Sonic Blaze Testnet
    /

    Contract Diff Checker

    Contract Name:
    PriceFeed

    Contract Source Code:

    // SPDX-License-Identifier: agpl-3.0
    pragma solidity 0.7.6;
    
    /**
     * @dev Wrappers over Solidity's arithmetic operations with added overflow
     * checks.
     *
     * Arithmetic operations in Solidity wrap on overflow. This can easily result
     * in bugs, because programmers usually assume that an overflow raises an
     * error, which is the standard behavior in high level programming languages.
     * `SafeMath` restores this intuition by reverting the transaction when an
     * operation overflows.
     *
     * Using this library instead of the unchecked operations eliminates an entire
     * class of bugs, so it's recommended to use it always.
     */
    library SafeMath {
      /**
       * @dev Returns the addition of two unsigned integers, reverting on
       * overflow.
       *
       * Counterpart to Solidity's `+` operator.
       *
       * Requirements:
       * - Addition cannot overflow.
       */
      function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, 'SafeMath: addition overflow');
    
        return c;
      }
    
      /**
       * @dev Returns the subtraction of two unsigned integers, reverting on
       * overflow (when the result is negative).
       *
       * Counterpart to Solidity's `-` operator.
       *
       * Requirements:
       * - Subtraction cannot overflow.
       */
      function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, 'SafeMath: subtraction overflow');
      }
    
      /**
       * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
       * overflow (when the result is negative).
       *
       * Counterpart to Solidity's `-` operator.
       *
       * Requirements:
       * - Subtraction cannot overflow.
       */
      function sub(
        uint256 a,
        uint256 b,
        string memory errorMessage
      ) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;
    
        return c;
      }
    
      /**
       * @dev Returns the multiplication of two unsigned integers, reverting on
       * overflow.
       *
       * Counterpart to Solidity's `*` operator.
       *
       * Requirements:
       * - Multiplication cannot overflow.
       */
      function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
        if (a == 0) {
          return 0;
        }
    
        uint256 c = a * b;
        require(c / a == b, 'SafeMath: multiplication overflow');
    
        return c;
      }
    
      /**
       * @dev Returns the integer division of two unsigned integers. Reverts on
       * division by zero. The result is rounded towards zero.
       *
       * Counterpart to Solidity's `/` operator. Note: this function uses a
       * `revert` opcode (which leaves remaining gas untouched) while Solidity
       * uses an invalid opcode to revert (consuming all remaining gas).
       *
       * Requirements:
       * - The divisor cannot be zero.
       */
      function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, 'SafeMath: division by zero');
      }
    
      /**
       * @dev Returns the integer division of two unsigned integers. Reverts with custom message on
       * division by zero. The result is rounded towards zero.
       *
       * Counterpart to Solidity's `/` operator. Note: this function uses a
       * `revert` opcode (which leaves remaining gas untouched) while Solidity
       * uses an invalid opcode to revert (consuming all remaining gas).
       *
       * Requirements:
       * - The divisor cannot be zero.
       */
      function div(
        uint256 a,
        uint256 b,
        string memory errorMessage
      ) internal pure returns (uint256) {
        // Solidity only automatically asserts when dividing by 0
        require(b > 0, errorMessage);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold
    
        return c;
      }
    
      /**
       * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
       * Reverts when dividing by zero.
       *
       * Counterpart to Solidity's `%` operator. This function uses a `revert`
       * opcode (which leaves remaining gas untouched) while Solidity uses an
       * invalid opcode to revert (consuming all remaining gas).
       *
       * Requirements:
       * - The divisor cannot be zero.
       */
      function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return mod(a, b, 'SafeMath: modulo by zero');
      }
    
