StandardBridge.sol

// SPDX-License-Identifier: MIT
pragma solidity 0.8.15;

import { IERC20 } from "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import { ERC165Checker } from "@openzeppelin/contracts/utils/introspection/ERC165Checker.sol";
import { Address } from "@openzeppelin/contracts/utils/Address.sol";
import { SafeERC20 } from "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";
import { SafeCall } from "src/libraries/SafeCall.sol";
import { IOptimismMintableERC20, ILegacyMintableERC20 } from "src/universal/IOptimismMintableERC20.sol";
import { CrossDomainMessenger } from "src/universal/CrossDomainMessenger.sol";
import { OptimismMintableERC20 } from "src/universal/OptimismMintableERC20.sol";
import { Initializable } from "@openzeppelin/contracts/proxy/utils/Initializable.sol";
import { Constants } from "src/libraries/Constants.sol";

/// @custom:upgradeable
/// @title StandardBridge
/// @notice StandardBridge is a base contract for the L1 and L2 standard ERC20 bridges. It handles
///         the core bridging logic, including escrowing tokens that are native to the local chain
///         and minting/burning tokens that are native to the remote chain.
abstract contract StandardBridge is Initializable {
    using SafeERC20 for IERC20;

    /// @notice The L2 gas limit set when eth is depoisited using the receive() function.
    uint32 internal constant RECEIVE_DEFAULT_GAS_LIMIT = 200_000;

    /// @custom:legacy
    /// @custom:spacer messenger
    /// @notice Spacer for backwards compatibility.
    bytes30 private spacer_0_2_30;

    /// @custom:legacy
    /// @custom:spacer l2TokenBridge
    /// @notice Spacer for backwards compatibility.
    address private spacer_1_0_20;

    /// @notice Mapping that stores deposits for a given pair of local and remote tokens.
    mapping(address => mapping(address => uint256)) public deposits;

    /// @notice Messenger contract on this domain.
    /// @custom:network-specific
    CrossDomainMessenger public messenger;

    /// @notice Corresponding bridge on the other domain.
    /// @custom:network-specific
    StandardBridge public otherBridge;

    /// @notice Reserve extra slots (to a total of 50) in the storage layout for future upgrades.
    ///         A gap size of 45 was chosen here, so that the first slot used in a child contract
    ///         would be a multiple of 50.
    uint256[45] private __gap;

    /// @notice Emitted when an ETH bridge is initiated to the other chain.
    /// @param from      Address of the sender.
    /// @param to        Address of the receiver.
    /// @param amount    Amount of ETH sent.
    /// @param extraData Extra data sent with the transaction.
    event ETHBridgeInitiated(address indexed from, address indexed to, uint256 amount, bytes extraData);

    /// @notice Emitted when an ETH bridge is finalized on this chain.
    /// @param from      Address of the sender.
    /// @param to        Address of the receiver.
    /// @param amount    Amount of ETH sent.
    /// @param extraData Extra data sent with the transaction.
    event ETHBridgeFinalized(address indexed from, address indexed to, uint256 amount, bytes extraData);

    /// @notice Emitted when an ERC20 bridge is initiated to the other chain.
    /// @param localToken  Address of the ERC20 on this chain.
    /// @param remoteToken Address of the ERC20 on the remote chain.
    /// @param from        Address of the sender.
    /// @param to          Address of the receiver.
    /// @param amount      Amount of the ERC20 sent.
    /// @param extraData   Extra data sent with the transaction.
    event ERC20BridgeInitiated(
        address indexed localToken,
        address indexed remoteToken,
        address indexed from,
        address to,
        uint256 amount,
        bytes extraData
    );

    /// @notice Emitted when an ERC20 bridge is finalized on this chain.
    /// @param localToken  Address of the ERC20 on this chain.
    /// @param remoteToken Address of the ERC20 on the remote chain.
    /// @param from        Address of the sender.
    /// @param to          Address of the receiver.
    /// @param amount      Amount of the ERC20 sent.
    /// @param extraData   Extra data sent with the transaction.
    event ERC20BridgeFinalized(
        address indexed localToken,
        address indexed remoteToken,
        address indexed from,
        address to,
        uint256 amount,
        bytes extraData
    );

