Introduce a minimum buy amount

Introduces a minimum buy Bitcoin amount similar to the maximum amount already present.
For the CLI the minimum amount is enforced by waiting until at least the minimum is available as max-giveable amount.

CHANGELOG.md

@@ -25,6 +25,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   By default we wait for finality of the redeem transaction; this can be disabled by setting `--do-not-await-finality`.
 - Resume-only mode for the ASB.
   When started with `--resume-only` the ASB does not accept new, incoming swap requests but only finishes swaps that are resumed upon startup.
+- A minimum accepted Bitcoin amount for the ASB similar to the maximum amount already present.
+  For the CLI the minimum amount is enforced by waiting until at least the minimum is available as max-giveable amount.
 
 ### Fixed
 
@@ -43,7 +45,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 
-- The ASB's `--max-buy`  and `ask-spread` parameter were removed in favour of entries in the config file.
+- The ASB's `--max-buy` and `ask-spread` parameter were removed in favour of entries in the config file.
   The initial setup includes setting these two values now.
 
 ## [0.5.0] - 2021-04-17

swap/src/asb/config.rs

@@ -20,6 +20,7 @@ const DEFAULT_ELECTRUM_RPC_URL: &str = "ssl://electrum.blockstream.info:60002";
 const DEFAULT_MONERO_WALLET_RPC_TESTNET_URL: &str = "http://127.0.0.1:38083/json_rpc";
 const DEFAULT_BITCOIN_CONFIRMATION_TARGET: usize = 3;
 
+const DEFAULT_MIN_BUY_AMOUNT: f64 = 0.002f64;
 const DEFAULT_MAX_BUY_AMOUNT: f64 = 0.02f64;
 const DEFAULT_SPREAD: f64 = 0.02f64;
 
@@ -81,6 +82,8 @@ pub struct TorConf {
 #[derive(Clone, Debug, Deserialize, PartialEq, Serialize)]
 #[serde(deny_unknown_fields)]
 pub struct Maker {
+    #[serde(with = "::bitcoin::util::amount::serde::as_btc")]
+    pub min_buy_btc: bitcoin::Amount,
     #[serde(with = "::bitcoin::util::amount::serde::as_btc")]
     pub max_buy_btc: bitcoin::Amount,
     pub ask_spread: Decimal,
@@ -200,6 +203,12 @@ pub fn query_user_for_initial_testnet_config() -> Result<Config> {
         .default(DEFAULT_SOCKS5_PORT.to_owned())
         .interact_text()?;
 
+    let min_buy = Input::with_theme(&ColorfulTheme::default())
+        .with_prompt("Enter minimum Bitcoin amount you are willing to accept per swap or hit enter to use default.")
+        .default(DEFAULT_MIN_BUY_AMOUNT)
+        .interact_text()?;
+    let min_buy = bitcoin::Amount::from_btc(min_buy)?;
+
     let max_buy = Input::with_theme(&ColorfulTheme::default())
         .with_prompt("Enter maximum Bitcoin amount you are willing to accept per swap or hit enter to use default.")
         .default(DEFAULT_MAX_BUY_AMOUNT)
@@ -234,6 +243,7 @@ pub fn query_user_for_initial_testnet_config() -> Result<Config> {
             socks5_port: tor_socks5_port,
         },
         maker: Maker {
+            min_buy_btc: min_buy,
             max_buy_btc: max_buy,
             ask_spread,
         },
@@ -271,6 +281,7 @@ mod tests {
             },
             tor: Default::default(),
             maker: Maker {
+                min_buy_btc: bitcoin::Amount::from_btc(DEFAULT_MIN_BUY_AMOUNT).unwrap(),
                 max_buy_btc: bitcoin::Amount::from_btc(DEFAULT_MAX_BUY_AMOUNT).unwrap(),
                 ask_spread: Decimal::from_f64(DEFAULT_SPREAD).unwrap(),
             },

