How to redirect on the same port from http to https with nginx reverse proxy

Found something that is working well :

server {
        listen 8001  ssl;
        ssl_certificate /home/xxx/server.crt;
        ssl_certificate_key /home/xxx/server.key;
        error_page 497 301 =307 https://$host:$server_port$request_uri;
        location /{
            proxy_pass http://localhost:8000;
            proxy_redirect off;
            proxy_set_header Host $host:$server_port;
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
            proxy_set_header X-Forwarded-Ssl on;
        }
}