mcchan1 · April 29, 2020 16:08
diff --git a/simple-escrow.sol b/simple-escrow.sol

 pragma solidity ^0.6.0;

 /**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
 library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, "SafeMath: division by zero");
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return mod(a, b, "SafeMath: modulo by zero");
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts with custom message when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
 }

 /**
 * @dev Collection of functions related to the address type
 */
 library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // According to EIP-1052, 0x0 is the value returned for not-yet created accounts
        // and 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470 is returned
        // for accounts without code, i.e. `keccak256('')`
        bytes32 codehash;
        bytes32 accountHash = 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470;
        // solhint-disable-next-line no-inline-assembly
        assembly { codehash := extcodehash(account) }
        return (codehash != accountHash && codehash != 0x0);
    }

    /**
     * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
     * `recipient`, forwarding all available gas and reverting on errors.
     *
     * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
     * of certain opcodes, possibly making contracts go over the 2300 gas limit
     * imposed by `transfer`, making them unable to receive funds via
     * `transfer`. {sendValue} removes this limitation.
     *
     * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
     *
     * IMPORTANT: because control is transferred to `recipient`, care must be
     * taken to not create reentrancy vulnerabilities. Consider using
     * {ReentrancyGuard} or the
     * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");

        // solhint-disable-next-line avoid-low-level-calls, avoid-call-value
        (bool success, ) = recipient.call{ value: amount }("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }
 }
 /*
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with GSN meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
 contract Context {
    // Empty internal constructor, to prevent people from mistakenly deploying
    // an instance of this contract, which should be used via inheritance.
    constructor () internal { }

    function _msgSender() internal view virtual returns (address payable) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes memory) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return msg.data;
    }
 }
 /**
 * @dev Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * By default, the owner account will be the one that deploys the contract. This
 * can later be changed with {transferOwnership}.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
 contract Ownable is Context {
    address private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor () internal {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view returns (address) {
        return _owner;
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(_owner == _msgSender(), "Ownable: caller is not the owner");
        _;
    }

    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions anymore. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby removing any functionality that is only available to the owner.
     */
    function renounceOwnership() public virtual onlyOwner {
        emit OwnershipTransferred(_owner, address(0));
        _owner = address(0);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
 }



 /**
  * @title Escrow
  * @dev Base escrow contract, holds funds designated for a payee until they
  * withdraw them.
  *
  * Intended usage: This contract (and derived escrow contracts) should be a
  * standalone contract, that only interacts with the contract that instantiated
  * it. That way, it is guaranteed that all Ether will be handled according to
  * the `Escrow` rules, and there is no need to check for payable functions or
  * transfers in the inheritance tree. The contract that uses the escrow as its
  * payment method should be its owner, and provide public methods redirecting
  * to the escrow's deposit and withdraw.
  */
 contract Escrow is Ownable {
    using SafeMath for uint256;
    using Address for address payable;

    event Deposited(address indexed payee, uint256 weiAmount);
    event Withdrawn(address indexed payee, uint256 weiAmount);

    mapping(address => uint256) private _deposits;

    function depositsOf(address payee) public view returns (uint256) {
        return _deposits[payee];
    }

    /**
     * @dev Stores the sent amount as credit to be withdrawn.
     * @param payee The destination address of the funds.
     */
    function deposit(address payee) public virtual payable onlyOwner {
        uint256 amount = msg.value;
        _deposits[payee] = _deposits[payee].add(amount);

        emit Deposited(payee, amount);
    }

    /**
     * @dev Withdraw accumulated balance for a payee, forwarding all gas to the
     * recipient.
     *
     * WARNING: Forwarding all gas opens the door to reentrancy vulnerabilities.
     * Make sure you trust the recipient, or are either following the
     * checks-effects-interactions pattern or using {ReentrancyGuard}.
     *
     * @param payee The address whose funds will be withdrawn and transferred to.
     */
    function withdraw(address payable payee) public virtual onlyOwner {
        uint256 payment = _deposits[payee];

        _deposits[payee] = 0;

        payee.sendValue(payment);

        emit Withdrawn(payee, payment);
    }
 }

	pragma solidity ^0.6.0;

	/**
	* @dev Wrappers over Solidity's arithmetic operations with added overflow
	* checks.
	*
	* Arithmetic operations in Solidity wrap on overflow. This can easily result
	* in bugs, because programmers usually assume that an overflow raises an
	* error, which is the standard behavior in high level programming languages.
	* `SafeMath` restores this intuition by reverting the transaction when an
	* operation overflows.
	*
	* Using this library instead of the unchecked operations eliminates an entire
	* class of bugs, so it's recommended to use it always.
	*/
	library SafeMath {
	/**
	* @dev Returns the addition of two unsigned integers, reverting on
	* overflow.
	*
	* Counterpart to Solidity's `+` operator.
	*
	* Requirements:
	* - Addition cannot overflow.
	*/
	function add(uint256 a, uint256 b) internal pure returns (uint256) {
	uint256 c = a + b;
	require(c >= a, "SafeMath: addition overflow");

	return c;
	}

	/**
	* @dev Returns the subtraction of two unsigned integers, reverting on
	* overflow (when the result is negative).
	*
	* Counterpart to Solidity's `-` operator.
	*
	* Requirements:
	* - Subtraction cannot overflow.
	*/
	function sub(uint256 a, uint256 b) internal pure returns (uint256) {
	return sub(a, b, "SafeMath: subtraction overflow");
	}

