Openzeppelin ERC777标准实现
ERC777是一种能够向后兼容ERC20的代币标准，与ERC20的区别在于其新功能：openrater和hooks。
一、Operator
operator可以代理用户进行transfer、mint、burn操作，并且没有allowance的限制。应用场景举例：
1.有些朋友有多个以太坊钱包地址，不管是用于薅空投还是分批管理自己的代币资产；这样的情况下有时候会遇到这样的情况，即多个地址中只有一个地址具有ETH，别的地址都没有ETH，当需要对没有ETH的钱包地址进行代币交易或者转账时候，一般情况下只能通过向这些地址发送一些ETH作为手续费，然后进行转账操作，这样的过程相对而言繁琐，且会耗费一定的手续费。而ERC777的运营商功能允许某个地址充作其它地址的运营商，即多个地址的持有人可以将自己唯一一个有ETH 的地址作为其它地址的运营商，当其它地址需要转移代币时，可以直接由有ETH的地址代为操作，及由运营商地址控制，且手续费由运营商地址出，实际转移代币的地址无需支付手续费，这样的情况大大降低了重复多个钱包地址之间切换的冗余操作。
2.又如，某区块链公司的老板使用某种基于ERC777的A代币作为工资发放，公司账户一共有500万的A代币，而经过人事的计算，本月共应发总工资为200万代币A，那么公司老板就可以将财务的以太坊钱包地址作为运营商，并授权200万 A代币的使用权限，那么财务便有权限使用公司地址500万中的200万 A代币，并且对于公司来说，其余的金额是安全的。
operator包括两种类型：defaultOperators和operators，即合约初始默认添加的operator和自定义的operator，defaultOperators在合约构建时必须定义，而operators可以通过调用函数来授权。
二、Hooks
hooks是与ERC777的sender和receipient绑定的函数，发送和接收ERC777资产需分别调用IERC777Sender接口的tokensToSend的函数，以及IERC777Recipient接口的tokensReceived函数。而IERC777Sender和IERC777Recipient接口不需要发送方和接收方地址本身实现，而可以通过ERC1820注册表来调用实现了接口的合约。也就是说无论外部地址和合约地址，都可以通过ERC1820标准来注册想要调用的hooks函数。
三、接口
FUNCTIONS
name()
symbol()
granularity()//代币的粒度，当设为1时和ERC20代币相同
totalSupply()
balanceOf(owner)
send(recipient, amount, data)
burn(amount, data)
isOperatorFor(operator, tokenHolder)//判断operator地址是否是tokenHolder的operator
authorizeOperator(operator)//授权operator地址为当前msg.sender的operator
revokeOperator(operator)//取消operator授权
defaultOperators()//输出defaultOperators的地址列表
operatorSend(sender, recipient, amount, data, operatorData)//operator代理sender调用send函数，同时可以传入operator想要传入的数据operatorData
operatorBurn(account, amount, data, operatorData)//operator代理account调用burn函数，同时可以传入operator想要传入的数据operatorData
四、实现
//继承了Context合约，context合约提供了_msgSender()和_msgData()函数，在metatransaction中，往往需要找到最初始的调用者地址，而不是代理的地址，所以可以通过_msgSender()实现而不是简单调用msg.sender
contract ERC777 is Context, IERC777, IERC20 {
using Address for address;
//IERC1820Registry合约地址
IERC1820Registry internal constant _ERC1820_REGISTRY = IERC1820Registry(0x1820a4B7618BdE71Dce8cdc73aAB6C95905faD24);
mapping(address => uint256) private _balances;
uint256 private _totalSupply;
string private _name;
string private _symbol;
//得到合约名的哈希，通过keccak256哈希来查询该接口
bytes32 private constant _TOKENS_SENDER_INTERFACE_HASH = keccak256("ERC777TokensSender");
bytes32 private constant _TOKENS_RECIPIENT_INTERFACE_HASH = keccak256("ERC777TokensRecipient");
// This isn't ever read from - it's only used to respond to the defaultOperators query.
address[] private _defaultOperatorsArray;
// Immutable, but accounts may revoke them (tracked in __revokedDefaultOperators).
mapping(address => bool) private _defaultOperators;
// For each account, a mapping of its operators and revoked default operators.
mapping(address => mapping(address => bool)) private _operators;
mapping(address => mapping(address => bool)) private _revokedDefaultOperators;
// ERC20-allowances
mapping(address => mapping(address => uint256)) private _allowances;
/**
* @dev `defaultOperators` may be an empty array.
