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Warnings and SHOULD

From: Mark Nottingham <mnot@mnot.net>
Date: Sun, 17 Jul 2011 11:52:48 +1000
Message-Id: <228261B5-B508-4FB3-AEC7-F05070FEF442@mnot.net>
To: HTTP Working Group <ietf-http-wg@w3.org>
Our text on Warnings <http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-15#section-3.6> currently includes the following requirements:

"""
   110 Response is stale

      A cache SHOULD include this whenever the returned response is
      stale.

   111 Revalidation failed

      A cache SHOULD include this when returning a stale response
      because an attempt to validate the response failed, due to an
      inability to reach the server.

   112 Disconnected operation

      A cache SHOULD b include this if it is intentionally disconnected
      from the rest of the network for a period of time.

   113 Heuristic expiration

      A cache SHOULD include this if it heuristically chose a freshness
      lifetime greater than 24 hours and the response's age is greater
      than 24 hours.
"""

(yes, there's a typo)

... along with a corresponding requirement in <http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-15#section-2.3.3>:

"""
   A cache SHOULD append a Warning header field with the 110 warn-code
   (see Section 3.6) to stale responses.  Likewise, a cache SHOULD add
   the 112 warn-code to stale responses if the cache is disconnected.
"""

I'd observe that the information in 110 and 113 duplicates what a client can already discover from examining the caching headers on the response (Date, Age, Expires, Last-Modified, Cache-Control), so I propose we downgrade these to MAYs (or just change it to prose).

While we're at it, the semantics of 111 and 112 seem purely advisory, and they're not implemented in clients or caches (at all, AFAIK). So, I'd propose we downgrade them at the same time.

This would allow us to remove the text in 2.3.3, or just turn it into an informative reference.

Thoughts?


--
Mark Nottingham   http://www.mnot.net/
Received on Sunday, 17 July 2011 01:53:15 GMT

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