Contract Address Details

// SPDX-License-Identifier: MIT

pragma solidity >=0.7.0 <0.9.0;
pragma experimental ABIEncoderV2;

/**
 * @dev Collection of functions related to the address type
 */
library AddressUpgradeable {
    /**
     * @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
     * ====
     *
     * [IMPORTANT]
     * ====
     * You shouldn't rely on `isContract` to protect against flash loan attacks!
     *
     * Preventing calls from contracts is highly discouraged. It breaks composability, breaks support for smart wallets
     * like Gnosis Safe, and does not provide security since it can be circumvented by calling from a contract
     * constructor.
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies on extcodesize/address.code.length, which returns 0
        // for contracts in construction, since the code is only stored at the end
        // of the constructor execution.

        return account.code.length > 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");

        (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 functionCallWithValue(target, data, 0, "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");
        (bool success, bytes memory returndata) = target.call{value: value}(data);
        return verifyCallResultFromTarget(target, 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) {
        (bool success, bytes memory returndata) = target.staticcall(data);
        return verifyCallResultFromTarget(target, success, returndata, errorMessage);
    }

    /**
     * @dev Tool to verify that a low level call to smart-contract was successful, and revert (either by bubbling
     * the revert reason or using the provided one) in case of unsuccessful call or if target was not a contract.
     *
     * _Available since v4.8._
     */
    function verifyCallResultFromTarget(
        address target,
        bool success,
        bytes memory returndata,
        string memory errorMessage
    ) internal view returns (bytes memory) {
        if (success) {
            if (returndata.length == 0) {
                // only check isContract if the call was successful and the return data is empty
                // otherwise we already know that it was a contract
                require(isContract(target), "Address: call to non-contract");
            }
            return returndata;
        } else {
            _revert(returndata, errorMessage);
        }
    }

    /**
     * @dev Tool to verify that a low level call was successful, and revert if it wasn't, either by bubbling the
     * revert reason or using the provided one.
     *
     * _Available since v4.3._
     */
    function verifyCallResult(
        bool success,
        bytes memory returndata,
        string memory errorMessage
    ) internal pure returns (bytes memory) {
        if (success) {
            return returndata;
        } else {
            _revert(returndata, errorMessage);
        }
    }

    function _revert(bytes memory returndata, string memory errorMessage) private pure {
        // 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
            /// @solidity memory-safe-assembly
            assembly {
                let returndata_size := mload(returndata)
                revert(add(32, returndata), returndata_size)
            }
        } else {
            revert(errorMessage);
        }
    }
}

/**
 * @dev This is a base contract to aid in writing upgradeable contracts, or any kind of contract that will be deployed
 * behind a proxy. Since proxied contracts do not make use of a constructor, it's common to move constructor logic to an
 * external initializer function, usually called `initialize`. It then becomes necessary to protect this initializer
 * function so it can only be called once. The {initializer} modifier provided by this contract will have this effect.
 *
 * The initialization functions use a version number. Once a version number is used, it is consumed and cannot be
 * reused. This mechanism prevents re-execution of each "step" but allows the creation of new initialization steps in
 * case an upgrade adds a module that needs to be initialized.
 *
 * For example:
 *
 * [.hljs-theme-light.nopadding]
 * ```
 * contract MyToken is ERC20Upgradeable {
 *     function initialize() initializer public {
 *         __ERC20_init("MyToken", "MTK");
 *     }
 * }
 * contract MyTokenV2 is MyToken, ERC20PermitUpgradeable {
 *     function initializeV2() reinitializer(2) public {
 *         __ERC20Permit_init("MyToken");
 *     }
 * }
 * ```
 *
 * TIP: To avoid leaving the proxy in an uninitialized state, the initializer function should be called as early as
 * possible by providing the encoded function call as the `_data` argument to {ERC1967Proxy-constructor}.
 *
 * CAUTION: When used with inheritance, manual care must be taken to not invoke a parent initializer twice, or to ensure
 * that all initializers are idempotent. This is not verified automatically as constructors are by Solidity.
 *
 * [CAUTION]
 * ====
 * Avoid leaving a contract uninitialized.
 *
 * An uninitialized contract can be taken over by an attacker. This applies to both a proxy and its implementation
 * contract, which may impact the proxy. To prevent the implementation contract from being used, you should invoke
 * the {_disableInitializers} function in the constructor to automatically lock it when it is deployed:
 *
 * [.hljs-theme-light.nopadding]
 * ```
 * /// @custom:oz-upgrades-unsafe-allow constructor
 * constructor() {
 *     _disableInitializers();
 * }
 * ```
 * ====
 */
abstract contract Initializable {
    /**
     * @dev Indicates that the contract has been initialized.
     * @custom:oz-retyped-from bool
     */
    uint8 private _initialized;

