ERC20代币合约规则简介

ERC20 是各个代币的标准接口。ERC20 代币仅仅是以太坊代币的子集，为了充分兼容 ERC20，开发者需要将一组特定的函数（接口）集成到他们的智能合约中，以便在高层面能够执行这些操作：获得代币总供应量、获得账户余额、转让代币、批准花费代币。

ERC20 让以太坊区块链上的其他智能合约和去中心化应用之间无缝交互。一些具有部分但非所有ERC20标准功能的代币被认为是部分ERC20兼容，这还要视其具体缺失的功能而定，但总体是它们仍然很容易与外部交互。

简单的来说：ERC20接口就是一套在智能合约上开发Token(代币)的规范协议。

需要说明的是：代币是运行在智能合约上的币，其没有自己的私链，交易代币需要调用函数而不是在以太坊上真正的发起一个交易，可以看做以太坊账户的附属品。每个账户可能在多个合约代币中有贮藏代币。

ERC20协议的详细讲解可见尚硅谷视频：https://www.bilibili.com/video/BV1NJ411D7rf?p=34

USDT代币

现在市值较大的代币都基本支持ERC20接口规范，ERC20接口规范构造简单。

本文主要通过研究目前在以太坊上运行的市值最高的USDT代币，以此来了解ERC20这一代币规范的使用。

USDT代币的合约架构

USDT代币功能

ERC20要求下的转账、余额查询、授权消费功能
代币紧急暂停与重起
代币用户黑名单
合约便捷升级，可适应非ERC20协议代币
代币管理者权限移交

USDT代币合约源码

对着源码撸了一遍，做了略微改动（适应编译器版本）以及详细的内容说明。

适应版本： 0.4.22版本编译器无warning无error

pragma solidity >0.4.17;/*** @title SafeMath 数学安全函数* @dev Math operations with safety checks that throw on error.*/
library SafeMath {function mul(uint256 a, uint256 b) internal pure returns (uint256) {if (a == 0) {return 0;}uint256 c = a * b;assert(c / a == b);return c;}function div(uint256 a, uint256 b) internal pure returns (uint256) {// 分母大于0在solidity合约中已经会自动判定了// assert(b > 0); // Solidity automatically throws when dividing by 0uint256 c = a / b;// assert(a == b * c + a % b); // There is no case in which this doesn't holdreturn c;}function sub(uint256 a, uint256 b) internal pure returns (uint256) {assert(b <= a);return a - b;}function add(uint256 a, uint256 b) internal pure returns (uint256) {uint256 c = a + b;assert(c >= a);return c;}
}/*** @title Ownable 代币的拥有者* @dev The Ownable contract has an owner address, and provides basic authorization control.* @dev functions, this simplifies the implementation of "user permissions".* @dev 这个合约主要是指明合约创建人为代币的创建者，还包括授权控制功能，简化“用户权限”.*/contract Ownable{//"拥有者"address public owner;/*** @dev The Ownable constructor sets the original `owner` of the contract to the sender* account.* @dev 把创建合约的人作为初始的“拥有者”.*/constructor() public{owner = msg.sender;}/*** @dev Throws if called by any account other than the owner.* @dev 暂时未知, 应该是只能拥有者进行的操作.*/modifier onlyOwner(){require(msg.sender == owner, "仅owner调用！");//这一行表示继承此合约中使用_;}/*** @dev Allows the current owner to transfer control of the contract to a newOwner.* @dev 权力转移给新的拥有者* @param newOwner The address to transfer ownership to.*/function transferOwnership(address newOwner) public onlyOwner{//先确保新用户不是0x0地址require(newOwner != address(0), "不能给地址0转移owner");owner = newOwner;}
}/*** @title ERC20Basic 基于REC20，不是直接继承，而是类似的代码* @dev Simpler version of ERC20 interface  对于ERC20标准接口的简化版本* @dev see https://github.com/ethereum/EIPs/issues/20* @dev 新版本的编译器0.6.1要求抽象合约前要加abstract，并且抽象函数要加上virtual*/
contract ERC20Basic{//定义接口的一系列函数uint public _totalSupply;//总发行货币量function totalSupply() public view returns(uint);//查看总货币量函数function balanceOf(address who) public view returns(uint);//查某人余额function transfer(address to, uint value) public;//转账交易函数event Transfer(address indexed from, address indexed to, uint value);//定义转账记录事件}/*** @title ERC20 interface* @dev see https://github.com/ethereum/EIPs/issues/20* @dev 继承与上面的接口*/
contract ERC20 is ERC20Basic{//拓展了第三方授权功能//授权给别人用自己的钱，返回钱数？function allowance(address owner, address spender) public view returns(uint);//借助谁（from）向谁（to）转币function transferFrom(address from, address to, uint value) public;//授权使用额度函数function approve(address spender, uint value) public;//记录授权event Approval(address indexed owner, address indexed spender, uint value);
