Validate debitGasFees execution in tx pool

contracts/erc20gas/erc20gas.go

@@ -8,6 +8,7 @@ import (
 	"github.com/celo-org/celo-blockchain/common"
 	"github.com/celo-org/celo-blockchain/common/hexutil"
 	"github.com/celo-org/celo-blockchain/contracts/internal/n"
+	"github.com/celo-org/celo-blockchain/core/types"
 	"github.com/celo-org/celo-blockchain/core/vm"
 	"github.com/celo-org/celo-blockchain/log"
 )
@@ -17,14 +18,34 @@ const (
 	maxGasForCreditGasFeesTransactions uint64 = 1 * n.Million
 )
 
+var (
+	// Recalculate with `cast sig 'debitGasFees(address from, uint256 value)'`
+	debitGasFeesSelector = hexutil.MustDecode("0x58cf9672")
+	// Recalculate with `cast sig 'creditGasFees(address,address,address,address,uint256,uint256,uint256,uint256)'`
+	creditGasFeesSelector = hexutil.MustDecode("0x6a30b253")
+)
+
+// Returns nil if debit is possible, used in tx pool validation
+func TryDebitFees(tx *types.Transaction, from common.Address, currentVMRunner vm.EVMRunner) error {
+	cost := new(big.Int).SetUint64(tx.Gas())
+	cost.Mul(cost, tx.GasFeeCap())
+
+	// The following code is similar to DebitFees, but that function does not work on a vm.EVMRunner,
+	// so we have to adapt it instead of reusing.
+	transactionData := common.GetEncodedAbi(debitGasFeesSelector, [][]byte{common.AddressToAbi(from), common.AmountToAbi(cost)})
+
+	ret, err := currentVMRunner.ExecuteAndDiscardChanges(*tx.FeeCurrency(), transactionData, maxGasForDebitGasFeesTransactions, common.Big0)
+	if err != nil {
+		revertReason, err2 := abi.UnpackRevert(ret)
+		if err2 == nil {
+			return fmt.Errorf("TryDebitFees reverted: %s", revertReason)
+		}
+	}
+	return err
+}
+
 func DebitFees(evm *vm.EVM, address common.Address, amount *big.Int, feeCurrency *common.Address) error {
-	// Function is "debitGasFees(address from, uint256 value)"
-	// selector is first 4 bytes of keccak256 of "debitGasFees(address,uint256)"
-	// Source:
-	// pip3 install pyethereum
-	// python3 -c 'from ethereum.utils import sha3; print(sha3("debitGasFees(address,uint256)")[0:4].hex())'
-	functionSelector := hexutil.MustDecode("0x58cf9672")
-	transactionData := common.GetEncodedAbi(functionSelector, [][]byte{common.AddressToAbi(address), common.AmountToAbi(amount)})
+	transactionData := common.GetEncodedAbi(debitGasFeesSelector, [][]byte{common.AddressToAbi(address), common.AmountToAbi(amount)})
 
 	// Run only primary evm.Call() with tracer
 	if evm.GetDebug() {
@@ -57,9 +78,7 @@ func CreditFees(
 	gatewayFee *big.Int,
 	baseTxFee *big.Int,
 	feeCurrency *common.Address) error {
-	// Function is "creditGasFees(address,address,address,address,uint256,uint256,uint256,uint256)"
-	functionSelector := hexutil.MustDecode("0x6a30b253")
-	transactionData := common.GetEncodedAbi(functionSelector, [][]byte{common.AddressToAbi(from), common.AddressToAbi(feeRecipient), common.AddressToAbi(*gatewayFeeRecipient), common.AddressToAbi(feeHandler), common.AmountToAbi(refund), common.AmountToAbi(tipTxFee), common.AmountToAbi(gatewayFee), common.AmountToAbi(baseTxFee)})
+	transactionData := common.GetEncodedAbi(creditGasFeesSelector, [][]byte{common.AddressToAbi(from), common.AddressToAbi(feeRecipient), common.AddressToAbi(*gatewayFeeRecipient), common.AddressToAbi(feeHandler), common.AmountToAbi(refund), common.AmountToAbi(tipTxFee), common.AmountToAbi(gatewayFee), common.AmountToAbi(baseTxFee)})
 
 	// Run only primary evm.Call() with tracer
 	if evm.GetDebug() {

contracts/testutil/fail_runner.go

@@ -22,6 +22,10 @@ func (fvm FailingVmRunner) ExecuteFrom(sender, recipient common.Address, input [
 	return nil, ErrFailingRunner
 }
 
