path: root/packages/contracts/src/2.0.0/tokens/ERC721Token/ERC721Token.sol

/*
The MIT License (MIT)

Copyright (c) 2016 Smart Contract Solutions, Inc.

Permission is hereby granted, free of charge, to any person obtaining
a copy of this software and associated documentation files (the
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The above copyright notice and this permission notice shall be included
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
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*/

pragma solidity ^0.4.24;

import "./IERC721Token.sol";
import "./IERC721Receiver.sol";
import "../../utils/SafeMath/SafeMath.sol";

/**
 * @title ERC721 Non-Fungible Token Standard basic implementation
 * @dev see https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
 * Modified from https://github.com/OpenZeppelin/zeppelin-solidity/blob/master/contracts/token/ERC721/ERC721BasicToken.sol
 */
contract ERC721Token is
    IERC721Token,
    SafeMath
{
    // 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));
        _;
    }

    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 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;
            emit 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;
        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
    * @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);

        emit 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)
    {
        // solium-disable-next-line arg-overflow
        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);
        // solium-disable-next-line arg-overflow
        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);
        emit 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);
        emit 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);
            emit 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] = safeAdd(ownedTokensCount[_to], 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] = safeSub(ownedTokensCount[_from], 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 (!isContract(_to)) {
            return true;
        }
        bytes4 retval = IERC721Receiver(_to).onERC721Received(_from, _tokenId, _data);
        return (retval == ERC721_RECEIVED);
    }

    function isContract(address addr)
        internal
        view
        returns (bool)
    {
        uint256 size;
        // XXX Currently there is no better way to check if there is a contract in an address
        // than to check the size of the code at that address.
        // See https://ethereum.stackexchange.com/a/14016/36603
        // for more details about how this works.
        // TODO Check this again before the Serenity release, because all addresses will be
        // contracts then.
        assembly { size := extcodesize(addr) }  // solium-disable-line security/no-inline-assembly
        return size > 0;
    }
}