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Proposed change to 14.6 (Age)

From: Koen Holtman <koen@win.tue.nl>
Date: Fri, 31 May 1996 01:19:55 +0200 (MET DST)
Message-Id: <199605302319.BAA00994@wsooti04.win.tue.nl>
To: http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com
Cc: Koen Holtman <koen@win.tue.nl>

Section 14.6 of the pre-04 draft contains the following text:

>The Age response-header field allows a ache to transmit age values
>using:
>
>        Age = "Age" ":" age-value
>
>        age-value = delta-seconds
>
>Age values are non-negative decimal integers, representing time in
>seconds.  See section 13.2.3 for discussion of the use of Age.
>
>If a cache receives a value larger than the largest positive integer it
>can represent, or if any of its age calculations overflows, it MUST
>transmit an Age header with a value of 2147483648 (2^31). HTTP/1.1
                                                           ^^^^^^^^
>caches MUST send an Age header in every response.  Caches SHOULD use an
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>arithmetic type of at least 31 bits of range.

It is unclear from this language if an Age header must also be added
to first-hand responses (including non-cachable responses) which
travel through a proxy cache.

Section 13.2.3 (Age Calculations) seems to indicate that the Age
header value is only calculated for responses that have been stored in
cache memory. In particular, a note at the end of this section says:

>  Note that a client cannot reliably tell that a response is first-
>  hand, but the presence of an Age header indicates that a response
>  is definitely not first-hand. Also, if the Date in a response is
>  earlier than the client's local request time, the response is
>  probably not first-hand (in the absence of serious clock skew).

It is believed that the caching design as discussed on the mailing
list intends for the Age header to be added only to responses that are
not first-hand.  This way, if 1.0 caches are absent from the response
chain, presence/absence of to the age header is analogous to the
non-authoritative/authoritative distinction in DNS.

Based on all this, I propose that the sentence

  HTTP/1.1 caches MUST send an Age header in every response.

in 16.4 is changed into

  HTTP/1.1 caches MUST send an Age header in every non-first-hand
  response.

Koen.
Received on Thursday, 30 May 1996 16:25:13 EDT

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