Add a mandatory `--change-address` parameter to `buy-xmr`

Fixes #513.

CHANGELOG.md

@@ -19,6 +19,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   The rendezvous node address (`rendezvous_point`), as well as the ASB's external addresses (`external_addresses`) to be registered, is configured in the `network` section of the ASB config file.
   A rendezvous node is provided at `/dnsaddr/rendezvous.coblox.tech/p2p/12D3KooWQUt9DkNZxEn2R5ymJzWj15MpG6mTW84kyd8vDaRZi46o` which is used as default for discovery in the CLI.
   Upon discovery using `list-sellers` CLI users are provided with quote and connection information for each ASB discovered through the rendezvous node.
+- A mandatory `--change-address` parameter to the CLI's `buy-xmr` command.
+  The provided address is used to transfer Bitcoin in case of a refund and in case the user transfers more than the specified amount into the swap.
+  For more information see [#513](https://github.com/comit-network/xmr-btc-swap/issues/513).
 
 ### Fixed
 

swap/Cargo.toml

@@ -45,7 +45,7 @@ rust_decimal_macros = "1"
 serde = { version = "1", features = [ "derive" ] }
 serde_cbor = "0.11"
 serde_json = "1"
-serde_with = { version = "1.9.4", features = [ "macros" ] }
+serde_with = { version = "1", features = [ "macros" ] }
 sha2 = "0.9"
 sigma_fun = { git = "https://github.com/LLFourn/secp256kfun", default-features = false, features = [ "ed25519", "serde" ] }
 sled = "0.34"

swap/src/bin/asb.rs

@@ -231,7 +231,9 @@ async fn main() -> Result<()> {
                 }
             };
 
-            let psbt = bitcoin_wallet.send_to_address(address, amount).await?;
+            let psbt = bitcoin_wallet
+                .send_to_address(address, amount, None)
+                .await?;
             let signed_tx = bitcoin_wallet.sign_and_finalize(psbt).await?;
 
             bitcoin_wallet.broadcast(signed_tx, "withdraw").await?;

swap/src/bin/swap.rs

@@ -59,6 +59,7 @@ async fn main() -> Result<()> {
             seller,
             bitcoin_electrum_rpc_url,
             bitcoin_target_block,
+            bitcoin_change_address,
             monero_receive_address,
             monero_daemon_address,
             tor_socks5_port,
@@ -122,6 +123,7 @@ async fn main() -> Result<()> {
                 env_config,
                 event_loop_handle,
                 monero_receive_address,
+                bitcoin_change_address,
                 amount,
             );
 

swap/src/bitcoin/lock.rs

@@ -24,6 +24,7 @@ impl TxLock {
         amount: Amount,
         A: PublicKey,
         B: PublicKey,
+        change: bitcoin::Address,
     ) -> Result<Self>
     where
         C: EstimateFeeRate,
@@ -34,7 +35,9 @@ impl TxLock {
             .address(wallet.get_network())
             .expect("can derive address from descriptor");
 
-        let psbt = wallet.send_to_address(address, amount).await?;
+        let psbt = wallet
+            .send_to_address(address, amount, Some(change))
+            .await?;
 
         Ok(Self {
             inner: psbt,
@@ -251,7 +254,11 @@ mod tests {
         wallet: &Wallet<(), bdk::database::MemoryDatabase, StaticFeeRate>,
         amount: Amount,
     ) -> PartiallySignedTransaction {
-        TxLock::new(&wallet, amount, A, B).await.unwrap().into()
+        let change = wallet.new_address().await.unwrap();
+        TxLock::new(&wallet, amount, A, B, change)
+            .await
+            .unwrap()
+            .into()
     }
 
     fn alice_and_bob() -> (PublicKey, PublicKey) {

swap/src/bitcoin/wallet.rs

@@ -309,11 +309,18 @@ where
         &self,
         address: Address,
         amount: Amount,
+        change_override: Option<Address>,
     ) -> Result<PartiallySignedTransaction> {
         if self.network != address.network {
             bail!("Cannot build PSBT because network of given address is {} but wallet is on network {}", address.network, self.network);
         }
 
+        if let Some(change) = change_override.as_ref() {
+            if self.network != change.network {
+                bail!("Cannot build PSBT because network of given address is {} but wallet is on network {}", change.network, self.network);
+            }
+        }
+
         let wallet = self.wallet.lock().await;
         let client = self.client.lock().await;
         let fee_rate = client.estimate_feerate(self.target_block)?;
@@ -340,6 +347,15 @@ where
             _ => bail!("Unexpected transaction layout"),
         }
 
