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thinking about etags

From: Larry Masinter <LMM@acm.org>
Date: Sat, 18 Aug 2007 09:05:21 -0700
To: <ietf-http-wg@w3.org>
Message-ID: <001b01c7e1b1$9531ac30$bf950490$@org>

I'm confused by the current concept of eTags (now embodied in several
RFCs and in the discussions, maybe I'm a few years late on this):

The original intent of eTag was that it was a namespace owned by the server
which corresponded to the content of a response, specifically, the body of
what the response to a GET would be.

ETag responses for other request methods were "this is what the eTag would
for the same request (including URI but also other request methods)
if you used the GET method instead".  

In this concept, the client can't make up an eTag because the client
doesn't own the eTag namespace, and so eTags on request messages (like PUT)
didn't make sense.

In this concept, you don't talk about the eTag of a 'resource', since
resources or variants don't have eTags, only the body of a GET response.

Perhaps 2616 didn't really explain this, but I don't really understand
the current concept of what an eTag really means if it is different
from the above concept.

Would it help to clarify the eTag description along these lines?
To not talk about "the eTag of a variant" but "the eTag that would
be returned in a response to a GET request with the same request
headers?" (I suppose including a Vary response header).

Received on Saturday, 18 August 2007 16:05:30 UTC

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