nginx catch tcp flag

I want to catch TCP flag of a packet to detect if a previous request is canceled. My goal is to detect FIN and RST flag.

My Nginx server receives some resquests from webservice. Some of these requests are long to proceed. I want to detect if client cancel its previous request. Requests are traited by an homemade process that Nginx call when it receives a request.

Where can I find these informations from Nginx ? I have to use fastcgi_param ? If yes, which one ? I search on Nginx documentation but doesn't find anything… I think I don't search on the good module…