using $upstream* variables inside map directive

[Kirill K.]

Thanks, Ruslan,
Thing is, I tried to "debug" whether $dontcache is being set at all by
exposing it via response headers (along with content-length), and it shows
that $upstream_response_length is ignored by map completely, i.e. no matter
where I use $dontcache, it will never get any value different from default
(i.e. 0). Even though $upstream_response_length  is validated correctly (and
can be exposed in headers), the map directive just ignores it.

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,249880,249895#msg-249895