Contract Address Details

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

import { ERC20 } from "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import { IProofVerifier } from "src/layer1/verifiers/IProofVerifier.sol";
import { ISignalService } from "src/shared/signal/ISignalService.sol";

contract MockERC20 is ERC20 {
    constructor() ERC20("Mock Token", "MOCK") {
        _mint(msg.sender, 1_000_000 ether);
    }

    function mint(address to, uint256 amount) external {
        _mint(to, amount);
    }
}

contract MockProofVerifier is IProofVerifier {
    function verifyProof(uint256, bytes32, bytes calldata) external pure { }
}

contract MockSignalService is ISignalService {
    mapping(uint48 => Checkpoint) public checkpoints;
    mapping(bytes32 => bool) public sentSignals;
    mapping(bytes32 => bool) public receivedSignals;

    function sendSignal(bytes32 _signal) external returns (bytes32 slot_) {
        slot_ = getSignalSlot(uint64(block.chainid), msg.sender, _signal);
        sentSignals[slot_] = true;
        emit SignalSent(msg.sender, _signal, slot_, _signal);
    }

    function sendSignalFrom(
        uint64 _chainId,
        address _app,
        bytes32 _signal
    )
        external
        returns (bytes32 slot_)
    {
        slot_ = getSignalSlot(_chainId, _app, _signal);
        sentSignals[slot_] = true;
        emit SignalSent(_app, _signal, slot_, _signal);
    }

    function proveSignalReceived(
        uint64 _chainId,
        address _app,
        bytes32 _signal,
        bytes calldata
    )
        external
        returns (uint256)
    {
        bytes32 slot = getSignalSlot(_chainId, _app, _signal);
        require(sentSignals[slot], "signal not sent");
        receivedSignals[slot] = true;
        return 0;
    }

    function verifySignalReceived(
        uint64 _chainId,
        address _app,
        bytes32 _signal,
        bytes calldata
    )
        external
        view
    {
        bytes32 slot = getSignalSlot(_chainId, _app, _signal);
        require(sentSignals[slot], "signal not sent");
        require(receivedSignals[slot], "signal not proved");
    }

    function isSignalSent(address _app, bytes32 _signal) external view returns (bool) {
        return sentSignals[getSignalSlot(uint64(block.chainid), _app, _signal)];
    }

    function isSignalSent(bytes32 _signalSlot) external view returns (bool) {
        return sentSignals[_signalSlot];
    }

    function getSignalSlot(
        uint64 _chainId,
        address _app,
        bytes32 _signal
    )
        public
        pure
        returns (bytes32)
    {
        return keccak256(abi.encodePacked("SIGNAL", _chainId, _app, _signal));
    }

    function saveCheckpoint(Checkpoint calldata _checkpoint) external {
        checkpoints[_checkpoint.blockNumber] = _checkpoint;
        emit CheckpointSaved(_checkpoint.blockNumber, _checkpoint.blockHash, _checkpoint.stateRoot);
    }

    function getCheckpoint(uint48 _blockNumber) external view returns (Checkpoint memory) {
        return checkpoints[_blockNumber];
    }
}
        

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

/// @title IProofVerifier
/// @notice Interface for verifying validity proofs for state transitions
/// @custom:security-contact security@taiko.xyz
interface IProofVerifier {
    /// @notice Verifies a validity proof for a state transition
    /// @dev This function must revert if the proof is invalid
    /// @param _proposalAge The age in seconds of the proposal being proven. Only set for
    ///        single-proposal proofs (calculated as block.timestamp - proposal.timestamp).
    ///        For multi-proposal batches, this is always 0, meaning "not applicable".
    ///        Verifiers should interpret _proposalAge == 0 as "not applicable" rather than
    ///        "instant proof". This parameter enables age-based verification logic, such as
    ///        detecting and handling prover-killer proposals differently.
    /// @param _commitmentHash Hash of the last proposal hash and commitment data
    /// @param _proof The proof data
    function verifyProof(
        uint256 _proposalAge,
        bytes32 _commitmentHash,
        bytes calldata _proof
    )
        external
        view;
}
          

