Soulbound NFT migration from v4.9 to v5.0

Smart Contracts
1

I am trying to migrate the current soulbound functionality of my NFT-ERC721 contract from v.4.9. to v5.0. Q:Can you give me a hint on how to ensure the soulbound functionaility in v5.0 ?

On openzeppelin version 4.9. Ive used:

function _beforeTokenTransfer(address from, address to, uint256 firstTokenId, uint256 batchSize) internal override virtual {
  require(from == address(0) || to == address(0), "Token transfer not allowed");
  super._beforeTokenTransfer(from, to, firstTokenId, batchSize);
}

function _afterTokenTransfer(address from, address to, uint256 firstTokenId, uint256 batchSize) internal override virtual {
   if (from == address)) {
       emit Attest(to, firstTokenId);
   } else if ( to == address(0)) {
       emit Revert(to, firstTokenId);
}
    super._afterTokenTransfer(from, to, firstTokenId, batchSize);
}

The new v5.0 introduced the _update function. The documentation (press release?: source) mentions: "In 5.0, token hooks were removed from ERC20, ERC721, and ERC1155, favoring a single _update function. This can also be overridden for custom behaviors in any mint, transfer, or burn operation."

With the example:

image
image1600×928 239 KB

I dont know how to ensure the soulbound functionality, additionally I dont understand the auth functionalitiy by ERC721.

1 Like
2

Hey, I am also stuck in a situation similar to this. Did you get ahead of this blocker, if yes, could you please share how to resolve this?

Thanks!

3

One solution would be to override the transferFrom() method and revert, since starting from v5.0, the safeTransferFrom() method also relies on it under the hood - e.g.:

function transferFrom(address from, address to, uint256 tokenId) public virtual override(ERC721, IERC721) {
  revert ERC721TransferNotAllowed();
}

FYI: have a look at these lines of code.

4

Simply override the _update from ERC721. When a transfer is attempted, the if statement checks if the token has an existing owner (from != address(0) ) and is not being sent to a zero address (to != address(0) ). If both conditions are met, it implies a valid transfer attempt.

In our scenario, the function is configured to fail any transfer attempt to a non-zero address, as indicated by the revert("Soulbound: Transfer failed"); statement. This ensures that transfers will be successful only when directed to the zero address, aligning with the burnable functionality of the token.

In other words, you will have a soulbound token which is burnable.

    /**
     * @dev Internal function to handle token transfers.
     * Restricts the transfer of Soulbound tokens.
     */

    function _update(address to, uint256 tokenId, address auth)
        internal
        override(ERC721, ERC721Pausable)
        returns (address)
    {
        address from = _ownerOf(tokenId);
        if (from != address(0) && to != address(0)) {
            revert("Soulbound: Transfer failed");
        }

        return super._update(to, tokenId, auth);
    }

If you don't want to have a burnable token, you can adjust the conditions so that a mint is enabled but any other transfer fails.

    if (from != address(0)) {
        revert("Soulbound: Transfer failed");  // Prevent all transfers, making the token soulbound and non-burnable
    }
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