# Reverse proxy replaces square brackets in request

**URL:** <https://www.ruby-forum.com/t/reverse-proxy-replaces-square-brackets-in-request/221422>\
**Category:** NGINX\
**Created:** [July 13, 2012, 12:49pm UTC](https://www.ruby-forum.com/t/reverse-proxy-replaces-square-brackets-in-request/221422 "2012-07-13T12:49:36Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![aris](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/258eb7/32.png) [@aris](https://www.ruby-forum.com/u/aris)\
**Post date:** [July 13, 2012, 12:49pm UTC](https://www.ruby-forum.com/t/reverse-proxy-replaces-square-brackets-in-request/221422/1 "2012-07-13T12:49:36Z")

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Hi,

I have a redirect loop problem with a website that gets reversed  
proxied. It looks like the following is the cause (which I don’t know  
how to solve)

Inspecting the site with httpfox, the request my browser sends looks  
like this:  
[https://www.acme.eu/acm/admin/gui\_call.php?Object=admin@GuiAdminStartpage&Params[gui]=&action=&no\_subtitle=1](https://www.acme.eu/acm/admin/gui_call.php?Object=admin@GuiAdminStartpage&Params%5Bgui%5D=&action=&no_subtitle=1)

My nginx log tells me this:  
GET  
/acm/admin/gui\_call.php?Object=admin@GuiAdminStartpage&Params%252525252525252525252525255bgui%252525252525252525252525255d=&action=&no\_subtitle=1  
HTTP/1.1"  
HTTP/1.1" 301 486 “[https://www.acme.eu/acm/ui/](https://www.acme.eu/acm/ui/)” “Mozilla/5.0 (X11;  
Ubuntu; Linux x86\_64; rv:13.0) Gecko/20100101 Firefox/13.0.1”

(This repeats over and over until firefox detects the loop)

To me it looks like somehow nginx changes the square brackets around  
“gui” into “252525252525252525252525255b” and  
“252525252525252525252525255d” respectively. I assume that because the  
script gui\_call.php gets wrong parameters, it redirects to /acm/ui.  
/acm/ui calls gui\_call.php with wrong paramters, and so on.

If my interpretation is correct, how can I stop this? If not, what is  
going on here?

Isaac

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**Author:** ![Isaac\_H](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/i/e480ec/32.png) [@Isaac\_H](https://www.ruby-forum.com/u/Isaac_H)\
**Post date:** [July 13, 2012, 9:50pm UTC](https://www.ruby-forum.com/t/reverse-proxy-replaces-square-brackets-in-request/221422/2 "2012-07-13T21:50:44Z")

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Hello!

On Fri, Jul 13, 2012 at 12:49:08PM +0200, Isaac H. wrote:

> My nginx log tells me this:  
> “252525252525252525252525255d” respectively. I assume that because  
> the script gui\_call.php gets wrong parameters, it redirects to  
> /acm/ui. /acm/ui calls gui\_call.php with wrong paramters, and so on.
> 
> If my interpretation is correct, how can I stop this? If not, what  
> is going on here?

The “GET … HTTP/1.1” in nginx logs is what your browser sent to  
nginx. Original request from browser likely had  
“…Params=%5bgui%5d…” in it (which is ok as per RFC 3986 square  
brackets must be escaped).

It’s not clear why and where additional escaping of a “%”  
character to “%25” happens, but likely in the same code which does  
redirects, i.e. it’s probably up to your php script.

Maxim D.