htlcswitch: add inbound routing fees receive support (routing)

https://github.com/lightningnetwork/lnd/pull/6703

Host: ziggie1984  -  PR author: joostjager

Notes

  • Short thread about inbound fees: https://twitter.com/uu7201/status/1685234826138251264
  • Initial Issue requesting inbound fees: https://github.com/lightning/bolts/issues/835
  • Lightning Network Email Thread: https://lists.linuxfoundation.org/pipermail/lightning-dev/2022-July/003643.html

Questions

  • What Problem are Inbound Fees trying to solve ? D* id you review the PR? If yes, what’s your overall verdict? (ACK, NACK, concept ACK, unknown)
  • How are Forwarding Fees currently calculated ? Who is allowed to set the price for liquidity on a channel, is the new approach incentive compatible ?
  • Are there some other approaches regarding this topic, if so describe them in a few words (e.g. Pairwise Fees).
  • Is the Inbound Fee a backwards compatible change meaning that Senders (building the route) who did not upgrade to the new PR will be able to send payments through nodes which enforce inbound fees ?
  • Normally when a payment fails, the failing node can add a channel_update msg for the sender to tell him about a potential different fee-policy to make the payment succeed after the new channel-update is applied. Will this also work for inbound fees ?
  • OutboundFees and InboundFees are only considered as a whole currently can you envision a use case where it might make sense to outline the Inbound and Outbound Fees separately ?
  • Will this change allow negative overall fees for a forward ?
  • After this change is merged, will your Pathfinding algorithm take advantage of inbound fees ?
  • Can I still send funds to my direct Peer without paying the Inbound Fee (Is it still possible to pay your direct peer for free)?