Solidity合约添加Uniswap流动性报错，如何实现代币兑ETH？

用户开发的Solidity合约中，调用swapTokensForEthAndAddLiquidity时出现Gas估算错误，控制台提示insufficient liquidity，无法完成代币兑换与流动性添加操作。

错误原因分析 #

1. 资金流向错误：swapExactTokensForETH的接收地址设为msg.sender，兑换得到的ETH直接转给了用户，合约账户没有ETH储备用于后续的流动性添加。
2. 代币余额不足：swap操作已经将用户的代币全部兑换为ETH，后续调用addLiquidityETH时传入的tokenAmount是初始代币数量，但此时合约内已无足够代币，导致流动性添加失败。
3. 授权逻辑错误：_approve(address(this), address(uniswapRouter), tokenAmount)是让合约自己授权Router使用代币，但用户的代币还在自己账户，Router无法直接转移用户的代币。

修正后的合约代码 #

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

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/security/ReentrancyGuard.sol";
import "@uniswap/v2-periphery/contracts/interfaces/IUniswapV2Router02.sol";
import "@uniswap/v2-core/contracts/interfaces/IUniswapV2Factory.sol";

contract YourToken is ERC20, Ownable, ReentrancyGuard {
    IUniswapV2Router02 public uniswapRouter;
    address public uniswapPair;

    event TokensSwappedForEth(uint256 tokenAmount, uint256 ethAmount);
    event LiquidityAdded(uint256 tokenAmount, uint256 ethAmount, uint256 liquidityTokens);
    event TokensMinted(address indexed account, uint256 amount);

    constructor(address _uniswapRouter) ERC20("Infuraa Token", "INXT") Ownable(msg.sender) {
        uniswapRouter = IUniswapV2Router02(_uniswapRouter);
        uniswapPair = IUniswapV2Factory(uniswapRouter.factory()).createPair(address(this), uniswapRouter.WETH());
        _mint(msg.sender, 980 * 10**12 * 10**18);
    }

    // 用户将代币兑换为ETH（前提是LP池已有流动性）
    function swapTokensForEth(uint256 tokenAmount) external nonReentrant {
        require(balanceOf(msg.sender) >= tokenAmount, "Insufficient balance");
        
        // 用户需先在前端调用approve授权Router使用自己的代币
        address[] memory path = new address[](2);
        path[0] = address(this);
        path[1] = uniswapRouter.WETH();

        uniswapRouter.swapExactTokensForETH(
            tokenAmount,
            1, // 设置最小接收ETH数量，防止滑点过大
            path,
            msg.sender,
            block.timestamp + 300 // 延长过期时间，避免交易超时
        );

        emit TokensSwappedForEth(tokenAmount, address(msg.sender).balance);
    }

    // 用户添加代币+ETH到Uniswap流动性池
    function addLiquidity(uint256 tokenAmount) external payable nonReentrant {
        require(balanceOf(msg.sender) >= tokenAmount, "Insufficient token balance");
        require(msg.value > 0, "ETH amount cannot be zero");

        // 转移用户的代币到合约，再授权Router使用
        _transfer(msg.sender, address(this), tokenAmount);
        _approve(address(this), address(uniswapRouter), tokenAmount);

        (uint256 tokenAdded, uint256 ethAdded, uint256 liquidity) = uniswapRouter.addLiquidityETH{value: msg.value}(
            address(this),
            tokenAmount,
            tokenAmount * 95 / 100, // 5%滑点容忍度
            msg.value * 95 / 100,
            msg.sender,
            block.timestamp + 300
        );

        emit LiquidityAdded(tokenAdded, ethAdded, liquidity);
    }

    // 合约所有者初始化流动性池（首次添加流动性）
    function initLiquidity(uint256 tokenAmount) external payable onlyOwner nonReentrant {
        require(balanceOf(msg.sender) >= tokenAmount, "Owner insufficient token balance");
        require(msg.value > 0, "ETH amount cannot be zero");

        _transfer(msg.sender, address(this), tokenAmount);
        _approve(address(this), address(uniswapRouter), tokenAmount);

        (uint256 tokenAdded, uint256 ethAdded, uint256 liquidity) = uniswapRouter.addLiquidityETH{value: msg.value}(
            address(this),
            tokenAmount,
            tokenAmount * 95 / 100,
            msg.value * 95 / 100,
            msg.sender,
            block.timestamp + 300
        );

        emit LiquidityAdded(tokenAdded, ethAdded, liquidity);
    }

    // 更新Uniswap Router地址
    function setUniswapRouter(address _uniswapRouter) external onlyOwner {
        uniswapRouter = IUniswapV2Router02(_uniswapRouter);
        address pair = IUniswapV2Factory(uniswapRouter.factory()).getPair(address(this), uniswapRouter.WETH());
        uniswapPair = pair == address(0) ? IUniswapV2Factory(uniswapRouter.factory()).createPair(address(this), uniswapRouter.WETH()) : pair;
    }

    // 铸造代币（仅所有者）
    function mint(address account, uint256 amount) external onlyOwner {
        _mint(account, amount);
        emit TokensMinted(account, amount);
    }

    receive() external payable {}
}

关键修改说明 #

• 拆分功能：将原函数拆分为swapTokensForEth（代币换ETH）和addLiquidity（添加流动性）两个独立函数，逻辑更清晰，符合Uniswap的使用流程。
• 修正资金流向：兑换ETH时直接转给用户，添加流动性时由用户通过msg.value传入ETH，确保合约有足够的ETH用于流动性添加。
• 授权逻辑修正：通过_transfer将用户代币转移到合约后，再授权Router使用，确保Router有足够的代币权限。
• 滑点与超时优化：设置5%的滑点容忍度和5分钟的交易过期时间，避免因市场波动导致交易失败。
• 初始化流动性：新增initLiquidity函数，由合约所有者首次添加流动性，为用户兑换提供基础储备。

内容的提问来源于stack exchange，提问作者Kellen Rippin