Read IntrinsicGas from FeeCurrencyDirectory (#178)

* Add FeeCurrencyContext object to BlockContext

This replaces the `BlockContext.ExchangeRates` with a wrapper object
`BlockContext.FeeCurrencyContext`.

This enables easier addition of fee-currency related information
to the block context and passing around that information.
The exchange-rates are now part of the `FeeCurrencyContext`

* Add intrinsic gas retrieval from FeeCurrencyDirectory

* Use intrinsic gas from FeeCurrencyDirectory in STF

* Add test for intrinsic gas too high in fee currency

* Add empty fee-currency context to tools and tests

* Add minor code improvements

Co-authored-by: Paul Lange <[email protected]>

* Add comment for nil fee-currency code path

* Add fee-currency-context to CeloBackend.NewEVM constructor

---------

Co-authored-by: Paul Lange <[email protected]>

cmd/evm/internal/t8ntool/execution.go

@@ -219,7 +219,12 @@ func (pre *Prestate) Apply(vmConfig vm.Config, chainConfig *params.ChainConfig,
 			rejectedTxs = append(rejectedTxs, &rejectedTx{i, errMsg})
 			continue
 		}
-		msg, err := core.TransactionToMessage(tx, signer, pre.Env.BaseFee, vmContext.ExchangeRates)
+		// NOTE: we can't provide exchange rates
+		// for fee-currencies here, since those are dynamically changing
+		// based on the oracle's exchange rates.
+		// When a Celo transaction with specified fee-currency is validated with this tool,
+		// this will thus result in a ErrUnregisteredFeeCurrency error for now.
+		msg, err := core.TransactionToMessage(tx, signer, pre.Env.BaseFee, vmContext.FeeCurrencyContext.ExchangeRates)
 		if err != nil {
 			log.Warn("rejected tx", "index", i, "hash", tx.Hash(), "error", err)
 			rejectedTxs = append(rejectedTxs, &rejectedTx{i, err.Error()})

cmd/evm/internal/t8ntool/transaction.go

@@ -133,8 +133,14 @@ func Transaction(ctx *cli.Context) error {
 			r.Address = sender
 		}
 		// Check intrinsic gas
+		// NOTE: we can't provide specific intrinsic gas costs
+		// for fee-currencies here, since those are written to the
+		// FeeCurrencyDirectory contract and are chain-specific.
+		// When a Celo transaction with specified fee-currency is validated with this tool,
+		// this will thus result in a ErrUnregisteredFeeCurrency error for now.
+		var feeIntrinsic common.IntrinsicGasCosts
 		if gas, err := core.IntrinsicGas(tx.Data(), tx.AccessList(), tx.To() == nil,
-			chainConfig.IsHomestead(new(big.Int)), chainConfig.IsIstanbul(new(big.Int)), chainConfig.IsShanghai(new(big.Int), 0), tx.FeeCurrency()); err != nil {
+			chainConfig.IsHomestead(new(big.Int)), chainConfig.IsIstanbul(new(big.Int)), chainConfig.IsShanghai(new(big.Int), 0), tx.FeeCurrency(), feeIntrinsic); err != nil {
 			r.Error = err
 			results = append(results, r)
 			continue

common/celo_types.go

@@ -9,6 +9,37 @@ var (
 )
 
 type ExchangeRates = map[Address]*big.Rat
+type IntrinsicGasCosts = map[Address]uint64
+
+type FeeCurrencyContext struct {
+	ExchangeRates     ExchangeRates
+	IntrinsicGasCosts IntrinsicGasCosts
+}
+
+func MaxAllowedIntrinsicGasCost(i IntrinsicGasCosts, feeCurrency *Address) (uint64, bool) {
+	intrinsicGas, ok := CurrencyIntrinsicGasCost(i, feeCurrency)
+	if !ok {
+		return 0, false
+	}
+	// Allow the contract to overshoot 2 times the deducted intrinsic gas
+	// during execution.
+	// If the feeCurrency is nil, then the max allowed intrinsic gas cost
+	// is 0 (i.e. not allowed) for a fee-currency specific EVM call within the STF.
+	return intrinsicGas * 3, true
+}
+
+func CurrencyIntrinsicGasCost(i IntrinsicGasCosts, feeCurrency *Address) (uint64, bool) {
+	// the additional intrinsic gas cost for a non fee-currency
+	// transaction is 0
+	if feeCurrency == nil {
+		return 0, true
+	}
+	gasCost, ok := i[*feeCurrency]
+	if !ok {
+		return 0, false
+	}
+	return gasCost, true
+}
 
 func CurrencyAllowlist(exchangeRates ExchangeRates) []Address {
 	addrs := make([]Address, len(exchangeRates))

contracts/celo_backend.go

@@ -61,14 +61,19 @@ func (b *CeloBackend) CallContract(ctx context.Context, call ethereum.CallMsg, b
 
