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RE: Expires: yesterday (was Re: Location Proposals)

From: Paul Leach <paulle@microsoft.com>
Date: Wed, 6 Sep 95 14:09:52 PDT
Message-Id: <9509062248.AA17783@netmail2.microsoft.com>
To: mogul@pa.dec.com
Cc: http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com
Jeff said:
] Frankly, it doesn't much matter to me if we use "Expires: yesterday"
] or "Cache-control: always-validate"; these are just syntactically
] different ways of expressing the same thing, IF (note the big IF)
] we agree on the basic rule that
]
] 	for an object with Expiration time T
] 		prior to time T, the cache is assumed to be valid
] 		after time T, validity MUST be checked with the server

I'll agree 100% that it doesn't matter to me either, if we can add the 
following rider:
	IF "Cache-control: always-validate" is present,
		THEN "Expires:" is not allowed

Otherwise, what do I do if both are present? That would seem to break 
your rule above, and necessitate changing it to:
 	for an object with Expiration time T
 		prior to time T, the cache is assumed to be valid, unless
			"Cache-control: always-validate" was present
			when it was fetched	
 		after time T, validity MUST be checked with the server, unless
			"Cache-control: always-validate" was present
			when it was fetched, in which case it must be refetched	

] Arguments about what is "natural" or not are pretty pointless, since
] it appears that two people have diametrically opposite ideas of what
] is natural here.

I agree. I should choose words more carefully. I was only claiming 
"naturalness" with respect to a particular sketch of how caches might 
work, where (I at least hoped) it was clear that the intended behavior 
fell out with very few changes. I make no claim that other people would 
find that sketch reasonable, or whether they would agree that that's 
the right metric of "natural". But at least people would know why I 
thought it was more natural.

] I would point out that the "Expires: yesterday"
] approach might be more likely to cause correct operation of existing
] proxies, but I don't have specific evidence to back this up.

I guess if their general approach to managing their cache was close to 
the sketch, then it would be likely.

Paul
Received on Wednesday, 6 September 1995 14:55:45 EDT

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