Apache Rewrite rules: How to check for host name in cookies?

Question

I am setting a cookie using rewrite rules, and that is working (simplified for the sake of brevity):

RewriteCond %{QUERY_STRING} set_cookie=1 [NC]
RewriteRule .* http://%{HTTP_HOST}%{REQUEST_URI}?skip=1 [QSA,NE,NC,L,CO=test_%{HTTP_HOST}:tmp:%{HTTP_HOST}:5:/]

This one sets a cookie with the name test_{host_name}. Now I want to read that cookie value the next request. I tried this (and some variants), but that does not seem to work.

RewriteCond %{QUERY_STRING} skip [NC]
RewriteCond %{HTTP_COOKIE} ^.*test_%{HTTP_HOST}=tmp.*$ [NC] 
RewriteRule ^(.*)$ - [L]

When I was googling, I found an article that stated the following:

If you are wondering, "Why not use %{HTTP_HOST} instead of corz.org, create universal code?", as far as I know, it's not possible to test one server variable against another with a RewriteCond without using Atomic Back References and some serious POSIX 1003.2+ Jiggery-Pokery.

I guess that's my problem, but I am sort of at a loss on how to solve it. Any help is greatly appreciated.

Regards, Joost.

Answer 1

There's a useful trick in this area. It is simple regex, but a unique kind of mod_rewrite style.

Note I am not too careful about the matching here especially in the first condition -- this is for illustration in the 2nd condition:

RewriteEngine ON
RewriteCond %{HTTP_COOKIE} test_([^;]*)=tmp.*$
RewriteCond %1<>%{HTTP_HOST} ^(.+)<>\1
RewriteRule .* - [F]

The novel part (for mod_rewrite) is that you can only use variables/backrefs in the first argument, but you can use backrefs (for the current expression, not the preceding one) in the 2nd parameter.

The little <> is just something unlikely to appear as a separator.

Answer 2

I have found a solution. This part in my original question

RewriteCond %{QUERY_STRING} skip [NC]
RewriteCond %{HTTP_COOKIE} ^.*test_%{HTTP_HOST}=tmp.*$ [NC] 
RewriteRule ^(.*)$ - [L]

should be replaced by the following

RewriteCond %{QUERY_STRING} skip [NC]
RewriteCond %{HTTP_HOST}@@%{HTTP_COOKIE} ^([^@]*)@@.*test_\1=tmp.* [NC]
RewriteRule ^(.*)$ - [L]

Only the second RewriteCond has changed. Its left hand side (%{HTTP_HOST}@@%{HTTP_COOKIE}) concatenates the http host and cookie values, using @@ as glue (@@ doesn't really mean something, it's just unlikely to be used in a normal host or cookie string).

The right hand side (^([^@]*)@@.*test_\1=tmp.*) matches everything to the first "@", which is the host name, and then checks if it can be found somewhere in the cookie values, preceded by "test_" and followed by "=tmp".