bug fixes

substrate/client/tests/dex.rs

@@ -111,7 +111,7 @@ serai_test!(
         send_to: pair.public().into(),
         path,
         amount_in: amount_in.0,
-        amount_out: 16633299966633
+        amount_out: 16599866399465
       }]
     );
 
@@ -131,7 +131,7 @@ serai_test!(
         send_to: pair.public().into(),
         path,
         amount_in: amount_in.0,
-        amount_out: 17254428681101
+        amount_out: 17166744497317
       }]
     );
   })
@@ -191,7 +191,7 @@ serai_test!(
         send_to: pair.public().into(),
         path,
         amount_in: amount_in.0,
-        amount_out: 12453103964435,
+        amount_out: 12406166091918,
       }]
     );
   })
@@ -246,8 +246,8 @@ serai_test!(
         mint_to: pair.public().into(),
         pool_id: Coin::Bitcoin,
         coin_amount: 10_000_000_000_000, // half of sent amount
-        sri_amount: 111_333_778_668,
-        lp_token_minted: 1_054_092_553_383
+        sri_amount: 111669009482,
+        lp_token_minted: 1055147701082
       }]
     );
   })
@@ -333,7 +333,7 @@ serai_test!(
           send_to: IN_INSTRUCTION_EXECUTOR,
           path,
           amount_in: 200_000_000_000_000,
-          amount_out: 19_044_944_233
+          amount_out: 18933113030
         }]
       );
     }
@@ -372,7 +372,7 @@ serai_test!(
           send_to: out_address.as_native().unwrap(),
           path,
           amount_in: 200_000_000_000,
-          amount_out: 1487294253782353
+          amount_out: 1473437558561637
         }]
       );
     }
@@ -410,7 +410,7 @@ serai_test!(
           send_to: out_address.as_native().unwrap(),
           path,
           amount_in: 100_000_000_000_000,
-          amount_out: 1_762_662_819
+          amount_out: 1751430396
         }]
       );
     }

substrate/dex/pallet/src/lib.rs

@@ -81,7 +81,7 @@ mod mock;
 use frame_support::ensure;
 use frame_system::{
   pallet_prelude::{BlockNumberFor, OriginFor},
-  ensure_signed,
+  ensure_signed, RawOrigin,
 };
 
 pub use pallet::*;
@@ -108,7 +108,7 @@ pub mod pallet {
   use sp_core::sr25519::Public;
   use sp_runtime::traits::IntegerSquareRoot;
 
-  use coins_pallet::{Pallet as CoinsPallet, Config as CoinsConfig};
+  use coins_pallet::{Pallet as Coins, Config as CoinsConfig};
 
   use serai_primitives::{Coin, Amount, Balance, SubstrateAmount, reverse_lexicographic_order};
 
@@ -812,7 +812,7 @@ pub mod pallet {
       to: &T::AccountId,
       balance: Balance,
     ) -> Result<Amount, DispatchError> {
-      CoinsPallet::<T>::transfer_internal(*from, *to, balance)?;
+      Coins::<T>::transfer_internal(*from, *to, balance)?;
       Ok(balance.amount)
     }
 
@@ -911,7 +911,7 @@ pub mod pallet {
     /// Get the `owner`'s balance of `coin`, which could be the chain's native coin or another
     /// fungible. Returns a value in the form of an `Amount`.
     fn get_balance(owner: &T::AccountId, coin: Coin) -> SubstrateAmount {
-      CoinsPallet::<T>::balance(*owner, coin).0
+      Coins::<T>::balance(*owner, coin).0
     }
 
     /// Returns a pool id constructed from 2 coins.
@@ -979,12 +979,36 @@ pub mod pallet {
           let prev_amount = amounts.last().expect("Always has at least one element");
           let amount_out = Self::get_amount_out(*prev_amount, reserve_in, reserve_out)?;
           amounts.push(amount_out);
+
+          // now that we got swap fee from the user, burn half of it.
+          Self::burn_half_of_swap_fee(Self::get_pool_id(*coin1, *coin2)?, *coin1)?;
         }
       }
 
       Ok(amounts)
     }
 
+    fn burn_half_of_swap_fee(pool: PoolId, coin: Coin) -> Result<(), DispatchError> {
+      let pool_account = Self::get_pool_account(pool);
+      let origin = RawOrigin::Signed(pool_account);
+
+      let balance = Coins::<T>::balance(pool_account, coin).0;
+      let burn_percent =
+        HigherPrecisionBalance::from(T::LPFee::get()).checked_div(2).ok_or(Error::<T>::Overflow)?;
+
+      let burn_amount = HigherPrecisionBalance::from(balance)
+        .checked_mul(burn_percent)
+        .ok_or(Error::<T>::Overflow)?
+        .checked_div(1000)
+        .ok_or(Error::<T>::Overflow)?;
+
+      Coins::<T>::burn(
+        origin.into(),
+        Balance { coin, amount: Amount(burn_amount.try_into().map_err(|_| Error::<T>::Overflow)?) },
+      )?;
+      Ok(())
+    }
+
     /// Used by the RPC service to provide current prices.
     pub fn quote_price_exact_tokens_for_tokens(
       coin1: Coin,

substrate/dex/pallet/src/tests.rs

@@ -26,6 +26,7 @@ pub use coins_pallet as coins;
 use coins::Pallet as CoinsPallet;
 
 use serai_primitives::{Balance, COINS, PublicKey, system_address, Amount};
+use sp_core::Get;
 
 type LiquidityTokens<T> = coins_pallet::Pallet<T, coins::Instance1>;
 type LiquidityTokensError<T> = coins_pallet::Error<T, coins::Instance1>;
@@ -60,6 +61,20 @@ fn pool_balance(owner: PublicKey, token_id: Coin) -> u64 {
   LiquidityTokens::<Test>::balance(owner, token_id).0
 }
 
