How can I add header conditionally in nginx configuration?

Question

How can I add header conditionally in nginx(1.4.6 ubuntu) configuration?

At first I tried like this.

 location / {
      add_header X-TEST-0 always-0;

      set $true 1;
      if ($true) {
          add_header X-TEST-1 only-true;
      }

      add_header X-TEST-2 always-2;
  }

Although I expected my nginx set all header(X-TEST-0,1,2), it added header only X-TEST-1.

Next I tried like this.

 location / {
      add_header X-TEST-0 always-0;

      ##set $true 1;
      ##if ($true) {
      ##    add_header X-TEST-1 only-true;
      ##}

      add_header X-TEST-2 always-2;
  }

My nginx added header X-TEST-1 and X-TEST-2 as I expected.

My quastions are...

How can I add header conditionally?
Why does nginx add only X-TEST-1 with my first example above?

Thanks in advance!

Thank you for the information! I could get all I wanted in the page you linked. — yazaki
– yazaki, Commented Apr 7, 2015 at 1:05

Ed Randall · Accepted Answer · 2019-10-02 10:55:25Z

17

This is simple if you think differently and use a map.

map $variable  $headervalue {
    1        only-true;
    default  '';
}

# ...later...
location / {
    add_header X-TEST-1   $headervalue;
}

If $variable is 1, $headervalue will be set and hence the header will be added. By default $headervalue will be empty and the header will not be added.

This is efficient because Nginx only evaluates the map when it's needed (when it gets to a point where $headervalue is referenced).

See similar: https://serverfault.com/questions/598085/nginx-add-header-conditional-on-an-upstream-http-variable

answered Oct 2, 2019 at 10:55

Ed Randall

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1 Comment

maganap Over a year ago

I believe it's important to add map is only valid on http context. I was using it on server context (right above the location directive) and got an error about "map" directive is not allowed here. nginx.org/en/docs/http/ngx_http_map_module.html#map

korya · Accepted Answer · 2015-12-15 17:38:51Z

6

I used lua nginx module to solve a similar problem:

localtion / {
  header_filter_by_lua_block {
    ngx.header["X-TEST-0"] = "always-0";
    # example of conditional header
    if ngx.req.get_method() == ngx.HTTP_POST {
      ngx.header["X-TEST-1"] = "only if POST request";
    }
    ngx.header["X-TEST-2"] = "always-2";
  }
}

https://github.com/openresty/lua-nginx-module#header_filter_by_lua_block ```

answered Dec 15, 2015 at 17:38

korya

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2 Comments

yazaki Over a year ago

Thanks for your useful information. It could be a solution for the nginx user who don't mind to use the modules which is not the standard of nginx.I voted +1.

Cosimo Over a year ago

If anybody is trying something like this, be aware that the correct lua syntax is possibly if ... then ... end :-)

Salem · Accepted Answer · 2022-01-03 20:19:58Z

0

I solve it this way, I wanted to print a specified country symbol first, I map the geo if certain IP's in the server blocks

geo $CNTRY {
    default '';
    192.104.49.0/24 ML;
    192.104.46.0/24 ML;
    192.104.47.0/24 ML;
}

Then I simply add it to server block, (anywhere doesn't matter)

add_header x-CNTRY $CNTRY;

answered Jan 3, 2022 at 20:19

Salem

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