Web3系列教程之进阶篇---10. Chainlink VRF(可验证的随机函数)

  • 李留白
  • 更新于 2022-08-31 16:56
  • 阅读 2970

在计算机处理计算时,由于计算机的确定性,随机性是一个重要但难以处理的问题。

简介

在计算机处理计算时,由于计算机的确定性,随机性是一个重要但难以处理的问题。说到区块链,情况更是如此,因为计算机不仅是确定性的,而且是透明的。因此,由于随机性将在链上计算,而链是所有矿工和用户的公共信息,因此无法生成可靠的本机随机数。

所以我们可以使用一些web2技术来生成随机性,然后在链上使用它们。

什么是oracle(预言机)?

  • 预言机是将数据从外部世界发送到区块链的智能合约,反之亦然。

  • 然后,智能合约可以使用这些数据做出决定并改变其状态。

  • 它们作为区块链和外部世界之间的桥梁。

  • 然而,需要注意的是,区块链预言机本身不是数据源,它的工作是查询、验证和认证外部数据,然后再将其传递给智能合约。

今天我们将学习其中一个名为Chainlink VRF的预言机。

开始吧🚀

介绍

  • Chainlink VRF 用来产生随机值的预言机。

  • 这些数值是用加密证明来验证的。

  • 这些证明验证了结果没有被预言机操作员、用户、矿工等篡改或操纵。

  • 证明是在链上公布的,因此可以被验证。

  • 在验证成功后,它们会被要求随机性的智能合约所使用。

官方的Chainlink文档将VRF描述为。

Chainlink VRF(可验证的随机函数)是一个为智能合约设计的可证明的公平和可验证的随机性来源。智能合约开发者可以使用Chainlink VRF作为防篡改的随机数发生器(RNG),为任何依赖不可预测结果的应用构建可靠的智能合约。

它是如何工作的?

  • Chainlink有两个合约,我们主要关注的是VRFConsumerBase.sol和VRFCoordinator。

  • VRFConsumerBase是将调用VRF协调员的合同,它最终负责发布随机性。

  • 我们将继承VRFConsumerBase,并将使用其中的两个函数。

    • requestRandomness,它对随机性提出初始请求。
    • fulfillRandomness,这是一个接收并对经过验证的随机性做一些事情的函数。

  • 如果你看一下图,你就可以理解这个流程,RandomGameWinner合约将继承VRFConsumerBase合约,并将在VRFConsumerBase中调用requestRandomness函数。

  • 在调用该函数时,对随机性的请求开始了,VRFConsumerBase进一步调用VRFCoordinator合约,该合约负责从外部世界获取随机性。

  • 在VRFCoordinator获得随机性后,它调用VRFConsumerBase中的fullFillRandomness函数,然后进一步选择赢家。

  • 注意重要的部分是,尽管你调用了 requestRandomness 函数,但你在 fullFillRandomness 函数中获得了随机性。

先决条件

要求

  • 我们今天将开发一个彩 票游戏
  • 每场比赛将有一个最大的玩家人数和参赛费
  • 在最大数量的玩家进入游戏后,将随机选择一名获胜者。
  • 赢家将获得maxplayers*entryfee数额的ether ,以赢得游戏。

构建

  • 最初开始时,在你的电脑中创建一个名为RandomWinnerGame的文件夹

  • 为了构建智能合约,我们将使用Hardhat。Hardhat是一个Ethereum开发环境和框架,为Solidity的全栈开发而设计。简单地说,你可以编写你的智能合约,部署它们,运行测试,并调试你的代码。

  • 要设置一个Hardhat项目,打开终端并在RandomWinnerGame文件夹内执行这些命令

mkdir hardhat-tutorial
cd hardhat-tutorial
npm init --yes
npm install --save-dev hardhat
  • 在你安装Hardhat的同一目录下运行。
npx hardhat
  • 选择 Create a Javascript project
  • Hardhat Project root下按下回车
  • 如果你想添加一个.gitignore,请按回车键询问。
  • Do you want to install this sample project's dependencies with npm (@nomicfoundation/hardhat-toolbox)?按下回车

现在你有一个准备好的hardhat项目了!

