Lightning Specification Meeting 2022/09/12

[t-bast]

The meeting will take place on Monday 2022/09/12 at 8pm UTC (5:30am Adelaide time) on Libera Chat IRC #lightning-dev. It is open to the public.

A video link is available for higher bandwidth communication: https://meet.jit.si/Lightning-Spec-Meeting

Pull Request Review

• Anchor outputs zero fee htlc txs test vectors Add test vectors for option_anchors_zero_fee_htlc_tx #1018
• Clarify bolt 4 blinding Bolt4: clarify packet forwarding blinding #1012
• Tlv stream in onion failures TLV failure message and length relaxation #1021
• Route blinding Route Blinding (Feature 24/25) #765
• Onion messages BOLT 7: Onion message support (features 38/39) #759
• Offers Offers #798
• Add dust exposure threshold Add a max_dust_htlc_exposure_msat #919
• Taproot extension-bolt: simple taproot channels (feature 80/81) #995
• Closing fee range turn-based protocol option_closing_rejected: turn-based fee_range coop close (feature 60/61) #1016
• Negative fees Negative fees #1022

Waiting for interop

• Channel update flags Bolt7: add channel update flag for scid alias #999
• Grace period for channel closes gossip: delay considering a channel edge deleted for 12-blocks #1004
• Dual funding interactive-tx: Add dual-funding flow, using the interactive tx protocol (feature 28/29) #851
• Don't force close until error is received after channel_reestablish Nodes shouldn't publish their commitment when receiving outdated channel_reestablish #934
• Graph dump on gossip_timestamp_filter Inconsistent behavior around graph dump on gossip_timestamp_filter. #980
• Handle update_fee during shutdown
• Websocket transport websocket address type: allow transport over RFC6455 #891

Long Term Updates

• Pinning attacks as related to splicing / dynamic commitments: https://lists.linuxfoundation.org/pipermail/lightning-dev/2022-August/003665.html
• Liquidity ads option_will_fund: liquidity ads #878
• Splicing Splice draft (feature 62/63) #863
• Simplified commitment Feature 106/107: option_simplified_update. #867
• Hold htlcs before forwarding Async Payments: Add the ability to hold HTLCs before forwarding (FEAT 52/53) #989
• Trampoline routing Trampoline Routing (2021 edition) (Feature 56/57) #829 and Trampoline onion format (Feature 56/57) #836
• Upfront payments / DoS protection Hold fees #843 and https://lists.linuxfoundation.org/pipermail/lightning-dev/2022-August/003673.html
• Peer storage backup Peer backup storage (feature 40/41/42/43) #881
• Anonymous gossip

Backlog

The following are topics that we should discuss at some point, so if we have time to discuss them great, otherwise they slip to the next meeting.

• lnprototest (https://github.com/rustyrussell/lnprototest)

[Roasbeef]

anchor test vectors:

• Question of if ppl allow non-zero fee anchors or not:
  • CL's version of dual funding lets ppl use the non-zero fee anchors (haven't implemented the zero fee version, coming 🔜)
  • LDK wants to remove support for signing (in the VLS) for the non-zero fee anchors version

tlv fields in the onion errors:

• Part of some other experiments w/ channel updates in the wild
• Sort of makes things more uniform
• There's a recommendation to keep them all the same length, but you can have a larger number if you want to pad things out for experiments, or w/e.
• Offshoot thread here to the old idea to add authentication to the onion messages so can know if someone garbled it along the way.
• Will update this now to remove the size limit for onion errors (many implementations reject anything > 256 bytes).

negative fees:

• changes an unsigned field to a signed fee
• introduces negative fees
• path finders may need to update to be able to handle potential cycles
• idea re using this for incentivizing rebalancing:
  • can create a sort of thundering herd effect?
  • people advertise the fee/discount, but then by they get there, it's all gone (?)
• not critical for inbound fees, but also useful
• synergistic w/ fee rate cards:
  • able to bound how much of your balance can be paid/used for negative fees

route blinding:

• Have all the comments from Rusty addressed. T-bast to now squash into a series of nice commits to more review
• Paying using route blinding:
  • Question one where ppl are w.r.t using the blinded paths for sending+recv'ing
  • Few other things that need to fall into place, easier to finish implementing all the offers stuff to test at the end/
  • BOLT 12 invoice format is more or less finalized (hasn't changed much), so then possible to generate an invoice w/ the proper fields. Can then be used for e2e testing:
    • If spun off, then could make some of the testing of blinded paths itself (independent of offers stuff) simpler

onion messaging:

• LDK tested forwarding/recv interop w/ eclair -- waiting on spec change re one custom TLV at a time
• CL has the latest and greatest in a side branch, PR up soon to catch up w/ latest on the spec side of things

offers:

• distinct feature bit class?
• question of if should be able to support offers that don't allow mpp
  • some complexity w/ multi-node recv stuff around doing mpp, possible, but needs distributed synchronization
• offers will add feature bit for no mpp

taproot:

• arik and laolu exchanging notes re implementation
• musig 1.0 seems to be coming 🔜, likely to wait until that to do proper interop to avoid needing to update test vectors, etc multiple times
• laolu pushed up changes re the sig encoding, message type, and switching to the signing+verification nonce terminology

#999

• eclair waiting for more interop before merging in

#934

• also waiting for interop here as well