ERC721解读

NFT(非同质化代币):类似于明朝、宋朝的青花瓷。虽然都是青花瓷。但是都具有唯一的典藏价值。而且价值可能不同。 NFT就是具有唯一价值的代币。

ERC721: 是以太坊规定实现NFT的一种标准了。实现ERC21标准的智能合约就是NFT代币了。

1.接口

1.ERC721

  定义接口参考：ERC 721 - OpenZeppelin 文档

下面是以太坊官方定义的标准,由于就是我写的代码运行环境不支持payable关键字，因此我打算围绕官方接口定义，按照自己要求稍微增删一下。

pragma solidity ^0.4.25;

interface ERC721 {
    
    ///
     Event
    ///
    event Transfer(address indexed _from, address indexed _to, uint256 indexed _tokenId);
    event Approval(address indexed _owner, address indexed _approved, uint256 indexed _tokenId);
    event ApprovalForAll(address indexed _owner, address indexed _operator, bool _approved);


    ///
     Function
    ///
    function balanceOf(address _owner) external view returns (uint256); // 返回所有者代币的总个数
    function ownerOf(uint256 _tokenId) external view returns (address); // 返回代币id对应所有者的账户地址
    // 安全的转账
    //  _to:是已经被指定 id 代币的所有者授予的账户 and (接受者不是智能合约 or 接受者实现ERC721Receiver接口的智能合约
    // 将给定id的代币转移到接受者账户
    // data是元数据，可有可不有(我觉得)
    function safeTransferFrom(address _from, address _to, uint256 _tokenId, bytes data) external; 
    function safeTransferFrom(address _from, address _to, uint256 _tokenId) external;
    // 这个转账对比上述安全转账(少了一个接受者地址实现是否是ERC721Receiver接口的智能合约地址的判断)
    function transferFrom(address _from, address _to, uint256 _tokenId) external;
    // 授权将代币转移到另一个账户的权限
    function approve(address _approved, uint256 _tokenId) external;
    // 授权接受者使用所有代币
    function setApprovalForAll(address _operator, bool _approved) external;
    // 返回授权指定id 代币的接受者账户
    function getApproved(uint256 _tokenId) external view returns (address);
    // 判断某账户代币的拥有者是否能被某账户全部使用
    function isApprovedForAll(address _owner, address _operator) external view returns (bool);
}

2.ERC721Metadata

以下就是ERC21的元数据接口，这是可选地。名称、标识符、每一个token对应的tokenURI。

pragma solidity ^0.4.25;

interface ERC721Metadata {
    function name() external view returns (string);
    function symbol() external view returns (string);
    function tokenURI(uint256 tokenId) external view returns (string); // 返回指定id的代币所对对应的uri
}

3.ERC721Enumerable

另一个额外的可选接口是枚举， 它包含了按索引获取到对应的代币。

pragma solidity ^0.4.25;

interface ERC721Enumerable {
    // 确定合约当前全部的nft数量(出去销毁)
    function totalSupply() external view returns (uint256);
    // 从代币列表返回第n个代币
    function tokenByIndex(uint256 _index) external view returns (uint256);
    // 返回所有者代币列表的第n个代币
    function tokenOfOwnerByIndex(address _owner, uint256 _index) external view returns (uint256);
}

4.ERC721Receiver

pragma solidity ^0.4.25;

// 资产合约
interface ERC721Receiver {
    function onERC721Received(address operator, address from, uint256 tokenId, bytes data) external
        returns (bytes);
}

2.实现

1.Jzm721

这是我针对ERC721接口的合约实现。基本满足官方接口标准。

pragma solidity ^0.4.25;
import "./ERC721.sol";
import "./ERC721Metadata.sol";
contract Jzm721 is ERC721,ERC721Metadata {

    ///
     Filed
    ///
    string public name;
    string public symbol;
    uint256  nftCount;
    mapping (address => uint[])  balanceMap; // owner => tokenId[]
    mapping (uint256=>string)  tokenURIMap; // tokenId => tokenURI
    mapping (uint256=>address)  tokenIdMap; // tokenId => owner
    mapping (uint256 => address) approveMap; // tokenId => operator(经营方)
    mapping (address=>mapping (address=>bool)) approveAllMap; // operator =>(owner => true/false)

    ///
     Function
    ///
    constructor(string memory _name,string memory _symbol) 
    public {
        name = _name;
        symbol = _symbol;
    }

    function name() external view returns (string) {
        return name;
    }

    function symbol() external view returns (string) {
        return symbol;
    }

    function tokenURI(uint256 tokenId) external view returns (string) {
        return tokenURIMap[tokenId];
    }

    // 创建代币
    function mint(address _owner,string _tokenURI) external  returns (uint256) {
        require(_owner != address(0),"owner is not empty address!");
        uint256 tokenId = _mint(_owner);
        _setTokenURI(tokenId, _tokenURI);
        return tokenId;
    }

    function balanceOf(address _owner) external view returns (uint256) {
        return balanceMap[_owner].length;
    }

    function ownerOf(uint256 _tokenId) external view returns (address) {
        return tokenIdMap[_tokenId];
    }