swap/src/bin/asb.rs

@@ -123,6 +123,7 @@ async fn main() -> Result<()> {
                 &seed,
                 current_balance,
                 lock_fee,
+                config.maker.min_buy_btc,
                 config.maker.max_buy_btc,
                 kraken_rate.clone(),
                 resume_only,
@@ -140,6 +141,7 @@ async fn main() -> Result<()> {
                 Arc::new(monero_wallet),
                 Arc::new(db),
                 kraken_rate,
+                config.maker.min_buy_btc,
                 config.maker.max_buy_btc,
             )
             .unwrap();

swap/src/bin/swap.rs

@@ -20,7 +20,7 @@ use std::path::PathBuf;
 use std::sync::Arc;
 use std::time::Duration;
 use structopt::StructOpt;
-use swap::bitcoin::{Amount, TxLock};
+use swap::bitcoin::TxLock;
 use swap::cli::command::{Arguments, Command, MoneroParams};
 use swap::database::Database;
 use swap::env::{Config, GetConfig};
@@ -94,23 +94,19 @@ async fn main() -> Result<()> {
                 EventLoop::new(swap_id, swarm, alice_peer_id, bitcoin_wallet.clone())?;
             let event_loop = tokio::spawn(event_loop.run());
 
-            let send_bitcoin = determine_btc_to_swap(
+            let max_givable = || bitcoin_wallet.max_giveable(TxLock::script_size());
+            let (send_bitcoin, fees) = determine_btc_to_swap(
                 event_loop_handle.request_quote(),
-                bitcoin_wallet.balance(),
+                max_givable().await?,
                 bitcoin_wallet.new_address(),
-                async {
-                    while bitcoin_wallet.balance().await? == Amount::ZERO {
-                        bitcoin_wallet.sync().await?;
-
-                        tokio::time::sleep(Duration::from_secs(1)).await;
-                    }
-
-                    bitcoin_wallet.balance().await
-                },
-                bitcoin_wallet.max_giveable(TxLock::script_size()),
+                || bitcoin_wallet.balance(),
+                max_givable,
+                || bitcoin_wallet.sync(),
             )
             .await?;
 
+            info!("Swapping {} with {} fees", send_bitcoin, fees);
+
             db.insert_peer_id(swap_id, alice_peer_id).await?;
 
             let swap = Swap::new(
@@ -332,51 +328,83 @@ async fn init_monero_wallet(
     Ok((monero_wallet, monero_wallet_rpc_process))
 }
 
-async fn determine_btc_to_swap(
-    request_quote: impl Future<Output = Result<BidQuote>>,
-    initial_balance: impl Future<Output = Result<bitcoin::Amount>>,
+async fn determine_btc_to_swap<FB, TB, FMG, TMG, FS, TS>(
+    bid_quote: impl Future<Output = Result<BidQuote>>,
+    mut current_maximum_giveable: bitcoin::Amount,
     get_new_address: impl Future<Output = Result<bitcoin::Address>>,
-    wait_for_deposit: impl Future<Output = Result<bitcoin::Amount>>,
-    max_giveable: impl Future<Output = Result<bitcoin::Amount>>,
-) -> Result<bitcoin::Amount> {
+    balance: FB,
+    max_giveable: FMG,
+    sync: FS,
+) -> Result<(bitcoin::Amount, bitcoin::Amount)>
+where
+    TB: Future<Output = Result<bitcoin::Amount>>,
+    FB: Fn() -> TB,
+    TMG: Future<Output = Result<bitcoin::Amount>>,
+    FMG: Fn() -> TMG,
+    TS: Future<Output = Result<()>>,
+    FS: Fn() -> TS,
+{
     debug!("Requesting quote");
-
-    let bid_quote = request_quote.await?;
-
+    let bid_quote = bid_quote.await?;
     info!("Received quote: 1 XMR ~ {}", bid_quote.price);
 
-    // TODO: Also wait for more funds if balance < dust
-    let initial_balance = initial_balance.await?;
+    let max_giveable = if current_maximum_giveable == bitcoin::Amount::ZERO
+        || current_maximum_giveable < bid_quote.min_quantity
+    {
+        let deposit_address = get_new_address.await?;
+        let minimum_amount = bid_quote.min_quantity;
+        let maximum_amount = bid_quote.max_quantity;
 
