"gzip on" duplicates Content-Encoding header if an empty one already exists

Server NGINX
1

Hi,

I have a (probably dodgy) application that is sending out uncompressed
XML with the following header. That is, an empty Content-Encoding
header.

Content-Encoding:

This works fine, until I enable gzip on Nginx 1.6.2 latest (which is a
proxy to the application.) Nginx compresses the XML, and adds ANOTHER
Content-Encoding header, containing “gzip”.
I end up with this response:

Content-Encoding:
Content-Encoding: gzip

This seems to break on Safari and Google Chrome (not tested other
browsers.) They seem to ignore the latter header, and assume that
content is not compressed, and try to render the binary compressed
output.
Is this an issue in the client implementations, an issue in the Nginx
GZIP implementation, an issue in the upstream application, or a mixture
of all 3?

Looking at Nginx 1.6.2’s ngx_http_gzip_filter_module.c lines 246 to 255
(which I believe is the correct place) it checks for existence of a
Content-Encoding header with a positive length (non-zero) - so it looks
like if any other Content-Encoding was already specified, Nginx GZIP
does not do anything and does not duplicate header. So it seems the case
of an empty Content-Encoding slips through. Should this be the case?
Should it remove the existing blank header first, or just not GZIP if it
exists and is empty?

Thanks in advance,

Jason

2

Hi Jason,

Probably discarding the Content-Encoding directive from the upstream
will
resolve this:
http://nginx.org/r/proxy_hide_header

On Wednesday, March 25, 2015 12:04:03 PM Jason W. wrote:

Looking at Nginx 1.6.2’s ngx_http_gzip_filter_module.c lines 246 to 255
Jason

nginx mailing list
[email protected]
nginx Info Page
–
Best regards,
Styopa S…

3

Content-Encoding header, containing “gzip”. I end up with this response:

Jason
On 25 Mar 2015, at 19:08, Styopa S. <[email protected]
mailto:[email protected]> wrote:

Probably discarding the Content-Encoding directive from the upstream will
resolve this:
Module ngx_http_proxy_module http://nginx.org/r/proxy_hide_header

Best regards,
Styopa S…
(Apologies - resending on-list.)

Thanks I’ll give that a go!

Though I do think this might be incorrect Nginx behaviour as the header
should be modified not duplicated.

I’d like to find out if that is the case. Hopefully an easy fix that
will save others time down the line!

Jason