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OpenZeppelinのERC721が更新されたので見てみる

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概要

OpenZeppelinのERC721が更新されました。(3/23)

https://github.com/OpenZeppelin/zeppelin-solidity/pull/803

ざっくり読んだ感じ、トークンの基本機能が決まった#640のと、譲渡不能なトークンの仕様#809が更新されたあたりの対応ぽい。

追加検討中の機能として、「譲渡不能トークンと譲渡可能トークンの両立#756」、「クラウドセール#776」等があった。

とりあえず大きめのマージだったのでいじってみる。


ソース


ERC721Basic

基本的なインタフェースのまとめ。


pragma solidity ^0.4.18;

/**
* @title ERC721 Non-Fungible Token Standard basic interface
* @dev see https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
*/
contract ERC721Basic {
event Transfer(address indexed _from, address indexed _to, uint256 _tokenId);
event Approval(address indexed _owner, address indexed _approved, uint256 _tokenId);
event ApprovalForAll(address indexed _owner, address indexed _operator, bool _approved);

function balanceOf(address _owner) public view returns (uint256 _balance);
function ownerOf(uint256 _tokenId) public view returns (address _owner);
function exists(uint256 _tokenId) public view returns (bool _exists);

function approve(address _to, uint256 _tokenId) public;
function getApproved(uint256 _tokenId) public view returns (address _operator);

function setApprovalForAll(address _operator, bool _approved) public;
function isApprovedForAll(address _owner, address _operator) public view returns (bool);

function transferFrom(address _from, address _to, uint256 _tokenId) public;
function safeTransferFrom(address _from, address _to, uint256 _tokenId) public;
function safeTransferFrom(address _from, address _to, uint256 _tokenId, bytes _data) public;
}

approveForがgetApprovedになって、削除予定メソッドがここから消えた感じ。

あとtransfer周りが分割されてる。送り主が承認→受け取り側が転送みたいな。

ちょっとわかんなかったのが、eip721だとトークンの承認と送信はexternalのpayableなのだけど、今回のOpenZeppelinの修正だとpublicなので、どうすんだろコレ的な。

https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md


ERC721

EnumerableとMetaを追加したERC721BasicがERC721だよーくらいのノリで。


pragma solidity ^0.4.18;

import "./ERC721Basic.sol";

/**
* @title ERC-721 Non-Fungible Token Standard, optional enumeration extension
* @dev See https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
*/
contract ERC721Enumerable is ERC721Basic {
function totalSupply() public view returns (uint256);
function tokenOfOwnerByIndex(address _owner, uint256 _index) public view returns (uint256 _tokenId);
function tokenByIndex(uint256 _index) public view returns (uint256);
}

/**
* @title ERC-721 Non-Fungible Token Standard, optional metadata extension
* @dev See https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
*/
contract ERC721Metadata is ERC721Basic {
function name() public view returns (string _name);
function symbol() public view returns (string _symbol);
function tokenURI(uint256 _tokenId) public view returns (string);
}

/**
* @title ERC-721 Non-Fungible Token Standard, full implementation interface
* @dev See https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
*/
contract ERC721 is ERC721Basic, ERC721Enumerable, ERC721Metadata {
}

個人的にMetaは個別にnameとかその他追加情報入れたいので、この辺は最終盤出たら自分でいじる。

今回はお試しなのでここにMetaなんてなかった体でスルーする。


ERC721Receiver / ERC721Holder

safeTransferFrom系の処理後処理。toがコントラクトの際に使ってね的な何か。

50000ガス以内でやれとのこと。

pragma solidity ^0.4.18;

/**
* @title ERC721 token receiver interface
* @dev Interface for any contract that wants to support safeTransfers
* from ERC721 asset contracts.
*/
contract ERC721Receiver {
/**
* @dev Magic value to be returned upon successful reception of an NFT
* Equals to `bytes4(keccak256("onERC721Received(address,uint256,bytes)"))`,
* which can be also obtained as `ERC721Receiver(0).onERC721Received.selector`
*/
bytes4 constant ERC721_RECEIVED = 0xf0b9e5ba;

/**
* @notice Handle the receipt of an NFT
* @dev The ERC721 smart contract calls this function on the recipient
* after a `safetransfer`. This function MAY throw to revert and reject the
* transfer. This function MUST use 50,000 gas or less. Return of other
* than the magic value MUST result in the transaction being reverted.
* Note: the contract address is always the message sender.
* @param _from The sending address
* @param _tokenId The NFT identifier which is being transfered
* @param _data Additional data with no specified format
* @return `bytes4(keccak256("onERC721Received(address,uint256,bytes)"))`
*/
function onERC721Received(address _from, uint256 _tokenId, bytes _data) public returns(bytes4);
}
===============================================
pragma solidity ^0.4.18;

import "./ERC721Receiver.sol";

contract ERC721Holder is ERC721Receiver {
function onERC721Received(address, uint256, bytes) public returns(bytes4) {
return ERC721_RECEIVED;
}
}


