Deposit and withdraw ERC20 tokens (USDT, SHIB, MATIC) from a Solidity contract (Hardhat, Ethers.js)

hardhat.config.js

require("@nomiclabs/hardhat-waffle");

/**
 * @type import('hardhat/config').HardhatUserConfig
 */
module.exports = {
  solidity: "0.8.0",
};

package.json

{
  "name": "erc20-bank",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "@nomiclabs/hardhat-ethers": "^2.0.5",
    "@nomiclabs/hardhat-waffle": "^2.0.3",
    "chai": "^4.3.6",
    "ethereum-waffle": "^3.4.0",
    "ethers": "^5.5.4",
    "hardhat": "^2.9.1"
  },
  "dependencies": {
    "@openzeppelin/contracts": "^4.5.0"
  }
}

Staking.js

const { expect } = require("chai");

describe('Staking', function () {
  beforeEach(async function() {
    [owner, wallet1, wallet2] = await ethers.getSigners();

    Staking = await ethers.getContractFactory('Staking', owner);
    Wbtc = await ethers.getContractFactory('Wbtc', wallet1);
    staking = await Staking.deploy();
    wbtc = await Wbtc.deploy();

    wbtc.connect(wallet1).transfer(wallet2.address, 1000);

    await wbtc.connect(wallet1).approve(
      staking.address,
      4000
    );
    await wbtc.connect(wallet2).approve(
      staking.address,
      1000
    );

    WBTC = ethers.utils.formatBytes32String('Wbtc');
    await staking.whitelistToken(
      WBTC,
      wbtc.address
    );
  });

  describe('deployment', function () {
    it('should mint tokens to wallet 1', async function () {
      expect(await wbtc.balanceOf(wallet1.address)).to.equal(4000);
    })

    it('should transfer tokens to wallet 2', async function () {
      expect(await wbtc.balanceOf(wallet2.address)).to.equal(1000);
    })

    it('should whitelist wbtc on the contract', async function () {
      expect(
        await staking.whitelistedTokens(WBTC)
      ).to.equal(wbtc.address);
    })
  })

  describe('depositTokens', function () {
    it('should deposit wbtc', async function () {
      await staking.connect(wallet1).depositTokens(
        100,
        WBTC,
      );
      await staking.connect(wallet2).depositTokens(
        50,
        WBTC,
      );

      expect(await wbtc.balanceOf(wallet1.address)).to.equal(3900);
      expect(await wbtc.balanceOf(wallet2.address)).to.equal(950);

      expect(
        await staking.accountBalances(wallet1.address, WBTC)
      ).to.equal(100);
      expect(
        await staking.accountBalances(wallet2.address, WBTC)
      ).to.equal(50);
    });
  })

  describe('withdraw', function () {
    it('should withdraw wbtc from the contract', async function () {
      await staking.connect(wallet1).depositTokens(
        600,
        WBTC,
      );
      await staking.connect(wallet1).withdrawTokens(
        100,
        WBTC,
      );

      expect(await wbtc.balanceOf(wallet1.address)).to.equal(3500);
      expect(
        await staking.accountBalances(wallet1.address, WBTC)
      ).to.equal(500);
    })

    it('should not allow withdrawing more than has been deposited', async function () {
      await expect(
        staking.connect(wallet1).withdrawTokens(10000, WBTC)
      ).to.be.revertedWith("Insufficent funds")
    })
  })
})

Staking.sol

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

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";

contract Staking {
  address owner;
  mapping(bytes32 => address) public whitelistedTokens;
  mapping(address => mapping(bytes32 => uint256)) public accountBalances;

  constructor() {
    owner = msg.sender;
  }

  function whitelistToken(bytes32 symbol, address tokenAddress) external {
    require(msg.sender == owner, 'This function is not public');

    whitelistedTokens[symbol] = tokenAddress;
  }

  function getWhitelistedTokenAddresses(bytes32 token) external returns(address) {
    return whitelistedTokens[token];
  }

  function depositTokens(uint256 amount, bytes32 symbol) external {
    accountBalances[msg.sender][symbol] += amount;
    ERC20(whitelistedTokens[symbol]).transferFrom(msg.sender, address(this), amount);
  }

  function withdrawTokens(uint256 amount, bytes32 symbol) external {
    require(accountBalances[msg.sender][symbol] >= amount, 'Insufficent funds');

    accountBalances[msg.sender][symbol] -= amount;
    ERC20(whitelistedTokens[symbol]).transfer(msg.sender, amount);
  }
}

Wbtc.sol

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

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";

contract Wbtc is ERC20 {
  constructor() ERC20('WBTC', 'Wrapped BTC') {
    _mint(msg.sender, 5000);
  }
}

Thanks for the tutorial. Where does the address() method come from in line 27 ERC20(whitelistedTokens[symbol]).transferFrom(msg.sender, address(this), amount); in the Staking.sol file?

@wuliwong

Thanks for the tutorial. Where does the address() method come from in line 27 ERC20(whitelistedTokens[symbol]).transferFrom(msg.sender, address(this), amount); in the Staking.sol file?

It's core Solidity

Gas estimation errored with the following message (see below). The transaction execution will likely fail. Do you want to force sending? Internal JSON-RPC error. { "code": 3, "message": "execution reverted: ERC20: transfer amount exceeds allowance", "data": "0x08c379a00000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000002845524332303a207472616e7366657220616d6f756e74206578636565647320616c6c6f77616e6365000000000000000000000000000000000000000000000000" }

I get the above error msg when run the depositTokens function of Staking.sol in remix, did i miss any step? thanks.

@kingerpku

Gas estimation errored with the following message (see below). The transaction execution will likely fail. Do you want to force sending? Internal JSON-RPC error. { "code": 3, "message": "execution reverted: ERC20: transfer amount exceeds allowance", "data": "0x08c379a00000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000002845524332303a207472616e7366657220616d6f756e74206578636565647320616c6c6f77616e6365000000000000000000000000000000000000000000000000" }

I get the above error msg when run the depositTokens function of Staking.sol in remix, did i miss any step? thanks.

It sounds like you need to increase the amount you're approving.
Are you calling .approve?
If yes, try increasing it to a crazy high amount.