Move `extract_monero_private_key` onto TxRefund

This functionality is domain-specific to the refund transaction.
Move it onto there.

swap/src/bitcoin/refund.rs

@@ -3,10 +3,10 @@ use crate::bitcoin::{
     verify_sig, Address, EmptyWitnessStack, NoInputs, NotThreeWitnesses, PublicKey, TooManyInputs,
     Transaction, TxCancel,
 };
+use crate::{bitcoin, monero};
 use ::bitcoin::util::bip143::SigHashCache;
-use ::bitcoin::{SigHash, SigHashType, Txid};
+use ::bitcoin::{Script, SigHash, SigHashType, Txid};
 use anyhow::{bail, Context, Result};
-use bitcoin::Script;
 use ecdsa_fun::Signature;
 use miniscript::{Descriptor, DescriptorTrait};
 use std::collections::HashMap;
@@ -77,7 +77,31 @@ impl TxRefund {
         Ok(tx_refund)
     }
 
-    pub fn extract_signature_by_key(
+    pub fn extract_monero_private_key(
+        &self,
+        published_refund_tx: bitcoin::Transaction,
+        s_a: monero::Scalar,
+        a: bitcoin::SecretKey,
+        S_b_bitcoin: bitcoin::PublicKey,
+    ) -> Result<monero::PrivateKey> {
+        let s_a = monero::PrivateKey { scalar: s_a };
+
+        let tx_refund_sig = self
+            .extract_signature_by_key(published_refund_tx, a.public())
+            .context("Failed to extract signature from Bitcoin refund tx")?;
+        let tx_refund_encsig = a.encsign(S_b_bitcoin, self.digest());
+
+        let s_b = bitcoin::recover(S_b_bitcoin, tx_refund_sig, tx_refund_encsig)
+            .context("Failed to recover Monero secret key from Bitcoin signature")?;
+
+        let s_b = monero::private_key_from_secp256k1_scalar(s_b.into());
+
+        let spend_key = s_a + s_b;
+
+        Ok(spend_key)
+    }
+
+    fn extract_signature_by_key(
         &self,
         candidate_transaction: Transaction,
         B: PublicKey,

swap/src/protocol/alice/steps.rs

@@ -2,7 +2,7 @@ use crate::bitcoin::{CancelTimelock, PunishTimelock, TxCancel, TxLock, TxRefund}
 use crate::protocol::alice;
 use crate::protocol::alice::event_loop::EventLoopHandle;
 use crate::{bitcoin, monero};
-use anyhow::{bail, Context, Result};
+use anyhow::{bail, Result};
 
 pub async fn lock_xmr(
     state3: alice::State3,
@@ -102,26 +102,3 @@ pub async fn wait_for_bitcoin_refund(
         }
     }
 }
-
-pub fn extract_monero_private_key(
-    published_refund_tx: bitcoin::Transaction,
-    tx_refund: &TxRefund,
-    s_a: monero::Scalar,
-    a: bitcoin::SecretKey,
-    S_b_bitcoin: bitcoin::PublicKey,
-) -> Result<monero::PrivateKey> {
-    let s_a = monero::PrivateKey { scalar: s_a };
-
-    let tx_refund_sig = tx_refund
-        .extract_signature_by_key(published_refund_tx, a.public())
-        .context("Failed to extract signature from Bitcoin refund tx")?;
-    let tx_refund_encsig = a.encsign(S_b_bitcoin, tx_refund.digest());
-
-    let s_b = bitcoin::recover(S_b_bitcoin, tx_refund_sig, tx_refund_encsig)
-        .context("Failed to recover Monero secret key from Bitcoin signature")?;
-    let s_b = monero::private_key_from_secp256k1_scalar(s_b.into());
-
-    let spend_key = s_a + s_b;
-
-    Ok(spend_key)
-}

swap/src/protocol/alice/swap.rs

@@ -7,7 +7,7 @@ use crate::monero_ext::ScalarExt;
 use crate::protocol::alice;
 use crate::protocol::alice::event_loop::EventLoopHandle;
 use crate::protocol::alice::steps::{
-    extract_monero_private_key, lock_xmr, publish_cancel_transaction, wait_for_bitcoin_refund,
+    lock_xmr, publish_cancel_transaction, wait_for_bitcoin_refund,
 };
 use crate::protocol::alice::AliceState;
 use crate::{bitcoin, database, monero};
@@ -315,9 +315,8 @@ async fn run_until_internal(
                         .await
                     }
                     Some(published_refund_tx) => {
-                        let spend_key = extract_monero_private_key(
+                        let spend_key = state3.tx_refund().extract_monero_private_key(
                             published_refund_tx,
-                            &state3.tx_refund(),
                             state3.s_a,
                             state3.a.clone(),
                             state3.S_b_bitcoin,
@@ -393,9 +392,8 @@ async fn run_until_internal(
                         let published_refund_tx =
                             bitcoin_wallet.get_raw_transaction(tx_refund.txid()).await?;
 
-                        let spend_key = extract_monero_private_key(
+                        let spend_key = tx_refund.extract_monero_private_key(
                             published_refund_tx,
-                            &tx_refund,
                             state3.s_a,
                             state3.a.clone(),
                             state3.S_b_bitcoin,