	/**
	* @dev Returns the subtraction of two unsigned integers, reverting with custom message on
	* overflow (when the result is negative).
	*
	* Counterpart to Solidity's `-` operator.
	*
	* Requirements:
	* - Subtraction cannot overflow.
	*/
	function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
	require(b <= a, errorMessage);
	uint256 c = a - b;

	return c;
	}

	/**
	* @dev Returns the multiplication of two unsigned integers, reverting on
	* overflow.
	*
	* Counterpart to Solidity's `*` operator.
	*
	* Requirements:
	* - Multiplication cannot overflow.
	*/
	function mul(uint256 a, uint256 b) internal pure returns (uint256) {
	// Gas optimization: this is cheaper than requiring 'a' not being zero, but the
	// benefit is lost if 'b' is also tested.
	// See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
	if (a == 0) {
	return 0;
	}

	uint256 c = a * b;
	require(c / a == b, "SafeMath: multiplication overflow");

	return c;
	}

	/**
	* @dev Returns the integer division of two unsigned integers. Reverts on
	* division by zero. The result is rounded towards zero.
	*
	* Counterpart to Solidity's `/` operator. Note: this function uses a
	* `revert` opcode (which leaves remaining gas untouched) while Solidity
	* uses an invalid opcode to revert (consuming all remaining gas).
	*
	* Requirements:
	* - The divisor cannot be zero.
	*/
	function div(uint256 a, uint256 b) internal pure returns (uint256) {
	return div(a, b, "SafeMath: division by zero");
	}

	/**
	* @dev Returns the integer division of two unsigned integers. Reverts with custom message on
	* division by zero. The result is rounded towards zero.
	*
	* Counterpart to Solidity's `/` operator. Note: this function uses a
	* `revert` opcode (which leaves remaining gas untouched) while Solidity
	* uses an invalid opcode to revert (consuming all remaining gas).
	*
	* Requirements:
	* - The divisor cannot be zero.
	*/
	function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
	require(b > 0, errorMessage);
	uint256 c = a / b;
	// assert(a == b * c + a % b); // There is no case in which this doesn't hold

	return c;
	}

	/**
	* @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
	* Reverts when dividing by zero.
	*
	* Counterpart to Solidity's `%` operator. This function uses a `revert`
	* opcode (which leaves remaining gas untouched) while Solidity uses an
	* invalid opcode to revert (consuming all remaining gas).
	*
	* Requirements:
	* - The divisor cannot be zero.
	*/
	function mod(uint256 a, uint256 b) internal pure returns (uint256) {
	return mod(a, b, "SafeMath: modulo by zero");
	}

	/**
	* @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
	* Reverts with custom message when dividing by zero.
	*
	* Counterpart to Solidity's `%` operator. This function uses a `revert`
	* opcode (which leaves remaining gas untouched) while Solidity uses an
	* invalid opcode to revert (consuming all remaining gas).
	*
	* Requirements:
	* - The divisor cannot be zero.
	*/
	function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
	require(b != 0, errorMessage);
	return a % b;
	}
	}

	/**
	* @dev Collection of functions related to the address type
	*/
	library Address {
	/**
	* @dev Returns true if `account` is a contract.
	*
	* [IMPORTANT]
	* ====
	* It is unsafe to assume that an address for which this function returns
	* false is an externally-owned account (EOA) and not a contract.
	*
	* Among others, `isContract` will return false for the following
	* types of addresses:
	*
	* - an externally-owned account
	* - a contract in construction
	* - an address where a contract will be created
	* - an address where a contract lived, but was destroyed
	* ====
	*/
	function isContract(address account) internal view returns (bool) {
	// According to EIP-1052, 0x0 is the value returned for not-yet created accounts
	// and 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470 is returned
	// for accounts without code, i.e. `keccak256('')`
	bytes32 codehash;
	bytes32 accountHash = 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470;
	// solhint-disable-next-line no-inline-assembly
	assembly { codehash := extcodehash(account) }
	return (codehash != accountHash && codehash != 0x0);
	}

	/**
	* @dev Replacement for Solidity's `transfer`: sends `amount` wei to
	* `recipient`, forwarding all available gas and reverting on errors.
	*
	* https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
	* of certain opcodes, possibly making contracts go over the 2300 gas limit
	* imposed by `transfer`, making them unable to receive funds via
	* `transfer`. {sendValue} removes this limitation.
	*
	* https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
	*
	* IMPORTANT: because control is transferred to `recipient`, care must be
	* taken to not create reentrancy vulnerabilities. Consider using
	* {ReentrancyGuard} or the
	* https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
	*/
	function sendValue(address payable recipient, uint256 amount) internal {
	require(address(this).balance >= amount, "Address: insufficient balance");

