Solidity学习记录

第一章创建生产僵尸的工厂
第二章设置僵尸的攻击功能
第三章编写DAPP所需的基础理论
第四章完善僵尸功能
第五章 ERC721 标准和加密资产

文章目录

Solidity学习记录
前言
一、本章主要目的
二、学习过程
- 1.本节课程知识点
- 2.最终代码
总结

前言

国庆假期，事情比较多，更新拖了两天，请见谅。

一、本章主要目的

在之前的课程，我们学习了Solidity的大部分知识，本章我们学习 payable 函数，学习如何开发可以接收其他玩家付款的DApp，并学习通过函数修饰符来完善我们的程序。

二、学习过程

1.本节课程知识点

1、payable 修饰符
payable 方法是让 Solidity 和以太坊变得如此酷的一部分 —— 它们是一种可以接收以太的特殊函数。在以太坊中，因为钱 (Ether), 数据 (transaction payload)，以及合约代码本身都存在于以太坊。你可以在同时调用函数并付钱给另外一个合约。如果一个函数没标记为payable，当用户尝试发送以太时，函数将拒绝事务。

2、msg.value 是一种可以查看向合约发送了多少以太的方法，常用msg.value == XXX 来表示。如果把事务想象成一个信封，你发送到函数的参数就是信的内容。添加一个 value 很像在信封里面放钱 —— 信件内容和钱同时发送给了接收者。

3、我们可以通过 transfer 向任何以太坊地址付钱。提现写法：

contract GetPaid is Ownable {function withdraw() external onlyOwner {owner.transfer(this.balance);}
}

4、Solidity 中最好的随机数生成器是 keccak256 哈希函数。但这个方法很容易被不诚实的节点攻击。

5、Solidity 的 keccak256 被攻击原理：
在以太坊上, 当你在和一个合约上调用函数的时候, 你会把它广播给一个节点或者在网络上的 transaction 节点们。网络上的节点将收集很多事务, 试着成为第一个解决计算密集型数学问题的人，作为“工作证明”，然后将“工作证明”(Proof of Work, PoW)和事务一起作为一个 block 发布在网络上。
一旦一个节点解决了一个PoW, 其他节点就会停止尝试解决这个 PoW, 并验证其他节点的事务列表是有效的，然后接受这个节点转而尝试解决下一个节点。
这就让我们的随机数函数变得可利用了
如果运行一个节点，可以 只对我自己的节点 发布一个事务，且 不分享它 。如果不是我想要的结果，我就不把这个事务包含进我要解决的下一个区块中去。我可以一直运行这个方法，直到获得了我想要的结果（类似于手游弱联网（并非实时监测是否联网）游戏，通过断网的方式来不断刷新出自己想要的东西，如：抽卡，掉落的稀有的物品等）。

2.最终代码

代码如下：

ownable.sol

//this is ownable.solpragma solidity ^0.4.19;/**
* @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;}
}

zombiefactory.sol

//this is zombiefactory.solpragma solidity ^0.4.19;import "./ownable.sol";contract ZombieFactory is Ownable {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 _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]++;emit NewZombie(id, _name, _dna);}function _generateRandomDna(string _str) private view returns (uint) {uint rand = uint(keccak256(abi.encodePacked(_str)));return rand % dnaModulus;}function createRandomZombie(string _name) public {require(ownerZombieCount[msg.sender] == 0);uint randDna = _generateRandomDna(_name);randDna = randDna - randDna % 100;_createZombie(_name, randDna);}}

zombiefeeding.sol

//this is zombiefeeding.solpragma solidity ^0.4.19;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 ownerOf(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 _species) internal ownerOf(_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");}
}

zombiehelper.sol

//this is zombiehelper.solpragma solidity ^0.4.19;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++;}function changeName(uint _zombieId, string _newName) external aboveLevel(2, _zombieId) ownerOf(_zombieId) {zombies[_zombieId].name = _newName;}function changeDna(uint _zombieId, uint _newDna) external aboveLevel(20, _zombieId) ownerOf(_zombieId) {zombies[_zombieId].dna = _newDna;}function getZombiesByOwner(address _owner) external view returns(uint[]) {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;}}

zombieattack.sol

//this is zombieattack.solpragma solidity ^0.4.19;import "./zombiehelper.sol";
contract ZombieAttack is ZombieHelper {uint randNonce = 0;uint attackVictoryProbability = 70;function randMod(uint _modulus) internal returns(uint) {randNonce++;return uint(keccak256(abi.encodePacked(now, msg.sender, randNonce))) % _modulus;}function attack(uint _zombieId, uint _targetId) external ownerOf(_zombieId) {Zombie storage myZombie = zombies[_zombieId];Zombie storage enemyZombie = zombies[_targetId];uint rand = randMod(100);if (rand <= attackVictoryProbability) {myZombie.winCount++;myZombie.level++;enemyZombie.lossCount++;feedAndMultiply(_zombieId, enemyZombie.dna, "zombie");} else {myZombie.lossCount++;enemyZombie.winCount++;_triggerCooldown(myZombie);}}
}

总结

本章知识点比较少，大部分是使用之前的知识内容，本章重点知识只有两个：

1.可以使用 payable 来付款，value 用来表示付多少钱，transfer 用来转账（可以转给任何人）。
2.keccak256 函数是不安全的，有一个随机数方法是利用 oracle 来访问以太坊区块链之外的随机数函数。