    /// @notice Only allow EOAs to call the functions. Note that this is not safe against contracts
    ///         calling code within their constructors, but also doesn't really matter since we're
    ///         just trying to prevent users accidentally depositing with smart contract wallets.
    modifier onlyEOA() {
        require(!Address.isContract(msg.sender), "StandardBridge: function can only be called from an EOA");
        _;
    }

    /// @notice Ensures that the caller is a cross-chain message from the other bridge.
    modifier onlyOtherBridge() {
        require(
            msg.sender == address(messenger) && messenger.xDomainMessageSender() == address(otherBridge),
            "StandardBridge: function can only be called from the other bridge"
        );
        _;
    }

    /// @notice Initializer.
    /// @param _messenger   Contract for CrossDomainMessenger on this network.
    /// @param _otherBridge Contract for the other StandardBridge contract.
    function __StandardBridge_init(
        CrossDomainMessenger _messenger,
        StandardBridge _otherBridge
    )
        internal
        onlyInitializing
    {
        messenger = _messenger;
        otherBridge = _otherBridge;
    }

    /// @notice Allows EOAs to bridge ETH by sending directly to the bridge.
    ///         Must be implemented by contracts that inherit.
    receive() external payable virtual;

    /// @notice Returns the address of the custom gas token and the token's decimals.
    function gasPayingToken() internal view virtual returns (address, uint8);

    /// @notice Returns whether the chain uses a custom gas token or not.
    function isCustomGasToken() internal view returns (bool) {
        (address token,) = gasPayingToken();
        return token != Constants.ETHER;
    }

    /// @notice Getter for messenger contract.
    ///         Public getter is legacy and will be removed in the future. Use `messenger` instead.
    /// @return Contract of the messenger on this domain.
    /// @custom:legacy
    function MESSENGER() external view returns (CrossDomainMessenger) {
        return messenger;
    }

    /// @notice Getter for the other bridge contract.
    ///         Public getter is legacy and will be removed in the future. Use `otherBridge` instead.
    /// @return Contract of the bridge on the other network.
    /// @custom:legacy
    function OTHER_BRIDGE() external view returns (StandardBridge) {
        return otherBridge;
    }

    /// @notice This function should return true if the contract is paused.
    ///         On L1 this function will check the SuperchainConfig for its paused status.
    ///         On L2 this function should be a no-op.
    /// @return Whether or not the contract is paused.
    function paused() public view virtual returns (bool) {
        return false;
    }

    /// @notice Sends ETH to the sender's address on the other chain.
    /// @param _minGasLimit Minimum amount of gas that the bridge can be relayed with.
    /// @param _extraData   Extra data to be sent with the transaction. Note that the recipient will
    ///                     not be triggered with this data, but it will be emitted and can be used
    ///                     to identify the transaction.
    function bridgeETH(uint32 _minGasLimit, bytes calldata _extraData) public payable onlyEOA {
        _initiateBridgeETH(msg.sender, msg.sender, msg.value, _minGasLimit, _extraData);
    }

    /// @notice Sends ETH to a receiver's address on the other chain. Note that if ETH is sent to a
    ///         smart contract and the call fails, the ETH will be temporarily locked in the
    ///         StandardBridge on the other chain until the call is replayed. If the call cannot be
    ///         replayed with any amount of gas (call always reverts), then the ETH will be
    ///         permanently locked in the StandardBridge on the other chain. ETH will also
    ///         be locked if the receiver is the other bridge, because finalizeBridgeETH will revert
    ///         in that case.
    /// @param _to          Address of the receiver.
    /// @param _minGasLimit Minimum amount of gas that the bridge can be relayed with.
    /// @param _extraData   Extra data to be sent with the transaction. Note that the recipient will
    ///                     not be triggered with this data, but it will be emitted and can be used
    ///                     to identify the transaction.
    function bridgeETHTo(address _to, uint32 _minGasLimit, bytes calldata _extraData) public payable {
        _initiateBridgeETH(msg.sender, _to, msg.value, _minGasLimit, _extraData);
    }

