Does the `Expires` HTTP header needs to be consistent across multiple cold-cache requests?

Posted by chakrit on Stack Overflow See other posts from Stack Overflow or by chakrit
Published on 2010-03-16T22:22:04Z Indexed on 2010/03/16 23:21 UTC
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http-headers

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expires

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http-caching

I'm implementing a custom web server of a kind. And am looking into adding an Expires header support. However, I'm a little unsure of how exactly to implement it.

If multiple cold-cache requests are being made to the same unchanged resource on the server and the server returned different Expires header (say it uses relative time to calculate the exact value of the Expires date e.g. +6 hours from the request time), does that invalidate the cache on all the proxy servers in-between as well? Or is it impossible to happen (per the spec)?

Does the Expires HTTP header needs to be consistent across multiple cold-cache requests?

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