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Accessing real-world data using the RedStone Oracle (Pull)

This page will explain how you can access oracle data using RedStone Pull.

RedStone is a data ecosystem that delivers frequently updated, reliable, and diverse data for your dApp and smart contracts deployed on Lisk.

How to pull oracle data from RedStone​

To create a smart contract that directly fetches the latest data from the RedStone oracle, follow this guide.

This guide uses the RedStone Pull model to fetch the data.

For an overview of the different modules that RedStone offers to receive oracle data, go to Oracles > RedStone.

Hardhat is used in this guide to create the smart contract. In case you want to use Foundry, check out the RedStone docs for instructions.

Dependencies​

  • ethers ^5.7.2
  • hardhat ^2.14.0

Install the evm connector​

Install the @redstone-finance/evm-connector package.

npm install @redstone-finance/evm-connector

Import the evm connector​

// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.9;

/**
* Imports the EVM connector
*/
import "@redstone-finance/evm-connector/contracts/data-services/RapidDemoConsumerBase.sol";

contract YourContract is RapidDemoConsumerBase {

    // ...

}

Get oracle data​

Get the oracle data using the functions provided by the EVM connector.

Get a single value​

To get a single price feed, use the function getOracleNumericValueFromTxMsg() and provide the data feed ID as a parameter.

// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.9;

/**
* Imports the EVM connector
*/
import "@redstone-finance/evm-connector/contracts/data-services/RapidDemoConsumerBase.sol";

contract YourContract is RapidDemoConsumerBase {

    // ...

    /**
    * Returns the latest price of ETH
    */
    function getLatestEthPrice() public view returns (uint256) {
        bytes32 dataFeedId = bytes32("ETH");
        return getOracleNumericValueFromTxMsg(dataFeedId);
    }
}

Get multiple values​

To get data from multiple price feeds, use the function getOracleNumericValuesFromTxMsg() and provide the data feed ID array as a parameter.

/**
* Returns the latest prices of ETH and BTC
*/
function getLatestEthBtcPrices() public view returns (uint256[] memory) {
    bytes32[] memory dataFeedIds = new bytes32[](2);
    dataFeedIds[0] = bytes32("ETH");
    dataFeedIds[1] = bytes32("BTC");
    uint256[] memory values = getOracleNumericValuesFromTxMsg(dataFeedIds);
    return values;
}

Testing​

In order to test the EVM connector related functions in your contract, it is necessary to wrap the contract using the WrapperBuilder provided by the @redstone-finance/evm-connector package.

test/YourContract.ts
import { expect } from "chai";
import { ethers } from "hardhat";
import { WrapperBuilder } from "@redstone-finance/evm-connector";

describe("YourContract", function () {
    describe("RedStone", function () {
        it("Get ETH price securely", async function () {
        const YourContract = await ethers.getContractFactory("YourContract");
        const contract = await YourContract.deploy();
        const wrappedContract = WrapperBuilder.wrap(contract).usingDataService({
            dataFeeds: ["ETH"],
        });

        // Interact with the contract (getting oracle value securely)
        const ethPriceFromContract = await wrappedContract.getLatestEthPrice();
        console.log("Latest ETH price:");
        console.log({ ethPriceFromContract });
        });
    });
});

Now run the test:

npx hardhat test

This should output the latest ETH price in the console:

Latest ETH price:
{ ethPriceFromContract: BigNumber { value: "250255087192" } }

Deploying on Lisk​

To deploy the smart contract on Lisk Sepolia or Lisk Mainnet, follow the guides