Introduce interactive signing state flags for funded states. #3637

dunxen · 2025-03-03T18:50:23Z

This PR includes some deferred follow-ups extracted from #3423 and introduces new state flags to track interactive signing along with persistence of the minimum information needed from a signing session to reconstruct it.

A top-level state flag was avoided so that this work is compatible with splicing as well as V2 channel establishment (dual-funding).

ldk-reviews-bot · 2025-03-03T18:50:25Z

👋 Thanks for assigning @wpaulino as a reviewer!
I'll wait for their review and will help manage the review process.
Once they submit their review, I'll check if a second reviewer would be helpful.

TheBlueMatt

Did you want to include test coverage for restarts here?

lightning/src/ln/channel.rs

Cargo.toml

lightning/src/ln/interactivetxs.rs

dunxen · 2025-03-04T15:29:10Z

Did you want to include test coverage for restarts here?

Not yet. Tracked in #3636. Will need to be able to contribute inputs first to test a useful order of message exchange + restart.

lightning/src/ln/channel.rs

codecov · 2025-03-05T10:13:38Z

Codecov Report

Attention: Patch coverage is 58.12500% with 67 lines in your changes missing coverage. Please review.

Project coverage is 89.14%. Comparing base (8b3f6cc) to head (bda2701).

Files with missing lines	Patch %	Lines
lightning/src/ln/channel.rs	57.94%	41 Missing and 4 partials ⚠️
lightning/src/ln/channelmanager.rs	45.45%	8 Missing and 4 partials ⚠️
lightning/src/ln/interactivetxs.rs	46.66%	8 Missing ⚠️
lightning/src/ln/dual_funding_tests.rs	87.50%	1 Missing ⚠️
lightning/src/util/ser.rs	85.71%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3637      +/-   ##
==========================================
- Coverage   89.17%   89.14%   -0.04%     
==========================================
  Files         155      155              
  Lines      120941   121022      +81     
  Branches   120941   121022      +81     
==========================================
+ Hits       107850   107880      +30     
- Misses      10447    10490      +43     
- Partials     2644     2652       +8

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wpaulino · 2025-03-05T21:15:29Z

@dunxen re-request when this is ready for review again, feel free to squash as well

ldk-reviews-bot · 2025-03-06T12:44:38Z

🔔 1st Reminder

Hey @TheBlueMatt @jkczyz @wpaulino! This PR has been waiting for your review.
Please take a look when you have a chance. If you're unable to review, please let us know so we can find another reviewer.

lightning/src/ln/channel.rs

wpaulino · 2025-03-06T16:39:56Z

lightning/src/ln/channel.rs

@@ -6924,11 +6933,72 @@ impl<SP: Deref> FundedChannel<SP> where
 				log_debug!(logger, "Reconnected channel {} with no loss", &self.context.channel_id());
 			}

+			// if next_funding_txid is set:


If possible, would be nice to get some test coverage in now for this

Might be tricky at the moment, but makes sense to try do that now 👍

Still tricky, but working on this now currently. I'll let you know if we'll have to defer this to a PR after "create outbound dual-funded channel" is complete.

lightning/src/ln/channelmanager.rs

lightning/src/ln/interactivetxs.rs

TheBlueMatt · 2025-03-06T23:01:54Z

Taking myself off since @wpaulino and @jkczyz are on this one. Aside from my first comment I don't have any more high-level feedback.

wpaulino · 2025-03-24T17:04:05Z

@dunxen let us know when this is ready for another round

lightning/src/ln/interactivetxs.rs

dunxen · 2025-03-27T12:43:43Z

@wpaulino, @jkczyz, sorry for the delay. This is ready for another round.

ldk-reviews-bot · 2025-03-29T12:44:39Z

🔔 1st Reminder

Hey @jkczyz @wpaulino! This PR has been waiting for your review.
Please take a look when you have a chance. If you're unable to review, please let us know so we can find another reviewer.

ldk-reviews-bot · 2025-03-31T12:45:05Z

🔔 2nd Reminder

Hey @jkczyz @wpaulino! This PR has been waiting for your review.
Please take a look when you have a chance. If you're unable to review, please let us know so we can find another reviewer.

jkczyz

Just one nit. Please re-request a review once all remaining comments are addressed.

lightning/src/ln/channel.rs

lightning/src/ln/interactivetxs.rs

lightning/src/ln/channel.rs

wpaulino · 2025-04-01T00:46:11Z

lightning/src/ln/channel.rs

@@ -2356,7 +2382,9 @@ impl<SP: Deref> PendingV2Channel<SP> where SP::Target: SignerProvider {
 			)));
 		};

-		self.context.channel_state = ChannelState::FundingNegotiated;
+		let mut channel_state = ChannelState::FundingNegotiated(FundingNegotiatedFlags::new());


The asymmetry between the channel state here and the ChannelPhase is a bit confusing. Here we consider the channel funded, but we remain in UnfundedV2 until we receive the initial commitment_signed.

