code: public function getTtl($key)
      {
          $getResult = $this->getValue($key);
          $unserialized = @unserialize($getResult);
  
          if (!Util::hasInternalExpireTime($unserialized)) {
              throw new \Exception('Cannot retrieve ttl');
          }
  
          return $this->handleTtl($key, $unserialized['ts'], $unserialized['s']);
      }
docs: Returns the remaining time to live of a key that has a timeout.
  
  @param string $key
  
  @return int Ttl in seconds.
  
  @throws KeyNotFoundException
  @throws \Exception