CODEWITHSUNDEEP
soliditysmartcontractserc20
zach
zach

Reputation: 11

Can a solidity smart contract execute the approve function in an erc20 contract on behalf of the msg.sender

Setting up a bank contract to perform deposits and withdraws. I was wondering if its possible for the bank contract can execute the approve function in the erc20 contract on behalf of the msg.sender for the tokens they are wanting to deposit. Below is my attempt for the bank contract to call the erc20 token contracts approve function. However wouldn't the msg.sender be the bank contract address instead of the original msg.sender (second line of the depositToken function.) This sounds silly but is there a way for the contract to send the request passing in the msg.senders address? If not is there an integrated way for the msg.sender to approve the bank contract address and the amount to enable the bank contract to call the transferFrom function and be provided the allowance.

//best guess on what that would look like inside the function depositTokens
msg.sender = customer;
customer.IER20(usdt).approve.address(this), uint _amount;

address public usdt;
  mapping(address => uint) public bankBalance;
  constructor() public {
      usdt = 0x77c24f0Af71257C0ee26e0E0a108F940D1698d53;
  }
usdt = 0x77c24f0Af71257C0ee26e0E0a108F940D1698d53;
  function depositTokens(uint _amount) public {
      IER20(usdt).approve.address(this), uint _amount;
      // Trasnfer usdt tokens to contract
      IERC20(usdt).transferFrom(msg.sender, address(this), _amount);
      // Update the bank balance in map
      bankBalance[msg.sender] = bankBalance[msg.sender] + _amount;
  }

//approve function in erc20
  function approve(address delegate, uint256 numTokens) public override returns (bool) {
      allowed[msg.sender][delegate] = numTokens;
      emit Approval(msg.sender, delegate, numTokens);
      return true;

Upvotes: 1

Views: 3732

Answers (2)

John Cramer
John Cramer

Reputation: 1

I see a typo in your depositTokens function: IER20 vs IERC20

Upvotes: 0

egjlmn1
egjlmn1

Reputation: 334

The answer is no, the approve function takes the msg.sender as the one that gives allowance. You can see the most used OpenZeppelin implementation here.

However I can see what you are trying to do and I want to add that there is a way to automatically ask an EOA (externally owned account) or a user with a wallet to approve some tokens to the contract before sending a transaction. I don't know if a wallet does it automatically or you have to code it in the UI but I think that is what you are looking for.

And then after the user already approved your bank, you can remove your first line in the deposit function

Upvotes: 0

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