For a certain endpoint (/upload), I would like to sometimes (when content-type matches) create a subrequest which calls an upstream with proxy_pass to include content before the actual response, which is also provided via proxy_pass. This isn't working right now and is only returning the content of the subrequest's upstream. Is this even possible? Here's the config that I'm using:

[code]
location "/" {
if ($content_type ~ "^multipart/form-data") {
echo_subrequest $request_method /saver2;
}

proxy_set_header X-Real-IP $remote_addr;
proxy_set_header Host $http_host;
proxy_pass http://assets;
}

location /saver2 {
internal;
rewrite / /__testing__/saver break;
proxy_pass http://filesaver;
}
[/code]