Merge pull request #99 from onflow/gregor/gas-estimate-fix

Fix gas estimation with configured account

api/api.go

@@ -503,30 +503,37 @@ func (b *BlockChainAPI) EstimateGas(
 		data = *args.Input
 	}
 
-	eoa := newEOATestAccount(b.config.COAKey.String()[2:])
-	// Provide a high enough gas for the tx to be able to execute
-	gas := uint64(15_000_000)
+	// provide a high enough gas for the tx to be able to execute
+	defaultGasLimit := uint64(15_000_000)
 	if args.Gas != nil {
-		gas = uint64(*args.Gas)
+		defaultGasLimit = uint64(*args.Gas)
 	}
 
-	txData := eoa.PrepareSignAndEncodeTx(
+	txData, err := signGasEstimationTx(
 		args.To,
 		data,
 		(*big.Int)(args.Value),
-		gas,
+		defaultGasLimit,
 		(*big.Int)(args.GasPrice),
 	)
+	if err != nil {
+		b.logger.Error().Err(err).Msg("failed to sign transaction for gas estimate")
+		return hexutil.Uint64(defaultGasLimit), nil // return default gas limit
+	}
 
-	gas, err := b.evm.EstimateGas(ctx, txData)
+	estimatedGas, err := b.evm.EstimateGas(ctx, txData)
 	if err != nil {
 		b.logger.Error().Err(err).Msg("failed to estimate gas")
 		return hexutil.Uint64(0), err
 	}
 
-	return hexutil.Uint64(gas), nil
+	return hexutil.Uint64(estimatedGas), nil
 }
 
+// handleError takes in an error and in case the error is of type ErrNotFound
+// it returns nil instead of an error since that is according to the API spec,
+// if the error is not of type ErrNotFound it will return the error and the generic
+// empty type.
 func handleError[T any](log zerolog.Logger, err error) (T, error) {
 	var zero T
 	if errors.Is(err, storageErrs.ErrNotFound) {

api/gas_estimation.go

@@ -0,0 +1,42 @@
+package api
+
+import (
+	"fmt"
+	"math/big"
+
+	gethCommon "github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/core/types"
+	gethCrypto "github.com/ethereum/go-ethereum/crypto"
+	"github.com/onflow/flow-go/fvm/evm/emulator"
+)
+
+var key, _ = gethCrypto.HexToECDSA("45a915e4d060149eb4365960e6a7a45f334393093061116b197e3240065ff2d8")
+var signer = emulator.GetDefaultSigner()
+
+// signGasEstimationTx will create a transaction and sign it with a test account
+// used only for gas estimation, since gas estimation is run inside a script
+// and does not change the state this account is not important it just has to be valid.
+func signGasEstimationTx(
+	to *gethCommon.Address,
+	data []byte,
+	amount *big.Int,
+	gasLimit uint64,
+	gasPrice *big.Int,
+) ([]byte, error) {
+	tx := types.NewTx(
+		&types.LegacyTx{
+			Nonce:    0,
+			To:       to,
+			Value:    amount,
+			Gas:      gasLimit,
+			GasPrice: gasPrice,
+			Data:     data,
+		},
+	)
+	tx, err := types.SignTx(tx, signer, key)
+	if err != nil {
+		return nil, fmt.Errorf("failed to sign tx for gas estimation: %w", err)
+	}
+
+	return tx.MarshalBinary()
+}