-    let balance = if initial_balance == Amount::ZERO {
         info!(
-            "Please deposit the BTC you want to swap to {} (max {})",
-            get_new_address.await?,
-            bid_quote.max_quantity
+            %deposit_address,
+            %current_maximum_giveable,
+            %minimum_amount,
+            %maximum_amount,
+            "Please deposit BTC you want to swap to",
         );
 
-        let new_balance = wait_for_deposit
-            .await
-            .context("Failed to wait for Bitcoin deposit")?;
+        loop {
+            sync().await?;
 
-        info!("Received {}", new_balance);
-        new_balance
+            let new_max_givable = max_giveable().await?;
+
+            if new_max_givable != current_maximum_giveable {
+                current_maximum_giveable = new_max_givable;
+
+                let new_balance = balance().await?;
+                tracing::info!(
+                    %new_balance,
+                    %current_maximum_giveable,
+                    "Received BTC",
+                );
+
+                if current_maximum_giveable >= bid_quote.min_quantity {
+                    break;
+                } else {
+                    tracing::info!(
+                        %minimum_amount,
+                        %deposit_address,
+                        "Please deposit more, not enough BTC to trigger swap with",
+                    );
+                }
+            }
+
+            tokio::time::sleep(Duration::from_secs(1)).await;
+        }
+
+        current_maximum_giveable
     } else {
-        info!("Found {} in wallet", initial_balance);
-        initial_balance
+        current_maximum_giveable
     };
 
-    let max_giveable = max_giveable
-        .await
-        .context("Failed to compute max 'giveable' Bitcoin amount")?;
+    let balance = balance().await?;
     let fees = balance - max_giveable;
 
     let max_accepted = bid_quote.max_quantity;
 
     let btc_swap_amount = min(max_giveable, max_accepted);
-    info!("Swapping {} with {} fees", btc_swap_amount, fees);
 
-    Ok(btc_swap_amount)
+    Ok((btc_swap_amount, fees))
 }
 
 #[cfg(test)]
@@ -390,74 +418,162 @@ mod tests {
     async fn given_no_balance_and_transfers_less_than_max_swaps_max_giveable() {
         let _guard = subscriber::set_default(tracing_subscriber::fmt().with_test_writer().finish());
 
-        let amount = determine_btc_to_swap(
+        let (amount, fees) = determine_btc_to_swap(
             async { Ok(quote_with_max(0.01)) },
-            async { Ok(Amount::ZERO) },
+            Amount::ZERO,
             get_dummy_address(),
-            async { Ok(Amount::from_btc(0.0001)?) },
-            async { Ok(Amount::from_btc(0.00009)?) },
+            || async { Ok(Amount::from_btc(0.001)?) },
+            || async { Ok(Amount::from_btc(0.0009)?) },
+            || async { Ok(()) },
         )
         .await
         .unwrap();
 
-        assert_eq!(amount, Amount::from_btc(0.00009).unwrap())
+        let expected_amount = Amount::from_btc(0.0009).unwrap();
+        let expected_fees = Amount::from_btc(0.0001).unwrap();
+
+        assert_eq!((amount, fees), (expected_amount, expected_fees))
     }
 
     #[tokio::test]
     async fn given_no_balance_and_transfers_more_then_swaps_max_quantity_from_quote() {
         let _guard = subscriber::set_default(tracing_subscriber::fmt().with_test_writer().finish());
 
-        let amount = determine_btc_to_swap(
+        let (amount, fees) = determine_btc_to_swap(
             async { Ok(quote_with_max(0.01)) },
-            async { Ok(Amount::ZERO) },
+            Amount::ZERO,
             get_dummy_address(),
-            async { Ok(Amount::from_btc(0.1)?) },
-            async { Ok(Amount::from_btc(0.09)?) },
+            || async { Ok(Amount::from_btc(0.1001)?) },
+            || async { Ok(Amount::from_btc(0.1)?) },
+            || async { Ok(()) },
         )
         .await
         .unwrap();
 
-        assert_eq!(amount, Amount::from_btc(0.01).unwrap())
+        let expected_amount = Amount::from_btc(0.01).unwrap();
+        let expected_fees = Amount::from_btc(0.0001).unwrap();
+
+        assert_eq!((amount, fees), (expected_amount, expected_fees))
     }
 
