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>