Introduce `FundingTransactionReadyForSignatures` event #3889

dunxen · 2025-06-24T12:12:50Z

Cherry-picked from #3735 as it is relevant to splicing and will unblock testing after #3736 lands.

The FundingTransactionReadyForSignatures event requests witnesses from the client for their contributed inputs to an interactively constructed transaction.

The client calls ChannelManager::funding_transaction_signed to provide the witnesses to LDK.

ldk-reviews-bot · 2025-06-24T12:12:52Z

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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.

lightning/src/events/mod.rs

lightning/src/ln/channelmanager.rs

jkczyz · 2025-06-24T16:31:27Z

lightning/src/ln/channelmanager.rs

+		let witnesses: Vec<_> = transaction
+			.input
+			.into_iter()
+			.filter_map(|input| if input.witness.is_empty() { None } else { Some(input.witness) })
+			.collect();


Don't have a strong opinion here, but seems we can avoid this by passing the Transaction through and only collecting witnesses when we are ready to construct TxSignatures.

Cool, yeah will look at changing this after fixups.

lightning/src/ln/interactivetxs.rs

codecov · 2025-06-25T11:08:53Z

Codecov Report

Attention: Patch coverage is 9.70874% with 93 lines in your changes missing coverage. Please review.

Project coverage is 88.82%. Comparing base (6771d84) to head (ff1489d).

Files with missing lines	Patch %	Lines
lightning/src/ln/channelmanager.rs	1.85%	52 Missing and 1 partial ⚠️
lightning/src/ln/channel.rs	11.11%	32 Missing ⚠️
lightning/src/ln/interactivetxs.rs	45.45%	6 Missing ⚠️
lightning/src/events/mod.rs	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3889      +/-   ##
==========================================
- Coverage   88.88%   88.82%   -0.07%     
==========================================
  Files         165      165              
  Lines      118886   118971      +85     
  Branches   118886   118971      +85     
==========================================
  Hits       105676   105676              
- Misses      10892    10976      +84     
- Partials     2318     2319       +1

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ldk-reviews-bot · 2025-06-26T12:13:27Z

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ldk-reviews-bot · 2025-06-26T12:13:29Z

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optout21

Looks good!

lightning/src/ln/channel.rs

ldk-reviews-bot · 2025-06-28T12:14:21Z

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ldk-reviews-bot · 2025-06-30T12:15:10Z

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jkczyz

Not sure if there was a problem rebasing, but some comments that had been marked resolved weren't fixed.

lightning/src/events/mod.rs

lightning/src/ln/channelmanager.rs

lightning/src/events/mod.rs

dunxen · 2025-07-01T08:08:04Z

Not sure if there was a problem rebasing, but some comments that had been marked resolved weren't fixed.

Yeah, they got lost on a rebase and somehow lost the commit. Rebased to get the one CI fix in. Fixing.

ldk-reviews-bot · 2025-07-02T12:15:51Z

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lightning/src/events/mod.rs

wpaulino · 2025-07-07T19:08:26Z

lightning/src/ln/channel.rs

+	fn verify_interactive_tx_signatures(&mut self, _witnesses: &Vec<Witness>) {
+		if let Some(ref mut _signing_session) = self.interactive_tx_signing_session {
+			// Check that sighash_all was used:
+			// TODO(dual_funding): Check sig for sighash


Any reason this isn't done yet?

Oh yeah we're actually unable to do this reliably, especially if inputs were spend P2WSH. The public comments warn the client to ensure it is SIGHASH_ALL (or SIGHASH_DEFAULT/SIGHASH_ALL) if spending a P2TR UTXO.

These TODOs need to be removed.

We should be able to use ScriptBuf::instructions to identify all pushes that match a signature length, parse those that match, and make sure they come with SIGHASH_ALL.

wpaulino · 2025-07-07T19:09:17Z

lightning/src/ln/channel.rs

+				.provide_holder_witnesses(self.context.channel_id, witnesses)
+				.map_err(|err| APIError::APIMisuseError { err })?
+			{
+				if self.is_awaiting_initial_mon_persist() {


In the splicing case, we'd want to check is_monitor_update_in_progress only

What's a reliable way to check if we're splicing at this point in time? is_quiescent()?

self.pending_slice.and_then(|pending_splice| pending_splice.pending_funding.is_some())

lightning/src/ln/channel.rs

The `FundingTransactionReadyForSignatures` event requests witnesses from the client for their contributed inputs to an interactively constructed transaction. The client calls `ChannelManager::funding_transaction_signed` to provide the witnesses to LDK.

…igned exchange

We directly get the holder `TxSignatures` when necessary.

dunxen added Dual-funding Splicing labels Jun 24, 2025

dunxen requested review from wpaulino, optout21 and jkczyz June 24, 2025 12:13

jkczyz reviewed Jun 24, 2025

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dunxen mentioned this pull request Jun 25, 2025

Contribute funding inputs on accepting dual-funded channel #3735

Draft

dunxen force-pushed the 2025-06-readyforsigningevent branch from 165d59d to 8ca6d79 Compare June 25, 2025 10:59

optout21 reviewed Jun 26, 2025

View reviewed changes

dunxen force-pushed the 2025-06-readyforsigningevent branch from 890633d to a1de384 Compare June 27, 2025 07:20

jkczyz reviewed Jun 27, 2025

View reviewed changes

lightning/src/ln/channel.rs Outdated Show resolved Hide resolved

dunxen force-pushed the 2025-06-readyforsigningevent branch 2 times, most recently from 7df5779 to c8f981c Compare June 30, 2025 10:29

jkczyz reviewed Jun 30, 2025

View reviewed changes

dunxen force-pushed the 2025-06-readyforsigningevent branch 2 times, most recently from c15f426 to ff1489d Compare July 1, 2025 09:18

dunxen force-pushed the 2025-06-readyforsigningevent branch from ff1489d to 0a586e6 Compare July 4, 2025 07:05

wpaulino reviewed Jul 7, 2025

View reviewed changes

dunxen added 2 commits July 10, 2025 14:14

f only emit FundingTransactionReadyForSigning on initial commitment_s…

32e93ac

…igned exchange

dunxen added 2 commits July 10, 2025 14:15

f remove TODOs sighash_all checks

894caef

Use bool for monitor_pending_tx_signatures over Option<TxSignatures>

a9e1a3a

We directly get the holder `TxSignatures` when necessary.

dunxen force-pushed the 2025-06-readyforsigningevent branch from 0a586e6 to a9e1a3a Compare July 10, 2025 13:22

Introduce FundingTransactionReadyForSignatures event #3889

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Introduce FundingTransactionReadyForSignatures event #3889

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Introduce `FundingTransactionReadyForSignatures` event #3889

Introduce `FundingTransactionReadyForSignatures` event #3889

ldk-reviews-bot commented Jun 24, 2025 •

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