diff --git a/CHANGELOG.md b/CHANGELOG.md index f978222ff5a..b856be6bb5d 100644 --- a/CHANGELOG.md +++ b/CHANGELOG.md @@ -5,6 +5,7 @@ * `Clones`: optimize clone creation ([#3329](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3329)) * `TimelockController`: Migrate `_call` to `_execute` and allow inheritance and overriding similar to `Governor`. ([#3317](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3317)) * `CrossChainEnabledPolygonChild`: replace the `require` statement with the custom error `NotCrossChainCall`. ([#3380](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3380)) + * `ERC20FlashMint`: Add customizable flash fee receiver. ([#3327](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3327)) ## 4.6.0 (2022-04-26) diff --git a/contracts/mocks/ERC20FlashMintMock.sol b/contracts/mocks/ERC20FlashMintMock.sol index 0bb7871fc70..c7772601b79 100644 --- a/contracts/mocks/ERC20FlashMintMock.sol +++ b/contracts/mocks/ERC20FlashMintMock.sol @@ -5,6 +5,9 @@ pragma solidity ^0.8.0; import "../token/ERC20/extensions/ERC20FlashMint.sol"; contract ERC20FlashMintMock is ERC20FlashMint { + uint256 _flashFeeAmount; + address _flashFeeReceiverAddress; + constructor( string memory name, string memory symbol, @@ -13,4 +16,29 @@ contract ERC20FlashMintMock is ERC20FlashMint { ) ERC20(name, symbol) { _mint(initialAccount, initialBalance); } + + function mint(address account, uint256 amount) public { + _mint(account, amount); + } + + function setFlashFee(uint256 amount) public { + _flashFeeAmount = amount; + } + + function flashFee(address token, uint256 amount) public view virtual override returns (uint256) { + super.flashFee(token, amount); + return _flashFeeAmount; + } + + function setFlashFeeReceiver(address receiver) public { + _flashFeeReceiverAddress = receiver; + } + + function flashFeeReceiver() public view returns (address) { + return _flashFeeReceiver(); + } + + function _flashFeeReceiver() internal view override returns (address) { + return _flashFeeReceiverAddress; + } } diff --git a/contracts/token/ERC20/extensions/ERC20FlashMint.sol b/contracts/token/ERC20/extensions/ERC20FlashMint.sol index dd124fb469b..8c8b88c751a 100644 --- a/contracts/token/ERC20/extensions/ERC20FlashMint.sol +++ b/contracts/token/ERC20/extensions/ERC20FlashMint.sol @@ -43,6 +43,16 @@ abstract contract ERC20FlashMint is ERC20, IERC3156FlashLender { return 0; } + /** + * @dev Returns the receiver address of the flash fee. By default this + * implementation returns the address(0) which means the fee amount will be burnt. + * This function can be overloaded to change the fee receiver. + * @return The address for which the flash fee will be sent to. + */ + function _flashFeeReceiver() internal view virtual returns (address) { + return address(0); + } + /** * @dev Performs a flash loan. New tokens are minted and sent to the * `receiver`, who is required to implement the {IERC3156FlashBorrower} @@ -73,8 +83,14 @@ abstract contract ERC20FlashMint is ERC20, IERC3156FlashLender { receiver.onFlashLoan(msg.sender, token, amount, fee, data) == _RETURN_VALUE, "ERC20FlashMint: invalid return value" ); + address flashFeeReceiver = _flashFeeReceiver(); _spendAllowance(address(receiver), address(this), amount + fee); - _burn(address(receiver), amount + fee); + if (fee == 0 || flashFeeReceiver == address(0)) { + _burn(address(receiver), amount + fee); + } else { + _burn(address(receiver), amount); + _transfer(address(receiver), flashFeeReceiver, fee); + } return true; } } diff --git a/test/token/ERC20/extensions/ERC20FlashMint.test.js b/test/token/ERC20/extensions/ERC20FlashMint.test.js index 0ecc056d667..01c08db598d 100644 --- a/test/token/ERC20/extensions/ERC20FlashMint.test.js +++ b/test/token/ERC20/extensions/ERC20FlashMint.test.js @@ -8,7 +8,7 @@ const ERC20FlashMintMock = artifacts.require('ERC20FlashMintMock'); const ERC3156FlashBorrowerMock = artifacts.require('ERC3156FlashBorrowerMock'); contract('ERC20FlashMint', function (accounts) { - const [ initialHolder, other ] = accounts; + const [ initialHolder, other, anotherAccount ] = accounts; const name = 'My Token'; const symbol = 'MTKN'; @@ -40,6 +40,12 @@ contract('ERC20FlashMint', function (accounts) { }); }); + describe('flashFeeReceiver', function () { + it('default receiver', async function () { + expect(await this.token.flashFeeReceiver()).to.be.eq(ZERO_ADDRESS); + }); + }); + describe('flashLoan', function () { it('success', async function () { const receiver = await ERC3156FlashBorrowerMock.new(true, true); @@ -86,5 +92,53 @@ contract('ERC20FlashMint', function (accounts) { // _mint overflow reverts using a panic code. No reason string. await expectRevert.unspecified(this.token.flashLoan(receiver.address, this.token.address, MAX_UINT256, data)); }); + + describe('custom flash fee & custom fee receiver', function () { + const receiverInitialBalance = new BN(200000); + const flashFee = new BN(5000); + + beforeEach('init reciever balance & set flash fee',async function () { + this.receiver = await ERC3156FlashBorrowerMock.new(true, true); + const receipt = await this.token.mint(this.receiver.address, receiverInitialBalance); + await expectEvent(receipt, 'Transfer', { from: ZERO_ADDRESS, to: this.receiver.address, value: receiverInitialBalance }); + expect(await this.token.balanceOf(this.receiver.address)).to.be.bignumber.equal(receiverInitialBalance); + + await this.token.setFlashFee(flashFee); + expect(await this.token.flashFee(this.token.address, loanAmount)).to.be.bignumber.equal(flashFee); + }); + + it('default flash fee receiver', async function () { + const { tx } = await this.token.flashLoan(this.receiver.address, this.token.address, loanAmount, '0x'); + await expectEvent.inTransaction(tx, this.token, 'Transfer', { from: ZERO_ADDRESS, to: this.receiver.address, value: loanAmount }); + await expectEvent.inTransaction(tx, this.token, 'Transfer', { from: this.receiver.address, to: ZERO_ADDRESS, value: loanAmount.add (flashFee)}); + await expectEvent.inTransaction(tx, this.receiver, 'BalanceOf', { token: this.token.address, account: this.receiver.address, value: receiverInitialBalance.add(loanAmount) }); + await expectEvent.inTransaction(tx, this.receiver, 'TotalSupply', { token: this.token.address, value: initialSupply.add (receiverInitialBalance).add(loanAmount) }); + + expect(await this.token.totalSupply()).to.be.bignumber.equal(initialSupply.add(receiverInitialBalance).sub(flashFee)); + expect(await this.token.balanceOf(this.receiver.address)).to.be.bignumber.equal(receiverInitialBalance.sub(flashFee)); + expect(await this.token.balanceOf(await this.token.flashFeeReceiver())).to.be.bignumber.equal('0'); + expect(await this.token.allowance(this.receiver.address, this.token.address)).to.be.bignumber.equal('0'); + }); + + it('custom flash fee receiver', async function () { + const flashFeeReceiverAddress = anotherAccount; + await this.token.setFlashFeeReceiver(flashFeeReceiverAddress); + expect(await this.token.flashFeeReceiver()).to.be.eq(flashFeeReceiverAddress); + + expect(await this.token.balanceOf(flashFeeReceiverAddress)).to.be.bignumber.equal('0'); + + const { tx } = await this.token.flashLoan(this.receiver.address, this.token.address, loanAmount, '0x'); + await expectEvent.inTransaction(tx, this.token, 'Transfer', { from: ZERO_ADDRESS, to: this.receiver.address, value: loanAmount }); + await expectEvent.inTransaction(tx, this.token, 'Transfer', { from: this.receiver.address, to: ZERO_ADDRESS, value: loanAmount }); + await expectEvent.inTransaction(tx, this.token, 'Transfer', { from: this.receiver.address, to: flashFeeReceiverAddress, value: flashFee }); + await expectEvent.inTransaction(tx, this.receiver, 'BalanceOf', { token: this.token.address, account: this.receiver.address, value: receiverInitialBalance.add(loanAmount) }); + await expectEvent.inTransaction(tx, this.receiver, 'TotalSupply', { token: this.token.address, value: initialSupply.add (receiverInitialBalance).add(loanAmount) }); + + expect(await this.token.totalSupply()).to.be.bignumber.equal(initialSupply.add(receiverInitialBalance)); + expect(await this.token.balanceOf(this.receiver.address)).to.be.bignumber.equal(receiverInitialBalance.sub(flashFee)); + expect(await this.token.balanceOf(flashFeeReceiverAddress)).to.be.bignumber.equal(flashFee); + expect(await this.token.allowance(this.receiver.address, flashFeeReceiverAddress)).to.be.bignumber.equal('0'); + }); + }); }); });