Flashloans sent back to driver

src/api/routes/solve/dto/auction.rs

@@ -58,6 +58,15 @@ pub fn to_domain(auction: &Auction) -> Result<auction::Auction, Error> {
                     Class::Limit => order::Class::Limit,
                 },
                 partially_fillable: order.partially_fillable,
+                flashloan_hint: order
+                    .flashloan_hint
+                    .clone()
+                    .map(|hint| order::FlashloanHint {
+                        lender: eth::Address(hint.lender),
+                        borrower: eth::Address(hint.borrower),
+                        token: eth::TokenAddress(hint.token),
+                        amount: hint.amount,
+                    }),
             })
             .collect(),
         liquidity: auction

src/api/routes/solve/dto/solution.rs

@@ -115,6 +115,16 @@ pub fn from_domain(solutions: &[solution::Solution]) -> super::Solutions {
                     })
                     .collect(),
                 gas: solution.gas.map(|gas| gas.0.as_u64()),
+                flashloans: solution
+                    .flashloans
+                    .iter()
+                    .map(|loan| Flashloan {
+                        lender: loan.lender.0,
+                        borrower: loan.borrower.0,
+                        token: loan.token.0,
+                        amount: loan.amount,
+                    })
+                    .collect(),
             })
             .collect(),
     }

src/domain/order.rs

@@ -15,6 +15,7 @@ pub struct Order {
     pub side: Side,
     pub class: Class,
     pub partially_fillable: bool,
+    pub flashloan_hint: Option<FlashloanHint>,
 }
 
 impl Order {
@@ -31,6 +32,15 @@ impl Order {
     }
 }
 
+/// A hint for the solver to use a flashloan for this order.
+#[derive(Debug, Clone)]
+pub struct FlashloanHint {
+    pub lender: eth::Address,
+    pub borrower: eth::Address,
+    pub token: eth::TokenAddress,
+    pub amount: eth::U256,
+}
+
 /// UID of an order.
 #[derive(Clone, Copy, Eq, Hash, PartialEq)]
 pub struct Uid(pub [u8; 56]);

src/domain/solution.rs

@@ -26,6 +26,7 @@ pub struct Solution {
     pub interactions: Vec<Interaction>,
     pub post_interactions: Vec<eth::Interaction>,
     pub gas: Option<eth::Gas>,
+    pub flashloans: Vec<Flashloan>,
 }
 
 impl Solution {
@@ -196,11 +197,22 @@ impl Single {
                 (order.sell.token, buy),
                 (order.buy.token, sell.checked_sub(surplus_fee)?),
             ]),
-            trades: vec![Trade::Fulfillment(Fulfillment::new(order, executed, fee)?)],
             pre_interactions: Default::default(),
             interactions,
             post_interactions: Default::default(),
             gas: Some(gas_offset + self.gas),
+            flashloans: order
+                .flashloan_hint
+                .clone()
+                .map(|hint| Flashloan {
+                    lender: hint.lender,
+                    borrower: hint.borrower,
+                    token: hint.token,
+                    amount: hint.amount,
+                })
+                .into_iter()
+                .collect(),
+            trades: vec![Trade::Fulfillment(Fulfillment::new(order, executed, fee)?)],
         })
     }
 }
@@ -385,3 +397,12 @@ pub const SETTLEMENT: u64 = 7365;
 /// Value was computed by taking 52 percentile median of `transfer()` costs
 /// of the 90% most traded tokens by volume in the month of Oct. 2021.
 pub const ERC20_TRANSFER: u64 = 27_513;
+
+/// A flashloan that is required to execute a solution.
+#[derive(Debug, Clone)]
+pub struct Flashloan {
+    pub lender: eth::Address,
+    pub borrower: eth::Address,
+    pub token: eth::TokenAddress,
+    pub amount: eth::U256,
+}