Track funding tx channelmonitor #4109

martinsaposnic · 2025-09-23T13:29:54Z

As part of the client_trusts_lsp LSPS2 work, we decided to move the channelmonitor logic into a new PR so the other part could get merged

~~This comment is not yet done #3838 (comment), hence this was created as draft~~

ldk-reviews-bot · 2025-09-23T13:29:57Z

👋 Thanks for assigning @TheBlueMatt 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.

codecov · 2025-09-23T13:43:51Z

Codecov Report

❌ Patch coverage is 99.27798% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.68%. Comparing base (aa813a2) to head (9bd2ccc).
⚠️ Report is 33 commits behind head on main.

Files with missing lines	Patch %	Lines
lightning/src/chain/channelmonitor.rs	99.45%	1 Missing and 2 partials ⚠️
lightning/src/ln/channel.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4109      +/-   ##
==========================================
+ Coverage   88.62%   88.68%   +0.06%     
==========================================
  Files         179      180       +1     
  Lines      134704   135770    +1066     
  Branches   134704   135770    +1066     
==========================================
+ Hits       119375   120412    +1037     
- Misses      12568    12588      +20     
- Partials     2761     2770       +9

Flag	Coverage Δ
fuzzing	`21.77% <53.06%> (+<0.01%)`	⬆️
tests	`88.53% <99.27%> (+0.07%)`	⬆️

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martinsaposnic · 2025-09-23T17:27:21Z

lightning/src/chain/channelmonitor.rs

+	/// `true` when absent during upgrade so holder broadcasts aren't gated unexpectedly.
+	funding_seen_onchain: bool,
+	/// Tracks whether manual-broadcasting was requested before the funding transaction appeared on-chain.
+	manual_broadcast_pending: bool,


original comment from @TheBlueMatt #3838 (comment)

Hmm, I feel like we can just use holder_tx_signed rather than adding a new bool.

@TheBlueMatt how do I prevent queue_latest_holder_commitment_txn_for_broadcast from being called multiple times? holder_tx_signed is never set to false, so not sure how could I prevent it

ISTM we could call queue_latest_holder_commitment_txn_for_broadcast when we set funding_seen_onchain if holder_tx_signed is true? That should make it called only once cause we can use funding_seen_onchain indirectly to control it.

would this be ok? 6d4f901

ldk-reviews-bot · 2025-09-25T14:38:17Z

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Hey @tnull! 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/chain/channelmonitor.rs

tnull

Did a first pass, changes look good so far I think.

Mind cleaning up the commit history to a) include a proper title/description for each feature commit b) maybe move the 'track funding transaction' and 'account for manual broadcast' parts into two different feature commits.

tnull · 2025-09-26T08:37:49Z

lightning/src/chain/channelmonitor.rs

 	pending_funding: Vec<FundingScope>,

+	/// True if this channel was configured for manual funding broadcasts. Monitors written by
+	/// versions prior to introducing the flag will load with `false` until a new update persists it.


Please be more specific on the version here and below, as it also gives us a hint when we can assume the new behavior and delete the comment/potentially old code.

Suggested change

/// versions prior to introducing the flag will load with `false` until a new update persists it.

/// versions prior to LDK 0.2 will load with `false` until a new update persists it.

tnull · 2025-09-26T08:43:49Z

lightning/src/chain/channelmonitor.rs

 			(32, pending_funding, optional_vec),
 			(33, htlcs_resolved_to_user, option),
 			(34, alternative_funding_confirmed, option),
+			(35, is_manual_broadcast, option),


Those could be simplified by reading with (default_value, X).

tnull · 2025-09-26T08:45:30Z

lightning/src/chain/channelmonitor.rs

+	/// transactions that cannot be confirmed until the funding transaction is visible.
+	///
+	/// [`Event::BumpTransaction`]: crate::events::Event::BumpTransaction
 	#[rustfmt::skip]


Mind dropping this rustfmt::skip in a separate (prefactor) commit while we're here?

tnull · 2025-09-26T09:59:14Z

lightning/src/chain/channelmonitor.rs

+
+		if self.is_manual_broadcast && !funding_seen_before && self.funding_seen_onchain && self.holder_tx_signed
+		{
+			self.queue_latest_holder_commitment_txn_for_broadcast(


I'm a bit confused - why do we queue the broadcast here immediately? Should we only do this if should_broadcast_commitment?

good catch. this was a silly mistake. I'm working on a fix but can't find the right answer. if I do

if self.is_manual_broadcast && !funding_seen_before && self.funding_seen_onchain && self.holder_tx_signed { should_broadcast_commitment = true; }

and not return immediately then it enqueues txs twice so tests fail. I'm working on it

TheBlueMatt · 2025-09-26T14:18:30Z

lightning/src/chain/channelmonitor.rs

+		// the funding transaction on-chain, do not queue any transactions.
+		if require_funding_seen && self.is_manual_broadcast && !self.funding_seen_onchain {
+			log_info!(logger, "Not broadcasting holder commitment for manual-broadcast channel before funding appears on-chain");
+			return;


I think we want to set holder_tx_signed and push the monitor event here. Basically, we should always call generate_claimable_outpoints_and_watch_outputs but we can skip actually passing them to the onchain_tx_handler, similar to what you did elsewhere.

