chore: remove segwit_add in favor of TXIN_BASE_WEIGHT

Author: storopoli

crates/bdk/src/wallet/coin_selection.rs

@@ -32,7 +32,6 @@
 //! # use bdk::*;
 //! # use bdk::wallet::coin_selection::decide_change;
 //! # use anyhow::Error;
-//! # const TXIN_BASE_WEIGHT: usize = (32 + 4 + 4) * 4;
 //! #[derive(Debug)]
 //! struct AlwaysSpendEverything;
 //!
@@ -55,7 +54,8 @@
 //!                 |(selected_amount, additional_weight), weighted_utxo| {
 //!                     **selected_amount += weighted_utxo.utxo.txout().value;
 //!                     **additional_weight += Weight::from_wu(
-//!                         (TXIN_BASE_WEIGHT + weighted_utxo.satisfaction_weight) as u64,
+//!                         (TxIn::default().segwit_weight() + weighted_utxo.satisfaction_weight)
+//!                             as u64,
 //!                     );
 //!                     Some(weighted_utxo.utxo)
 //!                 },
@@ -109,6 +109,7 @@ use crate::WeightedUtxo;
 use alloc::vec::Vec;
 use bitcoin::consensus::encode::serialize;
 use bitcoin::OutPoint;
+use bitcoin::TxIn;
 use bitcoin::{Script, Weight};
 
 use core::convert::TryInto;
@@ -119,10 +120,6 @@ use rand::seq::SliceRandom;
 /// overridden
 pub type DefaultCoinSelectionAlgorithm = BranchAndBoundCoinSelection;
 
-// Base weight of a Txin, not counting the weight needed for satisfying it.
-// prev_txid (32 bytes) + prev_vout (4 bytes) + sequence (4 bytes)
-pub(crate) const TXIN_BASE_WEIGHT: usize = (32 + 4 + 4) * 4;
-
 /// Errors that can be thrown by the [`coin_selection`](crate::wallet::coin_selection) module
 #[derive(Debug)]
 pub enum Error {
@@ -345,7 +342,8 @@ fn select_sorted_utxos(
             |(selected_amount, fee_amount), (must_use, weighted_utxo)| {
                 if must_use || **selected_amount < target_amount + **fee_amount {
                     **fee_amount += fee_rate.fee_wu(Weight::from_wu(
-                        (TXIN_BASE_WEIGHT + weighted_utxo.satisfaction_weight) as u64,
+                        (TxIn::default().segwit_weight() + weighted_utxo.satisfaction_weight)
+                            as u64,
                     ));
                     **selected_amount += weighted_utxo.utxo.txout().value;
                     Some(weighted_utxo.utxo)
@@ -388,7 +386,7 @@ struct OutputGroup {
 impl OutputGroup {
     fn new(weighted_utxo: WeightedUtxo, fee_rate: FeeRate) -> Self {
         let fee = fee_rate.fee_wu(Weight::from_wu(
-            (TXIN_BASE_WEIGHT + weighted_utxo.satisfaction_weight) as u64,
+            (TxIn::default().segwit_weight() + weighted_utxo.satisfaction_weight) as u64,
         ));
         let effective_value = weighted_utxo.utxo.txout().value as i64 - fee as i64;
         OutputGroup {
@@ -738,7 +736,7 @@ mod test {
     use core::str::FromStr;
 
     use bdk_chain::ConfirmationTime;
-    use bitcoin::{OutPoint, ScriptBuf, TxOut};
+    use bitcoin::{OutPoint, ScriptBuf, TxIn, TxOut};
 
     use super::*;
     use crate::types::*;
@@ -749,9 +747,9 @@ mod test {
     use rand::seq::SliceRandom;
     use rand::{Rng, RngCore, SeedableRng};
 
-    // n. of items on witness (1WU) + signature len (1WU) + signature and sighash (72WU)
-    // + pubkey len (1WU) + pubkey (33WU) + script sig len (1 byte, 4WU)
-    const P2WPKH_SATISFACTION_SIZE: usize = 1 + 1 + 72 + 1 + 33 + 4;
+    // n. of items on witness (1WU) signature and sighash (72WU)
+    // + pubkey len (1WU) + pubkey (33WU)
+    const P2WPKH_SATISFACTION_SIZE: usize = 1 + 72 + 1 + 33;
 
     const FEE_AMOUNT: u64 = 50;
 
@@ -1240,7 +1238,7 @@ 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::default().segwit_weight() + P2WPKH_SATISFACTION_SIZE).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);
     }

crates/bdk/src/wallet/mod.rs

@@ -1714,17 +1714,10 @@ impl<D> Wallet<D> {
 
                 let weighted_utxo = match txout_index.index_of_spk(&txout.script_pubkey) {
                     Some((keychain, derivation_index)) => {
-                        let is_segwit = self.get_descriptor_for_keychain(keychain).is_witness()
-                            || self.get_descriptor_for_keychain(keychain).is_taproot();
-                        let segwit_add = match is_segwit {
-                            true => 4,
-                            false => 0,
-                        };
                         let satisfaction_weight = self
                             .get_descriptor_for_keychain(keychain)
                             .max_weight_to_satisfy()
-                            .unwrap()
-                            + segwit_add;
+                            .unwrap();
                         WeightedUtxo {
                             utxo: Utxo::Local(LocalOutput {
                                 outpoint: txin.previous_output,
@@ -2051,16 +2044,9 @@ impl<D> Wallet<D> {
             .map(|utxo| {
                 let keychain = utxo.keychain;
                 (utxo, {
-                    let is_segwit = self.get_descriptor_for_keychain(keychain).is_witness()
-                        || self.get_descriptor_for_keychain(keychain).is_taproot();
-                    let segwit_add = match is_segwit {
-                        true => 4,
-                        false => 0,
-                    };
                     self.get_descriptor_for_keychain(keychain)
                         .max_weight_to_satisfy()
                         .unwrap()
-                        + segwit_add
                 })
             })
             .collect()