Arbitrage tx mempool filter (#741)

* Add Arb checktx filter, to raise gas

* Add config params for min fee for arbitrage tx

* Small improvements, add changelog

* Fix bug in swap_msg logic

CHANGELOG.md

@@ -43,6 +43,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Features
 
+- [#741](https://github.com/osmosis-labs/osmosis/pull/741) Allow node operators to set a second min gas price for arbitrage txs.
 - [#623](https://github.com/osmosis-labs/osmosis/pull/623) Use gosec for staticly linting for common non-determinism issues in SDK applications.
 
 ## Minor improvements & Bug Fixes

app/ante.go

@@ -1,6 +1,9 @@
 package app
 
 import (
+	"fmt"
+
+	servertypes "github.com/cosmos/cosmos-sdk/server/types"
 	sdk "github.com/cosmos/cosmos-sdk/types"
 	sdkerrors "github.com/cosmos/cosmos-sdk/types/errors"
 
@@ -18,19 +21,24 @@ import (
 // Link to default ante handler used by cosmos sdk:
 // https://github.com/cosmos/cosmos-sdk/blob/v0.43.0/x/auth/ante/ante.go#L41
 func NewAnteHandler(
+	appOpts servertypes.AppOptions,
 	ak ante.AccountKeeper, bankKeeper authtypes.BankKeeper,
 	txFeesKeeper *txfeeskeeper.Keeper, spotPriceCalculator txfeestypes.SpotPriceCalculator,
 	sigGasConsumer ante.SignatureVerificationGasConsumer,
 	signModeHandler signing.SignModeHandler,
 	channelKeeper channelkeeper.Keeper,
 ) sdk.AnteHandler {
+	mempoolFeeDecorator := txfeeskeeper.NewMempoolFeeDecorator(*txFeesKeeper)
+	// Optional if anyone else is using this repo. Primarily of impact for Osmosis.
+	// TODO: Abstract this better
+	mempoolFeeDecorator.SetArbMinGasFee(parseArbGasFromConfig(appOpts))
 	return sdk.ChainAnteDecorators(
 		ante.NewSetUpContextDecorator(), // outermost AnteDecorator. SetUpContext must be called first
 		ante.NewRejectExtensionOptionsDecorator(),
 		NewMempoolMaxGasPerTxDecorator(),
 		// Use Mempool Fee Decorator from our txfees module instead of default one from auth
 		// https://github.com/cosmos/cosmos-sdk/blob/master/x/auth/middleware/fee.go#L34
-		txfeeskeeper.NewMempoolFeeDecorator(*txFeesKeeper),
+		mempoolFeeDecorator,
 		ante.NewValidateBasicDecorator(),
 		ante.TxTimeoutHeightDecorator{},
 		ante.NewValidateMemoDecorator(ak),
@@ -45,6 +53,25 @@ func NewAnteHandler(
 	)
 }
 
+// TODO: Abstract this function better. We likely need a parse `osmosis-mempool` config section.
+func parseArbGasFromConfig(appOpts servertypes.AppOptions) sdk.Dec {
+	arbMinFeeInterface := appOpts.Get("osmosis-mempool.arbitrage-min-gas-fee")
+	arbMinFee := txfeeskeeper.DefaultArbMinGasFee
+	if arbMinFeeInterface != nil {
+		arbMinFeeStr, ok := arbMinFeeInterface.(string)
+		if !ok {
+			panic("invalidly configured osmosis-mempool.arbitrage-min-gas-fee")
+		}
+		var err error
+		// pre-pend 0 to allow the config to start with a decimal, e.g. ".01"
+		arbMinFee, err = sdk.NewDecFromStr("0" + arbMinFeeStr)
+		if err != nil {
+			panic(fmt.Errorf("invalidly configured osmosis-mempool.arbitrage-min-gas-fee, err= %v", err))
+		}
+	}
+	return arbMinFee
+}
+
 // NewMempoolMaxGasPerTxDecorator will check if the transaction's gas
 // is greater than the local validator's max_gas_wanted_per_tx.
 // TODO: max_gas_per_tx is hardcoded here, should move to being defined in app.toml.