如果你不是在mac上,请做这个额外的步骤,也安装这些库 :)

npm install --save-dev @nomicfoundation/hardhat-toolbox

并对所有问题按回车键。

  • 在同一个终端中,现在安装@openzeppelin/contracts,因为我们要导入Openzeppelin的合同。
npm install @openzeppelin/contracts
  • 我们还将验证我们的合同,所以让我们安装hardhat etherscan库
npm install --save-dev @nomiclabs/hardhat-etherscan
  • 最后,我们将安装chainlink 合约,以使用chainlink VRF
npm install --save @chainlink/contracts
  • 现在在contracts目录内创建一个新文件,名为RandomWinnerGame.sol,并粘贴以下几行代码。
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.4;

import "@openzeppelin/contracts/access/Ownable.sol";
import "@chainlink/contracts/src/v0.8/VRFConsumerBase.sol";

contract RandomWinnerGame is VRFConsumerBase, Ownable {

    //Chainlink variables
    // The amount of LINK to send with the request
    uint256 public fee;
    // ID of public key against which randomness is generated
    bytes32 public keyHash;

    // Address of the players
    address[] public players;
    //Max number of players in one game
    uint8 maxPlayers;
    // Variable to indicate if the game has started or not
    bool public gameStarted;
    // the fees for entering the game
    uint256 entryFee;
    // current game id
    uint256 public gameId;

    // emitted when the game starts
    event GameStarted(uint256 gameId, uint8 maxPlayers, uint256 entryFee);
    // emitted when someone joins a game
    event PlayerJoined(uint256 gameId, address player);
    // emitted when the game ends
    event GameEnded(uint256 gameId, address winner,bytes32 requestId);

   /**
   * constructor inherits a VRFConsumerBase and initiates the values for keyHash, fee and gameStarted
   * @param vrfCoordinator address of VRFCoordinator contract
   * @param linkToken address of LINK token contract
   * @param vrfFee the amount of LINK to send with the request
   * @param vrfKeyHash ID of public key against which randomness is generated
   */
    constructor(address vrfCoordinator, address linkToken,
    bytes32 vrfKeyHash, uint256 vrfFee)
    VRFConsumerBase(vrfCoordinator, linkToken) {
        keyHash = vrfKeyHash;
        fee = vrfFee;
        gameStarted = false;
    }

    /**
    * startGame starts the game by setting appropriate values for all the variables
    */
    function startGame(uint8 _maxPlayers, uint256 _entryFee) public onlyOwner {
        // Check if there is a game already running
        require(!gameStarted, "Game is currently running");
        // empty the players array
        delete players;
        // set the max players for this game
        maxPlayers = _maxPlayers;
        // set the game started to true
        gameStarted = true;
        // setup the entryFee for the game
        entryFee = _entryFee;
        gameId += 1;
        emit GameStarted(gameId, maxPlayers, entryFee);
    }

    /**
    joinGame is called when a player wants to enter the game
     */
    function joinGame() public payable {
        // Check if a game is already running
        require(gameStarted, "Game has not been started yet");
        // Check if the value sent by the user matches the entryFee
        require(msg.value == entryFee, "Value sent is not equal to entryFee");
        // Check if there is still some space left in the game to add another player
        require(players.length < maxPlayers, "Game is full");
        // add the sender to the players list
        players.push(msg.sender);
        emit PlayerJoined(gameId, msg.sender);
        // If the list is full start the winner selection process
        if(players.length == maxPlayers) {
            getRandomWinner();
        }
    }

    /**
    * fulfillRandomness is called by VRFCoordinator when it receives a valid VRF proof.
    * This function is overrided to act upon the random number generated by Chainlink VRF.
    * @param requestId  this ID is unique for the request we sent to the VRF Coordinator
    * @param randomness this is a random unit256 generated and returned to us by the VRF Coordinator
   */
    function fulfillRandomness(bytes32 requestId, uint256 randomness) internal virtual override  {
        // We want out winnerIndex to be in the length from 0 to players.length-1
        // For this we mod it with the player.length value
        uint256 winnerIndex = randomness % players.length;
        // get the address of the winner from the players array
        address winner = players[winnerIndex];
        // send the ether in the contract to the winner
        (bool sent,) = winner.call{value: address(this).balance}("");
        require(sent, "Failed to send Ether");
        // Emit that the game has ended
        emit GameEnded(gameId, winner,requestId);
        // set the gameStarted variable to false
        gameStarted = false;
    }

