APE Price: $1.00 (+1.98%)

Contract Diff Checker

Contract Name:
PythPriceOracle

Contract Source Code:

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "openzeppelin-contracts/contracts/access/Ownable.sol";
import "openzeppelin-contracts/contracts/token/ERC20/extensions/IERC20Metadata.sol";
import "./interfaces/IPyth.sol";
import "../../interfaces/IPriceOracle.sol";

contract PythPriceOracle is Ownable, IPriceOracle {
    /// @notice The min update interval (5 minutes)
    uint256 public constant UPDATE_INTERVAL = 5 minutes;

    /// @notice The max swing of the price per update (20%)
    uint256 public constant MAX_SWING = 2000;

    /// @notice The pyth oracle
    address public immutable pyth;

    /// @notice The poster address
    address public poster;

    struct PriceId {
        bytes32 priceId;
        bool reciprocal;
    }

    /// @notice The pyth price IDs
    mapping(address => PriceId[]) public pythPriceIds;

    /// @notice The fallback price of the assets
    mapping(address => uint256) public fallbackPrices;

    /// @notice The last updated time of the assets
    mapping(address => uint256) public lastUpdated;

    event PosterSet(address poster);

    event PriceIdSet(address asset, PriceId[] priceId);

    event FallbackPriceSet(address asset, uint256 price);

    modifier onlyPoster() {
        _checkPoster();
        _;
    }

    constructor(address _pyth) {
        pyth = _pyth;
    }

    /**
     * @notice Gets the pyth price IDs of an asset
     * @param asset The asset address
     * @return The pyth price IDs
     */
    function getPythPriceIds(address asset) external view returns (bytes32[] memory) {
        PriceId[] storage priceIds = pythPriceIds[asset];
        if (priceIds.length == 0) {
            return new bytes32[](0);
        }

        bytes32[] memory result = new bytes32[](priceIds.length);
        for (uint256 i = 0; i < priceIds.length;) {
            result[i] = priceIds[i].priceId;
            unchecked {
                i++;
            }
        }
        return result;
    }

    /**
     * @notice Gets the price of an asset
     * @param asset The asset to get the price of
     * @return The price of the asset
     */
    function getPrice(address asset) external view returns (uint256) {
        PriceId[] memory priceIds = pythPriceIds[asset];
        if (priceIds.length != 0) {
            uint256 price = 1e18;
            for (uint256 i = 0; i < priceIds.length;) {
                PriceId memory priceId = priceIds[i];

                if (priceId.reciprocal) {
                    price = price * 1e18 / _getPriceFromPyth(priceId.priceId);
                } else {
                    price = price * _getPriceFromPyth(priceId.priceId) / 1e18;
                }

                unchecked {
                    i++;
                }
            }
            return _getNormalizedPrice(price, asset);
        }

        uint256 fallbackPrice = fallbackPrices[asset];
        require(fallbackPrice > 0, "invalid fallback price");
        return fallbackPrice;
    }

    struct PriceData {
        address asset;
        uint256 price;
    }

    /**
     * @notice Sets the fallback price of the assets
     * @param priceData The price data
     */
    function setFallbackPrices(PriceData[] memory priceData) external onlyPoster {
        for (uint256 i = 0; i < priceData.length;) {
            address asset = priceData[i].asset;
            uint256 price = priceData[i].price;
            require(price > 0, "invalid price");

            // Check the max swing and last update time.
            if (fallbackPrices[asset] != 0) {
                uint256 maxPrice = fallbackPrices[asset] * (MAX_SWING + 10000) / 10000;
                uint256 minPrice = fallbackPrices[asset] * (10000 - MAX_SWING) / 10000;
                require(price <= maxPrice && price >= minPrice, "price swing too high");
                require(block.timestamp - lastUpdated[asset] >= UPDATE_INTERVAL, "min update interval not reached");
            }