+        if let ([_, change], [_, psbt_output], Some(change_override)) = (
+            &mut psbt.global.unsigned_tx.output.as_mut_slice(),
+            &mut psbt.outputs.as_mut_slice(),
+            change_override,
+        ) {
+            change.script_pubkey = change_override.script_pubkey();
+            psbt_output.bip32_derivation.clear();
+        }
+
         Ok(psbt)
     }
 
@@ -1059,7 +1075,8 @@ mod tests {
         // if the change output is below dust it will be dropped by the BDK
         for amount in above_dust..(balance - (above_dust - 1)) {
             let (A, B) = (PublicKey::random(), PublicKey::random());
-            let txlock = TxLock::new(&wallet, bitcoin::Amount::from_sat(amount), A, B)
+            let change = wallet.new_address().await.unwrap();
+            let txlock = TxLock::new(&wallet, bitcoin::Amount::from_sat(amount), A, B, change)
                 .await
                 .unwrap();
             let txlock_output = txlock.script_pubkey();
@@ -1074,4 +1091,30 @@ mod tests {
             );
         }
     }
+
+    #[tokio::test]
+    async fn can_override_change_address() {
+        let wallet = Wallet::new_funded_default_fees(50_000);
+        let custom_change = "bcrt1q08pfqpsyrt7acllzyjm8q5qsz5capvyahm49rw"
+            .parse::<Address>()
+            .unwrap();
+
+        let psbt = wallet
+            .send_to_address(
+                wallet.new_address().await.unwrap(),
+                Amount::from_sat(10_000),
+                Some(custom_change.clone()),
+            )
+            .await
+            .unwrap();
+        let transaction = wallet.sign_and_finalize(psbt).await.unwrap();
+
+        match transaction.output.as_slice() {
+            [first, change] => {
+                assert_eq!(first.value, 10_000);
+                assert_eq!(change.script_pubkey, custom_change.script_pubkey());
+            }
+            _ => panic!("expected exactly two outputs"),
+        }
+    }
 }

swap/src/cli/command.rs

@@ -74,6 +74,7 @@ where
                     bitcoin_electrum_rpc_url,
                     bitcoin_target_block,
                 },
+            bitcoin_change_address,
             monero:
                 Monero {
                     monero_receive_address,
@@ -92,6 +93,7 @@ where
                     is_testnet,
                 )?,
                 bitcoin_target_block: bitcoin_target_block_from(bitcoin_target_block, is_testnet),
+                bitcoin_change_address,
                 monero_receive_address: validate_monero_address(
                     monero_receive_address,
                     is_testnet,
@@ -214,6 +216,7 @@ pub enum Command {
         seller: Multiaddr,
         bitcoin_electrum_rpc_url: Url,
         bitcoin_target_block: usize,
+        bitcoin_change_address: bitcoin::Address,
         monero_receive_address: monero::Address,
         monero_daemon_address: String,
         tor_socks5_port: u16,
@@ -287,6 +290,12 @@ pub enum RawCommand {
         #[structopt(flatten)]
         bitcoin: Bitcoin,
 
+        #[structopt(
+            long = "change-address",
+            help = "The bitcoin address where any form of change or excess funds should be sent to"
+        )]
+        bitcoin_change_address: bitcoin::Address,
+
         #[structopt(flatten)]
         monero: Monero,
 
@@ -347,7 +356,7 @@ pub enum RawCommand {
 #[derive(structopt::StructOpt, Debug)]
 pub struct Monero {
     #[structopt(long = "receive-address",
-        help = "Provide the monero address where you would like to receive monero",
+        help = "The monero address where you would like to receive monero",
         parse(try_from_str = parse_monero_address)
     )]
     pub monero_receive_address: monero::Address,
@@ -520,7 +529,9 @@ mod tests {
     const MAINNET: &str = "mainnet";
 
