Optimism standard bridge contract walkthrough

1// SPDX-License-Identifier: MIT
 Kopyahin

1pragma solidity >0.5.0 <0.9.0;
 Kopyahin

1/**
2 * @title IL1ERC20Bridge
3 */
4interface IL1ERC20Bridge {
5    /**********
6     * Events *
7     **********/
8
9    event ERC20DepositInitiated(
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1        address indexed _l1Token,
2        address indexed _l2Token,
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1        address indexed _from,
2        address _to,
3        uint256 _amount,
4        bytes _data
5    );
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1    event ERC20WithdrawalFinalized(
2        address indexed _l1Token,
3        address indexed _l2Token,
4        address indexed _from,
5        address _to,
6        uint256 _amount,
7        bytes _data
8    );
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1
2    /********************
3     * Public Functions *
4     ********************/
5
6    /**
7     * @dev get the address of the corresponding L2 bridge contract.
8     * @return Address of the corresponding L2 bridge contract.
9     */
10    function l2TokenBridge() external returns (address);
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1    /**
2     * @dev deposit an amount of the ERC20 to the caller's balance on L2.
3     * @param _l1Token Address of the L1 ERC20 we are depositing
4     * @param _l2Token Address of the L1 respective L2 ERC20
5     * @param _amount Amount of the ERC20 to deposit
6     * @param _l2Gas Gas limit required to complete the deposit on L2.
7     * @param _data Optional data to forward to L2. This data is provided
8     *        solely as a convenience for external contracts. Aside from enforcing a maximum
9     *        length, these contracts provide no guarantees about its content.
10     */
11    function depositERC20(
12        address _l1Token,
13        address _l2Token,
14        uint256 _amount,
15        uint32 _l2Gas,
16        bytes calldata _data
17    ) external;
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1    /**
2     * @dev deposit an amount of ERC20 to a recipient's balance on L2.
3     * @param _l1Token Address of the L1 ERC20 we are depositing
4     * @param _l2Token Address of the L1 respective L2 ERC20
5     * @param _to L2 address to credit the withdrawal to.
6     * @param _amount Amount of the ERC20 to deposit.
7     * @param _l2Gas Gas limit required to complete the deposit on L2.
8     * @param _data Optional data to forward to L2. This data is provided
9     *        solely as a convenience for external contracts. Aside from enforcing a maximum
10     *        length, these contracts provide no guarantees about its content.
11     */
12    function depositERC20To(
13        address _l1Token,
14        address _l2Token,
15        address _to,
16        uint256 _amount,
17        uint32 _l2Gas,
18        bytes calldata _data
19    ) external;
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1    /*************************
2     * Cross-chain Functions *
3     *************************/
4
5    /**
6     * @dev Complete a withdrawal from L2 to L1, and credit funds to the recipient's balance of the
7     * L1 ERC20 token.
8     * This call will fail if the initialized withdrawal from L2 has not been finalized.
9     *
10     * @param _l1Token Address of L1 token to finalizeWithdrawal for.
11     * @param _l2Token Address of L2 token where withdrawal was initiated.
12     * @param _from L2 address initiating the transfer.
13     * @param _to L1 address to credit the withdrawal to.
14     * @param _amount Amount of the ERC20 to deposit.
15     * @param _data Data provided by the sender on L2. This data is provided
16     *   solely as a convenience for external contracts. Aside from enforcing a maximum
17     *   length, these contracts provide no guarantees about its content.
18     */
19    function finalizeERC20Withdrawal(
20        address _l1Token,
21        address _l2Token,
22        address _from,
23        address _to,
24        uint256 _amount,
25        bytes calldata _data
26    ) external;
27}
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1// SPDX-License-Identifier: MIT
2pragma solidity >0.5.0 <0.9.0;
3
4import "./IL1ERC20Bridge.sol";
5
6/**
7 * @title IL1StandardBridge
8 */
9interface IL1StandardBridge is IL1ERC20Bridge {
10    /**********
11     * Events *
12     **********/
13    event ETHDepositInitiated(
14        address indexed _from,
15        address indexed _to,
16        uint256 _amount,
17        bytes _data
18    );
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1    event ETHWithdrawalFinalized(
2        .
