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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optout21

Looks good!

lightning/src/ln/channel.rs

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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.

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lightning/src/events/mod.rs

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.

dunxen · 2025-07-17T09:59:25Z

lightning/src/ln/channel.rs

@@ -7605,6 +7586,188 @@ where
 		}
 	}

+	fn verify_interactive_tx_signatures(


Needs some clean up and tests but pushed it for some review.

Is test coverage for this actually feasible yet?

lightning/src/events/mod.rs

lightning/src/ln/channel.rs

wpaulino · 2025-07-17T22:55:35Z

lightning/src/ln/channel.rs

@@ -1840,15 +1840,15 @@ where
 				let res = if has_negotiated_pending_splice && !session_received_commitment_signed {
 					funded_channel
 						.splice_initial_commitment_signed(msg, logger)
-						.map(|monitor_update_opt| (None, monitor_update_opt))
+						.map(|monitor_update_opt| (None, monitor_update_opt, None))


We will also need to return the unsigned transaction here for splices.

Shall we defer this to a splice PR? I'm not 100% sure of the specifics in splice_initial_commitment_signed().

wpaulino · 2025-07-17T23:09:21Z

lightning/src/ln/channelmanager.rs

+					if let Some(unsigned_transaction) = funding_tx_opt {
+						let mut pending_events = self.pending_events.lock().unwrap();
+						pending_events.push_back((
+							Event::FundingTransactionReadyForSigning {


I think we'll also need to generate this on reestablish when we have already received commitment_signed but not tx_signatures.

Working on this still.

lightning/src/ln/interactivetxs.rs

lightning/src/ln/channel.rs

dunxen

Pushed latest fixups. Comments left on remaining ones.

dunxen · 2025-07-21T17:57:55Z

lightning/src/ln/channel.rs

@@ -1840,15 +1840,15 @@ where
 				let res = if has_negotiated_pending_splice && !session_received_commitment_signed {
 					funded_channel
 						.splice_initial_commitment_signed(msg, logger)
-						.map(|monitor_update_opt| (None, monitor_update_opt))
+						.map(|monitor_update_opt| (None, monitor_update_opt, None))


Shall we defer this to a splice PR? I'm not 100% sure of the specifics in splice_initial_commitment_signed().

dunxen · 2025-07-21T17:58:09Z

lightning/src/ln/channelmanager.rs

+					if let Some(unsigned_transaction) = funding_tx_opt {
+						let mut pending_events = self.pending_events.lock().unwrap();
+						pending_events.push_back((
+							Event::FundingTransactionReadyForSigning {


Working on this still.

lightning/src/ln/interactivetxs.rs

lightning/src/ln/channelmanager.rs

lightning/src/ln/channel.rs

wpaulino · 2025-07-23T18:00:21Z

lightning/src/ln/channel.rs

@@ -7605,6 +7586,188 @@ where
 		}
 	}

+	fn verify_interactive_tx_signatures(


Is test coverage for this actually feasible yet?

lightning/src/ln/channel.rs

The `handle_channel_resumption` method handles resumption from both a channel re-establish and a monitor update. When the corresponding monitor update for the commitment_signed message completes, we will push the event here. We can thus only ever provide holder signatures after a monitor update has completed. We can also get rid of the reestablish code involved with `monitor_pending_tx_signatures` and remove that field too.

The return type of commitment_signed() started groing into a really long and unwieldy tuple. We introduce a dedicated enum return type for it here.

…hecks In a following commit, We'll use the contained scriptPubKeys to validate P2WPKH and P2TR key path spends and to assist in checking that signatures in provided holder witnesses use SIGHASH_ALL to prevent funds being frozen or held ransom.

LDK checks the following: * Each input spends an output that is one of P2WPKH, P2WSH, or P2TR. These were already checked by LDK when the inputs to be contributed were provided. * All signatures use the `SIGHASH_ALL` sighash type. * P2WPKH and P2TR key path spends are valid (verifies signatures) NOTE: * When checking P2WSH spends, LDK tries to decode 70-72 byte witness elements as ECDSA signatures with a sighash flag. If the internal DER-decoding fails, then LDK just assumes it wasn't a signature and carries with checks. If the element can be decoded as an ECDSA signature, the the sighash flag must be `SIGHASH_ALL`. * When checking P2TR script-path spends, LDK assumes all elements of exactly 65 bytes with the last byte matching any valid sighash flag byte are schnorr signatures and checks that the sighash type is `SIGHASH_ALL`. If the last byte is not any valid sighash flag, the element is assumed not to be a signature and is ignored. Elements of 64 bytes are not checked because if they were schnorr signatures then they would implicitly be `SIGHASH_DEFAULT` which is an alias of `SIGHASH_ALL`.

