FeeRate calculation fixes

src/testutils/blockchain_tests.rs

@@ -1021,7 +1021,7 @@ macro_rules! bdk_blockchain_tests {
                 assert_eq!(details.received, 1_000 - details.fee.unwrap_or(0), "incorrect received after send");
 
                 let mut builder = wallet.build_fee_bump(details.txid).unwrap();
-                builder.fee_rate(FeeRate::from_sat_per_vb(123.0));
+                builder.fee_rate(FeeRate::from_sat_per_vb(124.0));
                 let (mut new_psbt, new_details) = builder.finish().unwrap();
                 println!("{:#?}", new_details);
 

src/types.rs

@@ -98,13 +98,15 @@ impl FeeRate {
 
     /// Calculate fee rate from `fee` and weight units (`wu`).
     pub fn from_wu(fee: u64, wu: usize) -> FeeRate {
-        Self::from_vb(fee, wu.vbytes())
+        let vbytes = wu as f32 / 4.0;
+        let rate = fee as f32 / vbytes;
+        Self::new_checked(rate)
     }
 
     /// Calculate fee rate from `fee` and `vbytes`.
-    pub fn from_vb(fee: u64, vbytes: usize) -> FeeRate {
-        let rate = fee as f32 / vbytes as f32;
-        Self::from_sat_per_vb(rate)
+    pub fn from_vb(fee: u64, vbytes: f32) -> FeeRate {
+        let rate = fee as f32 / vbytes;
+        Self::new_checked(rate)
     }
 
     /// Return the value as satoshi/vbyte
@@ -114,12 +116,13 @@ impl FeeRate {
 
     /// Calculate absolute fee in Satoshis using size in weight units.
     pub fn fee_wu(&self, wu: usize) -> u64 {
-        self.fee_vb(wu.vbytes())
+        let vbytes = wu as f32 / 4.0;
+        (self.0 * vbytes).ceil() as u64
     }
 
     /// Calculate absolute fee in Satoshis using size in virtual bytes.
-    pub fn fee_vb(&self, vbytes: usize) -> u64 {
-        (self.as_sat_per_vb() * vbytes as f32).ceil() as u64
+    pub fn fee_vb(&self, vbytes: f32) -> u64 {
+        (self.0 * vbytes).ceil() as u64
     }
 }
 
@@ -138,15 +141,15 @@ impl Sub for FeeRate {
 }
 
 /// Trait implemented by types that can be used to measure weight units.
-pub trait Vbytes {
+pub trait WeightUnits {
     /// Convert weight units to virtual bytes.
-    fn vbytes(self) -> usize;
+    fn to_vbytes(self) -> f32;
 }
 
-impl Vbytes for usize {
-    fn vbytes(self) -> usize {
+impl WeightUnits for usize {
+    fn to_vbytes(self) -> f32 {
         // ref: https://github.com/bitcoin/bips/blob/master/bip-0141.mediawiki#transaction-size-calculations
-        (self as f32 / 4.0).ceil() as usize
+        self as f32 / 4.0
     }
 }
 

src/wallet/coin_selection.rs

@@ -304,9 +304,8 @@ impl<D: Database> CoinSelectionAlgorithm<D> for OldestFirstCoinSelection {
 /// - `fee_rate`: required fee rate for the current selection
 /// - `drain_script`: script to consider change creation
 pub fn decide_change(remaining_amount: u64, fee_rate: FeeRate, drain_script: &Script) -> Excess {
-    // drain_output_len = size(len(script_pubkey)) + len(script_pubkey) + size(output_value)
-    let drain_output_len = serialize(drain_script).len() + 8usize;
-    let change_fee = fee_rate.fee_vb(drain_output_len);
+    let drain_output_len = serialize(drain_script).len() + 8_usize;
+    let change_fee = fee_rate.fee_vb(drain_output_len as f32);
     let drain_val = remaining_amount.saturating_sub(change_fee);
 
     if drain_val.is_dust(drain_script) {
@@ -728,7 +727,7 @@ mod test {
     use super::*;
     use crate::database::{BatchOperations, MemoryDatabase};
     use crate::types::*;
-    use crate::wallet::Vbytes;
+    use crate::wallet::WeightUnits;
 
     use rand::rngs::StdRng;
     use rand::seq::SliceRandom;
@@ -1319,7 +1318,7 @@ mod test {
 
         assert_eq!(result.selected.len(), 1);
         assert_eq!(result.selected_amount(), 100_000);
-        let input_size = (TXIN_BASE_WEIGHT + P2WPKH_SATISFACTION_SIZE).vbytes();
+        let input_size = (TXIN_BASE_WEIGHT + P2WPKH_SATISFACTION_SIZE).to_vbytes();
         // the final fee rate should be exactly the same as the fee rate given
         assert!((1.0 - (result.fee_amount as f32 / input_size as f32)).abs() < f32::EPSILON);
     }

src/wallet/mod.rs

@@ -2649,7 +2649,7 @@ pub(crate) mod test {
         builder
             .drain_to(addr.script_pubkey())
             .drain_wallet()
-            .fee_rate(FeeRate::from_sat_per_vb(453.0));
+            .fee_rate(FeeRate::from_sat_per_vb(455.0));
         builder.finish().unwrap();
     }