Lightning Specification Meeting 2025/02/24

[t-bast]

The meeting will take place on Monday 2025/02/24 at 7pm 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

Recently Updated Proposals / Seeking Review

This section contains changes that have been opened or updated recently and need feedback from the meeting participants.

• 0-fee commitments Zero-fee commitments using v3 transactions (feature 40/41) #1228
• 0-fee commitments for mobile wallet: https://delvingbitcoin.org/t/zero-fee-commitments-for-mobile-wallets/1453
• Splicing Channel Splicing (feature 62/63) #1160
• Taproot extension-bolt: simple taproot channels (feature 80/81) #995
• Taproot gossip extension-bolt: taproot gossip (features 32/33) #1059
• Channel jamming draft: HTLC Endorsement to Mitigate Channel Jamming #1071 Project Updates: Hybrid Channel Jamming Mitigation #1218
• Dynamic Commitments Extension/dynamic commitments #1117
• Bolt 12 contacts: blip-0042: Bolt 12 Contacts blips#42
• Liquidity ads Extensible Liquidity Ads #1153
• Trampoline routing Trampoline Routing (2021 edition) (Feature 56/57) #829 and Trampoline onion format (Feature 56/57) #836
• Async payments Support async payments in BOLT 12 #1149

Stale Proposals

This section contains pending changes that may not need feedback from the meeting participants, unless someone explicitly asks for it during the meeting. These changes are usually waiting for implementation work to happen to drive more feedback.

• Inbound fees Inbound routing fees blips#18 and Add a bLIP for backwards-compatible inbound fees blips#22

Waiting for interop

This section contains changes that have been conceptually ACKed and are waiting for at least two implementations to fully interoperate.
They most likely don't need to be covered during the meeting, unless someone asks for updates.

• Dual funding reconnect commit_sig retransmission Do not unnecessarily retransmit commitment_signed in dual funding #1214
• Zero reserve Add option_zero_reserve (FEATURE 64/65) #1140 (follow-up on bolt2: relax channel_reserve_satoshis requirements #1133 to include a feature bit)
• Attributable errors Attributable failures (feature 36/37) #1044
• Don't force close until error is received after channel_reestablish Nodes shouldn't publish their commitment when receiving outdated channel_reestablish #934

Long Term Updates

This section contains long-term changes that need review, but require a substantial implementation effort.

• Simplified commitment Feature 106/107: option_simplified_update. #867
• lnprototest (https://github.com/rustyrussell/lnprototest)

[joostjager]

Would like to put attributable errors back on the agenda for today's meeting. In particular #1044 (comment)

[Roasbeef]

zero fee commitments:

• rn take all dusted funds and put to fees
  • other edge cases re dusting attacks, now a party can
• if anchor is below dust, commitment txn fee must be zero
  • bitcoind policy, must be spent in the same block anyway
  • part of ephemeral dust: Ephemeral Dust bitcoin/bitcoin#30239
    • extra policy, not BIP'd (yet)
• side effect of needing to always have funds on chain
  • t-bast has proposal to still sign fees for the HTLC transactions for the mobile client: https://delvingbitcoin.org/t/zero-fee-commitments-for-mobile-wallets/1453
    • success txn race condition?
    • how many sigs?
      • more than 2? 10?
      • only need two given it's all about settling an HTLC?
  • mobile client don't need to worry about HTLC race conditions
    * using P2A now?
  • need to have some sort of threshold re allocation?
  • P2A means that anyone can claim it, only the miners can claim the dust
    • must be spent in block -- not very easy to actually enforce that policy
      • ways to still have it be relayed? mining algo would need to mine just the parent instead of the child
      • potential other ways leak zero value outputs or normal
• implementation progress:
  • LDK started an impl, small patch nearly all there
  • Eclair, mostly done with everything, needs to hook up into package submission API
    • using sendrawtransaction, can't submit just that, need to use submitpackage API
      • testpackageaccept? doesn't apply the package policies (yet)
        * HTLC txns use sequence zero
    • removing the CSV 1 cutout, so don't need the sequence there anymore, can either be max seq or zero
    • need to keep logic to broadcast HTLC txns after one block
      • TRUC stuff can't have more than one dependent?
      • can spend both in one transaction? 3 inputs potentially (P2A, HTLC txn, extra fee input), 2 output

splicing:

• waiting for dusty to give feedback on retransmission stuff
  • looking at new changes by this week
• matt's PR for changing dual funding sig during reconnection
  • eclair ready to cut new release w/ logic, wants to do interop

taproot:

• next steps:
  • integrate nonce work from splicing
  • add rbf awareness

attributable errors:

• lot of talk about signalling:
  • when ppl start to add the new legacy errors, so ppl now how to transform it and if they should expect it or not
• new view:
  • populate a TLV field w/ everything extra, those in a special TLV field, if they don't understand it, they just drop the TLV field
  • more natural way of updating possibly
    • but maybe still want to know if preferred?
  • need to factor in a max route length, to avoid having both errors there which can lead to the max msg size being exceeded
  • can detect who supports it, based on which errors are returned
• joost to give implementation a shot, will see if anythings pops up during impl