      /**
       * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
       * Reverts with custom message when dividing by zero.
       *
       * Counterpart to Solidity's `%` operator. This function uses a `revert`
       * opcode (which leaves remaining gas untouched) while Solidity uses an
       * invalid opcode to revert (consuming all remaining gas).
       *
       * Requirements:
       * - The divisor cannot be zero.
       */
      function mod(
        uint256 a,
        uint256 b,
        string memory errorMessage
      ) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
      }
    }

    pragma solidity 0.7.6;
    
    
    interface IBandStdReference {
    
        /// Returns the price data for the given base/quote pair. Revert if not available.
        function getReferenceData(string memory _base, string memory _quote)
            external
            view
            returns (uint256 rate, uint256 lastUpdatedBase, uint256 lastUpdatedRate);
    
    }

    // SPDX-License-Identifier: MIT
    // Code from https://github.com/smartcontractkit/chainlink/blob/master/evm-contracts/src/v0.6/interfaces/AggregatorV3Interface.sol
    
    pragma solidity 0.7.6;
    
    interface IChainlinkAggregator {
    
      function decimals() external view returns (uint8);
      function description() external view returns (string memory);
      function version() external view returns (uint256);
    
      // getRoundData and latestRoundData should both raise "No data present"
      // if they do not have data to report, instead of returning unset values
      // which could be misinterpreted as actual reported values.
      function getRoundData(uint80 _roundId)
        external
        view
        returns (
          uint80 roundId,
          int256 answer,
          uint256 startedAt,
          uint256 updatedAt,
          uint80 answeredInRound
        );
    
      function latestRoundData()
        external
        view
        returns (
          uint80 roundId,
          int256 answer,
          uint256 startedAt,
          uint256 updatedAt,
          uint80 answeredInRound
        );
    }

    // SPDX-License-Identifier: MIT
    
    pragma solidity 0.7.6;
    
    interface IPriceFeed {
    
        // --- Function ---
        function fetchPrice() external view returns (uint);
        function updatePrice() external returns (uint);
    }

    // SPDX-License-Identifier: MIT
    
    pragma solidity 0.7.6;
    
    import "../interfaces/IPriceFeed.sol";
    import "../interfaces/IBandStdReference.sol";
    import "../interfaces/IChainlinkAggregator.sol";
    import "../dependencies/openzeppelin/contracts/SafeMath.sol";
    
    /*
    * PriceFeed for mainnet deployment, to be connected to Chainlink's live ETH:USD aggregator reference
    * contract, and a wrapper contract bandOracle, which connects to BandMaster contract.
    *
    * The PriceFeed uses Chainlink as primary oracle, and Band as fallback. It contains logic for
    * switching oracles based on oracle failures, timeouts, and conditions for returning to the primary
    * Chainlink oracle.
    */
    contract PriceFeed is IPriceFeed {
        using SafeMath for uint256;
    
        uint constant public DECIMAL_PRECISION = 1e18;
    
        IChainlinkAggregator public chainlinkOracle;  // Mainnet Chainlink aggregator
        IBandStdReference public bandOracle;  // Wrapper contract that calls the Band system
    
        string public bandBase;
        string public constant bandQuote = "USD";
    
        // Use to convert a price answer to an 18-digit precision uint
        uint constant public TARGET_DIGITS = 18;
    
        // Maximum time period allowed since Chainlink's latest round data timestamp, beyond which Chainlink is considered frozen.
        // For stablecoins we recommend 90000, as Chainlink updates once per day when there is no significant price movement
        // For volatile assets we recommend 14400 (4 hours)
        uint immutable public TIMEOUT;
    
        // Maximum deviation allowed between two consecutive Chainlink oracle prices. 18-digit precision.
        uint constant public MAX_PRICE_DEVIATION_FROM_PREVIOUS_ROUND =  5e17; // 50%
    
        /*
        * The maximum relative price difference between two oracle responses allowed in order for the PriceFeed
        * to return to using the Chainlink oracle. 18-digit precision.
        */
        uint constant public MAX_PRICE_DIFFERENCE_BETWEEN_ORACLES = 5e16; // 5%
    
