Solidity Zombies学习笔记

以太坊的一个加密僵尸游戏。为了便于记忆，将其中的教程产出code贴了出来。

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;
    }

    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))) - 1;
        zombieToOwner[id] = msg.sender;
        ownerZombieCount[msg.sender]++;
        NewZombie(id, _name, _dna);
    }

    function _generateRandomDna(string _str) private view returns (uint) {
        uint rand = uint(keccak256(_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);
    }

}

Ownable是来自 OpenZeppelin Solidity 库的 Ownable 合约。事件是合约和区块链通讯的一种机制。你的前端应用“监听”某些事件，并做出反应。如：

var abi = // abi是由编译器生成的  
var ZombieFactoryContract = web3.eth.contract(abi)  
var contractAddress = /// 发布之后在以太坊上生成的合约地址  
var ZombieFactory = ZombieFactoryContract.at(contractAddress)   
// ZombieFactory能访问公共的函数以及事件
>
// 监听NewZombie事件, 并且更新UI  
var event = ZombieFactory.NewZombie(function(error, result) {  
  if (error) return
  generateZombie(result.zombieId, result.name, result.dna)
})

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(_species) == keccak256("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");
  }
}

在 Solidity 中，有一些全局变量可以被所有函数调用。其中一个就是 msg.sender，它指的是当前调用者（或智能合约）的 address。
Solidity 使用自己的本地时间单位。

变量 now 将返回当前的unix时间戳（自1970年1月1日以来经过的秒数）。我写这句话时 unix 时间是 1515527488。

注意：Unix时间传统用一个32位的整数进行存储。这会导致“2038年”问题，当这个32位的unix时间戳不够用，产生溢出，使用这个时间的遗留系统就麻烦了。所以，如果我们想让我们的 DApp 跑够20年，我们可以使用64位整数表示时间，但为此我们的用户又得支付更多的 gas。真是个两难的设计啊！

Solidity 还包含秒(seconds)，分钟(minutes)，小时(hours)，天(days)，周(weeks) 和年(years) 等时间单位。它们都会转换成对应的秒数放入 uint 中。所以 1分钟就是 60，1小时是 3600（60秒×60分钟），1天是86400（24小时×60分钟×60秒），以此类推。

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 {
    owner.transfer(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;
  }

}

msg.value 是一种可以查看向合约发送了多少以太的方法，另外 ether 是一个內建单元。
这里发生的事是，一些人会从 web3.js 调用这个函数 (从DApp的前端)，像这样 :

// 假设 OnlineStore 在以太坊上指向你的合约:
OnlineStore.buySomething().send(from: web3.eth.defaultAccount, value: web3.utils.toWei(0.001))

ZombieBattle.sol

pragma solidity ^0.4.19;
import "./zombiehelper.sol";
contract ZombieBattle is ZombieHelper {
  uint randNonce = 0;
  uint attackVictoryProbability = 70;

  function randMod(uint _modulus) internal returns(uint) {
    randNonce++;
    return uint(keccak256(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);
    }
  }
}

Solidity Zombies学习笔记

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