update token bridge fee approximation

onflow · Oct 25, 2024 · 2e871cb · 2e871cb
1 parent 3df1914
commit 2e871cb
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Showing 4 changed files with 14 additions and 16 deletions.
diff --git a/cadence/transactions/bridge/tokens/bridge_tokens_from_evm.cdc b/cadence/transactions/bridge/tokens/bridge_tokens_from_evm.cdc
@@ -74,8 +74,10 @@ transaction(vaultIdentifier: String, amount: UInt256) {
 
         /* --- Configure a ScopedFTProvider --- */
         //
-        // Calculate the bridge fee - bridging from EVM consumes no storage, so flat fee
-        let approxFee = FlowEVMBridgeUtils.calculateBridgeFee(bytes: 0)
+        // Set a cap on the withdrawable bridge fee
+        var approxFee = FlowEVMBridgeUtils.calculateBridgeFee(
+                bytes: 200_000 // 200 kB as upper bound on movable storage used in a single transaction
+            )
         // Issue and store bridge-dedicated Provider Capability in storage if necessary
         if signer.storage.type(at: FlowEVMBridgeConfig.providerCapabilityStoragePath) == nil {
             let providerCap = signer.capabilities.storage.issue<auth(FungibleToken.Withdraw) &{FungibleToken.Provider}>(

diff --git a/cadence/transactions/bridge/tokens/bridge_tokens_to_any_cadence_address.cdc b/cadence/transactions/bridge/tokens/bridge_tokens_to_any_cadence_address.cdc
@@ -77,8 +77,10 @@ transaction(vaultIdentifier: String, amount: UInt256, recipient: Address) {
 
         /* --- Configure a ScopedFTProvider --- */
         //
-        // Calculate the bridge fee - bridging from EVM consumes no storage, so flat fee
-        let approxFee = FlowEVMBridgeUtils.calculateBridgeFee(bytes: 0)
+        // Set a cap on the withdrawable bridge fee
+        var approxFee = FlowEVMBridgeUtils.calculateBridgeFee(
+                bytes: 200_000 // 200 kB as upper bound on movable storage used in a single transaction
+            )
         // Issue and store bridge-dedicated Provider Capability in storage if necessary
         if signer.storage.type(at: FlowEVMBridgeConfig.providerCapabilityStoragePath) == nil {
             let providerCap = signer.capabilities.storage.issue<auth(FungibleToken.Withdraw) &{FungibleToken.Provider}>(

diff --git a/cadence/transactions/bridge/tokens/bridge_tokens_to_any_evm_address.cdc b/cadence/transactions/bridge/tokens/bridge_tokens_to_any_evm_address.cdc
@@ -54,14 +54,11 @@ transaction(vaultIdentifier: String, amount: UFix64, recipient: String) {
                 from: vaultData.storagePath
             ) ?? panic("Could not access signer's FungibleToken Vault")
 
-        // Withdraw the requested balance & calculate the approximate bridge fee based on storage usage
-        let currentStorageUsage = signer.storage.used
+        // Withdraw the requested balance & set a cap on the withdrawable bridge fee
         self.sentVault <- vault.withdraw(amount: amount)
-        let withdrawnStorageUsage = signer.storage.used
-        // Approximate the bridge fee based on the difference in storage usage with some buffer
         var approxFee = FlowEVMBridgeUtils.calculateBridgeFee(
-                bytes: currentStorageUsage - withdrawnStorageUsage
-            ) * 1.10
+                bytes: 200_000 // 200 kB as upper bound on movable storage used in a single transaction
+            )
         // Determine if the Vault requires onboarding - this impacts the fee required
         self.requiresOnboarding = FlowEVMBridge.typeRequiresOnboarding(self.sentVault.getType())
             ?? panic("Bridge does not support this asset type")

diff --git a/cadence/transactions/bridge/tokens/bridge_tokens_to_evm.cdc b/cadence/transactions/bridge/tokens/bridge_tokens_to_evm.cdc
@@ -58,14 +58,11 @@ transaction(vaultIdentifier: String, amount: UFix64) {
                 from: vaultData.storagePath
             ) ?? panic("Could not access signer's FungibleToken Vault")
 
-        // Withdraw the requested balance & calculate the approximate bridge fee based on storage usage
-        let currentStorageUsage = signer.storage.used
+        // Withdraw the requested balance & set a cap on the withdrawable bridge fee
         self.sentVault <- vault.withdraw(amount: amount)
-        let withdrawnStorageUsage = signer.storage.used
-        // Approximate the bridge fee based on the difference in storage usage with some buffer
         var approxFee = FlowEVMBridgeUtils.calculateBridgeFee(
-                bytes: currentStorageUsage - withdrawnStorageUsage
-            ) * 1.10
+                bytes: 200_000 // 200 kB as upper bound on movable storage used in a single transaction
+            )
         // Determine if the Vault requires onboarding - this impacts the fee required
         self.requiresOnboarding = FlowEVMBridge.typeRequiresOnboarding(self.sentVault.getType())
             ?? panic("Bridge does not support this asset type")