Use static 0.3% exchange fee rate and fix set_fee_point

Author: icodezjb

README.md

@@ -27,7 +27,6 @@ Through the `UAI`(unified asset identifier) and `MultiAssetsHandler` interfaces,
 ## Zenlink Protocol v0.4.0 Features
 - Based on the `newest` XCM design
 - Based on `FRAMEv2`
-- Swap exchange fee `configurable`
 - `Compatible` Polkadot XCMP cross-chain asset processing
 - Zenlink Protocol registration whitelist-XCM `trust collection management`
 - Through Transfer-By-XCM, `assets can flow freely` between parachains

example/runtime/src/zenlink.rs

@@ -14,7 +14,6 @@ use super::{
 
 parameter_types! {
 	pub const ZenlinkPalletId: PalletId = PalletId(*b"/zenlink");
-	pub const GetExchangeFee: (u32, u32) = (3, 1000);   // 0.3%
 	pub SelfParaId: u32 = ParachainInfo::get().into();
 
 	// xcm
@@ -132,7 +131,6 @@ pub type MultiAssets = ZenlinkMultiAssets<ZenlinkProtocol, Balances, LocalAssetA
 
 impl zenlink_protocol::Config for Runtime {
 	type Event = Event;
-	type GetExchangeFee = GetExchangeFee;
 	type MultiAssetsHandler = MultiAssets;
 	type PalletId = ZenlinkPalletId;
 	type SelfParaId = SelfParaId;

zenlink-protocol/src/README.md

@@ -9,7 +9,6 @@ Through the `UAI`(unified asset identifier) and `MultiAssetsHandler` interfaces,
 ## Zenlink Protocol v0.4.0 Features
 - Based on the `newest` XCM design
 - Based on `FRAMEv2`
-- Swap exchange fee rate `configurable`
 - `Compatible` Polkadot XCMP cross-chain asset processing
 - Zenlink Protocol registration whitelist-XCM `trust collection management`
 - Through Transfer-By-XCM, `assets can flow freely` between parachains

zenlink-protocol/src/fee/mock.rs

@@ -32,7 +32,6 @@ parameter_types! {
 
 	pub const BlockHashCount: u64 = 250;
 	pub const ZenlinkPalletId: PalletId = PalletId(*b"/zenlink");
-	pub const GetExchangeFee: (u32, u32) = (3, 1000);   // 0.3%
 	pub const MaxReserves: u32 = 50;
 }
 
@@ -76,7 +75,6 @@ impl pallet_balances::Config for Test {
 
 impl Config for Test {
 	type Event = Event;
-	type GetExchangeFee = GetExchangeFee;
 	type MultiAssetsHandler = ZenlinkMultiAssets<Zenlink, Balances>;
 	type PalletId = ZenlinkPalletId;
 	type TargetChains = ();

zenlink-protocol/src/fee/tests.rs

@@ -66,6 +66,11 @@ fn fee_meta_setter_should_not_work() {
 			DexPallet::set_fee_point(Origin::signed(BOB), 0),
 			Error::<Test>::RequireProtocolAdmin
 		);
+
+		assert_noop!(
+			DexPallet::set_fee_point(Origin::signed(ALICE), 31u8),
+			Error::<Test>::InvalidFeePoint
+		);
 	})
 }
 
@@ -278,11 +283,12 @@ fn turn_on_protocol_fee_remove_liquidity_should_work() {
 fn turn_on_protocol_fee_swap_have_fee_should_work() {
 	new_test_ext().execute_with(|| {
 		// 1. turn on the protocol fee
-		// use default rate: 1/6
 
 		let sorted_pair = DexPallet::sort_asset_id(DOT_ASSET_ID, BTC_ASSET_ID);
 
 		assert_ok!(DexPallet::set_fee_receiver(Origin::signed(ALICE), Some(BOB)));
+		// use default rate: 0.3% * 1 / 6 = 0.0005
+		assert_ok!(DexPallet::set_fee_point(Origin::signed(ALICE), 5u8));
 		assert_eq!(DexPallet::k_last(sorted_pair), 0);
 
 		// 2. first add_liquidity

zenlink-protocol/src/foreign/mock.rs

@@ -32,7 +32,6 @@ parameter_types! {
 
 	pub const BlockHashCount: u64 = 250;
 	pub const ZenlinkPalletId: PalletId = PalletId(*b"/zenlink");
-	pub const GetExchangeFee: (u32, u32) = (3, 1000);   // 0.3%
 	pub const MaxReserves: u32 = 50;
 }
 
