Describe the feature you'd like to add to nginx

I would like some functions or directives to check file size and other stuff eg. a line content of a web app file. This new feature should provide the software backend to check the web app components before to serve them live.

Describe the problem this feature solves

web app security on live stage

Additional context

map $file_size = file size list
/run/launch.sh = /scripts file sizes gen batch
webapp.conf: req_size_check $file $file_size 403