asb: subtract reserved monero from quote volume

dev-docs/asb/README.md

@@ -32,6 +32,7 @@ Consider joining the designated [Matrix chat](https://matrix.to/#/%23unstoppable
 ### Using Docker
 
 Running the ASB and its required services (Bitcoin node, Monero node, wallet RPC) can be complex to set up manually. We provide a Docker Compose solution that handles all of this automatically. See our [docker-compose repository](https://github.com/UnstoppableSwap/asb-docker-compose) for setup instructions and configuration details.
+
 ## ASB Details
 
 The ASB is a long running daemon that acts as the trading partner to the swap CLI.

swap/src/asb/event_loop.rs

@@ -1,5 +1,5 @@
 use crate::asb::{Behaviour, OutEvent, Rate};
-use crate::monero::Amount;
+use crate::monero::{Amount, MONERO_FEE};
 use crate::network::cooperative_xmr_redeem_after_punish::CooperativeXmrRedeemRejectReason;
 use crate::network::cooperative_xmr_redeem_after_punish::Response::{Fullfilled, Rejected};
 use crate::network::quote::BidQuote;
@@ -479,16 +479,34 @@ where
         // use unlocked monero balance for quote
         let xmr_balance = Amount::from_piconero(balance.unlocked_balance);
 
-        let max_bitcoin_for_monero =
-            xmr_balance
-                .max_bitcoin_for_price(ask_price)
-                .ok_or_else(|| {
-                    anyhow!(
-                        "Bitcoin price ({}) x Monero ({}) overflow",
-                        ask_price,
-                        xmr_balance
-                    )
-                })?;
+        // From our full balance we need to subtract any Monero that is 'reserved' for ongoing swaps
+        // (where the Bitcoin has been (or is being) locked but we haven't sent the Monero yet).
+
+        let reserved: Amount = self
+            .db
+            .all()
+            .await?
+            .iter()
+            .filter_map(|(_, state)| match state {
+                State::Alice(AliceState::BtcLockTransactionSeen { state3 })
+                | State::Alice(AliceState::BtcLocked { state3 }) => Some(state3.xmr + MONERO_FEE),
+                _ => None,
+            })
+            .fold(Amount::ZERO, |acc, amount| acc + amount);
+
+        let free_monero_balance = xmr_balance
+            .checked_sub(reserved)
+            .context("reserved more monero than we've got")?;
+
+        let max_bitcoin_for_monero = free_monero_balance
+            .max_bitcoin_for_price(ask_price)
+            .ok_or_else(|| {
+                anyhow!(
+                    "Bitcoin price ({}) x Monero ({}) overflow",
+                    ask_price,
+                    xmr_balance
+                )
+            })?;
 
         tracing::trace!(%ask_price, %xmr_balance, %max_bitcoin_for_monero, "Computed quote");
 

swap/src/monero.rs

@@ -9,7 +9,7 @@ pub use wallet::Wallet;
 pub use wallet_rpc::{WalletRpc, WalletRpcProcess};
 
 use crate::bitcoin;
-use anyhow::Result;
+use anyhow::{bail, Result};
 use rand::{CryptoRng, RngCore};
 use rust_decimal::prelude::*;
 use rust_decimal::Decimal;
@@ -164,6 +164,15 @@ impl Amount {
             .ok_or_else(|| OverflowError(amount.to_string()))?;
         Ok(Amount(piconeros))
     }
+
+    /// Subtract but throw an error on underflow.
+    pub fn checked_sub(self, rhs: Amount) -> Result<Self> {
+        if self.0 < rhs.0 {
+            bail!("checked sub would underflow");
+        }
+
+        Ok(Amount::from_piconero(self.0 - rhs.0))
+    }
 }
 
 impl Add for Amount {
@@ -174,7 +183,7 @@ impl Add for Amount {
     }
 }
 
-impl Sub for Amount {
+impl Sub<Amount> for Amount {
     type Output = Amount;
 
     fn sub(self, rhs: Self) -> Self::Output {