@@ -76,7 +75,6 @@ impl pallet_balances::Config for Test {
 
 impl Config for Test {
 	type Event = Event;
-	type GetExchangeFee = GetExchangeFee;
 	type MultiAssetsHandler = ZenlinkMultiAssets<Zenlink, Balances>;
 	type PalletId = ZenlinkPalletId;
 	type TargetChains = ();

zenlink-protocol/src/lib.rs

@@ -18,7 +18,7 @@ use frame_support::{
 	PalletId, RuntimeDebug,
 };
 use sp_core::U256;
-use sp_runtime::traits::{AccountIdConversion, Hash, IntegerSquareRoot, One, StaticLookup, UniqueSaturatedInto, Zero};
+use sp_runtime::traits::{AccountIdConversion, Hash, IntegerSquareRoot, One, StaticLookup, Zero};
 use sp_std::{convert::TryInto, marker::PhantomData, prelude::*};
 
 // -------xcm--------
@@ -67,12 +67,6 @@ pub mod pallet {
 	pub trait Config: frame_system::Config {
 		/// Because this pallet emits events, it depends on the runtime's definition of an event.
 		type Event: From<Event<Self>> + IsType<<Self as frame_system::Config>::Event>;
-		/// Trading fee rate
-		/// The first item of the tuple is the numerator of the fee rate, second
-		/// item is the denominator, fee_rate = numerator / denominator,
-		/// use (u32, u32) over `Rate` type to minimize internal division operation.
-		#[pallet::constant]
-		type GetExchangeFee: Get<(u32, u32)>;
 		/// The assets interface beyond native currency and other assets.
 		type MultiAssetsHandler: MultiAssetsHandler<Self::AccountId>;
 		/// This pallet id.
@@ -147,8 +141,10 @@ pub mod pallet {
 		pub fee_admin: T::AccountId,
 		/// The receiver of the protocol fee.
 		pub fee_receiver: Option<T::AccountId>,
-		/// The fee point which integer between [0,256),
-		/// 0 means 100% new liquidity and 255 means 1/256.
+		/// The fee point which integer between [0,30]
+		/// 0 means no protocol fee.
+		/// 30 means 0.3% * 100% = 0.0030.
+		/// default is 5 and means 0.3% * 1 / 6 = 0.0005.
 		pub fee_point: u8,
 	}
 
@@ -230,6 +226,8 @@ pub mod pallet {
 	pub enum Error<T> {
 		/// Require the admin who can reset the admin and receiver of the protocol fee.
 		RequireProtocolAdmin,
+		/// Invalid fee_point
+		InvalidFeePoint,
 		/// Unsupported AssetId by this ZenlinkProtocol Version.
 		UnsupportedAssetType,
 		/// Account balance must be greater than or equal to the transfer amount.
@@ -329,12 +327,15 @@ pub mod pallet {
 		/// # Arguments
 		///
 		/// - `fee_point`:
-		/// The fee point which integer between [0,256),
-		/// 0 means mint 100% new liquidity and 255 means 1/256.
+		/// The fee_point which integer between [0,30]
+		/// 0 means no protocol fee.
+		/// 30 means 0.3% * 100% = 0.0030.
+		/// default is 5 and means 0.3% * 1 / 6 = 0.0005.
 		#[pallet::weight(1_000_000)]
 		pub fn set_fee_point(origin: OriginFor<T>, fee_point: u8) -> DispatchResult {
 			let origin = ensure_signed(origin)?;
 			ensure!(origin == Self::fee_meta().0, Error::<T>::RequireProtocolAdmin);
+			ensure!(fee_point <= 30, Error::<T>::InvalidFeePoint);
 
 			FeeMeta::<T>::mutate(|fee_meta| (*fee_meta).2 = fee_point);
 

zenlink-protocol/src/liquidity/mock.rs

@@ -32,7 +32,6 @@ parameter_types! {
 
 	pub const BlockHashCount: u64 = 250;
 	pub const ZenlinkPalletId: PalletId = PalletId(*b"/zenlink");
-	pub const GetExchangeFee: (u32, u32) = (3, 1000);   // 0.3%
 	pub const MaxReserves: u32 = 50;
 }
 
