🐬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

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

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

Taiko Katla

Here are Apollo consumer examples:

• RaffleExample (randomness)

• ApolloConsumerExample (price feed)