     #[tokio::test]
     async fn given_initial_balance_below_max_quantity_swaps_max_givable() {
         let _guard = subscriber::set_default(tracing_subscriber::fmt().with_test_writer().finish());
 
-        let amount = determine_btc_to_swap(
+        let (amount, fees) = determine_btc_to_swap(
             async { Ok(quote_with_max(0.01)) },
-            async { Ok(Amount::from_btc(0.005)?) },
+            Amount::from_btc(0.0049).unwrap(),
             async { panic!("should not request new address when initial balance is > 0") },
-            async { panic!("should not wait for deposit when initial balance > 0") },
-            async { Ok(Amount::from_btc(0.0049)?) },
+            || async { Ok(Amount::from_btc(0.005)?) },
+            || async { panic!("should not wait for deposit when initial balance > 0") },
+            || async { Ok(()) },
         )
         .await
         .unwrap();
 
-        assert_eq!(amount, Amount::from_btc(0.0049).unwrap())
+        let expected_amount = Amount::from_btc(0.0049).unwrap();
+        let expected_fees = Amount::from_btc(0.0001).unwrap();
+
+        assert_eq!((amount, fees), (expected_amount, expected_fees))
     }
 
     #[tokio::test]
     async fn given_initial_balance_above_max_quantity_swaps_max_quantity() {
         let _guard = subscriber::set_default(tracing_subscriber::fmt().with_test_writer().finish());
 
-        let amount = determine_btc_to_swap(
+        let (amount, fees) = determine_btc_to_swap(
             async { Ok(quote_with_max(0.01)) },
-            async { Ok(Amount::from_btc(0.1)?) },
+            Amount::from_btc(0.1).unwrap(),
             async { panic!("should not request new address when initial balance is > 0") },
-            async { panic!("should not wait for deposit when initial balance > 0") },
-            async { Ok(Amount::from_btc(0.09)?) },
+            || async { Ok(Amount::from_btc(0.1001)?) },
+            || async { panic!("should not wait for deposit when initial balance > 0") },
+            || async { Ok(()) },
         )
         .await
         .unwrap();
 
-        assert_eq!(amount, Amount::from_btc(0.01).unwrap())
+        let expected_amount = Amount::from_btc(0.01).unwrap();
+        let expected_fees = Amount::from_btc(0.0001).unwrap();
+
+        assert_eq!((amount, fees), (expected_amount, expected_fees))
+    }
+
+    #[tokio::test]
+    async fn given_no_initial_balance_then_min_wait_for_sufficient_deposit() {
+        let _guard = subscriber::set_default(tracing_subscriber::fmt().with_test_writer().finish());
+
+        let (amount, fees) = determine_btc_to_swap(
+            async { Ok(quote_with_min(0.01)) },
+            Amount::ZERO,
+            get_dummy_address(),
+            || async { Ok(Amount::from_btc(0.0101)?) },
+            || async { Ok(Amount::from_btc(0.01)?) },
+            || async { Ok(()) },
+        )
+        .await
+        .unwrap();
+
+        let expected_amount = Amount::from_btc(0.01).unwrap();
+        let expected_fees = Amount::from_btc(0.0001).unwrap();
+
+        assert_eq!((amount, fees), (expected_amount, expected_fees))
+    }
+
+    #[tokio::test]
+    async fn given_balance_less_then_min_wait_for_sufficient_deposit() {
+        let _guard = subscriber::set_default(tracing_subscriber::fmt().with_test_writer().finish());
+
+        let (amount, fees) = determine_btc_to_swap(
+            async { Ok(quote_with_min(0.01)) },
+            Amount::from_btc(0.0001).unwrap(),
+            get_dummy_address(),
+            || async { Ok(Amount::from_btc(0.0101)?) },
+            || async { Ok(Amount::from_btc(0.01)?) },
+            || async { Ok(()) },
+        )
+        .await
+        .unwrap();
+
+        let expected_amount = Amount::from_btc(0.01).unwrap();
+        let expected_fees = Amount::from_btc(0.0001).unwrap();
+
+        assert_eq!((amount, fees), (expected_amount, expected_fees))
+    }
+
+    #[tokio::test]
+    async fn given_no_initial_balance_and_transfers_less_than_min_keep_waiting() {
+        let _guard = subscriber::set_default(tracing_subscriber::fmt().with_test_writer().finish());
+
+        let error = tokio::time::timeout(
+            Duration::from_secs(1),
+            determine_btc_to_swap(
+                async { Ok(quote_with_min(0.1)) },
+                Amount::ZERO,
+                get_dummy_address(),
+                || async { Ok(Amount::from_btc(0.0101)?) },
+                || async { Ok(Amount::from_btc(0.01)?) },
+                || async { Ok(()) },
+            ),
+        )
+        .await
+        .unwrap_err();
+
+        assert!(matches!(error, tokio::time::error::Elapsed { .. }))
     }
 
