Small improvements, add changelog

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

@@ -53,18 +53,20 @@ 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")
+			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))
+			panic(fmt.Errorf("invalidly configured osmosis-mempool.arbitrage-min-gas-fee, err= %v", err))
 		}
 	}
 	return arbMinFee

cmd/osmosisd/cmd/root.go

@@ -111,8 +111,8 @@ func initAppConfig() (string, interface{}) {
 
 [osmosis-mempool]
 # This is the minimum gas fee any arbitrage tx should have, denominated in uosmo per gas
-# Default value of ".01" then means that a tx with 1 million gas costs (.01 uosmo/gas) * 1_000_000 gas = .01 osmo
-arbitrage-min-gas-fee = ".01"
+# 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

x/gamm/types/msg_lp.go

@@ -7,7 +7,8 @@ const (
 	RemoveLiquidity
 )
 
-// SwapMsg defines a simple interface for getting the token denoms on a swap message route.
+// LiquidityChangeMsg defines a simple interface for determining if an LP msg
+// is removing or adding liquidity.
 type LiquidityChangeMsg interface {
 	LiquidityChangeType() LiquidityChangeType
 }

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

@@ -8,7 +8,10 @@ import (
 	"github.com/osmosis-labs/osmosis/x/txfees/types"
 )
 
-var DefaultArbMinGasFee sdk.Dec = sdk.NewDecWithPrec(1, 2) // .01uosmo/gas
+// 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).