 // Get a vm.EVM object of you can't use the abi wrapper via the ContractCaller interface
 // This is usually the case when executing functions that modify state.
-func (b *CeloBackend) NewEVM() *vm.EVM {
-	blockCtx := vm.BlockContext{BlockNumber: new(big.Int), Time: 0,
+func (b *CeloBackend) NewEVM(feeCurrencyContext *common.FeeCurrencyContext) *vm.EVM {
+	blockCtx := vm.BlockContext{
+		BlockNumber: new(big.Int),
+		Time:        0,
 		Transfer: func(state vm.StateDB, from common.Address, to common.Address, value *uint256.Int) {
 			if value.Cmp(common.U2560) != 0 {
 				panic("Non-zero transfers not implemented, yet.")
 			}
 		},
 	}
+	if feeCurrencyContext != nil {
+		blockCtx.FeeCurrencyContext = *feeCurrencyContext
+	}
 	txCtx := vm.TxContext{}
 	vmConfig := vm.Config{}
 	return vm.NewEVM(blockCtx, txCtx, b.State, b.ChainConfig, vmConfig)

contracts/fee_currencies.go

@@ -1,28 +1,22 @@
 package contracts
 
 import (
+	"errors"
 	"fmt"
+	"math"
 	"math/big"
 
 	"github.com/ethereum/go-ethereum/accounts/abi"
 	"github.com/ethereum/go-ethereum/accounts/abi/bind"
 	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/common/exchange"
 	"github.com/ethereum/go-ethereum/contracts/addresses"
 	"github.com/ethereum/go-ethereum/contracts/celo/abigen"
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/core/vm"
 	"github.com/ethereum/go-ethereum/log"
 )
 
-const (
-	Thousand = 1000
-
-	// Default intrinsic gas cost of transactions paying for gas in alternative currencies.
-	// Calculated to estimate 1 balance read, 1 debit, and 4 credit transactions.
-	IntrinsicGasForAlternativeFeeCurrency uint64 = 50 * Thousand
-	maxAllowedGasForDebitAndCredit        uint64 = 3 * IntrinsicGasForAlternativeFeeCurrency
-)
-
 var feeCurrencyABI *abi.ABI
 
 func init() {
@@ -34,31 +28,42 @@ func init() {
 }
 
 // Returns nil if debit is possible, used in tx pool validation
-func TryDebitFees(tx *types.Transaction, from common.Address, backend *CeloBackend) error {
+func TryDebitFees(tx *types.Transaction, from common.Address, backend *CeloBackend, feeContext common.FeeCurrencyContext) error {
 	amount := new(big.Int).SetUint64(tx.Gas())
 	amount.Mul(amount, tx.GasFeeCap())
 
 	snapshot := backend.State.Snapshot()
-	err := DebitFees(backend.NewEVM(), tx.FeeCurrency(), from, amount)
+	evm := backend.NewEVM(&feeContext)
+	_, err := DebitFees(evm, tx.FeeCurrency(), from, amount)
 	backend.State.RevertToSnapshot(snapshot)
 	return err
 }
 
 // Debits transaction fees from the transaction sender and stores them in the temporary address
-func DebitFees(evm *vm.EVM, feeCurrency *common.Address, address common.Address, amount *big.Int) error {
+func DebitFees(evm *vm.EVM, feeCurrency *common.Address, address common.Address, amount *big.Int) (uint64, error) {
 	if amount.Cmp(big.NewInt(0)) == 0 {
-		return nil
+		return 0, nil
+	}
+
+	maxIntrinsicGasCost, ok := common.MaxAllowedIntrinsicGasCost(evm.Context.FeeCurrencyContext.IntrinsicGasCosts, feeCurrency)
+	if !ok {
+		return 0, fmt.Errorf("%w: %x", exchange.ErrUnregisteredFeeCurrency, feeCurrency)
 	}
 
