错误：返回的错误：处理事务时的VM异常：还原

如何解决错误：返回的错误：处理事务时的VM异常：还原

我有一个合同 GetNewToken ，该合同收到 OldToken ，并通过 buyTokens

功能提供了 NewToken >

// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

import './NewToken.sol';
import './OldToken.sol';
import "@openzeppelin/contracts/token/ERC20/ERC20.sol";

contract GetNewToken {

    string  public name = "Get New Token Contract";
    address public owner;
    NewToken public newToken;
    OldToken public oldToken;

    event Bought(address buyer,uint256 amount);
    event TransferFromFailed(uint256 amount);
    
    constructor(NewToken _newToken,OldToken _oldToken) public {
        newToken = _newToken;
        oldToken = _oldToken;
        owner = msg.sender;
    }

    function buyTokens(uint256 _amount) public {
        require(_amount > 0,"amount can not be 0");
        uint256 userBalance = oldToken.balanceOf(msg.sender);

        require(userBalance >= _amount,"Not enough Old Token in your account");
        bool success = oldToken.transferFrom(msg.sender,address(this),_amount);

        if(success) {
            uint256 newBalance = newToken.balanceOf(address(this));
            require(_amount <= newBalance,"Not enough New Tokens in the contract");
            newToken.transfer(msg.sender,_amount);
            emit Bought(msg.sender,_amount);
        } else {
            emit TransferFromFailed(_amount);
            revert("oldToken.transferFrom function failed");
        }

    }
}

OldTokens 和 NewTokens 是标准的ERC20实现。其中之一如下所示（其他名称和名称完全相同）

// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

contract OldToken {
    string  public name = "Old Token";
    string  public symbol = "OLDT";
    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,_value);
        return true;
    }
}

2_deployed_token.js 如下所示。它还将一些 NewToken 转移到 GetNewToken 合同，并将一些 OldToken 转移到帐户[1]，然后将其用于调用 buyTokens 函数。


const NewToken = artifacts.require("NewToken");
const OldToken = artifacts.require("OldToken");
const GetNewToken = artifacts.require("GetNewToken");

module.exports = async function(deployer,network,accounts) {
    await deployer.deploy(NewToken);
    const newToken = await NewToken.deployed();

    await deployer.deploy(OldToken);
    const oldToken = await OldToken.deployed();

    await deployer.deploy(GetNewToken,newToken.address,oldToken.address);
    const getNewToken = await GetNewToken.deployed();

    await newToken.transfer(GetNewToken.address,"1000000000000000000000"); // 1000 tokens
    await oldToken.transfer(accounts[1],"1000000000000000000000"); // 1000 tokens
};

truffle-config.js 如下：

module.exports = {
  networks: {
    development: {
      host: "127.0.0.1",port: 7545,network_id: "*"
    }
  },contracts_directory: './contracts/',contracts_build_directory: './abis/',compilers: {
    solc: {
      version: "0.6.2",optimizer: {
        enabled: true,runs: 200
      },evmVersion: "petersburg"
    }
  }
};

现在编译和迁移工作正常（我使用ganache作为本地区块链）：

truffle compile
truffle migrate --reset

地址如下（以ganache为单位）：旧令牌 0xaA47e5555db895b230A16AF6860bf5DF442C7dB9

NewToken 0x43C68Efa858a9eA2F2DdD4e1AbDeA90a96f5C56E

GetNewToken 0x4b4a5d3Ad0ed472876e50FB0daa6ED2FA78488e2

以下是在松露控制台中执行的步骤：

NewToken.deployed().then(function(instance){newToken = instance})
OldToken.deployed().then(function(instance){oldToken = instance})

GetNewToken.deployed(newToken,oldToken).then(function(instance){return instance.buyTokens('1000000000000000000',{from:accounts[1]});});

