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Declare a smaller gas limit for bounded read-only EVM calls #216

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47 changes: 47 additions & 0 deletions cadence/contracts/bridge/FlowEVMBridgeConfig.cdc
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Original file line number Diff line number Diff line change
Expand Up @@ -101,6 +101,40 @@ contract FlowEVMBridgeConfig {
return self.paused
}

/// StoragePath at which an operator-set read gas limit is stored, if one has been set
///
access(all)
view fun readGasLimitStoragePath(): StoragePath {
return /storage/flowEVMBridgeReadGasLimit
}

/// Returns the read gas limit applied when no operator override has been set
///
access(all)
view fun defaultReadGasLimit(): UInt64 {
return 500_000
}

/// Returns the gas limit the bridge declares for read-only EVM calls whose cost is bounded by the
/// ERC20/ERC721 standards, such as decimals(), balanceOf(address) and ownerOf(uint256).
///
/// A limit smaller than `gasLimit` matters because the FVM admits an EVM call only if the remaining Cadence
/// computation budget covers the *declared* gas limit, not the gas the call actually consumes. At the mainnet
/// execution effort weight for EVM gas, a declared limit of 15,000,000 reserves roughly 1,600 of the 9,999
/// computation units a transaction may spend, so a single cheap read can be refused with most of the budget
/// still unspent. Reads whose cost is not bounded by the standards, notably tokenURI and contractURI, keep
/// using `gasLimit` because they may run arbitrary on-chain metadata generation.
///
/// This is a function reading from account storage rather than a contract field because Cadence rejects a
/// contract update that adds a field to an already deployed contract, and the bridge is live on Mainnet and
/// Testnet. Storage holds a value only once an operator sets one; otherwise the default applies.
///
access(all)
view fun readGasLimit(): UInt64 {
return self.account.storage.copy<UInt64>(from: self.readGasLimitStoragePath())
?? self.defaultReadGasLimit()
}

/// Returns whether operations for a given Type are paused.
///
/// Note: the return type is `Bool?` for API compatibility, but this function currently always returns a
Expand Down Expand Up @@ -503,6 +537,19 @@ contract FlowEVMBridgeConfig {
FlowEVMBridgeConfig.gasLimit = limit
}

/// Sets the gas limit for read-only EVM calls whose cost is bounded by the ERC20/ERC721 standards.
/// The value is kept in account storage rather than a contract field so that this can ship as a
/// contract update; see FlowEVMBridgeConfig.readGasLimit().
///
/// @param limit the new read gas limit
///
access(Gas)
fun setReadGasLimit(_ limit: UInt64) {
let path = FlowEVMBridgeConfig.readGasLimitStoragePath()
let _ = FlowEVMBridgeConfig.account.storage.load<UInt64>(from: path)
FlowEVMBridgeConfig.account.storage.save(limit, to: path)
}

/// Updates the onboarding fee
///
/// @param new: UFix64 - new onboarding fee
Expand Down
6 changes: 3 additions & 3 deletions cadence/contracts/bridge/FlowEVMBridgeHandlers.cdc
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Expand Up @@ -282,7 +282,7 @@ access(all) contract FlowEVMBridgeHandlers {
// Confirm bridge COA's WFLOW balance has incremented by the expected amount
assert(
postBalance - preBalance == uintAmount,
message: "Escrowed WFLOW balance after wrapping does not match requested amount - expected: \(preBalance + uintAmount).toString()) | actual: \(postBalance - preBalance).toString())"
message: "Escrowed WFLOW balance after wrapping does not match requested amount - expected: \((preBalance + uintAmount).toString()) | actual: \((postBalance - preBalance).toString())"
)

// Transfer WFLOW to recipient
Expand Down Expand Up @@ -315,7 +315,7 @@ access(all) contract FlowEVMBridgeHandlers {
)
assert(
ufixAmount > 0.0,
message: "Requested UInt256 amount \(amount.toString()) converted to 0.0 - try bridging a larger amount to avoid UFix64 precision loss during conversion"
message: "Requested UInt256 amount \(amount.toString()) converted to 0.0 - try bridging a larger amount to avoid UFix64 precision loss during conversion"
)

// Transfers WFLOW to bridge COA as escrow
Expand Down Expand Up @@ -351,7 +351,7 @@ access(all) contract FlowEVMBridgeHandlers {
// Confirm bridge COA's FLOW balance has incremented by the expected amount
assert(
UInt256(postBalance - preBalance) == amount,
message: "Escrowed WFLOW balance after unwrapping does not match requested amount - expected: \(UInt256(preBalance) + amount).toString()) | actual: \(postBalance - preBalance).toString())"
message: "Escrowed WFLOW balance after unwrapping does not match requested amount - expected: \((UInt256(preBalance) + amount).toString()) | actual: \((postBalance - preBalance).toString())"
)

