'checkExpectation' 事件

每当接收到一个带有 HTTP Expect 请求头(值不为 100-continue)的请求时触发。 如果该事件未被监听,则服务器会自动响应 417 Expectation Failed

当该事件被触发且处理后,'request' 事件不会被触发。

Emitted each time a request with an HTTP Expect header is received, where the value is not 100-continue. If this event is not listened for, the server will automatically respond with a 417 Expectation Failed as appropriate.

Note that when this event is emitted and handled, the 'request' event will not be emitted.