[Mod_gzip] "mod_gzip_send_vary=Yes" disables caching on IE? (1.3.26.1a)

[Jordan Russell]

Hello,

(Please forgive me if this has been discussed before; I did check the
archives but nothing turned up.)

While looking through my http access logs today I was alarmed to find a lot
of repeat requests for the same .gif files from the same hosts in a very
short period of time. As it turns out, Internet Explorer (6.0, at least)
doesn't want to cache objects that have a Vary header, so the same images
were being reloaded on each and every page visit. I did some searching and
found this:

http://groups.google.com/groups?selm=uTYe1IjgCHA.2324%40tkmsftngp08
"IE completely refuses to honor this VARY header and fetches new page
each time regardless of Cache-Control directive if it encounters VARY
header in server response. Now, RFC compliant browser (like Mozilla)
sees that header and make separate requests for separate VARY headers
specified)."

Changing mod_gzip_send_vary to No solved the problem, but of course that
creates issues with Squid...

This seems like a significant 'gotcha' to me, as it can defeat the purpose
of using gzip compression in the first place. If you have a site with static
pages and a lot of repeat visitors using IE, the total bandwidth consumed by
"mod_gzip + no caching" could end up being higher than "no mod_gzip +
caching".

Am I the first to notice this? Can anything be done about it? (Maybe
mod_gzip should avoid sending Vary headers unless it detects signs of a
proxy server?)

Thanks,
Jordan Russell