A client sends Expect: 100-continue. How long must it wait before sending the request content?
For a server-defined interval carried in Retry-After
For no specific length of time; the client MAY proceed to send the content even with no response yet✓Правильный ответ
Until it receives 100 (Continue) or a final status code, with no timeout permitted
Until it receives 100 (Continue), or the request is invalid
Объяснение
The expectation is a request for an early verdict, not a handshake the client is bound by: it is not required to wait any specific length of time, and since 100 responses cannot cross an HTTP/1.0 intermediary it should not wait indefinitely. The MUST here is on the origin server, which may not wait for the content before sending its 100 (Continue).