ERC721BasicToken

今回追加の肝。

基本的な実装をここで大体やっててくれてる。

計算とアドレス評価を安全にやるために、SafeMathとAddressUtilsがインポートされてる。

pragma solidity ^0.4.18;

import "./ERC721Basic.sol";
import "./ERC721Receiver.sol";
import "./SafeMath.sol";
import "./AddressUtils.sol";

/**
* @title ERC721 Non-Fungible Token Standard basic implementation
* @dev see https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
*/
contract ERC721BasicToken is ERC721Basic {
using SafeMath for uint256;
using AddressUtils for address;

// Equals to `bytes4(keccak256("onERC721Received(address,uint256,bytes)"))`
// which can be also obtained as `ERC721Receiver(0).onERC721Received.selector`
bytes4 constant ERC721_RECEIVED = 0xf0b9e5ba;

// Mapping from token ID to owner
mapping (uint256 => address) internal tokenOwner;

// Mapping from token ID to approved address
mapping (uint256 => address) internal tokenApprovals;

// Mapping from owner to number of owned token
mapping (address => uint256) internal ownedTokensCount;

// Mapping from owner to operator approvals
mapping (address => mapping (address => bool)) internal operatorApprovals;

/**
* @dev Guarantees msg.sender is owner of the given token
* @param _tokenId uint256 ID of the token to validate its ownership belongs to msg.sender
*/
modifier onlyOwnerOf(uint256 _tokenId) {
require(ownerOf(_tokenId) == msg.sender);
_;
}

/**
* @dev Checks msg.sender can transfer a token, by being owner, approved, or operator
* @param _tokenId uint256 ID of the token to validate
*/
modifier canTransfer(uint256 _tokenId) {
require(isApprovedOrOwner(msg.sender, _tokenId));
_;
}

/**
* @dev Gets the balance of the specified address
* @param _owner address to query the balance of
* @return uint256 representing the amount owned by the passed address
*/
function balanceOf(address _owner) public view returns (uint256) {
require(_owner != address(0));
return ownedTokensCount[_owner];
}

/**
* @dev Gets the owner of the specified token ID
* @param _tokenId uint256 ID of the token to query the owner of
* @return owner address currently marked as the owner of the given token ID
*/
function ownerOf(uint256 _tokenId) public view returns (address) {
address owner = tokenOwner[_tokenId];
require(owner != address(0));
return owner;
}

/**
* @dev Returns whether the specified token exists
* @param _tokenId uint256 ID of the token to query the existance of
* @return whether the token exists
*/
function exists(uint256 _tokenId) public view returns (bool) {
address owner = tokenOwner[_tokenId];
return owner != address(0);
}

/**
* @dev Approves another address to transfer the given token ID
* @dev The zero address indicates there is no approved address.
* @dev There can only be one approved address per token at a given time.
* @dev Can only be called by the token owner or an approved operator.
* @param _to address to be approved for the given token ID
* @param _tokenId uint256 ID of the token to be approved
*/
function approve(address _to, uint256 _tokenId) public {
address owner = ownerOf(_tokenId);
require(_to != owner);
require(msg.sender == owner || isApprovedForAll(owner, msg.sender));

if (getApproved(_tokenId) != address(0) || _to != address(0)) {
tokenApprovals[_tokenId] = _to;
Approval(owner, _to, _tokenId);
}
}

/**
* @dev Gets the approved address for a token ID, or zero if no address set
* @param _tokenId uint256 ID of the token to query the approval of
* @return address currently approved for a the given token ID
*/
function getApproved(uint256 _tokenId) public view returns (address) {
return tokenApprovals[_tokenId];
}

/**
* @dev Sets or unsets the approval of a given operator
* @dev An operator is allowed to transfer all tokens of the sender on their behalf
* @param _to operator address to set the approval
* @param _approved representing the status of the approval to be set
*/
function setApprovalForAll(address _to, bool _approved) public {
require(_to != msg.sender);
operatorApprovals[msg.sender][_to] = _approved;
ApprovalForAll(msg.sender, _to, _approved);
}

