Token USD Coin

// SPDX-License-Identifier: MIT
pragma solidity >=0.6.11;

// ============ External Imports ============
import {Address} from "@openzeppelin/contracts/utils/Address.sol";

/**
 * @title UpgradeBeaconProxy
 * @notice
 * Proxy contract which delegates all logic, including initialization,
 * to an implementation contract.
 * The implementation contract is stored within an Upgrade Beacon contract;
 * the implementation contract can be changed by performing an upgrade on the Upgrade Beacon contract.
 * The Upgrade Beacon contract for this Proxy is immutably specified at deployment.
 * @dev This implementation combines the gas savings of keeping the UpgradeBeacon address outside of contract storage
 * found in 0age's implementation:
 * https://github.com/dharma-eng/dharma-smart-wallet/blob/master/contracts/proxies/smart-wallet/UpgradeBeaconProxyV1.sol
 * With the added safety checks that the UpgradeBeacon and implementation are contracts at time of deployment
 * found in OpenZeppelin's implementation:
 * https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/proxy/beacon/BeaconProxy.sol
 */
contract UpgradeBeaconProxy {
    // ============ Immutables ============

    // Upgrade Beacon address is immutable (therefore not kept in contract storage)
    address private immutable upgradeBeacon;

    // ============ Constructor ============

    /**
     * @notice Validate that the Upgrade Beacon is a contract, then set its
     * address immutably within this contract.
     * Validate that the implementation is also a contract,
     * Then call the initialization function defined at the implementation.
     * The deployment will revert and pass along the
     * revert reason if the initialization function reverts.
     * @param _upgradeBeacon Address of the Upgrade Beacon to be stored immutably in the contract
     * @param _initializationCalldata Calldata supplied when calling the initialization function
     */
    constructor(address _upgradeBeacon, bytes memory _initializationCalldata)
        payable
    {
        // Validate the Upgrade Beacon is a contract
        require(Address.isContract(_upgradeBeacon), "beacon !contract");
        // set the Upgrade Beacon
        upgradeBeacon = _upgradeBeacon;
        // Validate the implementation is a contract
        address _implementation = _getImplementation(_upgradeBeacon);
        require(
            Address.isContract(_implementation),
            "beacon implementation !contract"
        );
        // Call the initialization function on the implementation
        if (_initializationCalldata.length > 0) {
            _initialize(_implementation, _initializationCalldata);
        }
    }

    // ============ External Functions ============

    /**
     * @notice Forwards all calls with data to _fallback()
     * No public functions are declared on the contract, so all calls hit fallback
     */
    fallback() external payable {
        _fallback();
    }

    /**
     * @notice Forwards all calls with no data to _fallback()
     */
    receive() external payable {
        _fallback();
    }

    // ============ Private Functions ============

    /**
     * @notice Call the initialization function on the implementation
     * Used at deployment to initialize the proxy
     * based on the logic for initialization defined at the implementation
     * @param _implementation - Contract to which the initalization is delegated
     * @param _initializationCalldata - Calldata supplied when calling the initialization function
     */
    function _initialize(
        address _implementation,
        bytes memory _initializationCalldata
    ) private {
        // Delegatecall into the implementation, supplying initialization calldata.
        (bool _ok, ) = _implementation.delegatecall(_initializationCalldata);
        // Revert and include revert data if delegatecall to implementation reverts.
        if (!_ok) {
            assembly {
                returndatacopy(0, 0, returndatasize())
                revert(0, returndatasize())
            }
        }
    }

    /**
     * @notice Delegates function calls to the implementation contract returned by the Upgrade Beacon
     */
    function _fallback() private {
        _delegate(_getImplementation());
    }

    /**
     * @notice Delegate function execution to the implementation contract
     * @dev This is a low level function that doesn't return to its internal
     * call site. It will return whatever is returned by the implementation to the
     * external caller, reverting and returning the revert data if implementation
     * reverts.
     * @param _implementation - Address to which the function execution is delegated
     */
    function _delegate(address _implementation) private {
        assembly {
            // Copy msg.data. We take full control of memory in this inline assembly
            // block because it will not return to Solidity code. We overwrite the
            // Solidity scratch pad at memory position 0.
            calldatacopy(0, 0, calldatasize())
            // Delegatecall to the implementation, supplying calldata and gas.
            // Out and outsize are set to zero - instead, use the return buffer.
            let result := delegatecall(
                gas(),
                _implementation,
                0,
                calldatasize(),
                0,
                0
            )
            // Copy the returned data from the return buffer.
            returndatacopy(0, 0, returndatasize())
            switch result
            // Delegatecall returns 0 on error.
            case 0 {
                revert(0, returndatasize())
            }
            default {
                return(0, returndatasize())
            }
        }
    }

