我已经实现了自己的 ERC20 令牌（基于 OpenZeppelin 的实现）。我为我的代币创建了一个供应，并根据本指南使用该供应创建了一个非常简单的去中心化交易所（DEX） 。我不明白为什么ERC20: mint to the zero address exception当我注释掉导致它的代码部分时我仍然得到。我确保我truffle migrate --reset在更改合同后跑步。我还重新启动了 Ganache，然后重新编译并再次迁移所有合约，但无济于事。
这是我的 ERC20 令牌的代码（与 OpenZeppelin 实现相同）MyCoin.sol：
/*
Taken from https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/token/ERC20/ERC20.sol
*/
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.3.2 (token/ERC20/ERC20.sol)
pragma solidity ^0.8.0;
import "./IERC20.sol";
import "./extensions/IERC20Metadata.sol";
import "./utils/Context.sol";
/**
* @dev Implementation of the {IERC20} interface.
*
* This implementation is agnostic to the way tokens are created. This means
* that a supply mechanism has to be added in a derived contract using {_mint}.
* For a generic mechanism see {ERC20PresetMinterPauser}.
*
* TIP: For a detailed writeup see our guide
* https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226[How
* to implement supply mechanisms].
*
* We have followed general OpenZeppelin Contracts guidelines: functions revert
* instead returning `false` on failure. This behavior is nonetheless
* conventional and does not conflict with the expectations of ERC20
* applications.
*
* Additionally, an {Approval} event is emitted on calls to {transferFrom}.
* This allows applications to reconstruct the allowance for all accounts just
* by listening to said events. Other implementations of the EIP may not emit
* these events, as it isn't required by the specification.
*
* Finally, the non-standard {decreaseAllowance} and {increaseAllowance}
* functions have been added to mitigate the well-known issues around setting
* allowances. See {IERC20-approve}.
*/
contract MyCoin is Context, IERC20, IERC20Metadata {
mapping(address => uint256) private _balances;
mapping(address => mapping(address => uint256)) private _allowances;
uint256 private _totalSupply;
string private _name;
string private _symbol;
/**
* @dev Sets the values for {name} and {symbol}.
*
* The default value of {decimals} is 18. To select a different value for
* {decimals} you should overload it.
*
* All two of these values are immutable: they can only be set once during
* construction.
*/
constructor(string memory name_, string memory symbol_) {
_name = name_;
_symbol = symbol_;
}
/**
* @dev Returns the name of the token.
*/
function name() public view virtual override returns (string memory) {
return _name;
}
/**
* @dev Returns the symbol of the token, usually a shorter version of the
* name.
*/
function symbol() public view virtual override returns (string memory) {
return _symbol;
}
/**
* @dev Returns the number of decimals used to get its user representation.
* For example, if `decimals` equals `2`, a balance of `505` tokens should
* be displayed to a user as `5.05` (`505 / 10 ** 2`).
*
* Tokens usually opt for a value of 18, imitating the relationship between
* Ether and Wei. This is the value {ERC20} uses, unless this function is
* overridden;
*
* NOTE: This information is only used for _display_ purposes: it in
* no way affects any of the arithmetic of the contract, including
* {IERC20-balanceOf} and {IERC20-transfer}.
*/
function decimals() public view virtual override returns (uint8) {
return 18;
}
/**
* @dev See {IERC20-totalSupply}.
*/
function totalSupply() public view virtual override returns (uint256) {
return _totalSupply;
}
/**
* @dev See {IERC20-balanceOf}.
*/
function balanceOf(address account) public view virtual override returns (uint256) {
return _balances[account];
}
/**
* @dev See {IERC20-transfer}.
*
* Requirements:
*
* - `recipient` cannot be the zero address.
* - the caller must have a balance of at least `amount`.
*/
function transfer(address recipient, uint256 amount) public virtual override returns (bool) {
_transfer(_msgSender(), recipient, amount);
return true;
}
/**
* @dev See {IERC20-allowance}.
*/
function allowance(address owner, address spender) public view virtual override returns (uint256) {
return _allowances[owner][spender];
}
/**
* @dev See {IERC20-approve}.
*
* Requirements:
*
* - `spender` cannot be the zero address.
*/
function approve(address spender, uint256 amount) public virtual override returns (bool) {
_approve(_msgSender(), spender, amount);
return true;
}
/**
* @dev See {IERC20-transferFrom}.
*
* Emits an {Approval} event indicating the updated allowance. This is not
* required by the EIP. See the note at the beginning of {ERC20}.
