Support HTLC interception by source channel by TheBlueMatt · Pull Request #4338 · lightningdevkit/rust-lightning

TheBlueMatt · 2026-01-23T02:21:36Z

Just a few more flags and a small cleanup.

Based on #4300

ldk-reviews-bot · 2026-01-23T02:21:39Z

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ldk-reviews-bot · 2026-01-26T00:00:23Z

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tnull

Please re-request review once #4300 lands and this is rebased.

TheBlueMatt · 2026-01-28T14:11:51Z

Rebased.

tnull

Seems CI is very unhappy as this doesn't build currently.

ldk-reviews-bot · 2026-01-29T09:34:51Z

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TheBlueMatt · 2026-01-29T15:03:23Z

Oops, silent conflict.

codecov · 2026-01-29T17:57:58Z

Codecov Report

❌ Patch coverage is 93.75000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.89%. Comparing base (3497b59) to head (9a9531f).
⚠️ Report is 13 commits behind head on main.

Files with missing lines	Patch %	Lines
lightning/src/ln/channelmanager.rs	93.75%	5 Missing and 1 partial ⚠️

Additional details and impacted files

@@ Coverage Diff @@## main #4338 +/- ##
==========================================
- Coverage 86.09% 85.89% -0.20% 
==========================================
Files 156 156 Lines 103623 103958 +335 Branches 103623 103958 +335 ==========================================
+ Hits 89211 89299 +88 - Misses 11895 12139 +244 - Partials 2517 2520 +3

Flag	Coverage Δ
tests	`85.89% <93.75%> (-0.20%)`	⬇️

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ldk-reviews-bot · 2026-01-31T15:04:02Z

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ldk-reviews-bot · 2026-02-02T15:04:55Z

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elnosh

rustfmt is unhappy but code changes look good to me

ldk-reviews-bot · 2026-02-04T15:05:59Z

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ldk-reviews-bot · 2026-02-07T00:00:15Z

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ldk-reviews-bot · 2026-02-09T00:00:38Z

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ldk-reviews-bot · 2026-02-11T00:01:05Z

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elnosh

fixups lgtm

tnull

LGTM, feel free to squash.

TheBlueMatt · 2026-02-12T15:16:33Z

Squashed without any further changes.

ldk-reviews-bot · 2026-02-12T17:35:02Z

✅ Added second reviewer: @tankyleo

ldk-reviews-bot · 2026-02-16T00:00:57Z

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TheBlueMatt · 2026-02-17T18:28:38Z

Rebased to address conflict.

We jump through some hoops in order to pass a small list of objects to `forward_htlcs` on a per-channel basis rather than per-HTLC. Then, `forward_htlcs` builds a `PendingAddHTLCInfo` for each HTLC for insertion. Worse, in some `forward_htlcs` callsites we're actually starting with a `PendingAddHTLCInfo`, converting it to a tuple, then back inside `forward_htlcs`. Instead, here we just pass a list of built `PendingAddHTLCInfo`s to `forward_htlcs`, cleaning up a good bit of code and even avoiding an allocation of the HTLCs vec in many cases.

It may be useful in some situations to select HTLCs for interception based on the source channel in addition to the sink. Here we add the ability to do so by adding new flags to `HTLCInterceptionFlags`.

TheBlueMatt · 2026-02-18T00:06:19Z

Grr, rebase broke rustfmt:

$ git diff-tree -U1 ec84d5549 9a9531f3c
diff --git a/lightning/src/ln/channelmanager.rs b/lightning/src/ln/channelmanager.rs
index a013b1905d..b417e023f4 100644
--- a/lightning/src/ln/channelmanager.rs+++ b/lightning/src/ln/channelmanager.rs@@ -9578,4 +9578,3 @@ This indicates a bug inside LDK. Please report this error at https://github.com/
user_channel_id: u128, unbroadcasted_batch_funding_txid: Option<Txid>,
- update_actions: Vec<MonitorUpdateCompletionAction>,- htlc_forwards: Vec<PendingAddHTLCInfo>,+ update_actions: Vec<MonitorUpdateCompletionAction>, htlc_forwards: Vec<PendingAddHTLCInfo>,
decode_update_add_htlcs: Option<(u64, Vec<msgs::UpdateAddHTLC>)>,

TheBlueMatt requested a review from tnull January 23, 2026 02:21

tnull removed their request for review January 27, 2026 10:22

tnull reviewed Jan 27, 2026
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TheBlueMatt force-pushed the 2026-01-intercept-by-source-v2 branch from b793c1e to 79952e1Compare January 28, 2026 14:11

TheBlueMatt requested a review from tnull January 28, 2026 14:11

TheBlueMatt force-pushed the 2026-01-intercept-by-source-v2 branch from 79952e1 to 779fce3Compare January 28, 2026 14:14

tnull reviewed Jan 29, 2026
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TheBlueMatt force-pushed the 2026-01-intercept-by-source-v2 branch from 779fce3 to 0bf2200Compare January 29, 2026 15:03

TheBlueMatt requested a review from tnull January 29, 2026 15:03

elnosh reviewed Feb 2, 2026
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Comment threadlightning/src/ln/channelmanager.rs
Comment threadlightning/src/ln/channelmanager.rs
Comment threadlightning/src/util/config.rs Outdated
Comment threadlightning/src/ln/channelmanager.rs Outdated

TheBlueMatt force-pushed the 2026-01-intercept-by-source-v2 branch from 0bf2200 to f6ecc61Compare February 7, 2026 16:51

elnosh reviewed Feb 11, 2026
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tnull reviewed Feb 12, 2026
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TheBlueMatt force-pushed the 2026-01-intercept-by-source-v2 branch from f6ecc61 to c4ae026Compare February 12, 2026 15:16

TheBlueMatt requested a review from tnull February 12, 2026 15:16

tnull previously approved these changes Feb 12, 2026
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ldk-reviews-bot requested a review from tankyleo February 12, 2026 17:35

TheBlueMatt dismissed tnull’s stale review via ec84d55February 17, 2026 18:28

TheBlueMatt force-pushed the 2026-01-intercept-by-source-v2 branch from c4ae026 to ec84d55Compare February 17, 2026 18:28

tankyleo previously approved these changes Feb 17, 2026
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tankyleo requested a review from tnull February 17, 2026 22:51

TheBlueMatt added 2 commits February 18, 2026 00:05

Allow intercepting HTLCs based on the source channel
9a9531f
It may be useful in some situations to select HTLCs for interception based on the source channel in addition to the sink. Here we add the ability to do so by adding new flags to `HTLCInterceptionFlags`.

TheBlueMatt dismissed tankyleo’s stale review via 9a9531fFebruary 18, 2026 00:05

TheBlueMatt force-pushed the 2026-01-intercept-by-source-v2 branch from ec84d55 to 9a9531fCompare February 18, 2026 00:05

tankyleo approved these changes Feb 18, 2026
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tnull approved these changes Feb 18, 2026
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tnull merged commit d09f1d2 into lightningdevkit:mainFeb 18, 2026
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