🐬Apollo: request feeds from EVM

Step-by-step integration real-world data to your EVM SC

Apollo architecture

Apollo is an intricate module developed to bridge the gap between EVM (Ethereum Virtual Machine) contracts and the data-rich environment of the Orally platform, particularly its Sybil component. Beyond mere data provisioning, Apollo is also configured to provide a level of randomness through a cryptographic measure, utilizing the unpredictable BLS signatures inherent to the Internet Computer (ICP) execution layer.

Integration Steps:

1. To start using the Apollo module, your smart contract needs to inherit from ApolloReceiver. This setup allows your contract to receive data from the Apollo network:

// Import the ApolloReceiver contract
import {ApolloReceiver} from "../apollo/ApolloReceiver.sol";

// Your contract inherits from ApolloReceiver
contract YourContract is ApolloReceiver {
    // Constructor initializes the ApolloReceiver with registry and coordinator addresses
    constructor(address _executorsRegistry, address _apolloCoordinator) 
        ApolloReceiver(_executorsRegistry, _apolloCoordinator) {}
}

1. To request data, such as a price feed, use the requestDataFeed (or requestRandomFeed for randomness) function from the ApolloCoordinator (interface). This function emits an event that the Apollo network listens for to provide the requested data.

Random Feed

// Example function to request a price feed
// `apolloCoordinator` is passing as public var from ApolloReceiver contract
function requestRandomFeed() public {
        // Requesting the randomness with a specified callback gas limit and number of random words
        apolloCoordinator.requestRandomFeed(300000, 1);
}

Data Feed

// Example function to request a price feed
// `apolloCoordinator` is passing as public var from ApolloReceiver contract
function requestPriceFeed() public {
        // Requesting the ICP/USD price feed with a specified callback gas limit
        apolloCoordinator.requestDataFeed("ICP/USD", 300000);
}

1. Override the fulfillData function to define how your contract should handle the incoming data. This function is called when the Apollo network delivers the data to your contract.

Random Feed

contract YourContract is ApolloReceiver {
    // ...

    // Overriding the fulfillData function to handle incoming data
    function fulfillData(bytes memory data) internal override {
        (, uint256[] memory randomWords) = abi.decode(data, (uint256, uint256[]));

        // transform the result to a number between 1 and 20 inclusively
        uint256 randomNumber = (randomWords[0] % entries.length) + 1;

        pickWinner(randomNumber);
    }
}

Data Feed

contract YourContract is ApolloReceiver {
    // Data storage variables
    uint256 public requestId;
    string public dataFeedId;
    uint256 public rate;
    uint256 public decimals;
    uint256 public timestamp;

    // Overriding the fulfillData function to handle incoming data
    function fulfillData(bytes memory data) internal override {
        (
            uint256 _requestId,
            string memory _dataFeedId,
            uint256 _rate,
            uint256 _decimals,
            uint256 _timestamp
        ) = abi.decode(data, (
            uint256,
            string,
            uint256,
            uint256,
            uint256
        ));


        requestId = _requestId;
        dataFeedId = _dataFeedId;
        rate = _rate;
        decimals = _decimals;
        timestamp = _timestamp;
    }
}

That's it! You successfully requested data and received it in the callback.

Here are contract addresses for IApolloCoordinator and IOrallyExecutorRegistry.

Sepolia

Contract
ApolloCoordinator	0xDC88B1919AF3AD86AAcE0FB19F125cb3Db3543e2
OrallyExecutorsRegistry	0x4531112808f8C0068768cC3fAE0939e0c05719D1

Zircuit

Contract
ApolloCoordinator	0x45f61bAD7e29a6FB9ec307daD7B895e63Db1940B
OrallyExecutorsRegistry	0x76d67e374391DF6363B72dA8530035Ee5f27a3Da

Taiko Katla

Contract
ApolloCoordinator	0x1FEa4E134c8BcDF6E1323C1Bf2Aa0899049CC754
OrallyExecutorsRegistry	0x81f8573B46895f65C7658Aa3A0eB90578F7F2dC9

Here are Apollo consumer examples:

• RaffleExample (randomness)
• ApolloConsumerExample (price feed)