Expose current dust exposure in ChannelDetails by Bortlesboat · Pull Request #4470 · lightningdevkit/rust-lightning

Bortlesboat · 2026-03-08T16:35:29Z

Summary

Adds a current_dust_exposure_msat field to ChannelDetails that surfaces the current total dust exposure on a channel.

The value is the maximum of the dust exposure across the holder and counterparty commitment transactions
Includes both dust HTLC values and the commitment transaction fee component (as noted by @TheBlueMatt in Expose current dust exposure #2264, dust exposure now includes commitment tx fees, not just dust HTLCs)
Users can compare this against ChannelConfig::max_dust_htlc_exposure to monitor how close a channel is to its dust limit
Field is Option<u64>, None for objects serialized prior to 0.2.1
TLV tag 49 for backwards-compatible serialization

Implementation

Added dust_exposure_msat to AvailableBalances — computed as max(local_dust_exposure_msat, remote_dust_exposure_msat) in get_available_balances (tx_builder.rs)
When folding across multiple funding scopes (splices), takes the max dust exposure
Added current_dust_exposure_msat: Option<u64> to ChannelDetails struct, populated from the balance computation in from_channel

Fixes #2264

ldk-reviews-bot · 2026-03-08T16:35:32Z

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codecov · 2026-03-09T21:55:17Z

Codecov Report

❌ Patch coverage is 75.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.18%. Comparing base (4a3aaef) to head (40ce774).
⚠️ Report is 92 commits behind head on main.

Files with missing lines	Patch %	Lines
lightning/src/ln/channel_state.rs	66.66%	1 Missing ⚠️
lightning/src/routing/router.rs	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4470      +/-   ##
==========================================
+ Coverage   86.01%   86.18%   +0.16%     
==========================================
  Files         159      160       +1     
  Lines      105430   107546    +2116     
  Branches   105430   107546    +2116     
==========================================
+ Hits        90690    92689    +1999     
- Misses      12229    12230       +1     
- Partials     2511     2627     +116

Flag	Coverage Δ
tests	`86.18% <75.00%> (+0.16%)`	⬆️

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ldk-reviews-bot · 2026-03-11T11:18:42Z

🔔 1st Reminder

Hey @tankyleo! 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.

Bortlesboat · 2026-03-12T17:29:22Z

Quick follow-up from my side: I’m treating review-required PRs as top priority this week. If you want any specific changes, rebase, or split, I can turn them around quickly.

ldk-reviews-bot · 2026-03-14T00:01:31Z

🔔 2nd Reminder

Hey @tankyleo! 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.

Add current_dust_exposure_msat field to ChannelDetails that surfaces the total dust exposure including both dust HTLC values and the commitment transaction fee component. This is the maximum of the holder and counterparty commitment transaction dust exposures. Users can compare this value against max_dust_htlc_exposure in ChannelConfig to understand how close a channel is to its dust exposure limit without needing internal channel access. Fixes lightningdevkit#2264

ldk-claude-review-bot · 2026-03-15T18:21:28Z

I've completed a thorough review of all files in this diff. The implementation is correct:

The dust exposure computation (max(local, remote)) in tx_builder.rs properly captures the worst-case dust exposure across both commitment transactions.
The fold across funding scopes using .max() is consistent with how a user would want to see the highest risk exposure.
TLV tag 49 (odd = optional) is correctly ordered after tag 47 for backwards-compatible serialization.
The error fallback path (dust_exposure_msat: 0) is consistent with how other fields default in that same block.
The serialization round-trip test and all test fixture updates are correct.

The only issue from my prior review (version string format) was partially addressed — changed from the wrong version "0.2.1" to "0.3", but the format still doesn't match the convention used by every other field in the file ("0.3.0", "0.2.0", "0.0.122", etc.). Since this was already flagged in the prior review pass, I'm not re-posting it.

No new issues found. The prior inline comment about the version format ("0.3" → "0.3.0" for consistency) remains partially unaddressed but was already flagged.

ldk-reviews-bot · 2026-03-16T00:02:42Z

🔔 3rd Reminder

Hey @tankyleo! 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.

Bortlesboat · 2026-03-17T14:30:04Z

Hi @tankyleo — no worries if you're busy! Could another maintainer pick this up? Happy to address any feedback quickly.

ldk-reviews-bot · 2026-03-18T00:02:59Z

🔔 4th Reminder

Hey @tankyleo! 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.

lightning/src/ln/channel.rs

tankyleo

Sorry for the delay

tankyleo · 2026-03-19T23:23:45Z

lightning/src/sign/tx_builder.rs

 		outbound_capacity_msat,
 		next_outbound_htlc_limit_msat: available_capacity_msat,
 		next_outbound_htlc_minimum_msat,
+		dust_exposure_msat,


@TheBlueMatt it's a current quirk of the tx_buider API we currently report the dust exposure on the commitment that matches the local: bool parameter in NextCommitmentStats. With this PR we'd now also take the max of both the local and the remote commitments here, and report it in AvailableBalances.

