Support manually selecting inputs consuming their entire value by wpaulino · Pull Request #4575 · lightningdevkit/rust-lightning

wpaulino · 2026-04-23T17:08:48Z

This commit introduces an alternative way of splicing in funds without coin selection by requiring the full UTXO to be provided. Each UTXO's entire value (minus fees) is allocated towards the channel, which provides unified balance wallets a more intuitive API when splicing funds into the channel, as they don't particularly care about maintaining a portion of their balance onchain.

To simplify the implementation, we require that contributions are not allowed to mix coin-selected inputs with manually-selected ones. Users will need to start a fresh contribution if they want to change the funding input mode.

ldk-reviews-bot · 2026-04-23T17:08:52Z

👋 I see @TheBlueMatt was un-assigned.
If you'd like another reviewer assignment, please click here.

ldk-claude-review-bot · 2026-04-23T17:16:47Z

 		);

-		if !self.inputs.is_empty() {
+		if !self.inputs.is_empty() && self.input_mode == Some(FundingInputMode::CoinSelected) {


Bug: Backwards compatibility issue with persisted FundingContribution objects.

FundingContribution is persisted in PendingFunding.contributions (channel.rs:2917). When deserializing contributions created before this PR, input_mode will be None (it's a new option TLV field). Old coin-selected contributions with inputs will have input_mode == None, causing this condition to be false even though they should take the coin-selected branch.

This causes two problems for old persisted coin-selected contributions:

Wrong fee buffer calculation: Uses holder_balance + net_value_without_fee instead of estimated_fee + change_value, potentially allowing or rejecting feerate adjustments incorrectly.

Change output silently dropped: compute_feerate_adjustment returns None for change, and at_feerate sets change_output = None, losing the change value.

This is reachable via for_acceptor_at_feerate / for_initiator_at_feerate called on contributions loaded from pending_splice.contributions (channel.rs lines 12504, 12944, 13127, 13145).

Fix: use self.input_mode != Some(FundingInputMode::Manual) instead of self.input_mode == Some(FundingInputMode::CoinSelected) to preserve old behavior for contributions where input_mode is None:

Suggested change

if !self.inputs.is_empty() && self.input_mode == Some(FundingInputMode::CoinSelected) {

if !self.inputs.is_empty() && self.input_mode != Some(FundingInputMode::Manual) {

There is no backwards compatibility concern because the serialized object has not been included in a release yet.

ldk-claude-review-bot · 2026-04-23T17:17:33Z

+		if let Some(PriorContribution { contribution: prior_contribution, .. }) =
+			self.prior_contribution.as_ref()
+		{
+			if prior_contribution.input_mode == Some(FundingInputMode::CoinSelected)


Minor: Same backwards-compat pattern as line 880. Old persisted coin-selected contributions will have input_mode == None, so this guard won't fire for them. In practice this is mostly mitigated by the check at line 1309 (value_added > 0 && manually_selected_inputs non-empty), but it could miss edge cases where the old prior had value_added() == 0 (inputs exactly covered outputs + fees).

Consider using != Some(FundingInputMode::Manual) combined with a non-empty inputs check:

Suggested change

if prior_contribution.input_mode == Some(FundingInputMode::CoinSelected)

if prior_contribution.input_mode != Some(FundingInputMode::Manual)

&& !prior_contribution.inputs.is_empty()

ldk-claude-review-bot · 2026-04-23T17:18:44Z

I've completed a thorough re-review of the entire PR diff and the current code. The previously flagged .take() bug (now line 1229) has been fixed to .clone(). The three other previously flagged issues remain open. I found no new issues.

Review Summary

Previously Flagged Issues — Status

FIXED — lightning/src/ln/funding.rs:1229 — .take() destroying funding_inputs on coin selection fallback path is now .clone().
Still open — lightning/src/ln/funding.rs:933 — Backwards-compat: old persisted coin-selected contributions have input_mode == None, causing them to take the manual-inputs fee buffer branch instead of the coin-selected branch in compute_feerate_adjustment.
Still open — lightning/src/ln/funding.rs:1401-1412 — Backwards-compat: old coin-selected priors with input_mode == None get funding_inputs = None in builder init, silently discarding their inputs when the request doesn't match and amend_without_coin_selection is called.
Still open — lightning/src/ln/funding.rs:1375-1381 — Duplicate-output validation (by script_pubkey) shadows MAX_MONEY sum tests since funding_output_sats() always produces the same script_pubkey.

No New Issues Found

The new FundingInputs/FundingInputMode enums, builder add_input/add_inputs/remove_input methods, splice_in_inputs convenience method, fee buffer calculation for manual inputs, duplicate input validation, ManuallySelectedInputsInsufficient error propagation (properly not falling through to coin selection), and all new tests are correct and consistent.

codecov · 2026-04-23T18:30:17Z

Codecov Report

❌ Patch coverage is 96.14874% with 29 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.54%. Comparing base (f408b17) to head (a9fa610).
⚠️ Report is 26 commits behind head on main.

Files with missing lines	Patch %	Lines
lightning/src/ln/funding.rs	96.07%	15 Missing and 14 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4575      +/-   ##
==========================================
+ Coverage   86.15%   86.54%   +0.38%     
==========================================
  Files         157      159       +2     
  Lines      109096   110371    +1275     
  Branches   109096   110371    +1275     
==========================================
+ Hits        93989    95517    +1528     
+ Misses      12485    12316     -169     
+ Partials     2622     2538      -84

Flag	Coverage Δ
fuzzing-fake-hashes	`5.73% <0.00%> (?)`
fuzzing-real-hashes	`23.11% <3.67%> (?)`
tests	`86.20% <96.14%> (+0.05%)`	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

TheBlueMatt

All LGTM. One question.

ldk-reviews-bot · 2026-04-27T00:00:09Z

🔔 1st Reminder

Hey @jkczyz! 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 · 2026-04-29T00:01:00Z

🔔 2nd Reminder

Hey @jkczyz! 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.

TheBlueMatt

thanks

elnosh

Not that familiar with splicing-related code in the codebase but looking at this for learning purposes. After much staring, changes make sense although agree with @jkczyz comment on making an enum since those fields (value_added and manually_selected_inputs) are mutually exclusive in the ways inputs can be provided.

elnosh · 2026-04-30T22:25:07Z

+/// used if the request cannot be satisfied by reusing a prior contribution, by using only
+/// manually selected inputs, or by building a pure splice-out directly.


I'm not sure I follow this comment. If we have a builder with either sync or async CoinSelectionSource then manually added inputs are not allowed.

Manually selected inputs are still allowed as long as the added_value is 0.

TheBlueMatt · 2026-05-07T21:31:01Z

Needs rebase again :/

ldk-claude-review-bot · 2026-05-13T18:47:37Z

+		for (idx, output) in self.outputs.iter().enumerate() {
+			if self.outputs[..idx]
+				.iter()
+				.any(|existing_output| existing_output.script_pubkey == output.script_pubkey)
+			{
+				return Err(FundingContributionError::InvalidSpliceValue);


Nit / test gap: this new duplicate-output check fires before the value_removed > MAX_MONEY accumulation below. Since funding_output_sats() always returns the same script_pubkey (new_p2wpkh(&WPubkeyHash::all_zeros())), the existing tests test_build_funding_contribution_validates_max_money ("splice_out with multiple outputs summing > MAX_MONEY", lines 2723-2734) and test_funding_builder_validates_mixed_request_max_money ("outputs summing > MAX_MONEY", lines 2755-2769) now hit this duplicate check first. They still pass because both paths yield InvalidSpliceValue, but the MAX_MONEY sum-of-outputs path has lost test coverage.

Consider using distinct script_pubkey values for each output in those tests.

TheBlueMatt · 2026-05-17T23:02:22Z

+		let value_added =
+			inner.funding_inputs.as_ref().map_or(Amount::ZERO, FundingInputs::value_added);
+
 		match inner.build_without_coin_selection() {


Its quite awkward that we call this here and it takes several fields from inner internally but then we reuse inner a few lines down as well as later. It probably makes sense to pay the penalty of either calling prepare_coin_selection_request upfront so we can make build_without_coin_selection take mut self without ref or cloneing internally to avoid ripping out parts of inner before we reuse it. Seems like too much opportunity for stuff to go wrong later.

Alright just decided to clone internally

Sorry, this wasn't the only place, we also take the prior_contribution in try_build_without_coin_selection and mutate inner that way too.

This commit introduces an alternative way of splicing in funds without coin selection by requiring the full UTXO to be provided. Each UTXO's entire value (minus fees) is allocated towards the channel, which provides unified balance wallets a more intuitive API when splicing funds into the channel, as they don't particularly care about maintaining a portion of their balance onchain. To simplify the implementation, we require that contributions are not allowed to mix coin-selected inputs with manually-selected ones. Users will need to start a fresh contribution if they want to change the funding input mode.

There's no reason not to do so, and it allows us to fail earlier when the user's net contribution exceeds their spliceable balance.