    /// @notice Sends ERC20 tokens to the sender's address on the other chain.
    /// @param _localToken  Address of the ERC20 on this chain.
    /// @param _remoteToken Address of the corresponding token on the remote chain.
    /// @param _amount      Amount of local tokens to deposit.
    /// @param _minGasLimit Minimum amount of gas that the bridge can be relayed with.
    /// @param _extraData   Extra data to be sent with the transaction. Note that the recipient will
    ///                     not be triggered with this data, but it will be emitted and can be used
    ///                     to identify the transaction.
    function bridgeERC20(
        address _localToken,
        address _remoteToken,
        uint256 _amount,
        uint32 _minGasLimit,
        bytes calldata _extraData
    )
        public
        virtual
        onlyEOA
    {
        _initiateBridgeERC20(_localToken, _remoteToken, msg.sender, msg.sender, _amount, _minGasLimit, _extraData);
    }

    /// @notice Sends ERC20 tokens to a receiver's address on the other chain.
    /// @param _localToken  Address of the ERC20 on this chain.
    /// @param _remoteToken Address of the corresponding token on the remote chain.
    /// @param _to          Address of the receiver.
    /// @param _amount      Amount of local tokens to deposit.
    /// @param _minGasLimit Minimum amount of gas that the bridge can be relayed with.
    /// @param _extraData   Extra data to be sent with the transaction. Note that the recipient will
    ///                     not be triggered with this data, but it will be emitted and can be used
    ///                     to identify the transaction.
    function bridgeERC20To(
        address _localToken,
        address _remoteToken,
        address _to,
        uint256 _amount,
        uint32 _minGasLimit,
        bytes calldata _extraData
    )
        public
        virtual
    {
        _initiateBridgeERC20(_localToken, _remoteToken, msg.sender, _to, _amount, _minGasLimit, _extraData);
    }

    /// @notice Finalizes an ETH bridge on this chain. Can only be triggered by the other
    ///         StandardBridge contract on the remote chain.
    /// @param _from      Address of the sender.
    /// @param _to        Address of the receiver.
    /// @param _amount    Amount of ETH being bridged.
    /// @param _extraData Extra data to be sent with the transaction. Note that the recipient will
    ///                   not be triggered with this data, but it will be emitted and can be used
    ///                   to identify the transaction.
    function finalizeBridgeETH(
        address _from,
        address _to,
        uint256 _amount,
        bytes calldata _extraData
    )
        public
        payable
        onlyOtherBridge
    {
        require(paused() == false, "StandardBridge: paused");
        require(isCustomGasToken() == false, "StandardBridge: cannot bridge ETH with custom gas token");
        require(msg.value == _amount, "StandardBridge: amount sent does not match amount required");
        require(_to != address(this), "StandardBridge: cannot send to self");
        require(_to != address(messenger), "StandardBridge: cannot send to messenger");

        // Emit the correct events. By default this will be _amount, but child
        // contracts may override this function in order to emit legacy events as well.
        _emitETHBridgeFinalized(_from, _to, _amount, _extraData);

        bool success = SafeCall.call(_to, gasleft(), _amount, hex"");
        require(success, "StandardBridge: ETH transfer failed");
    }

    /// @notice Finalizes an ERC20 bridge on this chain. Can only be triggered by the other
    ///         StandardBridge contract on the remote chain.
    /// @param _localToken  Address of the ERC20 on this chain.
    /// @param _remoteToken Address of the corresponding token on the remote chain.
    /// @param _from        Address of the sender.
    /// @param _to          Address of the receiver.
    /// @param _amount      Amount of the ERC20 being bridged.
    /// @param _extraData   Extra data to be sent with the transaction. Note that the recipient will
    ///                     not be triggered with this data, but it will be emitted and can be used
    ///                     to identify the transaction.
    function finalizeBridgeERC20(
        address _localToken,
        address _remoteToken,
        address _from,
        address _to,
        uint256 _amount,
        bytes calldata _extraData
    )
        public
        onlyOtherBridge
    {
        require(paused() == false, "StandardBridge: paused");
        if (_isOptimismMintableERC20(_localToken)) {
            require(
                _isCorrectTokenPair(_localToken, _remoteToken),
                "StandardBridge: wrong remote token for Optimism Mintable ERC20 local token"
            );