3        .
4        .
5    );
6
7    /********************
8     * Public Functions *
9     ********************/
10
11    /**
12     * @dev Deposit an amount of the ETH to the caller's balance on L2.
13            .
14            .
15            .
16     */
17    function depositETH(uint32 _l2Gas, bytes calldata _data) external payable;
18
19    /**
20     * @dev Deposit an amount of ETH to a recipient's balance on L2.
21            .
22            .
23            .
24     */
25    function depositETHTo(
26        address _to,
27        uint32 _l2Gas,
28        bytes calldata _data
29    ) external payable;
30
31    /*************************
32     * Cross-chain Functions *
33     *************************/
34
35    /**
36     * @dev Complete a withdrawal from L2 to L1, and credit funds to the recipient's balance of the
37     * L1 ETH token. Since only the xDomainMessenger can call this function, it will never be called
38     * before the withdrawal is finalized.
39                .
40                .
41                .
42     */
43    function finalizeETHWithdrawal(
44        address _from,
45        address _to,
46        uint256 _amount,
47        bytes calldata _data
48    ) external;
49}
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1// SPDX-License-Identifier: MIT
2pragma solidity >0.5.0 <0.9.0;
3
4/* Interface Imports */
5import { ICrossDomainMessenger } from "./ICrossDomainMessenger.sol";
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1/**
2 * @title CrossDomainEnabled
3 * @dev Helper contract for contracts performing cross-domain communications
4 *
5 * Compiler used: defined by inheriting contract
6 */
7contract CrossDomainEnabled {
8    /*************
9     * Variables *
10     *************/
11
12    // Messenger contract used to send and receive messages from the other domain.
13    address public messenger;
14
15    /***************
16     * Constructor *
17     ***************/
18
19    /**
20     * @param _messenger Address of the CrossDomainMessenger on the current layer.
21     */
22    constructor(address _messenger) {
23        messenger = _messenger;
24    }
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1
2    /**********************
3     * Function Modifiers *
4     **********************/
5
6    /**
7     * Enforces that the modified function is only callable by a specific cross-domain account.
8     * @param _sourceDomainAccount The only account on the originating domain which is
9     *  authenticated to call this function.
10     */
11    modifier onlyFromCrossDomainAccount(address _sourceDomainAccount) {
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1        require(
2            msg.sender == address(getCrossDomainMessenger()),
3            "OVM_XCHAIN: messenger contract unauthenticated"
4        );
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1
2        require(
3            getCrossDomainMessenger().xDomainMessageSender() == _sourceDomainAccount,
4            "OVM_XCHAIN: wrong sender of cross-domain message"
5        );
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1
2        _;
3    }
4
5    /**********************
6     * Internal Functions *
7     **********************/
8
9    /**
10     * Gets the messenger, usually from storage. This function is exposed in case a child contract
11     * needs to override.
12     * @return The address of the cross-domain messenger contract which should be used.
13     */
14    function getCrossDomainMessenger() internal virtual returns (ICrossDomainMessenger) {
15        return ICrossDomainMessenger(messenger);
16    }
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1
2    /**
3     * Sends a message to an account on another domain
4     * @param _crossDomainTarget The intended recipient on the destination domain
5     * @param _message The data to send to the target (usually calldata to a function with
6     *  `onlyFromCrossDomainAccount()`)
7     * @param _gasLimit The gasLimit for the receipt of the message on the target domain.
