P2P isn't a single thing. But if you know more about what you want to do, you can usually find libraries to do it with.
I recommend Indy's courses for getting the map of the territory: https://www.coursera.org/instructor/indygupta
I recommend Indy's courses for getting the map of the territory: https://www.coursera.org/instructor/indygupta
He had early lectures but made them fun so I ended up not minding it. If the Coursera follows the same curriculum, I remember it being a pretty comprehensive introduction.