            OptimismMintableERC20(_localToken).mint(_to, _amount);
        } else {
            deposits[_localToken][_remoteToken] = deposits[_localToken][_remoteToken] - _amount;
            IERC20(_localToken).safeTransfer(_to, _amount);
        }

        // Emit the correct events. By default this will be ERC20BridgeFinalized, but child
        // contracts may override this function in order to emit legacy events as well.
        _emitERC20BridgeFinalized(_localToken, _remoteToken, _from, _to, _amount, _extraData);
    }

    /// @notice Initiates a bridge of ETH through the CrossDomainMessenger.
    /// @param _from        Address of the sender.
    /// @param _to          Address of the receiver.
    /// @param _amount      Amount of ETH being bridged.
    /// @param _minGasLimit Minimum amount of gas that the bridge can be relayed with.
    /// @param _extraData   Extra data to be sent with the transaction. Note that the recipient will
    ///                     not be triggered with this data, but it will be emitted and can be used
    ///                     to identify the transaction.
    function _initiateBridgeETH(
        address _from,
        address _to,
        uint256 _amount,
        uint32 _minGasLimit,
        bytes memory _extraData
    )
        internal
    {
        require(isCustomGasToken() == false, "StandardBridge: cannot bridge ETH with custom gas token");
        require(msg.value == _amount, "StandardBridge: bridging ETH must include sufficient ETH value");

        // Emit the correct events. By default this will be _amount, but child
        // contracts may override this function in order to emit legacy events as well.
        _emitETHBridgeInitiated(_from, _to, _amount, _extraData);

        messenger.sendMessage{ value: _amount }({
            _target: address(otherBridge),
            _message: abi.encodeWithSelector(this.finalizeBridgeETH.selector, _from, _to, _amount, _extraData),
            _minGasLimit: _minGasLimit
        });
    }

    /// @notice Sends ERC20 tokens to a receiver's address on the other chain.
    /// @param _localToken  Address of the ERC20 on this chain.
    /// @param _remoteToken Address of the corresponding token on the remote chain.
    /// @param _to          Address of the receiver.
    /// @param _amount      Amount of local tokens to deposit.
    /// @param _minGasLimit Minimum amount of gas that the bridge can be relayed with.
    /// @param _extraData   Extra data to be sent with the transaction. Note that the recipient will
    ///                     not be triggered with this data, but it will be emitted and can be used
    ///                     to identify the transaction.
    function _initiateBridgeERC20(
        address _localToken,
        address _remoteToken,
        address _from,
        address _to,
        uint256 _amount,
        uint32 _minGasLimit,
        bytes memory _extraData
    )
        internal
    {
        require(msg.value == 0, "StandardBridge: cannot send value");

        if (_isOptimismMintableERC20(_localToken)) {
            require(
                _isCorrectTokenPair(_localToken, _remoteToken),
                "StandardBridge: wrong remote token for Optimism Mintable ERC20 local token"
            );

            OptimismMintableERC20(_localToken).burn(_from, _amount);
        } else {
            IERC20(_localToken).safeTransferFrom(_from, address(this), _amount);
            deposits[_localToken][_remoteToken] = deposits[_localToken][_remoteToken] + _amount;
        }

        // Emit the correct events. By default this will be ERC20BridgeInitiated, but child
        // contracts may override this function in order to emit legacy events as well.
        _emitERC20BridgeInitiated(_localToken, _remoteToken, _from, _to, _amount, _extraData);

        messenger.sendMessage({
            _target: address(otherBridge),
            _message: abi.encodeWithSelector(
                this.finalizeBridgeERC20.selector,
                // Because this call will be executed on the remote chain, we reverse the order of
                // the remote and local token addresses relative to their order in the
                // finalizeBridgeERC20 function.
                _remoteToken,
                _localToken,
                _from,
                _to,
                _amount,
                _extraData
            ),
            _minGasLimit: _minGasLimit
        });
    }

