Thank you for your response.
I've made a mistake. I've made my initial tests with a lot of different
combinations and last value I have used, which doesn't add header at all, is
indeed an empty string, not 0. So it seems this works as expected.
I think it is functionality worth documenting though. When I searched the
internet for "how to add nginx header conditionally" there was dozen of
examples which used only ifs, or a combination of maps and ifs, but none of
them actually mentioned that add_header is on itself conditional.
--
Best Regards,
Vilius
-----Original Message-----
From: nginx <[email protected]> On Behalf Of Maxim Dounin
Sent: Monday, March 27, 2023 7:09 PM
To: [email protected]
Subject: Re: nginx configuration variable interpolation
Hello!
On Mon, Mar 27, 2023 at 03:24:06PM +0000, Vilius Šumskas wrote:
> I have the following directive in Nginx configuration:
>
> location /docs {
> add_header Access-Control-Allow-Origin $cors_origin; }
>
> $cors_origin comes from the map {} where the value is set to * or something
> else.
>
> I have noticed that if $cors_origin is set to 0, add_header doesn’t
> add Access-Control-Allow-Origin header at all. Is this expected? I
> don’t see anything about such behaviour in the add_header
> documentation.
The header will not be added if the value is an empty string. If it is not
empty but "0", the header will be added just fine. For example, consider the
following configuration:
map $uri $cors_origin {
default 0;
}
server {
...
location / {
add_header Access-Control-Allow-Origin $cors_origin;
return 204;
}
}
Test:
$ telnet 127.0.0.1 8080
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
GET / HTTP/1.0
HTTP/1.1 204 No Content
Server: nginx/1.22.1
Date: Mon, 27 Mar 2023 16:01:05 GMT
Connection: close
Access-Control-Allow-Origin: 0
Connection closed by foreign host.
As you can see from the telnet output, the Access-Control-Allow-Origin is
properly added. If you are seeing a different behaviour, you may want to
recheck the value actually being used. If it is indeed "0", and not an empty
string, please provide more details.
--
Maxim Dounin
http://mdounin.ru/
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