8     */
9    function sendCrossDomainMessage(
10        address _crossDomainTarget,
11        uint32 _gasLimit,
12        bytes memory _message
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1    ) internal {
2        // slither-disable-next-line reentrancy-events, reentrancy-benign
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1        getCrossDomainMessenger().sendMessage(_crossDomainTarget, _message, _gasLimit);
2    }
3}
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1// SPDX-License-Identifier: MIT
2pragma solidity ^0.8.9;
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1/* Interface Imports */
2import { IL1StandardBridge } from "./IL1StandardBridge.sol";
3import { IL1ERC20Bridge } from "./IL1ERC20Bridge.sol";
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1import { IL2ERC20Bridge } from "../../L2/messaging/IL2ERC20Bridge.sol";
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1import { IERC20 } from "@openzeppelin/contracts/token/ERC20/IERC20.sol";
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1/* Library Imports */
2import { CrossDomainEnabled } from "../../libraries/bridge/CrossDomainEnabled.sol";
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1import { Lib_PredeployAddresses } from "../../libraries/constants/Lib_PredeployAddresses.sol";
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1import { Address } from "@openzeppelin/contracts/utils/Address.sol";
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1import { SafeERC20 } from "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";
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1/**
2 * @title L1StandardBridge
3 * @dev The L1 ETH and ERC20 Bridge is a contract which stores deposited L1 funds and standard
4 * tokens that are in use on L2. It synchronizes a corresponding L2 Bridge, informing it of deposits
5 * and listening to it for newly finalized withdrawals.
6 *
7 */
8contract L1StandardBridge is IL1StandardBridge, CrossDomainEnabled {
9    using SafeERC20 for IERC20;
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1
2    /********************************
3     * External Contract References *
4     ********************************/
5
6    address public l2TokenBridge;
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1
2    // Maps L1 token to L2 token to balance of the L1 token deposited
3    mapping(address => mapping(address => uint256)) public deposits;
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1
2    /***************
3     * Constructor *
4     ***************/
5
6    // This contract lives behind a proxy, so the constructor parameters will go unused.
7    constructor() CrossDomainEnabled(address(0)) {}
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1    /******************
2     * Initialization *
3     ******************/
4
5    /**
6     * @param _l1messenger L1 Messenger address being used for cross-chain communications.
7     * @param _l2TokenBridge L2 standard bridge address.
8     */
9    // slither-disable-next-line external-function
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1    function initialize(address _l1messenger, address _l2TokenBridge) public {
2        require(messenger == address(0), "Contract has already been initialized.");
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1        messenger = _l1messenger;
2        l2TokenBridge = _l2TokenBridge;
3    }
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1
2    /**************
3     * Depositing *
4     **************/
5
6    /** @dev Modifier requiring sender to be EOA.  This check could be bypassed by a malicious
7     *  contract via initcode, but it takes care of the user error we want to avoid.
8     */
9    modifier onlyEOA() {
10        // Used to stop deposits from contracts (avoid accidentally lost tokens)
11        require(!Address.isContract(msg.sender), "Account not EOA");
12        _;
13    }
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1    /**
2     * @dev This function can be called with no data
3     * to deposit an amount of ETH to the caller's balance on L2.
4     * Since the receive function doesn't take data, a conservative
5     * default amount is forwarded to L2.
6     */
7    receive() external payable onlyEOA {
8        _initiateETHDeposit(msg.sender, msg.sender, 200_000, bytes(""));
9    }
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1    /**
2     * @inheritdoc IL1StandardBridge
3     */
4    function depositETH(uint32 _l2Gas, bytes calldata _data) external payable onlyEOA {
5        _initiateETHDeposit(msg.sender, msg.sender, _l2Gas, _data);
6    }
7
8    /**
9     * @inheritdoc IL1StandardBridge
10     */
11    function depositETHTo(
12        address _to,
13        uint32 _l2Gas,
14        bytes calldata _data
15    ) external payable {
16        _initiateETHDeposit(msg.sender, _to, _l2Gas, _data);
17    }
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1    /**
2     * @dev Performs the logic for deposits by storing the ETH and informing the L2 ETH Gateway of
3     * the deposit.
4     * @param _from Account to pull the deposit from on L1.
5     * @param _to Account to give the deposit to on L2.
6     * @param _l2Gas Gas limit required to complete the deposit on L2.
