ABS only sends quote response if sufficient XMR balance

swap/src/monero.rs

@@ -206,12 +206,18 @@ pub trait WatchForTransfer {
 }
 
 #[derive(Debug, Clone, Copy, thiserror::Error)]
-#[error("transaction does not pay enough: expected {expected:?}, got {actual:?}")]
+#[error("transaction does not pay enough: expected {expected}, got {actual}")]
 pub struct InsufficientFunds {
     pub expected: Amount,
     pub actual: Amount,
 }
 
+#[derive(Debug, Clone, Copy, thiserror::Error)]
+#[error("The balance is too low, current balance: {balance}")]
+pub struct BalanceTooLow {
+    pub balance: Amount,
+}
+
 #[async_trait]
 pub trait CreateWalletForOutput {
     async fn create_and_load_wallet_for_output(

swap/src/monero/wallet.rs

@@ -68,6 +68,11 @@ impl Wallet {
     pub async fn refresh(&self) -> Result<Refreshed> {
         self.inner.lock().await.refresh().await
     }
+
+    pub fn static_tx_fee_estimate(&self) -> Amount {
+        // Median tx fees on Monero as found here: https://www.monero.how/monero-transaction-fees, 0.000_015 * 2 (to be on the safe side)
+        Amount::from_monero(0.000_03f64).expect("static fee to be convertible without problems")
+    }
 }
 
 #[async_trait]

swap/src/protocol/alice/event_loop.rs

@@ -3,7 +3,9 @@ use crate::{
     bitcoin,
     database::Database,
     execution_params::ExecutionParams,
-    monero, network,
+    monero,
+    monero::BalanceTooLow,
+    network,
     network::{transport, TokioExecutor},
     protocol::{
         alice,
@@ -14,7 +16,7 @@ use crate::{
     },
     seed::Seed,
 };
-use anyhow::{Context, Result};
+use anyhow::{anyhow, Context, Result};
 use futures::future::RemoteHandle;
 use libp2p::{
     core::Multiaddr, futures::FutureExt, request_response::ResponseChannel, PeerId, Swarm,
@@ -164,7 +166,7 @@ where
                             debug!("Connection Established with {}", alice);
                         }
                         OutEvent::QuoteRequest { msg, channel, bob_peer_id } => {
-                            if let Err(error) = self.handle_quote_request(msg, channel, bob_peer_id).await {
+                            if let Err(error) = self.handle_quote_request(msg, channel, bob_peer_id, self.monero_wallet.clone()).await {
                                 error!("Failed to handle quote request: {:#}", error);
                             }
                         }
@@ -201,6 +203,7 @@ where
         quote_request: QuoteRequest,
         channel: ResponseChannel<QuoteResponse>,
         bob_peer_id: PeerId,
+        monero_wallet: Arc<monero::Wallet>,
     ) -> Result<()> {
         // 1. Check if acceptable request
         // 2. Send response
@@ -212,6 +215,16 @@ where
 
         let btc_amount = quote_request.btc_amount;
         let xmr_amount = rate.sell_quote(btc_amount)?;
+
+        let xmr_balance = monero_wallet.get_balance().await?;
+        let xmr_lock_fees = monero_wallet.static_tx_fee_estimate();
+
+        if xmr_balance < xmr_amount + xmr_lock_fees {
+            anyhow!(BalanceTooLow {
+                balance: xmr_balance
+            });
+        }
+
         let quote_response = QuoteResponse { xmr_amount };
 
         self.swarm