*
* Requirements:
*
* - `sender` and `recipient` cannot be the zero address.
* - `sender` must have a balance of at least `amount`.
* - the caller must have allowance for ``sender``'s tokens of at least
* `amount`.
*/
function transferFrom(
address sender,
address recipient,
uint256 amount
) public virtual override returns (bool) {
_transfer(sender, recipient, amount);
uint256 currentAllowance = _allowances[sender][_msgSender()];
require(currentAllowance >= amount, "ERC20: transfer amount exceeds allowance");
unchecked {
_approve(sender, _msgSender(), currentAllowance - amount);
}
return true;
}
/**
* @dev Atomically increases the allowance granted to `spender` by the caller.
*
* This is an alternative to {approve} that can be used as a mitigation for
* problems described in {IERC20-approve}.
*
* Emits an {Approval} event indicating the updated allowance.
*
* Requirements:
*
* - `spender` cannot be the zero address.
*/
function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
_approve(_msgSender(), spender, _allowances[_msgSender()][spender] + addedValue);
return true;
}
/**
* @dev Atomically decreases the allowance granted to `spender` by the caller.
*
* This is an alternative to {approve} that can be used as a mitigation for
* problems described in {IERC20-approve}.
*
* Emits an {Approval} event indicating the updated allowance.
*
* Requirements:
*
* - `spender` cannot be the zero address.
* - `spender` must have allowance for the caller of at least
* `subtractedValue`.
*/
function decreaseAllowance(address spender, uint256 subtractedValue) public virtual returns (bool) {
uint256 currentAllowance = _allowances[_msgSender()][spender];
require(currentAllowance >= subtractedValue, "ERC20: decreased allowance below zero");
unchecked {
_approve(_msgSender(), spender, currentAllowance - subtractedValue);
}
return true;
}
/**
* @dev Moves `amount` of tokens from `sender` to `recipient`.
*
* This internal function is equivalent to {transfer}, and can be used to
* e.g. implement automatic token fees, slashing mechanisms, etc.
*
* Emits a {Transfer} event.
*
* Requirements:
*
* - `sender` cannot be the zero address.
* - `recipient` cannot be the zero address.
* - `sender` must have a balance of at least `amount`.
*/
function _transfer(
address sender,
address recipient,
uint256 amount
) internal virtual {
require(sender != address(0), "ERC20: transfer from the zero address");
require(recipient != address(0), "ERC20: transfer to the zero address");
_beforeTokenTransfer(sender, recipient, amount);
uint256 senderBalance = _balances[sender];
require(senderBalance >= amount, "ERC20: transfer amount exceeds balance");
unchecked {
_balances[sender] = senderBalance - amount;
}
_balances[recipient] += amount;
emit Transfer(sender, recipient, amount);
_afterTokenTransfer(sender, recipient, amount);
}
/** @dev Creates `amount` tokens and assigns them to `account`, increasing
* the total supply.
*
* Emits a {Transfer} event with `from` set to the zero address.
*
* Requirements:
*
* - `account` cannot be the zero address.
*/
function _mint(address account, uint256 amount) internal virtual {
// require(account != address(0), "ERC20: mint to the zero address"); // this is commented out for development purposes; TODO: uncomment this in production
_beforeTokenTransfer(address(0), account, amount);
_totalSupply += amount;
_balances[account] += amount;
emit Transfer(address(0), account, amount);
_afterTokenTransfer(address(0), account, amount);
}
/**
* @dev Destroys `amount` tokens from `account`, reducing the
* total supply.
*
* Emits a {Transfer} event with `to` set to the zero address.
*
* Requirements:
*
* - `account` cannot be the zero address.
* - `account` must have at least `amount` tokens.
*/
function _burn(address account, uint256 amount) internal virtual {
require(account != address(0), "ERC20: burn from the zero address");
_beforeTokenTransfer(account, address(0), amount);
uint256 accountBalance = _balances[account];
require(accountBalance >= amount, "ERC20: burn amount exceeds balance");
unchecked {
_balances[account] = accountBalance - amount;
}
_totalSupply -= amount;
emit Transfer(account, address(0), amount);
_afterTokenTransfer(account, address(0), amount);
}
/**
* @dev Sets `amount` as the allowance of `spender` over the `owner` s tokens.
*
* This internal function is equivalent to `approve`, and can be used to
* e.g. set automatic allowances for certain subsystems, etc.
*
* Emits an {Approval} event.
*
* Requirements:
*
* - `owner` cannot be the zero address.