}/*** @title Basic token 基础代币* @dev Basic version of StandardToken, with no allowances.* @dev 仅实现代币基本功能（没有第三方授权）* */contract BasicToken is Ownable, ERC20Basic{//使用安全数学函数using SafeMath for uint;mapping(address => uint) public balances;// additional variables for use if transaction fees ever became necessary// 如果有必要收取交易费用，可使用其他变量uint public basisPointsRate = 0; //基本利率uint public maximunFee = 0; //最大利息金额/*** @dev Fix for the ERC20 short address attack. 防止短地址攻击，具体可看博客ERC20文章* @dev 凡是涉及转账交易（合约调用）都需要加上这一限制*/modifier onlyPayloadSize(uint size){//msg.data就是data域（calldata）中的内容，一般来说都是4（函数名）+32（转账地址）+32（转账金额）=68字节//短地址攻击简单来说就是转账地址后面为0但故意缺省，导致金额32字节前面的0被当做地址而后面自动补0导致转账金额激增。//参数size就是除函数名外的剩下字节数//解决方法：对后面的的字节数的长度限制要求require(!(msg.data.length < size+4), "Invalid short address");_;}/*** @dev transfer token for a specified address 转给一个符合规定（非短地址）的地址* @param _to The address to transfer to. 转账地址* @param _value The amount to be transferred. 转账金额*/function transfer(address _to, uint _value) public onlyPayloadSize(2 * 32){//先算利息: （转账金额*基本利率)/10000  (ps:因为浮点会精度缺失，所以这样计算)uint fee = (_value.mul(basisPointsRate)).div(10000);//判断是否超最大额if (fee > maximunFee) fee = maximunFee;//计算剩下的钱uint sendAmount = _value.sub(fee);//转账的钱要够   源码没加这个判断不知为何？//不需要检查，因为后面balances[msg.sender].sub(sendAmount)其中会检查，不够会报异常。//require(balances[msg.sender] >= _value);//有安全数学函数就不用判断溢出了//扣钱balances[msg.sender] = balances[msg.sender].sub(sendAmount);//加钱balances[_to] = balances[_to].add(sendAmount);//利息去向->ownerif (fee > 0){//因为继承于Ownable，所以可以拿到ownerbalances[owner] = balances[owner].add(fee);//继承于ERCBasic接口，其中申明了Transfer记录//记录利息去向emit Transfer(msg.sender, owner, fee);}//记录转账去向,注意记录的不是总金额而是去除交易费的金额emit Transfer(msg.sender, _to, sendAmount);}/*** @dev Gets the balance of the specified address. 查余额函数* @param _owner The address to query the the balance of.* @return An uint representing the amount owned by the passed address.*/function balanceOf(address _owner) public view returns(uint balance){return balances[_owner];}}
/*** @title Standard ERC20 token ERC20标准代币** @dev Implementation of the basic standard token.  依据基本代币准则* @dev https://github.com/ethereum/EIPs/issues/20* @dev Based oncode by FirstBlood: https://github.com/Firstbloodio/token/blob/master/smart_contract/FirstBloodToken.sol* @dev 借鉴了firstblood代币* @dev 对代币基础功能的拓展-> 添加了第三方授权功能*/
contract StandardToken is BasicToken, ERC20{//授权金额映射：某人对其他所有人授权的金额的映射mapping(address => mapping(address => uint)) public allowed;//uint最大值uint public constant MAX_UINT = 2**256-1;/*** @dev Transfer tokens from one address to another 授权转账：从一个账户转到另一个账户* @param _from address The address which you want to send tokens from 已得到授权的账户* @param _to address The address which you want to transfer to 转向的账户* @param _value uint the amount of tokens to be transferred 转账金额*/function transferFrom(address _from, address _to, uint _value) public onlyPayloadSize(2 * 32){//授权金额：授权者对于当前调用者授权其可使用的金额量uint _allowance = allowed[_from][msg.sender];//在这里同样不需要检查授权金额是否足够,后面的sub函数这种情况会检测// require(_allowance >= _value);//1.先算利息uint fee = (_value.mul(basisPointsRate)).div(10000);if (fee > maximunFee) fee = maximunFee;//2.扣钱// 这里为什么要判断？if (_allowance < MAX_UINT){//注意这里扣去的是总金额，包括了利息都要从授权方的授权金额去除allowed[_from][msg.sender] = _allowance.sub(_value);}balances[_from] = balances[_from].sub(_value);//3.加钱uint sendAmount = _value.sub(fee);balances[_to] = balances[_to].add(sendAmount);//4.利息去向if (fee > 0){balances[owner] = balances[owner].add(fee);emit Transfer(_from, owner, fee);}//5.记录emit Transfer(_from, _to, sendAmount);}/*** @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender.* @dev 调用者授权给他人可使用金额* @param _spender The address which will spend the funds. 被授权者* @param _value The amount of tokens to be spent. 金额*/function approve(address _spender, uint _value) public onlyPayloadSize(2 * 32){// To change the approve amount you first have to reduce the addresses`//  allowance to zero by calling `approve(_spender, 0)` if it is not//  already 0 to mitigate the race condition described here://  https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729//这里的限定条件是：不能将已设置过的授权金额改动，除非改为0。