*/
constructor(
string memory name_,
string memory symbol_,
address[] memory defaultOperators_
) {
_name = name_;
_symbol = symbol_;
_defaultOperatorsArray = defaultOperators_;
for (uint256 i = 0; i < defaultOperators_.length; i++) {
_defaultOperators[defaultOperators_[i]] = true;
}
// register interfaces
_ERC1820_REGISTRY.setInterfaceImplementer(address(this), keccak256("ERC777Token"), address(this));
_ERC1820_REGISTRY.setInterfaceImplementer(address(this), keccak256("ERC20Token"), address(this));
}
/**
* @dev See {IERC777-name}.
*/
function name() public view virtual override returns (string memory) {
return _name;
}
/**
* @dev See {IERC777-symbol}.
*/
function symbol() public view virtual override returns (string memory) {
return _symbol;
}
/**
* @dev See {ERC20-decimals}.
*
* Always returns 18, as per the
* [ERC777 EIP](https://eips.ethereum.org/EIPS/eip-777#backward-compatibility).
*/
function decimals() public pure virtual returns (uint8) {
return 18;
}
/**
* @dev See {IERC777-granularity}.
*
* This implementation always returns `1`.
*/
function granularity() public view virtual override returns (uint256) {
return 1;
}
/**
* @dev See {IERC777-totalSupply}.
*/
function totalSupply() public view virtual override(IERC20, IERC777) returns (uint256) {
return _totalSupply;
}
/**
* @dev Returns the amount of tokens owned by an account (`tokenHolder`).
*/
function balanceOf(address tokenHolder) public view virtual override(IERC20, IERC777) returns (uint256) {
return _balances[tokenHolder];
}
/**
* @dev See {IERC777-send}.
*
* Also emits a {IERC20-Transfer} event for ERC20 compatibility.
*/
function send(
address recipient,
uint256 amount,
bytes memory data
) public virtual override {
_send(_msgSender(), recipient, amount, data, "", true);
}
/**
* @dev See {IERC20-transfer}.
*
* Unlike `send`, `recipient` is _not_ required to implement the {IERC777Recipient}
* interface if it is a contract.
*
* Also emits a {Sent} event.
*/
function transfer(address recipient, uint256 amount) public virtual override returns (bool) {
_send(_msgSender(), recipient, amount, "", "", false);
return true;
}
/**
* @dev See {IERC777-burn}.
*
* Also emits a {IERC20-Transfer} event for ERC20 compatibility.
*/
function burn(uint256 amount, bytes memory data) public virtual override {
_burn(_msgSender(), amount, data, "");
}
/**
* @dev See {IERC777-isOperatorFor}.
*/
function isOperatorFor(address operator, address tokenHolder) public view virtual override returns (bool) {
return
operator == tokenHolder ||
(_defaultOperators[operator] && !_revokedDefaultOperators[tokenHolder][operator]) ||
_operators[tokenHolder][operator];
}
/**
* @dev See {IERC777-authorizeOperator}.
*/
function authorizeOperator(address operator) public virtual override {
require(_msgSender() != operator, "ERC777: authorizing self as operator");
if (_defaultOperators[operator]) {
delete _revokedDefaultOperators[_msgSender()][operator];
} else {
_operators[_msgSender()][operator] = true;
}
emit AuthorizedOperator(operator, _msgSender());
}
/**
* @dev See {IERC777-revokeOperator}.
*/
function revokeOperator(address operator) public virtual override {
require(operator != _msgSender(), "ERC777: revoking self as operator");
if (_defaultOperators[operator]) {
_revokedDefaultOperators[_msgSender()][operator] = true;
} else {
delete _operators[_msgSender()][operator];
}
emit RevokedOperator(operator, _msgSender());
}
/**
* @dev See {IERC777-defaultOperators}.
*/
function defaultOperators() public view virtual override returns (address[] memory) {
return _defaultOperatorsArray;
}
/**
* @dev See {IERC777-operatorSend}.
*
* Emits {Sent} and {IERC20-Transfer} events.
*/
function operatorSend(
address sender,
address recipient,
uint256 amount,
bytes memory data,
bytes memory operatorData
) public virtual override {
require(isOperatorFor(_msgSender(), sender), "ERC777: caller is not an operator for holder");
_send(sender, recipient, amount, data, operatorData, true);
}
/**
* @dev See {IERC777-operatorBurn}.
*
* Emits {Burned} and {IERC20-Transfer} events.
*/
function operatorBurn(
address account,
uint256 amount,
bytes memory data,
bytes memory operatorData
) public virtual override {
require(isOperatorFor(_msgSender(), account), "ERC777: caller is not an operator for holder");
_burn(account, amount, data, operatorData);
}
/**
* @dev See {IERC20-allowance}.