It's unfortunate. Are you thinking it warrants another variant of ChannelPhase?

wpaulino · 2025-04-01T00:47:17Z

lightning/src/ln/channel.rs

 		where L::Target: Logger
 	{
-		if !matches!(self.context.channel_state, ChannelState::AwaitingChannelReady(_)) {
+		if !matches!(self.context.channel_state, ChannelState::FundingNegotiated(flags) if flags.is_interactive_signing()) {


Should this also check if they already sent it? Unclear if the spec is fine with retransmitting even if we didn't ask for it.

What if they sent this first but we were supposed to? Should we disconnect/fail?

This isn't clear in the spec if we should disconnect/fail.

wpaulino · 2025-04-01T01:00:39Z

lightning/src/ln/channel.rs


 			if funding_tx_opt.is_some() {
 				// We have a finalized funding transaction, so we can set the funding transaction and reset the
 				// signing session fields.
-				self.funding.funding_transaction = funding_tx_opt;
+				self.funding.funding_transaction = funding_tx_opt.clone();
 				self.interactive_tx_signing_session = None;
 			}

 			if holder_tx_signatures_opt.is_some() && self.is_awaiting_initial_mon_persist() {
 				log_debug!(logger, "Not sending tx_signatures: a monitor update is in progress. Setting monitor_pending_tx_signatures.");
 				self.context.monitor_pending_tx_signatures = holder_tx_signatures_opt;


IIUC, this should've already been done when we created the monitor if we need to send first. In this case, it seems we assume we send second, so it has not been set in the monitor?

I've attempted to clear it up in a comment, although I think we still need to address the spec issue on tx_signatures exchange order violation.

lightning/src/ln/channel.rs

Instead of having an explicit `ChannelContext::next_funding_txid` to set and read, we can get this value on the fly when it is appropriate to do so.

This follows the the specification closely in branching without being too verbose, so that it should be easy to follow the logic. See: https://github.com/lightning/bolts/blob/aa5207a/02-peer-protocol.md?plain=1#L2520-L2531

This intoduces the INTERACTIVE_SIGNING, THEIR_TX_SIGNATURES_SENT, and OUR_TX_SIGNATURES_SENT funded state flags. A top-level state flag for INTERACTIVE_SIGNING was avoided so that this work is compatible with splicing as well as V2 channel establishment (dual-funding).

…m peer

We fully persist `InteractiveTxSigningSession` as it provides the full context of the constructed transaction which is still needed for signing.

When this config field is enabled, the dual_fund feature bit will be set which determines support when receiving `open_channel2` messages.

dunxen marked this pull request as draft March 3, 2025 18:50

dunxen mentioned this pull request Dec 5, 2024

Dual-funded channels and Splicing Project Tracking #1621

Open

7 tasks

dunxen force-pushed the 2025-02-interactivesigningstate branch 2 times, most recently from 4c6b6ab to c1f430a Compare March 4, 2025 09:02

dunxen changed the title ~~DRAFT: Introduce interactive signing state flags for funded states.~~ Introduce interactive signing state flags for funded states. Mar 4, 2025

dunxen marked this pull request as ready for review March 4, 2025 09:03

dunxen requested review from TheBlueMatt, jkczyz and wpaulino March 4, 2025 09:04

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dunxen added weekly goal Someone wants to land this this week Dual-funding labels Mar 6, 2025

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dunxen force-pushed the 2025-02-interactivesigningstate branch from bda2701 to 5291edc Compare April 2, 2025 13:15

dunxen added 13 commits April 3, 2025 12:23

Get next_funding_txid from the funding_outpoint based on state

637e897

Instead of having an explicit `ChannelContext::next_funding_txid` to set and read, we can get this value on the fly when it is appropriate to do so.

Handle receiving channel_reestablish with next_funding_txid

a492154

This follows the the specification closely in branching without being too verbose, so that it should be easy to follow the logic. See: https://github.com/lightning/bolts/blob/aa5207a/02-peer-protocol.md?plain=1#L2520-L2531

wip f generalise next_funding_txid handling for splicing

20bfccd

f include expected txid in tx_abort data

fa268c5

f rename

18ad145

f gate batching branch on v2 check

cc82bde

f debug assert we don't unset funding if our or their tx signatures sent

5cd15df

f simplify match

4621e97

f clarify holder_tx_signatures_opt when receiving tx_signatures fro…

c58d5b4

…m peer

Persist InteractiveTxSigningSession to resume signing across restarts

3b1309d

We fully persist `InteractiveTxSigningSession` as it provides the full context of the constructed transaction which is still needed for signing.

f document lifetime of interactive_tx_signing_session

ce02067

Add enable_dual_funded_channels to UserConfig

c99182e

When this config field is enabled, the dual_fund feature bit will be set which determines support when receiving `open_channel2` messages.

dunxen force-pushed the 2025-02-interactivesigningstate branch from 5291edc to c99182e Compare April 3, 2025 11:10

dunxen requested review from jkczyz and wpaulino April 3, 2025 11:20

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Introduce interactive signing state flags for funded states. #3637

Introduce interactive signing state flags for funded states. #3637

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Introduce interactive signing state flags for funded states. #3637

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Introduce interactive signing state flags for funded states. #3637

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