    /**
     * @dev Indicates that the contract is in the process of being initialized.
     */
    bool private _initializing;

    /**
     * @dev Triggered when the contract has been initialized or reinitialized.
     */
    event Initialized(uint8 version);

    /**
     * @dev A modifier that defines a protected initializer function that can be invoked at most once. In its scope,
     * `onlyInitializing` functions can be used to initialize parent contracts.
     *
     * Similar to `reinitializer(1)`, except that functions marked with `initializer` can be nested in the context of a
     * constructor.
     *
     * Emits an {Initialized} event.
     */
    modifier initializer() {
        bool isTopLevelCall = !_initializing;
        require(
            (isTopLevelCall && _initialized < 1) || (!AddressUpgradeable.isContract(address(this)) && _initialized == 1),
            "Initializable: contract is already initialized"
        );
        _initialized = 1;
        if (isTopLevelCall) {
            _initializing = true;
        }
        _;
        if (isTopLevelCall) {
            _initializing = false;
            emit Initialized(1);
        }
    }

    /**
     * @dev A modifier that defines a protected reinitializer function that can be invoked at most once, and only if the
     * contract hasn't been initialized to a greater version before. In its scope, `onlyInitializing` functions can be
     * used to initialize parent contracts.
     *
     * A reinitializer may be used after the original initialization step. This is essential to configure modules that
     * are added through upgrades and that require initialization.
     *
     * When `version` is 1, this modifier is similar to `initializer`, except that functions marked with `reinitializer`
     * cannot be nested. If one is invoked in the context of another, execution will revert.
     *
     * Note that versions can jump in increments greater than 1; this implies that if multiple reinitializers coexist in
     * a contract, executing them in the right order is up to the developer or operator.
     *
     * WARNING: setting the version to 255 will prevent any future reinitialization.
     *
     * Emits an {Initialized} event.
     */
    modifier reinitializer(uint8 version) {
        require(!_initializing && _initialized < version, "Initializable: contract is already initialized");
        _initialized = version;
        _initializing = true;
        _;
        _initializing = false;
        emit Initialized(version);
    }

    /**
     * @dev Modifier to protect an initialization function so that it can only be invoked by functions with the
     * {initializer} and {reinitializer} modifiers, directly or indirectly.
     */
    modifier onlyInitializing() {
        require(_initializing, "Initializable: contract is not initializing");
        _;
    }

    /**
     * @dev Locks the contract, preventing any future reinitialization. This cannot be part of an initializer call.
     * Calling this in the constructor of a contract will prevent that contract from being initialized or reinitialized
     * to any version. It is recommended to use this to lock implementation contracts that are designed to be called
     * through proxies.
     *
     * Emits an {Initialized} event the first time it is successfully executed.
     */
    function _disableInitializers() internal virtual {
        require(!_initializing, "Initializable: contract is initializing");
        if (_initialized < type(uint8).max) {
            _initialized = type(uint8).max;
            emit Initialized(type(uint8).max);
        }
    }

    /**
     * @dev Internal function that returns the initialized version. Returns `_initialized`
     */
    function _getInitializedVersion() internal view returns (uint8) {
        return _initialized;
    }