/**
* @dev Tells whether an operator is approved by a given owner
* @param _owner owner address which you want to query the approval of
* @param _operator operator address which you want to query the approval of
* @return bool whether the given operator is approved by the given owner
*/
function isApprovedForAll(address _owner, address _operator) public view returns (bool) {
return operatorApprovals[_owner][_operator];
}

/**
* @dev Transfers the ownership of a given token ID to another address
* @dev Usage of this method is discouraged, use `safeTransferFrom` whenever possible
* @dev Requires the msg sender to be the owner, approved, or operator
* @param _from current owner of the token
* @param _to address to receive the ownership of the given token ID
* @param _tokenId uint256 ID of the token to be transferred
*/
function transferFrom(address _from, address _to, uint256 _tokenId) public canTransfer(_tokenId) {
require(_from != address(0));
require(_to != address(0));

clearApproval(_from, _tokenId);
removeTokenFrom(_from, _tokenId);
addTokenTo(_to, _tokenId);

Transfer(_from, _to, _tokenId);
}

/**
* @dev Safely transfers the ownership of a given token ID to another address
* @dev If the target address is a contract, it must implement `onERC721Received`,
* which is called upon a safe transfer, and return the magic value
* `bytes4(keccak256("onERC721Received(address,uint256,bytes)"))`; otherwise,
* the transfer is reverted.
* @dev Requires the msg sender to be the owner, approved, or operator
* @param _from current owner of the token
* @param _to address to receive the ownership of the given token ID
* @param _tokenId uint256 ID of the token to be transferred
*/
function safeTransferFrom(address _from, address _to, uint256 _tokenId) public canTransfer(_tokenId) {
safeTransferFrom(_from, _to, _tokenId, "");
}

/**
* @dev Safely transfers the ownership of a given token ID to another address
* @dev If the target address is a contract, it must implement `onERC721Received`,
* which is called upon a safe transfer, and return the magic value
* `bytes4(keccak256("onERC721Received(address,uint256,bytes)"))`; otherwise,
* the transfer is reverted.
* @dev Requires the msg sender to be the owner, approved, or operator
* @param _from current owner of the token
* @param _to address to receive the ownership of the given token ID
* @param _tokenId uint256 ID of the token to be transferred
* @param _data bytes data to send along with a safe transfer check
*/
function safeTransferFrom(address _from, address _to, uint256 _tokenId, bytes _data) public canTransfer(_tokenId) {
transferFrom(_from, _to, _tokenId);
require(checkAndCallSafeTransfer(_from, _to, _tokenId, _data));
}

/**
* @dev Returns whether the given spender can transfer a given token ID
* @param _spender address of the spender to query
* @param _tokenId uint256 ID of the token to be transferred
* @return bool whether the msg.sender is approved for the given token ID,
* is an operator of the owner, or is the owner of the token
*/
function isApprovedOrOwner(address _spender, uint256 _tokenId) internal view returns (bool) {
address owner = ownerOf(_tokenId);
return _spender == owner || getApproved(_tokenId) == _spender || isApprovedForAll(owner, _spender);
}

/**
* @dev Internal function to mint a new token
* @dev Reverts if the given token ID already exists
* @param _to The address that will own the minted token
* @param _tokenId uint256 ID of the token to be minted by the msg.sender
*/
function _mint(address _to, uint256 _tokenId) internal {
require(_to != address(0));
addTokenTo(_to, _tokenId);
Transfer(address(0), _to, _tokenId);
}

/**
* @dev Internal function to burn a specific token
* @dev Reverts if the token does not exist
* @param _tokenId uint256 ID of the token being burned by the msg.sender
*/
function _burn(address _owner, uint256 _tokenId) internal {
clearApproval(_owner, _tokenId);
removeTokenFrom(_owner, _tokenId);
Transfer(_owner, address(0), _tokenId);
}

/**
* @dev Internal function to clear current approval of a given token ID
* @dev Reverts if the given address is not indeed the owner of the token
* @param _owner owner of the token
* @param _tokenId uint256 ID of the token to be transferred
*/
function clearApproval(address _owner, uint256 _tokenId) internal {
require(ownerOf(_tokenId) == _owner);
if (tokenApprovals[_tokenId] != address(0)) {
tokenApprovals[_tokenId] = address(0);
Approval(_owner, address(0), _tokenId);
}
}

/**
* @dev Internal function to add a token ID to the list of a given address
* @param _to address representing the new owner of the given token ID
* @param _tokenId uint256 ID of the token to be added to the tokens list of the given address
*/
function addTokenTo(address _to, uint256 _tokenId) internal {
require(tokenOwner[_tokenId] == address(0));
tokenOwner[_tokenId] = _to;
ownedTokensCount[_to] = ownedTokensCount[_to].add(1);
}

