test: add e2e test for usdt special case (#6784)

* feat: revoke USDT approvals in ConfirmSwapModal

* chore: fix bad merge

* test: add e2e test for usdt special case

* fix: refactor test

* fix: make variable static

* fix: comments

cypress/e2e/permit2.test.ts

+import { BigNumber } from '@ethersproject/bignumber'
 import { MaxUint160, MaxUint256 } from '@uniswap/permit2-sdk'
+import { CurrencyAmount, Token } from '@uniswap/sdk-core'
 
-import { DAI, USDC_MAINNET } from '../../src/constants/tokens'
+import { DAI, USDC_MAINNET, USDT } from '../../src/constants/tokens'
 import { getTestSelector } from '../utils'
 
 /** Initiates a swap. */
@@ -13,30 +15,26 @@ function initiateSwap() {
 }
 
 describe('Permit2', () => {
-  // The same tokens are used for all permit2 tests.
-  const INPUT_TOKEN = DAI
-  const OUTPUT_TOKEN = USDC_MAINNET
-
-  beforeEach(() => {
-    // Sets up a swap between INPUT_TOKEN and OUTPUT_TOKEN.
-    cy.visit(`/swap/?inputCurrency=${INPUT_TOKEN.address}&outputCurrency=${OUTPUT_TOKEN.address}`, {
+  function setupInputs(inputToken: Token, outputToken: Token) {
+    // Sets up a swap between inputToken and outputToken.
+    cy.visit(`/swap/?inputCurrency=${inputToken.address}&outputCurrency=${outputToken.address}`, {
       ethereum: 'hardhat',
     })
     cy.get('#swap-currency-input .token-amount-input').type('0.01')
-  })
+  }
 
   /** Asserts permit2 has a max approval for spend of the input token on-chain. */
-  function expectTokenAllowanceForPermit2ToBeMax() {
+  function expectTokenAllowanceForPermit2ToBeMax(inputToken: Token) {
     // check token approval
     cy.hardhat()
-      .then(({ approval, wallet }) => approval.getTokenAllowanceForPermit2({ owner: wallet, token: INPUT_TOKEN }))
+      .then(({ approval, wallet }) => approval.getTokenAllowanceForPermit2({ owner: wallet, token: inputToken }))
       .should('deep.equal', MaxUint256)
   }
 
   /** Asserts the universal router has a max permit2 approval for spend of the input token on-chain. */
-  function expectPermit2AllowanceForUniversalRouterToBeMax() {
+  function expectPermit2AllowanceForUniversalRouterToBeMax(inputToken: Token) {
     cy.hardhat()
-      .then((hardhat) => hardhat.approval.getPermit2Allowance({ owner: hardhat.wallet, token: INPUT_TOKEN }))
+      .then((hardhat) => hardhat.approval.getPermit2Allowance({ owner: hardhat.wallet, token: inputToken }))
       .then((allowance) => {
         cy.wrap(MaxUint160.eq(allowance.amount)).should('eq', true)
         // Asserts that the on-chain expiration is in 30 days, within a tolerance of 40 seconds.
@@ -51,6 +49,7 @@ describe('Permit2', () => {
     beforeEach(() => cy.hardhat({ automine: false }))
 
     it('swaps after completing full permit2 approval process', () => {
+      setupInputs(DAI, USDC_MAINNET)
       initiateSwap()
 
       // verify that the modal retains its state when the window loses focus
@@ -61,7 +60,7 @@ describe('Permit2', () => {
       cy.wait('@eth_sendRawTransaction')
       cy.hardhat().then((hardhat) => hardhat.mine())
       cy.get(getTestSelector('popups')).contains('Approved')
-      expectTokenAllowanceForPermit2ToBeMax()
+      expectTokenAllowanceForPermit2ToBeMax(DAI)
 
