在前面两篇文章《Solidity合约代理模式的简单示例》和《Solidity合约代理模式的几个技术技巧》中，我们探究了代理合约的作用以及写法，这一篇我们来看看ERC里的代理合约标准。
1. ERC1967Proxy
/**
* @dev This contract implements an upgradeable proxy. It is upgradeable because calls are delegated to an
* implementation address that can be changed. This address is stored in storage in the location specified by
* https://eips.ethereum.org/EIPS/eip-1967[EIP1967], so that it doesn't conflict with the storage layout of the
* implementation behind the proxy.
*/
contract ERC1967Proxy is Proxy, ERC1967Upgrade {
/**
* @dev Initializes the upgradeable proxy with an initial implementation specified by `_logic`.
*
* If `_data` is nonempty, it's used as data in a delegate call to `_logic`. This will typically be an encoded
* function call, and allows initializing the storage of the proxy like a Solidity constructor.
*/
constructor(address _logic, bytes memory _data) payable {
assert(_IMPLEMENTATION_SLOT == bytes32(uint256(keccak256("eip1967.proxy.implementation")) - 1));
_upgradeToAndCall(_logic, _data, false);
}
/**
* @dev Returns the current implementation address.
*/
function _implementation() internal view virtual override returns (address impl) {
return ERC1967Upgrade._getImplementation();
}
}
ERC1967Proxy继承了Proxy和ERC1967Upgrade。
构造函数中，需要两个参数，_logic即是逻辑合约的地址，data是ecode的代码bytes，如果不为空的话，可用于_logic的delegatecall。构造函数中，首先是做了断言，确保基类合约ERC1967Upgrade中的_IMPLEMENTATION_SLOT常量为the keccak-256 hash of "eip1967.proxy.implementation" subtracted by 1；然后就是执行了_upgradeToAndCall——这个函数同样来自于基类合约ERC1967Upgrade，就是用于_logic的delegatecall，可完成初始化操作。
_implementation函数就是获取到逻辑合约的地址，我们之前说过，逻辑合约的地址藏在某个很大的数值索引_IMPLEMENTATION_SLOT指向的storage内存中。
2.ERC1967Upgrade
/**
* @dev This abstract contract provides getters and event emitting update functions for
* https://eips.ethereum.org/EIPS/eip-1967[EIP1967] slots.
*/
abstract contract ERC1967Upgrade {
// This is the keccak-256 hash of "eip1967.proxy.rollback" subtracted by 1
bytes32 private constant _ROLLBACK_SLOT = 0x4910fdfa16fed3260ed0e7147f7cc6da11a60208b5b9406d12a635614ffd9143;
/**
* @dev Storage slot with the address of the current implementation.
* This is the keccak-256 hash of "eip1967.proxy.implementation" subtracted by 1, and is
* validated in the constructor.
*/
bytes32 internal constant _IMPLEMENTATION_SLOT = 0x360894a13ba1a3210667c828492db98dca3e2076cc3735a920a3ca505d382bbc;
/**
* @dev Emitted when the implementation is upgraded.
*/
event Upgraded(address indexed implementation);
/**
* @dev Returns the current implementation address.
*/
function _getImplementation() internal view returns (address) {
return StorageSlot.getAddressSlot(_IMPLEMENTATION_SLOT).value;
}
/**
* @dev Stores a new address in the EIP1967 implementation slot.
*/
function _setImplementation(address newImplementation) private {
require(Address.isContract(newImplementation), "ERC1967: new implementation is not a contract");
StorageSlot.getAddressSlot(_IMPLEMENTATION_SLOT).value = newImplementation;
}
/**
* @dev Perform implementation upgrade
*
* Emits an {Upgraded} event.
*/
function _upgradeTo(address newImplementation) internal {
_setImplementation(newImplementation);
emit Upgraded(newImplementation);
}
/**
* @dev Perform implementation upgrade with additional setup call.
*
* Emits an {Upgraded} event.
*/
function _upgradeToAndCall(
address newImplementation,
bytes memory data,
bool forceCall
) internal {
_upgradeTo(newImplementation);
if (data.length > 0 || forceCall) {
Address.functionDelegateCall(newImplementation, data);
}
}
/**
* @dev Perform implementation upgrade with security checks for UUPS proxies, and additional setup call.
*
* Emits an {Upgraded} event.