/**
* @dev Internal function to remove a token ID from the list of a given address
* @param _from address representing the previous owner of the given token ID
* @param _tokenId uint256 ID of the token to be removed from the tokens list of the given address
*/
function removeTokenFrom(address _from, uint256 _tokenId) internal {
require(ownerOf(_tokenId) == _from);
ownedTokensCount[_from] = ownedTokensCount[_from].sub(1);
tokenOwner[_tokenId] = address(0);
}

/**
* @dev Internal function to invoke `onERC721Received` on a target address
* @dev The call is not executed if the target address is not a contract
* @param _from address representing the previous owner of the given token ID
* @param _to target address that will receive the tokens
* @param _tokenId uint256 ID of the token to be transferred
* @param _data bytes optional data to send along with the call
* @return whether the call correctly returned the expected magic value
*/
function checkAndCallSafeTransfer(address _from, address _to, uint256 _tokenId, bytes _data) internal returns (bool) {
if (!_to.isContract()) {
return true;
}
bytes4 retval = ERC721Receiver(_to).onERC721Received(_from, _tokenId, _data);
return (retval == ERC721_RECEIVED);
}
}

NTFなのでトークンの送信は、譲渡ではなく削除後再精製みたいになってる。

checkAndCallSafeTransferでERC721Receiverが使われてる。

コレ自体はsafeTransferFromから転送実行後に呼ばれている。

_toがコントラクトの時に動くぽいけど、どういうケースなんだろう。

checkAndCallSafeTransferがfalseで返るとrequireに引っかかってリバートされる。


DeprecatedERC721

ERC721で廃止されたメソッド。

下位互換のために必要なら実装すれば的な。

tokensOfの代替どこだろう、これ結構便利なのに。

pragma solidity ^0.4.18;

import "./ERC721.sol";

/**
* @title ERC-721 methods shipped in OpenZeppelin v1.7.0, removed in the latest version of the standard
* @dev Only use this interface for compatibility with previously deployed contracts
* @dev Use ERC721 for interacting with new contracts which are standard-compliant
*/
contract DeprecatedERC721 is ERC721 {
function takeOwnership(uint256 _tokenId) public;
function transfer(address _to, uint256 _tokenId) public;
function tokensOf(address _owner) public view returns (uint256[]);
}


ERC721Token

コメントにあるように、必要なメソッドとオマケのメソッドの実装しといたで的な。

approve allがどうこう言ってるので、後で調べる。

pragma solidity ^0.4.18;

import "./ERC721.sol";
import "./DeprecatedERC721.sol";
import "./ERC721BasicToken.sol";

/**
* @title Full ERC721 Token
* This implementation includes all the required and some optional functionality of the ERC721 standard
* Moreover, it includes approve all functionality using operator terminology
* @dev see https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
*/
contract ERC721Token is ERC721, ERC721BasicToken {
// Token name
string internal name_;

// Token symbol
string internal symbol_;

// Mapping from owner to list of owned token IDs
mapping (address => uint256[]) internal ownedTokens;

// Mapping from token ID to index of the owner tokens list
mapping(uint256 => uint256) internal ownedTokensIndex;

// Array with all token ids, used for enumeration
uint256[] internal allTokens;

// Mapping from token id to position in the allTokens array
mapping(uint256 => uint256) internal allTokensIndex;

// Optional mapping for token URIs
mapping(uint256 => string) internal tokenURIs;

/**
* @dev Constructor function
*/
function ERC721Token(string _name, string _symbol) public {
name_ = _name;
symbol_ = _symbol;
}

/**
* @dev Gets the token name
* @return string representing the token name
*/
function name() public view returns (string) {
return name_;
}

/**
* @dev Gets the token symbol
* @return string representing the token symbol
*/
function symbol() public view returns (string) {
return symbol_;
}

/**
* @dev Returns an URI for a given token ID
* @dev Throws if the token ID does not exist. May return an empty string.
* @param _tokenId uint256 ID of the token to query
*/
function tokenURI(uint256 _tokenId) public view returns (string) {
require(exists(_tokenId));
return tokenURIs[_tokenId];
}

/**
* @dev Internal function to set the token URI for a given token
* @dev Reverts if the token ID does not exist
* @param _tokenId uint256 ID of the token to set its URI
* @param _uri string URI to assign
*/
function _setTokenURI(uint256 _tokenId, string _uri) internal {
require(exists(_tokenId));
tokenURIs[_tokenId] = _uri;
}

