Question

我是区块链技术的新手。我正在关注 Dapp 大学教程，当我尝试测试 sellTokens 函数时，它给了我“错误：返回错误：处理交易时出现 VM 异常：还原”。我想我已经成功实现了批准功能，为什么它会显示以下错误以下是审查项目所需的文件 Ethswap.sol

pragma solidity ^0.5.0;

import "./Token.sol";

contract Ethswap {
    string public name = "Ethswap Instant Exchange";
    Token public token;
    uint public rate = 100;

    event TokenPurchased(
    address account,
    address token,
    uint amount,
    uint rate
    );

    event TokenSold(
    address account,
    address token,
    uint amount,
    uint rate
    );

    constructor(Token _token) public {
        token = _token;
    }

    function buytokens() public payable {
         // Calculate the no of tokens to buy
        uint tokenAmount = msg.value * rate;

        // require Ethswap has enough balance to perform transfer of tokens
        require(token.balanceOf(address(this)) >= tokenAmount);

        token.transfer(msg.sender, tokenAmount);

        // Emit an event
        emit TokenPurchased(msg.sender, address(token), tokenAmount, rate);
    }
    
    function sellTokens(uint256 _amount) public payable {
        //Calculate amoutn of ether to redeem
        uint etherAmount = _amount / rate;

        // require Ethswap has enough ether to perform transfer
        require(address(this).balance >= etherAmount);

        //Perform Sale
        token.transferFrom(msg.sender, address(this), _amount);
        msg.sender.transfer(etherAmount);

        //Emit an event
        emit TokenSold(msg.sender, address(token), _amount, rate);
    }
}

以下是Dapp Token的智能合约代码 Token.sol

pragma solidity ^0.5.0;

contract Token {
    string  public name = "DApp Token";
    string  public symbol = "DAPP";
    uint256 public totalSupply = 1000000000000000000000000; // 1 million tokens
    uint8   public decimals = 18;

    event Transfer(
        address indexed _from,
        address indexed _to,
        uint256 _value
    );

    event Approval(
        address indexed _owner,
        address indexed _spender,
        uint256 _value
    );

    mapping(address => uint256) public balanceOf;
    mapping(address => mapping(address => uint256)) public allowance;

    constructor() public {
        balanceOf[msg.sender] = totalSupply;
    }

    function transfer(address _to, uint256 _value) public returns (bool success) {
        require(balanceOf[msg.sender] >= _value);
        balanceOf[msg.sender] -= _value;
        balanceOf[_to] += _value;
        emit Transfer(msg.sender, _to, _value);
        return true;
    }

    function approve(address _spender, uint256 _value) public returns (bool success) {
        allowance[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value);
        return true;
    }

    function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
        require(_value <= balanceOf[_from]);
        require(_value <= allowance[_from][msg.sender]);
        balanceOf[_from] -= _value;
        balanceOf[_to] += _value;
        allowance[_from][msg.sender] -= _value;
        emit Transfer(_from, _to, _value);
        return true;
    }
}

以下是测试智能合约的测试javascript代码 Ethswap.test.js

列表项

const { assert } = require("chai")
const { default: Web3 } = require("web3")

const Token = artifacts.require("Token")
const Ethswap = artifacts.require("Ethswap")

require("chai")
  .use(require("chai-as-promised"))
  .should()

function tokens(n) {
  return web3.utils.toWei(n, "ether")
}

contract("Ethswap", ([deployer, investor]) => {
  let token
  let ethSwap

  before(async () => {
    token = await Token.new()
    ethSwap = await Ethswap.new(token.address)
    await token.transfer(ethSwap.address, tokens("1000000"))
  })

  describe("Token Deployment", async () => {
    it("contract has a name", async () => {
      let token = await Token.new()
      const name = await token.name()
      assert.equal(name, "DApp Token")
    })
  })

  describe("EthSwap Deployment", async () => {
    it("contract has a name", async () => {
      let ethSwap = await Ethswap.new(token.address)
      const name = await ethSwap.name()
      assert.equal(name, "Ethswap Instant Exchange")
    })

    it("contract has tokens", async () => {
      let balance = await token.balanceOf(ethSwap.address)
      assert.equal(balance.toString(), tokens("1000000"))
    })
  })

  describe("TokenPurchased", async () => {
    it("Details of the investor", async () => {
      let result

      before(async () => {
        result = await ethSwap.buytokens({from: investor, value: web3.utils.toWei("1", "ether"),
        })

        //Check investor token balance after purchase
        let investorBalance = await token.balanceOf(investor)
        assert.equal(investorBalance.toString(), token("100"))

        //Check ethswap balance after purchase
        let ethSwapBalance;
        ethSwapBalance = await token.balanceOf(ethSwap.address)
        assert.equal(ethSwapBalance.toString(), tokens("999900"))
        ethSwapBalance = await web3.eth.getBalance(ethSwap.address)
        assert.equal(ethSwapBalance.toString(), web3.utils.toWei("1", "Ether"))

        const event = result.logs[0].args
        assert.equal(event.account, investor)
        assert.equal(event.token, token.address)
        assert.equal(event.amount.toString(), tokens("100").toString())
        assert.equal(event.rate.toString(), "100")
      })
    })
  })

  describe("SellTokens()", async () => {
    let result

    before(async () => {
      //Investor must approve token before purchase
      await token.approve(ethSwap.address, tokens('100'))
      // Investor sells token
      result = await ethSwap.sellTokens(tokens('100'), { from : investor })
    })
    it("Allows user to instantly sell tokens", async () => {})
  })
})

“错误：返回错误：处理事务时出现 VM 异常：还原”

0 个答案: