Dual funding extension, needed also for splicing: begin_interactive_funding_tx_construction #3443

optout21 · 2024-12-05T09:10:35Z

Add these two methods to the current dual funding implementation:
begin_interactive_funding_tx_construction()
calculate_change_output_value()

These changes are in the pipeline for dual funding implementation, and needed for dual funding negotiation during splicing, in #3444 .

dunxen · 2024-12-05T10:53:25Z

Makes sense to get this this in so it can unblock you as #2302 will still take time. Is this much different from what is in #2302/any of the splicing PRs?

optout21 · 2024-12-05T17:56:11Z

~~TODO: I need to run a comparison against current version of dual funding WIP~~

optout21 · 2024-12-06T15:21:59Z

Did the following:

break up maybe_add_funding_change_output() into two: one part for determining if a change needs to be added, and the other to actually add it
moved need_to_add_funding_change_output() into interactivetxs.rs
added unit tests for need_to_add_funding_change_output()

lightning/src/ln/interactivetxs.rs

lightning/src/ln/channel.rs

jkczyz

Could you update the commit message with the rationale for the change? (i.e., specifically how it will be used in splicing)

lightning/src/ln/channel.rs

optout21 · 2024-12-11T16:55:53Z

Review comments addressed, all resolved from my side (left a few open for visibility)

codecov · 2024-12-11T19:46:55Z

Codecov Report

Attention: Patch coverage is 51.69082% with 100 lines in your changes missing coverage. Please review.

Project coverage is 88.28%. Comparing base (7c77daf) to head (665be4e).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
lightning/src/ln/channel.rs	0.00%	100 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3443      +/-   ##
==========================================
- Coverage   88.35%   88.28%   -0.07%     
==========================================
  Files         149      149              
  Lines      112876   113074     +198     
  Branches   112876   113074     +198     
==========================================
+ Hits        99727    99829     +102     
- Misses      10669    10760      +91     
- Partials     2480     2485       +5

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optout21 · 2025-01-06T10:05:52Z

Rebased.

wpaulino · 2025-01-07T00:38:01Z

lightning/src/ln/channel.rs

+		}
+
+		let mut funding_inputs_prev_outputs: Vec<&TxOut> = Vec::with_capacity(funding_inputs.len());
+		// Check that vouts exist for each TxIn in provided transactions.


This seems better suited as a validation check when we construct the DualFundingChannelContext.

Shouldn't this also check the txid of the txin matches the transaction's?

Good point, I will check.

This check makes sense when we obtain the prev TxOut's from the full prev transactions.
I considered the case when in DualFundingChannelContext we would store only the TxOut's, and check and obtain at creation, but the full txs are needed later.
As a middle ground I extracted the logic of checking and extracting into a helper method in DualFundingChannelContext , that can be called when the TxOut's are needed.
Also CC @dunxen

We need to do the same validation for the counterparty's provided inputs, I wonder if we already have code for that, or if we can use this new one there now?

lightning/src/ln/channel.rs

wpaulino · 2025-01-07T00:52:38Z

lightning/src/ln/channel.rs

+		}
+
+		// Add output for funding tx
+		let mut funding_outputs = Vec::new();


I believe the spec allows you to specify additional outputs here as part of the interactive negotiation, which would be included here. I noticed we don't seem to track/request these from the user though, is this something we're not planning to support? cc @dunxen

I think it's planned, but not in this PR.

wpaulino · 2025-01-07T23:12:39Z

lightning/src/ln/channel.rs

+			};
+			let change_output_weight = get_output_weight(&change_output.script_pubkey).to_wu();
+			let change_output_fee = fee_for_weight(self.dual_funding_context().funding_feerate_sat_per_1000_weight, change_output_weight);
+			change_output.value = Amount::from_sat(change_value.saturating_sub(change_output_fee));


If the resulting value is below dust then we shouldn't include the output.

Good point! Turns out this is checked, in holder_dust_limit_satoshis(), invoked a few lines above.