    /**
     * @dev Internal function that returns the initialized version. Returns `_initializing`
     */
    function _isInitializing() internal view returns (bool) {
        return _initializing;
    }
}

abstract contract Proxiable {
    /// @dev Complying with EIP-1822: Universal Upgradeable Proxy Standard (UUPS)
    /// @dev See https://eips.ethereum.org/EIPS/eip-1822.
    function proxiableUUID() virtual external view returns (bytes32);

    struct ProxiableSlot {
        address implementation;
        address proxy;
    }

    function __implementation() internal view returns (address) {
        return __proxiable().implementation;
    }

    function __proxy() internal view returns (address) {
        return __proxiable().proxy;
    }

    function __proxiable() internal pure returns (ProxiableSlot storage proxiable) {
        assembly {
            // bytes32(uint256(keccak256('eip1967.proxy.implementation')) - 1)
            proxiable.slot := 0x360894a13ba1a3210667c828492db98dca3e2076cc3735a920a3ca505d382bbc
        }
    }
}

abstract contract Upgradeable is Initializable, Proxiable {

    address internal immutable _BASE;
    bytes32 internal immutable _CODEHASH;
    bool internal immutable _UPGRADABLE;

    modifier onlyDelegateCalls virtual {
        require(
            address(this) != _BASE,
            "Upgradeable: not a delegate call"
        );
        _;
    }

    /// Emitted every time the contract gets upgraded.
    /// @param from The address who ordered the upgrading. Namely, the WRB operator in "trustable" implementations.
    /// @param baseAddr The address of the new implementation contract.
    /// @param baseCodehash The EVM-codehash of the new implementation contract.
    /// @param versionTag Ascii-encoded version literal with which the implementation deployer decided to tag it.
    event Upgraded(
        address indexed from,
        address indexed baseAddr,
        bytes32 indexed baseCodehash,
        string  versionTag
    );

    constructor (bool _isUpgradable) {
        address _base = address(this);
        bytes32 _codehash;        
        assembly {
            _codehash := extcodehash(_base)
        }
        _BASE = _base;
        _CODEHASH = _codehash;
        _UPGRADABLE = _isUpgradable;
    }

    /// @dev Retrieves base contract. Differs from address(this) when called via delegate-proxy pattern.
    function base() public view returns (address) {
        return _BASE;
    }

    /// @dev Retrieves the immutable codehash of this contract, even if invoked as delegatecall.
    function codehash() public view returns (bytes32) {
        return _CODEHASH;
    }

    /// @dev Determines whether the logic of this contract is potentially upgradable.
    function isUpgradable() public view returns (bool) {
        return _UPGRADABLE;
    }

    /// @dev Tells whether provided address could eventually upgrade the contract.
    function isUpgradableFrom(address from) virtual external view returns (bool);

    /// @notice Re-initialize contract's storage context upon a new upgrade from a proxy.    
    /// @dev Must fail when trying to upgrade to same logic contract more than once.
    function initialize(bytes memory) virtual external;

    /// @dev Retrieves human-redable named version of current implementation.
    function version() virtual public view returns (string memory); 
}

/// @title WitnetProxy: upgradable delegate-proxy contract. 
/// @author The Witnet Foundation.
contract WitnetProxy {

    /// Event emitted every time the implementation gets updated.
    event Upgraded(address indexed implementation);  

    /// Constructor with no params as to ease eventual support of Singleton pattern (i.e. ERC-2470).
    constructor () {}

    receive() virtual external payable {}

    /// Payable fallback accepts delegating calls to payable functions.  
    fallback() external payable { /* solhint-disable no-complex-fallback */
        address _implementation = implementation();
        assembly { /* solhint-disable avoid-low-level-calls */
            // Gas optimized delegate call to 'implementation' contract.
            // Note: `msg.data`, `msg.sender` and `msg.value` will be passed over 
            //       to actual implementation of `msg.sig` within `implementation` contract.
            let ptr := mload(0x40)
            calldatacopy(ptr, 0, calldatasize())
            let result := delegatecall(gas(), _implementation, ptr, calldatasize(), 0, 0)
            let size := returndatasize()
            returndatacopy(ptr, 0, size)
            switch result
                case 0  { 
                    // pass back revert message:
                    revert(ptr, size) 
                }
                default {
                  // pass back same data as returned by 'implementation' contract:
                  return(ptr, size) 
                }
        }
    }