        // The last good price seen from an oracle by Liquity
        uint public lastGoodPrice;
    
        struct ChainlinkResponse {
            uint80 roundId;
            uint256 answer;
            uint256 timestamp;
            bool success;
            uint8 decimals;
        }
    
        struct BandResponse {
            uint256 value;
            uint256 timestamp;
            bool success;
        }
    
        enum Status {
            chainlinkWorking,
            usingBandChainlinkUntrusted,
            bothOraclesUntrusted,
            usingBandChainlinkFrozen,
            usingChainlinkBandUntrusted
        }
    
        // The current status of the PricFeed, which determines the conditions for the next price fetch attempt
        Status public status;
    
        event LastGoodPriceUpdated(uint _lastGoodPrice);
        event PriceFeedStatusChanged(Status newStatus);
    
        // --- Dependency setters ---
    
        constructor(
            IChainlinkAggregator _chainlinkOracleAddress,
            IBandStdReference _bandOracleAddress,
            uint256 _timeout,
            string memory _bandBase
        ) {
            chainlinkOracle = _chainlinkOracleAddress;
            bandOracle = _bandOracleAddress;
    
            TIMEOUT = _timeout;
    
            bandBase = _bandBase;
    
            // Explicitly set initial system status
            status = Status.chainlinkWorking;
    
            // Get an initial price from Chainlink to serve as first reference for lastGoodPrice
            ChainlinkResponse memory chainlinkResponse = _getCurrentChainlinkResponse();
            ChainlinkResponse memory prevChainlinkResponse = _getPrevChainlinkResponse(chainlinkResponse.roundId, chainlinkResponse.decimals);
    
            require(
                !_chainlinkIsBroken(chainlinkResponse, prevChainlinkResponse) &&
                block.timestamp.sub(chainlinkResponse.timestamp) < _timeout,
                "PriceFeed: Chainlink must be working and current"
            );
    
            lastGoodPrice = _scaleChainlinkPriceByDigits(uint256(chainlinkResponse.answer), chainlinkResponse.decimals);
        }
    
        // --- Functions ---
    
        /*
        * fetchPrice():
        * Returns the latest price obtained from the Oracle. Called by Liquity functions that require a current price.
        *
        * Also callable by anyone externally.
        *
        * Non-view function - it stores the last good price seen by Liquity.
        *
        * Uses a main oracle (Chainlink) and a fallback oracle (Band) in case Chainlink fails. If both fail,
        * it uses the last good price seen by Liquity.
        *
        */
        function fetchPrice() external view override returns (uint) {
            (,uint price) = _fetchPrice();
            return price;
        }
    
        function updatePrice() external override returns (uint) {
            (Status newStatus, uint price) = _fetchPrice();
            lastGoodPrice = price;
            if (status != newStatus) {
                status = newStatus;
                emit PriceFeedStatusChanged(newStatus);
            }
            return price;
        }
    
    
        function _fetchPrice() internal view returns (Status, uint) {
            // Get current and previous price data from Chainlink, and current price data from Band
            ChainlinkResponse memory chainlinkResponse = _getCurrentChainlinkResponse();
            ChainlinkResponse memory prevChainlinkResponse = _getPrevChainlinkResponse(chainlinkResponse.roundId, chainlinkResponse.decimals);
            BandResponse memory bandResponse = _getCurrentBandResponse();
    
            // --- CASE 1: System fetched last price from Chainlink  ---
            if (status == Status.chainlinkWorking) {
                // If Chainlink is broken, try Band
                if (_chainlinkIsBroken(chainlinkResponse, prevChainlinkResponse)) {
                    // If Band is broken then both oracles are untrusted, so return the last good price
                    if (_bandIsBroken(bandResponse)) {
                        return (Status.bothOraclesUntrusted, lastGoodPrice);
                    }
                    /*
                    * If Band is only frozen but otherwise returning valid data, return the last good price.
                    */
                    if (_bandIsFrozen(bandResponse)) {
                        return (Status.usingBandChainlinkUntrusted, lastGoodPrice);
                    }
    
