nginx Expires header based on mime type for proxied content?

Question

My setup uses a map to define different Expires headers for various static files (based on their mime type). For proxied content (uwsgi_pass), I use a static Expires header:

map $sent_http_content_type $expires {
    default                    off;
    text/html                  7d;
    text/css                   180d;
    application/font-woff2      1y;
    application/pdf             1y;
    ~image/                     1y;
}

server {
    listen       443 ssl http2;
    server_name  example.com;
    
    location / {
            uwsgi_pass django;
            expires 7d;
    }
    
    location ~ ^/(css|fonts|images|pdf|html)/ {
            root /var/www/django/static/;
            expires $expires;
    }
}

Using the map (via the $expires variable) for proxied content does not work. Is there any way for nginx to identify the mime type of proxied content in order to make this work?

location / {
        uwsgi_pass django;
        expires $expires;
}

(Edit) As Alexey suggested, I did this:

map $upstream_http_content_type $expires2 {
         default                    off;
         text/html                  2d;
         text/plain                  20d;
         text/css                   180d;
}

location / {
        uwsgi_pass      django;
        expires $expires2;
}

Unfortunately, there is still no Expires header added to the content delivered via uwsgi.

Answer 1

The solution was provided by Alexey and Richard in the comments. I had to use a different nginx variable, and a regex for (at least) the map entry for HTML files:

map $upstream_http_content_type $expires2 {
         default                    off;
         ~text/html                  2d;
         text/plain                  20d;
         text/css                   180d;
}

location / {
        uwsgi_pass      django;
        expires $expires2;
}