Allgemeine HeaderDate
Beispiel:
Date: Tue, 15 Nov 1994 08:12:31 GMT
Original Beschreibung (engl.):
The Date general-header field represents the date and time at which
the message was originated, having the same semantics as orig-date in
RFC 822. The field value is an HTTP-date, as described in section
3.3.1; it MUST be sent in RFC 1123 [8]-date format.
Date = "Date" ":" HTTP-date
An example is
Date: Tue, 15 Nov 1994 08:12:31 GMT
Origin servers MUST include a Date header field in all responses,
except in these cases:
1. If the response status code is 100 (Continue) or 101 (Switching
Protocols), the response MAY include a Date header field, at
the server's option.
2. If the response status code conveys a server error, e.g. 500
(Internal Server Error) or 503 (Service Unavailable), and it is
inconvenient or impossible to generate a valid Date.
3. If the 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. In this case, the rules
in section 14.18.1 MUST be followed.
A received message that does not have a Date header field MUST be
assigned one by the recipient if the message will be cached by that
recipient or gatewayed via a protocol which requires a Date. An HTTP
implementation without a clock MUST NOT cache responses without
revalidating them on every use. An HTTP cache, especially a shared
cache, SHOULD use a mechanism, such as NTP [28], to synchronize its
clock with a reliable external standard.
Clients SHOULD only send a Date header field in messages that include
an entity-body, as in the case of the PUT and POST requests, and even
then it is optional. A client without a clock MUST NOT send a Date
header field in a request.
The HTTP-date sent in a Date header SHOULD NOT represent a date and
time subsequent to the generation of the message. It SHOULD represent
the best available approximation of the date and time of message
generation, unless the implementation has no means of generating a
reasonably accurate date and time. In theory, the date ought to
represent the moment just before the entity is generated. In
practice, the date can be generated at any time during the message
origination without affecting its semantic value.
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