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12-safemath-4.md

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title actions requireLogin material
SafeMath Part 4
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true
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language startingCode answer
sol
zombieattack.sol zombieownership.sol zombiehelper.sol zombiefeeding.sol zombiefactory.sol ownable.sol safemath.sol erc721.sol
pragma solidity >=0.5.0 <0.6.0; import "./zombiehelper.sol"; contract ZombieAttack is ZombieHelper { uint randNonce = 0; uint attackVictoryProbability = 70; function randMod(uint _modulus) internal returns(uint) { // Here's one! randNonce++; return uint(keccak256(abi.encodePacked(now, msg.sender, randNonce))) % _modulus; } function attack(uint _zombieId, uint _targetId) external onlyOwnerOf(_zombieId) { Zombie storage myZombie = zombies[_zombieId]; Zombie storage enemyZombie = zombies[_targetId]; uint rand = randMod(100); if (rand <= attackVictoryProbability) { // Here's 3 more! myZombie.winCount++; myZombie.level++; enemyZombie.lossCount++; feedAndMultiply(_zombieId, enemyZombie.dna, "zombie"); } else { // ...annnnd another 2! myZombie.lossCount++; enemyZombie.winCount++; _triggerCooldown(myZombie); } } }
pragma solidity >=0.5.0 <0.6.0; import "./zombieattack.sol"; import "./erc721.sol"; import "./safemath.sol"; contract ZombieOwnership is ZombieAttack, ERC721 { using SafeMath for uint256; mapping (uint => address) zombieApprovals; function balanceOf(address _owner) external view returns (uint256) { return ownerZombieCount[_owner]; } function ownerOf(uint256 _tokenId) external view returns (address) { return zombieToOwner[_tokenId]; } function _transfer(address _from, address _to, uint256 _tokenId) private { ownerZombieCount[_to] = ownerZombieCount[_to].add(1); ownerZombieCount[msg.sender] = ownerZombieCount[msg.sender].sub(1); zombieToOwner[_tokenId] = _to; emit Transfer(_from, _to, _tokenId); } function transferFrom(address _from, address _to, uint256 _tokenId) external payable { require (zombieToOwner[_tokenId] == msg.sender || zombieApprovals[_tokenId] == msg.sender); _transfer(_from, _to, _tokenId); } function approve(address _approved, uint256 _tokenId) external payable onlyOwnerOf(_tokenId) { zombieApprovals[_tokenId] = _approved; emit Approval(msg.sender, _approved, _tokenId); } }
pragma solidity >=0.5.0 <0.6.0; import "./zombiefeeding.sol"; contract ZombieHelper is ZombieFeeding { uint levelUpFee = 0.001 ether; modifier aboveLevel(uint _level, uint _zombieId) { require(zombies[_zombieId].level >= _level); _; } function withdraw() external onlyOwner { address _owner = owner(); _owner.transfer(address(this).balance); } function setLevelUpFee(uint _fee) external onlyOwner { levelUpFee = _fee; } function levelUp(uint _zombieId) external payable { require(msg.value == levelUpFee); zombies[_zombieId].level = zombies[_zombieId].level.add(1); } function changeName(uint _zombieId, string calldata _newName) external aboveLevel(2, _zombieId) onlyOwnerOf(_zombieId) { zombies[_zombieId].name = _newName; } function changeDna(uint _zombieId, uint _newDna) external aboveLevel(20, _zombieId) onlyOwnerOf(_zombieId) { zombies[_zombieId].dna = _newDna; } function getZombiesByOwner(address _owner) external view returns(uint[] memory) { uint[] memory result = new uint[](ownerZombieCount[_owner]); uint counter = 0; for (uint i = 0; i < zombies.length; i++) { if (zombieToOwner[i] == _owner) { result[counter] = i; counter++; } } return result; } }
