I am developing proxy for Flash game, it must sniff all the traffic from the game, edit some of it and send to the game main server, where requests are directed. I searched for solutions, but i've founded only solutions with using Wireshark or Python one's that can't sniff content, only ports and IPs.
I think you can use mitmproxy which is an open source and interactive TLS-capable HTTP proxy interceptor. It has a web interface and a Python API. Check below pages if it meets your needs.