uniswap-v2/contracts/UniswapV2ERC20.sol

pragma solidity =0.5.16;

import './interfaces/IUniswapV2ERC20.sol';
import './libraries/SafeMath.sol';

/**
 * @title UniswapV2ERC20 流动性代币合约
 * @notice 实现ERC20标准的流动性代币，支持EIP-712 permit功能
 * @dev 为Uniswap V2交易对提供流动性代币功能
 */
contract UniswapV2ERC20 is IUniswapV2ERC20 {
    using SafeMath for uint;

    // ERC20标准属性
    string public constant name = 'Uniswap V2';        // 代币名称
    string public constant symbol = 'UNI-V2';          // 代币符号
    uint8 public constant decimals = 18;               // 小数位数
    uint  public totalSupply;                          // 总供应量
    mapping(address => uint) public balanceOf;         // 余额映射
    mapping(address => mapping(address => uint)) public allowance; // 授权映射

    // EIP-712相关
    bytes32 public DOMAIN_SEPARATOR;                   // 域分隔符
    // permit函数的类型哈希
    bytes32 public constant PERMIT_TYPEHASH = 0x6e71edae12b1b97f4d1f60370fef10105fa2faae0126114a169c64845d6126c9;
    mapping(address => uint) public nonces;            // 防重放nonce

    // ERC20标准事件
    event Approval(address indexed owner, address indexed spender, uint value);
    event Transfer(address indexed from, address indexed to, uint value);

    /**
     * @dev 构造函数，初始化EIP-712域分隔符
     */
    constructor() public {
        uint chainId;
        // 内联汇编获取链ID
        assembly {
            chainId := chainid
        }
        // 计算域分隔符
        DOMAIN_SEPARATOR = keccak256(
            abi.encode(
                keccak256('EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)'),
                keccak256(bytes(name)),
                keccak256(bytes('1')),
                chainId,
                address(this)
            )
        );
    }

    /**
     * @dev 内部函数：铸造代币
     * @param to 接收地址
     * @param value 铸造数量
     */
    function _mint(address to, uint value) internal {
        totalSupply = totalSupply.add(value);
        balanceOf[to] = balanceOf[to].add(value);
        emit Transfer(address(0), to, value);
    }

    /**
     * @dev 内部函数：销毁代币
     * @param from 销毁地址
     * @param value 销毁数量
     */
    function _burn(address from, uint value) internal {
        balanceOf[from] = balanceOf[from].sub(value);
        totalSupply = totalSupply.sub(value);
        emit Transfer(from, address(0), value);
    }

    /**
     * @dev 内部函数：设置授权
     * @param owner 授权者
     * @param spender 被授权者
     * @param value 授权数量
     */
    function _approve(address owner, address spender, uint value) private {
        allowance[owner][spender] = value;
        emit Approval(owner, spender, value);
    }

    /**
     * @dev 内部函数：转账
     * @param from 发送者
     * @param to 接收者
     * @param value 转账数量
     */
    function _transfer(address from, address to, uint value) private {
        balanceOf[from] = balanceOf[from].sub(value);
        balanceOf[to] = balanceOf[to].add(value);
        emit Transfer(from, to, value);
    }

    /**
     * @notice 授权spender使用value数量的代币
     * @param spender 被授权地址
     * @param value 授权数量
     * @return 是否成功
     */
    function approve(address spender, uint value) external returns (bool) {
        _approve(msg.sender, spender, value);
        return true;
    }

    /**
     * @notice 转账代币给to地址
     * @param to 接收地址
     * @param value 转账数量
     * @return 是否成功
     */
    function transfer(address to, uint value) external returns (bool) {
        _transfer(msg.sender, to, value);
        return true;
    }

    /**
     * @notice 从from地址转账代币给to地址（需要授权）
     * @param from 发送地址
     * @param to 接收地址
     * @param value 转账数量
     * @return 是否成功
     */
    function transferFrom(address from, address to, uint value) external returns (bool) {
        // 如果授权量不是最大值，则减少授权量
        if (allowance[from][msg.sender] != uint(-1)) {
            allowance[from][msg.sender] = allowance[from][msg.sender].sub(value);
        }
        _transfer(from, to, value);
        return true;
    }

    /**
     * @notice EIP-712签名授权，无需发送交易即可设置授权
     * @param owner 代币所有者
     * @param spender 被授权者
     * @param value 授权数量
     * @param deadline 授权截止时间
     * @param v 签名参数v
     * @param r 签名参数r
     * @param s 签名参数s
     */
    function permit(address owner, address spender, uint value, uint deadline, uint8 v, bytes32 r, bytes32 s) external {
        require(deadline >= block.timestamp, 'UniswapV2: EXPIRED');
        
        // 构造EIP-712消息哈希
        bytes32 digest = keccak256(
            abi.encodePacked(
                '\x19\x01',                 // EIP-191前缀
                DOMAIN_SEPARATOR,
                keccak256(abi.encode(PERMIT_TYPEHASH, owner, spender, value, nonces[owner]++, deadline))
            )
        );
        
        // 恢复签名者地址
        address recoveredAddress = ecrecover(digest, v, r, s);
        require(recoveredAddress != address(0) && recoveredAddress == owner, 'UniswapV2: INVALID_SIGNATURE');
        
        // 设置授权
        _approve(owner, spender, value);
    }
}