       // Verify permit2 approval
       cy.contains('Allow DAI to be used for swapping')
@@ -70,12 +69,13 @@ describe('Permit2', () => {
       cy.hardhat().then((hardhat) => hardhat.mine())
       cy.contains('Success')
       cy.get(getTestSelector('popups')).contains('Swapped')
-      expectPermit2AllowanceForUniversalRouterToBeMax()
+      expectPermit2AllowanceForUniversalRouterToBeMax(DAI)
     })
 
     it('swaps with existing permit approval and missing token approval', () => {
+      setupInputs(DAI, USDC_MAINNET)
       cy.hardhat().then(async (hardhat) => {
-        await hardhat.approval.setPermit2Allowance({ owner: hardhat.wallet, token: INPUT_TOKEN })
+        await hardhat.approval.setPermit2Allowance({ owner: hardhat.wallet, token: DAI })
         await hardhat.mine()
       })
       initiateSwap()
@@ -85,7 +85,50 @@ describe('Permit2', () => {
       cy.wait('@eth_sendRawTransaction')
       cy.hardhat().then((hardhat) => hardhat.mine())
       cy.get(getTestSelector('popups')).contains('Approved')
-      expectTokenAllowanceForPermit2ToBeMax()
+      expectTokenAllowanceForPermit2ToBeMax(DAI)
+
+      // Verify transaction
+      cy.wait('@eth_sendRawTransaction')
+      cy.hardhat().then((hardhat) => hardhat.mine())
+      cy.contains('Success')
+      cy.get(getTestSelector('popups')).contains('Swapped')
+    })
+
+    /**
+     * On mainnet, you have to revoke USDT approval before increasing it.
+     * From the token contract:
+     *   To change the approve amount you first have to reduce the addresses`
+     *   allowance to zero by calling `approve(_spender, 0)` if it is not
+     *   already 0 to mitigate the race condition described here:
+     *   https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
+     */
+    it('swaps USDT with existing permit, and existing but insufficient token approval', () => {
+      cy.hardhat().then(async (hardhat) => {
+        await hardhat.fund(hardhat.wallet, CurrencyAmount.fromRawAmount(USDT, 2e6))
+        await hardhat.mine()
+        await hardhat.approval.setTokenAllowanceForPermit2({ owner: hardhat.wallet, token: USDT }, 1e6)
+        await hardhat.mine()
+        await hardhat.approval.setPermit2Allowance({ owner: hardhat.wallet, token: USDT })
+        await hardhat.mine()
+      })
+      setupInputs(USDT, USDC_MAINNET)
+      cy.get('#swap-currency-input .token-amount-input').clear().type('2')
+      initiateSwap()
+
+      // Verify allowance revocation
+      cy.contains('Reset USDT')
+      cy.wait('@eth_sendRawTransaction')
+      cy.hardhat().then((hardhat) => hardhat.mine())
+      cy.hardhat()
+        .then(({ approval, wallet }) => approval.getTokenAllowanceForPermit2({ owner: wallet, token: USDT }))
+        .should('deep.equal', BigNumber.from(0))
+
+      // Verify token approval
+      cy.contains('Enable spending USDT on Uniswap')
+      cy.wait('@eth_sendRawTransaction')
+      cy.hardhat().then((hardhat) => hardhat.mine())
+      cy.get(getTestSelector('popups')).contains('Approved')
+      expectTokenAllowanceForPermit2ToBeMax(USDT)
 
       // Verify transaction
       cy.wait('@eth_sendRawTransaction')
@@ -98,10 +141,11 @@ describe('Permit2', () => {
   it('swaps when user has already approved token and permit2', () => {
     cy.hardhat().then(({ approval, wallet }) =>
       Promise.all([
-        approval.setTokenAllowanceForPermit2({ owner: wallet, token: INPUT_TOKEN }),
-        approval.setPermit2Allowance({ owner: wallet, token: INPUT_TOKEN }),
+        approval.setTokenAllowanceForPermit2({ owner: wallet, token: DAI }),
+        approval.setPermit2Allowance({ owner: wallet, token: DAI }),
       ])
     )
+    setupInputs(DAI, USDC_MAINNET)
     initiateSwap()
 
     // Verify transaction
@@ -110,6 +154,7 @@ describe('Permit2', () => {
   })
 
   it('swaps after handling user rejection of both approval and signature', () => {
+    setupInputs(DAI, USDC_MAINNET)
     const USER_REJECTION = { code: 4001 }
     cy.hardhat().then((hardhat) => {
       // Reject token approval
@@ -132,7 +177,7 @@ describe('Permit2', () => {
 
       // Verify token approval
       cy.get(getTestSelector('popups')).contains('Approved')
-      expectTokenAllowanceForPermit2ToBeMax()
+      expectTokenAllowanceForPermit2ToBeMax(DAI)
 
