// SPDX-License-Identifier: MIT // OpenZeppelin Contracts (last updated v4.8.0) (token/ERC20/utils/SafeERC20.sol) pragma solidity ^0.8.0; import "../IERC20Upgradeable.sol"; import "../extensions/draft-IERC20PermitUpgradeable.sol"; import "../../../utils/AddressUpgradeable.sol"; /** * @title SafeERC20 * @dev Wrappers around ERC20 operations that throw on failure (when the token * contract returns false). Tokens that return no value (and instead revert or * throw on failure) are also supported, non-reverting calls are assumed to be * successful. * To use this library you can add a `using SafeERC20 for IERC20;` statement to your contract, * which allows you to call the safe operations as `token.safeTransfer(...)`, etc. */ library SafeERC20Upgradeable { using AddressUpgradeable for address; function safeTransfer( IERC20Upgradeable token, address to, uint256 value ) internal { _callOptionalReturn(token, abi.encodeWithSelector(token.transfer.selector, to, value)); } function safeTransferFrom( IERC20Upgradeable token, address from, address to, uint256 value ) internal { _callOptionalReturn(token, abi.encodeWithSelector(token.transferFrom.selector, from, to, value)); } /** * @dev Deprecated. This function has issues similar to the ones found in * {IERC20-approve}, and its usage is discouraged. * * Whenever possible, use {safeIncreaseAllowance} and * {safeDecreaseAllowance} instead. */ function safeApprove( IERC20Upgradeable token, address spender, uint256 value ) internal { // safeApprove should only be called when setting an initial allowance, // or when resetting it to zero. To increase and decrease it, use // 'safeIncreaseAllowance' and 'safeDecreaseAllowance' require( (value == 0) || (token.allowance(address(this), spender) == 0), "SafeERC20: approve from non-zero to non-zero allowance" ); _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, value)); } function safeIncreaseAllowance( IERC20Upgradeable token, address spender, uint256 value ) internal { uint256 newAllowance = token.allowance(address(this), spender) + value; _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance)); } function safeDecreaseAllowance( IERC20Upgradeable token, address spender, uint256 value ) internal { unchecked { uint256 oldAllowance = token.allowance(address(this), spender); require(oldAllowance >= value, "SafeERC20: decreased allowance below zero"); uint256 newAllowance = oldAllowance - value; _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance)); } } function safePermit( IERC20PermitUpgradeable token, address owner, address spender, uint256 value, uint256 deadline, uint8 v, bytes32 r, bytes32 s ) internal { uint256 nonceBefore = token.nonces(owner); token.permit(owner, spender, value, deadline, v, r, s); uint256 nonceAfter = token.nonces(owner); require(nonceAfter == nonceBefore + 1, "SafeERC20: permit did not succeed"); } /** * @dev Imitates a Solidity high-level call (i.e. a regular function call to a contract), relaxing the requirement * on the return value: the return value is optional (but if data is returned, it must not be false). * @param token The token targeted by the call. * @param data The call data (encoded using abi.encode or one of its variants). */ function _callOptionalReturn(IERC20Upgradeable token, bytes memory data) private { // We need to perform a low level call here, to bypass Solidity's return data size checking mechanism, since // we're implementing it ourselves. We use {Address-functionCall} to perform this call, which verifies that // the target address contains contract code and also asserts for success in the low-level call. bytes memory returndata = address(token).functionCall(data, "SafeERC20: low-level call failed"); if (returndata.length > 0) { // Return data is optional require(abi.decode(returndata, (bool)), "SafeERC20: ERC20 operation did not succeed"); } } }