     const MONERO_STAGENET_ADDRESS: &str = "53gEuGZUhP9JMEBZoGaFNzhwEgiG7hwQdMCqFxiyiTeFPmkbt1mAoNybEUvYBKHcnrSgxnVWgZsTvRBaHBNXPa8tHiCU51a";
+    const BITCOIN_TESTNET_ADDRESS: &str = "tb1qr3em6k3gfnyl8r7q0v7t4tlnyxzgxma3lressv";
     const MONERO_MAINNET_ADDRESS: &str = "44Ato7HveWidJYUAVw5QffEcEtSH1DwzSP3FPPkHxNAS4LX9CqgucphTisH978FLHE34YNEx7FcbBfQLQUU8m3NUC4VqsRa";
+    const BITCOIN_MAINNET_ADDRESS: &str = "bc1qe4epnfklcaa0mun26yz5g8k24em5u9f92hy325";
     const MULTI_ADDRESS: &str =
         "/ip4/127.0.0.1/tcp/9939/p2p/12D3KooWCdMKjesXMJz1SiZ7HgotrxuqhQJbP5sgBm2BwP1cqThi";
     const SWAP_ID: &str = "ea030832-3be9-454f-bb98-5ea9a788406b";
@@ -532,6 +543,8 @@ mod tests {
             "buy-xmr",
             "--receive-address",
             MONERO_MAINNET_ADDRESS,
+            "--change-address",
+            BITCOIN_MAINNET_ADDRESS,
             "--seller",
             MULTI_ADDRESS,
         ];
@@ -550,6 +563,8 @@ mod tests {
             "buy-xmr",
             "--receive-address",
             MONERO_STAGENET_ADDRESS,
+            "--change-address",
+            BITCOIN_TESTNET_ADDRESS,
             "--seller",
             MULTI_ADDRESS,
         ];
@@ -569,6 +584,8 @@ mod tests {
             "buy-xmr",
             "--receive-address",
             MONERO_STAGENET_ADDRESS,
+            "--change-address",
+            BITCOIN_TESTNET_ADDRESS,
             "--seller",
             MULTI_ADDRESS,
         ];
@@ -592,6 +609,8 @@ mod tests {
             "buy-xmr",
             "--receive-address",
             MONERO_MAINNET_ADDRESS,
+            "--change-address",
+            BITCOIN_MAINNET_ADDRESS,
             "--seller",
             MULTI_ADDRESS,
         ];
@@ -703,6 +722,8 @@ mod tests {
             "--data-dir",
             data_dir,
             "buy-xmr",
+            "--change-address",
+            BITCOIN_MAINNET_ADDRESS,
             "--receive-address",
             MONERO_MAINNET_ADDRESS,
             "--seller",
@@ -725,6 +746,8 @@ mod tests {
             "--data-dir",
             data_dir,
             "buy-xmr",
+            "--change-address",
+            BITCOIN_TESTNET_ADDRESS,
             "--receive-address",
             MONERO_STAGENET_ADDRESS,
             "--seller",
@@ -791,6 +814,8 @@ mod tests {
             BINARY_NAME,
             "--debug",
             "buy-xmr",
+            "--change-address",
+            BITCOIN_MAINNET_ADDRESS,
             "--receive-address",
             MONERO_MAINNET_ADDRESS,
             "--seller",
@@ -808,6 +833,8 @@ mod tests {
             "--testnet",
             "--debug",
             "buy-xmr",
+            "--change-address",
+            BITCOIN_TESTNET_ADDRESS,
             "--receive-address",
             MONERO_STAGENET_ADDRESS,
             "--seller",
@@ -860,6 +887,8 @@ mod tests {
             BINARY_NAME,
             "--json",
             "buy-xmr",
+            "--change-address",
+            BITCOIN_MAINNET_ADDRESS,
             "--receive-address",
             MONERO_MAINNET_ADDRESS,
             "--seller",
@@ -877,6 +906,8 @@ mod tests {
             "--testnet",
             "--json",
             "buy-xmr",
+            "--change-address",
+            BITCOIN_TESTNET_ADDRESS,
             "--receive-address",
             MONERO_STAGENET_ADDRESS,
             "--seller",
@@ -935,6 +966,7 @@ mod tests {
                     bitcoin_electrum_rpc_url: Url::from_str(DEFAULT_ELECTRUM_RPC_URL_TESTNET)
                         .unwrap(),
                     bitcoin_target_block: DEFAULT_BITCOIN_CONFIRMATION_TARGET_TESTNET,
+                    bitcoin_change_address: BITCOIN_TESTNET_ADDRESS.parse().unwrap(),
                     monero_receive_address: monero::Address::from_str(MONERO_STAGENET_ADDRESS)
                         .unwrap(),
                     monero_daemon_address: DEFAULT_MONERO_DAEMON_ADDRESS_STAGENET.to_string(),
@@ -953,6 +985,7 @@ mod tests {
                     seller: Multiaddr::from_str(MULTI_ADDRESS).unwrap(),
                     bitcoin_electrum_rpc_url: Url::from_str(DEFAULT_ELECTRUM_RPC_URL).unwrap(),
                     bitcoin_target_block: DEFAULT_BITCOIN_CONFIRMATION_TARGET,
+                    bitcoin_change_address: BITCOIN_MAINNET_ADDRESS.parse().unwrap(),
                     monero_receive_address: monero::Address::from_str(MONERO_MAINNET_ADDRESS)
                         .unwrap(),
                     monero_daemon_address: DEFAULT_MONERO_DAEMON_ADDRESS.to_string(),

swap/src/database/bob.rs

@@ -3,13 +3,17 @@ use crate::protocol::bob;
 use crate::protocol::bob::BobState;
 use monero_rpc::wallet::BlockHeight;
 use serde::{Deserialize, Serialize};
+use serde_with::{serde_as, DisplayFromStr};
 use std::fmt;
 