    /// Returns proxy's current implementation address.
    function implementation() public view returns (address) {
        return __proxySlot().implementation;
    }

    /// Upgrades the `implementation` address.
    /// @param _newImplementation New implementation address.
    /// @param _initData Raw data with which new implementation will be initialized.
    /// @return Returns whether new implementation would be further upgradable, or not.
    function upgradeTo(address _newImplementation, bytes memory _initData)
        public returns (bool)
    {
        // New implementation cannot be null:
        require(_newImplementation != address(0), "WitnetProxy: null implementation");

        address _oldImplementation = implementation();
        if (_oldImplementation != address(0)) {
            // New implementation address must differ from current one:
            require(_newImplementation != _oldImplementation, "WitnetProxy: nothing to upgrade");

            // Assert whether current implementation is intrinsically upgradable:
            try Upgradeable(_oldImplementation).isUpgradable() returns (bool _isUpgradable) {
                require(_isUpgradable, "WitnetProxy: not upgradable");
            } catch {
                revert("WitnetProxy: unable to check upgradability");
            }

            // Assert whether current implementation allows `msg.sender` to upgrade the proxy:
            (bool _wasCalled, bytes memory _result) = _oldImplementation.delegatecall(
                abi.encodeWithSignature(
                    "isUpgradableFrom(address)",
                    msg.sender
                )
            );
            require(_wasCalled, "WitnetProxy: not compliant");
            require(abi.decode(_result, (bool)), "WitnetProxy: not authorized");
            require(
                Upgradeable(_oldImplementation).proxiableUUID() == Upgradeable(_newImplementation).proxiableUUID(),
                "WitnetProxy: proxiableUUIDs mismatch"
            );
        }

        // Initialize new implementation within proxy-context storage:
        (bool _wasInitialized,) = _newImplementation.delegatecall(
            abi.encodeWithSignature(
                "initialize(bytes)",
                _initData
            )
        );
        require(_wasInitialized, "WitnetProxy: unable to initialize");

        // If all checks and initialization pass, update implementation address:
        __proxySlot().implementation = _newImplementation;
        emit Upgraded(_newImplementation);

        // Asserts new implementation complies w/ minimal implementation of Upgradeable interface:
        try Upgradeable(_newImplementation).isUpgradable() returns (bool _isUpgradable) {
            return _isUpgradable;
        }
        catch {
            revert ("WitnetProxy: not compliant");
        }
    }

    /// @dev Complying with EIP-1967, retrieves storage struct containing proxy's current implementation address.
    function __proxySlot() private pure returns (Proxiable.ProxiableSlot storage _slot) {
        assembly {
            // bytes32(uint256(keccak256('eip1967.proxy.implementation')) - 1)
            _slot.slot := 0x360894a13ba1a3210667c828492db98dca3e2076cc3735a920a3ca505d382bbc
        }
    }

}

[{"type":"constructor","stateMutability":"nonpayable","inputs":[]},{"type":"event","name":"Upgraded","inputs":[{"type":"address","name":"implementation","internalType":"address","indexed":true}],"anonymous":false},{"type":"fallback","stateMutability":"payable"},{"type":"function","stateMutability":"view","outputs":[{"type":"address","name":"","internalType":"address"}],"name":"implementation","inputs":[]},{"type":"function","stateMutability":"nonpayable","outputs":[{"type":"bool","name":"","internalType":"bool"}],"name":"upgradeTo","inputs":[{"type":"address","name":"_newImplementation","internalType":"address"},{"type":"bytes","name":"_initData","internalType":"bytes"}]},{"type":"receive","stateMutability":"payable"}]