I think we need to check again after we subtract the fee of the change output because it may not be enough anymore.

lightning/src/ln/interactivetxs.rs

optout21 · 2025-01-09T11:15:05Z

Rebased (post Inbound/OutboundV2Channel merge #3498 )

optout21 requested a review from dunxen December 5, 2024 09:10

This was referenced Dec 5, 2024

[Draft][Splicing] Partial, perform interactive transaction negotiation for new funding #3444

Draft

Dual-funded channels and Splicing Project Tracking #1621

Open

jkczyz self-requested a review December 5, 2024 15:22

optout21 force-pushed the splicing-dual-reqs2 branch 2 times, most recently from 4f7e41b to 0448cf9 Compare December 6, 2024 15:20

optout21 changed the title ~~[Draft] Dual funding extension needed for Splicing, begin_interactive_funding_tx_construction~~ Dual funding extension needed for Splicing, begin_interactive_funding_tx_construction Dec 6, 2024

optout21 marked this pull request as ready for review December 6, 2024 15:23

optout21 changed the title ~~Dual funding extension needed for Splicing, begin_interactive_funding_tx_construction~~ Dual funding extension needed also for splicing: begin_interactive_funding_tx_construction Dec 6, 2024

optout21 force-pushed the splicing-dual-reqs2 branch from 0448cf9 to 0e47819 Compare December 6, 2024 15:43

dunxen reviewed Dec 6, 2024

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optout21 requested a review from dunxen December 6, 2024 16:39

optout21 force-pushed the splicing-dual-reqs2 branch from 48e0518 to 9e44d2b Compare December 6, 2024 16:41

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optout21 force-pushed the splicing-dual-reqs2 branch from 9e44d2b to b7e7a34 Compare December 9, 2024 07:20

optout21 requested a review from dunxen December 9, 2024 07:22

jkczyz reviewed Dec 9, 2024

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optout21 force-pushed the splicing-dual-reqs2 branch from 70fde13 to b1ae668 Compare December 11, 2024 16:49

optout21 force-pushed the splicing-dual-reqs2 branch from b1ae668 to 86f9680 Compare December 11, 2024 16:56

optout21 requested a review from jkczyz December 11, 2024 16:57

optout21 force-pushed the splicing-dual-reqs2 branch from 86f9680 to a379f1d Compare December 11, 2024 19:37

optout21 force-pushed the splicing-dual-reqs2 branch from a379f1d to 9256a47 Compare December 14, 2024 12:40

optout21 force-pushed the splicing-dual-reqs2 branch from 9256a47 to 5194458 Compare January 6, 2025 09:57

optout21 added the Splicing label Jan 6, 2025

jkczyz requested a review from wpaulino January 6, 2025 18:35

wpaulino reviewed Jan 7, 2025

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optout21 force-pushed the splicing-dual-reqs2 branch from 27868f8 to fce05cb Compare January 9, 2025 10:42

optout21 added 6 commits January 9, 2025 12:03

Add begin_interactive_funding_tx_construction()

2aa29de

Rename method, review

451a296

Rename extra_input to prev_funding_input

a5e8287

Minor changes post review

25f4103

Minor comments added, review

6c45e4f

Extract helper method in DualFundingChannelContext to extract prev outs

fbde31f

optout21 force-pushed the splicing-dual-reqs2 branch from fce05cb to fbde31f Compare January 9, 2025 11:13

Remove splicing-specific part (a parameter)

665be4e

optout21 changed the title ~~Dual funding extension needed also for splicing: begin_interactive_funding_tx_construction~~ Dual funding extension, needed also for splicing: begin_interactive_funding_tx_construction Jan 9, 2025

optout21 mentioned this pull request Jan 9, 2025

Extend begin_interactive_funding_tx_construction() with splicing-specific extra input (on top of #3443) #3516

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Dual funding extension, needed also for splicing: begin_interactive_funding_tx_construction #3443

Dual funding extension, needed also for splicing: begin_interactive_funding_tx_construction #3443

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optout21 commented Jan 9, 2025

Dual funding extension, needed also for splicing: begin_interactive_funding_tx_construction #3443

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Dual funding extension, needed also for splicing: begin_interactive_funding_tx_construction #3443

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