openzeppelin-contracts/contracts/token/ERC20/SafeERC20.sol

pragma solidity ^0.4.24;

import "./IERC20.sol";
import "../../math/SafeMath.sol";

/**
 * @title SafeERC20
 * @dev Wrappers around ERC20 operations that throw on failure.
 * To use this library you can add a `using SafeERC20 for ERC20;` statement to your contract,
 * which allows you to call the safe operations as `token.safeTransfer(...)`, etc.
 */
library SafeERC20 {
    using SafeMath for uint256;

    function safeTransfer(IERC20 token, address to, uint256 value) internal {
        require(token.transfer(to, value));
    }

    function safeTransferFrom(IERC20 token, address from, address to, uint256 value) internal {
        require(token.transferFrom(from, to, value));
    }

    function safeApprove(IERC20 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(msg.sender, spender) == 0));
        require(token.approve(spender, value));
    }

    function safeIncreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).add(value);
        require(token.approve(spender, newAllowance));
    }

    function safeDecreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).sub(value);
        require(token.approve(spender, newAllowance));
    }
}