pragma solidity >=0.5.0 <0.6.0; import "./zombiefactory.sol"; contract KittyInterface { function getKitty(uint256 _id) external view returns ( bool isGestating, bool isReady, uint256 cooldownIndex, uint256 nextActionAt, uint256 siringWithId, uint256 birthTime, uint256 matronId, uint256 sireId, uint256 generation, uint256 genes ); } contract ZombieFeeding is ZombieFactory { KittyInterface kittyContract; modifier onlyOwnerOf(uint _zombieId) { require(msg.sender == zombieToOwner[_zombieId]); _; } function setKittyContractAddress(address _address) external onlyOwner { kittyContract = KittyInterface(_address); } function _triggerCooldown(Zombie storage _zombie) internal { _zombie.readyTime = uint32(now + cooldownTime); } function _isReady(Zombie storage _zombie) internal view returns (bool) { return (_zombie.readyTime <= now); } function feedAndMultiply(uint _zombieId, uint _targetDna, string memory _species) internal onlyOwnerOf(_zombieId) { Zombie storage myZombie = zombies[_zombieId]; require(_isReady(myZombie)); _targetDna = _targetDna % dnaModulus; uint newDna = (myZombie.dna + _targetDna) / 2; if (keccak256(abi.encodePacked(_species)) == keccak256(abi.encodePacked("kitty"))) { newDna = newDna - newDna % 100 + 99; } _createZombie("NoName", newDna); _triggerCooldown(myZombie); } function feedOnKitty(uint _zombieId, uint _kittyId) public { uint kittyDna; (,,,,,,,,,kittyDna) = kittyContract.getKitty(_kittyId); feedAndMultiply(_zombieId, kittyDna, "kitty"); } }
pragma solidity >=0.5.0 <0.6.0; import "./ownable.sol"; import "./safemath.sol"; contract ZombieFactory is Ownable { using SafeMath for uint256; using SafeMath32 for uint32; using SafeMath16 for uint16; event NewZombie(uint zombieId, string name, uint dna); uint dnaDigits = 16; uint dnaModulus = 10 ** dnaDigits; uint cooldownTime = 1 days; struct Zombie { string name; uint dna; uint32 level; uint32 readyTime; uint16 winCount; uint16 lossCount; } Zombie[] public zombies; mapping (uint => address) public zombieToOwner; mapping (address => uint) ownerZombieCount; function _createZombie(string memory _name, uint _dna) internal { uint id = zombies.push(Zombie(_name, _dna, 1, uint32(now + cooldownTime), 0, 0)) - 1; zombieToOwner[id] = msg.sender; ownerZombieCount[msg.sender] = ownerZombieCount[msg.sender].add(1); emit NewZombie(id, _name, _dna); } function _generateRandomDna(string memory _str) private view returns (uint) { uint rand = uint(keccak256(abi.encodePacked(_str))); return rand % dnaModulus; } function createRandomZombie(string memory _name) public { require(ownerZombieCount[msg.sender] == 0); uint randDna = _generateRandomDna(_name); randDna = randDna - randDna % 100; _createZombie(_name, randDna); } }
pragma solidity >=0.5.0 <0.6.0; /** * @title Ownable * @dev The Ownable contract has an owner address, and provides basic authorization control * functions, this simplifies the implementation of "user permissions". */ contract Ownable { address private _owner; event OwnershipTransferred( address indexed previousOwner, address indexed newOwner ); /** * @dev The Ownable constructor sets the original `owner` of the contract to the sender * account. */ constructor() internal { _owner = msg.sender; emit OwnershipTransferred(address(0), _owner); } /** * @return the address of the owner. */ function owner() public view returns(address) { return _owner; } /** * @dev Throws if called by any account other than the owner. */ modifier onlyOwner() { require(isOwner()); _; } /** * @return true if `msg.sender` is the owner of the contract. */ function isOwner() public view returns(bool) { return msg.sender == _owner; } /** * @dev Allows the current owner to relinquish control of the contract. * @notice Renouncing to ownership will leave the contract without an owner. * It will not be possible to call the functions with the `onlyOwner` * modifier anymore. */ function renounceOwnership() public onlyOwner { emit OwnershipTransferred(_owner, address(0)); _owner = address(0); } /** * @dev Allows the current owner to transfer control of the contract to a newOwner. * @param newOwner The address to transfer ownership to. */ function transferOwnership(address newOwner) public onlyOwner { _transferOwnership(newOwner); } /** * @dev Transfers control of the contract to a newOwner. * @param newOwner The address to transfer ownership to. */ function _transferOwnership(address newOwner) internal { require(newOwner != address(0)); emit OwnershipTransferred(_owner, newOwner); _owner = newOwner; } }
