Deposit USDC to smart contract

Smart Contracts
1

I change DaiToken address to an polygon testnet usdc token address (0xe11A86849d99F524cAC3E7A0Ec1241828e332C62) but the function is not working.

End goal

  1. deposit USDC to contract
  2. withdraw USDC after I deposit it on step 1
pragma solidity ^0.5.0;

interface DaiToken {
    function transfer(address dst, uint wad) external returns (bool);
    function transferFrom(address src, address dst, uint wad) external returns (bool);
    function balanceOf(address guy) external view returns (uint);
}

contract TokenFarm {
    DaiToken public daiToken;
    address owner;
    mapping(address => uint) public stakingBalance;

    /*
       Kovan DAI: 0x4F96Fe3b7A6Cf9725f59d353F723c1bDb64CA6Aa
    */
    constructor() public {
        daiToken = DaiToken(0x4F96Fe3b7A6Cf9725f59d353F723c1bDb64CA6Aa);
        owner = msg.sender;
    }

    function stakeTokens(uint _amount) public {

        // amount should be > 0
        require(_amount > 0, "amount should be > 0");

        // transfer Dai to this contract for staking
        daiToken.transferFrom(msg.sender, address(this), _amount);
        
        // update staking balance
        stakingBalance[msg.sender] = stakingBalance[msg.sender] + _amount;
    }

    // Unstaking Tokens (Withdraw)
    function unstakeTokens() public {
        uint balance = stakingBalance[msg.sender];

        // balance should be > 0
        require (balance > 0, "staking balance cannot be 0");

        // Transfer Mock Dai tokens to this contract for staking
        daiToken.transfer(msg.sender, balance);

        // reset staking balance to 0
        stakingBalance[msg.sender] = 0;
    }
}
2

You will need to let the USDC/DAI token contract approve this contract, because this contract will move funds on the msg.sender's behalf either from the wallet to this contract or from this contract to the wallet.

3

Thanks I am a newbie to this how could it perform the approve on usdc contract?

4

The USDC or DAI contract is also an ERC20 contract. You can call the approve function on those contracts.

5

I face an error when I use stakeTokens function. error: Internal JSON-RPC error. { "code": -32000, "message": "execution reverted" }

I changed my code as below:

// SPDX-License-Identifier: GPL-3.0
pragma solidity ^0.8.0;

import "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";

contract TokenFarm {
    IERC20 public daiToken;
    address owner;
    mapping(address => uint) public stakingBalance;

    /*
       Kovan DAI: 0x4F96Fe3b7A6Cf9725f59d353F723c1bDb64CA6Aa
    */
    constructor()  {
        daiToken = IERC20(0x4F96Fe3b7A6Cf9725f59d353F723c1bDb64CA6Aa);
        owner = msg.sender;
    }

    function stakeTokens(uint _amount) public {

        // amount should be > 0
        require(_amount > 0, "amount should be > 0");

        daiToken.approve(0x4F96Fe3b7A6Cf9725f59d353F723c1bDb64CA6Aa,  _amount);

        // transfer Dai to this contract for staking
        daiToken.transferFrom(msg.sender, address(this), _amount);
        
        // update staking balance
        stakingBalance[msg.sender] = stakingBalance[msg.sender] + _amount;
    }

    // Unstaking Tokens (Withdraw)
    function unstakeTokens() public {
        uint balance = stakingBalance[msg.sender];

        // balance should be > 0
        require (balance > 0, "staking balance cannot be 0");

        // Transfer Mock Dai tokens to this contract for staking
        daiToken.transfer(msg.sender, balance);

        // reset staking balance to 0
        stakingBalance[msg.sender] = 0;
    }
}
6

In this code, it is this contract approving 0x4F96Fe3b7A6Cf9725f59d353F723c1bDb64CA6Aa, but I think in your original logic, it should be the msg.sender approving this contract on USDC/DAI contract.

The approval by msg.sender on this contract happens on USDC/DAI contracts. They do not need to be written in this contract. It's a separate manual operation.

7

You need to approve dai for this contract to transfer it outside of contract before calling stakeTokens function.