swap token for usdt, create function send 1 usdt and receive 1 token

Question

I need to create a smart contract where each token of mine will be exchanged for 1 usdt, that is, a person sends 1 usdt to the function and he adds 1 token to his balance sheet. How can I do it? with eth it is simple but usdt is being a challenge for me. Does anyone have an example? How can I test on the ropsten network?

Answer 1

For ERC20 the usual approach is to require the user to approve your contract.

You have to do something like this from the front end.

// USDT parameters
const erc20Token = new web3.eth.Contract(USDT_ABI, USDT_ADDRESS)

// Contract that will receive USDT
const recipient = new web3.eth.Contract(RECIPIENT_ABI, RECIPIENT_ADDRESS)

// Require user approval
await erc20Token.approve(AMOUNT, RECIPIENT_ADDRESS).send({from: USER_ADDRESS})

// Call function on recipient to retrieve USDT
await recipient.deposit(AMOUNT).send({from: USER_ADDRESS})

Smart contract

contract Recipient {
    // USDT token
    IERC20 usdt = IERC20(USDT_ADDRESS);

    // Token to send for USDT
    IERC20 token = IERC20(token);

    function deposit(uint256 amount) public {
        // Transfer amount USDT tokens from msg.sender to contract
        usdt.transferFrom(msg.sender, address(this), amount);

        // Send amount tokens to msg.sender
        token.transfer(msg.sender, amount);
    }
}