 	leftoverGas, err := evm.CallWithABI(
-		feeCurrencyABI, "debitGasFees", *feeCurrency, maxAllowedGasForDebitAndCredit,
+		feeCurrencyABI, "debitGasFees", *feeCurrency, maxIntrinsicGasCost,
 		// debitGasFees(address from, uint256 value) parameters
 		address, amount,
 	)
-	gasUsed := maxAllowedGasForDebitAndCredit - leftoverGas
-	evm.Context.GasUsedForDebit = gasUsed
+	if errors.Is(err, vm.ErrOutOfGas) {
+		// This basically is a configuration / contract error, since
+		// the contract itself used way more gas than was expected (including grace limit)
+		return 0, fmt.Errorf("surpassed maximum allowed intrinsic gas for fee currency: %w", err)
+	}
+
+	gasUsed := maxIntrinsicGasCost - leftoverGas
 	log.Trace("DebitFees called", "feeCurrency", *feeCurrency, "gasUsed", gasUsed)
-	return err
+	return gasUsed, err
 }
 
 // Credits fees to the respective parties
@@ -71,6 +76,7 @@ func CreditFees(
 	feeCurrency *common.Address,
 	txSender, tipReceiver, baseFeeReceiver, l1DataFeeReceiver common.Address,
 	refund, feeTip, baseFee, l1DataFee *big.Int,
+	gasUsedDebit uint64,
 ) error {
 	// Our old `creditGasFees` function does not accept an l1DataFee and
 	// the fee currencies do not implement the new interface yet. Since tip
@@ -85,8 +91,12 @@ func CreditFees(
 	if tipReceiver.Cmp(common.ZeroAddress) == 0 {
 		tipReceiver = baseFeeReceiver
 	}
+	maxAllowedGasForDebitAndCredit, ok := common.MaxAllowedIntrinsicGasCost(evm.Context.FeeCurrencyContext.IntrinsicGasCosts, feeCurrency)
+	if !ok {
+		return fmt.Errorf("%w: %x", exchange.ErrUnregisteredFeeCurrency, feeCurrency)
+	}
 
-	maxAllowedGasForCredit := maxAllowedGasForDebitAndCredit - evm.Context.GasUsedForDebit
+	maxAllowedGasForCredit := maxAllowedGasForDebitAndCredit - gasUsedDebit
 	leftoverGas, err := evm.CallWithABI(
 		feeCurrencyABI, "creditGasFees", *feeCurrency, maxAllowedGasForCredit,
 		// function creditGasFees(
@@ -101,43 +111,72 @@ func CreditFees(
 		// )
 		txSender, tipReceiver, common.ZeroAddress, baseFeeReceiver, refund, feeTip, common.Big0, baseFee,
 	)
+	if errors.Is(err, vm.ErrOutOfGas) {
+		// This is a configuration / contract error, since
+		// the contract itself used way more gas than was expected (including grace limit)
+		return fmt.Errorf("surpassed maximum allowed intrinsic gas for fee currency: %w", err)
+	}
 
 	gasUsed := maxAllowedGasForCredit - leftoverGas
 	log.Trace("CreditFees called", "feeCurrency", *feeCurrency, "gasUsed", gasUsed)
 
-	gasUsedForDebitAndCredit := evm.Context.GasUsedForDebit + gasUsed
-	if gasUsedForDebitAndCredit > IntrinsicGasForAlternativeFeeCurrency {
-		log.Info("Gas usage for debit+credit exceeds intrinsic gas!", "gasUsed", gasUsedForDebitAndCredit, "intrinsicGas", IntrinsicGasForAlternativeFeeCurrency, "feeCurrency", feeCurrency)
+	intrinsicGas, ok := common.CurrencyIntrinsicGasCost(evm.Context.FeeCurrencyContext.IntrinsicGasCosts, feeCurrency)
+	if !ok {
+		// this will never happen
+		return fmt.Errorf("%w: %x", exchange.ErrUnregisteredFeeCurrency, feeCurrency)
+	}
+	gasUsedForDebitAndCredit := gasUsedDebit + gasUsed
+	if gasUsedForDebitAndCredit > intrinsicGas {
+		log.Info("Gas usage for debit+credit exceeds intrinsic gas!", "gasUsed", gasUsedForDebitAndCredit, "intrinsicGas", intrinsicGas, "feeCurrency", feeCurrency)
 	}
 	return err
 }
 