…t_txn

…y overridden

…nd stuff prior to ldk 0.2

TheBlueMatt · 2025-09-26T17:25:58Z

Feel free to squash, I think this is mostly there. Looks like CI is failing and can you write a commit message for the commit?

martinsaposnic · 2025-09-26T17:32:11Z

can you write a commit message for the commit?

sorry, what do you mean by this? @TheBlueMatt

TheBlueMatt · 2025-09-26T17:50:04Z

Err, sorry, write commit messages for all the commits. Your commits currently only have titles (and many of them are too long). The subject line should be no longer than ~70 chars, followed by description of why and what was done, as well as anything that might be surprising to someone reading the commit in 5 years. See https://cbea.ms/git-commit/ for more info.

martinsaposnic · 2025-09-30T11:18:31Z

@TheBlueMatt @tnull what do you think about the last fixup? I'm really not sure about the solution here, and I want your ack before I squash&rebase&rewrite the commit message

TheBlueMatt · 2025-10-01T09:37:26Z

lightning/src/chain/channelmonitor.rs

-				watch_outputs.append(&mut outputs);
+			// Only generate claims immediately if block_confirmed 
+			// won't also generate them to avoid duplicate registrations.
+			let should_broadcast = self.should_broadcast_holder_commitment_txn(logger);


Hmmm, yea, it does seem a bit strange to check if block_confirmed will do something and disable an important step if it will. But then if block_confirmed changes this code will be automatically broken without touching this code. Rather, ISTM block_confirmed needs to check if we already broadcasted before broadcasting.

… skip passing it to onchain_tx_handler on queue_latest_holder_commitment_txn_for_broadcast

…instead mark it as should_broadcast_commitment for later queueing

…casting

TheBlueMatt added this to the 0.2 milestone Sep 23, 2025

martinsaposnic mentioned this pull request Sep 23, 2025

Support client_trusts_lsp on LSPS2 #3838

Merged

tnull self-requested a review September 23, 2025 14:37

martinsaposnic commented Sep 23, 2025

View reviewed changes

martinsaposnic force-pushed the track-funding-tx-channelmonitor branch from 236e01f to 6d4f901 Compare September 25, 2025 16:13

martinsaposnic marked this pull request as ready for review September 25, 2025 16:14

graphite-app bot reviewed Sep 25, 2025

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lightning/src/chain/channelmonitor.rs Show resolved Hide resolved

martinsaposnic requested a review from TheBlueMatt September 25, 2025 17:33

tnull reviewed Sep 26, 2025

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TheBlueMatt reviewed Sep 26, 2025

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martinsaposnic added 8 commits September 26, 2025 12:36

Prefactor: drop #[rustfmt::skip] on broadcast_latest_holder_commitmen…

8376197

…t_txn

Add manual-funding broadcast flags to ChannelMonitor

8d96490

Set funding_seen_onchain=true on filter_block if seen

6ebe0b1

Gate holder broadcast queueing until funding is seen unless explicitl…

e652b1f

…y overridden

Defer claimable tracking until manual funding is seen

74023dd

Queue holder commit once manual funding hits chain

021b95e

Test manual broadcast tracking and commitment broadcast functionality

bd70a4f

fixup: be more specific on doc when explaining about older monitors a…

5622a33

…nd stuff prior to ldk 0.2

martinsaposnic force-pushed the track-funding-tx-channelmonitor branch from a257c8e to 61d9c28 Compare September 26, 2025 16:18

TheBlueMatt reviewed Oct 1, 2025

View reviewed changes

martinsaposnic added 2 commits October 2, 2025 10:59

fixup: always call generate_claimable_outpoints_and_watch_outputs but…

260febb

… skip passing it to onchain_tx_handler on queue_latest_holder_commitment_txn_for_broadcast

fixup: do not immediately queue broadcast on transactions_confirmed, …

75af535

…instead mark it as should_broadcast_commitment for later queueing

martinsaposnic added 2 commits October 2, 2025 10:59

fixup: avoid dup tx on transactions_confirmed and block_confirmed

8e510cd

fixup: make block_confirmed check if already broadcasted before broad…

9bd2ccc

…casting

martinsaposnic force-pushed the track-funding-tx-channelmonitor branch from 3db3230 to 9bd2ccc Compare October 2, 2025 08:59

	/// versions prior to introducing the flag will load with `false` until a new update persists it.
	/// versions prior to LDK 0.2 will load with `false` until a new update persists it.

Track funding tx channelmonitor #4109

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Track funding tx channelmonitor #4109

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TheBlueMatt commented Sep 26, 2025

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martinsaposnic commented Sep 23, 2025 •

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