币安链BSC众筹系统开发技术详细分析

在一定时间（deadline）内，质押（stake）一定数量（threshold）的代币。到期之后可以将代币转入（execute）到另一个合约，也可以将代币提取出来（withdraw）。

所以我们抽像出来了三个关键函数：

1. stake()
2. execute()
3. withdraw()

scaffold-eth也为我们提供了这样的一个脚手架，只需要把代码拉下来，我们本次就在这个基础上逐步来实现。

代码语言：javascript复制

git clone https://github.com/scaffold-eth/scaffold-eth-challenges.git
cd scaffold-eth-challenges
git checkout challenge-1-decentralized-staking
yarn install

然后开三个终端窗口，执行如下三个命令：

代码语言：javascript复制

yarn chain

代码语言：javascript复制

yarn start

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yarn deploy --reset

0x04 Live Coding

4.1 stake

• 关键点1，每次质押一定数量的eth。

代码语言：javascript复制

pragma solidity 0.8.4;

import "hardhat/console.sol";
import "./ExampleExternalContract.sol";

contract Staker {
    mapping(address => uint256) public balances;

    event Stake(address indexed staker, uint256 amount);

    function stake() public payable {
        balances[msg.sender]  = msg.value;
        emit Stake(msg.sender, msg.value);
    }
}

• 关键点2，部署脚本移除构造函数的参数

代码语言：javascript复制

// deploy/01_deploy_staker.js
// ....

await deploy("Staker", {
    // Learn more about args here: https://www.npmjs.com/package/hardhat-deploy#deploymentsdeploy
    from: deployer,
    // args: [exampleExternalContract.address],
    log: true,
  });

//...

• 关键点3，部署

代码语言：javascript复制

yarn deploy --reset

• 关键点4，空投一些测试币
• 关键点5，测试stake

4.2 execute

筹集到的资金，在满足一定条件之后，转移给另一个合约中。

• 关键点1，另一个合约

代码语言：javascript复制

contract ExampleExternalContract {

  bool public completed;

  function complete() public payable {
    completed = true;
  }

}

很简单，有一个flag代表是否已经结束了。

• 关键点2，构造函数

在stake合约中，要把这个合约引入进来，同时要有一个构造函数

代码语言：javascript复制

ExampleExternalContract public exampleExternalContract;

constructor(address exampleExternalContractAddress) public {
        exampleExternalContract = ExampleExternalContract(
            exampleExternalContractAddress
        );
}

• 关键点3，部署的时候要初始化

代码语言：javascript复制

// deploy/01_deploy_staker.js
// ....

await deploy("Staker", {
    // Learn more about args here: https://www.npmjs.com/package/hardhat-deploy#deploymentsdeploy
    from: deployer,
    args: [exampleExternalContract.address],
    log: true,
  });

//...

• 关键点4，质押上限

代码语言：javascript复制

uint256 public constant threshold = 1 ether;

• 关键点5，向第二个合约转账。

代码语言：javascript复制

    function execute() public {
        uint256 contractBalance = address(this).balance;

        // check the contract has enough ETH to reach the treshold
        require(contractBalance >= threshold, "Threshold not reached");

        // Execute the external contract, transfer all the balance to the contract
        // (bool sent, bytes memory data) = exampleExternalContract.complete{value: contractBalance}();
        (bool sent, ) = address(exampleExternalContract).call{
            value: contractBalance
        }(abi.encodeWithSignature("complete()"));
        require(sent, "exampleExternalContract.complete failed");
    }

• 最终代码如下

代码语言：javascript复制

// SPDX-License-Identifier: MIT
pragma solidity 0.8.4;

import "hardhat/console.sol";
import "./ExampleExternalContract.sol";

contract Staker {
    ExampleExternalContract public exampleExternalContract;

    mapping(address => uint256) public balances;
    
    uint256 public constant threshold = 1 ether;

    event Stake(address indexed staker, uint256 amount);

    constructor(address exampleExternalContractAddress) public {
        exampleExternalContract = ExampleExternalContract(
            exampleExternalContractAddress
        );
    }

    function stake() public payable {
        balances[msg.sender]  = msg.value;
        emit Stake(msg.sender, msg.value);
    }

    function execute() public {
        uint256 contractBalance = address(this).balance;

        require(contractBalance >= threshold, "Threshold not reached");

        (bool sent, ) = address(exampleExternalContract).call{
            value: contractBalance
        }(abi.encodeWithSignature("complete()"));
        require(sent, "exampleExternalContract.complete() failed");
    }
}

• 部署

代码语言：javascript复制

yarn deploy --reset

• 空投测试币
• stake 一些币到达上限
• 测试 execute

4.3 withdraw

将质押的钱提取出来，这个比较简单，就是将钱转移出来即可。

代码语言：javascript复制

    function withdraw() public {
        uint256 userBalance = balances[msg.sender];

        require(userBalance > 0, "You don't have balance to withdraw");

        balances[msg.sender] = 0;

        (bool sent, ) = msg.sender.call{value: userBalance}("");
        require(sent, "Failed to send user balance back to the user");
    }