+#[serde_as]
 #[derive(Clone, Debug, Deserialize, Serialize, PartialEq)]
 pub enum Bob {
     Started {
         #[serde(with = "::bitcoin::util::amount::serde::as_sat")]
         btc_amount: bitcoin::Amount,
+        #[serde_as(as = "DisplayFromStr")]
+        change_address: bitcoin::Address,
     },
     ExecutionSetupDone {
         state2: bob::State2,
@@ -45,7 +49,13 @@ pub enum BobEndState {
 impl From<BobState> for Bob {
     fn from(bob_state: BobState) -> Self {
         match bob_state {
-            BobState::Started { btc_amount } => Bob::Started { btc_amount },
+            BobState::Started {
+                btc_amount,
+                change_address,
+            } => Bob::Started {
+                btc_amount,
+                change_address,
+            },
             BobState::SwapSetupCompleted(state2) => Bob::ExecutionSetupDone { state2 },
             BobState::BtcLocked(state3) => Bob::BtcLocked { state3 },
             BobState::XmrLockProofReceived {
@@ -77,7 +87,13 @@ impl From<BobState> for Bob {
 impl From<Bob> for BobState {
     fn from(db_state: Bob) -> Self {
         match db_state {
-            Bob::Started { btc_amount } => BobState::Started { btc_amount },
+            Bob::Started {
+                btc_amount,
+                change_address,
+            } => BobState::Started {
+                btc_amount,
+                change_address,
+            },
             Bob::ExecutionSetupDone { state2 } => BobState::SwapSetupCompleted(state2),
             Bob::BtcLocked { state3 } => BobState::BtcLocked(state3),
             Bob::XmrLockProofReceived {

swap/src/protocol/bob.rs

@@ -33,10 +33,14 @@ impl Swap {
         env_config: env::Config,
         event_loop_handle: cli::EventLoopHandle,
         monero_receive_address: monero::Address,
+        bitcoin_change_address: bitcoin::Address,
         btc_amount: bitcoin::Amount,
     ) -> Self {
         Self {
-            state: BobState::Started { btc_amount },
+            state: BobState::Started {
+                btc_amount,
+                change_address: bitcoin_change_address,
+            },
             event_loop_handle,
             db,
             bitcoin_wallet,
@@ -47,6 +51,7 @@ impl Swap {
         }
     }
 
+    #[allow(clippy::too_many_arguments)]
     pub fn from_db(
         db: Database,
         id: Uuid,

swap/src/protocol/bob/state.rs

@@ -25,6 +25,7 @@ use uuid::Uuid;
 pub enum BobState {
     Started {
         btc_amount: bitcoin::Amount,
+        change_address: bitcoin::Address,
     },
     SwapSetupCompleted(State2),
     BtcLocked(State3),
@@ -169,7 +170,14 @@ impl State0 {
             bail!("Alice's dleq proof doesn't verify")
         }
 
-        let tx_lock = bitcoin::TxLock::new(wallet, self.btc, msg.A, self.b.public()).await?;
+        let tx_lock = bitcoin::TxLock::new(
+            wallet,
+            self.btc,
+            msg.A,
+            self.b.public(),
+            self.refund_address.clone(),
+        )
+        .await?;
         let v = msg.v_a + self.v_b;
 
         Ok(State1 {

swap/src/protocol/bob/swap.rs

@@ -61,8 +61,10 @@ async fn next_state(
     tracing::trace!(%state, "Advancing state");
 
     Ok(match state {
-        BobState::Started { btc_amount } => {
-            let bitcoin_refund_address = bitcoin_wallet.new_address().await?;
+        BobState::Started {
+            btc_amount,
+            change_address,
+        } => {
             let tx_refund_fee = bitcoin_wallet
                 .estimate_fee(TxRefund::weight(), btc_amount)
                 .await?;
@@ -76,7 +78,7 @@ async fn next_state(
                     btc: btc_amount,
                     tx_refund_fee,
                     tx_cancel_fee,
-                    bitcoin_refund_address,
+                    bitcoin_refund_address: change_address,
                 })
                 .await?;
 

swap/tests/harness/mod.rs

@@ -434,6 +434,7 @@ impl BobParams {
             self.env_config,
             handle,
             self.monero_wallet.get_main_address(),
+            self.bitcoin_wallet.new_address().await?,
             btc_amount,
         );