is ETag a representation header field?

[julian.reschke@…]

Reported by zhong.j.yu@…:

"​http://tools.ietf.org/html/draft-ietf-httpbis-p3-payload-17#section-4.1 Section 4.1. Representation Header Fields

"Last-Modified" is included, but not "ETag".

Isn't "ETag" also part of representation metadata?

Cheers, Zhong Yu"

[masinter@…]

I think so, the eTag for a representation tells the validity of that representation as corresponding to the current state of the resource.

[masinter@…]

unlike lastModified, which could be construed as information about the resource, independent of this particular representation.

As such it might be that content-negotiated resources could be matched against any one of the eTags of cached content. Resource --> Representations w/etags --> (selection by varying request headers) --> Representation with eTag

eTags are only URI/resource-unique, or the caching could be extended. Is it feasible in future to add an indication to eTag that it is in fact a GUID?

[fielding@…]

ETag and Last-Modified are metadata for the selected representation, which is not always the same as the representation enclosed in the response. I have added those terms from p4 and used a separate table to reference the fields.

Incorporated in [1571].

[julian.reschke@…]

From [1573]:

Note change for [1571] (see #330)