openzeppelin学习笔记 - 6

上次说了ERC20,也就是一般的代币使用的合约接口,通过这种合同可以快速实现一种代币的开发。还有另外一种常见的合约接口ERC721,其中比较出名的以太猫(CryptoKitties)就是使用的ERC721
ERC721的特点是它的代币是不可以被分割并却独一无二的,如以太猫中的猫咪一样,每一个都是唯一的有着自己的TokenID。
因为每个TokenID可能对应着一种自定义的结构,在ERC721中,没有定义对应Token的结构,他定义了用户账户和TokenID之间的对应关系,需要自己定义TokenID和数据结构之间的关系。
另外就是和ERC20的授权金额不同,ERC721有两种授权模式,一种是对对应tokenID的授权,被授权者有权利使用对应TokenID的代币,还有一种是全部授权,被授权者有权利使用对应账户下所有的Token。

另外还有一点就是openzeppelinERC721继承了ERC165,这个合约可以被扫描到暴露的接口。详细的我还不是很清楚,后续会继续了解。

ERC721目录下存在以下文件:

  • ERC721.sol

ERC721的合约文件

  • ERC721Burnable.sol

在ERC721基础上添加了燃币操作

  • ERC721Enumerable.sol

在ERC721的基础上对访问性进行了扩展(需要再看看源码加深了解)

  • ERC721Full.sol

在ERC721的基础上继承了ERC721Enumerable, ERC721Metadata

  • ERC721Holder.sol

TODO:这个不是很清楚

  • ERC721Metadata.sol

在ERC721基础上扩展了元数据name , symbol 及 URI

  • ERC721MetadataMintable.sol

在对ERC721Metadata的扩展,添加了铸币的支持,铸币时可以指定URI

  • ERC721Mintable.sol

在ERC721基础上添加了铸币的支持

  • ERC721Pausable.sol

在ERC721基础上引入了Pausable,可以冻结整个代币的流转

  • IERC721.sol

ERC721的实现接口

  • IERC721Enumerable.sol

ERC721Enumerable的实现接口

  • IERC721Full.sol

ERC721Full的实现接口

  • IERC721Metadata

ERC721Metadata的实现接口

  • IERC721Receiver

TODO:觉得和ERC165相关,但是具体也是不太清楚

ERC721

全局变量

  • 应该而ERC165相关,用于暴露接口
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bytes4 private constant _ERC721_RECEIVED = 0x150b7a02;
bytes4 private constant _InterfaceId_ERC721 = 0x80ac58cd;
  • 存储 token所有者
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mapping (uint256 => address) private _tokenOwner
  • 对应tokenID的授权
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mapping (uint256 => address) private _tokenApprovals
  • 对应用户账户的授权
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mapping (address => mapping (address => bool)) private _operatorApprovals
  • 账户下token数量
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mapping (address => uint256) private _ownedTokensCount

事件


  • token交易事件
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event Transfer(
address indexed from,
address indexed to,
uint256 indexed tokenId
);
  • token授权事件
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event Approval(
address indexed owner,
address indexed approved,
uint256 indexed tokenId
);
  • 账户下token授权
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event ApprovalForAll(
address indexed owner,
address indexed operator,
bool approved
);

方法


  • 获取账户下token数量
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function balanceOf(address owner) public view returns (uint256 balance);
  • 获取对应token拥有者地址
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function ownerOf(uint256 tokenId) public view returns (address owner);
  • 对token进行授权
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function approve(address to, uint256 tokenId) public;
  • 获取获取token对应的被授权账户
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function getApproved(uint256 tokenId) public view returns (address operator);
  • 对账户进行授权
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function setApprovalForAll(address operator, bool _approved) public;
  • 判断是否是账户的被授权者
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function isApprovedForAll(address owner, address operator) public view returns (bool);
  • 使用授权交易token
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function transferFrom(address from, address to, uint256 tokenId) public;
  • 使用安全授权交易token,不支持发送数据
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function safeTransferFrom(address from, address to, uint256 tokenId) public;
  • 使用安全授权交易token,支持发送数据
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function safeTransferFrom(
address from,
address to,
uint256 tokenId,
bytes data
) public;