// Withdraw escrowed FLOW from bridge COA.
Expand Down
60 changes: 32 additions & 28 deletions cadence/contracts/bridge/FlowEVMBridgeUtils.cdc
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Original file line number Diff line number Diff line change
Expand Up @@ -193,7 +193,7 @@ contract FlowEVMBridgeUtils {
signature: "allowsBridging()",
targetEVMAddress: address,
args: [],
gasLimit: FlowEVMBridgeConfig.gasLimit,
gasLimit: FlowEVMBridgeConfig.readGasLimit(),
value: 0.0,
resultTypes: [Type<Bool>()]
)
Expand Down Expand Up @@ -260,7 +260,7 @@ contract FlowEVMBridgeUtils {
signature: "isBridgeDeployed(address)",
targetEVMAddress: self.bridgeFactoryEVMAddress,
args: [evmContractAddress],
gasLimit: FlowEVMBridgeConfig.gasLimit,
gasLimit: FlowEVMBridgeConfig.readGasLimit(),
value: 0.0,
resultTypes: [Type<Bool>()]
)
Expand All @@ -283,7 +283,7 @@ contract FlowEVMBridgeUtils {
signature: "isERC721(address)",
targetEVMAddress: self.bridgeFactoryEVMAddress,
args: [evmContractAddress],
gasLimit: FlowEVMBridgeConfig.gasLimit,
gasLimit: FlowEVMBridgeConfig.readGasLimit(),
value: 0.0,
resultTypes: [Type<Bool>()]
)
Expand All @@ -307,7 +307,7 @@ contract FlowEVMBridgeUtils {
signature: "isERC20(address)",
targetEVMAddress: self.bridgeFactoryEVMAddress,
args: [evmContractAddress],
gasLimit: FlowEVMBridgeConfig.gasLimit,
gasLimit: FlowEVMBridgeConfig.readGasLimit(),
value: 0.0,
resultTypes: [Type<Bool>()]
)
Expand All @@ -330,7 +330,7 @@ contract FlowEVMBridgeUtils {
signature: "isValidAsset(address)",
targetEVMAddress: self.bridgeFactoryEVMAddress,
args: [evmContractAddress],
gasLimit: FlowEVMBridgeConfig.gasLimit,
gasLimit: FlowEVMBridgeConfig.readGasLimit(),
value: 0.0,
resultTypes: [Type<Bool>()]
)
Expand Down Expand Up @@ -475,7 +475,7 @@ contract FlowEVMBridgeUtils {
let isERC20 = self.isERC20(evmContractAddress: evmContractAddress)
assert(
isERC20,
message: "Contract \(evmContractAddress.toString())defines an asset that is not currently supported by the bridge"
message: "Contract \(evmContractAddress.toString()) defines an asset that is not currently supported by the bridge"
)
cadenceContractName = self.deriveBridgedTokenContractName(from: evmContractAddress)
decimals = self.getTokenDecimals(evmContractAddress: evmContractAddress)
Expand Down Expand Up @@ -530,7 +530,7 @@ contract FlowEVMBridgeUtils {
signature: "name()",
targetEVMAddress: evmContractAddress,
args: [],
gasLimit: FlowEVMBridgeConfig.gasLimit,
gasLimit: FlowEVMBridgeConfig.readGasLimit(),
value: 0.0,
resultTypes: [Type<String>()]
)
Expand All @@ -554,7 +554,7 @@ contract FlowEVMBridgeUtils {
signature: "symbol()",
targetEVMAddress: evmContractAddress,
args: [],
gasLimit: FlowEVMBridgeConfig.gasLimit,
gasLimit: FlowEVMBridgeConfig.readGasLimit(),
value: 0.0,
resultTypes: [Type<String>()]
)
Expand All @@ -577,6 +577,8 @@ contract FlowEVMBridgeUtils {
signature: "tokenURI(uint256)",
targetEVMAddress: evmContractAddress,
args: [id],
// Uses the full gasLimit rather than readGasLimit: tokenURI may generate metadata on-chain,
// so its cost is not bounded by the ERC721 standard.
gasLimit: FlowEVMBridgeConfig.gasLimit,
value: 0.0,
resultTypes: [Type<String>()]
Expand All @@ -600,6 +602,8 @@ contract FlowEVMBridgeUtils {
signature: "contractURI()",
targetEVMAddress: evmContractAddress,
args: [],
// Uses the full gasLimit rather than readGasLimit: contractURI may generate metadata on-chain,
// so its cost is not bounded by the ERC721 standard.
gasLimit: FlowEVMBridgeConfig.gasLimit,
value: 0.0,
resultTypes: [Type<String>()]