*
* Note that operator and allowance concepts are orthogonal: operators may
* not have allowance, and accounts with allowance may not be operators
* themselves.
*/
function allowance(address holder, address spender) public view virtual override returns (uint256) {
return _allowances[holder][spender];
}
/**
* @dev See {IERC20-approve}.
*
* NOTE: If `value` is the maximum `uint256`, the allowance is not updated on
* `transferFrom`. This is semantically equivalent to an infinite approval.
*
* Note that accounts cannot have allowance issued by their operators.
*/
function approve(address spender, uint256 value) public virtual override returns (bool) {
address holder = _msgSender();
_approve(holder, spender, value);
return true;
}
/**
* @dev See {IERC20-transferFrom}.
*
* NOTE: Does not update the allowance if the current allowance
* is the maximum `uint256`.
*
* Note that operator and allowance concepts are orthogonal: operators cannot
* call `transferFrom` (unless they have allowance), and accounts with
* allowance cannot call `operatorSend` (unless they are operators).
*
* Emits {Sent}, {IERC20-Transfer} and {IERC20-Approval} events.
*/
function transferFrom(
address holder,
address recipient,
uint256 amount
) public virtual override returns (bool) {
address spender = _msgSender();
_spendAllowance(holder, spender, amount);
_send(holder, recipient, amount, "", "", false);
return true;
}
/**
* @dev Creates `amount` tokens and assigns them to `account`, increasing
* the total supply.
*
* If a send hook is registered for `account`, the corresponding function
* will be called with the caller address as the `operator` and with
* `userData` and `operatorData`.
*
* See {IERC777Sender} and {IERC777Recipient}.
*
* Emits {Minted} and {IERC20-Transfer} events.
*
* Requirements
*
* - `account` cannot be the zero address.
* - if `account` is a contract, it must implement the {IERC777Recipient}
* interface.
*/
function _mint(
address account,
uint256 amount,
bytes memory userData,
bytes memory operatorData
) internal virtual {
_mint(account, amount, userData, operatorData, true);
}
/**
* @dev Creates `amount` tokens and assigns them to `account`, increasing
* the total supply.
*
* If `requireReceptionAck` is set to true, and if a send hook is
* registered for `account`, the corresponding function will be called with
* `operator`, `data` and `operatorData`.
*
* See {IERC777Sender} and {IERC777Recipient}.
*
* Emits {Minted} and {IERC20-Transfer} events.
*
* Requirements
*
* - `account` cannot be the zero address.
* - if `account` is a contract, it must implement the {IERC777Recipient}
* interface.
*/
function _mint(
address account,
uint256 amount,
bytes memory userData,
bytes memory operatorData,
bool requireReceptionAck
) internal virtual {
require(account != address(0), "ERC777: mint to the zero address");
address operator = _msgSender();
_beforeTokenTransfer(operator, address(0), account, amount);
// Update state variables
_totalSupply += amount;
_balances[account] += amount;
_callTokensReceived(operator, address(0), account, amount, userData, operatorData, requireReceptionAck);
emit Minted(operator, account, amount, userData, operatorData);
emit Transfer(address(0), account, amount);
}
/**
* @dev Send tokens
* @param from address token holder address
* @param to address recipient address
* @param amount uint256 amount of tokens to transfer
* @param userData bytes extra information provided by the token holder (if any)
* @param operatorData bytes extra information provided by the operator (if any)
* @param requireReceptionAck if true, contract recipients are required to implement ERC777TokensRecipient
*/
function _send(
address from,
address to,
uint256 amount,
bytes memory userData,
bytes memory operatorData,
bool requireReceptionAck
) internal virtual {
require(from != address(0), "ERC777: transfer from the zero address");
require(to != address(0), "ERC777: transfer to the zero address");
address operator = _msgSender();
_callTokensToSend(operator, from, to, amount, userData, operatorData);
_move(operator, from, to, amount, userData, operatorData);
_callTokensReceived(operator, from, to, amount, userData, operatorData, requireReceptionAck);
}
/**
* @dev Burn tokens
* @param from address token holder address
* @param amount uint256 amount of tokens to burn
* @param data bytes extra information provided by the token holder
* @param operatorData bytes extra information provided by the operator (if any)
*/
function _burn(
address from,
uint256 amount,
bytes memory data,
bytes memory operatorData
) internal virtual {
require(from != address(0), "ERC777: burn from the zero address");
address operator = _msgSender();
_callTokensToSend(operator, from, address(0), amount, data, operatorData);
_beforeTokenTransfer(operator, from, address(0), amount);
// Update state variables
uint256 fromBalance = _balances[from];
require(fromBalance >= amount, "ERC777: burn amount exceeds balance");
unchecked {
_balances[from] = fromBalance - amount;
}
_totalSupply -= amount;
emit Burned(operator, from, amount, data, operatorData);
emit Transfer(from, address(0), amount);
}
function _move(
address operator,
address from,
address to,
uint256 amount,
bytes memory userData,
bytes memory operatorData
) private {
_beforeTokenTransfer(operator, from, to, amount);
uint256 fromBalance = _balances[from];
require(fromBalance >= amount, "ERC777: transfer amount exceeds balance");
//unchecked用来减少gas消耗，因为0.8.0版本以后的solidity默认检查over/underflow，
//而如果能保证计算不会over/underflow或者已经添加过检查的逻辑，则可以使用unchecked关键字包裹跳过溢出check
unchecked {
_balances[from] = fromBalance - amount;
}
_balances[to] += amount;
emit Sent(operator, from, to, amount, userData, operatorData);
emit Transfer(from, to, amount);
}
/**
* @dev See {ERC20-_approve}.
