PHP封装的数据库保存session功能类

<?php
class SafeSessionHandler implements SessionHandlerInterface {
  public $save_path;
  public $session_name;
  public $table;
  public function __construct() {
    $this->table = new Table("safe_session");
  }
  private function session_id_parse($session_id) {
    $time = hexdec(substr($session_id, 0, 8));
    $skey = substr($session_id, 8);
    return array($time, $skey);
  }
  public function close() {
    loginfo("close: ");
    return true;
  }
  public function create_sid() {
    loginfo("create_sid: ");
    $time = time();
    $skey = "";
    $char = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
    for ($i=0; $i<52; $i++) {
      $skey .= $char{mt_rand(0, 61)};
    }
    $session = array(
      "time" => $time,
      "skey" => $skey,
      "sval" => "",
    );
    $this->table->insert($session);
    return dechex($time) . $skey;
  }
  public function destroy($session_id) {
    loginfo("destroy: %s", $session_id);
    list($time, $skey) = $this->session_id_parse($session_id);
    $this->table->where("time = ?", $time)->where("skey = ?", $skey)->delete();
    return true;
  }
  public function gc($maxlifetime) {
    loginfo("gc: %s", $maxlifetime);
    $this->table->where("time < ?", time() - 86400  30)->delete();
    return true;
  }
  public function open($save_path, $session_name) {
    loginfo("open: %s, %s", $save_path, $session_name);
    $this->save_path = $save_path;
    $this->session_name = $session_name;
    return true;
  }
  public function read($session_id) {
    loginfo("read: %s", $session_id);
    list($time, $skey) = $this->session_id_parse($session_id);
    $row = $this->table->where("time = ?", $time)->where("skey = ?", $skey)->select()->fetch();
    if (empty($row)) {
      return "";
    }
    return $row["sval"];
  }
  public function write($session_id, $session_data) {
    loginfo("write: %s, %s", $session_id, $session_data);
    $session = array("sval" => $session_data,);
    list($time, $skey) = $this->session_id_parse($session_id);
    $this->table->where("time = ?", $time)->where("skey = ?", $skey)->update($session);
    return true;
  }
}