Add fee multiplier to protocol

contracts/src/DeployScript.sol

@@ -80,7 +80,8 @@ contract DeployScript is Script {
             assetHubAgentID: assetHubAgentID,
             assetHubCreateAssetFee: uint128(vm.envUint("CREATE_ASSET_FEE")),
             assetHubReserveTransferFee: uint128(vm.envUint("RESERVE_TRANSFER_FEE")),
-            exchangeRate: ud60x18(vm.envUint("EXCHANGE_RATE"))
+            exchangeRate: ud60x18(vm.envUint("EXCHANGE_RATE")),
+            multiplier: ud60x18(vm.envUint("FEE_MULTIPLIER"))
         });
 
         GatewayProxy gateway = new GatewayProxy(address(gatewayLogic), abi.encode(config));

contracts/src/Gateway.sol

@@ -390,6 +390,7 @@ contract Gateway is IGateway, IInitializable {
         SetPricingParametersParams memory params = abi.decode(data, (SetPricingParametersParams));
         pricing.exchangeRate = params.exchangeRate;
         pricing.deliveryCost = params.deliveryCost;
+        pricing.multiplier = params.multiplier;
         emit PricingParametersChanged();
     }
 
@@ -462,19 +463,24 @@ contract Gateway is IGateway, IInitializable {
     }
 
     // Convert foreign currency to native currency (ROC/KSM/DOT -> ETH)
-    function _convertToNative(UD60x18 exchangeRate, uint256 amount) internal view returns (uint256) {
+    function _convertToNative(UD60x18 exchangeRate, UD60x18 multiplier, uint256 amount)
+        internal
+        view
+        returns (uint256)
+    {
         UD60x18 amountFP = convert(amount);
         UD60x18 ethDecimals = convert(1e18);
         UD60x18 foreignDecimals = convert(10).pow(convert(uint256(FOREIGN_TOKEN_DECIMALS)));
-        UD60x18 nativeAmountFP = amountFP.mul(exchangeRate).div(foreignDecimals).mul(ethDecimals);
+        UD60x18 nativeAmountFP = multiplier.mul(amountFP).mul(exchangeRate).div(foreignDecimals).mul(ethDecimals);
         uint256 nativeAmount = convert(nativeAmountFP);
         return nativeAmount;
     }
 
     // Calculate the fee for accepting an outbound message
     function _calculateFee(Costs memory costs) internal view returns (uint256) {
         PricingStorage.Layout storage pricing = PricingStorage.layout();
-        return costs.native + _convertToNative(pricing.exchangeRate, pricing.deliveryCost + costs.foreign);
+        return costs.native
+            + _convertToNative(pricing.exchangeRate, pricing.multiplier, pricing.deliveryCost + costs.foreign);
     }
 
     // Submit an outbound message to Polkadot, after taking fees
@@ -569,6 +575,8 @@ contract Gateway is IGateway, IInitializable {
         uint128 assetHubReserveTransferFee;
         /// @dev extra fee to discourage spamming
         uint256 registerTokenFee;
+        /// @dev Fee multiplier
+        UD60x18 multiplier;
     }
 
     /// @dev Initialize storage in the gateway
@@ -613,6 +621,7 @@ contract Gateway is IGateway, IInitializable {
         PricingStorage.Layout storage pricing = PricingStorage.layout();
         pricing.exchangeRate = config.exchangeRate;
         pricing.deliveryCost = config.deliveryCost;
+        pricing.multiplier = config.multiplier;
 
         // Initialize assets storage
         AssetsStorage.Layout storage assets = AssetsStorage.layout();

contracts/src/Params.sol

@@ -79,4 +79,6 @@ struct SetPricingParametersParams {
     UD60x18 exchangeRate;
     /// @dev The cost of delivering messages to BridgeHub in DOT
     uint128 deliveryCost;
+    /// @dev Fee multiplier
+    UD60x18 multiplier;
 }

contracts/src/storage/PricingStorage.sol

@@ -10,6 +10,8 @@ library PricingStorage {
         UD60x18 exchangeRate;
         /// @dev The cost of delivering messages to BridgeHub in DOT
         uint128 deliveryCost;
+        /// @dev Fee multiplier
+        UD60x18 multiplier;
     }
 
     bytes32 internal constant SLOT = keccak256("org.snowbridge.storage.pricing");

contracts/test/Gateway.t.sol

@@ -90,6 +90,7 @@ contract GatewayTest is Test {
 
     // ETH/DOT exchange rate
     UD60x18 public exchangeRate = ud60x18(0.0025e18);
+    UD60x18 public multiplier = ud60x18(1e18);
 
     function setUp() public {
         AgentExecutor executor = new AgentExecutor();
@@ -103,7 +104,8 @@ contract GatewayTest is Test {
             assetHubAgentID: assetHubAgentID,
             assetHubCreateAssetFee: createTokenFee,
             assetHubReserveTransferFee: sendTokenFee,
-            exchangeRate: exchangeRate
+            exchangeRate: exchangeRate,
+            multiplier: multiplier
         });
         gateway = new GatewayProxy(address(gatewayLogic), abi.encode(config));
         GatewayMock(address(gateway)).setCommitmentsAreVerified(true);
@@ -497,7 +499,8 @@ contract GatewayTest is Test {
             assetHubAgentID: assetHubAgentID,
             assetHubCreateAssetFee: createTokenFee,
             assetHubReserveTransferFee: sendTokenFee,
-            exchangeRate: exchangeRate
+            exchangeRate: exchangeRate,
+            multiplier: multiplier
         });
 
         UpgradeParams memory params = UpgradeParams({
@@ -516,7 +519,7 @@ contract GatewayTest is Test {
 
         testSetPricingParameters();
         uint256 fee = IGateway(address(gateway)).quoteRegisterTokenFee();
-        assertEq(fee, 10000000000000000);
+        assertEq(fee, 20000000000000001);
 
         testCreateAgent();
         assertNotEq(GatewayMock(address(gateway)).agentOf(agentID), address(0));
@@ -538,7 +541,7 @@ contract GatewayTest is Test {
 
         // Verify that storage was not overwritten
         fee = IGateway(address(gateway)).quoteRegisterTokenFee();
-        assertEq(fee, 10000000000000000);
+        assertEq(fee, 20000000000000001);
         assertNotEq(GatewayMock(address(gateway)).agentOf(agentID), address(0));
     }
 
@@ -875,14 +878,19 @@ contract GatewayTest is Test {
     function testSetPricingParameters() public {
         uint256 fee = IGateway(address(gateway)).quoteRegisterTokenFee();
         assertEq(fee, 5000000000000000);
-        // Double the exchangeRate
+        // Double the exchangeRate and multiplier.
         GatewayMock(address(gateway)).setPricingParametersPublic(
             abi.encode(
-                SetPricingParametersParams({exchangeRate: exchangeRate.mul(convert(2)), deliveryCost: outboundFee})
+                SetPricingParametersParams({
+                    exchangeRate: exchangeRate.mul(convert(2)),
+                    multiplier: multiplier.mul(convert(2)),
+                    deliveryCost: outboundFee
+                })
             )
         );
+        // Should expect 4x fee increase
         fee = IGateway(address(gateway)).quoteRegisterTokenFee();
-        assertEq(fee, 10000000000000000);
+        assertEq(fee, 20000000000000001);
     }
 
     function testSendTokenToForeignDestWithInvalidFee() public {