+fn get_burn_amount(liquidity: u64) -> u64 {
+  // burn half of the swap fee left in the pool
+  let burn_percent = HigherPrecisionBalance::from(<<Test as Config>::LPFee as Get<u32>>::get())
+    .checked_div(2)
+    .unwrap();
+
+  let burn_amount = HigherPrecisionBalance::from(liquidity)
+    .checked_mul(burn_percent)
+    .unwrap()
+    .checked_div(1000)
+    .unwrap();
+  u64::try_from(burn_amount).unwrap()
+}
+
 macro_rules! bvec {
 	($( $x:tt )*) => {
 		vec![$( $x )*].try_into().unwrap()
@@ -1013,15 +1028,16 @@ fn swap_exact_tokens_for_tokens_in_multi_hops() {
     assert_ok!(CoinsPallet::<Test>::mint(user, Balance { coin: coin2, amount: Amount(base2) }));
     assert_ok!(CoinsPallet::<Test>::mint(user, Balance { coin: coin3, amount: Amount(base2) }));
 
-    let liquidity1 = 10000;
-    let liquidity2 = 200;
+    let liquidity1_pool1 = 10000;
+    let mut liquidity1_pool2 = liquidity1_pool1;
+    let mut liquidity2 = 200;
     let liquidity3 = 2000;
 
     assert_ok!(Dex::add_liquidity(
       RuntimeOrigin::signed(user),
       coin2,
       liquidity2,
-      liquidity1,
+      liquidity1_pool1,
       1,
       1,
       user,
@@ -1030,15 +1046,15 @@ fn swap_exact_tokens_for_tokens_in_multi_hops() {
       RuntimeOrigin::signed(user),
       coin3,
       liquidity3,
-      liquidity1,
+      liquidity1_pool2,
       1,
       1,
       user,
     ));
 
     let input_amount = 500;
-    let expect_out2 = Dex::get_amount_out(input_amount, liquidity2, liquidity1).ok().unwrap();
-    let expect_out3 = Dex::get_amount_out(expect_out2, liquidity1, liquidity3).ok().unwrap();
+    let expect_out2 = Dex::get_amount_out(input_amount, liquidity2, liquidity1_pool1).ok().unwrap();
+    let expect_out3 = Dex::get_amount_out(expect_out2, liquidity1_pool2, liquidity3).ok().unwrap();
 
     assert_noop!(
       Dex::swap_exact_tokens_for_tokens(
@@ -1070,6 +1086,13 @@ fn swap_exact_tokens_for_tokens_in_multi_hops() {
       user,
     ));
 
+    // burn half of the taken fees
+    let burn_amount = get_burn_amount(liquidity2);
+    liquidity2 -= burn_amount;
+
+    let burn_amount = get_burn_amount(liquidity1_pool2);
+    liquidity1_pool2 -= burn_amount;
+
     let pool_id1 = Dex::get_pool_id(coin1, coin2).unwrap();
     let pool_id2 = Dex::get_pool_id(coin1, coin3).unwrap();
     let pallet_account1 = Dex::get_pool_account(pool_id1);
@@ -1077,8 +1100,8 @@ fn swap_exact_tokens_for_tokens_in_multi_hops() {
 
     assert_eq!(balance(user, coin2), base2 - liquidity2 - input_amount);
     assert_eq!(balance(pallet_account1, coin2), liquidity2 + input_amount);
-    assert_eq!(balance(pallet_account1, coin1), liquidity1 - expect_out2);
-    assert_eq!(balance(pallet_account2, coin1), liquidity1 + expect_out2);
+    assert_eq!(balance(pallet_account1, coin1), liquidity1_pool1 - expect_out2);
+    assert_eq!(balance(pallet_account2, coin1), liquidity1_pool2 + expect_out2);
     assert_eq!(balance(pallet_account2, coin3), liquidity3 - expect_out3);
     assert_eq!(balance(user, coin3), 10000 - liquidity3 + expect_out3);
   });

substrate/runtime/src/lib.rs

@@ -214,7 +214,8 @@ impl coins::Config<coins::Instance1> for Runtime {
 impl dex::Config for Runtime {
   type RuntimeEvent = RuntimeEvent;
 
-  type LPFee = ConstU32<3>; // 0.3%
+  // 0.6% in total but only half will go to LPs(0.3%) other half to be burned.
+  type LPFee = ConstU32<6>;
   type MintMinLiquidity = ConstU64<10000>;
 
   type MaxSwapPathLength = ConstU32<3>; // coin1 -> SRI -> coin2