openzeppelin-contracts/contracts/proxy/transparent/TransparentUpgradeableProxy.sol

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.9.0) (proxy/transparent/TransparentUpgradeableProxy.sol)

pragma solidity ^0.8.0;

import "../ERC1967/ERC1967Proxy.sol";

/**
 * @dev Interface for {TransparentUpgradeableProxy}. In order to implement transparency, {TransparentUpgradeableProxy}
 * does not implement this interface directly, and some of its functions are implemented by an internal dispatch
 * mechanism. The compiler is unaware that these functions are implemented by {TransparentUpgradeableProxy} and will not
 * include them in the ABI so this interface must be used to interact with it.
 */
interface ITransparentUpgradeableProxy is IERC1967 {
    function changeAdmin(address) external;

    function upgradeTo(address) external;

    function upgradeToAndCall(address, bytes memory) external payable;
}

/**
 * @dev This contract implements a proxy that is upgradeable by an admin.
 *
 * To avoid https://medium.com/nomic-labs-blog/malicious-backdoors-in-ethereum-proxies-62629adf3357[proxy selector
 * clashing], which can potentially be used in an attack, this contract uses the
 * https://blog.openzeppelin.com/the-transparent-proxy-pattern/[transparent proxy pattern]. This pattern implies two
 * things that go hand in hand:
 *
 * 1. If any account other than the admin calls the proxy, the call will be forwarded to the implementation, even if
 * that call matches one of the admin functions exposed by the proxy itself.
 * 2. If the admin calls the proxy, it can access the admin functions, but its calls will never be forwarded to the
 * implementation. If the admin tries to call a function on the implementation it will fail with an error that says
 * "admin cannot fallback to proxy target".
 *
 * These properties mean that the admin account can only be used for admin actions like upgrading the proxy or changing
 * the admin, so it's best if it's a dedicated account that is not used for anything else. This will avoid headaches due
 * to sudden errors when trying to call a function from the proxy implementation.
 *
 * Our recommendation is for the dedicated account to be an instance of the {ProxyAdmin} contract. If set up this way,
 * you should think of the `ProxyAdmin` instance as the real administrative interface of your proxy.
 *
 * NOTE: The real interface of this proxy is that defined in `ITransparentUpgradeableProxy`. This contract does not
 * inherit from that interface, and instead the admin functions are implicitly implemented using a custom dispatch
 * mechanism in `_fallback`. Consequently, the compiler will not produce an ABI for this contract. This is necessary to
 * fully implement transparency without decoding reverts caused by selector clashes between the proxy and the
 * implementation.
 *
 * WARNING: It is not recommended to extend this contract to add additional external functions. If you do so, the compiler
 * will not check that there are no selector conflicts, due to the note above. A selector clash between any new function
 * and the functions declared in {ITransparentUpgradeableProxy} will be resolved in favor of the new one. This could
 * render the admin operations inaccessible, which could prevent upgradeability. Transparency may also be compromised.
 */
contract TransparentUpgradeableProxy is ERC1967Proxy {
    /**
     * @dev Initializes an upgradeable proxy managed by `_admin`, backed by the implementation at `_logic`, and
     * optionally initialized with `_data` as explained in {ERC1967Proxy-constructor}.
     */
    constructor(address _logic, address admin_, bytes memory _data) payable ERC1967Proxy(_logic, _data) {
        _changeAdmin(admin_);
    }

    /**
     * @dev If caller is the admin process the call internally, otherwise transparently fallback to the proxy behavior
     */
    function _fallback() internal virtual override {
        if (msg.sender == _getAdmin()) {
            bytes memory ret;
            bytes4 selector = msg.sig;
            if (selector == ITransparentUpgradeableProxy.upgradeTo.selector) {
                ret = _dispatchUpgradeTo();
            } else if (selector == ITransparentUpgradeableProxy.upgradeToAndCall.selector) {
                ret = _dispatchUpgradeToAndCall();
            } else if (selector == ITransparentUpgradeableProxy.changeAdmin.selector) {
                ret = _dispatchChangeAdmin();
            } else {
                revert("TransparentUpgradeableProxy: admin cannot fallback to proxy target");
            }
            assembly {
                return(add(ret, 0x20), mload(ret))
            }
        } else {
            super._fallback();
        }
    }

    /**
     * @dev Changes the admin of the proxy.
     *
     * Emits an {AdminChanged} event.
     */
    function _dispatchChangeAdmin() private returns (bytes memory) {
        _requireZeroValue();

        address newAdmin = abi.decode(msg.data[4:], (address));
        _changeAdmin(newAdmin);

        return "";
    }

    /**
     * @dev Upgrade the implementation of the proxy.
     */
    function _dispatchUpgradeTo() private returns (bytes memory) {
        _requireZeroValue();

        address newImplementation = abi.decode(msg.data[4:], (address));
        _upgradeToAndCall(newImplementation, bytes(""), false);

        return "";
    }

    /**
     * @dev Upgrade the implementation of the proxy, and then call a function from the new implementation as specified
     * by `data`, which should be an encoded function call. This is useful to initialize new storage variables in the
     * proxied contract.
     */
    function _dispatchUpgradeToAndCall() private returns (bytes memory) {
        (address newImplementation, bytes memory data) = abi.decode(msg.data[4:], (address, bytes));
        _upgradeToAndCall(newImplementation, data, true);

        return "";
    }

    /**
     * @dev To keep this contract fully transparent, the fallback is payable. This helper is here to enforce
     * non-payability of function implemented through dispatchers while still allowing value to pass through.
     */
    function _requireZeroValue() private {
        require(msg.value == 0);
    }
}