From 2e0b88ba76ebb5543c49d4184badaa1fe46fff39 Mon Sep 17 00:00:00 2001
From: "Tobin C. Harding" <me@tobin.cc>
Date: Wed, 21 May 2025 11:09:06 +1000
Subject: [PATCH] bitcoin: Fix dust 'fee' identifiers

Currently we get the fee_rate per kwu then multiply it by 4. Instead
lets add a per_kvb function to `FeeRate`. We are about to change the
internal representation of `FeeRate` to use MvB so for now just panic on
ovelflow.

Also these are fee _rates_ - we already have suboptimal names from Core
in the consts in `policy`, no need to let them infect other identifiers.
---
 bitcoin/src/blockdata/script/borrowed.rs | 8 ++++----
 units/src/fee_rate/mod.rs                | 3 +++
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/bitcoin/src/blockdata/script/borrowed.rs b/bitcoin/src/blockdata/script/borrowed.rs
index 41a89e4a7..97c294b33 100644
--- a/bitcoin/src/blockdata/script/borrowed.rs
+++ b/bitcoin/src/blockdata/script/borrowed.rs
@@ -289,8 +289,8 @@ crate::internal_macros::define_extension_trait! {
         /// To use the default Bitcoin Core value, use [`minimal_non_dust`].
         ///
         /// [`minimal_non_dust`]: Script::minimal_non_dust
-        fn minimal_non_dust_custom(&self, dust_relay_fee: FeeRate) -> Option<Amount> {
-            self.minimal_non_dust_internal(dust_relay_fee.to_sat_per_kwu_ceil() * 4)
+        fn minimal_non_dust_custom(&self, dust_relay: FeeRate) -> Option<Amount> {
+            self.minimal_non_dust_internal(dust_relay.to_sat_per_kvb())
         }
 
         /// Counts the sigops for this Script using accurate counting.
@@ -407,10 +407,10 @@ mod sealed {
 
 crate::internal_macros::define_extension_trait! {
     pub(crate) trait ScriptExtPriv impl for Script {
-        fn minimal_non_dust_internal(&self, dust_relay_fee: u64) -> Option<Amount> {
+        fn minimal_non_dust_internal(&self, dust_relay_fee_rate_per_kvb: u64) -> Option<Amount> {
             // This must never be lower than Bitcoin Core's GetDustThreshold() (as of v0.21) as it may
             // otherwise allow users to create transactions which likely can never be broadcast/confirmed.
-            let sats = dust_relay_fee
+            let sats = dust_relay_fee_rate_per_kvb
                 .checked_mul(if self.is_op_return() {
                     0
                 } else if self.is_witness_program() {
diff --git a/units/src/fee_rate/mod.rs b/units/src/fee_rate/mod.rs
index 84e8d9f86..f2f73e162 100644
--- a/units/src/fee_rate/mod.rs
+++ b/units/src/fee_rate/mod.rs
@@ -78,6 +78,9 @@ impl FeeRate {
         (self.to_sat_per_kwu_floor() + (1000 / 4 - 1)) / (1000 / 4)
     }
 
+    /// Converts to sat/kvb.
+    pub const fn to_sat_per_kvb(self) -> u64 { self.to_sat_per_kwu_floor() * 4 }
+
     /// Checked multiplication.
     ///
     /// Computes `self * rhs` returning [`None`] if overflow occurred.