-// GetExchangeRates returns the exchange rates for all gas currencies from CELO
+func GetRegisteredCurrencies(caller *abigen.FeeCurrencyDirectoryCaller) ([]common.Address, error) {
+	currencies, err := caller.GetCurrencies(&bind.CallOpts{})
+	if err != nil {
+		return currencies, fmt.Errorf("failed to get registered tokens: %w", err)
+	}
+	return currencies, nil
+}
+
+// GetExchangeRates returns the exchange rates for the provided gas currencies
 func GetExchangeRates(caller *CeloBackend) (common.ExchangeRates, error) {
-	exchangeRates := map[common.Address]*big.Rat{}
 	directory, err := abigen.NewFeeCurrencyDirectoryCaller(addresses.GetAddresses(caller.ChainConfig.ChainID).FeeCurrencyDirectory, caller)
 	if err != nil {
 		return common.ExchangeRates{}, fmt.Errorf("failed to access FeeCurrencyDirectory: %w", err)
 	}
-
-	registeredTokens, err := directory.GetCurrencies(&bind.CallOpts{})
+	currencies, err := GetRegisteredCurrencies(directory)
 	if err != nil {
-		return exchangeRates, fmt.Errorf("Failed to get whitelisted tokens: %w", err)
+		return common.ExchangeRates{}, err
 	}
-	for _, tokenAddress := range registeredTokens {
-		rate, err := directory.GetExchangeRate(&bind.CallOpts{}, tokenAddress)
-		if err != nil {
-			log.Error("Failed to get medianRate for gas currency!", "err", err, "tokenAddress", tokenAddress.Hex())
-			continue
-		}
-		if rate.Numerator.Sign() <= 0 || rate.Denominator.Sign() <= 0 {
-			log.Error("Bad exchange rate for fee currency", "tokenAddress", tokenAddress.Hex(), "numerator", rate.Numerator, "denominator", rate.Denominator)
-			continue
-		}
-		exchangeRates[tokenAddress] = new(big.Rat).SetFrac(rate.Numerator, rate.Denominator)
+	return getExchangeRatesForTokens(directory, currencies)
+}
+
+// GetFeeCurrencyContext returns the fee currency block context for all registered gas currencies from CELO
+func GetFeeCurrencyContext(caller *CeloBackend) (common.FeeCurrencyContext, error) {
+	var feeContext common.FeeCurrencyContext
+	directory, err := abigen.NewFeeCurrencyDirectoryCaller(addresses.GetAddresses(caller.ChainConfig.ChainID).FeeCurrencyDirectory, caller)
+	if err != nil {
+		return feeContext, fmt.Errorf("failed to access FeeCurrencyDirectory: %w", err)
 	}
 
-	return exchangeRates, nil
+	currencies, err := GetRegisteredCurrencies(directory)
+	if err != nil {
+		return feeContext, err
+	}
+	rates, err := getExchangeRatesForTokens(directory, currencies)
+	if err != nil {
+		return feeContext, err
+	}
+	intrinsicGas, err := getIntrinsicGasForTokens(directory, currencies)
+	if err != nil {
+		return feeContext, err
+	}
+	return common.FeeCurrencyContext{
+		ExchangeRates:     rates,
+		IntrinsicGasCosts: intrinsicGas,
+	}, nil
 }
 