• 完整代码如下

代码语言：javascript复制

// SPDX-License-Identifier: MIT
pragma solidity 0.8.4;

import "hardhat/console.sol";
import "./ExampleExternalContract.sol";

contract Staker {
    ExampleExternalContract public exampleExternalContract;

    mapping(address => uint256) public balances;

    uint256 public constant threshold = 1 ether;

    uint256 public deadline = block.timestamp   30 seconds;

    event Stake(address indexed sender, uint256 amount);

    constructor(address exampleExternalContractAddress) public {
        exampleExternalContract = ExampleExternalContract(
            exampleExternalContractAddress
        );
    }

    function stake() public payable {
        balances[msg.sender]  = msg.value;

        emit Stake(msg.sender, msg.value);
    }

    function execute() public {
        uint256 contractBalance = address(this).balance;

        require(contractBalance >= threshold, "Threshold not reached");

        (bool sent, ) = address(exampleExternalContract).call{
            value: contractBalance
        }(abi.encodeWithSignature("complete()"));
        require(sent, "exampleExternalContract.complete failed");
    }

    function withdraw() public {
        uint256 userBalance = balances[msg.sender];

        require(userBalance > 0, "You don't have balance to withdraw");

        balances[msg.sender] = 0;

        (bool sent, ) = msg.sender.call{value: userBalance}("");
        require(sent, "Failed to send user balance back to the user");
    }
}

• 部署

代码语言：javascript复制

yarn deploy --reset

• 空投测试币
• stake一些币
• 测试withdraw

4.4 加上时间或质押到期限制

这里有两个判断的标准

首先是是否到达时间，另一个就是质押是否已经完成。

• 第一个是否完成，直接去看另一个合约的标志即可

代码语言：javascript复制

		modifier stakeNotCompleted() {
        bool completed = exampleExternalContract.completed();
        require(!completed, "staking process is already completed");
        _;
    }

• 第二个是否到时间了 uint256 public deadline = block.timestamp 60 seconds; function timeLeft() public view returns (uint256 timeleft) { if (block.timestamp >= deadline) { return 0; } else { return deadline - block.timestamp; } } modifier deadlineReached(bool requireReached) { uint256 timeRemaining = timeLeft(); if (requireReached) { require(timeRemaining == 0, "deadline is not reached yet"); } else { require(timeRemaining > 0, "deadline has already reached"); } _; }
  • 接着是deadlineReached函数
  • 然后还要有一个timeLeft函数
  • 首先要有一个deadline变量
• 如何修饰这些函数 function stake() public payable deadlineReached(false) stakeNotCompleted { balances[msg.sender] = msg.value; emit Stake(msg.sender, msg.value); } function execute() public stakeNotCompleted deadlineReached(false) { uint256 contractBalance = address(this).balance; require(contractBalance >= threshold, "Threshold not reached"); (bool sent, ) = address(exampleExternalContract).call{ value: contractBalance }(abi.encodeWithSignature("complete()")); require(sent, "exampleExternalContract.complete() failed"); } function withdraw() public deadlineReached(true) stakeNotCompleted { uint256 userBalance = balances[msg.sender]; require(userBalance > 0, "You don't have balance to withdraw"); balances[msg.sender] = 0; (bool sent, ) = msg.sender.call{value: userBalance}(""); require(sent, "Failed to send user balance back to the user"); }
  • withdraw函数
  • execute函数
  • stake
• 可以被外部合约调用的函数

代码语言：javascript复制

	receive() external payable {
        stake();
    }

最终代码如下：

代码语言：javascript复制

// SPDX-License-Identifier: MIT
pragma solidity 0.8.4;

import "hardhat/console.sol";
import "./ExampleExternalContract.sol";

contract Staker {
    ExampleExternalContract public exampleExternalContract;

    mapping(address => uint256) public balances;

    uint256 public constant threshold = 1 ether;

    event Stake(address indexed staker, uint256 amount);

    uint256 public deadline = block.timestamp   60 seconds;

    constructor(address exampleExternalContractAddress) public {
        exampleExternalContract = ExampleExternalContract(
            exampleExternalContractAddress
        );
    }

    modifier stakeNotCompleted() {
        bool completed = exampleExternalContract.completed();
        require(!completed, "staking process is already completed");
        _;
    }

    modifier deadlineReached(bool requireReached) {
        uint256 timeRemaining = timeLeft();
        if (requireReached) {
            require(timeRemaining == 0, "deadline is not reached yet");
        } else {
            require(timeRemaining > 0, "deadline has already reached");
        }
        _;
    }

    function timeLeft() public view returns (uint256 timeleft) {
        if (block.timestamp >= deadline) {
            return 0;
        } else {
            return deadline - block.timestamp;
        }
    }

    function stake() public payable deadlineReached(false) stakeNotCompleted {
        balances[msg.sender]  = msg.value;
        emit Stake(msg.sender, msg.value);
    }

    function execute() public stakeNotCompleted deadlineReached(false) {
        uint256 contractBalance = address(this).balance;

        require(contractBalance >= threshold, "Threshold not reached");

        (bool sent, ) = address(exampleExternalContract).call{
            value: contractBalance
        }(abi.encodeWithSignature("complete()"));
        require(sent, "exampleExternalContract.complete() failed");
    }

    function withdraw() public deadlineReached(true) stakeNotCompleted {
        uint256 userBalance = balances[msg.sender];

        require(userBalance > 0, "You don't have balance to withdraw");

        balances[msg.sender] = 0;

        (bool sent, ) = msg.sender.call{value: userBalance}("");
        require(sent, "Failed to send user balance back to the user");
    }

    receive() external payable {
        stake();
    }
}

• 部署

代码语言：javascript复制

yarn deploy --reset

• 测试

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