partial urlEncoding when using if and $request_uri

[mte03]

Hi,

I have observed strange behavior with nginx rewrites. What happens: I get
request going to myserver.com/appID/path1/path2/uglyID and I need to proxy
this to appID.backend.internal/path1/path2/uglyID. The uglyID is URL encoded
because it contains characters like commas and forward slashes. When I do
location matching in nginx, nginx will url decode $uri parameter on which it
does matches. That's not a problem, when the location matches, I can extract
the appID and then extract the rest from $request_uri. And here the issue
happens. If I use:  

if ($request_uri ~ ^/[^\/]+(/.*)$ ) { set $path $1; }, the uglyID (but only
uglyID) gets URL encoded again. The $path simply is
/path1/path2/urlEncoded(uglyID). However, when I do 

if ($uri ~ ^/[^\/]+(/.*)$ ) { set $path $1; }, then $path will be the
urlDecoded(/path1/path2/uglyID) - as expected.

I have tested this on ubuntu 12.04 (Linux ip-10-50-20-57 3.2.0-36-virtual
#57-Ubuntu SMP Tue Jan 8 22:04:49 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux)
and nginx versions nginx/1.1.19 and nginx/1.5.6 - and the behavior is
consistently same in both versions. The nginx config is identical in all
cases, only difference is the name of the variable in the if statement,
where using $request_uri simply implies uglyID (but only uglyID - not the
whole matched string) will be url encoded again. Meanwhile I have found
possible workaround using maps, where matching on $request_uri works
correctly and doesn't modify matched data anyhow. 

So I wonder, has anyone else experienced this? Is this expected? Why is the
uglyID (but only uglyID) url encoded again? I would expect either
urlEncoding of the whole match, or none at all - as it doesn't happen when I
try to match e.g. $uri... Could this indicate a possible bug?

Thanks,

Michael

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,244573,244573#msg-244573