feat: Handle fee-on-transfer token taxes in price impact calculations

package.json

@@ -27,7 +27,7 @@
   "license": "MIT",
   "dependencies": {
     "@ethersproject/abi": "^5.5.0",
-    "@uniswap/sdk-core": "^4",
+    "@uniswap/sdk-core": "^4.0.7",
     "@uniswap/swap-router-contracts": "^1.1.0",
     "@uniswap/v2-sdk": "^3.2.0",
     "@uniswap/v3-sdk": "^3.10.0"

src/constants.ts

@@ -1,3 +1,4 @@
+import { Percent } from '@uniswap/sdk-core'
 import JSBI from 'jsbi'
 
 export const MSG_SENDER = '0x0000000000000000000000000000000000000001'
@@ -8,3 +9,5 @@ export const ONE = JSBI.BigInt(1)
 
 // = 1 << 23 or 100000000000000000000000
 export const V2_FEE_PATH_PLACEHOLDER = 8388608
+
+export const ZERO_PERCENT = new Percent(ZERO)

src/entities/trade.test.ts

@@ -1,4 +1,5 @@
 import { sqrt, Token, CurrencyAmount, TradeType, WETH9, Ether, Percent, Price } from '@uniswap/sdk-core'
+import { BigNumber } from '@ethersproject/bignumber'
 import JSBI from 'jsbi'
 import { MixedRoute, RouteV2, RouteV3 } from './route'
 import { Trade } from './trade'
@@ -21,6 +22,26 @@ describe('Trade', () => {
   const token1 = new Token(1, '0x0000000000000000000000000000000000000002', 18, 't1', 'token1')
   const token2 = new Token(1, '0x0000000000000000000000000000000000000003', 18, 't2', 'token2')
   const token3 = new Token(1, '0x0000000000000000000000000000000000000004', 18, 't3', 'token3')
+  const token4WithTax = new Token(
+    1,
+    '0x0000000000000000000000000000000000000005',
+    18,
+    't4',
+    'token4',
+    false,
+    BigNumber.from(100),
+    BigNumber.from(100)
+  )
+  const token5WithTax = new Token(
+    1,
+    '0x0000000000000000000000000000000000000005',
+    18,
+    't5',
+    'token5',
+    false,
+    BigNumber.from(500),
+    BigNumber.from(500)
+  )
 
   function v2StylePool(
     reserve0: CurrencyAmount<Token>,
@@ -101,6 +122,16 @@ describe('Trade', () => {
     CurrencyAmount.fromRawAmount(token2, JSBI.BigInt(10000))
   )
 
+  const pair_tax_output = new Pair(
+    CurrencyAmount.fromRawAmount(weth, JSBI.BigInt(100000)),
+    CurrencyAmount.fromRawAmount(token4WithTax, JSBI.BigInt(100000))
+  )
+
+  const pair_tax_input = new Pair(
+    CurrencyAmount.fromRawAmount(token5WithTax, JSBI.BigInt(100000)),
+    CurrencyAmount.fromRawAmount(weth, JSBI.BigInt(100000))
+  )
+
   const pool_weth_0 = v2StylePool(
     CurrencyAmount.fromRawAmount(weth, JSBI.BigInt(100000)),
     CurrencyAmount.fromRawAmount(token0, JSBI.BigInt(100000))
@@ -1160,6 +1191,50 @@ describe('Trade', () => {
   })
   // v3 sdk price impact tests
   describe('#priceImpact', () => {
+    describe('with FOT sell fees', () => {
+      const routev2 = new V2RouteSDK([pair_tax_output], weth, token4WithTax)
+      const trade = new Trade({
+        v2Routes: [
+          {
+            routev2,
+            inputAmount: CurrencyAmount.fromRawAmount(weth, 100),
+            outputAmount: CurrencyAmount.fromRawAmount(token4WithTax, 69),
+          },
+        ],
+        v3Routes: [],
+        tradeType: TradeType.EXACT_INPUT,
+      })
+
+      it('is cached', () => {
+        expect(trade.priceImpact === trade.priceImpact).toStrictEqual(true)
+      })
+      it('is correct', () => {
+        expect(trade.priceImpact.toSignificant(3)).toEqual('30.3')
+      })
+    })
+
+    describe('with FOT buy fees', () => {
+      const routev2 = new V2RouteSDK([pair_tax_input], token5WithTax, weth)
+      const trade = new Trade({
+        v2Routes: [
+          {
+            routev2,
+            inputAmount: CurrencyAmount.fromRawAmount(token5WithTax, 100),
+            outputAmount: CurrencyAmount.fromRawAmount(weth, 69),
+          },
+        ],
+        v3Routes: [],
+        tradeType: TradeType.EXACT_INPUT,
+      })
+
+      it('is cached', () => {
+        expect(trade.priceImpact === trade.priceImpact).toStrictEqual(true)
+      })
+      it('is correct', () => {
+        expect(trade.priceImpact.toSignificant(3)).toEqual('27.4')
+      })
+    })
+
     describe('tradeType = EXACT_INPUT', () => {
       const routev3 = new V3RouteSDK([pool_0_1, pool_1_2], token0, token2)
       const mixedRoute = new MixedRouteSDK([pool_0_1, pool_1_2], token0, token2)