*/
function _upgradeToAndCallSecure(
address newImplementation,
bytes memory data,
bool forceCall
) internal {
address oldImplementation = _getImplementation();
// Initial upgrade and setup call
_setImplementation(newImplementation);
if (data.length > 0 || forceCall) {
Address.functionDelegateCall(newImplementation, data);
}
// Perform rollback test if not already in progress
StorageSlot.BooleanSlot storage rollbackTesting = StorageSlot.getBooleanSlot(_ROLLBACK_SLOT);
if (!rollbackTesting.value) {
// Trigger rollback using upgradeTo from the new implementation
rollbackTesting.value = true;
Address.functionDelegateCall(
newImplementation,
abi.encodeWithSignature("upgradeTo(address)", oldImplementation)
);
rollbackTesting.value = false;
// Check rollback was effective
require(oldImplementation == _getImplementation(), "ERC1967Upgrade: upgrade breaks further upgrades");
// Finally reset to the new implementation and log the upgrade
_upgradeTo(newImplementation);
}
}
/**
* @dev Storage slot with the admin of the contract.
* This is the keccak-256 hash of "eip1967.proxy.admin" subtracted by 1, and is
* validated in the constructor.
*/
bytes32 internal constant _ADMIN_SLOT = 0xb53127684a568b3173ae13b9f8a6016e243e63b6e8ee1178d6a717850b5d6103;
/**
* @dev Emitted when the admin account has changed.
*/
event AdminChanged(address previousAdmin, address newAdmin);
/**
* @dev Returns the current admin.
*/
function _getAdmin() internal view returns (address) {
return StorageSlot.getAddressSlot(_ADMIN_SLOT).value;
}
/**
* @dev Stores a new address in the EIP1967 admin slot.
*/
function _setAdmin(address newAdmin) private {
require(newAdmin != address(0), "ERC1967: new admin is the zero address");
StorageSlot.getAddressSlot(_ADMIN_SLOT).value = newAdmin;
}
/**
* @dev Changes the admin of the proxy.
*
* Emits an {AdminChanged} event.
*/
function _changeAdmin(address newAdmin) internal {
emit AdminChanged(_getAdmin(), newAdmin);
_setAdmin(newAdmin);
}
/**
* @dev The storage slot of the UpgradeableBeacon contract which defines the implementation for this proxy.
* This is bytes32(uint256(keccak256('eip1967.proxy.beacon')) - 1)) and is validated in the constructor.
*/
bytes32 internal constant _BEACON_SLOT = 0xa3f0ad74e5423aebfd80d3ef4346578335a9a72aeaee59ff6cb3582b35133d50;
/**
* @dev Emitted when the beacon is upgraded.
*/
event BeaconUpgraded(address indexed beacon);
/**
* @dev Returns the current beacon.
*/
function _getBeacon() internal view returns (address) {
return StorageSlot.getAddressSlot(_BEACON_SLOT).value;
}
/**
* @dev Stores a new beacon in the EIP1967 beacon slot.
*/
function _setBeacon(address newBeacon) private {
require(Address.isContract(newBeacon), "ERC1967: new beacon is not a contract");
require(
Address.isContract(IBeacon(newBeacon).implementation()),
"ERC1967: beacon implementation is not a contract"
);
StorageSlot.getAddressSlot(_BEACON_SLOT).value = newBeacon;
}
/**
* @dev Perform beacon upgrade with additional setup call. Note: This upgrades the address of the beacon, it does
* not upgrade the implementation contained in the beacon (see {UpgradeableBeacon-_setImplementation} for that).
*
* Emits a {BeaconUpgraded} event.
*/
function _upgradeBeaconToAndCall(
address newBeacon,
bytes memory data,
bool forceCall
) internal {
_setBeacon(newBeacon);
emit BeaconUpgraded(newBeacon);
if (data.length > 0 || forceCall) {
Address.functionDelegateCall(IBeacon(newBeacon).implementation(), data);
}
}
}
/**
* @dev Library for reading and writing primitive types to specific storage slots.
*
* Storage slots are often used to avoid storage conflict when dealing with upgradeable contracts.
* This library helps with reading and writing to such slots without the need for inline assembly.
*
* The functions in this library return Slot structs that contain a `value` member that can be used to read or write.
*/
library StorageSlot {
struct AddressSlot {
address value;
}
struct BooleanSlot {
bool value;
}
struct Bytes32Slot {
bytes32 value;
}
struct Uint256Slot {
uint256 value;
}
/**
* @dev Returns an `AddressSlot` with member `value` located at `slot`.
*/
function getAddressSlot(bytes32 slot) internal pure returns (AddressSlot storage r) {
assembly {
r.slot := slot
}
}
/**
* @dev Returns an `BooleanSlot` with member `value` located at `slot`.
*/
function getBooleanSlot(bytes32 slot) internal pure returns (BooleanSlot storage r) {
assembly {
r.slot := slot
}
}
/**
* @dev Returns an `Bytes32Slot` with member `value` located at `slot`.
*/
function getBytes32Slot(bytes32 slot) internal pure returns (Bytes32Slot storage r) {
assembly {
r.slot := slot
}
}
/**
* @dev Returns an `Uint256Slot` with member `value` located at `slot`.
