[Twisted-Python] Best way to write a modularized proxy?

[Andrew Warkentin]

I am writing a modular multi-protocol proxy (initially for HTTP, and 
later HTTPS and possibly FTP as well) using Twisted. It will consist of 
a small core that handles initialization and loading of modules, a 
module for each protocol (which will consist of a part that accepts 
connections and a part that connects to the remote server), and several 
"filter" modules (which will be inserted in a "stack" between the two 
halves of the protocol module) for things like caching and filtering. 
Would there be a better way to structure it?

Would the best way to handle the modules be to write a ServerFactory 
subclass that wraps the stack of modules? I understand the basic 
concepts behind Twisted, but am not totally familiar with the API, so I 
am not exactly sure what is the best way to do things.