     fn quote_with_max(btc: f64) -> BidQuote {
         BidQuote {
             price: Amount::from_btc(0.001).unwrap(),
             max_quantity: Amount::from_btc(btc).unwrap(),
+            min_quantity: Amount::ZERO,
+        }
+    }
+
+    fn quote_with_min(btc: f64) -> BidQuote {
+        BidQuote {
+            price: Amount::from_btc(0.001).unwrap(),
+            max_quantity: Amount::max_value(),
+            min_quantity: Amount::from_btc(btc).unwrap(),
         }
     }
 

swap/src/network/quote.rs

@@ -30,6 +30,9 @@ pub struct BidQuote {
     /// The price at which the maker is willing to buy at.
     #[serde(with = "::bitcoin::util::amount::serde::as_sat")]
     pub price: bitcoin::Amount,
+    /// The minimum quantity the maker is willing to buy.
+    #[serde(with = "::bitcoin::util::amount::serde::as_sat")]
+    pub min_quantity: bitcoin::Amount,
     /// The maximum quantity the maker is willing to buy.
     #[serde(with = "::bitcoin::util::amount::serde::as_sat")]
     pub max_quantity: bitcoin::Amount,

swap/src/network/spot_price.rs

@@ -43,7 +43,13 @@ pub enum Response {
 #[derive(Clone, Debug, Serialize, Deserialize)]
 pub enum Error {
     NoSwapsAccepted,
-    MaxBuyAmountExceeded {
+    AmountBelowMinimum {
+        #[serde(with = "::bitcoin::util::amount::serde::as_sat")]
+        min: bitcoin::Amount,
+        #[serde(with = "::bitcoin::util::amount::serde::as_sat")]
+        buy: bitcoin::Amount,
+    },
+    AmountAboveMaximum {
         #[serde(with = "::bitcoin::util::amount::serde::as_sat")]
         max: bitcoin::Amount,
         #[serde(with = "::bitcoin::util::amount::serde::as_sat")]
@@ -74,8 +80,16 @@ mod tests {
         let serialized = serde_json::to_string(&Response::Error(Error::NoSwapsAccepted)).unwrap();
         assert_eq!(error, serialized);
 
-        let error = r#"{"Error":{"MaxBuyAmountExceeded":{"max":0,"buy":0}}}"#.to_string();
-        let serialized = serde_json::to_string(&Response::Error(Error::MaxBuyAmountExceeded {
+        let error = r#"{"Error":{"AmountBelowMinimum":{"min":0,"buy":0}}}"#.to_string();
+        let serialized = serde_json::to_string(&Response::Error(Error::AmountBelowMinimum {
+            min: Default::default(),
+            buy: Default::default(),
+        }))
+        .unwrap();
+        assert_eq!(error, serialized);
+
+        let error = r#"{"Error":{"AmountAboveMaximum":{"max":0,"buy":0}}}"#.to_string();
+        let serialized = serde_json::to_string(&Response::Error(Error::AmountAboveMaximum {
             max: Default::default(),
             buy: Default::default(),
         }))

