fix zero fee coins

rpc/ethereum/backend/backend.go

@@ -10,10 +10,8 @@ import (
 	"time"
 
 	"github.com/cosmos/cosmos-sdk/client/flags"
-	codectypes "github.com/cosmos/cosmos-sdk/codec/types"
 	"github.com/cosmos/cosmos-sdk/server"
 	sdkerrors "github.com/cosmos/cosmos-sdk/types/errors"
-	authtx "github.com/cosmos/cosmos-sdk/x/auth/tx"
 	"github.com/ethereum/go-ethereum/accounts/keystore"
 	"github.com/ethereum/go-ethereum/params"
 	"github.com/ethereum/go-ethereum/rpc"
@@ -802,43 +800,23 @@ func (e *EVMBackend) SendTransaction(args evmtypes.TransactionArgs) (common.Hash
 		return common.Hash{}, err
 	}
 
-	// Assemble transaction from fields
-	builder, ok := e.clientCtx.TxConfig.NewTxBuilder().(authtx.ExtensionOptionsTxBuilder)
-	if !ok {
-		e.logger.Error("clientCtx.TxConfig.NewTxBuilder returns unsupported builder", "error", err.Error())
-	}
-
-	option, err := codectypes.NewAnyWithValue(&evmtypes.ExtensionOptionsEthereumTx{})
-	if err != nil {
-		e.logger.Error("codectypes.NewAnyWithValue failed to pack an obvious value", "error", err.Error())
-		return common.Hash{}, err
-	}
-
-	builder.SetExtensionOptions(option)
-	if err = builder.SetMsgs(msg); err != nil {
-		e.logger.Error("builder.SetMsgs failed", "error", err.Error())
-	}
-
 	// Query params to use the EVM denomination
 	res, err := e.queryClient.QueryClient.Params(e.ctx, &evmtypes.QueryParamsRequest{})
 	if err != nil {
 		e.logger.Error("failed to query evm params", "error", err.Error())
 		return common.Hash{}, err
 	}
 
-	txData, err := evmtypes.UnpackTxData(msg.Data)
+	// Assemble transaction from fields
+	tx, err := msg.BuildTx(e.clientCtx.TxConfig.NewTxBuilder(), res.Params.EvmDenom)
 	if err != nil {
-		e.logger.Error("failed to unpack tx data", "error", err.Error())
+		e.logger.Error("build cosmos tx failed", "error", err.Error())
 		return common.Hash{}, err
 	}
 
-	fees := sdk.Coins{sdk.NewCoin(res.Params.EvmDenom, sdk.NewIntFromBigInt(txData.Fee()))}
-	builder.SetFeeAmount(fees)
-	builder.SetGasLimit(msg.GetGas())
-
 	// Encode transaction by default Tx encoder
 	txEncoder := e.clientCtx.TxConfig.TxEncoder()
-	txBytes, err := txEncoder(builder.GetTx())
+	txBytes, err := txEncoder(tx)
 	if err != nil {
 		e.logger.Error("failed to encode eth tx using default encoder", "error", err.Error())
 		return common.Hash{}, err

x/evm/keeper/utils.go

@@ -66,6 +66,11 @@ func (k Keeper) DeductTxCostsFromUserBalance(
 		feeAmt = txData.Fee()
 	}
 
+	if feeAmt.Sign() == 0 {
+		// zero fee, no need to deduct
+		return sdk.NewCoins(), nil
+	}
+
 	fees := sdk.Coins{sdk.NewCoin(denom, sdk.NewIntFromBigInt(feeAmt))}
 
 	// deduct the full gas cost from the user balance

x/evm/types/msg.go

@@ -330,11 +330,10 @@ func (msg *MsgEthereumTx) BuildTx(b client.TxBuilder, evmDenom string) (signing.
 	if err != nil {
 		return nil, err
 	}
-	fees := sdk.Coins{
-		{
-			Denom:  evmDenom,
-			Amount: sdk.NewIntFromBigInt(txData.Fee()),
-		},
+	fees := make(sdk.Coins, 0)
+	feeAmt := sdk.NewIntFromBigInt(txData.Fee())
+	if feeAmt.Sign() > 0 {
+		fees = append(fees, sdk.NewCoin(evmDenom, feeAmt))
 	}
 
 	builder.SetExtensionOptions(option)