	// solhint-disable-next-line avoid-low-level-calls, avoid-call-value
	(bool success, ) = recipient.call{ value: amount }("");
	require(success, "Address: unable to send value, recipient may have reverted");
	}
	}
	/*
	* @dev Provides information about the current execution context, including the
	* sender of the transaction and its data. While these are generally available
	* via msg.sender and msg.data, they should not be accessed in such a direct
	* manner, since when dealing with GSN meta-transactions the account sending and
	* paying for execution may not be the actual sender (as far as an application
	* is concerned).
	*
	* This contract is only required for intermediate, library-like contracts.
	*/
	contract Context {
	// Empty internal constructor, to prevent people from mistakenly deploying
	// an instance of this contract, which should be used via inheritance.
	constructor () internal { }

	function _msgSender() internal view virtual returns (address payable) {
	return msg.sender;
	}

	function _msgData() internal view virtual returns (bytes memory) {
	this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
	return msg.data;
	}
	}
	/**
	* @dev Contract module which provides a basic access control mechanism, where
	* there is an account (an owner) that can be granted exclusive access to
	* specific functions.
	*
	* By default, the owner account will be the one that deploys the contract. This
	* can later be changed with {transferOwnership}.
	*
	* This module is used through inheritance. It will make available the modifier
	* `onlyOwner`, which can be applied to your functions to restrict their use to
	* the owner.
	*/
	contract Ownable is Context {
	address private _owner;

	event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

	/**
	* @dev Initializes the contract setting the deployer as the initial owner.
	*/
	constructor () internal {
	address msgSender = _msgSender();
	_owner = msgSender;
	emit OwnershipTransferred(address(0), msgSender);
	}

	/**
	* @dev Returns the address of the current owner.
	*/
	function owner() public view returns (address) {
	return _owner;
	}

	/**
	* @dev Throws if called by any account other than the owner.
	*/
	modifier onlyOwner() {
	require(_owner == _msgSender(), "Ownable: caller is not the owner");
	_;
	}

	/**
	* @dev Leaves the contract without owner. It will not be possible to call
	* `onlyOwner` functions anymore. Can only be called by the current owner.
	*
	* NOTE: Renouncing ownership will leave the contract without an owner,
	* thereby removing any functionality that is only available to the owner.
	*/
	function renounceOwnership() public virtual onlyOwner {
	emit OwnershipTransferred(_owner, address(0));
	_owner = address(0);
	}

	/**
	* @dev Transfers ownership of the contract to a new account (`newOwner`).
	* Can only be called by the current owner.
	*/
	function transferOwnership(address newOwner) public virtual onlyOwner {
	require(newOwner != address(0), "Ownable: new owner is the zero address");
	emit OwnershipTransferred(_owner, newOwner);
	_owner = newOwner;
	}
	}



	/**
	* @title Escrow
	* @dev Base escrow contract, holds funds designated for a payee until they
	* withdraw them.
	*
	* Intended usage: This contract (and derived escrow contracts) should be a
	* standalone contract, that only interacts with the contract that instantiated
	* it. That way, it is guaranteed that all Ether will be handled according to
	* the `Escrow` rules, and there is no need to check for payable functions or
	* transfers in the inheritance tree. The contract that uses the escrow as its
	* payment method should be its owner, and provide public methods redirecting
	* to the escrow's deposit and withdraw.
	*/
	contract Escrow is Ownable {
	using SafeMath for uint256;
	using Address for address payable;

	event Deposited(address indexed payee, uint256 weiAmount);
	event Withdrawn(address indexed payee, uint256 weiAmount);

	mapping(address => uint256) private _deposits;

	function depositsOf(address payee) public view returns (uint256) {
	return _deposits[payee];
	}

	/**
	* @dev Stores the sent amount as credit to be withdrawn.
	* @param payee The destination address of the funds.
	*/
	function deposit(address payee) public virtual payable onlyOwner {
	uint256 amount = msg.value;
	_deposits[payee] = _deposits[payee].add(amount);

	emit Deposited(payee, amount);
	}

	/**
	* @dev Withdraw accumulated balance for a payee, forwarding all gas to the
	* recipient.
	*
	* WARNING: Forwarding all gas opens the door to reentrancy vulnerabilities.
	* Make sure you trust the recipient, or are either following the
	* checks-effects-interactions pattern or using {ReentrancyGuard}.
	*
	* @param payee The address whose funds will be withdrawn and transferred to.
	*/
	function withdraw(address payable payee) public virtual onlyOwner {
	uint256 payment = _deposits[payee];

	_deposits[payee] = 0;

	payee.sendValue(payment);

	emit Withdrawn(payee, payment);
	}
	}