@@ -76,7 +75,6 @@ impl pallet_balances::Config for Test {
 
 impl Config for Test {
 	type Event = Event;
-	type GetExchangeFee = GetExchangeFee;
 	type MultiAssetsHandler = ZenlinkMultiAssets<Zenlink, Balances>;
 	type PalletId = ZenlinkPalletId;
 	type TargetChains = ();

zenlink-protocol/src/swap/mock.rs

@@ -32,7 +32,6 @@ parameter_types! {
 
 	pub const BlockHashCount: u64 = 250;
 	pub const ZenlinkPalletId: PalletId = PalletId(*b"/zenlink");
-	pub const GetExchangeFee: (u32, u32) = (3, 1000);   // 0.3%
 	pub const MaxReserves: u32 = 50;
 }
 
@@ -76,7 +75,6 @@ impl pallet_balances::Config for Test {
 
 impl Config for Test {
 	type Event = Event;
-	type GetExchangeFee = GetExchangeFee;
 	type MultiAssetsHandler = ZenlinkMultiAssets<Zenlink, Balances>;
 	type PalletId = ZenlinkPalletId;
 	type TargetChains = ();

zenlink-protocol/src/swap/mod.rs

@@ -92,7 +92,7 @@ impl<T: Config> Pallet<T> {
 
 				let mint_fee = Self::mint_protocol_fee(reserve_0, reserve_1, asset_0, asset_1, *total_liquidity);
 				if let Some(fee_to) = Self::fee_meta().1 {
-					if mint_fee > 0 {
+					if mint_fee > 0 && Self::fee_meta().2 > 0 {
 						Self::mutate_liquidity(asset_0, asset_1, &fee_to, mint_fee, true)?;
 
 						let old_total_liquidity = *total_liquidity;
@@ -116,12 +116,14 @@ impl<T: Config> Pallet<T> {
 				T::MultiAssetsHandler::transfer(asset_1, who, &pair_account, amount_1)?;
 
 				if let Some(_fee_to) = Self::fee_meta().1 {
-					// update reserve_0 and reserve_1
-					let reserve_0 = T::MultiAssetsHandler::balance_of(asset_0, pair_account);
-					let reserve_1 = T::MultiAssetsHandler::balance_of(asset_1, pair_account);
+					if Self::fee_meta().2 > 0 {
+						// update reserve_0 and reserve_1
+						let reserve_0 = T::MultiAssetsHandler::balance_of(asset_0, pair_account);
+						let reserve_1 = T::MultiAssetsHandler::balance_of(asset_1, pair_account);
 
-					// We allow reserve_0.saturating_mul(reserve_1) to overflow
-					Self::mutate_k_last(asset_0, asset_1, reserve_0.saturating_mul(reserve_1));
+						// We allow reserve_0.saturating_mul(reserve_1) to overflow
+						Self::mutate_k_last(asset_0, asset_1, reserve_0.saturating_mul(reserve_1));
+					}
 				}
 
 				Self::deposit_event(Event::LiquidityAdded(
@@ -170,7 +172,7 @@ impl<T: Config> Pallet<T> {
 
 				let mint_fee = Self::mint_protocol_fee(reserve_0, reserve_1, asset_0, asset_1, *total_liquidity);
 				if let Some(fee_to) = Self::fee_meta().1 {
-					if mint_fee > 0 {
+					if mint_fee > 0 && Self::fee_meta().2 > 0 {
 						Self::mutate_liquidity(asset_0, asset_1, &fee_to, mint_fee, true)?;
 
 						let old_total_liquidity = *total_liquidity;
@@ -190,12 +192,14 @@ impl<T: Config> Pallet<T> {
 				T::MultiAssetsHandler::transfer(asset_1, &pair_account, recipient, amount_1)?;
 
 				if let Some(_fee_to) = Self::fee_meta().1 {
-					// update reserve_0 and reserve_1
-					let reserve_0 = T::MultiAssetsHandler::balance_of(asset_0, pair_account);
-					let reserve_1 = T::MultiAssetsHandler::balance_of(asset_1, pair_account);
+					if Self::fee_meta().2 > 0 {
+						// update reserve_0 and reserve_1
+						let reserve_0 = T::MultiAssetsHandler::balance_of(asset_0, pair_account);
+						let reserve_1 = T::MultiAssetsHandler::balance_of(asset_1, pair_account);
 