+func (fvm FailingVmRunner) ExecuteAndDiscardChanges(recipient common.Address, input []byte, gas uint64, value *big.Int) (ret []byte, err error) {
+	return nil, ErrFailingRunner
+}
+
 func (fvm FailingVmRunner) Query(recipient common.Address, input []byte, gas uint64) (ret []byte, err error) {
 	return nil, ErrFailingRunner
 }

contracts/testutil/runner.go

@@ -50,6 +50,10 @@ func (ev *MockEVMRunner) ExecuteFrom(sender, recipient common.Address, input []b
 	return ev.Execute(recipient, input, gas, value)
 }
 
+func (ev *MockEVMRunner) ExecuteAndDiscardChanges(recipient common.Address, input []byte, gas uint64, value *big.Int) (ret []byte, err error) {
+	return ev.Execute(recipient, input, gas, value)
+}
+
 func (ev *MockEVMRunner) Query(recipient common.Address, input []byte, gas uint64) (ret []byte, err error) {
 	mock, ok := ev.contracts[recipient]
 	if !ok {

core/tx_pool.go

@@ -31,6 +31,7 @@ import (
 	"github.com/celo-org/celo-blockchain/consensus"
 	"github.com/celo-org/celo-blockchain/contracts/blockchain_parameters"
 	"github.com/celo-org/celo-blockchain/contracts/currency"
+	"github.com/celo-org/celo-blockchain/contracts/erc20gas"
 	gpm "github.com/celo-org/celo-blockchain/contracts/gasprice_minimum"
 	"github.com/celo-org/celo-blockchain/core/state"
 	"github.com/celo-org/celo-blockchain/core/types"
@@ -1717,63 +1718,27 @@ func (pool *TxPool) demoteUnexecutables() {
 // ValidateTransactorBalanceCoversTx validates transactor has enough funds to cover transaction cost, the rules are consistent with state_transition.
 //
 // For native token(CELO) as feeCurrency:
-//   - Pre-Espresso: it ensures balance >= GasPrice * gas + value + gatewayFee (1)
-//   - Post-Espresso: it ensures balance >= GasFeeCap * gas + value + gatewayFee (2)
+//   - it ensures balance >= GasFeeCap * gas + value
 //
 // For non-native tokens(cUSD, cEUR, ...) as feeCurrency:
-//   - Pre-Espresso: it ensures balance > GasPrice * gas + gatewayFee (3)
-//   - Post-Espresso: it ensures balance >= GasFeeCap * gas + gatewayFee (4)
+//   - It executes a static call on debitGasFees, implicitly ensuring balance >= GasFeeCap * gas and that `from` is not on the token's block list
 func ValidateTransactorBalanceCoversTx(tx *types.Transaction, from common.Address, currentState *state.StateDB, currentVMRunner vm.EVMRunner, espresso bool) error {
-	if tx.FeeCurrency() == nil {
-		balance := currentState.GetBalance(from)
-		var cost *big.Int
-
-		if espresso {
-			// cost = GasFeeCap * gas + value + gatewayFee, as in (2)
-			cost = new(big.Int).SetUint64(tx.Gas())
-			cost.Mul(cost, tx.GasFeeCap())
-			cost.Add(cost, tx.Value())
-			if tx.GatewayFeeRecipient() != nil {
-				cost.Add(cost, tx.GatewayFee())
-			}
-		} else {
-			// cost = GasPrice * gas + value + gatewayFee, as in (1)
-			cost = tx.Cost()
-		}
-
-		if balance.Cmp(cost) < 0 {
-			log.Debug("ValidateTransactorBalanceCoversTx: insufficient CELO funds",
-				"from", from, "Transaction cost", cost, "to", tx.To(),
-				"gas", tx.Gas(), "gas price", tx.GasPrice(), "nonce", tx.Nonce(),
-				"value", tx.Value(), "fee currency", tx.FeeCurrency(), "balance", balance)
-			return ErrInsufficientFunds
-		}
-	} else {
-		balance, err := currency.GetBalanceOf(currentVMRunner, from, *tx.FeeCurrency())
-		if err != nil {
-			log.Debug("ValidateTransactorBalanceCoversTx: error in getting fee currency balance", "feeCurrency", tx.FeeCurrency())
-			return err
-		}
-
-		if espresso {
-			// cost = GasFeeCap * gas + gatewayFee, as in (4)
-			cost := new(big.Int).SetUint64(tx.Gas())
-			cost.Mul(cost, tx.GasFeeCap())
-			if tx.GatewayFeeRecipient() != nil {
-				cost.Add(cost, tx.GatewayFee())
-			}
-			if balance.Cmp(cost) < 0 {
-				log.Debug("ValidateTransactorBalanceCoversTx: insufficient funds", "feeCurrency", tx.FeeCurrency(), "balance", balance)
-				return ErrInsufficientFunds
-			}
-		} else {
-			// cost = GasPrice * gas + gatewayFee, as in (3)
-			cost := tx.Fee()
-			if balance.Cmp(cost) <= 0 {
-				log.Debug("ValidateTransactorBalanceCoversTx: insufficient funds", "feeCurrency", tx.FeeCurrency(), "balance", balance)
-				return ErrInsufficientFunds
-			}
-		}
+	if tx.FeeCurrency() != nil {
+		return erc20gas.TryDebitFees(tx, from, currentVMRunner)
+	}
+	balance := currentState.GetBalance(from)
+
+	// cost = GasFeeCap * gas + value
+	cost := new(big.Int).SetUint64(tx.Gas())
+	cost.Mul(cost, tx.GasFeeCap())
+	cost.Add(cost, tx.Value())
+
+	if balance.Cmp(cost) < 0 {
+		log.Debug("ValidateTransactorBalanceCoversTx: insufficient CELO funds",
+			"from", from, "Transaction cost", cost, "to", tx.To(),
+			"gas", tx.Gas(), "gas price", tx.GasPrice(), "nonce", tx.Nonce(),
+			"value", tx.Value(), "fee currency", tx.FeeCurrency(), "balance", balance)
+		return ErrInsufficientFunds
 	}
 
