http消息结构：http://www.runoob.com/http/http-messages.html
http请求方式：http://www.runoob.com/http/http-methods.html
http状态码：http://www.runoob.com/http/http-status-codes.html
http content-type：http://www.runoob.com/http/http-status-codes.html
常用http请求头和响应头：https://blog.csdn.net/qq_30553235/article/details/79282113