/**
* @dev Gets the token ID at a given index of the tokens list of the requested owner
* @param _owner address owning the tokens list to be accessed
* @param _index uint256 representing the index to be accessed of the requested tokens list
* @return uint256 token ID at the given index of the tokens list owned by the requested address
*/
function tokenOfOwnerByIndex(address _owner, uint256 _index) public view returns (uint256) {
require(_index < balanceOf(_owner));
return ownedTokens[_owner][_index];
}

/**
* @dev Gets the total amount of tokens stored by the contract
* @return uint256 representing the total amount of tokens
*/
function totalSupply() public view returns (uint256) {
return allTokens.length;
}

/**
* @dev Gets the token ID at a given index of all the tokens in this contract
* @dev Reverts if the index is greater or equal to the total number of tokens
* @param _index uint256 representing the index to be accessed of the tokens list
* @return uint256 token ID at the given index of the tokens list
*/
function tokenByIndex(uint256 _index) public view returns (uint256) {
require(_index < totalSupply());
return allTokens[_index];
}

/**
* @dev Internal function to add a token ID to the list of a given address
* @param _to address representing the new owner of the given token ID
* @param _tokenId uint256 ID of the token to be added to the tokens list of the given address
*/
function addTokenTo(address _to, uint256 _tokenId) internal {
super.addTokenTo(_to, _tokenId);
uint256 length = ownedTokens[_to].length;
ownedTokens[_to].push(_tokenId);
ownedTokensIndex[_tokenId] = length;
}

/**
* @dev Internal function to remove a token ID from the list of a given address
* @param _from address representing the previous owner of the given token ID
* @param _tokenId uint256 ID of the token to be removed from the tokens list of the given address
*/
function removeTokenFrom(address _from, uint256 _tokenId) internal {
super.removeTokenFrom(_from, _tokenId);

uint256 tokenIndex = ownedTokensIndex[_tokenId];
uint256 lastTokenIndex = ownedTokens[_from].length.sub(1);
uint256 lastToken = ownedTokens[_from][lastTokenIndex];

ownedTokens[_from][tokenIndex] = lastToken;
ownedTokens[_from][lastTokenIndex] = 0;
// Note that this will handle single-element arrays. In that case, both tokenIndex and lastTokenIndex are going to
// be zero. Then we can make sure that we will remove _tokenId from the ownedTokens list since we are first swapping
// the lastToken to the first position, and then dropping the element placed in the last position of the list

ownedTokens[_from].length--;
ownedTokensIndex[_tokenId] = 0;
ownedTokensIndex[lastToken] = tokenIndex;
}

/**
* @dev Internal function to mint a new token
* @dev Reverts if the given token ID already exists
* @param _to address the beneficiary that will own the minted token
* @param _tokenId uint256 ID of the token to be minted by the msg.sender
*/
function _mint(address _to, uint256 _tokenId) internal {
super._mint(_to, _tokenId);

allTokensIndex[_tokenId] = allTokens.length;
allTokens.push(_tokenId);
}

/**
* @dev Internal function to burn a specific token
* @dev Reverts if the token does not exist
* @param _owner owner of the token to burn
* @param _tokenId uint256 ID of the token being burned by the msg.sender
*/
function _burn(address _owner, uint256 _tokenId) internal {
super._burn(_owner, _tokenId);

// Clear metadata (if any)
if (bytes(tokenURIs[_tokenId]).length != 0) {
delete tokenURIs[_tokenId];
}

// Reorg all tokens array
uint256 tokenIndex = allTokensIndex[_tokenId];
uint256 lastTokenIndex = allTokens.length.sub(1);
uint256 lastToken = allTokens[lastTokenIndex];

allTokens[tokenIndex] = lastToken;
allTokens[lastTokenIndex] = 0;

allTokens.length--;
allTokensIndex[_tokenId] = 0;
allTokensIndex[lastToken] = tokenIndex;
}

}

ERC721Tokenではトークンの管理ぽいことをやっている。

自分でトークン作る時は、今の所コレを継承しとけば楽ができる。

2018/3/27時点ではまだドラフト版なため、今後も実装が変わる可能性あり。

というかまず変わる。


感想

譲渡周りを綺麗にして、metaはとりあえず保留のような印象を受けた。

ゲームに使用する場合だと一般的なトークン取引所は使わないで自前の取引所作る気もするので、今回の修正でうんこれはすげーやみたいなのはあんまり。

というかゲームに特化したERC721後継のERCXXXXが欲しい。

※ 長くなったので実装は別記事でやる。