'upgrade' 事件

每次客户端请求 HTTP 升级时发出。 监听此事件是可选的,客户端无法坚持更改协议。

触发此事件后,请求的套接字将没有 'data' 事件监听器,这意味着它需要绑定才能处理发送到该套接字上的服务器的数据。

Emitted each time a client requests an HTTP upgrade. Listening to this event is optional and clients cannot insist on a protocol change.

After this event is emitted, the request's socket will not have a 'data' event listener, meaning it will need to be bound in order to handle data sent to the server on that socket.