       // Verify permit2 approval rejection
       cy.wrap(permitApprovalStub).should('be.calledWith', 'eth_signTypedData_v4')
@@ -145,30 +190,32 @@ describe('Permit2', () => {
       // Verify permit2 approval
       cy.contains('Success')
       cy.get(getTestSelector('popups')).contains('Swapped')
-      expectPermit2AllowanceForUniversalRouterToBeMax()
+      expectPermit2AllowanceForUniversalRouterToBeMax(DAI)
     })
   })
 
   it('prompts token approval when existing approval amount is too low', () => {
+    setupInputs(DAI, USDC_MAINNET)
     cy.hardhat().then(({ approval, wallet }) =>
       Promise.all([
-        approval.setPermit2Allowance({ owner: wallet, token: INPUT_TOKEN }),
-        approval.setTokenAllowanceForPermit2({ owner: wallet, token: INPUT_TOKEN }, 1),
+        approval.setPermit2Allowance({ owner: wallet, token: DAI }),
+        approval.setTokenAllowanceForPermit2({ owner: wallet, token: DAI }, 1),
       ])
     )
     initiateSwap()
 
     // Verify token approval
     cy.get(getTestSelector('popups')).contains('Approved')
-    expectPermit2AllowanceForUniversalRouterToBeMax()
+    expectPermit2AllowanceForUniversalRouterToBeMax(DAI)
   })
 
   it('prompts signature when existing permit approval is expired', () => {
+    setupInputs(DAI, USDC_MAINNET)
     const expiredAllowance = { expiration: Math.floor((Date.now() - 1) / 1000) }
     cy.hardhat().then(({ approval, wallet }) =>
       Promise.all([
-        approval.setTokenAllowanceForPermit2({ owner: wallet, token: INPUT_TOKEN }),
-        approval.setPermit2Allowance({ owner: wallet, token: INPUT_TOKEN }, expiredAllowance),
+        approval.setTokenAllowanceForPermit2({ owner: wallet, token: DAI }),
+        approval.setPermit2Allowance({ owner: wallet, token: DAI }, expiredAllowance),
       ])
     )
     initiateSwap()
@@ -177,15 +224,16 @@ describe('Permit2', () => {
     cy.wait('@eth_signTypedData_v4')
     cy.contains('Success')
     cy.get(getTestSelector('popups')).contains('Swapped')
-    expectPermit2AllowanceForUniversalRouterToBeMax()
+    expectPermit2AllowanceForUniversalRouterToBeMax(DAI)
   })
 
   it('prompts signature when existing permit approval amount is too low', () => {
+    setupInputs(DAI, USDC_MAINNET)
     const smallAllowance = { amount: 1 }
     cy.hardhat().then(({ approval, wallet }) =>
       Promise.all([
-        approval.setTokenAllowanceForPermit2({ owner: wallet, token: INPUT_TOKEN }),
-        approval.setPermit2Allowance({ owner: wallet, token: INPUT_TOKEN }, smallAllowance),
+        approval.setTokenAllowanceForPermit2({ owner: wallet, token: DAI }),
+        approval.setPermit2Allowance({ owner: wallet, token: DAI }, smallAllowance),
       ])
     )
     initiateSwap()
@@ -194,6 +242,6 @@ describe('Permit2', () => {
     cy.wait('@eth_signTypedData_v4')
     cy.contains('Success')
     cy.get(getTestSelector('popups')).contains('Swapped')
-    expectPermit2AllowanceForUniversalRouterToBeMax()
+    expectPermit2AllowanceForUniversalRouterToBeMax(DAI)
   })
 })

src/hooks/useTokenAllowance.ts

@@ -7,6 +7,8 @@ import { ApproveTransactionInfo, TransactionType } from 'state/transactions/type
 import { UserRejectedRequestError } from 'utils/errors'
 import { didUserReject } from 'utils/swapErrorToUserReadableMessage'
 
+const MAX_ALLOWANCE = MaxUint256.toString()
+
 export function useTokenAllowance(
   token?: Token,
   owner?: string,
@@ -48,8 +50,7 @@ export function useUpdateTokenAllowance(
       if (!contract) throw new Error('missing contract')
       if (!spender) throw new Error('missing spender')
 
-      const maxAllowance = MaxUint256.toString()
-      const allowance = amount.equalTo(0) ? '0' : maxAllowance
+      const allowance = amount.equalTo(0) ? '0' : MAX_ALLOWANCE
       const response = await contract.approve(spender, allowance)
       return {
         response,