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ERC Standards

约 600 个字 133 行代码 预计阅读时间 4 分钟

Info

参考：

ERC-20

ERC-721

Events

  • event Transfer(address indexed from, address indexed to, uint256 indexed tokenId);
    • Emitted when tokenId token is transferred from from to to.
  • event Approval(address indexed owner, address indexed approved, uint256 indexed tokenId);
    • Emitted when owner enables approved to manage the tokenId token.
  • event ApprovalForAll(address indexed owner, address indexed operator, bool approved);
    • Emitted when owner enables or disables (approved) operator to manage all of its assets.

Approve

  • function approve(address to, uint256 tokenId) public virtual;
    • 作用：授权 tokenId 给 to。
    • 细节：见 _approve，只有在需要发出事件（emitEvent 为真）或者授权者不为 0 时才读取所有者，这时候会检查代币拥有者是否是授权者、auth 是否被代币的拥有者授权，这两个条件均不满足就会抛出异常。我们经常使用的 approve 函数就默认了 emitEvent 为真，这时候会仔细检查授权情况。在最后将 _tokenApprovals[tokenId] 设置为 to。
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      function approve(address to, uint256 tokenId) public virtual {
    _approve(to, tokenId, _msgSender());
}

function _approve(address to, uint256 tokenId, address auth) internal {
    _approve(to, tokenId, auth, true);
}

function _approve(address to, uint256 tokenId, address auth, bool emitEvent) internal virtual {
    // Avoid reading the owner unless necessary
    if (emitEvent || auth != address(0)) {
        address owner = _requireOwned(tokenId);
        // We do not use _isAuthorized because single-token approvals should not be able to call approve
        if (auth != address(0) && owner != auth && !isApprovedForAll(owner, auth)) {
            revert ERC721InvalidApprover(auth);
        }
        if (emitEvent) {
            emit Approval(owner, to, tokenId);
        }
    }
    _tokenApprovals[tokenId] = to;
}
  • function setApprovalForAll(address operator, bool approved) public virtual;
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      function setApprovalForAll(address operator, bool approved) public virtual {
    _setApprovalForAll(_msgSender(), operator, approved);
}

function _setApprovalForAll(address owner, address operator, bool approved) internal virtual {
    if (operator == address(0)) {
        revert ERC721InvalidOperator(operator);
    }
    _operatorApprovals[owner][operator] = approved;
    emit ApprovalForAll(owner, operator, approved);
}

Inquire

  • function balanceOf(address owner) public view virtual returns (uint256);

  • function ownerOf(uint256 tokenId) public view virtual returns (address);

  • function getApproved(uint256 tokenId) public view virtual returns (address);

    • 作用：查询 tokenId 的授权者，也就是返回 _tokenApprovals[tokenId]，同时要求该代币存在（拥有者不为 0）。
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      function getApproved(uint256 tokenId) public view virtual returns (address) {
    _requireOwned(tokenId);
    return _getApproved(tokenId);
}

function _getApproved(uint256 tokenId) internal view virtual returns (address) {
    return _tokenApprovals[tokenId];
}
  • function isApprovedForAll(address owner, address operator) public view virtual returns (bool);
    • 实现： 
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      function isApprovedForAll(address owner, address operator) public view virtual returns (bool) {
    return _operatorApprovals[owner][operator];
}

