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
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.sol
pragma 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.sol
pragma 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.sol
pragma 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.sol
pragma 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 zombiehelper.sol
pragma 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。