Re: Still trying to make sense of HTTP caching model
Paul Leach (paulle@microsoft.com)
Wed, 6 Sep 95 19:24:06 PDT
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