Filter out the evm denom from min gas prices in the cosmos-sdk ante (#1253)

* Filter out the evm denom from min gas prices in the cosmos-sdk ante
chain; this allows '0ukava;1000000000akava' to be used in order to
still support zero fees for cosmos based transactions

* support called context in mock

* ensure min gas prices is always a valid (and sorted) DecCoins

* add doc comments

app/ante/ante.go

@@ -103,6 +103,7 @@ func newCosmosAnteHandler(options HandlerOptions) sdk.AnteHandler {
 		decorators = append(decorators, NewAuthenticatedMempoolDecorator(options.AddressFetchers...))
 	}
 	decorators = append(decorators,
+		NewEvmMinGasFilter(options.EvmKeeper), // filter out evm denom from min-gas-prices
 		authante.NewMempoolFeeDecorator(),
 		NewVestingAccountDecorator(),
 		NewAuthzLimiterDecorator(

app/ante/authorized_test.go

@@ -16,10 +16,12 @@ var _ sdk.AnteHandler = (&MockAnteHandler{}).AnteHandle
 
 type MockAnteHandler struct {
 	WasCalled bool
+	CalledCtx sdk.Context
 }
 
 func (mah *MockAnteHandler) AnteHandle(ctx sdk.Context, tx sdk.Tx, simulate bool) (sdk.Context, error) {
 	mah.WasCalled = true
+	mah.CalledCtx = ctx
 	return ctx, nil
 }
 

app/ante/min_gas_filter.go

@@ -0,0 +1,44 @@
+package ante
+
+import (
+	sdk "github.com/cosmos/cosmos-sdk/types"
+	evmtypes "github.com/tharsis/ethermint/x/evm/types"
+)
+
+var _ sdk.AnteDecorator = EvmMinGasFilter{}
+
+// EVMKeeper specifies the interface that EvmMinGasFilter requires
+type EVMKeeper interface {
+	GetParams(ctx sdk.Context) evmtypes.Params
+}
+
+// EvmMinGasFilter filters out the EvmDenom min gas price and calls the next ante handle with an updated context
+type EvmMinGasFilter struct {
+	evmKeeper EVMKeeper
+}
+
+// NewEvmMinGasFilter takes an EVMKeeper and returns a new min gas filter for it's EvmDenom
+func NewEvmMinGasFilter(evmKeeper EVMKeeper) EvmMinGasFilter {
+	return EvmMinGasFilter{
+		evmKeeper: evmKeeper,
+	}
+}
+
+// AnteHandle checks the EvmDenom from the evmKeeper and filters out the EvmDenom from the ctx
+func (emgf EvmMinGasFilter) AnteHandle(ctx sdk.Context, tx sdk.Tx, simulate bool, next sdk.AnteHandler) (sdk.Context, error) {
+	evmDenom := emgf.evmKeeper.GetParams(ctx).EvmDenom
+
+	if ctx.MinGasPrices().AmountOf(evmDenom).IsPositive() {
+		filteredMinGasPrices := sdk.NewDecCoins()
+
+		for _, gasPrice := range ctx.MinGasPrices() {
+			if gasPrice.Denom != evmDenom {
+				filteredMinGasPrices = filteredMinGasPrices.Add(gasPrice)
+			}
+		}
+
+		ctx = ctx.WithMinGasPrices(filteredMinGasPrices)
+	}
+
+	return next(ctx, tx, simulate)
+}

app/ante/min_gas_filter_test.go

@@ -0,0 +1,88 @@
+package ante_test
+
+import (
+	"strings"
+	"testing"
+
+	sdk "github.com/cosmos/cosmos-sdk/types"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	tmproto "github.com/tendermint/tendermint/proto/tendermint/types"
+	tmtime "github.com/tendermint/tendermint/types/time"
+	evmtypes "github.com/tharsis/ethermint/x/evm/types"
+
+	"github.com/kava-labs/kava/app"
+	"github.com/kava-labs/kava/app/ante"
+)
+
+func mustParseDecCoins(value string) sdk.DecCoins {
+	coins, err := sdk.ParseDecCoins(strings.ReplaceAll(value, ";", ","))
+	if err != nil {
+		panic(err)
+	}
+
+	return coins
+}
+
+func TestEvmMinGasFilter(t *testing.T) {
+	tApp := app.NewTestApp()
+	handler := ante.NewEvmMinGasFilter(tApp.GetEvmKeeper())
+
+	ctx := tApp.NewContext(true, tmproto.Header{Height: 1, Time: tmtime.Now()})
+	tApp.GetEvmKeeper().SetParams(ctx, evmtypes.Params{
+		EvmDenom: "akava",
+	})
+
+	testCases := []struct {
+		name                 string
+		minGasPrices         sdk.DecCoins
+		expectedMinGasPrices sdk.DecCoins
+	}{
+		{
+			"no min gas prices",
+			mustParseDecCoins(""),
+			mustParseDecCoins(""),
+		},
+		{
+			"zero ukava gas price",
+			mustParseDecCoins("0ukava"),
+			mustParseDecCoins("0ukava"),
+		},
+		{
+			"non-zero ukava gas price",
+			mustParseDecCoins("0.001ukava"),
+			mustParseDecCoins("0.001ukava"),
+		},
+		{
+			"zero ukava gas price, min akava price",
+			mustParseDecCoins("0ukava;100000akava"),
+			mustParseDecCoins("0ukava"), // akava is removed
+		},
+		{
+			"zero ukava gas price, min akava price, other token",
+			mustParseDecCoins("0ukava;100000akava;0.001other"),
+			mustParseDecCoins("0ukava;0.001other"), // akava is removed
+		},
+		{
+			"non-zero ukava gas price, min akava price",
+			mustParseDecCoins("0.25ukava;100000akava;0.001other"),
+			mustParseDecCoins("0.25ukava;0.001other"), // akava is removed
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			ctx := tApp.NewContext(true, tmproto.Header{Height: 1, Time: tmtime.Now()})
+
+			ctx = ctx.WithMinGasPrices(tc.minGasPrices)
+			mmd := MockAnteHandler{}
+
+			_, err := handler.AnteHandle(ctx, nil, false, mmd.AnteHandle)
+			require.NoError(t, err)
+			require.True(t, mmd.WasCalled)
+
+			assert.NoError(t, mmd.CalledCtx.MinGasPrices().Validate())
+			assert.Equal(t, tc.expectedMinGasPrices, mmd.CalledCtx.MinGasPrices())
+		})
+	}
+}