Merge #119

119: Remember the block-height before XMR lock for generated monero wallet r=da-kami a=da-kami

The first approach https://github.com/comit-network/xmr-btc-swap/pull/121 was using `get_transfer_by_txid` that allows extrancting the exact tx-lock 1st confirmation block height. 
But that introduced an additional error scenario, and I actually ran into that error scenario (`transaction not found`) once I ran it on `stagenet`. Might be that `get_transfer_by_txid` requires running the node in a specific way (like `txindex` on bitcoin).  
I am not sure at this stage and don't want to invest more time.

Long story short: 
I opted for just recording the height before watching for XMR locked. This means that we record a height right after sending the Bitcoin lock tx. (Because we start watching for XMR lock right after that.) 
Bob's new wallet unnecessarily scans an additional 7+ blocks (assuming inclusion in the next Bitcoin block and one confirmation for Monero lock) every time which is a matter of milliseconds. Not worth optimising this further at this stage. This solution is more resilient as well, because it does not add another error scenario.

Co-authored-by: Daniel Karzel <daniel@comit.network>

monero-harness/src/rpc/wallet.rs

@@ -186,7 +186,7 @@ impl Client {
     }
 
     /// Get wallet block height, this might be behind monerod height.
-    pub(crate) async fn block_height(&self) -> Result<BlockHeight> {
+    pub async fn block_height(&self) -> Result<BlockHeight> {
         let request = Request::new("get_height", "");
 
         let response = self
@@ -238,9 +238,16 @@ impl Client {
         address: &str,
         spend_key: &str,
         view_key: &str,
+        restore_height: Option<u32>,
     ) -> Result<GenerateFromKeys> {
+        let restore_height = if let Some(restore_height) = restore_height {
+            restore_height
+        } else {
+            0
+        };
+
         let params = GenerateFromKeysParams {
-            restore_height: 0,
+            restore_height,
             filename: view_key.into(),
             address: address.into(),
             spendkey: spend_key.into(),

swap/src/monero.rs

@@ -210,6 +210,7 @@ pub trait CreateWalletForOutput {
         &self,
         private_spend_key: PrivateKey,
         private_view_key: PrivateViewKey,
+        restore_height: Option<u32>,
     ) -> anyhow::Result<()>;
 }
 

swap/src/monero/wallet.rs

@@ -68,6 +68,7 @@ impl CreateWalletForOutput for Wallet {
         &self,
         private_spend_key: PrivateKey,
         private_view_key: PrivateViewKey,
+        restore_height: Option<u32>,
     ) -> Result<()> {
         let public_spend_key = PublicKey::from_private_key(&private_spend_key);
         let public_view_key = PublicKey::from_private_key(&private_view_key.into());
@@ -80,6 +81,7 @@ impl CreateWalletForOutput for Wallet {
                 &address.to_string(),
                 &private_spend_key.to_string(),
                 &PrivateKey::from(private_view_key).to_string(),
+                restore_height,
             )
             .await?;
 

swap/src/protocol/alice/state.rs

@@ -538,10 +538,11 @@ impl State5 {
 
         let s = s_b.scalar + self.s_a.into_ed25519();
 
+        // TODO: Optimized rescan height should be passed for refund as well.
         // NOTE: This actually generates and opens a new wallet, closing the currently
         // open one.
         monero_wallet
-            .create_and_load_wallet_for_output(monero::PrivateKey::from_scalar(s), self.v)
+            .create_and_load_wallet_for_output(monero::PrivateKey::from_scalar(s), self.v, None)
             .await?;
 
         Ok(())

swap/src/protocol/alice/swap.rs

@@ -405,7 +405,7 @@ pub async fn run_until(
                 let view_key = state3.v;
 
                 monero_wallet
-                    .create_and_load_wallet_for_output(spend_key, view_key)
+                    .create_and_load_wallet_for_output(spend_key, view_key, None)
                     .await?;
 
                 let state = AliceState::XmrRefunded;

swap/src/protocol/bob/state.rs

@@ -304,7 +304,12 @@ pub struct State3 {
 }
 
 impl State3 {
-    pub async fn watch_for_lock_xmr<W>(self, xmr_wallet: &W, msg: alice::Message2) -> Result<State4>
+    pub async fn watch_for_lock_xmr<W>(
+        self,
+        xmr_wallet: &W,
+        msg: alice::Message2,
+        monero_wallet_restore_blockheight: u32,
+    ) -> Result<State4>
     where
         W: monero::WatchForTransfer,
     {
@@ -340,6 +345,7 @@ impl State3 {
             tx_lock: self.tx_lock,
             tx_cancel_sig_a: self.tx_cancel_sig_a,
             tx_refund_encsig: self.tx_refund_encsig,
+            monero_wallet_restore_blockheight,
         })
     }
 
@@ -373,6 +379,7 @@ impl State3 {
             tx_lock: self.tx_lock.clone(),
             tx_cancel_sig_a: self.tx_cancel_sig_a.clone(),
             tx_refund_encsig: self.tx_refund_encsig.clone(),
+            monero_wallet_restore_blockheight: 0u32,
         }
     }
 
@@ -413,6 +420,7 @@ pub struct State4 {
     pub tx_lock: bitcoin::TxLock,
     pub tx_cancel_sig_a: Signature,
     pub tx_refund_encsig: EncryptedSignature,
+    pub monero_wallet_restore_blockheight: u32,
 }
 
 impl State4 {
@@ -509,6 +517,7 @@ impl State4 {
             tx_lock: self.tx_lock.clone(),
             tx_refund_encsig: self.tx_refund_encsig.clone(),
             tx_cancel_sig: self.tx_cancel_sig_a.clone(),
+            monero_wallet_restore_blockheight: self.monero_wallet_restore_blockheight,
         })
     }
 
@@ -606,6 +615,7 @@ pub struct State5 {
     pub tx_lock: bitcoin::TxLock,
     tx_refund_encsig: EncryptedSignature,
     tx_cancel_sig: Signature,
+    pub monero_wallet_restore_blockheight: u32,
 }
 
 impl State5 {
@@ -622,7 +632,11 @@ impl State5 {
         // NOTE: This actually generates and opens a new wallet, closing the currently
         // open one.
         monero_wallet
-            .create_and_load_wallet_for_output(s, self.v)
+            .create_and_load_wallet_for_output(
+                s,
+                self.v,
+                Some(self.monero_wallet_restore_blockheight),
+            )
             .await?;
 
         Ok(())

swap/src/protocol/bob/swap.rs

@@ -142,11 +142,19 @@ where
                     let cancel_timelock_expires =
                         state3.wait_for_cancel_timelock_to_expire(bitcoin_wallet.as_ref());
 
+                    // Record the current monero wallet block height so we don't have to scan from
+                    // block 0 once we create the redeem wallet.
+                    // TODO: This can be optimized further by extracting the block height when
+                    //  tx-lock was included. However, scanning a few more blocks won't do any harm
+                    //  and is simpler.
+                    let monero_wallet_restore_blockheight =
+                        monero_wallet.inner.block_height().await?;
+
                     select! {
                         msg2 = msg2_watcher => {
 
                             let xmr_lock_watcher = state3.clone()
-                                .watch_for_lock_xmr(monero_wallet.as_ref(), msg2?);
+                                .watch_for_lock_xmr(monero_wallet.as_ref(), msg2?, monero_wallet_restore_blockheight.height);
                             let cancel_timelock_expires = state3.wait_for_cancel_timelock_to_expire(bitcoin_wallet.as_ref());
 
                             select! {