How do I get the client IP and Port from it's NAT via HTTP?

Question

I want to make an application to send email and messages directly to other clients as a P2P service, using a web server to maintain a list of clients online with registration of the IP and Port sent by the NAT in which the client will read the list to connect directly to destiny client.

Is it possible to receive this information in an HTTP Web Server? How do I do it? Or may I use only an UDP server (UDP Hole Punch)?

Something like primordial Skype, but with web server.

Answer 1

You cannot.

From the "outside" NAT acts as your only client and you only know its (NAT's) source IP and (not always) source port.