app/app.go

@@ -436,6 +436,7 @@ func NewOsmosisApp(
 	app.SetBeginBlocker(app.BeginBlocker)
 	app.SetAnteHandler(
 		NewAnteHandler(
+			appOpts,
 			app.AccountKeeper, app.BankKeeper,
 			app.TxFeesKeeper, app.GAMMKeeper,
 			ante.DefaultSigVerificationGasConsumer,

cmd/osmosisd/cmd/root.go

@@ -82,8 +82,14 @@ func NewRootCmd() (*cobra.Command, params.EncodingConfig) {
 // return "", nil if no custom configuration is required for the application.
 func initAppConfig() (string, interface{}) {
 
+	type OsmosisMempoolConfig struct {
+		ArbitrageMinGasPrice string `mapstructure:"arbitrage-min-gas-fee"`
+	}
+
 	type CustomAppConfig struct {
 		serverconfig.Config
+
+		OsmosisMempoolConfig OsmosisMempoolConfig `mapstructure:"osmosis-mempool"`
 	}
 
 	// Optionally allow the chain developer to overwrite the SDK's default
@@ -94,7 +100,22 @@ func initAppConfig() (string, interface{}) {
 	srvCfg.StateSync.SnapshotKeepRecent = 2
 	srvCfg.MinGasPrices = "0uosmo"
 
-	return serverconfig.DefaultConfigTemplate, CustomAppConfig{Config: *srvCfg}
+	memCfg := OsmosisMempoolConfig{ArbitrageMinGasPrice: "0.01"}
+
+	OsmosisAppCfg := CustomAppConfig{Config: *srvCfg, OsmosisMempoolConfig: memCfg}
+
+	OsmosisAppTemplate := serverconfig.DefaultConfigTemplate + `
+###############################################################################
+###                      Osmosis Mempool Configuration                      ###
+###############################################################################
+
+[osmosis-mempool]
+# This is the minimum gas fee any arbitrage tx should have, denominated in uosmo per gas
+# Default value of ".005" then means that a tx with 1 million gas costs (.005 uosmo/gas) * 1_000_000 gas = .005 osmo
+arbitrage-min-gas-fee = ".005"
+`
+
+	return OsmosisAppTemplate, OsmosisAppCfg
 }
 
 func initRootCmd(rootCmd *cobra.Command, encodingConfig params.EncodingConfig) {

x/gamm/types/msg_lp.go

@@ -0,0 +1,42 @@
+package types
+
+type LiquidityChangeType int
+
+const (
+	AddLiquidity LiquidityChangeType = iota
+	RemoveLiquidity
+)
+
+// LiquidityChangeMsg defines a simple interface for determining if an LP msg
+// is removing or adding liquidity.
+type LiquidityChangeMsg interface {
+	LiquidityChangeType() LiquidityChangeType
+}
+
+var _ LiquidityChangeMsg = MsgExitPool{}
+var _ LiquidityChangeMsg = MsgExitSwapShareAmountIn{}
+var _ LiquidityChangeMsg = MsgExitSwapExternAmountOut{}
+
+var _ LiquidityChangeMsg = MsgJoinPool{}
+var _ LiquidityChangeMsg = MsgJoinSwapExternAmountIn{}
+var _ LiquidityChangeMsg = MsgJoinSwapShareAmountOut{}
+
+func (msg MsgExitPool) LiquidityChangeType() LiquidityChangeType {
+	return RemoveLiquidity
+}
+func (msg MsgExitSwapShareAmountIn) LiquidityChangeType() LiquidityChangeType {
+	return RemoveLiquidity
+}
+func (msg MsgExitSwapExternAmountOut) LiquidityChangeType() LiquidityChangeType {
+	return RemoveLiquidity
+}
+
+func (msg MsgJoinPool) LiquidityChangeType() LiquidityChangeType {
+	return AddLiquidity
+}
+func (msg MsgJoinSwapExternAmountIn) LiquidityChangeType() LiquidityChangeType {
+	return AddLiquidity
+}
+func (msg MsgJoinSwapShareAmountOut) LiquidityChangeType() LiquidityChangeType {
+	return AddLiquidity
+}