swap/src/network/swarm.rs

@@ -12,6 +12,7 @@ pub fn alice<LR>(
     seed: &Seed,
     balance: monero::Amount,
     lock_fee: monero::Amount,
+    min_buy: bitcoin::Amount,
     max_buy: bitcoin::Amount,
     latest_rate: LR,
     resume_only: bool,
@@ -21,7 +22,14 @@ where
 {
     with_clear_net(
         seed,
-        alice::Behaviour::new(balance, lock_fee, max_buy, latest_rate, resume_only),
+        alice::Behaviour::new(
+            balance,
+            lock_fee,
+            min_buy,
+            max_buy,
+            latest_rate,
+            resume_only,
+        ),
     )
 }
 

swap/src/protocol/alice/behaviour.rs

@@ -84,6 +84,7 @@ where
     pub fn new(
         balance: monero::Amount,
         lock_fee: monero::Amount,
+        min_buy: bitcoin::Amount,
         max_buy: bitcoin::Amount,
         latest_rate: LR,
         resume_only: bool,
@@ -93,6 +94,7 @@ where
             spot_price: spot_price::Behaviour::new(
                 balance,
                 lock_fee,
+                min_buy,
                 max_buy,
                 latest_rate,
                 resume_only,

swap/src/protocol/alice/event_loop.rs

@@ -43,6 +43,7 @@ where
     monero_wallet: Arc<monero::Wallet>,
     db: Arc<Database>,
     latest_rate: LR,
+    min_buy: bitcoin::Amount,
     max_buy: bitcoin::Amount,
 
     swap_sender: mpsc::Sender<Swap>,
@@ -74,6 +75,7 @@ where
         monero_wallet: Arc<monero::Wallet>,
         db: Arc<Database>,
         latest_rate: LR,
+        min_buy: bitcoin::Amount,
         max_buy: bitcoin::Amount,
     ) -> Result<(Self, mpsc::Receiver<Swap>)> {
         let swap_channel = MpscChannels::default();
@@ -86,6 +88,7 @@ where
             db,
             latest_rate,
             swap_sender: swap_channel.sender,
+            min_buy,
             max_buy,
             recv_encrypted_signature: Default::default(),
             inflight_encrypted_signatures: Default::default(),
@@ -206,7 +209,9 @@ where
                         }
                         SwarmEvent::Behaviour(OutEvent::SwapRequestDeclined { peer, error }) => {
                             match error {
-                                Error::ResumeOnlyMode | Error::MaxBuyAmountExceeded { .. } => {
+                                Error::ResumeOnlyMode
+                                | Error::AmountBelowMinimum { .. }
+                                | Error::AmountAboveMaximum { .. } => {
                                     tracing::warn!(%peer, "Ignoring spot price request because: {}", error);
                                 }
                                 Error::BalanceTooLow { .. }
@@ -228,7 +233,7 @@ where
                                 }
                             }
 
-                            let quote = match self.make_quote(self.max_buy).await {
+                            let quote = match self.make_quote(self.min_buy, self.max_buy).await {
                                 Ok(quote) => quote,
                                 Err(e) => {
                                     tracing::warn!(%peer, "Failed to make quote: {:#}", e);
@@ -355,7 +360,11 @@ where
         }
     }
 
-    async fn make_quote(&mut self, max_buy: bitcoin::Amount) -> Result<BidQuote> {
+    async fn make_quote(
+        &mut self,
+        min_buy: bitcoin::Amount,
+        max_buy: bitcoin::Amount,
+    ) -> Result<BidQuote> {
         let rate = self
             .latest_rate
             .latest_rate()
@@ -363,6 +372,7 @@ where
 
         Ok(BidQuote {
             price: rate.ask().context("Failed to compute asking price")?,
+            min_quantity: min_buy,
             max_quantity: max_buy,
         })
     }

swap/src/protocol/alice/spot_price.rs

@@ -44,6 +44,8 @@ where
     #[behaviour(ignore)]
     lock_fee: monero::Amount,
     #[behaviour(ignore)]
+    min_buy: bitcoin::Amount,
+    #[behaviour(ignore)]
     max_buy: bitcoin::Amount,
     #[behaviour(ignore)]
     latest_rate: LR,
@@ -62,6 +64,7 @@ where
     pub fn new(
         balance: monero::Amount,
         lock_fee: monero::Amount,
+        min_buy: bitcoin::Amount,
         max_buy: bitcoin::Amount,
         latest_rate: LR,
         resume_only: bool,
@@ -75,6 +78,7 @@ where
             events: Default::default(),
             balance,
             lock_fee,
+            min_buy,
             max_buy,
             latest_rate,
             resume_only,
@@ -156,8 +160,17 @@ where
         }
 