 // GetBalanceERC20 returns an account's balance on a given ERC20 currency
@@ -167,3 +206,41 @@ func GetFeeBalance(backend *CeloBackend, account common.Address, feeCurrency *co
 	}
 	return balance
 }
+
+// getIntrinsicGasForTokens returns the intrinsic gas costs for the provided gas currencies from CELO
+func getIntrinsicGasForTokens(caller *abigen.FeeCurrencyDirectoryCaller, tokens []common.Address) (common.IntrinsicGasCosts, error) {
+	gasCosts := common.IntrinsicGasCosts{}
+	for _, tokenAddress := range tokens {
+		config, err := caller.GetCurrencyConfig(&bind.CallOpts{}, tokenAddress)
+		if err != nil {
+			log.Error("Failed to get intrinsic gas cost for gas currency!", "err", err, "tokenAddress", tokenAddress.Hex())
+			continue
+		}
+		if !config.IntrinsicGas.IsUint64() {
+			log.Error("Intrinsic gas cost exceeds MaxUint64 limit, capping at MaxUint64", "err", err, "tokenAddress", tokenAddress.Hex())
+			gasCosts[tokenAddress] = math.MaxUint64
+		} else {
+			gasCosts[tokenAddress] = config.IntrinsicGas.Uint64()
+		}
+	}
+	return gasCosts, nil
+}
+
+// getExchangeRatesForTokens returns the exchange rates for the provided gas currencies from CELO
+func getExchangeRatesForTokens(caller *abigen.FeeCurrencyDirectoryCaller, tokens []common.Address) (common.ExchangeRates, error) {
+	exchangeRates := common.ExchangeRates{}
+	for _, tokenAddress := range tokens {
+		rate, err := caller.GetExchangeRate(&bind.CallOpts{}, tokenAddress)
+		if err != nil {
+			log.Error("Failed to get medianRate for gas currency!", "err", err, "tokenAddress", tokenAddress.Hex())
+			continue
+		}
+		if rate.Numerator.Sign() <= 0 || rate.Denominator.Sign() <= 0 {
+			log.Error("Bad exchange rate for fee currency", "tokenAddress", tokenAddress.Hex(), "numerator", rate.Numerator, "denominator", rate.Denominator)
+			continue
+		}
+		exchangeRates[tokenAddress] = new(big.Rat).SetFrac(rate.Numerator, rate.Denominator)
+	}
+
+	return exchangeRates, nil
+}

core/bench_test.go

@@ -83,7 +83,7 @@ func genValueTx(nbytes int) func(int, *BlockGen) {
 	return func(i int, gen *BlockGen) {
 		toaddr := common.Address{}
 		data := make([]byte, nbytes)
-		gas, _ := IntrinsicGas(data, nil, false, false, false, false, nil)
+		gas, _ := IntrinsicGas(data, nil, false, false, false, false, nil, common.IntrinsicGasCosts{})
 		signer := gen.Signer()
 		gasPrice := big.NewInt(0)
 		if gen.header.BaseFee != nil {

core/celo_evm.go

@@ -9,8 +9,19 @@ import (
 	"github.com/ethereum/go-ethereum/params"
 )
 
+// XXYXX
 func setCeloFieldsInBlockContext(blockContext *vm.BlockContext, header *types.Header, config *params.ChainConfig, statedb vm.StateDB) {
-	blockContext.ExchangeRates = GetExchangeRates(header, config, statedb)
+	if !config.IsCel2(header.Time) {
+		return
+	}
+
+	caller := &contracts.CeloBackend{ChainConfig: config, State: statedb}
+
+	feeCurrencyContext, err := contracts.GetFeeCurrencyContext(caller)
+	if err != nil {
+		log.Error("Error fetching exchange rates!", "err", err)
+	}
+	blockContext.FeeCurrencyContext = feeCurrencyContext
 }
 
 func GetExchangeRates(header *types.Header, config *params.ChainConfig, statedb vm.StateDB) common.ExchangeRates {
@@ -20,10 +31,9 @@ func GetExchangeRates(header *types.Header, config *params.ChainConfig, statedb
 
 	caller := &contracts.CeloBackend{ChainConfig: config, State: statedb}
 
-	// Add fee currency exchange rates
-	exchangeRates, err := contracts.GetExchangeRates(caller)
+	feeCurrencyContext, err := contracts.GetFeeCurrencyContext(caller)
 	if err != nil {
 		log.Error("Error fetching exchange rates!", "err", err)
 	}
-	return exchangeRates
+	return feeCurrencyContext.ExchangeRates
 }

core/state_prefetcher.go

@@ -60,7 +60,7 @@ func (p *statePrefetcher) Prefetch(block *types.Block, statedb *state.StateDB, c
 			return
 		}
 		// Convert the transaction into an executable message and pre-cache its sender
-		msg, err := TransactionToMessage(tx, signer, header.BaseFee, blockContext.ExchangeRates)
+		msg, err := TransactionToMessage(tx, signer, header.BaseFee, blockContext.FeeCurrencyContext.ExchangeRates)
 		if err != nil {
 			return // Also invalid block, bail out
 		}