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

👋 Thanks for assigning @jkczyz 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.

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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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 · 2025-07-05T00:01:03Z

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ldk-reviews-bot · 2025-07-07T00:01:47Z

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wpaulino · 2025-07-07T19:00:58Z

lightning/src/events/mod.rs

+				45u8.write(writer)?;
+				// We never write out FundingTransactionReadyForSigning events as, upon disconnection, peers
+				// drop any V2-established/spliced channels which have not yet exchanged the initial `commitment_signed`.
+				// We only exhange the initial `commitment_signed` after the client calls


wpaulino · 2025-07-07T19:06:53Z

lightning/src/events/mod.rs

+				// We never write out FundingTransactionReadyForSigning events as, upon disconnection, peers
+				// drop any V2-established/spliced channels which have not yet exchanged the initial `commitment_signed`.
+				// We only exhange the initial `commitment_signed` after the client calls
+				// `ChannelManager::funding_transaction_signed` and ALWAYS before we send a `tx_signatures`


This seems wrong, we immediately send the initial commitment_signed as soon as funding_tx_constructed. We may want to wait to emit FundingTransactionReadyForSigning until we exchange commitment_signed though. Doing so may help unify the logic for when we need to regenerate the event upon channel_reestablish.

Thanks, yeah this comment is outdated. And agreed, I'll move the event emit to after commitment_signed exchange.

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.

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

wpaulino · 2025-07-07T19:10:37Z

lightning/src/ln/channel.rs

+			{
+				if 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 = Some(holder_tx_signatures);


Let's not store the signatures here as well and just keep them in the session instead

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

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

jkczyz reviewed Jun 27, 2025

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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

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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

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Introduce FundingTransactionReadyForSignatures event #3889

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Introduce FundingTransactionReadyForSignatures event #3889

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Introduce `FundingTransactionReadyForSignatures` event #3889

Introduce `FundingTransactionReadyForSignatures` event #3889

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