Oracle预言机充当智能合约与外部世界之间的桥梁，它们可以从外部获取数据，并将这些数据传递给智能合约。
智能合约在接收到来自预言机的数据后，可以根据这些数据执行相应的逻辑。
contract ContractTest is Test {AggregatorV3Interface internal priceFeed;function setUp() public {vm.createSelectFork("mainnet", 17568400);priceFeed = AggregatorV3Interface(0x5f4eC3Df9cbd43714FE2740f5E3616155c5b8419); // ETH/USD}
function testUnSafePrice() public {//没有经过二次的校验(, int256 answer, , , ) = priceFeed.latestRoundData();emit log_named_decimal_int("price", answer, 8);}
function testSafePrice() public {(uint80 roundId,int256 answer,,uint256 updatedAt,uint80 answeredInRound) = priceFeed.latestRoundData();/*Mitigation:answeredInRound: The round ID in which the answer was computedupdatedAt: Timestamp of when the round was updatedanswer: The answer for this round*/require(answeredInRound >= roundId, "answer is stale");require(updatedAt > 0, "round is incomplete");require(answer > 0, "Invalid feed answer");emit log_named_decimal_int("price", answer, 8);}
interface AggregatorV3Interface {functionlatestRoundData()externalviewreturns(uint80 roundId,int256 answer,uint256 startedAt,uint256 updatedAt,uint80 answeredInRound);}
contract ContractTest is Test {AggregatorV3Interface internal priceFeed;functionsetUp() public{vm.createSelectFork("mainnet", 17568400);priceFeed = AggregatorV3Interface(0x5f4eC3Df9cbd43714FE2740f5E3616155c5b8419); // ETH/USD}functiontestUnSafePrice() public{//Chainlink oracle data feed is not sufficiently validated and can return stale price.(, int256 answer, , , ) = priceFeed.latestRoundData();emit log_named_decimal_int("price", answer, 8);}functiontestSafePrice() public{(uint80 roundId,int256 answer,,uint256 updatedAt,uint80 answeredInRound) = priceFeed.latestRoundData();/*Mitigation:answeredInRound: The round ID in which the answer was computedupdatedAt: Timestamp of when the round was updatedanswer: The answer for this round*/require(answeredInRound >= roundId, "answer is stale");require(updatedAt > 0, "round is incomplete");require(answer > 0, "Invalid feed answer");emit log_named_decimal_int("price", answer, 8);}receive() external payable {}}
answer：答案，也就我们要的值
updatedAt：答案最后更新的时间戳
require(answeredInRound >= roundId, "answer is stale");require(updatedAt > 0, "round is incomplete");require(answer > 0, "Invalid feed answer");
原文始发于微信公众号（Ice ThirdSpace）：DeFiVulnLabs靶场全系列详解（三十四）预言机产生了过时的价格
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