MTJ Hax

Nginx gzip config and image problems in IE

Posted in web hosting by mtjhax on February 2, 2010

I am running a web site under Nginx and noticed that when you right-click images on that site using IE, even if they are obviously JPEGs you can only save them as bitmaps (.BMP). If you get properties on the image the type comes up as unknown and the last modified date is missing. I tracked this down to my Nginx gzip configuration, specifically the option gzip_vary on;.

I won’t discuss what the gzip_vary option is supposed to do, partly because I don’t know and partly because I don’t care — it’s supposed to help tell browsers that gzip compression is available on the server or somesuch. After a little trial and error I realized that if I disabled this option, IE started treating my images normally. Apparently, if IE sees a HTTP response header that it doesn’t understand or is in the wrong place, it pitches a hissy fit and skips some of your headers. WTF.

I am using Nginx version 0.7.61. After reading the release notes of Nginx it appears this may have been a bug that is now fixed. One release mentioned that the gzip_vary header was being sent at inappropriate times. I can’t update that server right now because it’s on the critical path for a project at the moment and needs to be stable, but I will repost if updating Nginx solves the issue.

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