*
* Note that accounts cannot have allowance issued by their operators.
*/
function _approve(
address holder,
address spender,
uint256 value
) internal virtual {
require(holder != address(0), "ERC777: approve from the zero address");
require(spender != address(0), "ERC777: approve to the zero address");
_allowances[holder][spender] = value;
emit Approval(holder, spender, value);
}
/**
* @dev Call from.tokensToSend() if the interface is registered
* @param operator address operator requesting the transfer
* @param from address token holder address
* @param to address recipient address
* @param amount uint256 amount of tokens to transfer
* @param userData bytes extra information provided by the token holder (if any)
* @param operatorData bytes extra information provided by the operator (if any)
*/
function _callTokensToSend(
address operator,
address from,
address to,
uint256 amount,
bytes memory userData,
bytes memory operatorData
) private {
address implementer = _ERC1820_REGISTRY.getInterfaceImplementer(from, _TOKENS_SENDER_INTERFACE_HASH);
if (implementer != address(0)) {
IERC777Sender(implementer).tokensToSend(operator, from, to, amount, userData, operatorData);
}
}
/**
* @dev Call to.tokensReceived() if the interface is registered. Reverts if the recipient is a contract but
* tokensReceived() was not registered for the recipient
* @param operator address operator requesting the transfer
* @param from address token holder address
* @param to address recipient address
* @param amount uint256 amount of tokens to transfer
* @param userData bytes extra information provided by the token holder (if any)
* @param operatorData bytes extra information provided by the operator (if any)
* @param requireReceptionAck if true, contract recipients are required to implement ERC777TokensRecipient
*/
function _callTokensReceived(
address operator,
address from,
address to,
uint256 amount,
bytes memory userData,
bytes memory operatorData,
bool requireReceptionAck
) private {
address implementer = _ERC1820_REGISTRY.getInterfaceImplementer(to, _TOKENS_RECIPIENT_INTERFACE_HASH);
if (implementer != address(0)) {
IERC777Recipient(implementer).tokensReceived(operator, from, to, amount, userData, operatorData);
} else if (requireReceptionAck) {
require(!to.isContract(), "ERC777: token recipient contract has no implementer for ERC777TokensRecipient");
}
}
/**
* @dev Updates `owner` s allowance for `spender` based on spent `amount`.
*
* Does not update the allowance amount in case of infinite allowance.
* Revert if not enough allowance is available.
*
* Might emit an {IERC20-Approval} event.
*/
function _spendAllowance(
address owner,
address spender,
uint256 amount
) internal virtual {
uint256 currentAllowance = allowance(owner, spender);
if (currentAllowance != type(uint256).max) {
require(currentAllowance >= amount, "ERC777: insufficient allowance");
unchecked {
_approve(owner, spender, currentAllowance - amount);
}
}
}
/**
* @dev Hook that is called before any token transfer. This includes
* calls to {send}, {transfer}, {operatorSend}, minting and burning.
*
* Calling conditions:
*
* - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
* will be to transferred to `to`.
* - when `from` is zero, `amount` tokens will be minted for `to`.
* - when `to` is zero, `amount` of ``from``'s tokens will be burned.
* - `from` and `to` are never both zero.
*
* To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
*/
function _beforeTokenTransfer(
address operator,
address from,
address to,
uint256 amount
) internal virtual {
}
}