-					// We allow reserve_0.saturating_mul(reserve_1) to overflow
-					Self::mutate_k_last(asset_0, asset_1, reserve_0.saturating_mul(reserve_1));
+						// We allow reserve_0.saturating_mul(reserve_1) to overflow
+						Self::mutate_k_last(asset_0, asset_1, reserve_0.saturating_mul(reserve_1));
+					}
 				}
 
 				Self::deposit_event(Event::LiquidityRemoved(
@@ -303,7 +307,7 @@ impl<T: Config> Pallet<T> {
 	}
 
 	/// Refer: https://github.com/Uniswap/uniswap-v2-core/blob/master/contracts/UniswapV2Pair.sol#L88
-	/// Take as a 1/(fee_point+1) cut of the ExchangeFeeRate fees earned by liquidity providers
+	/// Take as a [0, 100%] cut of the exchange fees earned by liquidity providers
 	pub(crate) fn mint_protocol_fee(
 		reserve_0: AssetBalance,
 		reserve_1: AssetBalance,
@@ -315,16 +319,18 @@ impl<T: Config> Pallet<T> {
 		let mut mint_fee: AssetBalance = 0;
 
 		if let Some(_fee_to) = Self::fee_meta().1 {
-			if new_k_last != 0 {
+			if new_k_last != 0 && Self::fee_meta().2 > 0 {
 				// u128 support integer_sqrt, but U256 not support
 				// thus we allow reserve_0.saturating_mul(reserve_1) to overflow
 				let root_k = U256::from(reserve_0.saturating_mul(reserve_1).integer_sqrt());
 				let root_k_last = U256::from(new_k_last.integer_sqrt());
 				if root_k > root_k_last {
 					let fee_point = Self::fee_meta().2;
+					let fix_fee_point = (30 - fee_point) / fee_point;
 					let numerator = U256::from(total_liquidity).saturating_mul(root_k.saturating_sub(root_k_last));
-
-					let denominator = root_k.saturating_mul(U256::from(fee_point)).saturating_add(root_k_last);
+					let denominator = root_k
+						.saturating_mul(U256::from(fix_fee_point))
+						.saturating_add(root_k_last);
 
 					let liquidity = numerator
 						.checked_div(denominator)
@@ -389,6 +395,7 @@ impl<T: Config> Pallet<T> {
 		})
 	}
 
+	// 0.3% exchange fee rate
 	fn get_amount_in(
 		output_amount: AssetBalance,
 		input_reserve: AssetBalance,
@@ -398,14 +405,12 @@ impl<T: Config> Pallet<T> {
 			return Zero::zero();
 		}
 
-		let (fee_numerator, fee_denominator) = T::GetExchangeFee::get();
-
 		let numerator = U256::from(input_reserve)
 			.saturating_mul(U256::from(output_amount))
-			.saturating_mul(U256::from(fee_denominator));
+			.saturating_mul(U256::from(1000));
 
-		let denominator = (U256::from(output_reserve).saturating_sub(U256::from(output_amount)))
-			.saturating_mul(U256::from(fee_denominator.saturating_sub(fee_numerator)));
+		let denominator =
+			(U256::from(output_reserve).saturating_sub(U256::from(output_amount))).saturating_mul(U256::from(997));
 
 		numerator
 			.checked_div(denominator)
@@ -414,6 +419,7 @@ impl<T: Config> Pallet<T> {
 			.unwrap_or_else(Zero::zero)
 	}
 
+	// 0.3% exchange fee rate
 	fn get_amount_out(
 		input_amount: AssetBalance,
 		input_reserve: AssetBalance,
@@ -423,16 +429,12 @@ impl<T: Config> Pallet<T> {
 			return Zero::zero();
 		}
 
-		let (fee_numerator, fee_denominator) = T::GetExchangeFee::get();
-
-		let input_amount_with_fee = U256::from(
-			input_amount.saturating_mul(fee_denominator.saturating_sub(fee_numerator).unique_saturated_into()),
-		);
+		let input_amount_with_fee = U256::from(input_amount).saturating_mul(U256::from(997));
 
 		let numerator = input_amount_with_fee.saturating_mul(U256::from(output_reserve));
 
 		let denominator = U256::from(input_reserve)
-			.saturating_mul(U256::from(fee_denominator))
+			.saturating_mul(U256::from(1000))
 			.saturating_add(input_amount_with_fee);
 
 		numerator