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Re: Still trying to make sense of HTTP caching model

From: Paul Leach <paulle@microsoft.com>
Date: Wed, 6 Sep 95 19:24:06 PDT
Message-Id: <9509070319.AA09437@netmail2.microsoft.com>
To: fielding%beach@w3.org, http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com
Roy says:
] >This usage encodes some very non-intuitive semantics in the Expires:
] >heading.  If you want to tell the proxy to cache a document but always
] >validate it then create a header or Pragma to do that.
]
] Just as an informational point, I already included these semantics
] in draft 01 for the "max-age" (now Cache-Control: max-age=NNN) parameter.

So this transfers my query about the ability to coexist of "Expires: 
<yesterday>" and a hypothetical "Cache-Control: always-validate" to the 
same question for "Expires: <yesterday>" and a spec'd "Cache-Control: 
max-age=0".

There are now three ways that have been proposed to say that the cache 
manager could construe as telling it it can cache but needs to check:
1. Expires: <yesterday>
2. Expires: value same as Date: value
3. Cache-Control: max-age=0

Ugggh.

In general, how is
	Expires: now+T
different than
	Cache-Control: max-age=T

(Modulo clock skew issues, which Jeff has sugegsted a way to fix.)

Paul
Received on Wednesday, 6 September 1995 19:26:40 EDT

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