         let btc = request.btc;
+
+        if btc < self.min_buy {
+            self.decline(peer, channel, Error::AmountBelowMinimum {
+                min: self.min_buy,
+                buy: btc,
+            });
+            return;
+        }
+
         if btc > self.max_buy {
-            self.decline(peer, channel, Error::MaxBuyAmountExceeded {
+            self.decline(peer, channel, Error::AmountAboveMaximum {
                 max: self.max_buy,
                 buy: btc,
             });
@@ -218,8 +231,13 @@ impl From<OutEvent> for alice::OutEvent {
 pub enum Error {
     #[error("ASB is running in resume-only mode")]
     ResumeOnlyMode,
-    #[error("Maximum buy {max} exceeded {buy}")]
-    MaxBuyAmountExceeded {
+    #[error("Amount {buy} below minimum {min}")]
+    AmountBelowMinimum {
+        min: bitcoin::Amount,
+        buy: bitcoin::Amount,
+    },
+    #[error("Amount {buy} above maximum {max}")]
+    AmountAboveMaximum {
         max: bitcoin::Amount,
         buy: bitcoin::Amount,
     },
@@ -240,7 +258,11 @@ impl Error {
     pub fn to_error_response(&self) -> spot_price::Error {
         match self {
             Error::ResumeOnlyMode => spot_price::Error::NoSwapsAccepted,
-            Error::MaxBuyAmountExceeded { max, buy } => spot_price::Error::MaxBuyAmountExceeded {
+            Error::AmountBelowMinimum { min, buy } => spot_price::Error::AmountBelowMinimum {
+                min: *min,
+                buy: *buy,
+            },
+            Error::AmountAboveMaximum { max, buy } => spot_price::Error::AmountAboveMaximum {
                 max: *max,
                 buy: *buy,
             },
@@ -268,6 +290,7 @@ mod tests {
             Self {
                 balance: monero::Amount::from_monero(1.0).unwrap(),
                 lock_fee: monero::Amount::ZERO,
+                min_buy: bitcoin::Amount::from_btc(0.001).unwrap(),
                 max_buy: bitcoin::Amount::from_btc(0.01).unwrap(),
                 rate: TestRate::default(), // 0.01
                 resume_only: false,
@@ -368,7 +391,32 @@ mod tests {
     }
 
     #[tokio::test]
-    async fn given_max_buy_exceeded_then_returns_error() {
+    async fn given_below_min_buy_then_returns_error() {
+        let min_buy = bitcoin::Amount::from_btc(0.001).unwrap();
+
+        let mut test =
+            SpotPriceTest::setup(AliceBehaviourValues::default().with_min_buy(min_buy)).await;
+
+        let btc_to_swap = bitcoin::Amount::from_btc(0.0001).unwrap();
+
+        let request = spot_price::Request { btc: btc_to_swap };
+
+        test.send_request(request);
+        test.assert_error(
+            alice::spot_price::Error::AmountBelowMinimum {
+                buy: btc_to_swap,
+                min: min_buy,
+            },
+            bob::spot_price::Error::AmountBelowMinimum {
+                buy: btc_to_swap,
+                min: min_buy,
+            },
+        )
+        .await;
+    }
+
+    #[tokio::test]
+    async fn given_above_max_buy_then_returns_error() {
         let max_buy = bitcoin::Amount::from_btc(0.001).unwrap();
 
