合约的代理与升级

合约主要有3种代理模式：

一、透明代理Transparent

contract TransparentAdminUpgradeableProxy {
    address implementation;
    address admin;

    fallback() external payable {
        require(msg.sender != admin);
        implementation.delegatecall.value(msg.value)(msg.data);
    }

    function upgrade(address newImplementation) external {
        if (msg.sender != admin) fallback();
        implementation = newImplementation;
    }
}

这种模式直观好理解，代理合约负责升级，实现合约负责具体逻辑。

二、UUPS

// 代理合约
contract UUPSProxy {
    address implementation;

    fallback() external payable {
        implementation.delegatecall.value(msg.value)(msg.data);
    }
}
// 实现合约要extend抽象接口
abstract contract UUPSProxiable {
    address implementation;
    address admin;

    function upgrade(address newImplementation) external {
        require(msg.sender == admin);
        implementation = newImplementation;
    }
}

代理合约是空的，几乎不包含任何逻辑；实现合约既要有具体业务逻辑，还要有升级逻辑。

升级时，调用代理合约的upgrade方法， 会deletegatecall到实现合约的upgrade方法； 因为delegate实现合约会运行在代理合约的上下文中，所以实现合约的upgrade方法修改implementation属性，实际上就修改了代理合约的implementation属性。

三、钻石模式

1个代理合约，会有多份实现合约

参考：https://blog.openzeppelin.com/the-state-of-smart-contract-upgrades