request.finished
如果 request.end() 已被调用，则 request.finished 属性将为 true。如果请求是通过 http.get() 发起的，则会自动调用 request.end()。
¥The request.finished property will be true if request.end()
has been called. request.end() will automatically be called if the
request was initiated via http.get().