InterSystems Response Content-Length

Hello, 
In short, I am trying to get the Content-Length of my response, 

We have a CSP application, when we get a new request we begin to process it, throughout the app we WRITE to the response in different places, 
now when the response is about to be sent back to the client - we would like to know its Content-Length (in the RESPONSE HEADERS). 
So it comes down to two questions:
1. How can we access the Content-Length of our response?

2. In case we CAN'T - Where in the broker.cls/page/base classes can I observe the moment we actually write the response itself and attach its headers?

Thank you!