            // Update the price and last updated time.
            fallbackPrices[asset] = price;
            lastUpdated[asset] = block.timestamp;

            emit FallbackPriceSet(asset, price);

            unchecked {
                i++;
            }
        }
    }

    /* ========== RESTRICTED FUNCTIONS ========== */

    /**
     * @notice Sets the poster address
     * @param _poster The poster address
     */
    function setPoster(address _poster) external onlyOwner {
        poster = _poster;

        emit PosterSet(_poster);
    }

    struct PythPriceIdData {
        address asset;
        PriceId[] priceIds;
    }

    /**
     * @notice Sets the pyth price IDs.
     * @param pythPriceIdData The pyth price ID data
     */
    function setPythPriceIds(PythPriceIdData[] memory pythPriceIdData) external onlyOwner {
        for (uint256 i = 0; i < pythPriceIdData.length;) {
            address asset = pythPriceIdData[i].asset;
            PriceId[] memory priceIds = pythPriceIdData[i].priceIds;

            if (priceIds.length == 0) {
                delete pythPriceIds[asset];
            } else {
                // Check the price IDs are valid.
                for (uint256 j = 0; j < priceIds.length;) {
                    bytes32 priceId = priceIds[j].priceId;
                    require(priceId != bytes32(0), "invalid price id");

                    IPyth.Price memory price = IPyth(pyth).getPriceUnsafe(priceId);
                    require(price.price > 0, "invalid price");

                    // Set the price feed.
                    pythPriceIds[asset].push(priceIds[j]);

                    unchecked {
                        j++;
                    }
                }

                emit PriceIdSet(asset, priceIds);
            }

            unchecked {
                i++;
            }
        }
    }

    /* ========== INTERNAL FUNCTIONS ========== */

    /**
     * @dev Checks whether the caller is the poster
     */
    function _checkPoster() internal view {
        require(msg.sender == poster, "caller is not the poster");
    }

    /**
     * @dev Gets the price from the pyth price feed
     * @param priceId The price ID
     * @return The price
     */
    function _getPriceFromPyth(bytes32 priceId) internal view returns (uint256) {
        IPyth.Price memory price = IPyth(pyth).getPriceUnsafe(priceId);
        require(price.price > 0, "invalid price");

        uint8 decimals = uint8(-1 * int8(price.expo));

        // Extend the decimals to 1e18.
        return uint256(int256(price.price)) * 10 ** (18 - decimals);
    }

    /**
     * @dev Get the normalized price.
     * @param price The price
     * @param asset The asset
     * @return The normalized price
     */
    function _getNormalizedPrice(uint256 price, address asset) internal view returns (uint256) {
        uint8 decimals = IERC20Metadata(asset).decimals();
        return price * 10 ** (18 - decimals);
    }
}

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.7.0) (access/Ownable.sol)

pragma solidity ^0.8.0;

import "../utils/Context.sol";

/**
 * @dev Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * By default, the owner account will be the one that deploys the contract. This
 * can later be changed with {transferOwnership}.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
abstract contract Ownable is Context {
    address private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor() {
        _transferOwnership(_msgSender());
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        _checkOwner();
        _;
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view virtual returns (address) {
        return _owner;
    }

    /**
     * @dev Throws if the sender is not the owner.
     */
    function _checkOwner() internal view virtual {
        require(owner() == _msgSender(), "Ownable: caller is not the owner");
    }

    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions anymore. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby removing any functionality that is only available to the owner.
     */
    function renounceOwnership() public virtual onlyOwner {
        _transferOwnership(address(0));
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        _transferOwnership(newOwner);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Internal function without access restriction.
     */
    function _transferOwnership(address newOwner) internal virtual {
        address oldOwner = _owner;
        _owner = newOwner;
        emit OwnershipTransferred(oldOwner, newOwner);
    }
}

// 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

pragma solidity ^0.8.0;

interface IPyth {
    struct Price {
        // Price
        int64 price;
        // Confidence interval around the price
        uint64 conf;
        // Price exponent
        int32 expo;
        // Unix timestamp describing when the price was published
        uint256 publishTime;
    }

    function getPriceUnsafe(bytes32 id) external view returns (Price memory price);
}

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

interface IPriceOracle {
    function getPrice(address asset) external view returns (uint256);
}

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (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;
    }
}

