evmos · GAtom22 · Sep 19, 2023 · Sep 6, 2023 · Sep 6, 2023 · Sep 6, 2023
@@ -69,6 +69,7 @@ Ref: https://keepachangelog.com/en/1.0.0/
 - (evm) [#1693](https://github.com/evmos/evmos/pull/1703) Prevent panic on uint64 conversion in EVM keeper `ApplyMessageWithConfig` function.
 - (deps) [#1718](https://github.com/evmos/evmos/pull/1718) Update rosetta types import.
 - (consensus) [#1740](https://github.com/evmos/evmos/pull/1740) Enable setting block gas limit to max by specifying it as -1 in the genesis file.
+- (ante) [#1753](https://github.com/evmos/evmos/pull/1753) Handle zero fee case on evm transactions.
 
 ## [v13.0.2] - 2023-07-05
 

@@ -191,17 +191,10 @@ func (egcd EthGasConsumeDecorator) AnteHandle(ctx sdk.Context, tx sdk.Tx, simula
 			return ctx, errorsmod.Wrapf(err, "failed to verify the fees")
 		}
 
-		// If the account balance is not sufficient, try to withdraw enough staking rewards
-		err = anteutils.ClaimStakingRewardsIfNecessary(ctx, egcd.bankKeeper, egcd.distributionKeeper, egcd.stakingKeeper, from, fees)
-		if err != nil {
+		if err = egcd.deductFee(ctx, fees, from); err != nil {
 			return ctx, err
 		}
 
-		err = egcd.evmKeeper.DeductTxCostsFromUserBalance(ctx, fees, common.HexToAddress(msgEthTx.From))
-		if err != nil {
-			return ctx, errorsmod.Wrapf(err, "failed to deduct transaction costs from user balance")
-		}
-
 		events = append(events,
 			sdk.NewEvent(
 				sdk.EventTypeTx,
@@ -248,6 +241,24 @@ func (egcd EthGasConsumeDecorator) AnteHandle(ctx sdk.Context, tx sdk.Tx, simula
 	return next(newCtx, tx, simulate)
 }
 
+// deductFee checks if the fee payer has enough funds to pay for the fees and deducts them.
+// If the spendable balance is not enough, it tries to claim enough staking rewards to cover the fees.
+func (egcd EthGasConsumeDecorator) deductFee(ctx sdk.Context, fees sdk.Coins, feePayer sdk.AccAddress) error {
+	if fees.IsZero() {
+		return nil
+	}
+
+	// If the account balance is not sufficient, try to withdraw enough staking rewards
+	if err := anteutils.ClaimStakingRewardsIfNecessary(ctx, egcd.bankKeeper, egcd.distributionKeeper, egcd.stakingKeeper, feePayer, fees); err != nil {
+		return err
+	}
+
+	if err := egcd.evmKeeper.DeductTxCostsFromUserBalance(ctx, fees, common.BytesToAddress(feePayer)); err != nil {
+		return errorsmod.Wrapf(err, "failed to deduct transaction costs from user balance")
+	}
+	return nil
+}
+
 // CanTransferDecorator checks if the sender is allowed to transfer funds according to the EVM block
 // context rules.
 type CanTransferDecorator struct {

@@ -197,6 +197,9 @@ func (suite *AnteTestSuite) TestEthGasConsumeDecorator() {
 	tx := evmtypes.NewTx(ethContractCreationTxParams)
 	tx.From = addr.Hex()
 
+	ethContractCreationTxParams.GasLimit = 55000
+	zeroFeeTx := makeZeroFeeTx(addr, *ethContractCreationTxParams)
+
 	ethCfg := suite.app.EvmKeeper.GetParams(suite.ctx).
 		ChainConfig.EthereumConfig(chainID)
 	baseFee := suite.app.EvmKeeper.GetBaseFee(suite.ctx, ethCfg)
@@ -243,6 +246,8 @@ func (suite *AnteTestSuite) TestEthGasConsumeDecorator() {
 
 	var vmdb *statedb.StateDB
 
+	initialBalance := suite.app.BankKeeper.GetBalance(suite.ctx, addr.Bytes(), utils.BaseDenom)
+
 	testCases := []struct {
 		name        string
 		tx          sdk.Tx
@@ -424,6 +429,36 @@ func (suite *AnteTestSuite) TestEthGasConsumeDecorator() {
 				)
 			},
 		},
+		{
+			"success - zero fees (no base fee)",
+			zeroFeeTx,
+			zeroFeeTx.GetGas(),
+			func(ctx sdk.Context) sdk.Context {
+				suite.disableBaseFee(ctx)
+				return ctx
+			},
+			true, false,
+			0,
+			func(ctx sdk.Context) {
+				finalBalance := suite.app.BankKeeper.GetBalance(ctx, addr.Bytes(), utils.
10000
BaseDenom)
+				suite.Require().Equal(initialBalance, finalBalance)
+			},
+		},
+		{
+			"success - zero fees (no base fee) - legacy tx",
+			makeZeroFeeTx(addr, *eth2TxContractParams),
+			tx2GasLimit,
+			func(ctx sdk.Context) sdk.Context {
+				suite.disableBaseFee(ctx)
+				return ctx
+			},
+			true, false,
+			0,
+			func(ctx sdk.Context) {
+				finalBalance := suite.app.BankKeeper.GetBalance(ctx, addr.Bytes(), utils.BaseDenom)
+				suite.Require().Equal(initialBalance, finalBalance)
+			},
+		},
 	}
 
