智能合约不断听取价格信息并在达到价格后立即执行的最佳方式是啥？

Posted 2023-02-19

【中文标题】智能合约不断听取价格信息并在达到价格后立即执行的最佳方式是啥？

【英文标题】：What is the best way for a smart contract to constantly listen to a price feed and execute immediately once a price is reached?智能合约不断听取价格信息并在达到价格后立即执行的最佳方式是什么？

【发布时间】：2021-08-16 02:38:58

【问题描述】：

我编写了一个智能合约，该合约应该从 2 个地址，一个下注创建者和一个下注接受者中进行下注。赌注是 ETH/USD 的价格（通过 ChainLink）。

智能合约持续监听 ETH/USD 价格的最佳方式是什么，这样只要价格达到赌注的一方或另一方，合约就会自动generateBetOutcome()？

pragma solidity ^0.8.4;

import "https://github.com/smartcontractkit/chainlink/blob/master/evm-contracts/src/v0.6/interfaces/AggregatorV3Interface.sol";

contract Bet 

    //bet status
    uint constant STATUS_WIN = 1;
    uint constant STATUS_LOSE = 2;
    uint constant STATUS_TIE = 3;
    uint constant STATUS_PENDING = 4;

    //game status
    uint constant STATUS_NOT_STARTED = 1;
    uint constant STATUS_STARTED = 2;
    uint constant STATUS_COMPLETE = 3;

    //general status
    uint constant STATUS_ERROR = 4;

    //the betting structure
    struct DoubleBet 
        uint guess;
        address addr;
        uint status;
    

    //the 'game' structure
    struct Game 
        uint256 betAmount;
        uint outcome;
        uint status;
        DoubleBet creator;
        DoubleBet taker;
    
    
    Game game;
    
    receive() external payable 
    
    
    address payable owner;
    
        AggregatorV3Interface internal priceFeed;

    /**
     * Network: Kovan
     * Aggregator: ETH/USD
     * Address: 0x9326BFA02ADD2366b30bacB125260Af641031331
     */
    constructor() public 
        priceFeed = AggregatorV3Interface(0x9326BFA02ADD2366b30bacB125260Af641031331);
    
    
    function createBet(uint _guess) public payable 
      game = Game(msg.value, 0, STATUS_STARTED, DoubleBet(_guess, msg.sender, STATUS_PENDING), DoubleBet(0, msg.sender, STATUS_NOT_STARTED));
      game.creator = DoubleBet(_guess, msg.sender, STATUS_PENDING);
    

    function takeBet(uint _guess) public payable  
      //requires the taker to make the same bet amount     
      require(msg.value == game.betAmount);
      game.taker = DoubleBet(_guess, msg.sender, STATUS_PENDING);
      generateBetOutcome();
    
    
    function generateBetOutcome() private 
        game.outcome = uint(getThePrice());
        game.status = STATUS_COMPLETE;
        
        if (game.creator.guess == game.taker.guess) 
          game.creator.status = STATUS_TIE;
          game.taker.status = STATUS_TIE;
         else if (game.creator.guess > game.outcome && game.taker.guess > game.outcome) 
          game.creator.status = STATUS_TIE;
          game.taker.status = STATUS_TIE;
         else 
           if ((game.outcome - game.creator.guess) < (game.outcome - game.taker.guess)) 
             game.creator.status = STATUS_WIN;
             game.taker.status = STATUS_LOSE;
            else if ((game.outcome - game.taker.guess) < (game.outcome - game.creator.guess)) 
             game.creator.status = STATUS_LOSE;
             game.taker.status = STATUS_WIN;
            else 
             game.creator.status = STATUS_ERROR;
             game.taker.status = STATUS_ERROR;
             game.status = STATUS_ERROR;
           
        
    
//returns - [<description>, 'originator', <originator status>, 'taker', <taker status>]
     function getBetOutcome() public view returns
     (string memory description, string memory originatorKey, uint originatorStatus, string memory takerKey, uint takerStatus) 
     
        if (game.creator.status == STATUS_TIE || game.taker.status == STATUS_TIE) 
          description = "Both bets were the same or were over the number, the pot will be split";
         else 
            if (game.creator.status == STATUS_WIN) 
             description = "Bet originator guess was closer to the number and will receive the pot";
            else if (game.taker.status == STATUS_WIN) 
             description = "Bet taker guess was closer to the number and will receive the pot";
            else 
             description = "Unknown Bet Outcome";
           
        
        originatorKey = "creator";
        originatorStatus = game.creator.status;
        takerKey = "taker";
        takerStatus = game.taker.status;
     

    /**
     * Returns the latest price
     */
    function getThePrice() public view returns (int) 
        (
            uint80 roundID, 
            int price,
            uint startedAt,
            uint timeStamp,
            uint80 answeredInRound
        ) = priceFeed.latestRoundData();
        return price;
    
    
    
    modifier onlyOwner() 
        require(msg.sender == owner);
        _;
    
    
    
    
    function getBalance() public view returns (uint balance) 
        return address(this).balance;
    
    
    

【参考方案1】：

智能合约无法访问区块链本身之外的任何内容。 唯一的方法是使用oracle。

预言机只是一个普通软件（你可以用 C++、php 或 Java 或任何你喜欢的东西编写），它访问外部资源，如 ChainLink 上的 ETH/USD 价格，然后根据你编写的逻辑调用满足条件时智能合约上的方法。

为确保只有您的 oracle 可以调用该方法（例如调用 generateBetOutcome）并通过过早调用该方法来避免第 3 方作弊，您可以编写代码来验证调用者是您的 oracle。