    /**
     * @notice Call the Upgrade Beacon to get the current implementation contract address
     * @return _implementation Address of the current implementation.
     */
    function _getImplementation()
        private
        view
        returns (address _implementation)
    {
        _implementation = _getImplementation(upgradeBeacon);
    }

    /**
     * @notice Call the Upgrade Beacon to get the current implementation contract address
     * @dev _upgradeBeacon is passed as a parameter so that
     * we can also use this function in the constructor,
     * where we can't access immutable variables.
     * @param _upgradeBeacon Address of the UpgradeBeacon storing the current implementation
     * @return _implementation Address of the current implementation.
     */
    function _getImplementation(address _upgradeBeacon)
        private
        view
        returns (address _implementation)
    {
        // Get the current implementation address from the upgrade beacon.
        (bool _ok, bytes memory _returnData) = _upgradeBeacon.staticcall("");
        // Revert and pass along revert message if call to upgrade beacon reverts.
        require(_ok, string(_returnData));
        // Set the implementation to the address returned from the upgrade beacon.
        _implementation = abi.decode(_returnData, (address));
    }
}

// SPDX-License-Identifier: MIT

pragma solidity >=0.6.2 <0.8.0;

/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies on extcodesize, which returns 0 for contracts in
        // construction, since the code is only stored at the end of the
        // constructor execution.

        uint256 size;
        // solhint-disable-next-line no-inline-assembly
        assembly { size := extcodesize(account) }
        return size > 0;
    }

    /**
     * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
     * `recipient`, forwarding all available gas and reverting on errors.
     *
     * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
     * of certain opcodes, possibly making contracts go over the 2300 gas limit
     * imposed by `transfer`, making them unable to receive funds via
     * `transfer`. {sendValue} removes this limitation.
     *
     * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
     *
     * IMPORTANT: because control is transferred to `recipient`, care must be
     * taken to not create reentrancy vulnerabilities. Consider using
     * {ReentrancyGuard} or the
     * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");

        // solhint-disable-next-line avoid-low-level-calls, avoid-call-value
        (bool success, ) = recipient.call{ value: amount }("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }

    /**
     * @dev Performs a Solidity function call using a low level `call`. A
     * plain`call` is an unsafe replacement for a function call: use this
     * function instead.
     *
     * If `target` reverts with a revert reason, it is bubbled up by this
     * function (like regular Solidity function calls).
     *
     * Returns the raw returned data. To convert to the expected return value,
     * use https://solidity.readthedocs.io/en/latest/units-and-global-variables.html?highlight=abi.decode#abi-encoding-and-decoding-functions[`abi.decode`].
     *
     * Requirements:
     *
     * - `target` must be a contract.
     * - calling `target` with `data` must not revert.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data) internal returns (bytes memory) {
      return functionCall(target, data, "Address: low-level call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`], but with
     * `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
        return functionCallWithValue(target, data, 0, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but also transferring `value` wei to `target`.
     *
     * Requirements:
     *
     * - the calling contract must have an ETH balance of at least `value`.
     * - the called Solidity function must be `payable`.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value) internal returns (bytes memory) {
        return functionCallWithValue(target, data, value, "Address: low-level call with value failed");
    }

    /**
     * @dev Same as {xref-Address-functionCallWithValue-address-bytes-uint256-}[`functionCallWithValue`], but
     * with `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value, string memory errorMessage) internal returns (bytes memory) {
        require(address(this).balance >= value, "Address: insufficient balance for call");
        require(isContract(target), "Address: call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.call{ value: value }(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data) internal view returns (bytes memory) {
        return functionStaticCall(target, data, "Address: low-level static call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data, string memory errorMessage) internal view returns (bytes memory) {
        require(isContract(target), "Address: static call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.staticcall(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionDelegateCall(target, data, "Address: low-level delegate call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
        require(isContract(target), "Address: delegate call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.delegatecall(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    function _verifyCallResult(bool success, bytes memory returndata, string memory errorMessage) private pure returns(bytes memory) {
        if (success) {
            return returndata;
        } else {
            // Look for revert reason and bubble it up if present
            if (returndata.length > 0) {
                // The easiest way to bubble the revert reason is using memory via assembly

                // solhint-disable-next-line no-inline-assembly
                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }
}

{
  "optimizer": {
    "enabled": true,
    "runs": 999999
  },
  "outputSelection": {
    "*": {
      "*": [
        "evm.bytecode",
        "evm.deployedBytecode",
        "devdoc",
        "userdoc",
        "metadata",
        "abi"
      ]
    }
  },
  "libraries": {}
}

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