//也就是说对他人的授权金额只能是从0改为value,这一次机会，再改就只能改回到0require(!(_value != 0 && allowed[msg.sender][_spender] != 0), "You have only one chance to approve , you can only change it to 0 later");//1.改allowedallowed[msg.sender][_spender] = _value;//2. 记录emit Approval(msg.sender, _spender, _value);}/*** @dev Function to check the amount of tokens than an owner allowed to a spender.* @param _owner address The address which owns the funds. 地址拥有资金的地址。* @param _spender address The address which will spend the funds. 查看授权了多少钱* @return A uint specifying the amount of tokens still available for the spender.*/function allowance(address _owner, address _spender) public view returns(uint remaining){return allowed[_owner][_spender];}
}/*** @title Pausable 中断* @dev Base contract which allows children to implement an emergency stop mechanism.* @dev 实现紧急停止机制*/
contract Pausable is Ownable{event Pause();event Unpause();bool public paused = false;/*** @dev Modifier to make a function callable only when the contract is not paused.* @dev 限制条件：函数只能是在合约未停止情况下执行.*/modifier whenNotPaused(){require(!paused, "Must be used without pausing");_;}/*** @dev Modifier to make a function callable only when the contract is paused.* @dev 函数只能在停止条件下执行*/modifier whenPaused(){require(paused, "Must be used under pause");_;}/*** @dev called by the owner to pause, triggers stopped state* @dev 只能由代币管理者进行停止**/function pause() public onlyOwner whenNotPaused {paused = true;emit Pause();}/*** @dev called by the owner to unpause, returns to normal state* @dev 只能是代币管理者进行重开*/function unpause() public onlyOwner whenPaused{paused = false;emit Unpause();}
}/*** @dev 列黑名单*/contract BlackList is Ownable, BasicToken{//黑名单映射mapping(address => bool) isBlackListed;//事件event DestroyedBlackFunds(address _blackListedUser, uint _balance);event AddedBlackList(address _user);event RemovedBlackList(address _user);//Getters to allow the same blacklist to be used also by other contracts (including upgraded Tether)//允许其他合约调用此黑名单(external)，查看此人是否被列入黑名单function getBlackListStatus(address _maker) external view returns(bool){return isBlackListed[_maker];}//获取当前代币的Ownerfunction getOwner() external view returns(address){return owner;}//增加黑名单function addBlackList(address _evilUser) public onlyOwner{isBlackListed[_evilUser] = true;emit AddedBlackList(_evilUser);}//去除某人黑名单function removeBlackList(address _clearUser) public onlyOwner{isBlackListed[_clearUser] = false;emit RemovedBlackList(_clearUser);}//去除掉黑名单账户的钱function destroyBlackFunds(address _blackListUser) public onlyOwner{//1. 检查是否在黑名单require(isBlackListed[_blackListUser], "You can only clear the money of users in the blacklist");//2. 查看要清除的钱uint dirtyFunds = balanceOf(_blackListUser);//3. 扣除清零balances[_blackListUser] = 0;//4. 总代币发行量减少_totalSupply = _totalSupply.sub(dirtyFunds);//5. 记录emit DestroyedBlackFunds(_blackListUser, dirtyFunds);}
}//标准代币拓展(为了适应不支持ERC20的情况或者是拓展)
contract UpgradedStandardToken is StandardToken{// those methods are called by the legacy contract// and they must ensure msg.sender to be the contract address// 这些拓展方法都是来自遗留合同// 并且合约调用者必须是合约地址function transferByLegacy(address from, address to, uint value) public;function transferFromByLegacy(address sender, address from, address spender, uint value) public;function approveByLegacy(address from, address spender, uint value) public;
}//主体代币
