Date is a TDateTime property that indicates the origin date and time for an HTTP message. Origin servers must include a Date value in all responses, except in the following cases:
- Response status code is 100 (Continue) or 101 (Switching Protocols); Date is an optional header field.
- Response status code is a server error, e.g. 500 (Internal Server Error) or 503 (Service Unavailable), and it is inconvenient or impossible to generate a valid Date.
- Server does not have a clock that can provide a reasonable approximation of the current time, its responses must not include a Date header field.
A received message without a Date header must have a Date header value constructed on the client after receipt.
A message sent by a client can contain an optional Date header value if the message has an entity body, as in HTTP PUT and POST requests.