🔮 第20课：预言机

DeFi 阶段四 ✅ 验证通过

📖 一、预言机问题

1.1 预言机安全挑战

📖 二、Chainlink架构

2.1 Chainlink Price Feed

// Chainlink聚合器接口
interface AggregatorV3Interface {
    function latestRoundData() external view returns (
        uint80 roundId,        // 轮次ID
        int256 answer,         // 价格（带精度）
        uint256 startedAt,     // 本轮开始时间
        uint256 updatedAt,     // 最后更新时间
        uint80 answeredInRound // 回答所在轮次
    );
    function decimals() external view returns (uint8);
    function description() external view returns (string memory);
}

// 常用Chainlink Price Feed地址（Sepolia测试网）
// ETH/USD: 0x694AA1769357215DE4FAC081bf1f309aDC325306
// BTC/USD: 0x1b44F3514812d835EB1BDB0acB33d3fA3351Ee43
// LINK/USD: 0xc59E3633BAAC79493d908e6364a2dAaFEEd3f681

📖 三、安全使用Chainlink

// contracts/OracleConsumer.sol — 安全使用Chainlink的示例
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

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

/**
 * @title OracleConsumer
 * @dev 安全消费Chainlink价格数据的合约
 */
contract OracleConsumer {
    AggregatorV3Interface internal priceFeed;
    
    // 安全参数
    uint256 public constant STALE_THRESHOLD = 1 hours;  // 数据过期阈值
    uint256 public constant MAX_DEVIATION = 20;        // 最大偏离20%
    uint256 private lastPrice;
    uint256 private lastPriceTimestamp;

    event PriceUpdated(uint256 price, uint256 timestamp);

    constructor(address _priceFeed) {
        priceFeed = AggregatorV3Interface(_priceFeed);
    }

    /// @notice 获取最新ETH/USD价格（带安全检查）
    function getLatestPrice() external returns (uint256) {
        // 1. 获取价格数据
        (
            uint80 roundId,
            int256 price,
            ,
            uint256 updatedAt,
            uint80 answeredInRound
        ) = priceFeed.latestRoundData();

        // 2. 安全检查：价格必须为正
        require(price > 0, "Invalid price");

        // 3. 安全检查：数据未过期
        require(
            block.timestamp - updatedAt < STALE_THRESHOLD,
            "Stale price data"
        );

        // 4. 安全检查：轮次匹配（防止使用旧轮次数据）
        require(
            answeredInRound >= roundId,
            "Stale round"
        );

        // 5. 安全检查：价格偏离（防止单次价格剧烈波动）
        if (lastPrice > 0) {
            uint256 deviation = _calculateDeviation(uint256(price), lastPrice);
            require(deviation <= MAX_DEVIATION, "Price deviation too high");
        }

        lastPrice = uint256(price);
        lastPriceTimestamp = block.timestamp;

        emit PriceUpdated(lastPrice, block.timestamp);
        return lastPrice;
    }

    /// @notice 获取人类可读的价格
    function getReadablePrice() external view returns (uint256) {
        (/*roundId*/, int256 price, , , ) = priceFeed.latestRoundData();
        uint8 decimals = priceFeed.decimals();
        // Chainlink ETH/USD: 8位小数 → 转为18位
        return uint256(price) * (10 ** (18 - decimals));
    }

    function _calculateDeviation(uint256 current, uint256 previous) internal pure returns (uint256) {
        if (previous == 0) return 0;
        uint256 diff = current > previous ? current - previous : previous - current;
        return (diff * 100) / previous;
    }
}

📖 四、链上价格获取替代方案

4.1 Uniswap TWAP（时间加权平均价格）

// 从Uniswap V3获取TWAP价格
interface IUniswapV3Pool {
    function slot0() external view returns (
        uint160 sqrtPriceX96,
        int24 tick,
        uint16 observationIndex,
        uint16 observationCardinality,
        uint16 observationCardinalityNext,
        uint8 feeProtocol,
        bool unlocked
    );
    function observe(uint32[] memory secondsAgos) external view returns (int56[] memory tickCumulatives, uint160[] memory secondsPerLiquidityCumulativeX128s);
}

contract TWAPOracle {
    IUniswapV3Pool public immutable pool;
    uint32 public constant TWAP_PERIOD = 1800; // 30分钟TWAP

    constructor(address _pool) {
        pool = IUniswapV3Pool(_pool);
    }

    function getTWAPPrice() external view returns (uint256) {
        uint32[] memory secondsAgos = new uint32[](2);
        secondsAgos[0] = TWAP_PERIOD;
        secondsAgos[1] = 0;

        (int56[] memory tickCumulatives, ) = pool.observe(secondsAgos);
        
        // 平均tick = (当前累计tick - 过去累计tick) / 时间间隔
        int56 tickDelta = tickCumulatives[1] - tickCumulatives[0];
        int24 avgTick = int24(tickDelta / int56(int32(TWAP_PERIOD)));

        // tick → 价格: price = sqrtRatio ≈ 1.0001^tick
        // 简化：返回tick用于外部计算
        return uint256(int256(avgTick));
    }
}

4.2 预言机方案对比

📖 五、预言机攻击案例

🧪 练习