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Extract dust exposure calculation in `tx_builder` to its own function
Public commit record
73/100 · Adequate
What the developer wrote
Authored by Leo Nash
Extract dust exposure calculation in `tx_builder` to its own function
This snippet is currently used in
`tx_builder::get_next_commitent_stats`, and will be used in an upcoming
commit in `get_available_balances_for_scope`.
There are no functional changes in this commit, as the
`extra_accepted_htlc_dust_exposure` member of `NextCommitmentStats` was
not used.
✓ Specific, descriptive subject✓ Names a concrete action or component✓ Provides detailed explanatory context
What changed, and why it matters
This commit is a pure code cleanup: it moves an existing dust-exposure calculation into a new helper function and removes an unused struct field. The commit message explicitly states there are no functional changes, and the diff confirms the logic is identical and the removed field was never used.
Recommended action
No action required; this is a non-functional refactor.
Security signals we found
No strong security signals were identified.
Evidence from the diff
The change refactors get_next_commitment_stats in lightning/src/sign/tx_builder.rs by extracting dust-exposure computation into a new get_dust_exposure_stats function. It also removes the extra_accepted_htlc_dust_exposure_msat field from NextCommitmentStats. The same arithmetic, control flow, and inputs are preserved; only code organization changed.
Changed components
lightning/src/sign/tx_builder.rsInspect captured patch +52 / −40
diff --git a/lightning/src/sign/tx_builder.rs b/lightning/src/sign/tx_builder.rs
index 6dae14b..cf06383 100644
--- a/lightning/src/sign/tx_builder.rs
+++ b/lightning/src/sign/tx_builder.rs
@@ -42,7 +42,6 @@ pub(crate) struct NextCommitmentStats {
pub nondust_htlc_count: usize,
pub commit_tx_fee_sat: u64,
pub dust_exposure_msat: u64,
- pub extra_accepted_htlc_dust_exposure_msat: u64,
}
pub(crate) struct ChannelStats {
@@ -184,6 +183,50 @@ pub(crate) struct ChannelConstraints {
pub counterparty_max_accepted_htlcs: u64,
}
+pub(crate) fn get_dust_exposure_stats(
+ local: bool, commitment_htlcs: &[HTLCAmountDirection], feerate_per_kw: u32,
+ dust_exposure_limiting_feerate: Option<u32>, broadcaster_dust_limit_satoshis: u64,
+ channel_type: &ChannelTypeFeatures,
+) -> (u64, Option<u64>) {
+ let excess_feerate =
+ feerate_per_kw.saturating_sub(dust_exposure_limiting_feerate.unwrap_or(feerate_per_kw));
+ if channel_type.supports_anchor_zero_fee_commitments() {
+ debug_assert_eq!(feerate_per_kw, 0);
+ debug_assert_eq!(excess_feerate, 0);
+ }
+
+ // Increment the feerate by a buffer to calculate dust exposure
+ let dust_buffer_feerate = get_dust_buffer_feerate(feerate_per_kw);
+
+ // Calculate dust exposure on commitment transaction
+ let dust_exposure_msat = commitment_htlcs
+ .iter()
+ .filter_map(|htlc| {
+ htlc.is_dust(local, dust_buffer_feerate, broadcaster_dust_limit_satoshis, channel_type)
+ .then_some(htlc.amount_msat)
+ })
+ .sum();
+
+ if local || excess_feerate == 0 {
+ (dust_exposure_msat, None)
+ } else {
+ // Add any excess fees to dust exposure on counterparty transactions
+ let (excess_fees_msat, extra_accepted_htlc_excess_fees_msat) =
+ commit_plus_htlc_tx_fees_msat(
+ local,
+ &commitment_htlcs,
+ dust_buffer_feerate,
+ excess_feerate,
+ broadcaster_dust_limit_satoshis,
+ channel_type,
+ );
+ (
+ dust_exposure_msat + excess_fees_msat,
+ Some(dust_exposure_msat + extra_accepted_htlc_excess_fees_msat),
+ )
+ }
+}
+
fn get_next_commitment_stats(
local: bool, is_outbound_from_holder: bool, channel_value_satoshis: u64,
value_to_holder_msat: u64, next_commitment_htlcs: &[HTLCAmountDirection],
@@ -191,11 +234,8 @@ fn get_next_commitment_stats(
dust_exposure_limiting_feerate: Option<u32>, broadcaster_dust_limit_satoshis: u64,
channel_type: &ChannelTypeFeatures,
) -> Result<NextCommitmentStats, ()> {
- let excess_feerate =
- feerate_per_kw.saturating_sub(dust_exposure_limiting_feerate.unwrap_or(feerate_per_kw));
if channel_type.supports_anchor_zero_fee_commitments() {
debug_assert_eq!(feerate_per_kw, 0);
- debug_assert_eq!(excess_feerate, 0);
}
// Calculate inbound htlc count
@@ -235,9 +275,6 @@ fn get_next_commitment_stats(
channel_type,
)?;
- // Increment the feerate by a buffer to calculate dust exposure
- let dust_buffer_feerate = get_dust_buffer_feerate(feerate_per_kw);
-
// Calculate fees on commitment transaction
let nondust_htlc_count = next_commitment_htlcs
.iter()
@@ -251,38 +288,14 @@ fn get_next_commitment_stats(
channel_type,
);
- // Calculate dust exposure on commitment transaction
- let dust_exposure_msat = next_commitment_htlcs
- .iter()
- .filter_map(|htlc| {
- htlc.is_dust(
- local,
- dust_buffer_feerate,
- broadcaster_dust_limit_satoshis,
- channel_type,
- )
- .then_some(htlc.amount_msat)
- })
- .sum();
-
- // Add any excess fees to dust exposure on counterparty transactions
- let (dust_exposure_msat, extra_accepted_htlc_dust_exposure_msat) = if local {
- (dust_exposure_msat, dust_exposure_msat)
- } else {
- let (excess_fees_msat, extra_accepted_htlc_excess_fees_msat) =
- commit_plus_htlc_tx_fees_msat(
- local,
- &next_commitment_htlcs,
- dust_buffer_feerate,
- excess_feerate,
- broadcaster_dust_limit_satoshis,
- channel_type,
- );
- (
- dust_exposure_msat + excess_fees_msat,
- dust_exposure_msat + extra_accepted_htlc_excess_fees_msat,
- )
- };
+ let (dust_exposure_msat, _extra_accepted_htlc_dust_exposure_msat) = get_dust_exposure_stats(
+ local,
+ next_commitment_htlcs,
+ feerate_per_kw,
+ dust_exposure_limiting_feerate,
+ broadcaster_dust_limit_satoshis,
+ channel_type,
+ );
Ok(NextCommitmentStats {
is_outbound_from_holder,
@@ -293,7 +306,6 @@ fn get_next_commitment_stats(
nondust_htlc_count: nondust_htlc_count + addl_nondust_htlc_count,
commit_tx_fee_sat,
dust_exposure_msat,
- extra_accepted_htlc_dust_exposure_msat,
})
}
Risk score
Our methodology →Why this scored 15/100
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