Substitute query string parameter based on query string params in nginx

Question

Preset:

We need to substitute a query parameter t=http://endpoint/:df01:/:df02:/:df03:/004.jpg with other query parameters ...?:df01:=1&:df02:=13&:df03:=9 we are passing in the request.

Result:

Redirect the request to http://endpoint/1/13/9/004.jpg.

By now we have a rule in our nginx.conf working well by executing the following rule :

    if ($args ~ "^rt=rt0010_01&.*&:df\d+:=(\d+)&:df\d+:=(\d+)&:df\d+:=(\d+)&t=(https?:\/\/.*)\/Newsletter\/.*\/.*\/.*\/(.*)") {
        set $location $4;
        set $params $2/$1/$3/$5;
        rewrite . $location/Newsletter/$params? redirect;
    }

Our problem is that we cannot dynamically change the arguments in the t= path like t=http://endpoint/:df01:/:df03:/:df02:/004.jpg, because the params argument is set "hardcoded" to $2/$1/$3/$5.

So my question is, can I build some kind of rewrite rule which parses the :dfxx: params in the t= variable and then substitute it with the other params suppied in the request or do I have to include some module extension which perhaps can do the job? (Btw, we also have to solve the hardcoded /Newsletter in the rewrite , it is yet present in the url supplied by the t=... param).

I was asked to add an example containing a full request and a corresponding response:

REQUEST:

http://nginx-srv.com/rd/?rt=rt0010_01&cid=609&:df01:=609&:df26:=02&:df08:=1&t=http://my.domain/Newsletter/:df26:/:df01:/:df08:/008.jpg

RESPONSE:

http://my.domain/Newsletter/02/609/1/008.jpg

I hope this is sufficient.

Could you please show a full request and the desired rewrite? — Gerard H. Pille
– Gerard H. Pille, Commented Jan 16, 2018 at 17:35

Gerard H. Pille · Accepted Answer · 2018-01-16 21:46:31Z

2

With the following rules you can shift the df parameters, and the endpoint is variable.

      if ($args ~ "(.*&?):(df\d\d):=(\d+)(&?.*/):\2:(/.*)" ) {
        set $args  $1$4$3$5;
      }
      if ($args ~ "(.*&?):(df\d\d):=(\d+)(&?.*/):\2:(/.*)" ) {
        set $args  $1$4$3$5;
      }
      if ($args ~ "(.*&?):(df\d\d):=(\d+)(&?.*/):\2:(/.*)" ) {
        set $args  $1$4$3$5;
      }
      if ( $args
           ~ "&?t=(https?:\/\/[^/]*/)([A-Za-z]*)(\/.*\/.*\/.*\/)([^&]*)&?" ) {
        set $rscheme $1;
        set $endpoint $2;
        set $arguments $3;
        set $image $4;
      }
      rewrite . $rscheme$endpoint$arguments$image? redirect;
      return 301;

An URL with the parameters

:df01:=1&:df02:=13&:df03:=9&t=http://my.domain/Newsletter/:df01:/:df02:/:df03:/004.jpg

gets rewritten to

http://my.domain/Newsletter/1/13/9/004.jpg

With parameters

:df02:=13&:df01:=1&:df03:=9&t=http://your.domain/Letternews/:df02:/:df03:/:df01:/lookatme.jpg

it gets redirected to

http://your.domain/Letternews/13/9/1/lookatme.jpg

edited Jan 16, 2018 at 21:46

answered Jan 16, 2018 at 20:17

Gerard H. Pille

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5 Comments

OliFausN Over a year ago

Hi Gerard, i simply have a problem to run it. I included your code in a location rd / {} block (the root url alwys starts with it) and nginx always responds with 302 found, but my browser is actually not doing any redirect. What am I doing wrong? (Btw., your rule looks far better than mine :-))

Gerard H. Pille Over a year ago

I suppose you have other locations that are more specific and match your URL. Without your complete configuration, I'm only guessing. But it's clear my code returns 301. Run an nginx -T, and look for all locations and 302's. What is a location rd / ?

OliFausN Over a year ago

Hi! thanks for responding. location rd was the part following nginx-srv.com as first path portion of the url. I will give a collegue a try. One more question: How would you implement some kind of dynamic path substitution in the t= param like t=your.domain/:df01:/:df02:/someImage.jpg in contrast to t=your.domain/:df01:/someImage.jpg, so that the third regexp group (\/.*\/.*\/.*\/) we have in t= can vary?

Gerard H. Pille Over a year ago

"location rd /" gives nginx: [emerg] invalid location modifier "rd". Regarding your one more question: I'd have a word with the designer of your site, and put him in a straitjacket.

Gerard H. Pille Over a year ago

put "&?t=(https?:\/\/[^/]*/)([A-Za-z]*)(\/[^/]*(\/[^/]*)*/)([^&]*)&?" and set $image $5;, then you can have less than 3 parameters.

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