    /// @notice Checks if a given address is an OptimismMintableERC20. Not perfect, but good enough.
    ///         Just the way we like it.
    /// @param _token Address of the token to check.
    /// @return True if the token is an OptimismMintableERC20.
    function _isOptimismMintableERC20(address _token) internal view returns (bool) {
        return ERC165Checker.supportsInterface(_token, type(ILegacyMintableERC20).interfaceId)
            || ERC165Checker.supportsInterface(_token, type(IOptimismMintableERC20).interfaceId);
    }

    /// @notice Checks if the "other token" is the correct pair token for the OptimismMintableERC20.
    ///         Calls can be saved in the future by combining this logic with
    ///         `_isOptimismMintableERC20`.
    /// @param _mintableToken OptimismMintableERC20 to check against.
    /// @param _otherToken    Pair token to check.
    /// @return True if the other token is the correct pair token for the OptimismMintableERC20.
    function _isCorrectTokenPair(address _mintableToken, address _otherToken) internal view returns (bool) {
        if (ERC165Checker.supportsInterface(_mintableToken, type(ILegacyMintableERC20).interfaceId)) {
            return _otherToken == ILegacyMintableERC20(_mintableToken).l1Token();
        } else {
            return _otherToken == IOptimismMintableERC20(_mintableToken).remoteToken();
        }
    }

    /// @notice Emits the ETHBridgeInitiated event and if necessary the appropriate legacy event
    ///         when an ETH bridge is finalized on this chain.
    /// @param _from      Address of the sender.
    /// @param _to        Address of the receiver.
    /// @param _amount    Amount of ETH sent.
    /// @param _extraData Extra data sent with the transaction.
    function _emitETHBridgeInitiated(
        address _from,
        address _to,
        uint256 _amount,
        bytes memory _extraData
    )
        internal
        virtual
    {
        emit ETHBridgeInitiated(_from, _to, _amount, _extraData);
    }

    /// @notice Emits the ETHBridgeFinalized and if necessary the appropriate legacy event when an
    ///         ETH bridge is finalized on this chain.
    /// @param _from      Address of the sender.
    /// @param _to        Address of the receiver.
    /// @param _amount    Amount of ETH sent.
    /// @param _extraData Extra data sent with the transaction.
    function _emitETHBridgeFinalized(
        address _from,
        address _to,
        uint256 _amount,
        bytes memory _extraData
    )
        internal
        virtual
    {
        emit ETHBridgeFinalized(_from, _to, _amount, _extraData);
    }

    /// @notice Emits the ERC20BridgeInitiated event and if necessary the appropriate legacy
    ///         event when an ERC20 bridge is initiated to the other chain.
    /// @param _localToken  Address of the ERC20 on this chain.
    /// @param _remoteToken Address of the ERC20 on the remote chain.
    /// @param _from        Address of the sender.
    /// @param _to          Address of the receiver.
    /// @param _amount      Amount of the ERC20 sent.
    /// @param _extraData   Extra data sent with the transaction.
    function _emitERC20BridgeInitiated(
        address _localToken,
        address _remoteToken,
        address _from,
        address _to,
        uint256 _amount,
        bytes memory _extraData
    )
        internal
        virtual
    {
        emit ERC20BridgeInitiated(_localToken, _remoteToken, _from, _to, _amount, _extraData);
    }

    /// @notice Emits the ERC20BridgeFinalized event and if necessary the appropriate legacy
    ///         event when an ERC20 bridge is initiated to the other chain.
    /// @param _localToken  Address of the ERC20 on this chain.
    /// @param _remoteToken Address of the ERC20 on the remote chain.
    /// @param _from        Address of the sender.
    /// @param _to          Address of the receiver.
    /// @param _amount      Amount of the ERC20 sent.
    /// @param _extraData   Extra data sent with the transaction.
    function _emitERC20BridgeFinalized(
        address _localToken,
        address _remoteToken,
        address _from,
        address _to,
        uint256 _amount,
        bytes memory _extraData
    )
        internal
        virtual
    {
        emit ERC20BridgeFinalized(_localToken, _remoteToken, _from, _to, _amount, _extraData);
    }
}