Expand All @@ -622,7 +626,7 @@ contract FlowEVMBridgeUtils {
signature: "decimals()",
targetEVMAddress: evmContractAddress,
args: [],
gasLimit: FlowEVMBridgeConfig.gasLimit,
gasLimit: FlowEVMBridgeConfig.readGasLimit(),
value: 0.0,
resultTypes: [Type<UInt8>()]
)
Expand Down Expand Up @@ -674,7 +678,7 @@ contract FlowEVMBridgeUtils {
signature: "ownerOf(uint256)",
targetEVMAddress: evmContractAddress,
args: [id],
gasLimit: FlowEVMBridgeConfig.gasLimit,
gasLimit: FlowEVMBridgeConfig.readGasLimit(),
value: 0.0,
resultTypes: [Type<EVM.EVMAddress>()]
)
Expand All @@ -698,7 +702,7 @@ contract FlowEVMBridgeUtils {
signature: "getApproved(uint256)",
targetEVMAddress: evmContractAddress,
args: [ofNFT],
gasLimit: FlowEVMBridgeConfig.gasLimit,
gasLimit: FlowEVMBridgeConfig.readGasLimit(),
value: 0.0,
resultTypes: [Type<EVM.EVMAddress>()]
)
Expand All @@ -725,7 +729,7 @@ contract FlowEVMBridgeUtils {
signature: "exists(uint256)",
targetEVMAddress: erc721Address,
args: [id],
gasLimit: FlowEVMBridgeConfig.gasLimit,
gasLimit: FlowEVMBridgeConfig.readGasLimit(),
value: 0.0,
resultTypes: [Type<Bool>()]
)
Expand All @@ -747,7 +751,7 @@ contract FlowEVMBridgeUtils {
signature: "balanceOf(address)",
targetEVMAddress: evmContractAddress,
args: [owner],
gasLimit: FlowEVMBridgeConfig.gasLimit,
gasLimit: FlowEVMBridgeConfig.readGasLimit(),
value: 0.0,
resultTypes: [Type<UInt256>()]
)
Expand Down Expand Up @@ -782,7 +786,7 @@ contract FlowEVMBridgeUtils {
signature: "totalSupply()",
targetEVMAddress: evmContractAddress,
args: [],
gasLimit: FlowEVMBridgeConfig.gasLimit,
gasLimit: FlowEVMBridgeConfig.readGasLimit(),
value: 0.0,
resultTypes: [Type<UInt256>()]
)
Expand Down Expand Up @@ -854,7 +858,7 @@ contract FlowEVMBridgeUtils {
signature: "getCadenceAddress()",
targetEVMAddress: evmContract,
args: [],
gasLimit: FlowEVMBridgeConfig.gasLimit,
gasLimit: FlowEVMBridgeConfig.readGasLimit(),
value: 0.0,
resultTypes: [Type<String>()]
)
Expand Down Expand Up @@ -885,7 +889,7 @@ contract FlowEVMBridgeUtils {
signature: "getCadenceIdentifier()",
targetEVMAddress: evmContract,
args: [],
gasLimit: FlowEVMBridgeConfig.gasLimit,
gasLimit: FlowEVMBridgeConfig.readGasLimit(),
value: 0.0,
resultTypes: [Type<String>()]
)
Expand All @@ -912,7 +916,7 @@ contract FlowEVMBridgeUtils {
signature: "supportsInterface(bytes4)",
targetEVMAddress: evmContract,
args: [interfaceID],
gasLimit: FlowEVMBridgeConfig.gasLimit,
gasLimit: FlowEVMBridgeConfig.readGasLimit(),
value: 0.0,
resultTypes: [Type<Bool>()]
)
Expand Down Expand Up @@ -940,7 +944,7 @@ contract FlowEVMBridgeUtils {
signature: "supportsInterface(bytes4)",
targetEVMAddress: evmContract,
args: [interfaceID],
gasLimit: FlowEVMBridgeConfig.gasLimit,
gasLimit: FlowEVMBridgeConfig.readGasLimit(),
value: 0.0,
resultTypes: [Type<Bool>()]
)
Expand Down Expand Up @@ -979,7 +983,7 @@ contract FlowEVMBridgeUtils {
signature: "vmBridgeAddress()",
targetEVMAddress: evmContract,
args: [],
gasLimit: FlowEVMBridgeConfig.gasLimit,
gasLimit: FlowEVMBridgeConfig.readGasLimit(),
value: 0.0,
resultTypes: [Type<EVM.EVMAddress>()]
)
Expand Down Expand Up @@ -1585,18 +1589,18 @@ contract FlowEVMBridgeUtils {
erc20Address: EVM.EVMAddress,
protectedTransferCall: fun (): EVM.ResultDecoded
) {
// Ensure the caller is has sufficient balance to bridge the requested amount
let hasSufficientBalance = self.hasSufficientBalance(
amount: amount,
owner: owner,
evmContractAddress: erc20Address
)
assert(hasSufficientBalance, message: "Caller does not have sufficient balance to bridge requested tokens")
let bridgeCOAAddress = self.getBridgeCOAEVMAddress()