7     * @param _data Optional data to forward to L2. This data is provided
8     *        solely as a convenience for external contracts. Aside from enforcing a maximum
9     *        length, these contracts provide no guarantees about its content.
10     */
11    function _initiateETHDeposit(
12        address _from,
13        address _to,
14        uint32 _l2Gas,
15        bytes memory _data
16    ) internal {
17        // Construct calldata for finalizeDeposit call
18        bytes memory message = abi.encodeWithSelector(
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1            IL2ERC20Bridge.finalizeDeposit.selector,
2            address(0),
3            Lib_PredeployAddresses.OVM_ETH,
4            _from,
5            _to,
6            msg.value,
7            _data
8        );
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1        // Send calldata into L2
2        // slither-disable-next-line reentrancy-events
3        sendCrossDomainMessage(l2TokenBridge, _l2Gas, message);
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1        // slither-disable-next-line reentrancy-events
2        emit ETHDepositInitiated(_from, _to, msg.value, _data);
3    }
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1    /**
2     * @inheritdoc IL1ERC20Bridge
3     */
4    function depositERC20(
5        .
6        .
7        .
8    ) external virtual onlyEOA {
9        _initiateERC20Deposit(_l1Token, _l2Token, msg.sender, msg.sender, _amount, _l2Gas, _data);
10    }
11
12    /**
13     * @inheritdoc IL1ERC20Bridge
14     */
15    function depositERC20To(
16        .
17        .
18        .
19    ) external virtual {
20        _initiateERC20Deposit(_l1Token, _l2Token, msg.sender, _to, _amount, _l2Gas, _data);
21    }
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1    /**
2     * @dev Performs the logic for deposits by informing the L2 Deposited Token
3     * contract of the deposit and calling a handler to lock the L1 funds. (e.g. transferFrom)
4     *
5     * @param _l1Token Address of the L1 ERC20 we are depositing
6     * @param _l2Token Address of the L1 respective L2 ERC20
7     * @param _from Account to pull the deposit from on L1
8     * @param _to Account to give the deposit to on L2
9     * @param _amount Amount of the ERC20 to deposit.
10     * @param _l2Gas Gas limit required to complete the deposit on L2.
11     * @param _data Optional data to forward to L2. This data is provided
12     *        solely as a convenience for external contracts. Aside from enforcing a maximum
13     *        length, these contracts provide no guarantees about its content.
14     */
15    function _initiateERC20Deposit(
16        address _l1Token,
17        address _l2Token,
18        address _from,
19        address _to,
20        uint256 _amount,
21        uint32 _l2Gas,
22        bytes calldata _data
23    ) internal {
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1        // When a deposit is initiated on L1, the L1 Bridge transfers the funds to itself for future
2        // withdrawals. safeTransferFrom also checks if the contract has code, so this will fail if
3        // _from is an EOA or address(0).
