Re: [OT] HTTP etag vs if-* vs range vs content-encoding?

[Rici Lake <lua@...>]

On 1-Feb-07, at 3:10 PM, PA wrote:

> Yes... but I'm still not 100% clear about somewhat basic things like 
> do you gzip a response first and then compute it's etag or the other 
> way around... when requesting a range, does that apply to the encoded 
> content or not... how does a conditional requests fits with a range 
> request, etc...

My understanding, which may not be right :), is that an Etag identifies 
an actual entity, not a transmission of an entity. So it's computed on 
the entire original object, not the transmission encoding of the object 
(or the bits of the object which are being transmitted on a range 
request.)

Note that there is a difference between requesting an object which is 
in compressed format, and compressing the tranmission of a request of 
an object. In the former case, the etag would apply to the compressed 
data; in the latter case to the uncompressed data. ("The bits of the 
entity" is what RFC-2616 says, non-normatively.)

Etags only have to be unique between different variants of the same 
resource; i.e. if the url's are identical. Using a hash is common but 
not obligatory; as RFC-2616 says, you could simply attach a version 
number to a given resource and increment it on each modification.