[module] Tracking connection status from accepted to closed

[Hung Nguyen]

Hello, 

I am writing a HTTP core module that track http connection to know when it’s accepted and closed within nginx.

What I am doing is register my module at PREACCESS_PHASE, and then adding a clean up callback to know when the connection closed (from nginx side). 
The problem is from my module i see nginx’s calling it twice, and calling my ngx_http_cleanup_t implement twice also. 

My question is: If I want to write my module to do exactly 2 things: 

1. Know when connection accepted by nginx 
2. and know when connection closed by nginx 

How should i implement my module? 

Thanks,