How do I compare two variables in an NGNIX conf file using the if statement or some other way?

Question

I have a variable say $foo and I need to do a case-insensitive match against a given pattern, but that pattern is also a variable received via a header. If that is true then I set a given variable to 1, which will be used later on. I tried with the following snippet:

set $variable 0; if ($foo ~* $http_header) { set $variable 1; } 

This didn't work. I also tried using ${http_header}, "$http_header", "${http_header}", but none of these worked. Can someone please tell me how to achieve this?

P.S. I know there will be a solution with LUA scripts, but we need to avoid using that for the purposes of the project I am working on.

Answer 1

You can concatenate the two variables then verify that the first half matches the second half using a regex. Is there an easier way in 2024?

set $room "$carpet:$curtains"; if ($room !~* "^(.*):\1$"){ return 403 '403 - Carpet ${carpet} did not match curtains ${curtains}'; } 

Borrowed from 2011

https://forum.nginx.org/read.php?2,206345,206620

Answer 2

I use following approach to map http_header $host to my custom variable.

In your case it would be something like:

map $http_header $foo { "~*{{REGEX_PATTERN}}" "{{FOO_CONTENT}}"; } 

You parse the content of your desired http_header with a {{REGEX_PATTERN}} and set your variable {{FOO_CONTENT}} accordingly.

Keep in mind, you can also use map without regex.

Please have a look at following stackoverflow answer, which sums it up really great.

https://stackoverflow.com/a/66381679/10891124

Nginx documenatation: https://nginx.org/en/docs/http/ngx_http_map_module.html