                    // If Chainlink is broken and Band is working, switch to Band and return current Band price
                    return (Status.usingBandChainlinkUntrusted, bandResponse.value);
                }
    
                // If Chainlink is frozen, try Band
                if (_chainlinkIsFrozen(chainlinkResponse)) {
                    // If Band is broken too, remember Band broke, and return last good price
                    if (_bandIsBroken(bandResponse)) {
                        return (Status.usingChainlinkBandUntrusted, lastGoodPrice);
                    }
    
                    // If Band is frozen or working, remember Chainlink froze, and switch to Band
                    if (_bandIsFrozen(bandResponse)) {return (Status.usingBandChainlinkFrozen, lastGoodPrice);}
    
                    // If Band is working, use it
                    return (Status.usingBandChainlinkFrozen, bandResponse.value);
                }
    
                // If Chainlink price has changed by > 50% between two consecutive rounds, compare it to Band's price
                if (_chainlinkPriceChangeAboveMax(chainlinkResponse, prevChainlinkResponse)) {
                    // If Band is broken, both oracles are untrusted, and return last good price
                     if (_bandIsBroken(bandResponse)) {
                        return (Status.bothOraclesUntrusted, lastGoodPrice);
                    }
    
                    // If Band is frozen, switch to Band and return last good price
                    if (_bandIsFrozen(bandResponse)) {
                        return (Status.usingBandChainlinkUntrusted, lastGoodPrice);
                    }
    
                    /*
                    * If Band is live and both oracles have a similar price, conclude that Chainlink's large price deviation between
                    * two consecutive rounds was likely a legitmate market price movement, and so continue using Chainlink
                    */
                    if (_bothOraclesSimilarPrice(chainlinkResponse, bandResponse)) {
                        return (Status.chainlinkWorking, chainlinkResponse.answer);
                    }
    
                    // If Band is live but the oracles differ too much in price, conclude that Chainlink's initial price deviation was
                    // an oracle failure. Switch to Band, and use Band price
                    return (Status.usingBandChainlinkUntrusted, bandResponse.value);
                }
    
                // If Chainlink is working and Band is broken, remember Band is broken
                if (_bandIsBroken(bandResponse)) {
                    return (Status.usingChainlinkBandUntrusted, chainlinkResponse.answer);
                }
    
                // If Chainlink is working, return Chainlink current price (no status change)
                return (Status.chainlinkWorking, chainlinkResponse.answer);
            }
    
    
            // --- CASE 2: The system fetched last price from Band ---
            if (status == Status.usingBandChainlinkUntrusted) {
                // If both Band and Chainlink are live, unbroken, and reporting similar prices, switch back to Chainlink
                if (_bothOraclesLiveAndUnbrokenAndSimilarPrice(chainlinkResponse, prevChainlinkResponse, bandResponse)) {
                    return (Status.chainlinkWorking, chainlinkResponse.answer);
                }
    
                if (_bandIsBroken(bandResponse)) {
                    return (Status.bothOraclesUntrusted, lastGoodPrice);
                }
    
                /*
                * If Band is only frozen but otherwise returning valid data, just return the last good price.
                * Band may need to be tipped to return current data.
                */
                if (_bandIsFrozen(bandResponse)) {return (Status.usingBandChainlinkUntrusted, lastGoodPrice);}
    
                // Otherwise, use Band price
                return (Status.usingBandChainlinkUntrusted, bandResponse.value);
            }
    
            // --- CASE 3: Both oracles were untrusted at the last price fetch ---
            if (status == Status.bothOraclesUntrusted) {
                /*
                * If both oracles are now live, unbroken and similar price, we assume that they are reporting
                * accurately, and so we switch back to Chainlink.
                */
                if (_bothOraclesLiveAndUnbrokenAndSimilarPrice(chainlinkResponse, prevChainlinkResponse, bandResponse)) {
                    return (Status.chainlinkWorking, chainlinkResponse.answer);
                }
    
