From 1f40ee739d1d4bb0457817ac5a924ac2e4edddbe Mon Sep 17 00:00:00 2001
From: pokkst <pokkst@protonmail.com>
Date: Sat, 12 Aug 2023 22:20:54 -0500
Subject: [PATCH] fix (Bob): Check if Bitcoin redeem transaction was published
 before transitioning to CancelTimelockExpired

---
 swap/src/protocol/bob/state.rs | 24 ++++++++++++++++++++++++
 swap/src/protocol/bob/swap.rs  | 14 ++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/swap/src/protocol/bob/state.rs b/swap/src/protocol/bob/state.rs
index aa0045ea..4e042a20 100644
--- a/swap/src/protocol/bob/state.rs
+++ b/swap/src/protocol/bob/state.rs
@@ -489,6 +489,30 @@ pub struct State4 {
 }
 
 impl State4 {
+    pub async fn check_for_tx_redeem(
+        &self,
+        bitcoin_wallet: &bitcoin::Wallet,
+    ) -> Result<State5> {
+        let tx_redeem =
+            bitcoin::TxRedeem::new(&self.tx_lock, &self.redeem_address, self.tx_redeem_fee);
+        let tx_redeem_encsig = self.b.encsign(self.S_a_bitcoin, tx_redeem.digest());
+
+        let tx_redeem_candidate = bitcoin_wallet.get_raw_transaction(tx_redeem.txid()).await?;
+
+        let tx_redeem_sig =
+            tx_redeem.extract_signature_by_key(tx_redeem_candidate, self.b.public())?;
+        let s_a = bitcoin::recover(self.S_a_bitcoin, tx_redeem_sig, tx_redeem_encsig)?;
+        let s_a = monero::private_key_from_secp256k1_scalar(s_a.into());
+
+        Ok(State5 {
+            s_a,
+            s_b: self.s_b,
+            v: self.v,
+            tx_lock: self.tx_lock.clone(),
+            monero_wallet_restore_blockheight: self.monero_wallet_restore_blockheight,
+        })
+    }
+
     pub fn tx_redeem_encsig(&self) -> bitcoin::EncryptedSignature {
         let tx_redeem =
             bitcoin::TxRedeem::new(&self.tx_lock, &self.redeem_address, self.tx_redeem_fee);
diff --git a/swap/src/protocol/bob/swap.rs b/swap/src/protocol/bob/swap.rs
index 37a6b65a..8eaa1489 100644
--- a/swap/src/protocol/bob/swap.rs
+++ b/swap/src/protocol/bob/swap.rs
@@ -183,6 +183,13 @@ async fn next_state(
             }
         }
         BobState::XmrLocked(state) => {
+            // In case we send the encrypted signature to Alice, but she doesn't give us a confirmation
+            // We need to check if she still published the Bitcoin redeem transaction
+            // Otherwise we risk staying stuck in "XmrLocked"
+            if let Ok(state5) = state.check_for_tx_redeem(bitcoin_wallet).await {
+                return Ok(BobState::BtcRedeemed(state5));
+            }
+
             let tx_lock_status = bitcoin_wallet.subscribe_to(state.tx_lock.clone()).await;
 
             if let ExpiredTimelocks::None { .. } = state.expired_timelock(bitcoin_wallet).await? {
@@ -207,6 +214,13 @@ async fn next_state(
             }
         }
         BobState::EncSigSent(state) => {
+            // We need to make sure that Alice did not publish the redeem transaction while we were offline
+            // Even if the cancel timelock expired, if Alice published the redeem transaction while we were away we cannot miss it
+            // If we do we cannot refund and will never be able to leave the "CancelTimelockExpired" state
+            if let Ok(state5) = state.check_for_tx_redeem(bitcoin_wallet).await {
+                return Ok(BobState::BtcRedeemed(state5));
+            }
+
             let tx_lock_status = bitcoin_wallet.subscribe_to(state.tx_lock.clone()).await;
 
             if let ExpiredTimelocks::None { .. } = state.expired_timelock(bitcoin_wallet).await? {