 	for _, tc := range testCases {

@@ -665,3 +665,22 @@ func (suite *AnteTestSuite) prepareAccount(ctx sdk.Context, addr sdk.AccAddress,
 		WithBlockGasMeter(sdk.NewGasMeter(1e19)).
 		WithBlockHeight(ctx.BlockHeight() + 1)
 }
+
+// disableBaseFee is a helper function that edits the
+// feemarket parameters to not use base fee
+func (suite *AnteTestSuite) disableBaseFee(ctx sdk.Context) {
+	params := suite.app.FeeMarketKeeper.GetParams(ctx)
+	params.NoBaseFee = true
+	params.MinGasPrice = sdk.ZeroDec()
+	err := suite.app.FeeMarketKeeper.SetParams(ctx, params)
+	suite.Require().NoError(err)
+}
+
+// makeZeroFeeTx is a helper function that sets
+// the GasPrice field to zero on the provided evmTxArgs
+func makeZeroFeeTx(from common.Address, args evmtypes.EvmTxArgs) *evmtypes.MsgEthereumTx {
+	args.GasPrice = sdk.ZeroInt().BigInt()
+	tx := evmtypes.NewTx(&args)
+	tx.From = from.Hex()
+	return tx
+}
@@ -0,0 +1,17 @@
+local config = import 'default.jsonnet';
+
+config {
+  'evmos_9000-1'+: {
+    genesis+: {
+      app_state+: {
+        feemarket+: {
+          params+: {
+            min_gas_price: '0',
+            no_base_fee: true,
+            base_fee: '0',            
+          },
+        },
+      },
+    },
+  },
+}
@@ -0,0 +1,96 @@
+from pathlib import Path
+
+import pytest
+from web3 import Web3
+
+from .network import setup_custom_evmos
+from .utils import ADDRS, eth_to_bech32, wait_for_fn
+
+
+@pytest.fixture(scope="module")
+def evmos(request, tmp_path_factory):
+    yield from setup_custom_evmos(
+        tmp_path_factory.mktemp("zero-fee"),
+        26900,
+        Path(__file__).parent / "configs/zero-fee.jsonnet",
+    )
+
+
+def test_cosmos_tx(evmos):
+    """
+    test basic cosmos transaction works with zero fees
+    """
+    denom = "aevmos"
+    cli = evmos.cosmos_cli()
+    sender = eth_to_bech32(ADDRS["signer1"])
+    receiver = eth_to_bech32(ADDRS["signer2"])
+    amt = 1000
+
+    old_src_balance = cli.balance(sender, denom)
+    old_dst_balance = cli.balance(receiver, denom)
+
+    tx = cli.transfer(
+        sender,
+        receiver,
+        f"{amt}{denom}",
+        gas_prices=f"0{denom}",
+        generate_only=True,
+    )
+
+    tx = cli.sign_tx_json(tx, sender, max_priority_price=0)
+
+    rsp = cli.broadcast_tx_json(tx, broadcast_mode="sync")
+    assert rsp["code"] == 0, rsp["raw_log"]
+
+    new_dst_balance = 0
+
+    def check_balance_change():
+        nonlocal new_dst_balance
+        new_dst_balance = cli.balance(receiver, denom)
+        return old_dst_balance != new_dst_balance
+
+    wait_for_fn("balance change", check_balance_change)
+    assert old_dst_balance + amt == new_dst_balance
+    new_src_balance = cli.balance(sender, denom)
+    # no fees paid, so sender balance should be
+    # initial_balance - amount_sent
+    assert old_src_balance - amt == new_src_balance
+
+
+def test_eth_tx(evmos):
+    """
+    test basic Ethereum transaction works with zero fees
+    """
+    w3: Web3 = evmos.w3
+
+    sender = ADDRS["signer1"]
+    receiver = ADDRS["signer2"]
+    amt = 1000
+
+    old_src_balance = w3.eth.get_balance(sender)
+    old_dst_balance = w3.eth.get_balance(receiver)
+
+    txhash = w3.eth.send_transaction(
+        {
+            "from": sender,
+            "to": receiver,
+            "value": amt,
+            "gasPrice": 0,
+        }
+    )
+    receipt = w3.eth.wait_for_transaction_receipt(txhash)
+    assert receipt.status == 1
+
+    new_dst_balance = 0
+
+    def check_balance_change():
+        nonlocal new_dst_balance
+        new_dst_balance = w3.eth.get_balance(receiver)
+        return old_dst_balance != new_dst_balance
+
+    wait_for_fn("balance change", check_balance_change)
+    assert old_dst_balance + amt == new_dst_balance
+    new_src_balance = w3.eth.get_balance(sender)
+    # no fees paid, so sender balance should be
+    # initial_balance - amount_sent
+    assert old_src_balance - amt == new_src_balance