126 lines
4.3 KiB
Markdown
126 lines
4.3 KiB
Markdown
---
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eip: 5560
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title: Redeemable NFTs
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description: Makes an NFT redeemable for a physical object
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author: Olivier Fernandez (@fernandezOli), Frédéric Le Coidic (@FredLC29), Julien Béranger (@julienbrg)
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discussions-to: https://ethereum-magicians.org/t/eip-redeemable-nft-extension/10589
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status: Stagnant
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type: Standards Track
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category: ERC
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created: 2022-08-30
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requires: 165, 721
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---
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## Abstract
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The EIP is a Redeemable NFT extension which adds a `redeem` function to [EIP-721](./eip-721.md). It can be implemented when an NFT issuer wants his/her NFT to be redeemed for a physical object.
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## Motivation
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An increasing amount of NFT issuers such as artists, fine art galeries, auction houses, brands and others want to offer a physical object to the holder of a given NFT. This standard allows EIP-721 NFTs to signal reedemability.
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## Specification
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_The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in RFC 2119._
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`EIP-721` compliant contracts MAY implement this EIP to provide a standard method of receiving information on redeemability.
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The NFT issuer **MUST** decide who is allowed to redeem the NFT, and restrict access to the `redeem()` function accordingly.
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Anyone **MAY** access the `isRedeemable()` function to check the redeemability status: it returns `true` when the NFT redeemable, and `false` when already redeemed.
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Third-party services that support this standard **MAY** use the `Redeem` event to listen to changes on the redeemable status of the NFT.
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Implementers of this standard **MUST** have all of the following functions:
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```solidity
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import '@openzeppelin/contracts/utils/introspection/ERC165.sol';
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/**
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* @dev Implementation of Redeemable for ERC-721s
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*
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*/
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interface IRedeemable is ERC165 {
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/*
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* ERC165 bytes to add to interface array - set in parent contract implementing this standard
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*
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* bytes4 private constant _INTERFACE_ID_ERC721REDEEM = 0x2f8ca953;
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*/
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/// @dev This event emits when a token is redeemed.
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event Redeem(address indexed from, uint256 indexed tokenId);
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/// @notice Returns the redeem status of a token
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/// @param tokenId Identifier of the token.
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function isRedeemable(uint256 _tokenId) external view returns (bool);
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/// @notice Redeeem a token
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/// @param tokenId Identifier of the token to redeeem
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function redeem(uint256 _tokenId) external;
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}
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```
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The `Redeem` event is emitted when the `redeem()` function is called.
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The `supportsInterface` method **MUST** return `true` when called with `0x2f8ca953`.
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## Rationale
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When the NFT contract is deployed, the `isRedeemable()` function returns `true` by default.
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By default, the `redeem()` function visibility is public, so anyone can trigger it. It is **RECOMMENDED** to add a `require` to restrict the access:
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```solidity
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require(ownerOf(tokenId) == msg.sender, "ERC721Redeemable: You are not the owner of this token");
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```
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After the `redeem()` function is triggered, `isRedeemable()` function returns `false`.
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### `Redeem` event
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When the `redeem()` function is triggered, the following event **MUST** be emitted:
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```solidity
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event Redeem(address indexed from, uint256 indexed tokenId);
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```
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## Backwards Compatibility
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This standard is compatible with EIP-721.
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## Reference Implementation
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Here's an example of an EIP-721 that includes the Redeemable extension:
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```solidity
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contract ERC721Redeemable is ERC721, Redeemable {
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constructor(string memory name, string memory symbol) ERC721(name, symbol) {
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}
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function isRedeemable(uint256 tokenId) public view virtual override returns (bool) {
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require(_exists(tokenId), "ERC721Redeemable: Redeem query for nonexistent token");
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return super.isRedeemable(tokenId);
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}
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function redeem(uint256 tokenId) public virtual override {
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require(_exists(tokenId), "ERC721Redeemable: Redeem query for nonexistent token");
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require(ownerOf(tokenId) == msg.sender, "ERC721Redeemable: You are not the owner of this token");
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super.redeem(tokenId);
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}
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function supportsInterface(bytes4 interfaceId) public view override(ERC721, Redeemable) returns (bool) {
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return super.supportsInterface(interfaceId);
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}
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}
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```
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## Security Considerations
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Needs discussion.
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## Copyright
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Copyright and related rights waived via [CC0](../LICENSE.md).
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