 	return nil

core/vm/interface.go

@@ -104,6 +104,9 @@ type EVMRunner interface {
 	// originally used the transaction's sender instead of the zero address.
 	ExecuteFrom(sender, recipient common.Address, input []byte, gas uint64, value *big.Int) (ret []byte, err error)
 
+	// Execute input after creating a snapshot and revert to that snapshot afterwards.
+	ExecuteAndDiscardChanges(recipient common.Address, input []byte, gas uint64, value *big.Int) (ret []byte, err error)
+
 	// Query performs a read operation over the runner's state
 	// It can be seen as a message (input,value) from sender to recipient that returns `ret`
 	Query(recipient common.Address, input []byte, gas uint64) (ret []byte, err error)

core/vm/vmcontext/runner.go

@@ -61,6 +61,17 @@ func (ev *evmRunner) ExecuteFrom(sender, recipient common.Address, input []byte,
 	return ret, err
 }
 
+func (ev *evmRunner) ExecuteAndDiscardChanges(recipient common.Address, input []byte, gas uint64, value *big.Int) (ret []byte, err error) {
+	evm := ev.newEVM(VMAddress)
+	var snapshot = evm.StateDB.Snapshot()
+	if ev.dontMeterGas {
+		evm.StopGasMetering()
+	}
+	ret, _, err = evm.Call(vm.AccountRef(evm.Origin), recipient, input, gas, value)
+	evm.StateDB.RevertToSnapshot(snapshot)
+	return ret, err
+}
+
 func (ev *evmRunner) Query(recipient common.Address, input []byte, gas uint64) (ret []byte, err error) {
 	evm := ev.newEVM(VMAddress)
 	if ev.dontMeterGas {
@@ -98,6 +109,13 @@ func (sev *SharedEVMRunner) ExecuteFrom(sender, recipient common.Address, input
 	return ret, err
 }
 
+func (sev *SharedEVMRunner) ExecuteAndDiscardChanges(recipient common.Address, input []byte, gas uint64, value *big.Int) (ret []byte, err error) {
+	var snapshot = sev.StateDB.Snapshot()
+	ret, _, err = sev.Call(vm.AccountRef(VMAddress), recipient, input, gas, value)
+	sev.StateDB.RevertToSnapshot(snapshot)
+	return ret, err
+}
+
 func (sev *SharedEVMRunner) Query(recipient common.Address, input []byte, gas uint64) (ret []byte, err error) {
 	ret, _, err = sev.StaticCall(vm.AccountRef(VMAddress), recipient, input, gas)
 	return ret, err