Dirtbags Netarch Library
This is a library for advanced network archaeology.
It provides a heavily field-tested framework for exploring unknown TCP-based protocols, and room to grow these explorations into full-blown decoders.
Documentation doesn't exist. Sorry. The way we go about things is to copy dumbdecode to a new file, and start hacking onto it.
You may find the example xmodem decoder to be helpful! It illustrates a fair amount of what the library provides.