4        // slither-disable-next-line reentrancy-events, reentrancy-benign
5        IERC20(_l1Token).safeTransferFrom(_from, address(this), _amount);
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1        // Construct calldata for _l2Token.finalizeDeposit(_to, _amount)
2        bytes memory message = abi.encodeWithSelector(
3            IL2ERC20Bridge.finalizeDeposit.selector,
4            _l1Token,
5            _l2Token,
6            _from,
7            _to,
8            _amount,
9            _data
10        );
11
12        // Send calldata into L2
13        // slither-disable-next-line reentrancy-events, reentrancy-benign
14        sendCrossDomainMessage(l2TokenBridge, _l2Gas, message);
15
16        // slither-disable-next-line reentrancy-benign
17        deposits[_l1Token][_l2Token] = deposits[_l1Token][_l2Token] + _amount;
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1
2        // slither-disable-next-line reentrancy-events
3        emit ERC20DepositInitiated(_l1Token, _l2Token, _from, _to, _amount, _data);
4    }
5
6    /*************************
7     * Cross-chain Functions *
8     *************************/
9
10    /**
11     * @inheritdoc IL1StandardBridge
12     */
13    function finalizeETHWithdrawal(
14        address _from,
15        address _to,
16        uint256 _amount,
17        bytes calldata _data
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1    ) external onlyFromCrossDomainAccount(l2TokenBridge) {
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1        // slither-disable-next-line reentrancy-events
2        (bool success, ) = _to.call{ value: _amount }(new bytes(0));
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1        require(success, "TransferHelper::safeTransferETH: ETH transfer failed");
2
3        // slither-disable-next-line reentrancy-events
4        emit ETHWithdrawalFinalized(_from, _to, _amount, _data);
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1    }
2
3    /**
4     * @inheritdoc IL1ERC20Bridge
5     */
6    function finalizeERC20Withdrawal(
7        address _l1Token,
8        address _l2Token,
9        address _from,
10        address _to,
11        uint256 _amount,
12        bytes calldata _data
13    ) external onlyFromCrossDomainAccount(l2TokenBridge) {
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1        deposits[_l1Token][_l2Token] = deposits[_l1Token][_l2Token] - _amount;
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1
2        // When a withdrawal is finalized on L1, the L1 Bridge transfers the funds to the withdrawer
3        // slither-disable-next-line reentrancy-events
4        IERC20(_l1Token).safeTransfer(_to, _amount);
5
6        // slither-disable-next-line reentrancy-events
7        emit ERC20WithdrawalFinalized(_l1Token, _l2Token, _from, _to, _amount, _data);
8    }
9
10
11    /*****************************
12     * Temporary - Migrating ETH *
13     *****************************/
14
15    /**
16     * @dev Adds ETH balance to the account. This is meant to allow for ETH
17     * to be migrated from an old gateway to a new gateway.
18     * NOTE: This is left for one upgrade only so we are able to receive the migrated ETH from the
19     * old contract
20     */
21    function donateETH() external payable {}
22}
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1// SPDX-License-Identifier: MIT
2pragma solidity ^0.8.9;
3
4import { IERC20 } from "@openzeppelin/contracts/token/ERC20/IERC20.sol";
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1import { IERC165 } from "@openzeppelin/contracts/utils/introspection/IERC165.sol";
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1interface IL2StandardERC20 is IERC20, IERC165 {
2    function l1Token() external returns (address);
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1
2    function mint(address _to, uint256 _amount) external;
3
4    function burn(address _from, uint256 _amount) external;
5
6    event Mint(address indexed _account, uint256 _amount);
7    event Burn(address indexed _account, uint256 _amount);
8}
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1// SPDX-License-Identifier: MIT
2pragma solidity ^0.8.9;
3
4import { ERC20 } from "@openzeppelin/contracts/token/ERC20/ERC20.sol";
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1import "./IL2StandardERC20.sol";
2
3contract L2StandardERC20 is IL2StandardERC20, ERC20 {
4    address public l1Token;
5    address public l2Bridge;
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1
2    /**
3     * @param _l2Bridge Address of the L2 standard bridge.
4     * @param _l1Token Address of the corresponding L1 token.
5     * @param _name ERC20 name.
6     * @param _symbol ERC20 symbol.