然后返回错误：

Uncaught Error: Returned error: VM Exception while processing transaction: revert
    at evalmachine.<anonymous>:0:75
    at processTicksAndRejections (internal/process/task_queues.js:93:5) {
  hijackedStack: 'Error: Returned error: VM Exception while processing transaction: revert\n' +
    '    at Object.ErrorResponse (/usr/local/lib/node_modules/truffle/build/webpack:/node_modules/web3-core-helpers/src/errors.js:29:1)\n' +
    '    at /usr/local/lib/node_modules/truffle/build/webpack:/node_modules/web3-core-requestmanager/src/index.js:140:1\n' +
    '    at /usr/local/lib/node_modules/truffle/build/webpack:/packages/provider/wrapper.js:112:1\n' +
    '    at XMLHttpRequest.request.onreadystatechange (/usr/local/lib/node_modules/truffle/build/webpack:/node_modules/web3-providers-http/src/index.js:96:1)\n' +
    '    at XMLHttpRequestEventTarget.dispatchEvent (/usr/local/lib/node_modules/truffle/build/webpack:/node_modules/xhr2-cookies/dist/xml-http-request-event-target.js:34:1)\n' +
    '    at XMLHttpRequest._setReadyState (/usr/local/lib/node_modules/truffle/build/webpack:/node_modules/xhr2-cookies/dist/xml-http-request.js:208:1)\n' +
    '    at XMLHttpRequest._onHttpResponseEnd (/usr/local/lib/node_modules/truffle/build/webpack:/node_modules/xhr2-cookies/dist/xml-http-request.js:318:1)\n' +
    '    at IncomingMessage.<anonymous> (/usr/local/lib/node_modules/truffle/build/webpack:/node_modules/xhr2-cookies/dist/xml-http-request.js:289:47)\n' +
    '    at IncomingMessage.emit (events.js:326:22)\n' +
    '    at IncomingMessage.EventEmitter.emit (domain.js:548:15)\n' +
    '    at endReadableNT (_stream_readable.js:1252:12)\n' +
    '    at processTicksAndRejections (internal/process/task_queues.js:80:21)'

使用 truffle debug 0xdf7af41dd709d19a75b497c25cde854328ea50176c35c6661416a316c382d9ad 调试交易哈希，然后按 o 突出显示 GetNewToken 函数 buyTokens

debug(development:0xdf7af41d...)> o

Transaction halted with a RUNTIME ERROR.

There was no revert message.  This may be due to an in intentional halting expression,such as assert(),revert(),or require(),or could be due to an unintentional exception such as out-of-gas exceptions.
Please inspect your transaction parameters and contract code to determine the meaning of this error.

Stacktrace:
Error: Revert or exceptional halt
  at unknown function [address 0xaA47e5555db895b230A16AF6860bf5DF442C7dB9] (/Users/someuser/projects/project-folder/contracts/GetNewToken.sol:40:24)
  at GetNewToken.buyTokens [address 0x4b4a5d3Ad0ed472876e50FB0daa6ED2FA78488e2] (/Users/someuser/projects/project-folder/contracts/GetNewToken.sol:40:24)
  at GetNewToken [address 0x4b4a5d3Ad0ed472876e50FB0daa6ED2FA78488e2] (/Users/someuser/projects/project-folder/contracts/GetNewToken.sol:27:5)

Location of error:

GetNewToken.sol:
         
40:         bool success = oldToken.transferFrom(msg.sender,_amount);
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 

debug(development:0xdf7af41d...)> o
Transaction has halted; cannot advance.

请忽略行号，因为GetNewToken.sol文件中的注释很少

为什么我不能使用transferFrom？帐户[1]已经具有OldTokens（根据迁移）。
此外，当我使用松露控制台时

truffle(development)> OldToken.deployed().then(function(instance){oldToken = instance})
truffle(development)> let a = oldToken.balanceOf(accounts[1])
undefined
truffle(development)> a
BN {
  negative: 0,words: [ 44040192,40595831,222044,<1 empty item> ],length: 3,red: null
}

为什么我没有得到1000000000000000000000（根据迁移脚本）？

谢谢！

错误：返回的错误：处理事务时的VM异常：还原

如何解决错误：返回的错误：处理事务时的VM异常：还原

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