How to transfer a NFT to another smart contract?

Question

I am trying to setup an escrow contract which takes a deposit as a NFT into the contract. I am struggling to deposit the NFT into the contract.

I start by having a simple NFT that gets minted to the address with an id.

contract MyEpicNFT is ERC721URIStorage {
  // Magic given to us by OpenZeppelin to help us keep track of tokenIds.
  using Counters for Counters.Counter;
  Counters.Counter private _tokenIds;

  // We need to pass the name of our NFTs token and its symbol.
  constructor() ERC721 ("SquareNFT", "SQUARE") {
    console.log("This is my NFT contract. Woah!");
    console.log(address(this));
  }

  // A function our user will hit to get their NFT.
  function makeNft() public {
    uint256 newItemId = _tokenIds.current();

    _safeMint(msg.sender, newItemId);

    _setTokenURI(newItemId, "https://jsonkeeper.com/b/1LHH");
    console.log("An NFT w/ ID %s has been minted to %s", newItemId, msg.sender);


    _tokenIds.increment();
  }
}

An NFT w/ ID 0 has been minted to the msg.sender of the contract in this case: 0xdD870fA1b7C4700F2BD7f44238821C26f7392148

I know now I need to approve the Escrow contract to be allowed to "spend" this token. To do this on MyEpicNft contract I call the approve function with the contract address of the MyEpicNft and the Id of the NFT that was minted.

console.log:
 This is my NFT contract. Woah!
 0x5fc7Dc95b4Bb48dbC9894fCaE417482cb8A6A45a

In my case I call the approve with (0x5fc7Dc95b4Bb48dbC9894fCaE417482cb8A6A45a, 0) - this seems to work. Now what I need to do in the NftEscrow contract is to deposit the NFT.

The approve function i am using is from the ERC721 lib

approve(address to, uint256 tokenId)

There is a depositNFT function which takes the NFT address - in our case 0x5fc7Dc95b4Bb48dbC9894fCaE417482cb8A6A45a and 0. But when i do this i get the error message:

The transaction has been reverted to the initial state.
Reason provided by the contract: "ERC721: transfer caller is not owner nor approved".
Debug the transaction to get more information.


contract NftEscrow is IERC721Receiver {
    
    enum ProjectState {newEscrow, nftDeposited, cancelNFT, ethDeposited, canceledBeforeDelivery, deliveryInitiated, delivered}
    
    address payable public sellerAddress;
    address payable public buyerAddress;
    address public nftAddress;
    uint256 tokenID;
    bool buyerCancel = false;
    bool sellerCancel = false;
    ProjectState public projectState;

    receive() external payable {
    
     }

    constructor(){
        sellerAddress = payable(msg.sender);
        projectState = ProjectState.newEscrow;
    }
    
    function onERC721Received( address , address , uint256 , bytes calldata  ) public pure override returns (bytes4) {
        return this.onERC721Received.selector;
    }
    
    function depositNFT(address _NFTAddress, uint256 _TokenID) public onlySeller {
        nftAddress = _NFTAddress;
        tokenID = _TokenID;
        ERC721(nftAddress).safeTransferFrom(msg.sender, address(this), tokenID);
        projectState = ProjectState.nftDeposited;
    }

    function depositEth() public payable {
        buyerAddress = payable(msg.sender);
        projectState = ProjectState.ethDeposited;
    }

    function confirmDelivery()public payable  {
        ERC721(nftAddress).safeTransferFrom(address(this), buyerAddress, tokenID);
        sellerAddress.transfer(address(this).balance);
    }
    

    modifier onlySeller() {
        require(msg.sender == sellerAddress);
        _;
    }

}

Not sure what I am doing wrong and been stuck on this for a day. Why can't i deposit the NFT to the smart contract?

keser · Accepted Answer · 2022-03-29T18:27:27.897

1

Your escrow contract will revert with "ERC721: transfer caller is not owner nor approved" if none of the following are true:

msg.sender is the owner of contract
msg.sender is approved for all for the owner
msg.sender is approved for that token by the owner

In your situation, we are opting for the 3rd option.

What we need to check is

Did you really approve correct address?
Did approve function revert?

When the escrow contract calls the NFT contract

ERC721(nftAddress).safeTransferFrom(msg.sender, address(this), tokenID);

in NFT contract's point of view, the msg.sender is the escrow contract. So the problem is 99% with your approval process. Please share more information about that.

EDIT:

We are trying to get the following condition true, where the spender is the escrow contract's adress

return (spender == owner || isApprovedForAll(owner, spender) || getApproved(tokenId) == spender);

If getApproved is really returns the contract address, try adding following function to your nft contract:

    /**
     * @dev Returns whether `spender` is allowed to manage `tokenId`.
     *
     * Requirements:
     *
     * - `tokenId` must exist.
     */
    function _isApprovedOrOwner(address spender, uint256 tokenId) internal view virtual override returns (bool) {
        require(_exists(tokenId), "ERC721: operator query for nonexistent token");
        address owner = ERC721.ownerOf(tokenId);
        console.log("spender %s", spender);
        console.log("getApproved %s", getApproved(tokenId);
        return (spender == owner || isApprovedForAll(owner, spender) || getApproved(tokenId) == spender);
    }

edited Mar 29 '22 at 18:27

answered Mar 29 '22 at 17:52

keser

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I am simply using the ERC721 approve function which takes the NFT contract address and the token id? https://docs.openzeppelin.com/contracts/2.x/api/token/erc721#IERC721-approve-address-uint256- – marcuspetty Mar 29 '22 at 18:04
what does it say when you call `getApproved(0)` – keser Mar 29 '22 at 18:06
I get the address of the contract of the NFT : – marcuspetty Mar 29 '22 at 18:19
``` constructor() ERC721 ("SquareNFT", "SQUARE") { console.log("This is my NFT contract. Woah!"); console.log(address(this)); } ``` which is address(this) – marcuspetty Mar 29 '22 at 18:19
@marcuspetty edited, please check – keser Mar 29 '22 at 18:27
getApproved is correct - but spender is an address i do not recognise ? – marcuspetty Mar 29 '22 at 18:44
it must be your own address that you are calling escrow with – keser Mar 29 '22 at 18:53
Im using remix and it is none of the addresses on the account? even made a getMessageSender function and that returns the correct address ? Any ideas ? – marcuspetty Mar 29 '22 at 19:11
Let us [continue this discussion in chat](https://chat.stackoverflow.com/rooms/243419/discussion-between-keser-and-marcuspetty). – keser Mar 29 '22 at 19:13
Please I need to know how @keser help solve the problem as I am facing same problem right now. – Jaylukmann Jun 20 '22 at 23:42

How to transfer a NFT to another smart contract?

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