    /**
    * getRandomWinner is called to start the process of selecting a random winner
    */
    function getRandomWinner() private returns (bytes32 requestId) {
        // LINK is an internal interface for Link token found within the VRFConsumerBase
        // Here we use the balanceOF method from that interface to make sure that our
        // contract has enough link so that we can request the VRFCoordinator for randomness
        require(LINK.balanceOf(address(this)) >= fee, "Not enough LINK");
        // Make a request to the VRF coordinator.
        // requestRandomness is a function within the VRFConsumerBase
        // it starts the process of randomness generation
        return requestRandomness(keyHash, fee);
    }

     // Function to receive Ether. msg.data must be empty
    receive() external payable {}

    // Fallback function is called when msg.data is not empty
    fallback() external payable {}
}
  • 构造函数接收以下参数。
    • vrfCoordinator,是VRFCoordinator合同的地址。
    • linkToken是链接令牌的地址,它是chainlink 获取其付款的令牌。
    • vrfFee是发送随机性请求所需的链接令牌的数量
    • vrfKeyHash,这是生成随机性的公钥的ID。这个值负责为我们的随机性请求生成一个唯一的ID,称为requestId

(所有这些数值都是由Chainlink提供给我们的)

/**
* startGame starts the game by setting appropriate values for all the variables
*/
function startGame(uint8 _maxPlayers, uint256 _entryFee) public onlyOwner {
    // Check if there is a game already running
    require(!gameStarted, "Game is currently running");
    // empty the players array
    delete players;
    // set the max players for this game
    maxPlayers = _maxPlayers;
    // set the game started to true
    gameStarted = true;
    // setup the entryFee for the game
    entryFee = _entryFee;
    gameId += 1;
    emit GameStarted(gameId, maxPlayers, entryFee);
}
  • onlyOwner函数意味着它只能由所有者调用。
  • 这个函数用于开始游戏,在这个函数被调用后,玩家可以进入游戏,直到达到极限。
  • 它还会触发GameStarted事件
/**
joinGame is called when a player wants to enter the game
 */
function joinGame() public payable {
    // Check if a game is already running
    require(gameStarted, "Game has not been started yet");
    // Check if the value sent by the user matches the entryFee
    require(msg.value == entryFee, "Value sent is not equal to entryFee");
    // Check if there is still some space left in the game to add another player
    require(players.length < maxPlayers, "Game is full");
    // add the sender to the players list
    players.push(msg.sender);
    emit PlayerJoined(gameId, msg.sender);
    // If the list is full start the winner selection process
    if(players.length == maxPlayers) {
        getRandomWinner();
    }
}
  • 当用户想进入一个游戏时,这个函数将被调用

  • 如果达到maxPlayers限制,它将调用getRandomWinner函数。

/**
* getRandomWinner is called to start the process of selecting a random winner
*/
function getRandomWinner() private returns (bytes32 requestId) {
    // LINK is an internal interface for Link token found within the VRFConsumerBase
    // Here we use the balanceOF method from that interface to make sure that our
    // contract has enough link so that we can request the VRFCoordinator for randomness
    require(LINK.balanceOf(address(this)) >= fee, "Not enough LINK");
    // Make a request to the VRF coordinator.
    // requestRandomness is a function within the VRFConsumerBase
    // it starts the process of randomness generation
    return requestRandomness(keyHash, fee);
}
  • 这个函数首先检查我们的合同是否有Link token,然后再申请随机,因为chainlink 合约以Link token的形式申请费用。

