Gzip_disable doesn't disable gzip_vary

Server NGINX
1

I noticed that with this setting:

gzip on;
gzip_vary on;
gzip_disable “msie6”;

Header “Vary: Accept-Encoding” will always be returned even though the
user agent is ie6 (and therefore not using gzip):

curl -I http://animebsd.net/about/feed -A "Mozilla/4.0 (compatible;

MSIE 6.0; Windows NT 5.0)"
HTTP/1.1 200 OK
Server: nginx/1.1.14
Date: Fri, 02 Mar 2012 07:04:25 GMT
Content-Type: text/xml; charset=UTF-8
Connection: keep-alive
Vary: Accept-Encoding
X-Pingback: http://animebsd.net/xmlrpc.php
Last-Modified: Fri, 02 Mar 2012 04:17:00 GMT
ETag: “92a5989a0949b85e303228490256ebf2”
X-Powered-By: W3 Total Cache/0.9.2.4
Link: http://wp.me/Pig2n-5B; rel=shortlink

I don’t think this is intentional as getting non-gzipped content
doesn’t return such header. (I’ve verified this is returned by nginx
by running same test with disabled gzip_vary)

(I don’t see mention of this being fixed in .15 and .16 in the
changelog so I haven’t tested with them)

2

Hello!

On Fri, Mar 02, 2012 at 02:08:05PM +0700, Edho A. wrote:

MSIE 6.0; Windows NT 5.0)"
Link: http://wp.me/Pig2n-5B; rel=shortlink

I don’t think this is intentional as getting non-gzipped content
doesn’t return such header. (I’ve verified this is returned by nginx
by running same test with disabled gzip_vary)

This is intentional, “Vary” is returned whenever gzip (and
gzip_vary) is enabled, as response representation depends on
header(s) listed.

Strictly speaking, it should also include User-Agent in case of
gzip_disable defined.

Maxim D.

3

2012/3/2 Maxim D. [email protected]:

This is intentional, “Vary” is returned whenever gzip (and
gzip_vary) is enabled, as response representation depends on
header(s) listed.

Strictly speaking, it should also include User-Agent in case of
gzip_disable defined.

Shouldn’t there be no change to header at all when client user agent
matches the gzip_disabled (ie. just like with gzip off)?

4

Hello!

On Fri, Mar 02, 2012 at 05:15:07PM +0700, Edho A. wrote:

Shouldn’t there be no change to header at all when client user agent
matches the gzip_disabled (ie. just like with gzip off)?

An HTTP/1.1 server SHOULD include a Vary header field with any
cacheable response that is subject to server-driven negotiation.

For sure with gzip enabled the response “is subject to server-driven
negotiation”.

Maxim D.

5

2012/3/2 Maxim D. [email protected]:

So, the “gzip enabled response” includes cases with non-gzip content as:

  • no “Accept-Encoding: gzip,deflate”
  • matches gzip_disabled
    and therefore “Vary: Accept-Encoding” will always be added even though
    the response isn’t compressed?

Or in other words, does “gzip on; gzip_vary on” means “add ‘Vary:
Accept-Encoding’ header on any responses matching gzip_types
regardless whether the response actually compressed or not”?

6

Hello!

On Fri, Mar 02, 2012 at 06:41:50PM +0700, Edho A. wrote:

negotiation".
regardless whether the response actually compressed or not"?
Yes.

Maxim D.