pragma solidity >=0.5.0 <0.6.0; /** * @title SafeMath * @dev Math operations with safety checks that throw on error */ library SafeMath { /** * @dev Multiplies two numbers, throws on overflow. */ function mul(uint256 a, uint256 b) internal pure returns (uint256) { if (a == 0) { return 0; } uint256 c = a * b; assert(c / a == b); return c; } /** * @dev Integer division of two numbers, truncating the quotient. */ function div(uint256 a, uint256 b) internal pure returns (uint256) { // assert(b > 0); // Solidity automatically throws when dividing by 0 uint256 c = a / b; // assert(a == b * c + a % b); // There is no case in which this doesn't hold return c; } /** * @dev Subtracts two numbers, throws on overflow (i.e. if subtrahend is greater than minuend). */ function sub(uint256 a, uint256 b) internal pure returns (uint256) { assert(b <= a); return a - b; } /** * @dev Adds two numbers, throws on overflow. */ function add(uint256 a, uint256 b) internal pure returns (uint256) { uint256 c = a + b; assert(c >= a); return c; } } /** * @title SafeMath32 * @dev SafeMath library implemented for uint32 */ library SafeMath32 { function mul(uint32 a, uint32 b) internal pure returns (uint32) { if (a == 0) { return 0; } uint32 c = a * b; assert(c / a == b); return c; } function div(uint32 a, uint32 b) internal pure returns (uint32) { // assert(b > 0); // Solidity automatically throws when dividing by 0 uint32 c = a / b; // assert(a == b * c + a % b); // There is no case in which this doesn't hold return c; } function sub(uint32 a, uint32 b) internal pure returns (uint32) { assert(b <= a); return a - b; } function add(uint32 a, uint32 b) internal pure returns (uint32) { uint32 c = a + b; assert(c >= a); return c; } } /** * @title SafeMath16 * @dev SafeMath library implemented for uint16 */ library SafeMath16 { function mul(uint16 a, uint16 b) internal pure returns (uint16) { if (a == 0) { return 0; } uint16 c = a * b; assert(c / a == b); return c; } function div(uint16 a, uint16 b) internal pure returns (uint16) { // assert(b > 0); // Solidity automatically throws when dividing by 0 uint16 c = a / b; // assert(a == b * c + a % b); // There is no case in which this doesn't hold return c; } function sub(uint16 a, uint16 b) internal pure returns (uint16) { assert(b <= a); return a - b; } function add(uint16 a, uint16 b) internal pure returns (uint16) { uint16 c = a + b; assert(c >= a); return c; } }
pragma solidity >=0.5.0 <0.6.0; contract ERC721 { event Transfer(address indexed _from, address indexed _to, uint256 indexed _tokenId); event Approval(address indexed _owner, address indexed _approved, uint256 indexed _tokenId); function balanceOf(address _owner) external view returns (uint256); function ownerOf(uint256 _tokenId) external view returns (address); function transferFrom(address _from, address _to, uint256 _tokenId) external payable; function approve(address _approved, uint256 _tokenId) external payable; }
pragma solidity >=0.5.0 <0.6.0; import "./zombiehelper.sol"; contract ZombieAttack is ZombieHelper { uint randNonce = 0; uint attackVictoryProbability = 70; function randMod(uint _modulus) internal returns(uint) { randNonce = randNonce.add(1); return uint(keccak256(abi.encodePacked(now, msg.sender, randNonce))) % _modulus; } function attack(uint _zombieId, uint _targetId) external onlyOwnerOf(_zombieId) { Zombie storage myZombie = zombies[_zombieId]; Zombie storage enemyZombie = zombies[_targetId]; uint rand = randMod(100); if (rand <= attackVictoryProbability) { myZombie.winCount = myZombie.winCount.add(1); myZombie.level = myZombie.level.add(1); enemyZombie.lossCount = enemyZombie.lossCount.add(1); feedAndMultiply(_zombieId, enemyZombie.dna, "zombie"); } else { myZombie.lossCount = myZombie.lossCount.add(1); enemyZombie.winCount = enemyZombie.winCount.add(1); _triggerCooldown(myZombie); } } }

Great, now we can implement SafeMath on all the types of uints we used in our DApp!

Let's fix all those potential issues in ZombieAttack. (There was also one zombies[_zombieId].level++; that needed to be fixed in ZombieHelper, but we've taken care of that one for you so we don't take an extra chapter to do so 😉).

Putting it to the Test

Go ahead and implement SafeMath methods on all the ++ increments in ZombieAttack. We've left comments in the code to make them easy to find.