                // Otherwise, return the last good price - both oracles are still untrusted (no status change)
                return (Status.bothOraclesUntrusted, lastGoodPrice);
            }
    
            // --- CASE 4: Using Band, and Chainlink is frozen ---
            if (status == Status.usingBandChainlinkFrozen) {
                if (_chainlinkIsBroken(chainlinkResponse, prevChainlinkResponse)) {
                    // If both Oracles are broken, return last good price
                    if (_bandIsBroken(bandResponse)) {
                        return (Status.bothOraclesUntrusted, lastGoodPrice);
                    }
    
                    // If Chainlink is broken, remember it and switch to using Band
    
                    if (_bandIsFrozen(bandResponse)) {return (Status.usingBandChainlinkUntrusted, lastGoodPrice);}
    
                    // If Band is working, return Band current price
                    return (Status.usingBandChainlinkUntrusted, bandResponse.value);
                }
    
                if (_chainlinkIsFrozen(chainlinkResponse)) {
                    // if Chainlink is frozen and Band is broken, remember Band broke, and return last good price
                    if (_bandIsBroken(bandResponse)) {
                        return (Status.usingChainlinkBandUntrusted, lastGoodPrice);
                    }
    
                    // If both are frozen, just use lastGoodPrice
                    if (_bandIsFrozen(bandResponse)) {return (Status.usingBandChainlinkFrozen, lastGoodPrice);}
    
                    // if Chainlink is frozen and Band is working, keep using Band (no status change)
                    return (Status.usingBandChainlinkFrozen, bandResponse.value);
                }
    
                // if Chainlink is live and Band is broken, remember Band broke, and return Chainlink price
                if (_bandIsBroken(bandResponse)) {
                    return (Status.usingChainlinkBandUntrusted, chainlinkResponse.answer);
                }
    
                 // If Chainlink is live and Band is frozen, just use last good price (no status change) since we have no basis for comparison
                if (_bandIsFrozen(bandResponse)) {return (Status.usingBandChainlinkFrozen, lastGoodPrice);}
    
                // If Chainlink is live and Band is working, compare prices. Switch to Chainlink
                // if prices are within 5%, and return Chainlink price.
                if (_bothOraclesSimilarPrice(chainlinkResponse, bandResponse)) {
                    return (Status.chainlinkWorking, chainlinkResponse.answer);
                }
    
                // Otherwise if Chainlink is live but price not within 5% of Band, distrust Chainlink, and return Band price
                return (Status.usingBandChainlinkUntrusted, bandResponse.value);
            }
    
            // --- CASE 5: Using Chainlink, Band is untrusted ---
             if (status == Status.usingChainlinkBandUntrusted) {
                // If Chainlink breaks, now both oracles are untrusted
                if (_chainlinkIsBroken(chainlinkResponse, prevChainlinkResponse)) {
                    return (Status.bothOraclesUntrusted, lastGoodPrice);
                }
    
                // If Chainlink is frozen, return last good price (no status change)
                if (_chainlinkIsFrozen(chainlinkResponse)) {
                    return (Status.usingChainlinkBandUntrusted, lastGoodPrice);
                }
    
                // If Chainlink and Band are both live, unbroken and similar price, switch back to chainlinkWorking and return Chainlink price
                if (_bothOraclesLiveAndUnbrokenAndSimilarPrice(chainlinkResponse, prevChainlinkResponse, bandResponse)) {
                    return (Status.chainlinkWorking, chainlinkResponse.answer);
                }
    
                // If Chainlink is live but deviated >50% from it's previous price and Band is still untrusted, switch
                // to bothOraclesUntrusted and return last good price
                if (_chainlinkPriceChangeAboveMax(chainlinkResponse, prevChainlinkResponse)) {
                    return (Status.bothOraclesUntrusted, lastGoodPrice);
                }
    