7     */
8    constructor(
9        address _l2Bridge,
10        address _l1Token,
11        string memory _name,
12        string memory _symbol
13    ) ERC20(_name, _symbol) {
14        l1Token = _l1Token;
15        l2Bridge = _l2Bridge;
16    }
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1
2    modifier onlyL2Bridge() {
3        require(msg.sender == l2Bridge, "Only L2 Bridge can mint and burn");
4        _;
5    }
6
7
8    // slither-disable-next-line external-function
9    function supportsInterface(bytes4 _interfaceId) public pure returns (bool) {
10        bytes4 firstSupportedInterface = bytes4(keccak256("supportsInterface(bytes4)")); // ERC165
11        bytes4 secondSupportedInterface = IL2StandardERC20.l1Token.selector ^
12            IL2StandardERC20.mint.selector ^
13            IL2StandardERC20.burn.selector;
14        return _interfaceId == firstSupportedInterface || _interfaceId == secondSupportedInterface;
15    }
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1    // slither-disable-next-line external-function
2    function mint(address _to, uint256 _amount) public virtual onlyL2Bridge {
3        _mint(_to, _amount);
4
5        emit Mint(_to, _amount);
6    }
7
8    // slither-disable-next-line external-function
9    function burn(address _from, uint256 _amount) public virtual onlyL2Bridge {
10        _burn(_from, _amount);
11
12        emit Burn(_from, _amount);
13    }
14}
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1// SPDX-License-Identifier: MIT
2pragma solidity ^0.8.9;
3
4/* Interface Imports */
5import { IL1StandardBridge } from "../../L1/messaging/IL1StandardBridge.sol";
6import { IL1ERC20Bridge } from "../../L1/messaging/IL1ERC20Bridge.sol";
7import { IL2ERC20Bridge } from "./IL2ERC20Bridge.sol";
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1/* Library Imports */
2import { ERC165Checker } from "@openzeppelin/contracts/utils/introspection/ERC165Checker.sol";
3import { CrossDomainEnabled } from "../../libraries/bridge/CrossDomainEnabled.sol";
4import { Lib_PredeployAddresses } from "../../libraries/constants/Lib_PredeployAddresses.sol";
5
6/* Contract Imports */
7import { IL2StandardERC20 } from "../../standards/IL2StandardERC20.sol";
8
9/**
10 * @title L2StandardBridge
11 * @dev The L2 Standard bridge is a contract which works together with the L1 Standard bridge to
12 * enable ETH and ERC20 transitions between L1 and L2.
13 * This contract acts as a minter for new tokens when it hears about deposits into the L1 Standard
14 * bridge.
15 * This contract also acts as a burner of the tokens intended for withdrawal, informing the L1
16 * bridge to release L1 funds.
17 */
18contract L2StandardBridge is IL2ERC20Bridge, CrossDomainEnabled {
19    /********************************
20     * External Contract References *
21     ********************************/
22
23    address public l1TokenBridge;
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1
2    /***************
3     * Constructor *
4     ***************/
5
6    /**
7     * @param _l2CrossDomainMessenger Cross-domain messenger used by this contract.
8     * @param _l1TokenBridge Address of the L1 bridge deployed to the main chain.
9     */
10    constructor(address _l2CrossDomainMessenger, address _l1TokenBridge)
11        CrossDomainEnabled(_l2CrossDomainMessenger)
12    {
13        l1TokenBridge = _l1TokenBridge;
14    }
15
16    /***************
17     * Withdrawing *
18     ***************/
19
20    /**
21     * @inheritdoc IL2ERC20Bridge
22     */
23    function withdraw(
24        address _l2Token,
25        uint256 _amount,
26        uint32 _l1Gas,
27        bytes calldata _data
28    ) external virtual {
29        _initiateWithdrawal(_l2Token, msg.sender, msg.sender, _amount, _l1Gas, _data);
30    }
31
32    /**
33     * @inheritdoc IL2ERC20Bridge
34     */
35    function withdrawTo(
36        address _l2Token,
37        address _to,
38        uint256 _amount,
39        uint32 _l1Gas,
40        bytes calldata _data
41    ) external virtual {
42        _initiateWithdrawal(_l2Token, msg.sender, _to, _amount, _l1Gas, _data);
43    }
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1
2    /**
3     * @dev Performs the logic for withdrawals by burning the token and informing
4     *      the L1 token Gateway of the withdrawal.
5     * @param _l2Token Address of L2 token where withdrawal is initiated.
6     * @param _from Account to pull the withdrawal from on L2.
7     * @param _to Account to give the withdrawal to on L1.
8     * @param _amount Amount of the token to withdraw.
9     * @param _l1Gas Unused, but included for potential forward compatibility considerations.
10     * @param _data Optional data to forward to L1. This data is provided
11     *        solely as a convenience for external contracts. Aside from enforcing a maximum
12     *        length, these contracts provide no guarantees about its content.