         let mut test =
@@ -380,11 +428,11 @@ mod tests {
 
         test.send_request(request);
         test.assert_error(
-            alice::spot_price::Error::MaxBuyAmountExceeded {
+            alice::spot_price::Error::AmountAboveMaximum {
                 buy: btc_to_swap,
                 max: max_buy,
             },
-            bob::spot_price::Error::MaxBuyAmountExceeded {
+            bob::spot_price::Error::AmountAboveMaximum {
                 buy: btc_to_swap,
                 max: max_buy,
             },
@@ -461,6 +509,7 @@ mod tests {
                 Behaviour::new(
                     values.balance,
                     values.lock_fee,
+                    values.min_buy,
                     values.max_buy,
                     values.rate.clone(),
                     values.resume_only,
@@ -540,8 +589,12 @@ mod tests {
                             assert_eq!(buy1, buy2);
                         }
                         (
-                            alice::spot_price::Error::MaxBuyAmountExceeded { .. },
-                            alice::spot_price::Error::MaxBuyAmountExceeded { .. },
+                            alice::spot_price::Error::AmountBelowMinimum { .. },
+                            alice::spot_price::Error::AmountBelowMinimum { .. },
+                        )
+                        | (
+                            alice::spot_price::Error::AmountAboveMaximum { .. },
+                            alice::spot_price::Error::AmountAboveMaximum { .. },
                         )
                         | (
                             alice::spot_price::Error::LatestRateFetchFailed(_),
@@ -583,6 +636,7 @@ mod tests {
     struct AliceBehaviourValues {
         pub balance: monero::Amount,
         pub lock_fee: monero::Amount,
+        pub min_buy: bitcoin::Amount,
         pub max_buy: bitcoin::Amount,
         pub rate: TestRate, // 0.01
         pub resume_only: bool,
@@ -599,6 +653,11 @@ mod tests {
             self
         }
 
+        pub fn with_min_buy(mut self, min_buy: bitcoin::Amount) -> AliceBehaviourValues {
+            self.min_buy = min_buy;
+            self
+        }
+
         pub fn with_max_buy(mut self, max_buy: bitcoin::Amount) -> AliceBehaviourValues {
             self.max_buy = max_buy;
             self

swap/src/protocol/bob/spot_price.rs

@@ -41,8 +41,13 @@ crate::impl_from_rr_event!(SpotPriceOutEvent, OutEvent, PROTOCOL);
 pub enum Error {
     #[error("Seller currently does not accept incoming swap requests, please try again later")]
     NoSwapsAccepted,
+    #[error("Seller refused to buy {buy} because the minimum configured buy limit is {min}")]
+    AmountBelowMinimum {
+        min: bitcoin::Amount,
+        buy: bitcoin::Amount,
+    },
     #[error("Seller refused to buy {buy} because the maximum configured buy limit is {max}")]
-    MaxBuyAmountExceeded {
+    AmountAboveMaximum {
         max: bitcoin::Amount,
         buy: bitcoin::Amount,
     },
@@ -59,8 +64,11 @@ impl From<spot_price::Error> for Error {
     fn from(error: spot_price::Error) -> Self {
         match error {
             spot_price::Error::NoSwapsAccepted => Error::NoSwapsAccepted,
-            spot_price::Error::MaxBuyAmountExceeded { max, buy } => {
-                Error::MaxBuyAmountExceeded { max, buy }
+            spot_price::Error::AmountBelowMinimum { min, buy } => {
+                Error::AmountBelowMinimum { min, buy }
+            }
+            spot_price::Error::AmountAboveMaximum { max, buy } => {
+                Error::AmountAboveMaximum { max, buy }
             }
             spot_price::Error::BalanceTooLow { buy } => Error::BalanceTooLow { buy },
             spot_price::Error::Other => Error::Other,

swap/tests/harness/mod.rs

@@ -226,6 +226,7 @@ async fn start_alice(
 
     let current_balance = monero_wallet.get_balance().await.unwrap();
     let lock_fee = monero_wallet.static_tx_fee_estimate();
+    let min_buy = bitcoin::Amount::from_sat(u64::MIN);
     let max_buy = bitcoin::Amount::from_sat(u64::MAX);
     let latest_rate = FixedRate::default();
     let resume_only = false;
@@ -234,6 +235,7 @@ async fn start_alice(
         &seed,
         current_balance,
         lock_fee,
+        min_buy,
         max_buy,
         latest_rate,
         resume_only,
@@ -248,7 +250,8 @@ async fn start_alice(
         monero_wallet,
         db,
         FixedRate::default(),
-        bitcoin::Amount::ONE_BTC,
+        min_buy,
+        max_buy,
     )
     .unwrap();