Hi Jordan,

On Thu, Nov 23, 2023 at 02:52:55PM +0000, J Carter wrote:
> # HG changeset patch
> # User J Carter <jordan.carter@outlook.com>
> # Date 1700751016 0
> # Thu Nov 23 14:50:16 2023 +0000
> # Node ID cc79903ca02eff8aa87238a0f801f8070425d9ab
> # Parent 7ec761f0365f418511e30b82e9adf80bc56681df
> Added merge inheritance to proxy_set_header
>
> This patch introduces 'inherit' argument to proxy_set_header
> directive. When marked as such it will be merge inherited into child
> contexts regardless of the presence of other proxy_set_header
> directives within those contexts.
>
> This patch also introduces the 'proxy_set_header_inherit' directive
> which blocks the merge inheritance in receiving contexts when set to off.
>
> The purpose of the added mechanics is to reduce repetition within the
> nginx configuration for universally set (or boilerplate) request
> headers, while maintaining flexibility to set additional headers for
> specific paths.
>
> There is no change in behavior for existing configurations.
>
> Example below:
>
> server {
>
> ...
>
> proxy_set_header Host $host inherit;
> proxy_set_header Connection "" inherit;
> proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for inherit;
>
> location /1/ {
> #sets this header in addition to server context ones.
> proxy_set_header customHeader1 "customvalue1";
> proxy_pass http://backend1;
> }
>
> location /2/ {
> #sets this header in addition to server context ones.
> proxy_set_header customheader2 "customValue2";
> proxy_pass http://backend1;
> }
>
> location /3/ {
> #no location specific headers, only server context ones set.
> proxy_pass http://backend1;
> }
>
> location /special/ {
> #Blocks merge inheritance from server context.
> proxy_set_header_inherit off;
> proxy_set_header Host "notserverthost.co";
> proxy_set_header Connection "";
> proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
> proxy_pass http://backend2;
> }
>
> }

Even though the inheritance rules we have now are not convenient for some
people, they do have one benefit - they are simple. Looking into a single
location is enough to have a full list of headers. You introduce inheritable
headers which break this simplicity.

I also though about this issue and I think it'd be better to add a separate
directive/parameter which would explicitly inherit all headers from the outer
scope.

server {
proxy_set_header Host "notserverthost.co";

location / {
...
proxy_set_header inherit; # explicitly inherit from above

proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
}
}

[..]

--
Roman Arutyunyan
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