Nginx Strip URL Parameters

Question

I want to strip url params before send it to proxy_pass

For visitor request url: => https://example.com/?wanted1=aaa&unwanted1=bbb&unwanted2=ccc&wanted2=ddd

Then it strip all the unwanted params to: => https://example.com/?wanted1=aaa&wanted2=ddd

My current way is like this:

if ($args ~ ^(.*)&(?:unwanted1|unwanted2)=[^&]*(&.*)?$ ) {
    set $args $1$2;
}

But It only remove 1 param and never do recursion. How to solve this? I want to modify the $args.

Have you tried using two if...set blocks, one for each unwanted parameter? — Richard Smith
– Richard Smith, Commented Aug 3, 2021 at 6:38
Does this question answer your question? stackoverflow.com/questions/26384776/… — Patrick Janser
– Patrick Janser, Commented Aug 3, 2021 at 7:10
@RichardSmith No. It will not work if I have the same string multiple times example.com/?unwanted2=aaa&unwanted2=aaa it will just remove the first unwanted2 — gidiwe2427
– gidiwe2427, Commented Aug 3, 2021 at 7:22

Richard Smith · Accepted Answer · 2021-08-03 08:14:01Z

1

If you want recursion, you can use a rewrite...last from within a location block. Nginx will only tolerate a small number of recursions (possibly ten iterations) before generating an internal server error.

For example:

location / {
    if ($args ~ ^(?<prefix>.*)&(?:unwanted1|unwanted2)=[^&]*(?<suffix>&.*)?$ ) {
        rewrite ^ $uri?$prefix$suffix? last;
    }
    ...
}

Note that you need to use named captures as the numbered captures are reset when the rewrite statement is evaluated.

Note that rewrite requires a trailing ? to prevent the existing arguments being appended to the rewritten URI. See this document for details.

answered Aug 3, 2021 at 8:14

Richard Smith

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2 Comments

gidiwe2427 Over a year ago

Its almost working. Just a little problem: hxxps://example.com/tester.php?unwanted1=111&unwanted2=222&unwanted2=222 will be rewrited to hxxps://example.com/tester.php?unwanted1=111 So our 'unwanted param' will not get stripped if its on the first place.

Richard Smith Over a year ago

Your regular expression currently requires the unwanted parameter to be proceeded by an &. Try: ^(?:(?<prefix>.*)&)?(?:unwanted1|unwanted2)=[^&]*(?<suffix>&.*)?$

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