x/gamm/types/msg_swap.go

@@ -0,0 +1,42 @@
+package types
+
+// SwapMsg defines a simple interface for getting the token denoms on a swap message route.
+type SwapMsgRoute interface {
+	TokenInDenom() string
+	TokenOutDenom() string
+	TokenDenomsOnPath() []string
+}
+
+var _ SwapMsgRoute = MsgSwapExactAmountOut{}
+var _ SwapMsgRoute = MsgSwapExactAmountIn{}
+
+func (msg MsgSwapExactAmountOut) TokenInDenom() string {
+	return msg.Routes[0].GetTokenInDenom()
+}
+func (msg MsgSwapExactAmountOut) TokenOutDenom() string {
+	return msg.TokenOut.Denom
+}
+func (msg MsgSwapExactAmountOut) TokenDenomsOnPath() []string {
+	denoms := make([]string, 0, len(msg.Routes)+1)
+	for i := 0; i < len(msg.Routes); i++ {
+		denoms = append(denoms, msg.Routes[i].TokenInDenom)
+	}
+	denoms = append(denoms, msg.TokenOutDenom())
+	return denoms
+}
+
+func (msg MsgSwapExactAmountIn) TokenInDenom() string {
+	return msg.TokenIn.Denom
+}
+func (msg MsgSwapExactAmountIn) TokenOutDenom() string {
+	lastRouteIndex := len(msg.Routes) - 1
+	return msg.Routes[lastRouteIndex].GetTokenOutDenom()
+}
+func (msg MsgSwapExactAmountIn) TokenDenomsOnPath() []string {
+	denoms := make([]string, 0, len(msg.Routes)+1)
+	denoms = append(denoms, msg.TokenInDenom())
+	for i := 0; i < len(msg.Routes); i++ {
+		denoms = append(denoms, msg.Routes[i].TokenOutDenom)
+	}
+	return denoms
+}

x/txfees/README.md

@@ -20,6 +20,14 @@ Currently the only supported metadata & spot price calculator is using a GAMM po
     * The simple alternative is only check fee equivalency at a txs entry into the mempool, which allows someone to manipulate price down to have many txs enter the chain at low cost.
     * Another alternative is to use TWAP instead of Spot Price once it is available on-chain
     * The former concern isn't very worrisome as long as some nodes have 0 min tx fees.
+* A separate min-gas-fee can be set on every node for arbitrage txs. Methods of detecting an arb tx atm
+  * does start token of a swap = final token of swap (definitionally correct)
+  * does it have multiple swap messages, with different tx ins. If so, we assume its an arb.
+    * This has false positives, but is intended to avoid the obvious solution of splitting an arb into multiple messages.
+  * We record all denoms seen across all swaps, and see if any duplicates. (TODO)
+  * Contains both JoinPool and ExitPool messages in one tx.
+    * Has some false positives.
+  * These false positives seem like they primarily will get hit during batching of many distinct operations, not really in one atomic action.
 
 ## New SDK messages
 

x/txfees/keeper/feedecorator.go

@@ -4,25 +4,37 @@ import (
 	sdk "github.com/cosmos/cosmos-sdk/types"
 	sdkerrors "github.com/cosmos/cosmos-sdk/types/errors"
 
+	"github.com/osmosis-labs/osmosis/x/txfees/keeper/txfee_filters"
 	"github.com/osmosis-labs/osmosis/x/txfees/types"
 )
 
+// DefaultArbMinGasFee if its not set in a config somewhere.
+// currently 0 uosmo/gas to preserve functionality with old node software
+// TODO: Bump after next minor version. (in 6.2+)
+var DefaultArbMinGasFee sdk.Dec = sdk.ZeroDec()
+
 // MempoolFeeDecorator will check if the transaction's fee is at least as large
 // as the local validator's minimum gasFee (defined in validator config).
 // If fee is too low, decorator returns error and tx is rejected from mempool.
 // Note this only applies when ctx.CheckTx = true
 // If fee is high enough or not CheckTx, then call next AnteHandler
 // CONTRACT: Tx must implement FeeTx to use MempoolFeeDecorator
 type MempoolFeeDecorator struct {
-	TxFeesKeeper Keeper
+	TxFeesKeeper       Keeper
+	ConfigArbMinGasFee sdk.Dec
 }
 
 func NewMempoolFeeDecorator(txFeesKeeper Keeper) MempoolFeeDecorator {
 	return MempoolFeeDecorator{
-		TxFeesKeeper: txFeesKeeper,
+		TxFeesKeeper:       txFeesKeeper,
+		ConfigArbMinGasFee: DefaultArbMinGasFee.Clone(),
 	}
 }
 