*/
function getUint256Slot(bytes32 slot) internal pure returns (Uint256Slot storage r) {
assembly {
r.slot := slot
}
}
}
ERC1967Upgrade合约中，我们可以看到_IMPLEMENTATION_SLOT是可见类型是internal的，用于继承。
_getImplementation是internal的用于继承，用来获取逻辑合约地址；_setImplementation则是给下一个函数_upgradeTo来调用的，用于设定新的逻辑合约地址。
这两个操作都使用了StorageSlot这个library，在合约下方给出了library StorageSlot这个库的代码，其定义了四种solot类型并且写了对应的getter方法。
_upgradeTo即用来做合约升级，主要就是设置了新的逻辑合约地址，发布了Upgrade的事件；
_upgradeToAndCall顾名思义，即先做合约升级，再做delegatecall传入的bytes类型的data；
_upgradeToAndCallSecure这个方法首先是给UUPSUpgradeable合约用的，在open zeppelin的github仓库中，这个方法是_upgradeToAndCallUUPS:
function _upgradeToAndCallUUPS(
address newImplementation,
bytes memory data,
bool forceCall
) internal {
// Upgrades from old implementations will perform a rollback test. This test requires the new
// implementation to upgrade back to the old, non-ERC1822 compliant, implementation. Removing
// this special case will break upgrade paths from old UUPS implementation to new ones.
if (StorageSlot.getBooleanSlot(_ROLLBACK_SLOT).value) {
_setImplementation(newImplementation);
} else {
try IERC1822Proxiable(newImplementation).proxiableUUID() returns (bytes32 slot) {
require(slot == _IMPLEMENTATION_SLOT, "ERC1967Upgrade: unsupported proxiableUUID");
} catch {
revert("ERC1967Upgrade: new implementation is not UUPS");
}
_upgradeToAndCall(newImplementation, data, forceCall);
}
}
_getAdmin、_setAdmin、_changeAdmin三个方法则是管理员相关信息；
_getBeacon、_setBeacon、_changeBeacon三个方法则是给Beacon合约用的；
3.Proxy
/**
* @dev This abstract contract provides a fallback function that delegates all calls to another contract using the EVM
* instruction `delegatecall`. We refer to the second contract as the _implementation_ behind the proxy, and it has to
* be specified by overriding the virtual {_implementation} function.
*
* Additionally, delegation to the implementation can be triggered manually through the {_fallback} function, or to a
* different contract through the {_delegate} function.
*
* The success and return data of the delegated call will be returned back to the caller of the proxy.
*/
abstract contract Proxy {
/**
* @dev Delegates the current call to `implementation`.
*
* This function does not return to its internal call site, it will return directly to the external caller.
*/
function _delegate(address implementation) internal virtual {
assembly {
// Copy msg.data. We take full control of memory in this inline assembly
// block because it will not return to Solidity code. We overwrite the
// Solidity scratch pad at memory position 0.
calldatacopy(0, 0, calldatasize())
// Call the implementation.
// out and outsize are 0 because we don't know the size yet.
let result := delegatecall(gas(), implementation, 0, calldatasize(), 0, 0)
// Copy the returned data.
returndatacopy(0, 0, returndatasize())
switch result
// delegatecall returns 0 on error.
case 0 {
revert(0, returndatasize())
}
default {
return(0, returndatasize())
}
}
}
/**
* @dev This is a virtual function that should be overridden so it returns the address to which the fallback function
* and {_fallback} should delegate.
*/
function _implementation() internal view virtual returns (address);
/**
* @dev Delegates the current call to the address returned by `_implementation()`.
*
* This function does not return to its internal call site, it will return directly to the external caller.
*/
function _fallback() internal virtual {
_beforeFallback();
_delegate(_implementation());
}
/**
* @dev Fallback function that delegates calls to the address returned by `_implementation()`. Will run if no other
* function in the contract matches the call data.
*/
fallback() external payable virtual {
_fallback();
}
/**
* @dev Fallback function that delegates calls to the address returned by `_implementation()`. Will run if call data
* is empty.
*/
receive() external payable virtual {
_fallback();
}
/**
* @dev Hook that is called before falling back to the implementation. Can happen as part of a manual `_fallback`
* call, or as part of the Solidity `fallback` or `receive` functions.
*
* If overridden should call `super._beforeFallback()`.
*/
function _beforeFallback() internal virtual {}
}
这个Proxy合约就和我们之前两篇文章中自己写的Proxy合约一样，关键就在于重写_delegate，然后在fallback函数中执行，这其中的原理如果不懂的话可以看之前那两篇文章，已经介绍得很详细了。
此外这个合约中多了个_beforeFallback函数，可以供开发者写入一些在做delegatecall之前的操作。
