- Onion Routing Protocol: https://github.com/lightningnetwork/lightning-rfc/blob/maste...
- P2P Node and Channel Discovery https://github.com/lightningnetwork/lightning-rfc/blob/maste...
This repo contains specs for a lot of parts of the LN, although probably there may be changes I imagine.
As for code, one of the implementations, LND (Go): https://github.com/lightningnetwork/lnd/tree/master/routing but there are at least 3 other implementations in the works.
https://github.com/ElementsProject/lightning (clang) https://github.com/ACINQ/eclair (Scala) https://github.com/mit-dci/lit (Go)