contract TetherToken is Pausable, StandardToken, BlackList{string public name;  //代币名string public symbol; //标志uint public decimals; //精度/小数点后几位address public upgradedAddress; //升级合约的地址（必须是合约地址）bool public deprecated; //弃用（支持ERC20与否）//  The contract can be initialized with a number of tokens 可初始化多个代币//  All the tokens are deposited to the owner address//// @param _balance Initial supply of the contract// @param _name Token Name// @param _symbol Token symbol// @param _decimals Token decimalsconstructor(uint _initialSupply,string _name,string _symbol,uint _decimals) public {//总发行币都给owner_totalSupply = _initialSupply;balances[owner] = _initialSupply;name = _name;symbol = _symbol;decimals = _decimals;deprecated = false;}// Called when new token are issuedevent Issue(uint amount);// Called when tokens are redeemedevent Redeem(uint amount);// Called when contract is deprecatedevent Deprecate(address newAddress);// Called if contract ever adds feesevent Params(uint feeBasisPoints, uint maxFee);// Forward ERC20 methods to upgraded contract if this one is deprecated//如果不推荐使用ERC20方法，则将其转为升级的合同function transfer(address _to, uint _value) public whenNotPaused{//排除黑名单require(!isBlackListed[msg.sender], "The account you applied for is on the blacklist and cannot be transferred");//判断是否支持ERC20if(deprecated){//不支持的话就调用用upgradedAddress实例化的对象的transferByLegacy函数//不知道这里为什么要传msg.sender？//我猜测是重新升级适配函数的话调用此函数的人(msg.sender)也要转过去return UpgradedStandardToken(upgradedAddress).transferByLegacy(msg.sender, _to, _value);}else{//支持的话就直接调用ERC20的转账//这里没有返回值，不知道为什么还要加returnreturn super.transfer(_to, _value);}}//同理：// Forward ERC20 methods to upgraded contract if this one is deprecatedfunction transferFrom(address _from, address _to, uint _value) public whenNotPaused{require(!isBlackListed[_from], "The account you applied for is on the blacklist and cannot be transferred");if(deprecated){return UpgradedStandardToken(upgradedAddress).transferFromByLegacy(msg.sender, _from, _to, _value);}else{return super.transferFrom(_from, _to, _value);}}// Forward ERC20 methods to upgraded contract if this one is deprecated//注意这里查询余额在代币暂停的情况下也是可以使用的function balanceOf(address who) public view returns(uint){if(deprecated){return UpgradedStandardToken(upgradedAddress).balanceOf(who);}else{return super.balanceOf(who);}}// Forward ERC20 methods to upgraded contract if this one is deprecatedfunction approve(address _spender, uint _value) public whenNotPaused{//这里不用检查了，如果是在黑名单中，那么授权再多也没用，transferFrom的时候就检测出来了if(deprecated){return UpgradedStandardToken(upgradedAddress).approveByLegacy(msg.sender, _spender, _value);}else{return super.approve(_spender, _value);}}// Forward ERC20 methods to upgraded contract if this one is deprecatedfunction allowance(address _owner, address _spender) public view returns(uint){if(deprecated){return UpgradedStandardToken(upgradedAddress).allowance(_owner, _spender);}else{return super.allowance(_owner, _spender);}}// deprecate current contract in favour of a new one//反对现行合同，改用新合同. upgradedAddress新合同地址function deprecate(address _upgradedAddress) public onlyOwner{deprecated = true;upgradedAddress = _upgradedAddress;//记录emit Deprecate(_upgradedAddress);}// deprecate current contract if favour of a new one//反对现行合同，如果想换一个新合约,需要提前知道当前发行量function totalSupply() public view returns(uint){if(deprecated){return UpgradedStandardToken(upgradedAddress).totalSupply();}else{return _totalSupply;}}// Issue a new amount of tokens 发行新数量的代币// these tokens are deposited into the owner address//// @param _amount Number of tokens to be issuedfunction issue(uint _amount) public onlyOwner{//增加拥有者的量balances[owner] = balances[owner].add(_amount);//增加发行的总代币量_totalSupply = _totalSupply.add(_amount);//记录emit Issue(_amount);}// 调整利息率和最大利息限制function setParams(uint newBasisPoints, uint newMaxFee) public onlyOwner{// Ensure transparency by hardcoding limit beyond which fees can never be added//通过硬编码限制来确保透明度，超过这个限度就不能再增加费用了require(newBasisPoints < 20, "The new BasisPoints cannot exceed 20"); //0.002require(newMaxFee < 50, "The new MaxFee cannot exceed 50"); //5*10**(decimals+1)basisPointsRate = newBasisPoints;maximunFee = newMaxFee.mul(10**decimals);//记录emit Params(newBasisPoints, newMaxFee);}
}