src/entities/trade.ts

@@ -2,7 +2,7 @@ import { Currency, CurrencyAmount, Fraction, Percent, Price, TradeType } from '@
 import { Pair, Route as V2RouteSDK, Trade as V2TradeSDK } from '@uniswap/v2-sdk'
 import { Pool, Route as V3RouteSDK, Trade as V3TradeSDK } from '@uniswap/v3-sdk'
 import invariant from 'tiny-invariant'
-import { ONE, ZERO } from '../constants'
+import { ONE, ZERO, ZERO_PERCENT } from '../constants'
 import { MixedRouteSDK } from './mixedRoute/route'
 import { MixedRouteTrade as MixedRouteTradeSDK } from './mixedRoute/trade'
 import { IRoute, MixedRoute, RouteV2, RouteV3 } from './route'
@@ -158,13 +158,35 @@ export class Trade<TInput extends Currency, TOutput extends Currency, TTradeType
     )
   }
 
+  /**
+   * Returns the sell tax of the input token
+   */
+  public get inputTax(): Percent {
+    const inputCurrency = this.inputAmount.currency
+    if (inputCurrency.isNative || !inputCurrency.wrapped.sellFeeBps) return ZERO_PERCENT
+
+    return new Percent(inputCurrency.wrapped.sellFeeBps.toNumber(), 10000)
+  }
+
+  /**
+   * Returns the buy tax of the output token
+   */
+  public get outputTax(): Percent {
+    const outputCurrency = this.outputAmount.currency
+    if (outputCurrency.isNative || !outputCurrency.wrapped.buyFeeBps) return ZERO_PERCENT
+
+    return new Percent(outputCurrency.wrapped.buyFeeBps.toNumber(), 10000)
+  }
+
   /**
    * The cached result of the price impact computation
    * @private
    */
   private _priceImpact: Percent | undefined
   /**
-   * Returns the percent difference between the route's mid price and the price impact
+   * Returns the percent difference between the route's mid price and the expected execution price
+   * In order to exclude token taxes from the price impact calculation, the spot price is calculated
+   * using a ratio of values that go into the pools, which are the post-tax input amount and pre-tax output amount.
    */
   public get priceImpact(): Percent {
     if (this._priceImpact) {
@@ -174,10 +196,12 @@ export class Trade<TInput extends Currency, TOutput extends Currency, TTradeType
     let spotOutputAmount = CurrencyAmount.fromRawAmount(this.outputAmount.currency, 0)
     for (const { route, inputAmount } of this.swaps) {
       const midPrice = route.midPrice
-      spotOutputAmount = spotOutputAmount.add(midPrice.quote(inputAmount))
+      const postTaxInputAmount = inputAmount.multiply(new Fraction(ONE).subtract(this.inputTax))
+      spotOutputAmount = spotOutputAmount.add(midPrice.quote(postTaxInputAmount))
     }
 
-    const priceImpact = spotOutputAmount.subtract(this.outputAmount).divide(spotOutputAmount)
+    const preTaxOutputAmount = this.outputAmount.divide(new Fraction(ONE).subtract(this.outputTax))
+    const priceImpact = spotOutputAmount.subtract(preTaxOutputAmount).divide(spotOutputAmount)
     this._priceImpact = new Percent(priceImpact.numerator, priceImpact.denominator)
 
     return this._priceImpact

yarn.lock

@@ -1575,10 +1575,10 @@
   resolved "https://registry.npmjs.org/@uniswap/lib/-/lib-4.0.1-alpha.tgz"
   integrity sha512-f6UIliwBbRsgVLxIaBANF6w09tYqc6Y/qXdsrbEmXHyFA7ILiKrIwRFXe1yOg8M3cksgVsO9N7yuL2DdCGQKBA==
 
-"@uniswap/sdk-core@^4", "@uniswap/sdk-core@^4.0.2":
-  version "4.0.2"
-  resolved "https://registry.yarnpkg.com/@uniswap/sdk-core/-/sdk-core-4.0.2.tgz#2eca2b5bf00bad74519aef918465c19218285b4b"
-  integrity sha512-rR5xobsAAP4yMYC7C+0+duVx0pFoDn2lV9kTWpoKgH1WJuw7hD1uDEvuevU2dL89TuixVgGvnYd0QxmrMtsIlg==
+"@uniswap/sdk-core@^4", "@uniswap/sdk-core@^4.0.2", "@uniswap/sdk-core@^4.0.7":
+  version "4.0.7"
+  resolved "https://registry.yarnpkg.com/@uniswap/sdk-core/-/sdk-core-4.0.7.tgz#90dfd070d7e44494234618af398da158363ae827"
+  integrity sha512-jscx7KUIWzQatcL5PHY6xy0gEL9IGQcL5h/obxzX9foP2KoNk9cq66Ia8I2Kvpa7zBcPOeW1hU0hJNBq6CzcIQ==
   dependencies:
     "@ethersproject/address" "^5.0.2"
     big.js "^5.2.2"