Introduce splice-compatible commitment update monitor variants #3855

wpaulino · 2025-06-12T21:42:42Z

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ldk-reviews-bot · 2025-06-12T21:42:44Z

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wpaulino · 2025-06-12T21:48:23Z

lightning/src/chain/channelmonitor.rs

+		let htlcs_for_commitment = |commitment: &CommitmentTransaction| {
+			let mut nondust_htlcs = commitment.nondust_htlcs().clone().into_iter();
+			let mut sources = htlc_data.nondust_htlc_sources.clone().into_iter();


I'm not too happy with this, but trying to not duplicatively track the HTLC sources across FundingScopes is a good bit of non-trivial work. At least they'll only exist in the current and previous counterparty commitments, but those are still per FundingScope. The simplest thing we could do for now is Arc them to reduce memory bandwidth (unfortunately on disk we'll still have duplicates), but I chose not to pursue that unless we're sure of it.

Given its just for the latest and prev commitment txn I feel like its okay. It also gives us room to relax the restriction on multiple splices having the same dust/non-dust HTLC sets in the future.

codecov · 2025-06-13T01:02:13Z

Codecov Report

Attention: Patch coverage is 50.93750% with 157 lines in your changes missing coverage. Please review.

Project coverage is 88.80%. Comparing base (c48e0a8) to head (4dc47f9).
Report is 43 commits behind head on main.

Files with missing lines	Patch %	Lines
lightning/src/chain/channelmonitor.rs	50.71%	96 Missing and 8 partials ⚠️
lightning/src/ln/channel.rs	50.00%	53 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3855      +/-   ##
==========================================
- Coverage   89.65%   88.80%   -0.86%     
==========================================
  Files         164      165       +1     
  Lines      134658   119288   -15370     
  Branches   134658   119288   -15370     
==========================================
- Hits       120734   105937   -14797     
+ Misses      11246    11020     -226     
+ Partials     2678     2331     -347

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tankyleo

Thanks dude, just went through the first commit, will continue tomorrow. I have a big-picture question in commitment_signed_batch take a look at that first.

lightning/src/chain/channelmonitor.rs

lightning/src/ln/channel.rs

tankyleo · 2025-06-13T04:31:44Z

lightning/src/ln/channel.rs

+			let msg = messages
+				.get(&funding_txid)
+				.ok_or_else(|| ChannelError::close(format!("Peer did not send a commitment_signed for pending splice transaction: {}", funding_txid)))?;
+			let (commitment_tx, htlcs_included) = self.context.validate_commitment_signed(


It might not be worth the pain let me know:

Can we avoid doing the work of populating and sorting this table for all the pending scopes in build_commitment_transaction ? We only need it for the current scope here.

(In validate_commitment_signed, let's read the HTLCs from the commitment transaction instead of the HTLC-source table).

Also wondering if we can make the state and dust-vs-nondust HTLC sorting only once for all scopes.

Hm yeah this would be nice, this code was mostly written before we made the change to populate the source table separately. I wouldn't consider it a blocker to this PR, unless @TheBlueMatt feels strongly.

tankyleo

Went through the second commit, some similar questions, some new ones.

tankyleo · 2025-06-13T23:52:17Z

lightning/src/chain/channelmonitor.rs

@@ -3175,11 +3171,11 @@ impl<Signer: EcdsaChannelSigner> ChannelMonitorImpl<Signer> {
 			self.counterparty_hash_commitment_number.insert(htlc.payment_hash, commitment_number);
 		}

-		log_trace!(logger, "Tracking new counterparty commitment transaction with txid {} at commitment number {} with {} HTLC outputs", txid, commitment_number, htlc_outputs.len());


You find this log not necessary ?

@wpaulino just want to confirm here - i think the worry is hey these could be used to cheat so make sure we are tracking them ?

lightning/src/chain/channelmonitor.rs

lightning/src/ln/channel.rs

ldk-reviews-bot · 2025-06-16T00:01:21Z

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ldk-reviews-bot · 2025-06-18T00:01:43Z

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lightning/src/chain/channelmonitor.rs

lightning/src/ln/channel.rs

TheBlueMatt · 2025-06-18T15:44:58Z

lightning/src/chain/channelmonitor.rs

+		let htlcs_for_commitment = |commitment: &CommitmentTransaction| {
+			let mut nondust_htlcs = commitment.nondust_htlcs().clone().into_iter();
+			let mut sources = htlc_data.nondust_htlc_sources.clone().into_iter();


Given its just for the latest and prev commitment txn I feel like its okay. It also gives us room to relax the restriction on multiple splices having the same dust/non-dust HTLC sets in the future.

lightning/src/chain/channelmonitor.rs

lightning/src/ln/channel.rs

tankyleo

Another pass on the first commit, will continue first thing tomorrow...

lightning/src/chain/channelmonitor.rs

lightning/src/ln/channel.rs

tankyleo

Done with the two other commits

lightning/src/chain/channelmonitor.rs

ldk-reviews-bot · 2025-06-25T18:33:15Z

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TheBlueMatt · 2025-06-27T19:15:49Z

Mind addressing @tankyleo's feedback?

