Add Support for Variant ETags

[Maxim Dounin]

Hello!

On Thu, Dec 12, 2013 at 04:30:07PM -0800, Aaron Peschel wrote:

> Hello,
> 
> Weak ETAGs proved to be insufficient to meet my requirements.
> 
> Apache has solved their issues with ETAGs by appending the type of the variant
> to the existing ETAG. For example, the ETAG for a gzip variant would have -gzip
> appended (EG "abc123" becomes "abc123-gzip"). This seems like a reasonable
> solution to me, and it should work with Nginx as well.

This is incorrect solution, as gzipping may result in many 
different byte representations of a resource.  Strict entity tags 
aren't allowed as a result.

See also this ticket for some related discussion:

http://trac.nginx.org/nginx/ticket/377

-- 
Maxim Dounin
http://nginx.org/