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Re: Weak and strong ETags

From: Julian Reschke <julian.reschke@gmx.de>
Date: Fri, 01 Dec 2006 10:14:28 +0100
Message-ID: <456FF274.80305@gmx.de>
To: Henrik Nordstrom <hno@squid-cache.org>
CC: Wilfredo Sánchez Vega <wsanchez@wsanchez.net>, ietf-http-wg@w3.org

Henrik Nordstrom schrieb:
> tor 2006-11-30 klockan 20:03 -0800 skrev Wilfredo Sánchez Vega:
> 
>>    Two, I don't think you can assume that "X" and W/"X" are at all  
>> related to each other.
> 
> HTTP specs do... see RFC2616 13.3.3, The weak comparison function.

You are right. However, the fact that this discussion has been going on 
for almost one year now, and nobody mentioned that before, may indicate 
that RFC2616bis potentially could make that clearer.

>> In Apache's case, there is no such guarantee,  
>> because the same weak ETag may be issues to different versions of the  
>> document (if it is edited more than once in the same 1-second window),  
>> the data you got with an ETag of W/"X" may be completely different  
>> than the data that later exists with an ETag of "X", or even the same  
>> W/"X" you got.
> 
> Then Apache is somewhat broken.

Yes, at least when the resource can be authored.

> Two identical weak etags SHOULD only be used if the objects is
> semantically equivalent, but not necessarily octet equivalent. Two
> different edits can not be considered semantically equivalent in this
> context.  RFC 2616 13.3.4.
> ...

Best regards, Julian
Received on Friday, 1 December 2006 09:14:41 GMT

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