13     */
14    function _initiateWithdrawal(
15        address _l2Token,
16        address _from,
17        address _to,
18        uint256 _amount,
19        uint32 _l1Gas,
20        bytes calldata _data
21    ) internal {
22        // When a withdrawal is initiated, we burn the withdrawer's funds to prevent subsequent L2
23        // usage
24        // slither-disable-next-line reentrancy-events
25        IL2StandardERC20(_l2Token).burn(msg.sender, _amount);
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1
2        // Construct calldata for l1TokenBridge.finalizeERC20Withdrawal(_to, _amount)
3        // slither-disable-next-line reentrancy-events
4        address l1Token = IL2StandardERC20(_l2Token).l1Token();
5        bytes memory message;
6
7        if (_l2Token == Lib_PredeployAddresses.OVM_ETH) {
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1            message = abi.encodeWithSelector(
2                IL1StandardBridge.finalizeETHWithdrawal.selector,
3                _from,
4                _to,
5                _amount,
6                _data
7            );
8        } else {
9            message = abi.encodeWithSelector(
10                IL1ERC20Bridge.finalizeERC20Withdrawal.selector,
11                l1Token,
12                _l2Token,
13                _from,
14                _to,
15                _amount,
16                _data
17            );
18        }
19
20        // Send message up to L1 bridge
21        // slither-disable-next-line reentrancy-events
22        sendCrossDomainMessage(l1TokenBridge, _l1Gas, message);
23
24        // slither-disable-next-line reentrancy-events
25        emit WithdrawalInitiated(l1Token, _l2Token, msg.sender, _to, _amount, _data);
26    }
27
28    /************************************
29     * Cross-chain Function: Depositing *
30     ************************************/
31
32    /**
33     * @inheritdoc IL2ERC20Bridge
34     */
35    function finalizeDeposit(
36        address _l1Token,
37        address _l2Token,
38        address _from,
39        address _to,
40        uint256 _amount,
41        bytes calldata _data
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1    ) external virtual onlyFromCrossDomainAccount(l1TokenBridge) {
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1        // Check the target token is compliant and
2        // verify the deposited token on L1 matches the L2 deposited token representation here
3        if (
4            // slither-disable-next-line reentrancy-events
5            ERC165Checker.supportsInterface(_l2Token, 0x1d1d8b63) &&
6            _l1Token == IL2StandardERC20(_l2Token).l1Token()
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1        ) {
2            // When a deposit is finalized, we credit the account on L2 with the same amount of
3            // tokens.
4            // slither-disable-next-line reentrancy-events
5            IL2StandardERC20(_l2Token).mint(_to, _amount);
6            // slither-disable-next-line reentrancy-events
7            emit DepositFinalized(_l1Token, _l2Token, _from, _to, _amount, _data);
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1        } else {
2            // Either the L2 token which is being deposited-into disagrees about the correct address
3            // of its L1 token, or does not support the correct interface.
4            // This should only happen if there is a  malicious L2 token, or if a user somehow
5            // specified the wrong L2 token address to deposit into.
6            // In either case, we stop the process here and construct a withdrawal
7            // message so that users can get their funds out in some cases.
8            // There is no way to prevent malicious token contracts altogether, but this does limit
9            // user error and mitigate some forms of malicious contract behavior.
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1            bytes memory message = abi.encodeWithSelector(
2                IL1ERC20Bridge.finalizeERC20Withdrawal.selector,
3                _l1Token,
4                _l2Token,
5                _to, // switched the _to and _from here to bounce back the deposit to the sender
6                _from,
7                _amount,
8                _data
9            );
10
11            // Send message up to L1 bridge
12            // slither-disable-next-line reentrancy-events
13            sendCrossDomainMessage(l1TokenBridge, 0, message);
14            // slither-disable-next-line reentrancy-events
15            emit DepositFailed(_l1Token, _l2Token, _from, _to, _amount, _data);
16        }
17    }
18}
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