  • 然后这个函数调用我们从VRFConsumerBase继承的requestRandomness,并开始随机数的生成过程。

  /**
    * fulfillRandomness is called by VRFCoordinator when it receives a valid VRF proof.
    * This function is overrided to act upon the random number generated by Chainlink VRF.
    * @param requestId  this ID is unique for the request we sent to the VRF Coordinator
    * @param randomness this is a random unit256 generated and returned to us by the VRF Coordinator
   */
    function fulfillRandomness(bytes32 requestId, uint256 randomness) internal virtual override  {
        // We want out winnerIndex to be in the length from 0 to players.length-1
        // For this we mod it with the player.length value
        uint256 winnerIndex = randomness % players.length;
        // get the address of the winner from the players array
        address winner = players[winnerIndex];
        // send the ether in the contract to the winner
        (bool sent,) = winner.call{value: address(this).balance}("");
        require(sent, "Failed to send Ether");
        // Emit that the game has ended
        emit GameEnded(gameId, winner,requestId);
        // set the gameStarted variable to false
        gameStarted = false;
    }
  • 这个函数从VRFConsumerBase继承而来。它由VRFCoordinator合约在接收到外部世界的随机性后调用。

  • 在接收到随机性(可以是uint256范围内的任何数字)后,我们使用mod 操作符从范围从0 to players.length-1取值

  • 这就为我们选择了一个索引,我们用这个索引从玩家数组中检索出赢家。

  • 它将合约中所有的ether 发送给赢家,并发出一个GameEnded事件。

  • 现在我们要安装dotenv包,以便能够导入env文件并在我们的配置中使用它。打开一个终端,指向hardhat-tutorial目录,执行以下命令

npm install dotenv
  • 现在在hardhat-tutorial文件夹下创建一个.env文件,并添加以下几行,使用注释中的说明来获得你的ALCHEMY_API_KEY_URLMUMBAI_PRIVATE_KEYPOLYGONSCAN_KEY.如果你的MetaMask上没有mumbai ,你可以按照这个来把它添加到你的MetaMask上,确保你获得mumbai 私钥的账户有mumbai Matic资金,你可以从这里得到一些。
// Go to https://www.alchemyapi.io, sign up, create
  // a new App in its dashboard and select the network as Mumbai, and replace "add-the-alchemy-key-url-here" with its key url
  ALCHEMY_API_KEY_URL="add-the-alchemy-key-url-here"

  // Replace this private key with your Mumbai account private key
  // To export your private key from Metamask, open Metamask and
  // go to Account Details > Export Private Key
  // Be aware of NEVER putting real Ether into testing accounts
  MUMBAI_PRIVATE_KEY="add-the-mumbai-private-key-here"

  // Go to https://polygonscan.com/, sign up, on your account overview page,
  // click on `API Keys`, add a new API key and copy the
  // `API Key Token`
  POLYGONSCAN_KEY="add-the-polygonscan-api-token-here"
  • 现在打开hardhat.config.js文件,我们将在这里添加mumbai网络,这样我们就可以把我们的合同部署到mumbai,还有一个etherscan对象,这样我们就可以在polygonscan上验证我们的合同。将hardhat.config.js文件中的所有行替换为下面给出的行。
require("@nomicfoundation/hardhat-toolbox");
require("dotenv").config({ path: ".env" });
require("@nomiclabs/hardhat-etherscan");

const ALCHEMY_API_KEY_URL = process.env.ALCHEMY_API_KEY_URL;

const MUMBAI_PRIVATE_KEY = process.env.MUMBAI_PRIVATE_KEY;

const POLYGONSCAN_KEY = process.env.POLYGONSCAN_KEY;

module.exports = {
  solidity: "0.8.9",
  networks: {
    mumbai: {
      url: ALCHEMY_API_KEY_URL,
      accounts: [MUMBAI_PRIVATE_KEY],
    },
  },
  etherscan: {
    apiKey: {
      polygonMumbai: POLYGONSCAN_KEY,
    },
  },
};
  • 创建一个名为constants的新文件夹,并在其中添加一个名为index.js的新文件。在index.js文件中添加这些行。
const { ethers, BigNumber } = require("hardhat");

const LINK_TOKEN = "0x326C977E6efc84E512bB9C30f76E30c160eD06FB";
const VRF_COORDINATOR = "0x8C7382F9D8f56b33781fE506E897a4F1e2d17255";
const KEY_HASH =
  "0x6e75b569a01ef56d18cab6a8e71e6600d6ce853834d4a5748b720d06f878b3a4";
const FEE = ethers.utils.parseEther("0.0001");
module.exports = { LINK_TOKEN, VRF_COORDINATOR, KEY_HASH, FEE };

