'finish' 事件

当发送请求时触发。 更具体地说，当响应头和正文的最后一段已移交给操作系统以通过网络传输时，则将触发此事件。 这并不意味着服务器已经收到任何东西。

Emitted when the request has been sent. More specifically, this event is emitted when the last segment of the response headers and body have been handed off to the operating system for transmission over the network. It does not imply that the server has received anything yet.