    // 这里我忽略了data这个元数据的作用
    function safeTransferFrom(address _from, address _to, uint256 _tokenId, bytes data) external {
        _transferFrom(_from, _to, _tokenId);
        if(_isContractAdd(_to)) {
            if(_checkIfFunctionExists(_to)) {
                _externalTransfer(_from, _to, _tokenId);
                emit Transfer(_from, _to, _tokenId);
            }  
        }
    }

    function safeTransferFrom(address _from, address _to, uint256 _tokenId) external {
        _transferFrom(_from, _to, _tokenId);
        if(_isContractAdd(_to)) {
            if(_checkIfFunctionExists(_to)) {
                _externalTransfer(_from, _to, _tokenId);
                emit Transfer(_from, _to, _tokenId);
            }
        }
    }

    function transferFrom(address _from, address _to, uint256 _tokenId) external {
        _transferFrom(_from, _to, _tokenId);
    }


    function approve(address _approved, uint256 _tokenId) external {
        require(_approved != address(0),"approved is not empty address!");
        address owner = msg.sender;
        approveMap[_tokenId] = _approved; 
        emit Approval(owner,_approved,_tokenId);
    }

    function setApprovalForAll(address _operator, bool _approved) external {
        require(_operator != address(0),"operator is not empty address!");
        address owner = msg.sender;
        approveAllMap[_operator][owner] = _approved;
        emit  ApprovalForAll(owner,_operator,_approved);
    }

    function getApproved(uint256 _tokenId) external view returns (address) {
        return _getApproved(_tokenId);
    }

    function isApprovedForAll(address _owner, address _operator) external view returns (bool) {
        return _isApprovedForAll(_owner,_operator);
    }

    function _checkIfFunctionExists(address _add)public  returns (bool) {
        bytes4 functionSelector = bytes4(keccak256("onERC721Received(address,address,uint256,bytes)")); // 函数选择器，基础原型前4个字节
        bytes memory data = abi.encodeWithSelector(functionSelector, address(0),address(0),0,"");
        bool success = _add.call(data);
        return success;
    }

    function _transferFrom(address _from, address _to, uint256 _tokenId) private {
        // from不能是零地址。
        require(_from != address(0),"from is not empty address!");
        // to不能是零地址。
        require(_to != address(0),"from is not empty address!");
        // tokenId令牌必须存在并由from拥有。
        require(tokenIdMap[_tokenId] == _from,"The tokenId  must exist and be owned by from!");
        // 接受者一方不是合约地址
        if (!_isContractAdd(_to)) {
            if (_isApproved(_from, _to, _tokenId)) { 
                // TODO
                _externalTransfer(_from, _to, _tokenId);
                emit Transfer(_from, _to, _tokenId);
            }
        }
    }

    function _externalTransfer(address _from,address _to,uint256 _tokenId) private {
        // 删除代币批准
        if(_getApproved(_tokenId) == _to) {
            approveMap[_tokenId] = address(0);   
        }
        // 转账
        _deleteAccountToken(_from,_tokenId);
        tokenIdMap[_tokenId] = _to;
        balanceMap[_to].push(_tokenId);
    }


    function _deleteAccountToken(address _owner,uint256 _tokenId) private {
        uint256[] storage tokenIds = balanceMap[_owner];
        uint len =  tokenIds.length;
        for (uint i = 0; i < len; i++) {
            if(tokenIds[i] == _tokenId) {
                // 交换
                uint swap;
                swap = tokenIds[i];
                tokenIds[i] = tokenIds[len - 1];
                tokenIds[len - 1] = swap;
            }
        }
        tokenIds.length--;
    }

    function _mint(address _owner) private  returns (uint256) {
        nftCount += 1;
        uint256 tokenId = nftCount + block.timestamp;
        balanceMap[_owner].push(tokenId);
        tokenIdMap[tokenId] = _owner;
        emit Transfer(address(0),_owner,tokenId);
        return tokenId;
    }

    function _setTokenURI(uint256 _tokenId,string _tokenURI) private{
        tokenURIMap[_tokenId] = _tokenURI;
    }

    // 判断该地址是否合约地址
    function _isContractAdd(address  _addr) private view returns (bool) {
        uint size;
        assembly {
            size := extcodesize(_addr) // 返回地址关联代码的长度
        }
        return size > 0;
    }

    function _getApproved(uint256 _tokenId) private view returns(address) {
        return approveMap[_tokenId];
    }

    function _isApproved(address _owner, address _operator,uint256 _tokenId) private view returns (bool) {
        bool approved = _getApproved(_tokenId) == _operator;
        return approved || _isApprovedForAll(_owner, _operator);
    }

    function _isApprovedForAll(address _owner, address _operator) private view returns(bool) {
        return approveAllMap[_operator][_owner];
    }




}

2.Jzm721Receiver

在这里我就是想要满足合约地址的合约实现ERC721Receiver接口的标准。原合约，这里该函数涉及代币的转账，由于环境的原因，不支持payable关键字，我这里是无法满足的。

pragma solidity ^0.4.25;
import "./ERC721Receiver.sol";

contract Jzm721Receiver is ERC721Receiver {
    function onERC721Received(address operator, address from, uint256 tokenId, bytes data) external
        returns (bytes) {
            return data;
        }
}