string(258) "get document error：https://zhidao.baidu.com/search?lm=0&rn=10&pn=0&fr=search&dyTabStr=null&word=%E4%BF%9D%E8%AF%81%E6%96%B9%E5%BC%8F%E7%9A%84%E6%A6%82%E5%BF%B5%E5%8F%8A%E7%89%B9%E7%82%B9 => Failed to connect to 125.88.227.171 port 38114: Connection refused"
保证方式的概念及特点