wpaulino

Almost there, the commit history could be cleaned up a bit to not have code added in one commit that gets removed in a later one

wpaulino · 2025-07-28T17:13:22Z

lightning/src/ln/interactivetxs.rs

@@ -460,7 +465,11 @@ impl InteractiveTxSigningSession {
 			shared_input_signature: None,
 		});

-		Ok(())
+		if self.holder_sends_tx_signatures_first && self.has_received_commitment_signed {


Nit: there's an unnecessary into_iter().collect() a few lines above

wpaulino · 2025-07-28T17:15:23Z

lightning/src/events/mod.rs

-				// We only exhange the initial `commitment_signed` after the client calls
-				// `ChannelManager::funding_transaction_signed` and ALWAYS before we send a `tx_signatures`
+				// We never write out FundingTransactionReadyForSigning events as they will be regenerated when
+				// necessary.


Nit: I would just squash this commit (1c6c08f) with the previous

wpaulino · 2025-07-28T17:22:00Z

lightning/src/ln/channel.rs

@@ -8435,41 +8412,14 @@ where
 								update_fee: None,
 							})
 						} else { None };
-						// TODO(dual_funding): For async signing support we need to hold back `tx_signatures` until the `commitment_signed` is ready.


This TODO is still relevant, it just has to be tracked in handle_channel_resumption now

wpaulino · 2025-07-28T17:24:03Z

lightning/src/ln/channel.rs

-						let tx_signatures = if (
-							// if it has not received tx_signatures for that funding transaction AND
-							// if it has already received commitment_signed AND it should sign first, as specified in the tx_signatures requirements:
-							//   MUST send its tx_signatures for that funding transaction.
-							!self.context.channel_state.is_their_tx_signatures_sent() && session.has_received_commitment_signed() && session.holder_sends_tx_signatures_first()
-							// else if it has already received tx_signatures for that funding transaction:
-							//   MUST send its tx_signatures for that funding transaction.
-						) || self.context.channel_state.is_their_tx_signatures_sent() {


We still have to send the message in these cases if it's ready

wpaulino · 2025-07-28T17:26:10Z

lightning/src/ln/channelmanager.rs

+						user_channel_id: channel.context.get_user_id(),
+					}, None));
+			} else if signing_session.local_inputs_count() == 0 {
+				pending_msg_events.push(MessageSendEvent::SendTxSignatures { node_id: counterparty_node_id, msg: msgs::TxSignatures { channel_id: channel.context.channel_id(), tx_hash: signing_session.unsigned_tx().compute_txid(), witnesses: vec![], shared_input_signature: None } });


We probably shouldn't send the message here, and should rely on either sending it after receiving a tx_signatures, sending it first as a result of funding_transaction_signed, or re-sending it on reestablish.

wpaulino · 2025-07-28T17:28:56Z

lightning/src/ln/channelmanager.rs

@@ -130,8 +130,10 @@ use crate::util::ser::{
 };
 use crate::util::wakers::{Future, Notifier};

+use super::channel::CommitmentSignedResult;


Nit: group with the other channel imports

wpaulino · 2025-07-28T17:30:17Z

lightning/src/ln/channel.rs

+				#[cfg(splicing)]
+				let is_monitor_update_in_progress = self.is_awaiting_initial_mon_persist()
+					|| self.is_splicing()
+						&& self.context.channel_state.is_monitor_update_in_progress();
+				#[cfg(not(splicing))]
+				let is_monitor_update_in_progress = self.is_awaiting_initial_mon_persist();
+
+				if is_monitor_update_in_progress {


Unreachable now as the event is guaranteed to be generated after the monitor persistence completes

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

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dunxen added 4 commits July 28, 2025 10:24

Create CommitmentSignedResult enum for Channel::commitment_signed();

f7e05f6

The return type of commitment_signed() started groing into a really long and unwieldy tuple. We introduce a dedicated enum return type for it here.

dunxen force-pushed the 2025-06-readyforsigningevent branch from ca2d5e0 to b45913a Compare July 28, 2025 09:01

dunxen requested review from wpaulino and jkczyz July 28, 2025 09:02

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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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