Check

  • function _isAuthorized(address owner, address spender, uint256 tokenId) internal view virtual returns (bool);
    • 作用：检查 spender 是否有权限操作 tokenId，但是不抛出异常。
    • 细节：要求 spender 不为 0，同时需要下面三个要求满足其一：
      • owner 与 spender 相同，拥有者自然有权操纵代币；
      • owner 授权给 spender，全局授权，spender 可以操纵 owner 的所有代币；
      • tokenId 的授权者是 spender。
    • 实现： 
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      function _isAuthorized(address owner, address spender, uint256 tokenId) internal view virtual returns (bool) {
    return
        spender != address(0) &&
        (owner == spender || isApprovedForAll(owner, spender) || _getApproved(tokenId) == spender);
}
  • function _checkAuthorized(address owner, address spender, uint256 tokenId) internal view virtual;
    • 作用：检查 spender 是否有权限操作 tokenId，如果没有就抛出异常。
    • 细节：首先调用 _isAuthorized 检查权限，如果没有权限就抛出异常，异常分为两种情况：
      • owner 为 0，代币不存在，抛出 ERC721NonexistentToken 异常；
      • owner 为 0，代币存在，但是 spender 没有权限，抛出 ERC721InsufficientApproval 异常，在做 SchoolBus Safe NFT 一题的过程中遇见最多的就是这个异常。
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      function _checkAuthorized(address owner, address spender, uint256 tokenId) internal view virtual {
    if (!_isAuthorized(owner, spender, tokenId)) {
        if (owner == address(0)) {
            revert ERC721NonexistentToken(tokenId);
        } else {
            revert ERC721InsufficientApproval(spender, tokenId);
        }
    }
}
  • function _update(address to, uint256 tokenId, address auth) internal virtual returns (address);
    • 实现： 
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      function _update(address to, uint256 tokenId, address auth) internal virtual returns (address) {
    address from = _ownerOf(tokenId);

    // Perform (optional) operator check
    if (auth != address(0)) {
        _checkAuthorized(from, auth, tokenId);
    }

    // Execute the update
    if (from != address(0)) {
        // Clear approval. No need to re-authorize or emit the Approval event
        _approve(address(0), tokenId, address(0), false);

        unchecked {
            _balances[from] -= 1;
        }
    }

    if (to != address(0)) {
        unchecked {
            _balances[to] += 1;
        }
    }

    _owners[tokenId] = to;

    emit Transfer(from, to, tokenId);

    return from;
}
  • function _requireOwned(uint256 tokenId) internal view virtual returns (address);
    • 作用：检查 tokenId 是否存在，如果不存在（也就是拥有者为地址 0）就抛出异常。
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      function _requireOwned(uint256 tokenId) internal view returns (address) {
    address owner = _ownerOf(tokenId);
    if (owner == address(0)) {
        revert ERC721NonexistentToken(tokenId);
    }
    return owner;
}

Transfer

  • function transferFrom(address from, address to, uint256 tokenId) public virtual;
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      function transferFrom(address from, address to, uint256 tokenId) public virtual {
    if (to == address(0)) {
        revert ERC721InvalidReceiver(address(0));
    }
    // Setting an "auth" arguments enables the `_isAuthorized` check which verifies that the token exists
    // (from != 0). Therefore, it is not needed to verify that the return value is not 0 here.
    address previousOwner = _update(to, tokenId, _msgSender());
    if (previousOwner != from) {
        revert ERC721IncorrectOwner(from, tokenId, previousOwner);
    }
}
  • function safeTransferFrom(address from, address to, uint256 tokenId) public;
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      function safeTransferFrom(address from, address to, uint256 tokenId) public {
    safeTransferFrom(from, to, tokenId, "");
}

function safeTransferFrom(address from, address to, uint256 tokenId, bytes memory data) public virtual {
    transferFrom(from, to, tokenId);
    _checkOnERC721Received(from, to, tokenId, data);
}

function _checkOnERC721Received(address from, address to, uint256 tokenId, bytes memory data) private {
    if (to.code.length > 0) {
        try IERC721Receiver(to).onERC721Received(_msgSender(), from, tokenId, data) returns (bytes4 retval) {
            if (retval != IERC721Receiver.onERC721Received.selector) {
                revert ERC721InvalidReceiver(to);
            }
        } catch (bytes memory reason) {
            if (reason.length == 0) {
                revert ERC721InvalidReceiver(to);
            } else {
                /// @solidity memory-safe-assembly
                assembly {
                    revert(add(32, reason), mload(reason))
                }
            }
        }
    }
}