Netkiller Blockchain 手札
作者正在找工作，聯繫方式 13113668890
Mr. Neo Chan, 陳景峯(BG7NYT)
中國廣東省深圳市望海路半島城邦三期
518067
+86 13113668890
<[email protected]>
文檔始創於2018-02-10
版權 © 2018 Netkiller(Neo Chan). All rights reserved.
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2.10.5. 資產投資與份額持有
傳統藝術品投資門檻非常高，一是用戶不知道從哪些渠道可以投資，二是藝術品價值過高，三是藝術品簡單難。這導致了投資藝術品門檻過高。 Token 能實現份額化，實現人人蔘與，人人持有，P2P交易。
例如某機構上鍊一件藝術品，用戶可以投資該藝術品的一定份額，可以轉讓他持有的權益。且交易去中心化，不受任何機構，管理者的制約。
下面的合約可以展示如何分割藝術品份額，最終達到鏈上資產的份額分割和持有與交易。
pragma solidity ^0.4.25;
/**
* @title SafeMath
* @dev Math operations with safety checks that revert on error
*/
library SafeMath {
/**
* @dev Multiplies two numbers, reverts on overflow.
*/
function mul(uint256 a, uint256 b) internal pure returns (uint256) {
// Gas optimization: this is cheaper than requiring 'a' not being zero, but the
// benefit is lost if 'b' is also tested.
// See: https://github.com/OpenZeppelin/openzeppelin-solidity/pull/522
if (a == 0) {
return 0;
}
uint256 c = a * b;
require(c / a == b);
return c;
}
/**
* @dev Integer division of two numbers truncating the quotient, reverts on division by zero.
*/
function div(uint256 a, uint256 b) internal pure returns (uint256) {
require(b > 0); // Solidity only automatically asserts when dividing by 0
uint256 c = a / b;
// assert(a == b * c + a % b); // There is no case in which this doesn't hold
return c;
}
/**
* @dev Subtracts two numbers, reverts on overflow (i.e. if subtrahend is greater than minuend).
*/
function sub(uint256 a, uint256 b) internal pure returns (uint256) {
require(b <= a);
uint256 c = a - b;
return c;
}
/**
* @dev Adds two numbers, reverts on overflow.
*/
function add(uint256 a, uint256 b) internal pure returns (uint256) {
uint256 c = a + b;
require(c >= a);
return c;
}
/**
* @dev Divides two numbers and returns the remainder (unsigned integer modulo),
* reverts when dividing by zero.
*/
function mod(uint256 a, uint256 b) internal pure returns (uint256) {
require(b != 0);
return a % b;
}
}
contract Ownable {
address public owner;
event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);
constructor() public {
owner = msg.sender;
}
modifier onlyOwner() {
require(msg.sender == owner);
_;
}
function transferOwnership(address newOwner) public onlyOwner {
require(newOwner != address(0));
emit OwnershipTransferred(owner, newOwner);
owner = newOwner;
}
}
contract NetkillerAssetsToken is Ownable {
using SafeMath for uint256;
string public name;
string public symbol;
uint public decimals;
uint256 public totalSupply;
mapping(address => mapping(string => uint256)) internal balances;
mapping(string => address) internal tokens;
event Transfer(address indexed _from, address indexed _to, string indexed _tokenId);
event Burn(address indexed from, string _tokenId);
constructor(
string tokenName,
string tokenSymbol,
uint decimalUnits
) public {
owner = msg.sender;
name = tokenName;
symbol = tokenSymbol;
decimals = decimalUnits;
totalSupply = 0;
}
function add(address _owner, string _tokenId) onlyOwner returns(bool status){
balances[_owner][_tokenId] = 100 * 10 ** uint256(decimals);
tokens[_tokenId] = _owner;
totalSupply = totalSupply.add(1);
return true;
}
function balanceOf(address _owner, string _tokenId) constant returns(uint balance){
return balances[_owner][_tokenId];
}
function ownerOf(string _tokenId) constant returns (address owner) {
return tokens[_tokenId];
}
function transfer(address _to, string _tokenId){
address _from = msg.sender;
uint256 amount = balances[_from][_tokenId];
transfer(_to, amount, _tokenId);
}
function transfer(address _to, uint256 _value, string _tokenId){
require(msg.sender == ownerOf(_tokenId));
require(msg.sender != _to);
require(_to != address(0));
address _from = msg.sender;
uint256 amount = balances[_from][_tokenId];
require(amount >= _value);
balances[_from][_tokenId] = balances[_from][_tokenId].sub(_value);
balances[_to][_tokenId] = balances[_to][_tokenId].add(_value);
tokens[_tokenId] = _to;
emit Transfer(_from, _to, _tokenId);
}
function burn(address _owner, string _tokenId) onlyOwner public returns (bool success) {
require(balances[_owner][_tokenId] > 0 && balances[_owner][_tokenId] == 100 * 10 ** uint256(decimals));
balances[_owner][_tokenId] = 0;
tokens[_tokenId] = address(0);
totalSupply = totalSupply.sub(1);
emit Burn(msg.sender, _tokenId);
return true;
}
}
由於 ERC721 不太符合我的需求，所以我結合 ERC20 和 ERC721 寫出了我的合約。合約儘量保持了ERC20的使用習慣，函數定義儘量兼容 ERC20。
我們來看下面的構造方法，每個種類的物品一個合約，例如字畫，陶瓷，青銅器。
constructor(
string tokenName,
string tokenSymbol,
uint decimalUnits
) public {
owner = msg.sender;
name = tokenName;
symbol = tokenSymbol;
decimals = decimalUnits;
totalSupply = 0;
}
通過下面函數，添加資產到 Token，使鏈上資產與Token綁定。
function add(address _owner, string _tokenId) onlyOwner returns(bool status){
balances[_owner][_tokenId] = 100 * 10 ** uint256(decimals);
tokens[_tokenId] = _owner;
totalSupply = totalSupply.add(1);
return true;
}
balances[_owner][_tokenId] = 100 * 10 ** uint256(decimals); 初始化份額是 100 表示 100%
totalSupply = totalSupply.add(1); 物品件數加一。可以用於統計鏈上資產的數量。
下面函數是查詢資產的持有人
function ownerOf(string _tokenId) constant returns (address owner) {
return tokens[_tokenId];
}
下面函數是，權益轉讓和權益份額轉讓。
function transfer(address _to, string _tokenId){
address _from = msg.sender;
uint256 amount = balances[_from][_tokenId];
transfer(_to, amount, _tokenId);
}
function transfer(address _to, uint256 _value, string _tokenId){
require(msg.sender == ownerOf(_tokenId));
require(msg.sender != _to);
require(_to != address(0));
address _from = msg.sender;
uint256 amount = balances[_from][_tokenId];
require(amount >= _value);
balances[_from][_tokenId] = balances[_from][_tokenId].sub(_value);
balances[_to][_tokenId] = balances[_to][_tokenId].add(_value);
tokens[_tokenId] = _to;
emit Transfer(_from, _to, _tokenId);
}
接下來，我們就是可以開發 Dapp 錢包了，在錢包中實現資產的轉移交易。
這個合約可以一直到 EOS 上，Hyperledger Fabric 不可以，因爲 Fabric 沒有鎖的機制，會導致計算出錯。
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