NFT: how to improve rentable NFT (erc-4907)

NFT： How to improve the leasable NFT (ERC-4907)

NFT It is not only the encryption guarantee of image ownership . With the same technical support , Things will depend on how we work 、 Change through interaction .

What is said here is practical NFT, They give the owner some privileges 、 Rights or rewards .

for example , In the field of games , practical NFT Provides a new way to manage in-game asset ownership , Or in social space , They help ensure that users can safely enter their own communities .

Another use case might be bound to “ Rentable smart physical assets ”( For example, lockers 、 Vacation home or car ) The associated NFT, Proving that he is NFT After the current owner of , Users can send commands to it （ for example “ To lock the door ”、“ Unlock the door ”）.

Speaking of practicality NFT, In some cases , Owners and users are not always the same .NFT The owner of can rent it to users for a period of time . in the meantime , The user has temporarily obtained NFT Privileges granted , But its ownership cannot be transferred .

The most advanced technology

Now there is one for rentable NFT Of EIP（EIP- 4907）, It points out that ：

“ The standard is EIP-721 An extension of . It proposes an additional role that can grant addresses （ user ）, And the role is automatically revoked （ expire ） Time for . User role representatives “ Use ”NFT Authority , But it doesn't mean transferring or setting the user's ability .

This standard is intended to be compatible with ERC-721 Fully compatible with , And basically, an interface is introduced to realize （IERC4907.sol）, The method is as follows ：

function setUser(uint256 tokenId, address user, uint64 expires)

If the caller is NFT The owner of or has been granted an address , Then this method can set new users and NFT The expiration date of .

function userOf(uint256 tokenId) external view returns(address);

This returns NFT The address of the current user , Zero address means there are no users or the lease term has expired .

function userExpires(uint256 tokenId) external view returns(uint256);

The last method returns NFT Expiration time of the user , among 0 Indicates that there are no users .

in the meantime , We will notice how the contract is extended ERC721 The standard , And will also notice the use NFT Mapping with its end users and expiration time .

contract ERC4907 is ERC721, IERC4907 {
  struct UserInfo
  {
    address user; // address of user role
    uint64 expires; // unix timestamp, user expires
  }
  mapping (uint256 => UserInfo) internal _users;
  …

Possible improvements

“ If EIP The title is Rental NFT, What then? IERC4907 Or the reference implementation lacks one “ lease ” Methods? ”?

There is one setUser Method , But when using it , Only NFT Owner ( Or an approved address ) You can set the user . In this case , This process sounds more like a loan process , Owners will work with utilities NFT The bound privileges are lent to the user , Besides , And pay for it gas cost .

My idea is similar to :

ad locum , The owner can choose ：

• Put him NFT Set to leasable .
• Set to rent him for a period of time NFT Number of ethers required .

If NFT Listed as leasable , Users can rent it , And pay the owner for this .

Want to rent NFT The user of must send a transaction to the contract , Specify what he wants to rent NFT And the rental time . Besides , The transaction must have the correct amount of ether within the selected time interval .

Let's see solidity Relevant parts of the code :

contract RentableNFT is ERC4907, Ownable

Of course ,RentableNFT The contract extends the reference implementation ERC4907 and OpenZeppelin Ownable contract (Ownable Extension is not absolutely necessary , But in this contract , I hope only the owner of the contract is allowed to coin ).

uint256 public baseAmount = 1000000000000000; //0.001 ethers
struct RentableItem {
   bool rentable;
   uint256 amountPerMinute;
}
mapping(uint256 => RentableItem) public rentables;

• baseAmount Is the default payment amount for one minute of lease ,
• RentableItem It's a structure , Used to store information about a NFT Rentability and cost information ,
• rentables yes NFT and RentableItem Mapping between structures .

function mint() public onlyOwner {
    currentTokenId.increment();
    uint256 newItemId = currentTokenId.current();
    _safeMint(owner(), newItemId);
    rentables[newItemId] = RentableItem({
        rentable: false,
        amountPerMinute: baseAmount
    });
}

By default , stay mint Function , The newly created NFT：

• It's for the owner of the contract ;
• Is set as non rentable ;
• Its cost is set to baseAmount.

function setRentFee(uint256 _tokenId, uint256 _amountPerMinute) public {
   require(_isApprovedOrOwner(_msgSender(), _tokenId), "Caller is not token owner nor approved");
   rentables[_tokenId].amountPerMinute = _amountPerMinute;
}

This is a NFT Of amountPerMinute Value setting method . This method can only be used by NFT Owner ( Or an approved address ) call .

function setRentable(uint256 _tokenId, bool _rentable) public {
   require(_isApprovedOrOwner(_msgSender(), _tokenId), "Caller is not token owner nor approved");
   rentables[_tokenId].rentable = _rentable;
}

This method will set a NFT Leasable Boolean value of . This method can only be used by NFT Owner ( Or an approved address ) call .

function rent(uint256 _tokenId, uint64 _expires) public payable virtual {
   uint256 dueAmount = rentables[_tokenId].amountPerMinute * _expires;
   require(msg.value == dueAmount, "Uncorrect amount");
   require(userOf(_tokenId) == address(0), "Already rented");
   require(rentables[_tokenId].rentable, "Renting disabled for the NFT");
   payable(ownerOf(_tokenId)).transfer(dueAmount);
   UserInfo storage info = _users[_tokenId];
   info.user = msg.sender;
   info.expires = block.timestamp + (_expires * 60);
   emit UpdateUser(_tokenId, msg.sender, _expires);
}

The core rental method here ：

• Calculate lease NFT The amount due
• Verify that the amount sent is correct
• verification NFT Whether it has been rented by others
• verify NFT Whether it is changed to leasable by its owner
• Transfer the amount payable to NFT owner
• Update user information and expiration time

Source：https://medium.com/coinmonks/rentable-nft-eip-4907-how-can-be-improved-b20a1b5a27bf

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