
    }

    public function destroy($key) {
        $redis = $this->connect($key);
        return $redis->del($key);
    }

    public function gc($maxlifetime) {
        // Handled by $redis->set(..., ini_get('session.gc_maxlifetime'))
        return 0;
    }
}