预言机与链下数据：Chainlink 与去中心化数据

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.19;

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

contract PriceConsumer {
    AggregatorV3Interface internal immutable priceFeed;

    // ETH/USD 主网 Feed 地址
    constructor() {
        priceFeed = AggregatorV3Interface(0x5f4eC3Df9cbd43714FE2740f5E3616155c5b8419);
    }

    /// @dev 返回以 USD 计价的 ETH 价格（8 位小数）
    function getLatestPrice() public view returns (uint256) {
        (, int256 answer, uint256 startedAt, uint256 updatedAt, ) =
            priceFeed.latestRoundData();

        require(updatedAt >= block.timestamp - 3600, "Stale price"); // 时效校验
        require(answer > 0, "Invalid price");

        return uint256(answer) * 1e10; // 放大到 18 位小数
    }
}

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.19;

import {VRFConsumerBaseV2Plus} from "@chainlink/contracts/src/v0.8/vrf/dev/VRFConsumerBaseV2Plus.sol";
import {VRFV2PlusClient} from "@chainlink/contracts/src/v0.8/vrf/dev/libraries/VRFV2PlusClient.sol";

contract MyLottery is VRFConsumerBaseV2Plus {
    uint256 internal s_lastRequestId;
    uint256[] internal s_randomWords;
    address internal s_owner;

    // Sepolia VRF：订阅式（Subscription）计费
    constructor() VRFConsumerBaseV2Plus(0x9DdfaCa8183c41ad5539B353c33A51BE1a8Ecb36) {
        s_owner = msg.sender;
    }

    function requestRandomWords() external onlyOwner returns (uint256 requestId) {
        requestId = s_vrfCoordinator.requestRandomWords(
            VRFV2PlusClient.RandomWordsRequest({
                keyHash: 0x787d74caea7b6a83439c23c78bfb8d1236d3d1c9e1a1b4e4f2d9f5a5e6f7a8b9, // 500 gwei keyHash
                subId: s_subscriptionId,       // 订阅 ID
                requestConfirmations: 3,       // 确认数（可 1-200）
                callbackGasLimit: 200_000,     // fulfill 回调 gas 上限
                numWords: 1,                   // 请求随机词个数
                extraArgs: VRFV2PlusClient._argsToBytes(
                    VRFV2PlusClient.ExtraArgsV1({nativePayment: false})
                )
            })
        );
        s_lastRequestId = requestId;
    }

    function fulfillRandomWords(uint256 requestId, uint256[] memory randomWords)
        internal
        override
    {
        require(requestId == s_lastRequestId, "Invalid request");
        s_randomWords = randomWords;
        // 用 randomWords[0] % N 决定中奖者...
    }
}

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.19;

import {Client} from "@chainlink/contracts-ccip/src/v0.8/ccip/libraries/Client.sol";
import {CCIPReceiver} from "@chainlink/contracts-ccip/src/v0.8/ccip/applications/CCIPReceiver.sol";
import {IRouterClient} from "@chainlink/contracts-ccip/src/v0.8/ccip/interfaces/IRouterClient.sol";
import {IERC20} from "@openzeppelin/contracts/token/ERC20/IERC20.sol";

contract CrossChainTransfer {
    IRouterClient private immutable i_router;
    IERC20 private immutable i_link;

    function sendTokens(
        uint64 destinationChainSelector,
        address receiver,
        address token,
        uint256 amount
    ) external returns (bytes32 messageId) {
        IERC20(token).approve(address(i_router), amount);
        Client.EVM2AnyMessage memory message = Client.EVM2AnyMessage({
            receiver: abi.encode(receiver),
            data: "",
            tokenAmounts: new Client.EVMTokenAmount[](1),
            extraArgs: Client._argsToBytes(Client.EVMExtraArgsV1({gasLimit: 0})),
            feeToken: address(i_link)
        });
        message.tokenAmounts[0] = Client.EVMTokenAmount({token: token, amount: amount});
        return i_router.ccipSend(destinationChainSelector, message);
    }
}

# 检查某个 Feed 的最近更新时间（通过 RPC 调用）
cast call 0x5f4eC3Df9cbd43714FE2740f5E3616155c5b8419 \
  "latestRoundData()(uint80,int256,uint256,uint256,uint80)" \
  --rpc-url https://eth-mainnet.g.alchemy.com/v2/KEY

// 监听价格更新（前端 ethers.js 示例）
{
  "event": "AnswerUpdated(int256 indexed current, uint256 indexed roundId, uint256 updatedAt)",
  "topics": ["0x0559884fd3a460db3073b7fc896cc77986f16e378210ded43186175bf646fc5f"],
  "contract": "0x5f4eC3Df9cbd43714FE2740f5E3616155c5b8419"
}

# 测试网部署 + 验证
forge create src/PriceConsumer.sol:PriceConsumer --rpc-url $SEPOLIA_RPC --private-key $KEY
forge verify-contract <ADDR> src/PriceConsumer.sol:PriceConsumer --chain sepolia