Seems ok to me for now.

Mmm, its weird that we return available_balances from get_channel_stats ignoring the local parameter but its true for the whole balances struct so...oh well.

ldk-claude-review-bot · 2026-03-20T01:56:06Z

lightning/src/ln/channel_state.rs

+	/// [`ChannelConfig::max_dust_htlc_exposure`] to determine whether new HTLCs can be
+	/// accepted or offered on this channel.
+	///
+	/// This field will be `None` for objects serialized with LDK versions prior to 0.2.1.


The version here says "prior to 0.2.1" but Cargo.toml has version = "0.3.0+git", so this field will first appear in 0.3.0. The previous field (funding_redeem_script) correctly says "prior to 0.2.0".

Suggested change

/// This field will be `None` for objects serialized with LDK versions prior to 0.2.1.

/// This field will be `None` for objects serialized with LDK versions prior to 0.3.0.

Yep, claude is right - this will be shipped in 0.3. We should write "0.3" here (not "0.3.0", though).

Bortlesboat · 2026-03-20T19:12:03Z

Hi — tankyleo appears to be unavailable (4 reminders sent). Could another reviewer pick this up? It's a small addition exposing dust exposure values that are already computed internally. Happy to address any feedback.

TheBlueMatt

Two small things, one that actually needs fixing, otherwise we'll land this. Thanks!

TheBlueMatt · 2026-03-22T18:13:20Z

lightning/src/ln/channel_state.rs

+	/// [`ChannelConfig::max_dust_htlc_exposure`] to determine whether new HTLCs can be
+	/// accepted or offered on this channel.
+	///
+	/// This field will be `None` for objects serialized with LDK versions prior to 0.2.1.


Yep, claude is right - this will be shipped in 0.3. We should write "0.3" here (not "0.3.0", though).

TheBlueMatt · 2026-03-22T18:15:17Z

lightning/src/ln/channel.rs

+	/// threshold as well as any excess commitment transaction fees that contribute to dust
+	/// exposure.
+	///
+	/// See [`ChannelConfig::max_dust_htlc_exposure`] for the config knob that limits this.


nit

Suggested change

/// See [`ChannelConfig::max_dust_htlc_exposure`] for the config knob that limits this.

/// See [`ChannelConfig::max_dust_htlc_exposure`] for more information on the dust calculation and to configure a limit.

TheBlueMatt · 2026-03-22T18:27:10Z

lightning/src/sign/tx_builder.rs

 		outbound_capacity_msat,
 		next_outbound_htlc_limit_msat: available_capacity_msat,
 		next_outbound_htlc_minimum_msat,
+		dust_exposure_msat,


Mmm, its weird that we return available_balances from get_channel_stats ignoring the local parameter but its true for the whole balances struct so...oh well.

Fix version string to 0.3 (not 0.2.1) and improve doc wording for dust_exposure_msat per TheBlueMatt's review.

TheBlueMatt

Please feel free to squash the fixup commits down so that the git history only contains the one main commit

ldk-reviews-bot requested a review from valentinewallace March 8, 2026 16:46

Bortlesboat force-pushed the feat/expose-dust-exposure branch from 06585ba to c571ad4 Compare March 9, 2026 01:31

tankyleo requested review from tankyleo and removed request for valentinewallace March 9, 2026 11:18

Bortlesboat force-pushed the feat/expose-dust-exposure branch from c571ad4 to 4f9b1e5 Compare March 9, 2026 18:25

Bortlesboat force-pushed the feat/expose-dust-exposure branch from 4f9b1e5 to 03c307d Compare March 13, 2026 04:41

Bortlesboat force-pushed the feat/expose-dust-exposure branch from 03c307d to b856d80 Compare March 15, 2026 18:19

TheBlueMatt reviewed Mar 19, 2026

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lightning/src/ln/channel.rs Show resolved Hide resolved

TheBlueMatt removed the request for review from tankyleo March 19, 2026 20:41

tankyleo reviewed Mar 19, 2026

View reviewed changes

Add config knob reference to dust_exposure_msat docs

6ea327e

ldk-claude-review-bot reviewed Mar 20, 2026

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TheBlueMatt reviewed Mar 22, 2026

View reviewed changes

Address review feedback on dust exposure docs

40ce774

Fix version string to 0.3 (not 0.2.1) and improve doc wording for dust_exposure_msat per TheBlueMatt's review.

TheBlueMatt reviewed Mar 23, 2026

View reviewed changes

	/// This field will be `None` for objects serialized with LDK versions prior to 0.2.1.
	/// This field will be `None` for objects serialized with LDK versions prior to 0.3.0.

	/// See [`ChannelConfig::max_dust_htlc_exposure`] for the config knob that limits this.
	/// See [`ChannelConfig::max_dust_htlc_exposure`] for more information on the dust calculation and to configure a limit.

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Bortlesboat commented Mar 8, 2026

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