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Re: why no-cache is not reload

From: Shel Kaphan <sjk@amazon.com>
Date: Sat, 17 Feb 1996 09:21:46 -0800
Message-Id: <199602171721.JAA13624@bert.amazon.com>
To: "Roy T. Fielding" <fielding@avron.ICS.UCI.EDU>
Cc: hardie@nasa.gov, http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com
Roy T. Fielding writes:
 > > 	On a related note, does cache-control: max-age 0 also force
 > > a reload (by asking for a copy of the resource that is no older than
 > > 0 seconds old?).
 > 
 > No, it forces a "refresh" (i.e., a conditional GET on the next inbound
 > server w/max-age=0, which results in a conditional GET on the origin).
 > It is possible that the refresh will result in a reload, but only if
 > the server decides that the resource has changed.
 > 


How is a request containing
	cache-control: max-age=0
but NOT
	if-modified-since:  <last modified date of resource>

conditional?   Without  if-modified-since, the origin server would
always have to return a full response, wouldn't it?  HTTP being stateless,
unless the server has something to compare to, it doesn't know the requestor
has the same version, or where it got the version it has.

In what way is the effect of an unconditional request containing:
	cache-control: no-cache

supposed to be different from an unconditional request containing:
	cache-control: max-age=0
?

Both will force the request to be forwarded to the origin server.
Both will allow the origin server to responsd with 200, but not 304.
Neither prevent the body of a 200 response from being stored into
any cache along the request chain.

In what way is the effect of a request containing:
	cache-control: no-cache
	if-modified-since:  <last-modified date associated with resource>

supposed to be different from a request containing:
	cache-control: max-age=0
	if-modified-since:  <last-modified date associated with resource>
?

Both will force the request to be forwarded to the origin server.
Both will allow the origin server to respond with 304 or 200.
Neither prevent the body of a 200 response from being stored into
any cache along the request chain.

--Shel
Received on Saturday, 17 February 1996 11:24:13 EST

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