+func (mfd *MempoolFeeDecorator) SetArbMinGasFee(dec sdk.Dec) {
+	mfd.ConfigArbMinGasFee = dec
+}
+
 func (mfd MempoolFeeDecorator) AnteHandle(ctx sdk.Context, tx sdk.Tx, simulate bool, next sdk.AnteHandler) (newCtx sdk.Context, err error) {
 	// The SDK currently requires all txs to be FeeTx's in CheckTx, within its mempool fee decorator.
 	// See: https://github.com/cosmos/cosmos-sdk/blob/f726a2398a26bdaf71d78dbf56a82621e84fd098/x/auth/middleware/fee.go#L34-L37
@@ -59,8 +71,7 @@ func (mfd MempoolFeeDecorator) AnteHandle(ctx sdk.Context, tx sdk.Tx, simulate b
 	// So we ensure that the provided fees meet a minimum threshold for the validator,
 	// converting every non-osmo specified asset into an osmo-equivalent amount, to determine sufficiency.
 	if (ctx.IsCheckTx() || ctx.IsReCheckTx()) && !simulate {
-		minGasPrices := ctx.MinGasPrices()
-		minBaseGasPrice := minGasPrices.AmountOf(baseDenom)
+		minBaseGasPrice := mfd.GetMinBaseGasPriceForTx(ctx, baseDenom, tx)
 		if !(minBaseGasPrice.IsZero()) {
 			if len(feeCoins) != 1 {
 				return ctx, sdkerrors.Wrapf(sdkerrors.ErrInsufficientFee, "no fee attached")
@@ -96,3 +107,12 @@ func (k Keeper) IsSufficientFee(ctx sdk.Context, minBaseGasPrice sdk.Dec, gasReq
 
 	return nil
 }
+
+func (mfd MempoolFeeDecorator) GetMinBaseGasPriceForTx(ctx sdk.Context, baseDenom string, tx sdk.Tx) sdk.Dec {
+	cfgMinGasPrice := ctx.MinGasPrices().AmountOf(baseDenom)
+
+	if txfee_filters.IsArbTxLoose(tx) {
+		return sdk.MaxDec(cfgMinGasPrice, mfd.ConfigArbMinGasFee)
+	}
+	return cfgMinGasPrice
+}

x/txfees/keeper/txfee_filters/README.md

@@ -0,0 +1,5 @@
+# TXfee filters
+
+See https://github.com/osmosis-labs/osmosis/issues/738
+
+Want to move towards that, right now this is a stepping stone for that. We currently define a filter for recognizing if a tx is an arb transaction, and if so raising its gas price accordingly.

x/txfees/keeper/txfee_filters/arb_tx.go

@@ -0,0 +1,51 @@
+package txfee_filters
+
+import (
+	sdk "github.com/cosmos/cosmos-sdk/types"
+	gammtypes "github.com/osmosis-labs/osmosis/x/gamm/types"
+)
+
+// We check if a tx is an arbitrage for the mempool right now by seeing:
+// 1) does start token of a msg = final token of msg (definitionally correct)
+// 2) does it have multiple swap messages, with different tx ins. If so, we assume its an arb.
+//    - This has false positives, but is intended to avoid the obvious solution of splitting
+//      an arb into multiple messages.
+// 3) We record all denoms seen across all swaps, and see if any duplicates. (TODO)
+// 4) Contains both JoinPool and ExitPool messages in one tx.
+//    - Has some false positives, but they seem relatively contrived.
+// TODO: Move the first component to a future router module
+func IsArbTxLoose(tx sdk.Tx) bool {
+	msgs := tx.GetMsgs()
+
+	swapInDenom := ""
+	lpTypesSeen := make(map[gammtypes.LiquidityChangeType]bool, 2)
+
+	for _, m := range msgs {
+		// (4) Check that the tx doesn't have both JoinPool & ExitPool msgs
+		lpMsg, isLpMsg := m.(gammtypes.LiquidityChangeMsg)
+		if isLpMsg {
+			lpTypesSeen[lpMsg.LiquidityChangeType()] = true
+			if len(lpTypesSeen) > 1 {
+				return true
+			}
+		}
+
+		swapMsg, isSwapMsg := m.(gammtypes.SwapMsgRoute)
+		if !isSwapMsg {
+			continue
+		}
+
+		// (1) Check that swap denom in != swap denom out
+		if swapMsg.TokenInDenom() == swapMsg.TokenOutDenom() {
+			return true
+		}
+
+		// (2)
+		if swapInDenom != "" && swapMsg.TokenInDenom() != swapInDenom {
+			return true
+		}
+		swapInDenom = swapMsg.TokenInDenom()
+	}
+
+	return false
+}