事件：'checkExpectation'

【Event: 'checkExpectation'】

• request <http.IncomingMessage>
• response <http.ServerResponse>

每当收到带有 HTTP Expect 头且其值不是 100-continue 的请求时都会触发此事件。如果没有监听此事件，服务器将自动使用适当的 417 Expectation Failed 响应。

【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.】

当此事件被触发并处理时，'request' 事件将不会被触发。

【When this event is emitted and handled, the 'request' event will not be emitted.】