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.

jkczyz · 2025-06-24T16:14:35Z

lightning/src/events/mod.rs

+	/// channel is ready to be signed by the client. This event will only be triggered
+	/// if at least one input was contributed by the holder and needs to be signed.
+	///
+	/// The transaction contains all inputs provided by both parties  along with the channel's funding


nit: extra space after "parties"

jkczyz · 2025-06-24T16:16:04Z

lightning/src/events/mod.rs

+	/// After signing, call [`ChannelManager::funding_transaction_signed`] with the (partially) signed
+	/// funding transaction.
+	///
+	/// Generated in [`ChannelManager`] message handling.


Could you add a "Failure Behavior and Persistence" section as is done for other events?

Yeah and it makes sense to replay this after failure to handle, but not to persist across restarts as the new channel/splice won't be persisted before signing, anyway.

jkczyz · 2025-06-24T16:17:59Z

lightning/src/events/mod.rs

+		// TODO(dual_funding): Enable links when methods are implemented
+		/// The `user_channel_id` value passed in to `ChannelManager::create_dual_funded_channel` for outbound
+		/// channels, or to [`ChannelManager::accept_inbound_channel`] or `ChannelManager::accept_inbound_channel_with_contribution`
+		/// for inbound channels if [`UserConfig::manually_accept_inbound_channels`] config flag is set to true.


Let's remove mentions of the dual-funded methods for now.

Likewise not yet resolved.

jkczyz · 2025-06-24T16:24:18Z

lightning/src/ln/channelmanager.rs

+	/// counterparty's signature(s) the funding transaction will automatically be broadcast via the
+	/// [`BroadcasterInterface`] provided when this `ChannelManager` was constructed.
+	///
+	/// SIGHASH_ALL MUST be used for all signatures when providing signatures.


nit: SIGHASH_ALL

Not resolved. Could you do the same in other docs?

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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Hey @wpaulino @optout21! 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 · 2025-06-26T12:13:29Z

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optout21

Looks good!

lightning/src/ln/channel.rs

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

🔔 2nd Reminder

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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.

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 · 2025-06-30T12:15:10Z

🔔 3rd Reminder

Hey @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

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

jkczyz · 2025-06-30T22:53:06Z

lightning/src/events/mod.rs

+	/// channel is ready to be signed by the client. This event will only be triggered
+	/// if at least one input was contributed by the holder and needs to be signed.
+	///
+	/// The transaction contains all inputs provided by both parties  along with the channel's funding


jkczyz · 2025-06-30T23:06:36Z

lightning/src/events/mod.rs

+	/// Indicates that a funding transaction constructed via interactive transaction construction for a
+	/// channel is ready to be signed by the client. This event will only be triggered
+	/// if at least one input was contributed by the holder and needs to be signed.


Suggested change

/// Indicates that a funding transaction constructed via interactive transaction construction for a

/// channel is ready to be signed by the client. This event will only be triggered

/// if at least one input was contributed by the holder and needs to be signed.

/// Indicates that a channel funding transaction constructed interactively is ready to be

/// signed. This event will only be triggered if at least one input was contributed.

jkczyz · 2025-06-30T23:08:54Z

lightning/src/events/mod.rs

+	/// Indicates that a funding transaction constructed via interactive transaction construction for a
+	/// channel is ready to be signed by the client. This event will only be triggered
+	/// if at least one input was contributed by the holder and needs to be signed.


Not sure if we should we expose "holder" to the user. We might do that elsewhere, but I'm not sure if readers of these docs will understand what that means. Instead, we may want to reference the method that is called to contribute inputs.

Yeah, that method for accepting a channel and contributing inputs would be in #3735. I imagine there would be a similar method to accept a splice. So can't reference it now.

jkczyz · 2025-06-30T23:12:23Z

lightning/src/ln/channelmanager.rs

+	/// counterparty's signature(s) the funding transaction will automatically be broadcast via the
+	/// [`BroadcasterInterface`] provided when this `ChannelManager` was constructed.
+	///
+	/// SIGHASH_ALL MUST be used for all signatures when providing signatures.


Not resolved. Could you do the same in other docs?

jkczyz · 2025-06-30T23:18:59Z

lightning/src/ln/channelmanager.rs

+				None => {
+					return Err(APIError::APIMisuseError {
+						err: format!(
+							"Channel with id {} not expecting funding signatures",
+							channel_id
+						),
+					})
+				},
+			},
+			None => {
+				return Err(APIError::ChannelUnavailable {
+					err: format!(
+						"Channel with id {} not found for the passed counterparty node_id {}",
+						channel_id, counterparty_node_id
+					),
+				})
+			},


Could you describe in the docs when each error type is returned?

jkczyz · 2025-06-30T23:21:34Z

lightning/src/events/mod.rs

+		// TODO(dual_funding): Enable links when methods are implemented
+		/// The `user_channel_id` value passed in to `ChannelManager::create_dual_funded_channel` for outbound
+		/// channels, or to [`ChannelManager::accept_inbound_channel`] or `ChannelManager::accept_inbound_channel_with_contribution`
+		/// for inbound channels if [`UserConfig::manually_accept_inbound_channels`] config flag is set to true.


Likewise not yet resolved.

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.

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

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

dunxen force-pushed the 2025-06-readyforsigningevent branch from a1de384 to 7df5779 Compare June 30, 2025 09:50

f create event within channelmanager and not channel

c8f981c

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

jkczyz reviewed Jun 30, 2025

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dunxen added 2 commits July 1, 2025 10:13

f doc formatting

dd7cb01

f remove mentions of dual-funding methods not existing

b473a48

dunxen force-pushed the 2025-06-readyforsigningevent branch from 7aa05ee to c15f426 Compare July 1, 2025 09:16

f describe errors in funding_transaction_signed

ff1489d

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

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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