合约源码


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contract ERC721 is ERC165, IERC721 {
using SafeMath for uint256;
using Address for address;
// Equals to `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`
// which can be also obtained as `IERC721Receiver(0).onERC721Received.selector`
bytes4 private constant _ERC721_RECEIVED = 0x150b7a02;
// Mapping from token ID to owner
mapping (uint256 => address) private _tokenOwner;
// Mapping from token ID to approved address
mapping (uint256 => address) private _tokenApprovals;
// Mapping from owner to number of owned token
mapping (address => uint256) private _ownedTokensCount;
// Mapping from owner to operator approvals
mapping (address => mapping (address => bool)) private _operatorApprovals;
bytes4 private constant _InterfaceId_ERC721 = 0x80ac58cd;
/*
* 0x80ac58cd ===
* bytes4(keccak256('balanceOf(address)')) ^
* bytes4(keccak256('ownerOf(uint256)')) ^
* bytes4(keccak256('approve(address,uint256)')) ^
* bytes4(keccak256('getApproved(uint256)')) ^
* bytes4(keccak256('setApprovalForAll(address,bool)')) ^
* bytes4(keccak256('isApprovedForAll(address,address)')) ^
* bytes4(keccak256('transferFrom(address,address,uint256)')) ^
* bytes4(keccak256('safeTransferFrom(address,address,uint256)')) ^
* bytes4(keccak256('safeTransferFrom(address,address,uint256,bytes)'))
*/
constructor()
public
{
// register the supported interfaces to conform to ERC721 via ERC165
_registerInterface(_InterfaceId_ERC721);
}
/**
* @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 Approves another address to transfer the given token ID
* The zero address indicates there is no approved address.
* There can only be one approved address per token at a given time.
* 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));
_tokenApprovals[tokenId] = to;
emit Approval(owner, to, tokenId);
}
/**
* @dev Gets the approved address for a token ID, or zero if no address set
* Reverts if the token ID does not exist.
* @param tokenId uint256 ID of the token to query the approval of
* @return address currently approved for the given token ID
*/
function getApproved(uint256 tokenId) public view returns (address) {
require(_exists(tokenId));
return _tokenApprovals[tokenId];
}
/**
* @dev Sets or unsets the approval of a given operator
* 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;
emit 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
* Usage of this method is discouraged, use `safeTransferFrom` whenever possible
* 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
{
require(_isApprovedOrOwner(msg.sender, tokenId));
require(to != address(0));
_clearApproval(from, tokenId);
_removeTokenFrom(from, tokenId);
_addTokenTo(to, tokenId);
emit Transfer(from, to, tokenId);
}
/**
* @dev Safely transfers the ownership of a given token ID to another address
* 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,address,uint256,bytes)"))`; otherwise,
* the transfer is reverted.
*
* 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
{
// solium-disable-next-line arg-overflow
safeTransferFrom(from, to, tokenId, "");
}
/**
* @dev Safely transfers the ownership of a given token ID to another address
* 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,address,uint256,bytes)"))`; otherwise,
* the transfer is reverted.
* 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
{
transferFrom(from, to, tokenId);
// solium-disable-next-line arg-overflow
require(_checkOnERC721Received(from, to, tokenId, _data));
}
/**
* @dev Returns whether the specified token exists
* @param tokenId uint256 ID of the token to query the existence of
* @return whether the token exists
*/
function _exists(uint256 tokenId) internal view returns (bool) {
address owner = _tokenOwner[tokenId];
return owner != address(0);
}
/**
* @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);
// Disable solium check because of
// https://github.com/duaraghav8/Solium/issues/175
// solium-disable-next-line operator-whitespace
return (
spender == owner ||
getApproved(tokenId) == spender ||
isApprovedForAll(owner, spender)
);
}
/**
* @dev Internal function to mint a new token
* 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);
emit Transfer(address(0), to, tokenId);
}
/**
* @dev Internal function to burn a specific token
* 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);
emit Transfer(owner, address(0), tokenId);
}
/**
* @dev Internal function to add a token ID to the list of a given address
* Note that this function is left internal to make ERC721Enumerable possible, but is not
* intended to be called by custom derived contracts: in particular, it emits no Transfer event.
* @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
* Note that this function is left internal to make ERC721Enumerable possible, but is not
* intended to be called by custom derived contracts: in particular, it emits no Transfer event,
* and doesn't clear approvals.
* @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
* 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 _checkOnERC721Received(
address from,
address to,
uint256 tokenId,
bytes _data
)
internal
returns (bool)
{
if (!to.isContract()) {
return true;
}
bytes4 retval = IERC721Receiver(to).onERC721Received(
msg.sender, from, tokenId, _data);
return (retval == _ERC721_RECEIVED);
}
/**
* @dev Private function to clear current approval of a given token ID
* 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) private {
require(ownerOf(tokenId) == owner);
if (_tokenApprovals[tokenId] != address(0)) {
_tokenApprovals[tokenId] = address(0);
}
}
}