For a tutorial see: http://cs.berry.edu/~nhamid/p2p
Also:
Nadeem Abdul Hamid. 2007. A lightweight framework for peer-to-peer programming. J. Comput. Sci. Coll. 22, 5 (May 2007), 98–104.
https://dl.acm.org/doi/10.5555/1229688.1229706
To run this Java application, from a working directory with the src/peerbase folder in the Java classpath, type
java -cp ... peerbase.sample.FileShareApp <my-port> <peer-port>
The peer node will be launched listening on <my-port> and will attempt to connect/register with a peer at <peer-port>. (Obviously the first peer created will not have a valid <peer-port> to connect to - just put anything.)
Files will actually be transferred from one peer's working directory to another if they exist as named.
(Written for Python 2.x.)
To run the demo Python application:
python filergui.py 9001 10 localhost:9000
In general,
filergui.py <server-port> <max-peers> <peer-ip>:<port>