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 33.19328% with 159 lines in your changes missing coverage. Please review.

Project coverage is 89.27%. Comparing base (aaef672) to head (0f61264).
Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
lightning/src/ln/interactivetxs.rs	6.60%	99 Missing ⚠️
lightning/src/ln/channel.rs	54.28%	43 Missing and 5 partials ⚠️
lightning/src/ln/channelmanager.rs	35.29%	8 Missing and 3 partials ⚠️
lightning/src/ln/dual_funding_tests.rs	87.50%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3637      +/-   ##
==========================================
+ Coverage   89.23%   89.27%   +0.03%     
==========================================
  Files         155      155              
  Lines      119329   121895    +2566     
  Branches   119329   121895    +2566     
==========================================
+ Hits       106488   108817    +2329     
- Misses      10243    10473     +230     
- Partials     2598     2605       +7

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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 👍

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.

ldk-reviews-bot · 2025-03-15T14:52:40Z

🔔 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 · 2025-03-17T14:53:05Z

🔔 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.

lightning/src/ln/channel.rs

lightning/src/ln/interactivetxs.rs

wpaulino · 2025-03-17T22:12:49Z

lightning/src/ln/channel.rs

+						let commitment_update = if !session.counterparty_sent_tx_signatures() && msg.next_local_commitment_number == 0 {
+							// if it has not received tx_signatures for that funding transaction AND
+							// if next_commitment_number is zero:
+							//   MUST retransmit its commitment_signed for that funding transaction.


I assume for splicing this will need to be generalized to return a commitment_signed for the current commitment number (still 0 for the open case). Is it worth taking care of that now?

For splicing this seems a bit up in the air still, but yes will have to generalise. Discussion here: https://github.com/lightning/bolts/pull/1214/files#discussion_r1882436204

lightning/src/ln/channel.rs

wpaulino · 2025-03-17T22:32:51Z

lightning/src/ln/channel.rs

+						(None, None, Some(msgs::TxAbort { channel_id: self.context.channel_id(), data: vec![] }))
+					}
+				} else {
+					return Err(ChannelError::close("Counterparty set `next_funding_txid` at incorrect state".into()));


We shouldn't close the channel here. It seems possible that we clear the session because we exchanged tx_signatures from our PoV, but they still need us to retransmit tx_signatures because they didn't receive it the first time around.

Yeah, I think it's then just fine to warn here since we are broadcasting the funding tx anyway. Unfortunately we don't have tx_signatures to send them since the session is cleared.

Hm, that sounds like a protocol violation then, no? It'd be weird for the counterparty to not have received the message but then see the channel confirm. We might need to guarantee the send, either by not clearing the session until a later point, or reconstructing the tx_signatures message from the fully-signed transaction we plan to broadcast.

Reconstructing may not be possible as we would have forgotten which inputs are the holder's at this point, so best to not clear until later.

Ok in latest push we now only clear the session later.

By not clearing this, when we process tx_signatures again, won't we add duplicative witness data?

rust-lightning/lightning/src/ln/interactivetxs.rs

Line 333 in 830ffa0

self.unsigned_tx.add_remote_witnesses(tx_signatures.witnesses.clone());

lightning/src/ln/channel.rs

lightning/src/ln/interactivetxs.rs

dunxen · 2025-03-19T10:55:44Z

Just pushed the change for full persistence of InteractiveTxConstructor. Still addressing other feedback.

wpaulino · 2025-03-24T17:04:05Z

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

lightning/src/ln/interactivetxs.rs

jkczyz · 2025-03-24T21:32:27Z

lightning/src/ln/interactivetxs.rs

+	{1, Local} => (),
+	{3, Remote} => (),


nit: typically we use:

(1, Local) => {}, (3, Remote) => {},

Also, can number these 0 and 1.

In this case these are both tuple variants, so the () => {} syntax doesn't work as it won't include the the 0 field of the tuple, so it doesn't compile. That syntax would only work for unit/struct variants, I believe.

jkczyz · 2025-03-24T21:32:44Z

lightning/src/ln/interactivetxs.rs

+	{1, Single} => (),
+	{3, SharedControlFullyOwned} => (),
+	{5, Shared} => (),


jkczyz · 2025-03-24T21:34:31Z

lightning/src/ln/interactivetxs.rs

+impl_writeable_tlv_based!(InteractiveTxSigningSession, {
+	(1, unsigned_tx, required),
+	(3, holder_sends_tx_signatures_first, required),
+	(5, has_received_commitment_signed, required),
+	(7, holder_tx_signatures, required),
+});


IIUC, when introducing a new serialization, we can number these starting at 0 and use both even and odd given no previous versions understand this. Likewise elsewhere.

Actually, given @wpaulino's comment on another PR, I'm not sure if this would be desirable. @TheBlueMatt What are the best practices when adding serialization for a new struct? IIRC, you had once suggested just numbering with both even and add. But Wilmer's comment of only using odd makes sense to me.

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

…no active signing session

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).

… funding tx when signed & clear signing session on channel_ready received

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

…tlv_based!` everywhere

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

dunxen · 2025-03-27T12:43:43Z

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

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

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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

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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 added 10 commits March 27, 2025 14:41

Get next_funding_txid from the funding_outpoint based on state

b00a9de

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

3799388

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

f match next_funding_txid logic to spec

d9f832f

f move recvd commit_sig check out of else & change close to warn for …

3b7e7b7

…no active signing session

f fix docs for FundingNegotiated

dfe17b6

f rename s/OUR_TX_SIGNATURES_SENT/OUR_TX_SIGNATURES_READY/ & only set…

780ac08

… funding tx when signed & clear signing session on channel_ready received

Persist InteractiveTxSigningSession to resume signing across restarts

8cc1bb2

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

f impl read/write for TxIn,absolute::LockTime to use `impl_writeable_…

6150390

…tlv_based!` everywhere

Add enable_dual_funded_channels to UserConfig

b78d5dc

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 11e52b8 to b78d5dc Compare March 27, 2025 12:41

dunxen requested review from jkczyz and wpaulino March 27, 2025 12:43

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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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