How to directly interact with already deployed smart contracts?

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I am tasked with interacting with a function in a smart contract that has already been deployed. I know the contract address and the function signature and I have a solution that uses interfaces. However, this function I am interacting with then sends an NFT to msg.sender which in this case is the contract with the interface solution as opposed to my personal account.

//SPDX-License-Identifier: Unlicense
pragma solidity ^0.8.4;

interface ITargetContract {
    function addWhitelist(bytes32 _something, string memory _id)
        external;
}

contract MyContract {
    function addWhitelist(
        address _t,
        bytes32 _something,
        string memory _id
    ) public {
        ITargetContract(_t).addWhitelist(_something, _id);
    }
}

So to avoid this NFT being sent to my contract, can I interact with the deployed contract directly with my personal account if I only know the contract address and function signature?

nft blockchain smartcontracts solidity ethereum
1 Answers

The only case when msg.sender is relayed is delegatecall. However, it also uses storage of the caller contract (and not of the called one), so it's mostly used in proxy contracts.

There's no way to both relay the msg.sender and use the storage of the called contract.

Assuming the target contract implements the ERC721 standard, you can implement the onERC721Received() function and resend the token to the end user after you've received it.

contract MyContract {
    mapping (string => address) tokenUsers;

    function addWhitelist(
        address _t,
        bytes32 _something,
        string memory _id
    ) public {
        // store the end user address by the token ID
        tokenUsers[_id] = msg.sender;
        ITargetContract(_t).addCandidateIdToWhitelist(_something, _id);
    }

    function onERC721Received(address _operator, address _from, uint256 _tokenId, bytes _data) external returns(bytes4) {
        // resend the token from your contract to the user
        ITargetContract.safeTransferFrom(
            address(this),
            tokenUsers[_tokenId],
            // TODO: transfer functions accept the token ID as uint, not as string
            _stringToUint(_tokenId)
        );
    }
}
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