// Get the owner and escrow balances before transfer
let ownerPreBalance = self.balanceOf(owner: owner, evmContractAddress: erc20Address)

// Ensure the caller has sufficient balance to bridge the requested amount. The owner's pre-transfer
// balance read above answers this, so calling hasSufficientBalance would repeat an identical
// balanceOf(address) call for a value already in scope.
assert(ownerPreBalance >= amount, message: "Caller does not have sufficient balance to bridge requested tokens")

let bridgePreBalance = self.balanceOf(
owner: self.getBridgeCOAEVMAddress(),
owner: bridgeCOAAddress,
evmContractAddress: erc20Address
)

Expand All @@ -1607,7 +1611,7 @@ contract FlowEVMBridgeUtils {
// Get the resulting balances after transfer
let ownerPostBalance = self.balanceOf(owner: owner, evmContractAddress: erc20Address)
let bridgePostBalance = self.balanceOf(
owner: self.getBridgeCOAEVMAddress(),
owner: bridgeCOAAddress,
evmContractAddress: erc20Address
)

Expand Down
11 changes: 11 additions & 0 deletions cadence/scripts/bridge/get_read_gas_limit.cdc
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Original file line number Diff line number Diff line change
@@ -0,0 +1,11 @@
import "FlowEVMBridgeConfig"

/// Returns the gas limit the bridge declares for read-only EVM calls whose cost is bounded by the
/// ERC20/ERC721 standards, such as decimals(), balanceOf(address) and ownerOf(uint256).
///
/// @returns The current read gas limit.
///
access(all)
fun main(): UInt64 {
return FlowEVMBridgeConfig.readGasLimit()
}
2 changes: 1 addition & 1 deletion cadence/scripts/utils/get_deployer_address.cdc
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Expand Up @@ -13,7 +13,7 @@ fun main(coaHost: Address, deployerTag: String): String {
to: FlowEVMBridgeUtils.getBridgeFactoryEVMAddress(),
signature: "getDeployer(string)",
args: [deployerTag],
gasLimit: FlowEVMBridgeConfig.gasLimit,
gasLimit: FlowEVMBridgeConfig.readGasLimit(),
value: 0,
resultTypes: [Type<EVM.EVMAddress>()]
)
Expand Down
2 changes: 1 addition & 1 deletion cadence/scripts/utils/get_registry_address.cdc
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Expand Up @@ -13,7 +13,7 @@ fun main(coaHost: Address): String {
to: FlowEVMBridgeUtils.getBridgeFactoryEVMAddress(),
signature: "getRegistry()",
args: [],
gasLimit: FlowEVMBridgeConfig.gasLimit,
gasLimit: FlowEVMBridgeConfig.readGasLimit(),
value: 0,
resultTypes: [Type<EVM.EVMAddress>()]
)
Expand Down
30 changes: 30 additions & 0 deletions cadence/tests/flow_evm_bridge_tests.cdc
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Expand Up @@ -115,6 +115,36 @@ fun testSetGasLimitSucceeds() {
Test.reset(to: snapshot)
}

access(all)
fun testSetReadGasLimitSucceeds() {

fun getReadGasLimit(): UInt64 {
let readGasLimitResult = executeScript(
"../scripts/bridge/get_read_gas_limit.cdc",
[]
)
Test.expect(readGasLimitResult, Test.beSucceeded())
return readGasLimitResult.returnValue as! UInt64? ?? panic("Problem getting read gas limit")
}

snapshot = getCurrentBlockHeight()

let preReadGasLimit = getReadGasLimit()
let readGasLimit = preReadGasLimit + 1_000

let setReadGasLimitResult = executeTransaction(
"../transactions/bridge/admin/gas/set_read_gas_limit.cdc",
[readGasLimit],
bridgeAccount
)
Test.expect(setReadGasLimitResult, Test.beSucceeded())

let postReadGasLimit = getReadGasLimit()
Test.assertEqual(readGasLimit, postReadGasLimit)

Test.reset(to: snapshot)
}

/* --- ASSET & ACCOUNT SETUP - Configure test accounts with assets to bridge --- */

access(all)
Expand Down
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