                // Otherwise if Chainlink is live and deviated <50% from it's previous price and Band is still untrusted,
                // return Chainlink price (no status change)
                return (Status.usingChainlinkBandUntrusted, chainlinkResponse.answer);
            }
        }
    
        // --- Helper functions ---
    
        /* Chainlink is considered broken if its current or previous round data is in any way bad. We check the previous round
        * for two reasons:
        *
        * 1) It is necessary data for the price deviation check in case 1,
        * and
        * 2) Chainlink is the PriceFeed's preferred primary oracle - having two consecutive valid round responses adds
        * peace of mind when using or returning to Chainlink.
        */
        function _chainlinkIsBroken(ChainlinkResponse memory _currentResponse, ChainlinkResponse memory _prevResponse) internal view returns (bool) {
            return _badChainlinkResponse(_currentResponse) || _badChainlinkResponse(_prevResponse);
        }
    
        function _badChainlinkResponse(ChainlinkResponse memory _response) internal view returns (bool) {
             // Check for response call reverted
            if (!_response.success) {return true;}
            // Check for an invalid roundId that is 0
            if (_response.roundId == 0) {return true;}
            // Check for an invalid timeStamp that is 0, or in the future
            if (_response.timestamp == 0 || _response.timestamp > block.timestamp) {return true;}
            // Check for non-positive price (original value returned from chainlink is int256)
            if (int256(_response.answer) <= 0) {return true;}
    
            return false;
        }
    
        function _chainlinkIsFrozen(ChainlinkResponse memory _response) internal view returns (bool) {
            return block.timestamp.sub(_response.timestamp) > TIMEOUT;
        }
    
        function _chainlinkPriceChangeAboveMax(ChainlinkResponse memory _currentResponse, ChainlinkResponse memory _prevResponse) internal pure returns (bool) {
            uint currentScaledPrice = _currentResponse.answer;
            uint prevScaledPrice = _prevResponse.answer;
    
            uint minPrice = (currentScaledPrice < prevScaledPrice) ? currentScaledPrice : prevScaledPrice;
            uint maxPrice = (currentScaledPrice >= prevScaledPrice) ? currentScaledPrice : prevScaledPrice;
    
            /*
            * Use the larger price as the denominator:
            * - If price decreased, the percentage deviation is in relation to the the previous price.
            * - If price increased, the percentage deviation is in relation to the current price.
            */
            uint percentDeviation = maxPrice.sub(minPrice).mul(DECIMAL_PRECISION).div(maxPrice);
    
            // Return true if price has more than doubled, or more than halved.
            return percentDeviation > MAX_PRICE_DEVIATION_FROM_PREVIOUS_ROUND;
        }
    
        function _bandIsBroken(BandResponse memory _response) internal view returns (bool) {
            // Check for response call reverted
            if (!_response.success) {return true;}
            // Check for an invalid timeStamp that is 0, or in the future
            if (_response.timestamp == 0 || _response.timestamp > block.timestamp) {return true;}
            // Check for zero price
            if (_response.value == 0) {return true;}
    
            return false;
        }
    
         function _bandIsFrozen(BandResponse  memory _bandResponse) internal view returns (bool) {
            return block.timestamp.sub(_bandResponse.timestamp) > TIMEOUT;
        }
    
        function _bothOraclesLiveAndUnbrokenAndSimilarPrice
        (
            ChainlinkResponse memory _chainlinkResponse,
            ChainlinkResponse memory _prevChainlinkResponse,
            BandResponse memory _bandResponse
        )
            internal
            view
            returns (bool)
        {
            // Return false if either oracle is broken or frozen
            if
            (
                _bandIsBroken(_bandResponse) ||
                _bandIsFrozen(_bandResponse) ||
                _chainlinkIsBroken(_chainlinkResponse, _prevChainlinkResponse) ||
                _chainlinkIsFrozen(_chainlinkResponse)
            )
            {
                return false;
            }
    
            return _bothOraclesSimilarPrice(_chainlinkResponse, _bandResponse);
        }
    
        function _bothOraclesSimilarPrice( ChainlinkResponse memory _chainlinkResponse, BandResponse memory _bandResponse) internal pure returns (bool) {
            uint scaledChainlinkPrice = _chainlinkResponse.answer;
            uint scaledBandPrice = _bandResponse.value;
    