我们从这里得到的数值,已经由Chainlink提供给我们。

  • 让我们把合同部署到mumbai网络。在scripts文件夹下创建一个新文件,或替换默认的现有文件,命名为deploy.js
const { ethers } = require("hardhat");
require("dotenv").config({ path: ".env" });
require("@nomiclabs/hardhat-etherscan");
const { FEE, VRF_COORDINATOR, LINK_TOKEN, KEY_HASH } = require("../constants");

async function main() {
  /*
 A ContractFactory in ethers.js is an abstraction used to deploy new smart contracts,
 so randomWinnerGame here is a factory for instances of our RandomWinnerGame contract.
 */
  const randomWinnerGame = await ethers.getContractFactory("RandomWinnerGame");
  // deploy the contract
  const deployedRandomWinnerGameContract = await randomWinnerGame.deploy(
    VRF_COORDINATOR,
    LINK_TOKEN,
    KEY_HASH,
    FEE
  );

  await deployedRandomWinnerGameContract.deployed();

  // print the address of the deployed contract
  console.log(
    "Verify Contract Address:",
    deployedRandomWinnerGameContract.address
  );

  console.log("Sleeping.....");
  // Wait for etherscan to notice that the contract has been deployed
  await sleep(30000);

  // Verify the contract after deploying
  await hre.run("verify:verify", {
    address: deployedRandomWinnerGameContract.address,
    constructorArguments: [VRF_COORDINATOR, LINK_TOKEN, KEY_HASH, FEE],
  });
}

function sleep(ms) {
  return new Promise((resolve) => setTimeout(resolve, ms));
}

// Call the main function and catch if there is any error
main()
  .then(() => process.exit(0))
  .catch((error) => {
    console.error(error);
    process.exit(1);
  });
  • 编译合同,打开终端,指向hardhat-tutorial目录,执行以下命令
  npx hardhat compile
  • 要进行部署,请打开终端,指向hardhat-tutorial目录,并执行以下命令
  npx hardhat run scripts/deploy.js --network mumbai
  • 它应该已经打印了一个到 mumbai polygonscan的链接,你的合同现在已经验证了。点击polygonscan链接,在那里与你的合同互动。

  • 让我们现在在polygonscan上玩游戏吧

  • 在你的终端,他们应该已经打印了一个链接到你的合同,如果没有,那么去 [Mumbai Polygon Scan](https://mumbai.polygonscan.com/)并搜索你的合同地址,它应该被验证。

  • 我们现在将用一些Chainlink来资助这个合同,这样我们就可以要求随机性,去Polygon Faucet,从下拉菜单中选择Link,然后输入你的合同地址

  • 一旦连接,它将看起来像这样

  • 然后在startGame函数中输入一些数值,并点击Write按钮

  • 现在你可以用你的地址加入游戏了。注意:我在这里输入的数值是10WEI,因为这是我指定的报名费的数值,但是因为加入游戏接受ether 而不是WEI,我必须将10WEI转换成ether 。你也可以用eth转换器将你的参赛费转换成ether

  • 现在刷新页面,并连接一个新的钱包,其中有一些matic,这样你就可以让另一个玩家加入。 注:我将最大玩家数设置为2,这样在我让另一个地址加入游戏后,它将选择赢家。

  • 如果你现在进入你的事件选项卡并不断刷新(VRFCoordinator调用fullFillRandomness函数需要一些时间,因为它必须从外部世界获得数据),在某一时刻你将能够看到一个事件,上面写着GameEnded

  • 从下拉菜单中为GameEnded事件中的第一个值转换Hex为地址,因为那是赢家的地址。

它完成了 🚀

你现在知道如何玩这个游戏了。在下一个教程中,我们将为此创建一个用户界面,并将学习如何使用代码本身来跟踪这些事件。

准备开始吧🚀🚀

原文: https://www.learnweb3.io/tracks/junior/chainlink-vrf

my.png

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