前置介绍

• Token 地址: 0x0223fc70574214f65813fe336d870ac47e147fae
• 合约代码 : https://etherscan.io/token/0x0223fc70574214f65813fe336d870ac47e147fae#code
• CoinMarketCap : https://coinmarketcap.com/currencies/cononchain/
• 官网: https://www.canonchain.com/

合约分析

这个是我所在公司的项目，代币合约是基于solidity ^0.4.16; 开发的，由三个合约组成。

• owned : 合约的 woner 权限处理
• TokenERC20 : Token 的核心处理
• CZRToken : 业务逻辑处理

下面逐个分析

第一、owned 合约

这个合约非常简单权限处理，单纯的做合约 owner，在构造函数中，将部署者地址作为合约的 owner。增加onlyOwner 函数修改器。

支持合约 owner 地址的转移，发起者必须是 owner 本人。

pragma solidity ^0.4.16;

contract owned {
    address public owner;

    function owned() public {
        owner = msg.sender;
    }

    modifier onlyOwner {
        require(msg.sender == owner);
        _;
    }

    function transferOwnership(address newOwner) onlyOwner public {
        owner = newOwner;
    }
}

第二、TokenERC20 合约

挑几个不错编程思想的代码演示。

1. 通过不带精度的数来设置真实值。

function TokenERC20(
    uint256 initialSupply,
) public {
    totalSupply = initialSupply * 10 ** uint256(decimals);
    balanceOf[msg.sender] = totalSupply;
}

2. transfer 函数拆分，以及内部逻辑处理

contract TokenERC20 {

     // Internal transfer : 只能被本合约调用
    function _transfer(address _from, address _to, uint _value) internal {
        // 不能适应 0x0 地址. 想要销毁可以使用 burn()
        require(_to != 0x0);

        // 检查sender是否有足够的金额
        require(balanceOf[_from] >= _value);

        // 检查溢出
        require(balanceOf[_to] + _value > balanceOf[_to]);

        // 保存此以供将来断言
        uint previousBalances = balanceOf[_from] + balanceOf[_to];

        // 先从 sender 中减去
        balanceOf[_from] -= _value;

        // 添加相同的值到 to 地址
        balanceOf[_to] += _value;

        // 抛出事件
        Transfer(_from, _to, _value);

        // Asserts 不应该失败，这里确保金额符合预期
        assert(balanceOf[_from] + balanceOf[_to] == previousBalances);
    }

    function transfer(address _to, uint256 _value) public {
        _transfer(msg.sender, _to, _value);
    }


    function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
        require(_value <= allowance[_from][msg.sender]);     // Check allowance
        allowance[_from][msg.sender] -= _value;
        _transfer(_from, _to, _value);
        return true;
    }
}

第三、CZRToken 合约

1. 冻结账户功能

mapping (address => bool) public frozenAccount;

/* This generates a public event on the blockchain that will notify clients */
event FrozenFunds(address target, bool frozen);

/* Internal transfer, only can be called by this contract */
function _transfer(address _from, address _to, uint _value) internal {
    require (_to != 0x0);                               //
    require (balanceOf[_from] >= _value);               // Check if the sender has enough
    require (balanceOf[_to] + _value > balanceOf[_to]); // Check for overflows
    require(!frozenAccount[_from]);                     // Check if sender is frozen
    require(!frozenAccount[_to]);                       // Check if recipient is frozen
    balanceOf[_from] -= _value;                         // Subtract from the sender
    balanceOf[_to] += _value;                           // Add the same to the recipient
    Transfer(_from, _to, _value);
}

/// @notice `freeze? Prevent | Allow` `target` from sending & receiving tokens
/// @param target Address to be frozen
/// @param freeze either to freeze it or not
function freezeAccount(address target, bool freeze) onlyOwner public {
    frozenAccount[target] = freeze;
    FrozenFunds(target, freeze);
}

2. 处理老逻辑，将老的 CNC 链上 Token 分发到新地址。批量将钱转到用户地址。

contract CZRToken is owned, TokenERC20 {
    /// Init balances from old CNC chain
    /// @param addrs Address array
    /// @param balances balance array
    function init(address[] addrs, uint256[] balances) onlyOwner public {
        require(addrs.length == balances.length);
        uint totalValue;
        for (uint i = 0; i < addrs.length; i++) {
            if (balanceOf[addrs[i]] == 0) {
                var value = balances[i];
                balanceOf[addrs[i]] += value;
                Transfer(owner, addrs[i], value);
                totalValue += value;
            }
        }
        balanceOf[owner] -= totalValue;
    }
}