Add `unannounced_channel_max_inbound_htlc_value_in_flight_percentage` by tankyleo · Pull Request #4529 · lightningdevkit/rust-lightning

tankyleo · 2026-04-01T06:34:47Z

    Add `unannounced_channel_max_inbound_htlc_value_in_flight_percentage`

    Users can now configure two different max percentages for the channel
    value that can be allocated to inbound HTLCs, one for announced
    channels, and another for unannounced channels.

    We also bump the default maximums to 25% for announced channels, and
    100% for unannounced channels, to bring them closer to what people would
    expect.

ldk-reviews-bot · 2026-04-01T06:34:51Z

👋 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.

lightning/src/ln/channel.rs

lightning/src/util/config.rs

ldk-claude-review-bot · 2026-04-01T06:45:54Z

No issues found. All three items from the previous review have been addressed:

Deserialization backward compatibility — Fixed. Both write (channel.rs:15713) and read (channel.rs:16151) paths now use get_legacy_default_holder_max_htlc_value_in_flight_msat() which hardcodes MAX_IN_FLIGHT_PERCENT_LEGACY = 10.
Missing test coverage for announced path — Fixed. test_configured_holder_max_htlc_value_in_flight now calls the helper with both true and false.
Doc default value — Fixed. announced_channel_max_inbound_htlc_value_in_flight_percentage doc now correctly states "Default value: 25".

I verified all test changes use the correct field (announced_* vs unannounced_*) matching the channel type in each test. The fuzzing Readable impl correctly maps a single byte to both fields. The ChannelHandshakeConfigUpdate::apply handles both fields correctly.

codecov · 2026-04-01T07:33:43Z

Codecov Report

❌ Patch coverage is 93.58974% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.10%. Comparing base (450c03a) to head (2867d5c).
⚠️ Report is 14 commits behind head on main.

Files with missing lines	Patch %	Lines
lightning/src/util/config.rs	75.00%	3 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4529      +/-   ##
==========================================
- Coverage   87.10%   87.10%   -0.01%     
==========================================
  Files         163      163              
  Lines      108740   108856     +116     
  Branches   108740   108856     +116     
==========================================
+ Hits        94723    94817      +94     
- Misses      11531    11550      +19     
- Partials     2486     2489       +3

Flag	Coverage Δ
fuzzing	`40.21% <65.71%> (+0.01%)`	⬆️
tests	`86.21% <95.65%> (+0.01%)`	⬆️

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TheBlueMatt · 2026-04-01T20:53:18Z

lightning/src/util/config.rs

+	///   See [`ChannelHandshakeConfig::our_to_self_delay`] and [`ChannelConfig::cltv_expiry_delta`]
+	///   for more information.
+	///
+	/// Default value: `25`


Let's definitely default to 100.

TheBlueMatt · 2026-04-01T20:53:53Z

lightning/src/util/config.rs

 			our_htlc_minimum_msat: Readable::read(reader)?,
-			max_inbound_htlc_value_in_flight_percent_of_channel: Readable::read(reader)?,
+			announced_channel_max_inbound_htlc_value_in_flight_percentage: Readable::read(reader)?,
+			unannounced_channel_max_inbound_htlc_value_in_flight_percentage: Readable::read(


nit; i dont think its worth reading a separate value here, just copy the one from the announced field so we don't end up invalidating existing fuzz corpuses.

tankyleo · 2026-04-02T16:39:16Z

@benthecarman @tnull a heads up we are revisiting some defaults here

TheBlueMatt · 2026-04-02T17:16:43Z

Feel free to squash.

benthecarman

concept ack for sure!

benthecarman · 2026-04-02T17:26:48Z

lightning/src/ln/chanmon_update_fail_tests.rs

+	// Set the percentage to the default value at the time this test was written
+	config.channel_handshake_config.announced_channel_max_inbound_htlc_value_in_flight_percentage =
+		10;
+	let configs = [


nit: I think you can do let configs: [Option<Config>; 9] = std::array::from_fn(|_| Some(config.clone())); to clean this up

tankyleo · 2026-04-02T18:29:41Z

Squashed with from_fn cleanups in the tests.

Users can now configure two different max percentages for the channel value that can be allocated to inbound HTLCs, one for announced channels, and another for unannounced channels. We also bump the default maximums to 25% for announced channels, and 100% for unannounced channels, to bring them closer to what people would expect.

tankyleo requested a review from TheBlueMatt April 1, 2026 06:37

ldk-claude-review-bot reviewed Apr 1, 2026

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ldk-claude-review-bot reviewed Apr 1, 2026

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ldk-claude-review-bot reviewed Apr 1, 2026

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tankyleo force-pushed the 2026-04-add-max-inflight-knob-for-unannounced-channels branch 2 times, most recently from 887ca41 to 3644da0 Compare April 1, 2026 08:40

TheBlueMatt reviewed Apr 1, 2026

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tankyleo requested a review from TheBlueMatt April 2, 2026 16:38

tnull self-requested a review April 2, 2026 16:41

tankyleo self-assigned this Apr 2, 2026

tankyleo added this to Weekly Goals Apr 2, 2026

tankyleo moved this to Goal: Merge in Weekly Goals Apr 2, 2026

benthecarman reviewed Apr 2, 2026

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TheBlueMatt removed their request for review April 2, 2026 18:13

tankyleo force-pushed the 2026-04-add-max-inflight-knob-for-unannounced-channels branch from a0e4183 to e12945f Compare April 2, 2026 18:27

tankyleo requested a review from TheBlueMatt April 2, 2026 18:30

tankyleo added this to the 0.3 milestone Apr 2, 2026

tankyleo force-pushed the 2026-04-add-max-inflight-knob-for-unannounced-channels branch from e12945f to 2867d5c Compare April 2, 2026 18:37

TheBlueMatt approved these changes Apr 2, 2026

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TheBlueMatt merged commit 369a2cf into lightningdevkit:main Apr 2, 2026
18 of 19 checks passed

github-project-automation bot moved this from Goal: Merge to Done in Weekly Goals Apr 2, 2026

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Add `unannounced_channel_max_inbound_htlc_value_in_flight_percentage`#4529

Add `unannounced_channel_max_inbound_htlc_value_in_flight_percentage`#4529
TheBlueMatt merged 1 commit intolightningdevkit:mainfrom
tankyleo:2026-04-add-max-inflight-knob-for-unannounced-channels

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