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A question about RFC7232#2.2.2

From: Michael Lee <michael.lee@zerustech.com>
Date: Sat, 3 Dec 2016 03:11:38 +0800
To: ietf-http-wg@w3.org
Message-ID: <5841C76A.9020103@zerustech.com>
I am currently working on a tutorial of HTTP/1.1 caching, but I got 
stuck with the following statement in RFC7232 section 2.2.2:

" This method relies on the fact that if two different responses were 
sent by the origin server during the same second, but both had the same 
Last-Modified time, then at least one of those responses would have a 
Date <http://httpwg.org/specs/rfc7231.html#header.date> value equal to 
its Last-Modified time. The arbitrary 60-second limit guards against the 
possibility that the Date and Last-Modified values are generated from 
different clocks or at somewhat different times during the preparation 
of the response. An implementation /MAY/ use a value larger than 60 
seconds, if it is believed that 60 seconds is too short."

I don't understand why under the circumstance above, at least one of 
those responses would have a Date value equal to its Last-Modified time.

And what's the point of ensuring a 60 seconds gap between the 
Last-Modified time and Date?

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Michael Lee / Managing Director / ZerusTech Ltd

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Received on Friday, 2 December 2016 19:12:13 UTC

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