Lightning Specification Meeting 2024/07/15

[t-bast]

The meeting will take place on Monday 2024/07/15 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

Recently Updated Proposals / Seeking Review

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

• Clarify blinded path max_cltv_expiry bolt4+proposals: fix max_cltv_expiry calculation #1176
• Clarify onion spec Clarify onion spec: part 1 (the uncontroversial bits) #1181 and Clarify onions part 2: a bit deeper rework #1182
• Offers Offers #798
• BIP 353 name in offers Include BIP 353 name info in invoice_requests #1180
• Taproot extension-bolt: simple taproot channels (feature 80/81) #995
• Taproot gossip extension-bolt: taproot gossip (features 32/33) #1059
• Channel jamming draft: Staking Credentials token issuance/redemption #1043 draft: HTLC Endorsement to Mitigate Channel Jamming #1071 blip-0004: experimental endorsement signaling in update_add_htlc blips#27
• Async payments Support async payments in BOLT 12 #1149
• Splicing Splice draft (feature 62/63) #863 Channel Splicing (feature 62/63) #1160
• Dynamic Commitments Extension/dynamic commitments #1117 vs Upgrade on Reestablish BOLT 2: upgrade protocol on reestablish #868
• Liquidity ads option_will_fund: liquidity ads #878 Advertise liquidity ads rates #1145 Extensible Liquidity Ads #1153
• Peer storage backup Peer backup storage (feature 40/41/42/43) #881 or Peer storage for nodes to distribute small encrypted blobs. #1110
• DNS-based offers Define a mechanism for looking up an offer from a user/domain pair #1136
• Attributable errors Attributable errors (feature 36/37) #1044
• Clarify channel_reestablish requirements Clarify channel_reestablish requirements #1049 or Rework channel_reestablish requirements #1051

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.

• Simplified mutual close option_simple_close (features 60/61) #1096
• Trampoline routing Trampoline Routing (2021 edition) (Feature 56/57) #829 and Trampoline onion format (Feature 56/57) #836
• 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)
• 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)

[Roasbeef]

mpp in blinded paths:

• how do ppl handle it today?
  • impls:
    • lnd: adds the blinded paths as hop hints of sort
    • ldk: similar hop hint generalization
    • eclair: similar hop hint generalization
    • CLN: super simple, just appends the onion
  • when you get an error from inside the path, do you try to split or not?
  • do you just split inside the same blinded path?
    • eclair has a trick where they add the blinded path multiple times
      • seems to work ok-ish, so they can have more vectors to split based off

channel udpate w/ max HTLC:

• does lnd allow channel updates that don't have it set?
  • observed with peering w/ certain lnd nodes

revamping bolt 4 spec:

• seeks to not change anything
• tightens up all the language, better requirements, etc
• touches mainly blinded paths and general onion processing
• next up would be to revamp the generation portion:
  • when we get here, can also add some of @ellemouton's diagrams from: https://ellemouton.com/posts/sphinx/

offers interop:

• phoenix and LDK doing a lot of interop rn
  • going well, exposed bugs that are being patched
• also want to test all the failure cases:
  • may be a bit more indirect, but worth it to make sure that everyone handles in the same
• CLN has some new test vectors, generated during rewrite
• exposed some other edge cases w/ the DNSSEC resolution, more robust now

BIP 354 DNS operations:

• wild card method for hosted providers: Include BIP 353 name info in invoice_requests #1180
• some using route 53 AWS API rn to handle automation for the multi-user case
• DNS servers generally pretty lightweight
• ₿ prefix on addrs
  • lost of prior discussion
  • wanting to be compat and support downgrade, etc w/ LN-URL
  • naming collisions possible, etc
    • spec tries find a good middle ground
    • overlap w/ email addresses, etc
      * composes well with silent addresses
  • whole new BIP to replace BIP 21, if you add a new addr format, put it in the query params
    * ppl wanting to add sending support
  • some are PSBT based, waiting on: https://delvingbitcoin.org/t/bip352-psbt-support/877
  • most important to be able to pay to them

taproot chans:

• eclair has some draft PRs up

taproot gossip:

• elle incorporated rusty's latest diff
• ppl working on reloading context
• seemingly some propagation issues in gossip today as well
• working on adding extensions w/ splicing re nonces, etc

channel jamming:

• nothing blocking really, waiting to her from thomas on the bLIP
• discussion directly on the bLIP

async payments:

• landing PRs in LDK
• t-bast working on the trampoline to blinded paths, and the other way around

splicing:

• eclair wanting to put up a PR using the official values for the TLV numbers
  • slight divergence in impl

dyn commits:

• splitting up the kick off upgrade part from the rest
  • to be distinct documents
  • may use the same negotiation mechanism

liquidity ads saga:

• few questions t-bast has
  • really useful is how to pay the fee, can be extended, can pay in interactive tx, or deduct fees from diff HTLCs, etc
    • subscription fee, etc
  • how do we also specify the lease duration, etc
    • script enforce or just advisory?
    • script enforce is nice in theory, but gets hairy once you factor in splicing and routing, etc
  • re lease duration:
    • just make it fixed?
    • can always partition the buckets later if needed

peer storage:

• spec PR pretty much done
• CLN impl set, working on expanding the set of capabilities