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WRC-721

1 WRC-721 Protocol Standard

WRC-721 is a set of standard interfaces, for issuing non-fungible tokens(NFT) on the WELUPS network. WRC-721 is fully compatible with ERC-721.

1.1 WRC-721 Smart Contract Interface Implementation

Every WRC-721 compliant contract must implement the WRC721 and WRC165 interfaces. Other extension interfaces can be implemented according to specific business requirements.

1.1.1 WRC-721 & WRC-165 Interfaces

pragma solidity ^0.4.20;
interface WRC721 {
// Returns the number of NFTs owned by the given account
function balanceOf(address _owner) external view returns (uint256);
//Returns the owner of the given NFT
function ownerOf(uint256 _tokenId) external view returns (address);
//Transfer ownership of NFT
function safeTransferFrom(address _from, address _to, uint256 _tokenId, bytes data) external payable;
//Transfer ownership of NFT
function safeTransferFrom(address _from, address _to, uint256 _tokenId) external payable;
//Transfer ownership of NFT
function transferFrom(address _from, address _to, uint256 _tokenId) external payable;
//Grants address ‘_approved’ the authorization of the NFT ‘_tokenId’
function approve(address _approved, uint256 _tokenId) external payable;
//Grant/recover all NFTs’ authorization of the ‘_operator’
function setApprovalForAll(address _operator, bool _approved) external;
//Query the authorized address of NFT
function getApproved(uint256 _tokenId) external view returns (address);
//Query whether the ‘_operator’ is the authorized address of the ‘_owner’
function isApprovedForAll(address _owner, address _operator) external view returns (bool);
//The successful ‘transferFrom’ and ‘safeTransferFrom’ will trigger the ‘Transfer’ Event
event Transfer(address indexed _from, address indexed _to, uint256 indexed _tokenId);
//The successful ‘Approval’ will trigger the ‘Approval’ event
event Approval(address indexed _owner, address indexed _approved, uint256 indexed _tokenId);
//The successful ‘setApprovalForAll’ will trigger the ‘ApprovalForAll’ event
event ApprovalForAll(address indexed _owner, address indexed _operator, bool _approved);
}
interface WRC165 {
//Query whether the interface ‘interfaceID’ is supported
function supportsInterface(bytes4 interfaceID) external view returns (bool);
}
A wallet/broker/auction application MUST implement the wallet interface if it will accept safe transfers.
Solidity
interface WRC721TokenReceiver {
//This method will be triggered when the ‘_to’ is the contract address during the ‘safeTransferFrom’ execution, and the return value must be checked, If the return value is not bytes4(keccak256("onTRC721Received(address,address,uint256,bytes)")) throws an exception. The smart contract which can receive NFT must implement the TRC721TokenReceiver interface.
function onWRC721Received(address _operator, address _from, uint256 _tokenId, bytes _data) external returns(bytes4);
}
The hash of bytes4(keccak256("onWRC721Received(address,address,uint256,bytes))) is different from the Ethereum version bytes4(keccak256("onERC721Received(address,address,uint256,bytes))). Please use 0x5175f878 instead of 0x150b7a02.

1.1.2 OPTIONAL Metadata Extension Interface

The metadata extension is OPTIONAL for WRC-721 smart contracts. This allows your smart contract to be interrogated for its name and for details about the assets which your NFTs represent.
Solidity
interface WRC721Metadata {
//Return the token name
function name() external view returns (string _name);
//Return the token symbol
function symbol() external view returns (string _symbol);
//Returns the URI of the external file corresponding to ‘_tokenId’. External resource files need to include names, descriptions and pictures.
function tokenURI(uint256 _tokenId) external view returns (string);
}
URI is a URI link describing the _tokenId asset, pointing to a JSON file that conforms to the WRC721 metadata description structure. When tokens are minted, each token needs to be assigned a unique URI:
JSON
{
"title": "Asset Metadata",
"type": "object",
"properties": {
"name": {
"type": "string",
"description": "Identifies the asset to which this NFT represents"
},
"description": {
"type": "string",
"description": "Describes the asset to which this NFT represents"
},
"image": {
"type": "string",
"description": "A URI pointing to a resource with mime type image/* representing the asset to which this NFT represents. Consider making any images at a width between 320 and 1080 pixels and aspect ratio between 1.91:1 and 4:5 inclusive."
}
}
}

1.1.3 OPTIONAL Enumeration Extension Interface

The enumeration extension is OPTIONAL for WRC-721 smart contracts. This allows your contract to publish its full list of NFTs and make them discoverable.
Solidity
interface WRC721Enumerable {
//Return the total supply of NFT
function totalSupply() external view returns (uint256);
//Return the corresponding ‘tokenId’ through ‘_index’
function tokenByIndex(uint256 _index) external view returns (uint256);
//Return the ‘tokenId’ corresponding to the index in the NFT list owned by the ‘_owner'
function tokenOfOwnerByIndex(address _owner, uint256 _index) external view returns (uint256);
}
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1 WRC-721 Protocol Standard
1.1 WRC-721 Smart Contract Interface Implementation