代币运行效果（功能测试）

测试账户：

0xca35b7d915458ef540ade6068dfe2f44e8fa733c(账户一733c)
0x14723a09acff6d2a60dcdf7aa4aff308fddc160c(账户二160c)

发布：

发布需要注意的是因为合约内容较多，gaslimit要设置的大一些，默认的值可能不够用。

消耗gas的操作函数：

view或public参数查询：

合约发布者就是当前的owner：

transfer 转账

代币发行总量（部署时已设置）：

这些代币都会初始化在owner账户上，由其转发给其他账户。

两种查询余额的方式：

账户一转账给账户二：

注意：此时应该是账户一发起交易调用。

余额变动：
transferFrom 授权转账

先查看授权额度：

账户一对账户二的授权默认都是0：

设置授权额度：

再次查询：

授权额度的使用：

登录账户二：

转788给自己，之前的余额是999

余额变化：

现在的额度还剩：

100

还剩100额度不够花了，能否直接增加授权额度？试试

不能。授权额度只能在第一次设置，设置后只能再设置回0再设置新的额度！

转移owner

此功能只能是当前的owner调用

owner是账户二了

紧急暂停合约（暂停所有交易，但是查询还是可以）

此功能只能是当前的owner调用

无参数：

交易无法实现：

恢复同理不再演示

黑名单功能

此功能只能是当前的owner调用

把账户一设置为黑名单

被列为黑名单后是无法交易的。

删除黑名单中人的钱（销毁）

总量少了：

去除黑名单人员：

新发行代币

此功能只能是当前的owner调用

这些币同样的会到当前owner账户中

设置交易利息率和最高利息

此功能只能是当前的owner调用

因为精度设置的是16

升级代币合约

此功能只能是当前的owner调用

填入新的合约地址，那么这些操作函数被调用时会执行新合约地址中的函数。

博主原创文章，未经许可禁止转载
更多文章请访问博主个人博客：https://myblog.gumptlu.work/

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