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Using the Reference Prices in Smart Contracts

To query prices from Band's oracle through smart contracts, the contract looking to use the price values should reference Band's StdReference contract. This contract exposes getReferenceData and getReferenceDataBulk functions.

getReferenceData takes two strings as the inputs, the base and quote symbol, respectively. It then queries the StdReference contract for the latest rates for those two tokens, and returns a ReferenceData struct, shown below.

struct ReferenceData {
    uint256 rate; // base/quote exchange rate, multiplied by 1e18.
    uint256 lastUpdatedBase; // UNIX epoch of the last time when base price gets updated.
    uint256 lastUpdatedQuote; // UNIX epoch of the last time when quote price gets updated.
}

getReferenceDataBulk instead takes two lists, one of the base tokens, and one of the quotes. It then proceeds to similarly queries the price for each base/quote pair at each index, and returns an array of ReferenceData structs.

For example, if we call getReferenceDataBulk with ['BTC','BTC','ETH'] and ['USD','ETH','BNB'], the returned ReferenceData array will contain information regarding the pairs:

  • BTC/USD
  • BTC/ETH
  • ETH/BNB

Example Usage​

The contract code below demonstrates a simple usage of the new StdReference contract and the getReferenceData function.

pragma solidity 0.6.11;
pragma experimental ABIEncoderV2;

interface IStdReference {
    /// A structure returned whenever someone requests for standard reference data.
    struct ReferenceData {
        uint256 rate; // base/quote exchange rate, multiplied by 1e18.
        uint256 lastUpdatedBase; // UNIX epoch of the last time when base price gets updated.
        uint256 lastUpdatedQuote; // UNIX epoch of the last time when quote price gets updated.
    }

    /// 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 (ReferenceData memory);

    /// Similar to getReferenceData, but with multiple base/quote pairs at once.
    function getReferenceDataBulk(string[] memory _bases, string[] memory _quotes)
        external
        view
        returns (ReferenceData[] memory);
}

contract DemoOracle {
    IStdReference ref;

    uint256 public price;

    constructor(IStdReference _ref) public {
        ref = _ref;
    }

    function getPrice() external view returns (uint256){
        IStdReference.ReferenceData memory data = ref.getReferenceData("BTC","USD");
        return data.rate;
    }

    function getMultiPrices() external view returns (uint256[] memory){
        string[] memory baseSymbols = new string[](2);
        baseSymbols[0] = "BTC";
        baseSymbols[1] = "BTC";

        string[] memory quoteSymbols = new string[](2);
        quoteSymbols[0] = "USD";
        quoteSymbols[1] = "ETH";
        IStdReference.ReferenceData[] memory data = ref.getReferenceDataBulk(baseSymbols,quoteSymbols);

        uint256[] memory prices = new uint256[](2);
        prices[0] = data[0].rate;
        prices[1] = data[1].rate;

        return prices;
    }

    function savePrice(string memory base, string memory quote) external {
        IStdReference.ReferenceData memory data = ref.getReferenceData(base,quote);
        price = data.rate;
    }
}