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.6.0) (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);
}

Contract Name:
PythPriceOracle

Contract Source Code:

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "openzeppelin-contracts/contracts/access/Ownable.sol";
import "openzeppelin-contracts/contracts/token/ERC20/extensions/IERC20Metadata.sol";
import "./interfaces/IPyth.sol";
import "../../interfaces/IPriceOracle.sol";

contract PythPriceOracle is Ownable, IPriceOracle {
    /// @notice The min update interval (5 minutes)
    uint256 public constant UPDATE_INTERVAL = 5 minutes;

    /// @notice The max swing of the price per update (20%)
    uint256 public constant MAX_SWING = 2000;

    /// @notice The pyth oracle
    address public immutable pyth;

    /// @notice The poster address
    address public poster;

    struct PriceId {
        bytes32 priceId;
        bool reciprocal;
    }

    /// @notice The pyth price IDs
    mapping(address => PriceId[]) public pythPriceIds;

    /// @notice The fallback price of the assets
    mapping(address => uint256) public fallbackPrices;

    /// @notice The last updated time of the assets
    mapping(address => uint256) public lastUpdated;

    event PosterSet(address poster);

    event PriceIdSet(address asset, PriceId[] priceId);

    event FallbackPriceSet(address asset, uint256 price);

    modifier onlyPoster() {
        _checkPoster();
        _;
    }

    constructor(address _pyth) {
        pyth = _pyth;
    }

    /**
     * @notice Gets the pyth price IDs of an asset
     * @param asset The asset address
     * @return The pyth price IDs
     */
    function getPythPriceIds(address asset) external view returns (bytes32[] memory) {
        PriceId[] storage priceIds = pythPriceIds[asset];
        if (priceIds.length == 0) {
            return new bytes32[](0);
        }

        bytes32[] memory result = new bytes32[](priceIds.length);
        for (uint256 i = 0; i < priceIds.length;) {
            result[i] = priceIds[i].priceId;
            unchecked {
                i++;
            }
        }
        return result;
    }

    /**
     * @notice Gets the price of an asset
     * @param asset The asset to get the price of
     * @return The price of the asset
     */
    function getPrice(address asset) external view returns (uint256) {
        PriceId[] memory priceIds = pythPriceIds[asset];
        if (priceIds.length != 0) {
            uint256 price = 1e18;
            for (uint256 i = 0; i < priceIds.length;) {
                PriceId memory priceId = priceIds[i];

                if (priceId.reciprocal) {
                    price = price * 1e18 / _getPriceFromPyth(priceId.priceId);
                } else {
                    price = price * _getPriceFromPyth(priceId.priceId) / 1e18;
                }

                unchecked {
                    i++;
                }
            }
            return _getNormalizedPrice(price, asset);
        }

        uint256 fallbackPrice = fallbackPrices[asset];
        require(fallbackPrice > 0, "invalid fallback price");
        return fallbackPrice;
    }

    struct PriceData {
        address asset;
        uint256 price;
    }

    /**
     * @notice Sets the fallback price of the assets
     * @param priceData The price data
     */
    function setFallbackPrices(PriceData[] memory priceData) external onlyPoster {
        for (uint256 i = 0; i < priceData.length;) {
            address asset = priceData[i].asset;
            uint256 price = priceData[i].price;
            require(price > 0, "invalid price");

            // Check the max swing and last update time.
            if (fallbackPrices[asset] != 0) {
                uint256 maxPrice = fallbackPrices[asset] * (MAX_SWING + 10000) / 10000;
                uint256 minPrice = fallbackPrices[asset] * (10000 - MAX_SWING) / 10000;
                require(price <= maxPrice && price >= minPrice, "price swing too high");
                require(block.timestamp - lastUpdated[asset] >= UPDATE_INTERVAL, "min update interval not reached");
            }

