Solidity 튜토리얼 #4 : 이더리움 전송 및 payable 함수

크립토 좀비에서 제공하는 튜토리얼을 통해 배우는 Solidity 문법을 정리하고 있습니다!

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Lesseon 4 에서는 payable 개념에 대해서 조금 더 다룬다.

이전 게시글에서 zombieattack.sol 을 추가해, 좀비가 공격할 수 있도록 만들었다!

 

 

이번 장을 정리한 내용은 다음과 같다.

1. payable Modifier

이더리움에는 Ether 를 주고 받을 수 있는, payable 함수라는 녀석이 존재한다.

contract OnlineStore {
  function buySomething() external payable {
    // Check to make sure 0.001 ether was sent to the function call:
    require(msg.value == 0.001 ether);
    // If so, some logic to transfer the digital item to the caller of the function:
    transferThing(msg.sender);
  }
}

msg.value 를 통해 얼마나 많은 Ether 가 해당 contract 로 보내졌는지 알 수 있다(ehter 는 buil-in unit 이다).

위의 함수를 호출하는 web3.js (DApp 의 자바스크립트 front-end) 코드는 다음과 같을 것이다 :

// Assuming `OnlineStore` points to your contract on Ethereum:
OnlineStore.buySomething({from: web3.eth.defaultAccount, value: web3.utils.toWei(0.001)})

 

2. withdraw 함수

이제 배운 내용을 바탕으로 Ether 를 전달 받은 contract 에서 실제 이더리움 주소로 Ether 를 보내는 코드를 짜 보자.

contract GetPaid is Ownable {
  function withdraw() external onlyOwner {
    address payable _owner = address(uint160(owner()));
    _owner.transfer(address(this).balance);
  }
}

// 다음과 같이 응용
uint itemFee = 0.001 ether;
msg.sender.transfer(msg.value - itemFee);

 

 

3. Random Numbers

Solidity 에서의 난수 생성은 여러가지 방식이 있다. 예제에서는 간단하게 인자로 들어가는 Nonce 값을 바꾸면서 keccak256 을 이용해 의사 난수를 생성한다.

난수 생성에 대해 더 자세히 알고 싶으면 이 글을 참고하자.

function randMod(uint _modulus) internal returns(uint) {
  randNonce++;
  return uint(keccak256(abi.encodePacked(now, msg.sender, randNonce))) % _modulus;
}

 

 

이제 완성된 코드를 보면서 Wrap-Up 을 하자!

zombieattack.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) {
    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);
    }
  }
}

 

zombiehelper.sol

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++;
  }

  function changeName(uint _zombieId, string calldata _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[] 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;
  }

}

 

zombiefeeding.sol

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 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 memory _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");
  }
}

 

zombiefactory.sol

pragma solidity >=0.5.0 <0.6.0;

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 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]++;
        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);
    }

}

 

ownable.sol

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;
  }
}