While this is already enforced when we get to the interactive negotiation phase, we choose to fail early anyway.

wpaulino added this to the 0.3 milestone Apr 23, 2026

wpaulino requested review from TheBlueMatt and jkczyz April 23, 2026 17:08

wpaulino self-assigned this Apr 23, 2026

wpaulino marked this pull request as ready for review April 23, 2026 17:08

ldk-claude-review-bot reviewed Apr 23, 2026

View reviewed changes

wpaulino force-pushed the funding-contribution-builder-manual-inputs branch from 12e5994 to 412ec3d Compare April 23, 2026 17:19

TheBlueMatt reviewed Apr 24, 2026

View reviewed changes

Comment thread lightning/src/ln/funding.rs Outdated

wpaulino force-pushed the funding-contribution-builder-manual-inputs branch from 412ec3d to 228cae8 Compare April 28, 2026 22:00

wpaulino requested a review from TheBlueMatt April 29, 2026 16:58

TheBlueMatt previously approved these changes Apr 29, 2026

View reviewed changes

jkczyz reviewed Apr 30, 2026

View reviewed changes

Comment thread lightning/src/ln/funding.rs Outdated

Comment thread lightning/src/ln/funding.rs Outdated

Comment thread lightning/src/ln/funding.rs Outdated

Comment thread lightning/src/ln/funding.rs Outdated

elnosh reviewed Apr 30, 2026

View reviewed changes

wpaulino dismissed TheBlueMatt’s stale review via 17c864b May 5, 2026 23:36

wpaulino force-pushed the funding-contribution-builder-manual-inputs branch 3 times, most recently from c3da7fe to 6e16493 Compare May 6, 2026 19:27

ldk-claude-review-bot reviewed May 6, 2026

View reviewed changes

Comment thread lightning/src/ln/funding.rs Outdated

wpaulino mentioned this pull request May 8, 2026

Drop QuiescentError::with_negotiation_failure_reason #4608

Merged

wpaulino force-pushed the funding-contribution-builder-manual-inputs branch from 6e16493 to c240f1b Compare May 13, 2026 18:40

ldk-claude-review-bot reviewed May 13, 2026

View reviewed changes

TheBlueMatt previously approved these changes May 17, 2026

View reviewed changes

wpaulino dismissed TheBlueMatt’s stale review via ed757b2 May 18, 2026 20:13

wpaulino force-pushed the funding-contribution-builder-manual-inputs branch from c240f1b to ed757b2 Compare May 18, 2026 20:13

wpaulino requested review from TheBlueMatt and jkczyz May 18, 2026 20:14

TheBlueMatt removed their request for review May 18, 2026 20:37

wpaulino added 3 commits May 18, 2026 15:03

Include spliceable balance in every FundingTemplate

0789285

There's no reason not to do so, and it allows us to fail earlier when the user's net contribution exceeds their spliceable balance.

Detect duplicate inputs and outputs upon building FundingBuilder

a9fa610

While this is already enforced when we get to the interactive negotiation phase, we choose to fail early anyway.

wpaulino force-pushed the funding-contribution-builder-manual-inputs branch from ed757b2 to a9fa610 Compare May 18, 2026 22:04

	if !self.inputs.is_empty() && self.input_mode == Some(FundingInputMode::CoinSelected) {
	if !self.inputs.is_empty() && self.input_mode != Some(FundingInputMode::Manual) {

	if prior_contribution.input_mode == Some(FundingInputMode::CoinSelected)
	if prior_contribution.input_mode != Some(FundingInputMode::Manual)
	&& !prior_contribution.inputs.is_empty()

		/// used if the request cannot be satisfied by reusing a prior contribution, by using only
		/// manually selected inputs, or by building a pure splice-out directly.

Conversation

wpaulino commented Apr 23, 2026

Uh oh!

ldk-reviews-bot commented Apr 23, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

ldk-claude-review-bot commented Apr 23, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Review Summary

Previously Flagged Issues — Status

No New Issues Found

Uh oh!

codecov Bot commented Apr 23, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Codecov Report

Uh oh!

TheBlueMatt left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

ldk-reviews-bot commented Apr 27, 2026

Uh oh!

ldk-reviews-bot commented Apr 29, 2026

Uh oh!

TheBlueMatt left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

elnosh left a comment

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

TheBlueMatt commented May 7, 2026

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

6 participants

ldk-reviews-bot commented Apr 23, 2026 •

edited

Loading

ldk-claude-review-bot commented Apr 23, 2026 •

edited

Loading

codecov Bot commented Apr 23, 2026 •

edited

Loading