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// This contract is part of Zellic’s smart contract dataset, which is a collection of publicly available contract code gathered as of March 2023.
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.8.0) (token/ERC20/extensions/ERC20FlashMint.sol)
pragma solidity ^0.8.0;
import "./IERC3156FlashBorrower.sol";
import "./IERC3156FlashLender.sol";
import "./ERC20.sol";
/**
* @dev Implementation of the ERC3156 Flash loans extension, as defined in
* https://eips.ethereum.org/EIPS/eip-3156[ERC-3156].
*
* Adds the {flashLoan} method, which provides flash loan support at the token
* level. By default there is no fee, but this can be changed by overriding {flashFee}.
*
* _Available since v4.1._
*/
abstract contract ERC20FlashMint is ERC20, IERC3156FlashLender {
bytes32 private constant _RETURN_VALUE = keccak256("ERC3156FlashBorrower.onFlashLoan");
/**
* @dev Returns the maximum amount of tokens available for loan.
* @param token The address of the token that is requested.
* @return The amount of token that can be loaned.
*/
function maxFlashLoan(address token) public view virtual override returns (uint256) {
return token == address(this) ? type(uint256).max - ERC20.totalSupply() : 0;
}
/**
* @dev Returns the fee applied when doing flash loans. This function calls
* the {_flashFee} function which returns the fee applied when doing flash
* loans.
* @param token The token to be flash loaned.
* @param amount The amount of tokens to be loaned.
* @return The fees applied to the corresponding flash loan.
*/
function flashFee(address token, uint256 amount) public view virtual override returns (uint256) {
require(token == address(this), "ERC20FlashMint: wrong token");
return _flashFee(token, amount);
}
/**
* @dev Returns the fee applied when doing flash loans. By default this
* implementation has 0 fees. This function can be overloaded to make
* the flash loan mechanism deflationary.
* @param token The token to be flash loaned.
* @param amount The amount of tokens to be loaned.
* @return The fees applied to the corresponding flash loan.
*/
function _flashFee(address token, uint256 amount) internal view virtual returns (uint256) {
// silence warning about unused variable without the addition of bytecode.
token;
amount;
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}
* interface. By the end of the flash loan, the receiver is expected to own
* amount + fee tokens and have them approved back to the token contract itself so
* they can be burned.
* @param receiver The receiver of the flash loan. Should implement the
* {IERC3156FlashBorrower-onFlashLoan} interface.
* @param token The token to be flash loaned. Only `address(this)` is
* supported.
* @param amount The amount of tokens to be loaned.
* @param data An arbitrary datafield that is passed to the receiver.
* @return `true` if the flash loan was successful.
*/
// This function can reenter, but it doesn't pose a risk because it always preserves the property that the amount
// minted at the beginning is always recovered and burned at the end, or else the entire function will revert.
// slither-disable-next-line reentrancy-no-eth
function flashLoan(
IERC3156FlashBorrower receiver,
address token,
uint256 amount,
bytes calldata data
) public virtual override returns (bool) {
require(amount <= maxFlashLoan(token), "ERC20FlashMint: amount exceeds maxFlashLoan");
uint256 fee = flashFee(token, amount);
_mint(address(receiver), amount);
require(
receiver.onFlashLoan(msg.sender, token, amount, fee, data) == _RETURN_VALUE,
"ERC20FlashMint: invalid return value"
);
address flashFeeReceiver = _flashFeeReceiver();
_spendAllowance(address(receiver), address(this), 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;
}
}
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