            // Get the relative price difference between the oracles. Use the lower price as the denominator, i.e. the reference for the calculation.
            uint minPrice = (scaledBandPrice < scaledChainlinkPrice) ? scaledBandPrice : scaledChainlinkPrice;
            uint maxPrice = (scaledBandPrice >= scaledChainlinkPrice) ? scaledBandPrice : scaledChainlinkPrice;
            uint percentPriceDifference = maxPrice.sub(minPrice).mul(DECIMAL_PRECISION).div(minPrice);
    
            /*
            * Return true if the relative price difference is <= 3%: if so, we assume both oracles are probably reporting
            * the honest market price, as it is unlikely that both have been broken/hacked and are still in-sync.
            */
            return percentPriceDifference <= MAX_PRICE_DIFFERENCE_BETWEEN_ORACLES;
        }
    
        function _scaleChainlinkPriceByDigits(uint _price, uint _answerDigits) internal pure returns (uint) {
            /*
            * Convert the price returned by the Chainlink oracle to an 18-digit decimal for use by Liquity.
            * At date of Liquity launch, Chainlink uses an 8-digit price, but we also handle the possibility of
            * future changes.
            *
            */
            uint price;
            if (_answerDigits >= TARGET_DIGITS) {
                // Scale the returned price value down to Liquity's target precision
                price = _price.div(10 ** (_answerDigits - TARGET_DIGITS));
            }
            else if (_answerDigits < TARGET_DIGITS) {
                // Scale the returned price value up to Liquity's target precision
                price = _price.mul(10 ** (TARGET_DIGITS - _answerDigits));
            }
            return price;
        }
    
        // --- Oracle response wrapper functions ---
    
        function _getCurrentBandResponse() internal view returns (BandResponse memory bandResponse) {
            try bandOracle.getReferenceData(bandBase, bandQuote) returns
            (
                uint256 value,
                uint256 lastUpdatedBase,
                uint256 lastUpdatedQuote
            )
            {
                // If call to Band succeeds, return the response and success = true
                bandResponse.value = value;
                bandResponse.timestamp =  lastUpdatedBase < lastUpdatedQuote ? lastUpdatedBase : lastUpdatedQuote;
                bandResponse.success = true;
    
                return (bandResponse);
            }catch {
                 // If call to Band reverts, return a zero response with success = false
                return (bandResponse);
            }
        }
    
        function _getCurrentChainlinkResponse() internal view returns (ChainlinkResponse memory chainlinkResponse) {
            // First, try to get current decimal precision:
            try chainlinkOracle.decimals() returns (uint8 decimals) {
                // If call to Chainlink succeeds, record the current decimal precision
                chainlinkResponse.decimals = decimals;
            } catch {
                // If call to Chainlink aggregator reverts, return a zero response with success = false
                return chainlinkResponse;
            }
    