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

/// @title ICheckpointStore
/// @notice Interface for storing and retrieving checkpoints
/// @custom:security-contact security@taiko.xyz
interface ICheckpointStore {
    // ---------------------------------------------------------------
    // Structs
    // ---------------------------------------------------------------

    /// @notice Represents a synced checkpoint
    struct Checkpoint {
        /// @notice The block number associated with the checkpoint.
        uint48 blockNumber;
        /// @notice The block hash for the referenced block.
        bytes32 blockHash;
        /// @notice The state root for the referenced block.
        bytes32 stateRoot;
    }

    // ---------------------------------------------------------------
    // Events
    // ---------------------------------------------------------------

    /// @notice Emitted when a checkpoint is saved
    /// @param blockNumber The block number
    /// @param blockHash The block hash
    /// @param stateRoot The state root
    event CheckpointSaved(uint48 indexed blockNumber, bytes32 blockHash, bytes32 stateRoot);

    // ---------------------------------------------------------------
    // External Functions
    // ---------------------------------------------------------------

    /// @notice Saves a checkpoint
    /// @param _checkpoint The checkpoint data to persist
    function saveCheckpoint(Checkpoint calldata _checkpoint) external;

    /// @notice Gets a checkpoint by its block number
    /// @param _blockNumber The block number associated with the checkpoint
    /// @return _ The checkpoint
    function getCheckpoint(uint48 _blockNumber) external view returns (Checkpoint memory);
}
          

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

import "./ICheckpointStore.sol";

/// @title ISignalService
/// @notice The SignalService contract serves as a secure cross-chain message
/// passing system. It defines methods for sending and verifying signals with
/// merkle proofs. The trust assumption is that the target chain has secure
/// access to the merkle root (such as Taiko injects it in the anchor
/// transaction). With this, verifying a signal is reduced to simply verifying
/// a merkle proof.
/// @custom:security-contact security@taiko.xyz
interface ISignalService is ICheckpointStore {
    /// @dev DEPRECATED
    /// @dev Caching is no longer supported
    enum CacheOption {
        CACHE_NOTHING,
        CACHE_SIGNAL_ROOT,
        CACHE_STATE_ROOT,
        CACHE_BOTH
    }

    struct HopProof {
        /// @notice This hop's destination chain ID. If there is a next hop, this ID is the next
        /// hop's source chain ID.
        uint64 chainId;
        /// @notice The ID of a source chain block whose state root has been synced to the hop's
        /// destination chain.
        /// Note that this block ID must be greater than or equal to the block ID where the signal
        /// was sent on the source chain.
        uint64 blockId;
        /// @notice The state root or signal root of the source chain at the above blockId. This
        /// value has been synced to the destination chain.
        /// @dev To get both the blockId and the rootHash, apps should subscribe to the
        /// ChainDataSynced event or query `topBlockId` first using the source chain's ID and
        /// LibStrings.H_STATE_ROOT to get the most recent block ID synced, then call
        /// `getSyncedChainData` to read the synchronized data.
        bytes32 rootHash;
        /// @notice Options to cache either the state roots or signal roots of middle-hops to the
        /// current chain.
        /// @dev DEPRECATED - this value will be ignored
        CacheOption cacheOption;
        /// @notice The signal service's account proof. If this value is empty, then `rootHash` will
        /// be used as the signal root, otherwise, `rootHash` will be used as the state root.
        bytes[] accountProof;
        /// @notice The signal service's storage proof.
        bytes[] storageProof;
    }

    /// @notice Emitted when a signal is sent.
    /// @param app The address that initiated the signal.
    /// @param signal The signal (message) that was sent.
    /// @param slot The location in storage where this signal is stored.
    /// @param value The value of the signal.
    event SignalSent(address app, bytes32 signal, bytes32 slot, bytes32 value);

    /// @notice Send a signal (message) by setting the storage slot to the same value as the signal
    /// itself.
    /// @param _signal The signal (message) to send.
    /// @return slot_ The location in storage where this signal is stored.
    function sendSignal(bytes32 _signal) external returns (bytes32 slot_);

