public function diffCommand($url = 'http://www.baidu.com')
    {
        $remote_ts = $this->_getRemoteTimestamp($url);
        $local_ts = time();
        if ($remote_ts === false) {
            return $this->console->error(['fetch remote timestamp failed: `:url`', 'url' => $url]);
        } else {
            $this->console->writeLn(' local: ' . date('Y-m-d H:i:s', $local_ts));
            $this->console->writeLn('remote: ' . date('Y-m-d H:i:s', $remote_ts));
            $this->console->writeLn('  diff: ' . ($local_ts - $remote_ts));
            return 0;
        }
    }