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 77.77778% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.19%. Comparing base (4a3aaef) to head (6ea327e).
⚠️ Report is 78 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%   86.19%   +0.17%     
==========================================
  Files         159      160       +1     
  Lines      105430   107450    +2020     
  Branches   105430   107450    +2020     
==========================================
+ Hits        90690    92619    +1929     
+ Misses      12229    12213      -16     
- Partials     2511     2618     +107

Flag	Coverage Δ
tests	`86.19% <77.77%> (+0.17%)`	⬆️

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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

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.

TheBlueMatt · 2026-03-19T20:41:37Z

lightning/src/ln/channel.rs

+	///
+	/// This is the maximum of the dust exposure on the holder and counterparty commitment
+	/// transactions, and includes both the value of all pending HTLCs that are below the dust
+	/// threshold as well as any excess commitment transaction fees that contribute to dust


Needs a link to the config knobs that limit it.

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.

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.

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

View reviewed changes

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

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.

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Bortlesboat commented Mar 8, 2026

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