# Can nginx handle/cache this robot handling case?

**URL:** <https://www.ruby-forum.com/t/can-nginx-handle-cache-this-robot-handling-case/235472>\
**Category:** NGINX\
**Created:** [June 24, 2013, 9:46am UTC](https://www.ruby-forum.com/t/can-nginx-handle-cache-this-robot-handling-case/235472 "2013-06-24T09:46:04Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![alcina](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/a587f6/32.png) [@alcina](https://www.ruby-forum.com/u/alcina)\
**Post date:** [June 24, 2013, 9:46am UTC](https://www.ruby-forum.com/t/can-nginx-handle-cache-this-robot-handling-case/235472/1 "2013-06-24T09:46:04Z")

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Hi everyone.

First some background. I’m trying to integrate the method used by  
Pixabay to handle Google Image Search’s new design which makes it very  
easy (one button click) for visitors to see an image outside of the  
site’s context. This has greatly slammed many sites’ traffic and income.

This is how Pixabay got nginx to handle hijacking the button so the  
image can be seen in the site’s context:

“Hotlinking protection and watermarking for Google Images”:  
([http://pixabay.com/en/blog/posts/hotlinking-protection-and-watermarking-for-google-32/](http://pixabay.com/en/blog/posts/hotlinking-protection-and-watermarking-for-google-32/))

Part of the method is using what they call “trap URLs”. i.e. adding “?i”  
to img URLs in the source when the page is seen by a human. Bots like  
googlebot don’t see the ?i and so they get handled differently by nginx:

if ($args = “i”) { set $watermark 0; }  
if ($watermark = 1) {  
add\_header Cache-Control “no-cache, must-revalidate”;  
// rewrite “IMAGE\_URL\_REGEX” WATERMARK\_URL last; \<-optional serving of  
a watermarked version of image.  
}

Pixabay handles creating the “?i” addendum to the img tag in their  
templates. I was looking for a method that was a little more  
caching/performance friendly, so I suggested using jQuery to append the  
“?i” to browsers at the document ready stage so bots would not get the  
?i and the page could still be cached because the “?i” was added on the  
client side. e.g.

var img= $(“img.myimg”);  
img.attr(“src”, img.attr(“src”)+“?i”);

The only problem is that the page now hits the server twice. Once when  
loading /the/file/location/img.jpg and a second time after jQuery  
changes it to loading /the/file/location/img.jpg?i

It was suggested that I could potentially add Varnish to my stack and  
strip out the ?i from the URLs for bots then but I didn’t want to add  
something else to the stack

Can nginx and, say, the fastcgi cache (which I use) handle this  
situation natively? Let’s say all pages have the “?i” at the end of  
their image locations so they’re already there for the majority (human  
traffic). Is there an efficient way for nginx, upon detecting a bot  
agent, to strip the ?i (perhaps with  
[Module ngx\_http\_sub\_module](http://wiki.nginx.org/HttpSubsModule)), serve and gzip and cache that  
version, while serving/caching the original version to browsers?

It’s a long post. (!) I just have an inkling that my fave server can  
handle this. Just don’t have the experience to configure it.

Thanks for any insight.