x/gamm: Add fixed gas cost for swaps (#2016)

* add gas for swap + test

* test file comments

* move swap consumption to balancer only

* fix one more test case

* add to changelog

* Update CHANGELOG.md

Co-authored-by: Aleksandr Bezobchuk <alexanderbez@users.noreply.github.com>

* rm TODO now that we have issue

* underscore for clarity

* gofmt

Co-authored-by: Aleksandr Bezobchuk <alexanderbez@users.noreply.github.com>

Author: rrrliu

CHANGELOG.md

@@ -42,6 +42,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+* [#2016](https://github.com/osmosis-labs/osmosis/pull/2016) Add fixed 10000 gas cost for each Balancer swap
+
 ### Breaking Changes
 
 

x/gamm/keeper/swap.go

@@ -114,6 +114,7 @@ func (k Keeper) swapExactAmountOut(
 		return sdk.Int{}, sdkerrors.Wrapf(types.ErrTooManyTokensOut,
 			"can't get more tokens out than there are tokens in the pool")
 	}
+
 	tokenIn, err := pool.SwapInAmtGivenOut(ctx, sdk.Coins{tokenOut}, tokenInDenom, swapFee)
 	if err != nil {
 		return sdk.Int{}, err

x/gamm/keeper/swap_test.go

@@ -95,9 +95,13 @@ func (suite *KeeperTestSuite) TestBalancerPoolSimpleSwapExactAmountIn() {
 				spotPriceBefore, err := keeper.CalculateSpotPrice(ctx, poolId, test.param.tokenIn.Denom, test.param.tokenOutDenom)
 				suite.NoError(err, "test: %v", test.name)
 
+				prevGasConsumed := suite.Ctx.GasMeter().GasConsumed()
 				tokenOutAmount, err := keeper.SwapExactAmountIn(ctx, suite.TestAccs[0], poolId, test.param.tokenIn, test.param.tokenOutDenom, test.param.tokenOutMinAmount)
 				suite.NoError(err, "test: %v", test.name)
 				suite.True(tokenOutAmount.Equal(test.param.expectedTokenOut), "test: %v", test.name)
+				gasConsumedForSwap := suite.Ctx.GasMeter().GasConsumed() - prevGasConsumed
+				// We consume `types.GasFeeForSwap` directly, so the extra I/O operation mean we end up consuming more.
+				suite.Assert().Greater(gasConsumedForSwap, uint64(types.BalancerGasFeeForSwap))
 
 				assertEventEmitted(suite, ctx, types.TypeEvtTokenSwapped, 1)
 
@@ -199,11 +203,15 @@ func (suite *KeeperTestSuite) TestBalancerPoolSimpleSwapExactAmountOut() {
 				spotPriceBefore, err := keeper.CalculateSpotPrice(ctx, poolId, test.param.tokenInDenom, test.param.tokenOut.Denom)
 				suite.NoError(err, "test: %v", test.name)
 
+				prevGasConsumed := suite.Ctx.GasMeter().GasConsumed()
 				tokenInAmount, err := keeper.SwapExactAmountOut(ctx, suite.TestAccs[0], poolId, test.param.tokenInDenom, test.param.tokenInMaxAmount, test.param.tokenOut)
 				suite.NoError(err, "test: %v", test.name)
 				suite.True(tokenInAmount.Equal(test.param.expectedTokenInAmount),
 					"test: %v\n expect_eq actual: %s, expected: %s",
 					test.name, tokenInAmount, test.param.expectedTokenInAmount)
+				gasConsumedForSwap := suite.Ctx.GasMeter().GasConsumed() - prevGasConsumed
+				// We consume `types.GasFeeForSwap` directly, so the extra I/O operation mean we end up consuming more.
+				suite.Assert().Greater(gasConsumedForSwap, uint64(types.BalancerGasFeeForSwap))
 
 				assertEventEmitted(suite, ctx, types.TypeEvtTokenSwapped, 1)
 

x/gamm/pool-models/balancer/pool.go

@@ -584,6 +584,8 @@ func (p *Pool) SwapInAmtGivenOut(
 
 // ApplySwap.
 func (p *Pool) applySwap(ctx sdk.Context, tokensIn sdk.Coins, tokensOut sdk.Coins) error {
+	// Fixed gas consumption per swap to prevent spam
+	ctx.GasMeter().ConsumeGas(types.BalancerGasFeeForSwap, "balancer swap computation")
 	// Also ensures that len(tokensIn) = 1 = len(tokensOut)
 	inPoolAsset, outPoolAsset, err := p.parsePoolAssetsCoins(tokensIn, tokensOut)
 	if err != nil {

x/gamm/types/constants.go

@@ -11,7 +11,8 @@ const (
 	OneShareExponent = 18
 	// Raise 10 to the power of SigFigsExponent to determine number of significant figures.
 	// i.e. SigFigExponent = 8 is 10^8 which is 100000000. This gives 8 significant figures.
-	SigFigsExponent = 8
+	SigFigsExponent       = 8
+	BalancerGasFeeForSwap = 10_000
 )
 
 var (