    /// @notice Checks whether a signal has been received on the target chain and caches the result if successful.
    /// @param _chainId The identifier for the source chain from which the
    /// signal originated.
    /// @param _app The address that initiated the signal.
    /// @param _signal The signal (message) to send.
    /// @param _proof Merkle proof that the signal was persisted on the
    /// source chain. If this proof is empty, then we check if this signal has been marked as
    /// received by TaikoL2.
    /// @return numCacheOps_ The number of newly cached items.
    function proveSignalReceived(
        uint64 _chainId,
        address _app,
        bytes32 _signal,
        bytes calldata _proof
    )
        external
        returns (uint256 numCacheOps_);

    /// @notice Verifies if a signal has been received on the target chain.
    /// This is the "readonly" version of proveSignalReceived.
    /// @param _chainId The identifier for the source chain from which the
    /// signal originated.
    /// @param _app The address that initiated the signal.
    /// @param _signal The signal (message) to send.
    /// @param _proof Merkle proof that the signal was persisted on the
    /// source chain. If this proof is empty, then we check if this signal has been marked as
    /// received by TaikoL2.
    function verifySignalReceived(
        uint64 _chainId,
        address _app,
        bytes32 _signal,
        bytes calldata _proof
    )
        external
        view;

    /// @notice Verifies if a particular signal has already been sent.
    /// @param _app The address that initiated the signal.
    /// @param _signal The signal (message) that was sent.
    /// @return true if the signal has been sent, otherwise false.
    function isSignalSent(address _app, bytes32 _signal) external view returns (bool);

    /// @notice Verifies if a particular signal has already been sent.
    /// @param _signalSlot The location in storage where this signal is stored.
    function isSignalSent(bytes32 _signalSlot) external view returns (bool);
}
          

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.9.0) (token/ERC20/ERC20.sol)

pragma solidity ^0.8.0;

import "./IERC20.sol";
import "./extensions/IERC20Metadata.sol";
import "../../utils/Context.sol";

/**
 * @dev Implementation of the {IERC20} interface.
 *
 * This implementation is agnostic to the way tokens are created. This means
 * that a supply mechanism has to be added in a derived contract using {_mint}.
 * For a generic mechanism see {ERC20PresetMinterPauser}.
 *
 * TIP: For a detailed writeup see our guide
 * https://forum.openzeppelin.com/t/how-to-implement-erc20-supply-mechanisms/226[How
 * to implement supply mechanisms].
 *
 * The default value of {decimals} is 18. To change this, you should override
 * this function so it returns a different value.
 *
 * We have followed general OpenZeppelin Contracts guidelines: functions revert
 * instead returning `false` on failure. This behavior is nonetheless
 * conventional and does not conflict with the expectations of ERC20
 * applications.
 *
 * Additionally, an {Approval} event is emitted on calls to {transferFrom}.
 * This allows applications to reconstruct the allowance for all accounts just
 * by listening to said events. Other implementations of the EIP may not emit
 * these events, as it isn't required by the specification.
 *
 * Finally, the non-standard {decreaseAllowance} and {increaseAllowance}
 * functions have been added to mitigate the well-known issues around setting
 * allowances. See {IERC20-approve}.
 */
contract ERC20 is Context, IERC20, IERC20Metadata {
    mapping(address => uint256) private _balances;

    mapping(address => mapping(address => uint256)) private _allowances;

    uint256 private _totalSupply;

    string private _name;
    string private _symbol;

    /**
     * @dev Sets the values for {name} and {symbol}.
     *
     * All two of these values are immutable: they can only be set once during
     * construction.
     */
    constructor(string memory name_, string memory symbol_) {
        _name = name_;
        _symbol = symbol_;
    }

    /**
     * @dev Returns the name of the token.
     */
    function name() public view virtual override returns (string memory) {
        return _name;
    }

    /**
     * @dev Returns the symbol of the token, usually a shorter version of the
     * name.
     */
    function symbol() public view virtual override returns (string memory) {
        return _symbol;
    }

    /**
     * @dev Returns the number of decimals used to get its user representation.
     * For example, if `decimals` equals `2`, a balance of `505` tokens should
     * be displayed to a user as `5.05` (`505 / 10 ** 2`).
     *
     * Tokens usually opt for a value of 18, imitating the relationship between
     * Ether and Wei. This is the default value returned by this function, unless
     * it's overridden.
     *
     * NOTE: This information is only used for _display_ purposes: it in
     * no way affects any of the arithmetic of the contract, including
     * {IERC20-balanceOf} and {IERC20-transfer}.
     */
    function decimals() public view virtual override returns (uint8) {
        return 18;
    }

    /**
     * @dev See {IERC20-totalSupply}.
     */
    function totalSupply() public view virtual override returns (uint256) {
        return _totalSupply;
    }

    /**
     * @dev See {IERC20-balanceOf}.
     */
    function balanceOf(address account) public view virtual override returns (uint256) {
        return _balances[account];
    }

    /**
     * @dev See {IERC20-transfer}.
     *
     * Requirements:
     *
     * - `to` cannot be the zero address.
     * - the caller must have a balance of at least `amount`.
     */
    function transfer(address to, uint256 amount) public virtual override returns (bool) {
        address owner = _msgSender();
        _transfer(owner, to, amount);
        return true;
    }

    /**
     * @dev See {IERC20-allowance}.
     */
    function allowance(address owner, address spender) public view virtual override returns (uint256) {
        return _allowances[owner][spender];
    }

    /**
     * @dev See {IERC20-approve}.
     *
     * NOTE: If `amount` is the maximum `uint256`, the allowance is not updated on
     * `transferFrom`. This is semantically equivalent to an infinite approval.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 amount) public virtual override returns (bool) {
        address owner = _msgSender();
        _approve(owner, spender, amount);
        return true;
    }

    /**
     * @dev See {IERC20-transferFrom}.
     *
     * Emits an {Approval} event indicating the updated allowance. This is not
     * required by the EIP. See the note at the beginning of {ERC20}.
     *
     * NOTE: Does not update the allowance if the current allowance
     * is the maximum `uint256`.
     *
     * Requirements:
     *
     * - `from` and `to` cannot be the zero address.
     * - `from` must have a balance of at least `amount`.
     * - the caller must have allowance for ``from``'s tokens of at least
     * `amount`.
     */
    function transferFrom(address from, address to, uint256 amount) public virtual override returns (bool) {
        address spender = _msgSender();
        _spendAllowance(from, spender, amount);
        _transfer(from, to, amount);
        return true;
    }

    /**
     * @dev Atomically increases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
        address owner = _msgSender();
        _approve(owner, spender, allowance(owner, spender) + addedValue);
        return true;
    }

    /**
     * @dev Atomically decreases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     * - `spender` must have allowance for the caller of at least
     * `subtractedValue`.
     */
    function decreaseAllowance(address spender, uint256 subtractedValue) public virtual returns (bool) {
        address owner = _msgSender();
        uint256 currentAllowance = allowance(owner, spender);
        require(currentAllowance >= subtractedValue, "ERC20: decreased allowance below zero");
        unchecked {
            _approve(owner, spender, currentAllowance - subtractedValue);
        }

        return true;
    }

    /**
     * @dev Moves `amount` of tokens from `from` to `to`.
     *
     * This internal function is equivalent to {transfer}, and can be used to
     * e.g. implement automatic token fees, slashing mechanisms, etc.
     *
     * Emits a {Transfer} event.
     *
     * Requirements:
     *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     * - `from` must have a balance of at least `amount`.
     */
    function _transfer(address from, address to, uint256 amount) internal virtual {
        require(from != address(0), "ERC20: transfer from the zero address");
        require(to != address(0), "ERC20: transfer to the zero address");

        _beforeTokenTransfer(from, to, amount);

        uint256 fromBalance = _balances[from];
        require(fromBalance >= amount, "ERC20: transfer amount exceeds balance");
        unchecked {
            _balances[from] = fromBalance - amount;
            // Overflow not possible: the sum of all balances is capped by totalSupply, and the sum is preserved by
            // decrementing then incrementing.
            _balances[to] += amount;
        }

        emit Transfer(from, to, amount);

        _afterTokenTransfer(from, to, amount);
    }

    /** @dev Creates `amount` tokens and assigns them to `account`, increasing
     * the total supply.
     *
     * Emits a {Transfer} event with `from` set to the zero address.
     *
     * Requirements:
     *
     * - `account` cannot be the zero address.
     */
    function _mint(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: mint to the zero address");

        _beforeTokenTransfer(address(0), account, amount);