            // Update the price and last updated time.
            fallbackPrices[asset] = price;
            lastUpdated[asset] = block.timestamp;

            emit FallbackPriceSet(asset, price);

            unchecked {
                i++;
            }
        }
    }

    /* ========== RESTRICTED FUNCTIONS ========== */

    /**
     * @notice Sets the poster address
     * @param _poster The poster address
     */
    function setPoster(address _poster) external onlyOwner {
        poster = _poster;

        emit PosterSet(_poster);
    }

    struct PythPriceIdData {
        address asset;
        PriceId[] priceIds;
    }

    /**
     * @notice Sets the pyth price IDs.
     * @param pythPriceIdData The pyth price ID data
     */
    function setPythPriceIds(PythPriceIdData[] memory pythPriceIdData) external onlyOwner {
        for (uint256 i = 0; i < pythPriceIdData.length;) {
            address asset = pythPriceIdData[i].asset;
            PriceId[] memory priceIds = pythPriceIdData[i].priceIds;

            if (priceIds.length == 0) {
                delete pythPriceIds[asset];
            } else {
                // Check the price IDs are valid.
                for (uint256 j = 0; j < priceIds.length;) {
                    bytes32 priceId = priceIds[j].priceId;
                    require(priceId != bytes32(0), "invalid price id");

                    IPyth.Price memory price = IPyth(pyth).getPriceUnsafe(priceId);
                    require(price.price > 0, "invalid price");

                    // Set the price feed.
                    pythPriceIds[asset].push(priceIds[j]);

                    unchecked {
                        j++;
                    }
                }

                emit PriceIdSet(asset, priceIds);
            }

            unchecked {
                i++;
            }
        }
    }

    /* ========== INTERNAL FUNCTIONS ========== */

    /**
     * @dev Checks whether the caller is the poster
     */
    function _checkPoster() internal view {
        require(msg.sender == poster, "caller is not the poster");
    }

    /**
     * @dev Gets the price from the pyth price feed
     * @param priceId The price ID
     * @return The price
     */
    function _getPriceFromPyth(bytes32 priceId) internal view returns (uint256) {
        IPyth.Price memory price = IPyth(pyth).getPriceUnsafe(priceId);
        require(price.price > 0, "invalid price");

        uint8 decimals = uint8(-1 * int8(price.expo));

        // Extend the decimals to 1e18.
        return uint256(int256(price.price)) * 10 ** (18 - decimals);
    }

    /**
     * @dev Get the normalized price.
     * @param price The price
     * @param asset The asset
     * @return The normalized price
     */
    function _getNormalizedPrice(uint256 price, address asset) internal view returns (uint256) {
        uint8 decimals = IERC20Metadata(asset).decimals();
        return price * 10 ** (18 - decimals);
    }
}

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.7.0) (access/Ownable.sol)

pragma solidity ^0.8.0;

import "../utils/Context.sol";

/**
 * @dev Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * By default, the owner account will be the one that deploys the contract. This
 * can later be changed with {transferOwnership}.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
abstract contract Ownable is Context {
    address private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor() {
        _transferOwnership(_msgSender());
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        _checkOwner();
        _;
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view virtual returns (address) {
        return _owner;
    }

    /**
     * @dev Throws if the sender is not the owner.
     */
    function _checkOwner() internal view virtual {
        require(owner() == _msgSender(), "Ownable: caller is not the owner");
    }

    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions anymore. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby removing any functionality that is only available to the owner.
     */
    function renounceOwnership() public virtual onlyOwner {
        _transferOwnership(address(0));
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        _transferOwnership(newOwner);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Internal function without access restriction.
     */
    function _transferOwnership(address newOwner) internal virtual {
        address oldOwner = _owner;
        _owner = newOwner;
        emit OwnershipTransferred(oldOwner, newOwner);
    }
}

// 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

pragma solidity ^0.8.0;

interface IPyth {
    struct Price {
        // Price
        int64 price;
        // Confidence interval around the price
        uint64 conf;
        // Price exponent
        int32 expo;
        // Unix timestamp describing when the price was published
        uint256 publishTime;
    }

    function getPriceUnsafe(bytes32 id) external view returns (Price memory price);
}

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

interface IPriceOracle {
    function getPrice(address asset) external view returns (uint256);
}

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (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;
    }
}

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.6.0) (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);
}

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