            // Secondly, try to get latest price data:
            try chainlinkOracle.latestRoundData() returns
            (
                uint80 roundId,
                int256 answer,
                uint256 /* startedAt */,
                uint256 timestamp,
                uint80 /* answeredInRound */
            )
            {
                // If call to Chainlink succeeds, return the response and success = true
                chainlinkResponse.roundId = roundId;
                chainlinkResponse.answer = _scaleChainlinkPriceByDigits(uint256(answer), chainlinkResponse.decimals);
                chainlinkResponse.timestamp = timestamp;
                chainlinkResponse.success = true;
                return chainlinkResponse;
            } catch {
                // If call to Chainlink aggregator reverts, return a zero response with success = false
                return chainlinkResponse;
            }
        }
    
        function _getPrevChainlinkResponse(uint80 _currentRoundId, uint8 _currentDecimals) internal view returns (ChainlinkResponse memory prevChainlinkResponse) {
            /*
            * NOTE: Chainlink only offers a current decimals() value - there is no way to obtain the decimal precision used in a
            * previous round.  We assume the decimals used in the previous round are the same as the current round.
            */
    
            // Try to get the price data from the previous round:
            try chainlinkOracle.getRoundData(_currentRoundId - 1) returns
            (
                uint80 roundId,
                int256 answer,
                uint256 /* startedAt */,
                uint256 timestamp,
                uint80 /* answeredInRound */
            )
            {
                // If call to Chainlink succeeds, return the response and success = true
                prevChainlinkResponse.roundId = roundId;
                prevChainlinkResponse.answer = _scaleChainlinkPriceByDigits(uint256(answer), _currentDecimals);
                prevChainlinkResponse.timestamp = timestamp;
                prevChainlinkResponse.decimals = _currentDecimals;
                prevChainlinkResponse.success = true;
                return prevChainlinkResponse;
            } catch {
                // If call to Chainlink aggregator reverts, return a zero response with success = false
                return prevChainlinkResponse;
            }
        }
    }

    Contract Name:
    LendingRateOracle

    Contract Source Code:

    // SPDX-License-Identifier: MIT
    pragma solidity 0.7.6;
    
    /*
     * @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 GSN 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 payable) {
        return msg.sender;
      }
    
      function _msgData() internal view virtual returns (bytes memory) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return msg.data;
      }
    }

    // SPDX-License-Identifier: MIT
    
    pragma solidity 0.7.6;
    
    import './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.
     */
    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() {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
      }
    
      /**
       * @dev Returns the address of the current owner.
       */
      function owner() public view returns (address) {
        return _owner;
      }
    
      /**
       * @dev Throws if called by any account other than the owner.
       */
      modifier onlyOwner() {
        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 {
        emit OwnershipTransferred(_owner, address(0));
        _owner = 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');
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
      }
    }

    // SPDX-License-Identifier: agpl-3.0
    pragma solidity 0.7.6;
    
    /**
     * @title ILendingRateOracle interface
     * @notice Interface for the Aave borrow rate oracle. Provides the average market borrow rate to be used as a base for the stable borrow rate calculations
     **/
    
    interface ILendingRateOracle {
      /**
        @dev returns the market borrow rate in ray
        **/
      function getMarketBorrowRate(address asset) external view returns (uint256);
    
      /**
        @dev sets the market borrow rate. Rate value must be in ray
        **/
      function setMarketBorrowRate(address asset, uint256 rate) external;
    }

    // SPDX-License-Identifier: agpl-3.0
    pragma solidity 0.7.6;
    
    import {ILendingRateOracle} from '../../interfaces/ILendingRateOracle.sol';
    import {Ownable} from '../../dependencies/openzeppelin/contracts/Ownable.sol';
    
    contract LendingRateOracle is ILendingRateOracle, Ownable {
      mapping(address => uint256) borrowRates;
      mapping(address => uint256) liquidityRates;
    
      function getMarketBorrowRate(address _asset) external view override returns (uint256) {
        return borrowRates[_asset];
      }
    
      function setMarketBorrowRate(address _asset, uint256 _rate) external override onlyOwner {
        borrowRates[_asset] = _rate;
      }
    
      function getMarketLiquidityRate(address _asset) external view returns (uint256) {
        return liquidityRates[_asset];
      }
    
      function setMarketLiquidityRate(address _asset, uint256 _rate) external onlyOwner {
        liquidityRates[_asset] = _rate;
      }
    }

    Context size (optional):