BSC网络使用BUSD铸造NFT支付失败问题排查与修复

我正在学习智能合约，目前使用Remix在BSC网络开发NFT铸造功能（该网络与ETH一样采用18位小数）。已实现免费铸造及BNB等原生代币支付的铸造功能，但尝试使用BUSD支付铸造时，虽能通过balanceOf查询到正确余额，执行铸造却触发报错：

Gas estimation errored with the following message (see below). The transaction execution will likely fail. Do you want to force sending?
Returned error: {"jsonrpc":"2.0","error":"execution reverted","id":5075618818565261}

测试合约代码如下：

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
import "@openzeppelin/contracts/utils/Counters.sol";
import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/token/ERC721/extensions/ERC721URIStorage.sol";
import "@openzeppelin/contracts/token/ERC20/ERC20.sol";

contract MyNFT is ERC721URIStorage, Ownable {

    using Counters for Counters.Counter;
    Counters.Counter private _tokenIds;

    ERC20 public _token; // Referencja do ERC20 tokenu
    uint256 public _mintingFee = 1e18; // Opłata za mintowanie NFT
    address tokenAddress = 0xeB3Eb991D39Dac92616da64b7c6D5af5cCFf1627;

    struct NFT {
        string collectionName;
    }

    mapping(uint256 => NFT) private _nfts;

    constructor(uint256 mintingFee) ERC721("MyNFT", "NFT") {
        _token = ERC20(tokenAddress);
        _mintingFee = mintingFee * 1e18;
    }

    function showBUSD() 
        public view 
        returns (uint256)
    {
        return _token.balanceOf(msg.sender);
    }

    function mintNFT(address recipient, string memory tokenURI, string memory _collectionName)
        public onlyOwner 
        returns (uint256)
    {   
        //require(msg.value >= _mintingFee, "Insufficient BNB amount");
        require(_token.balanceOf(msg.sender) >= _mintingFee, "Insufficient balance");
        //require(_token.allowance(msg.sender, address(this)) >= _mintingFee, "Insufficient allowance");
        
        _token.transferFrom(msg.sender, address(this), _mintingFee);
        
        _tokenIds.increment();

        uint256 newItemId = _tokenIds.current();
        _mint(recipient, newItemId);
        _nfts[newItemId].collectionName = _collectionName;
        _setTokenURI(newItemId, tokenURI);

        /*if (msg.value > _mintingFee) {
            payable(msg.sender).transfer(msg.value - _mintingFee);
        }*/

        return newItemId;
    }

    function getCollectionName(uint256 tokenId) 
        public view 
        returns (string memory) 
    {
        return _nfts[tokenId].collectionName;
    }

    function setMintingFee(uint256 newFee) 
        external onlyOwner 
    {
        _mintingFee = newFee * 1e18;
    }
}

问题出在以下几个点，对应修复步骤如下：

• 恢复授权检查逻辑
  ERC20的transferFrom要求用户必须先给合约授权足够的代币额度，即使余额充足，没有授权的话transferFrom会直接触发 revert。取消注释require(_token.allowance(msg.sender, address(this)) >= _mintingFee, "Insufficient allowance");这行代码，确保用户已授权合约转移指定数量的BUSD。

• 检查ERC20转账返回值
  包括BUSD在内的部分ERC20代币，transferFrom会返回布尔值表示操作成功，但当前代码未检查该返回值。如果转账失败，合约会因返回值不匹配而 revert。将_token.transferFrom(msg.sender, address(this), _mintingFee);替换为：

  bool success = _token.transferFrom(msg.sender, address(this), _mintingFee);
  require(success, "BUSD transfer failed");
  

• 补充前端授权操作
  在调用mintNFT之前，必须先调用BUSD合约的approve方法，授权你的NFT合约转移_mintingFee数量的BUSD。比如在Remix中，先切换到BUSD合约地址，调用approve，参数填入NFT合约地址和铸造费用（注意保留18位小数），之后再执行mintNFT。

• 可选：用SafeERC20增强安全性
  导入@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol，使用SafeERC20.safeTransferFrom代替原生transferFrom，它会自动检查返回值并处理异常。修改后核心代码如下：

  import "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";
  
  contract MyNFT is ERC721URIStorage, Ownable {
      using SafeERC20 for ERC20;
      
      // ...其他代码
      function mintNFT(...) public onlyOwner returns (uint256) {
          // ...余额和授权检查
          _token.safeTransferFrom(msg.sender, address(this), _mintingFee);
          // ...其他铸造逻辑
      }
  }
  

内容的提问来源于stack exchange，提问作者Wraith