        _totalSupply += amount;
        unchecked {
            // Overflow not possible: balance + amount is at most totalSupply + amount, which is checked above.
            _balances[account] += amount;
        }
        emit Transfer(address(0), account, amount);

        _afterTokenTransfer(address(0), account, amount);
    }

    /**
     * @dev Destroys `amount` tokens from `account`, reducing the
     * total supply.
     *
     * Emits a {Transfer} event with `to` set to the zero address.
     *
     * Requirements:
     *
     * - `account` cannot be the zero address.
     * - `account` must have at least `amount` tokens.
     */
    function _burn(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: burn from the zero address");

        _beforeTokenTransfer(account, address(0), amount);

        uint256 accountBalance = _balances[account];
        require(accountBalance >= amount, "ERC20: burn amount exceeds balance");
        unchecked {
            _balances[account] = accountBalance - amount;
            // Overflow not possible: amount <= accountBalance <= totalSupply.
            _totalSupply -= amount;
        }

        emit Transfer(account, address(0), amount);

        _afterTokenTransfer(account, address(0), amount);
    }

    /**
     * @dev Sets `amount` as the allowance of `spender` over the `owner` s tokens.
     *
     * This internal function is equivalent to `approve`, and can be used to
     * e.g. set automatic allowances for certain subsystems, etc.
     *
     * Emits an {Approval} event.
     *
     * Requirements:
     *
     * - `owner` cannot be the zero address.
     * - `spender` cannot be the zero address.
     */
    function _approve(address owner, address spender, uint256 amount) internal virtual {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");

        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }

    /**
     * @dev Updates `owner` s allowance for `spender` based on spent `amount`.
     *
     * Does not update the allowance amount in case of infinite allowance.
     * Revert if not enough allowance is available.
     *
     * Might emit an {Approval} event.
     */
    function _spendAllowance(address owner, address spender, uint256 amount) internal virtual {
        uint256 currentAllowance = allowance(owner, spender);
        if (currentAllowance != type(uint256).max) {
            require(currentAllowance >= amount, "ERC20: insufficient allowance");
            unchecked {
                _approve(owner, spender, currentAllowance - amount);
            }
        }
    }

    /**
     * @dev Hook that is called before any transfer of tokens. This includes
     * minting and burning.
     *
     * Calling conditions:
     *
     * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
     * will be transferred to `to`.
     * - when `from` is zero, `amount` tokens will be minted for `to`.
     * - when `to` is zero, `amount` of ``from``'s tokens will be burned.
     * - `from` and `to` are never both zero.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _beforeTokenTransfer(address from, address to, uint256 amount) internal virtual {}

    /**
     * @dev Hook that is called after any transfer of tokens. This includes
     * minting and burning.
     *
     * Calling conditions:
     *
     * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
     * has been transferred to `to`.
     * - when `from` is zero, `amount` tokens have been minted for `to`.
     * - when `to` is zero, `amount` of ``from``'s tokens have been burned.
     * - `from` and `to` are never both zero.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _afterTokenTransfer(address from, address to, uint256 amount) internal virtual {}
}
          

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.9.0) (token/ERC20/IERC20.sol)

pragma solidity ^0.8.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);

    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `to`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address to, uint256 amount) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `from` to `to` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(address from, address to, uint256 amount) external returns (bool);
}
          

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (token/ERC20/extensions/IERC20Metadata.sol)

pragma solidity ^0.8.0;

import "../IERC20.sol";

/**
 * @dev Interface for the optional metadata functions from the ERC20 standard.
 *
 * _Available since v4.1._
 */
interface IERC20Metadata is IERC20 {
    /**
     * @dev Returns the name of the token.
     */
    function name() external view returns (string memory);

    /**
     * @dev Returns the symbol of the token.
     */
    function symbol() external view returns (string memory);

    /**
     * @dev Returns the decimals places of the token.
     */
    function decimals() external view returns (uint8);
}
          

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.9.4) (utils/Context.sol)

pragma solidity ^0.8.0;

/**
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
abstract contract Context {
    function _msgSender() internal view virtual returns (address) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes calldata) {
        return msg.data;
    }

    function _contextSuffixLength() internal view virtual returns (uint256) {
        return 0;
    }
}