Blockchain Oracles

Price feeds, data oracles, Chainlink integration, and oracle design patterns.

Overview

Oracles connect blockchains to external data.

Oracle Types

Chainlink Price Feed

import "@chainlink/contracts/src/v0.8/interfaces/AggregatorV3Interface.sol";

contract PriceConsumer {
    AggregatorV3Interface internal priceFeed;
    
    constructor(address _priceFeed) {
        priceFeed = AggregatorV3Interface(_priceFeed);
    }
    
    function getLatestPrice() public view returns (int) {
        (
            ,
            int price,
            ,
            uint256 updatedAt,
            
        ) = priceFeed.latestRoundData();
        
        require(block.timestamp - updatedAt < 3600, "Stale price");
        return price;
    }
}

Chainlink VRF

import "@chainlink/contracts/src/v0.8/VRFConsumerBaseV2.sol";

contract RandomNFT is VRFConsumerBaseV2 {
    uint256 public lastRandom;
    
    constructor() VRFConsumerBaseV2(vrfCoordinator) {
        vrfCoordinator = 0x...');
        keyHash = 0x...';
        subscriptionId = 1;
    }
    
    function requestRandomNumber() public {
        s_vrfCoordinator.requestRandomWords(
            keyHash,
            subscriptionId,
            3,
            200000,
            1
        );
    }
    
    function fulfillRandomWords(uint256 requestId, uint256[] memory randomWords) internal override {
        lastRandom = randomWords[0];
    }
}

Oracle Design Patterns

┌─────────────────────────────────────┐
│           Smart Contract            │
│  (On-chain request)                 │
├─────────────────────────────────────┤
│           Oracle Network            │
│  (Decentralized nodes)              │
├─────────────────────────────────────┤
│           External Data             │
│  (APIs, databases)                  │
└─────────────────────────────────────┘

Best Practices

1. Multiple sources — Avoid single point
2. Staleness checks — Fresh data
3. Fallback mechanisms — Graceful degradation
4. Cost optimization — Batch requests

Practice

Integrate Chainlink price feeds into a DeFi protocol.