This new variant is a backwards-incompatible successor to `LatestHolderCommitmentTXInfo` that is capable of handling holder commitment updates while a splice is pending. Since all holder commitment candidates share the same set of non-dust and dust HTLCs (though each non-dust HTLC can have differing output indices), we can share the same set of HTLC source data across all candidates.

This new variant is a backwards-incompatible successor to `LatestCounterpartyCommitmentTXInfo` that is capable of handling counterparty commitment updates while a splice is pending. Since all counterparty commitment candidates share the same set of non-dust and dust HTLCs (though each non-dust HTLC can have differing output indices), we can share the same set of HTLC source data across all candidates. Unfortunately, each `FundingScope` tracks its own set of `counterparty_claimable_outpoints`, which includes the HTLC source data (though only for the current and previous counterparty commitments), so we end up duplicating it (both in memory and on disk) temporarily.

They don't need to be tracked as we can recompute them easily, though we still write them in the `ChannelMonitor` for the current `FundingScope` for backwards compatibility. The serialization implementation for `FundingScope` can now use the `impl_writeable_tlv_based` macro as a result.

graphite-app · 2025-06-27T21:56:31Z

lightning/src/chain/channelmonitor.rs

+	fn update_counterparty_commitment_data(
+		&mut self, commitment_txs: &[CommitmentTransaction], htlc_data: &CommitmentHTLCData,
+	) -> Result<(), &'static str> {
+		self.verify_matching_commitment_transactions(commitment_txs.iter())?;


The function verify_matching_commitment_transactions returns a Result, but the error case isn't being handled here. Consider propagating the error back to the caller by changing this to:

self.verify_matching_commitment_transactions(commitment_txs.iter())?;

This matches the pattern used in update_holder_commitment_data and ensures errors aren't silently ignored.

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ldk-reviews-bot · 2025-06-30T00:00:48Z

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ldk-reviews-bot · 2025-06-30T00:00:49Z

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TheBlueMatt · 2025-06-29T23:47:17Z

lightning/src/chain/channelmonitor.rs

+
+		let current_funding_commitment_tx = commitment_txs.first().unwrap();
+		self.current_holder_commitment_number = current_funding_commitment_tx.commitment_number();
+		self.onchain_tx_handler.provide_latest_holder_tx(current_funding_commitment_tx.clone());


Mind leaving a comment here on why OnchainTxHandler doesn't need to know about other commitments?

TheBlueMatt · 2025-06-30T00:17:54Z

lightning/src/chain/channelmonitor.rs

+				let source = (!htlc.offered).then(|| {
+					let source = sources
+						.next()
+						.expect("Every inbound non-dust HTLC should have a corresponding source")


We generally call these "outbound" HTLCs, since they're outbound, just !offered on the commitment tx.

Ah yes my bad should be every outbound :)

lightning/src/ln/channel.rs

tankyleo

Nothing blocking, just have a pending question further above about why we delete

log_trace!(logger, "Tracking new counterparty commitment transaction with txid {} at commitment number {} with {} HTLC outputs", txid, commitment_number, htlc_outputs.len());

TheBlueMatt · 2025-07-01T23:41:52Z

Landing this, we can figure out the logging and comments in a followup.

wpaulino requested a review from tankyleo June 12, 2025 21:43

wpaulino commented Jun 12, 2025

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wpaulino requested a review from TheBlueMatt June 12, 2025 21:48

tankyleo reviewed Jun 13, 2025

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tankyleo mentioned this pull request Jun 20, 2025

[Custom Transactions] Add TxBuilder trait, support fixed additional outputs #3775

Open

jkczyz mentioned this pull request Jun 21, 2025

Dual-funded channels and Splicing Project Tracking #1621

Open

7 tasks

wpaulino force-pushed the splice-commitment-monitor-update branch from 7f942f4 to fedd0ff Compare June 23, 2025 18:31

wpaulino requested review from TheBlueMatt and tankyleo June 23, 2025 18:32

wpaulino force-pushed the splice-commitment-monitor-update branch from fedd0ff to 0e88cdf Compare June 24, 2025 21:50

wpaulino mentioned this pull request Jun 24, 2025

Introduce RenegotiatedFunding monitor update variant #3822

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jkczyz added this to Weekly Goals Jun 26, 2025

TheBlueMatt removed their request for review June 27, 2025 19:16

wpaulino added 3 commits June 27, 2025 14:52

wpaulino force-pushed the splice-commitment-monitor-update branch from 0e88cdf to 4dc47f9 Compare June 27, 2025 21:54

wpaulino requested review from TheBlueMatt and tankyleo June 27, 2025 21:55

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TheBlueMatt approved these changes Jun 30, 2025

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tankyleo approved these changes Jul 1, 2025

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TheBlueMatt merged commit 34664bc into lightningdevkit:main Jul 1, 2025
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github-project-automation bot moved this to Done in Weekly Goals Jul 1, 2025

Introduce splice-compatible commitment update monitor variants #3855

Introduce splice-compatible commitment update monitor variants #3855

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