* - `spender` cannot be the zero address.
*/
function _approve(
address owner,
address spender,
uint256 amount
) internal virtual {
require(owner != address(0), "ERC20: approve from the zero address");
require(spender != address(0), "ERC20: approve to the zero address");
_allowances[owner][spender] = amount;
emit Approval(owner, spender, amount);
}
/**
* @dev Hook that is called before any transfer of tokens. This includes
* minting and burning.
*
* Calling conditions:
*
* - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
* will be 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 from,
address to,
uint256 amount
) internal virtual {}
/**
* @dev Hook that is called after any transfer of tokens. This includes
* minting and burning.
*
* Calling conditions:
*
* - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
* has been transferred to `to`.
* - when `from` is zero, `amount` tokens have been minted for `to`.
* - when `to` is zero, `amount` of ``from``'s tokens have been 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 _afterTokenTransfer(
address from,
address to,
uint256 amount
) internal virtual {}
}
注意我是如何注释掉require._mint
这是代码MyCoinSupply.sol：
/*
Adapted from from https://forum.openzeppelin.com/t/how-to-implement-erc20-supply-mechanisms/226
*/
pragma solidity ^0.8.0;
import "./MyCoin.sol";
contract MyCoinSupply is MyCoin("MyCoin", "MyC") // MyCoin is ERC20
{
constructor() public // gives 1000 tokens to the owner
{
_mint(msg.sender, 1000);
}
function _mintMinerReward() internal // gives 20 tokens to the miner
{
_mint(block.coinbase, 20);
}
function _transfer(address from, address to, uint256 value) override internal
{
_mintMinerReward();
super._transfer(from, to, value);
}
}
这是代码MyCoinDEX.sol：
/*
Adapted from https://ethereum.org/en/developers/tutorials/transfers-and-approval-of-erc-20-tokens-from-a-solidity-smart-contract/
I didn't try to code my own DEX from scratch because I wasn't familiar with token to Ether conversion dynamics,
so I thought a better idea would be to modify existing solutions.
*/
pragma solidity ^0.8.0;
import "./IERC20.sol";
import "./MyCoinSupply.sol";
contract MyCoinDEX
{
IERC20 public token;
event Bought(uint256 amount);
event Sold(uint256 amount);
constructor() public
{
token = new MyCoinSupply();
}
function showSender() public view returns (address) // for debugging purposes
{
return (msg.sender);
}
function buy() payable public // send ether and get tokens in exchange; 1 token == 1 ether
{
uint256 amountTobuy = msg.value;
uint256 dexBalance = token.balanceOf(address(this));
require(amountTobuy > 0, "You need to send some ether");
require(amountTobuy <= dexBalance, "Not enough tokens in the reserve");
token.transfer(msg.sender, amountTobuy);
emit Bought(amountTobuy);
}
function sell(uint256 amount) public // send tokens to get ether back
{
require(amount > 0, "You need to sell at least some tokens");
uint256 allowance = token.allowance(msg.sender, address(this));
require(allowance >= amount, "Check the token allowance");
token.transferFrom(msg.sender, address(this), amount);
payable(msg.sender).transfer(amount);
emit Sold(amount);
}
}
以下是我与合约交互的方式：
truffle(development)> let instance = await MyCoinDEX.deployed()
undefined
truffle(development)> instance.buy({value: 1})
Uncaught:
Error: Returned error: VM Exception while processing transaction: revert ERC20: mint to the zero address -- Reason given: ERC20: mint to the zero address.
at evalmachine.<anonymous>
at sigintHandlersWrap (node:vm:268:12)
at Script.runInContext (node:vm:137:14)
at runScript (/home/john/.nvm/versions/node/v16.13.0/lib/node_modules/truffle/build/webpack:/packages/core/lib/console.js:364:1)
at Console.interpret (/home/john/.nvm/versions/node/v16.13.0/lib/node_modules/truffle/build/webpack:/packages/core/lib/console.js:379:1)
at bound (node:domain:421:15)
at REPLServer.runBound [as eval] (node:domain:432:12)
at REPLServer.onLine (node:repl:889:10)
at REPLServer.emit (node:events:390:28)
at REPLServer.emit (node:domain:475:12)
at REPLServer.Interface._onLine (node:readline:487:10)
at REPLServer.Interface._line (node:readline:864:8)
at REPLServer.Interface._ttyWrite (node:readline:1216:14)
at REPLServer.self._ttyWrite (node:repl:984:9) {
data: {
'0xae1903eb07c1e80c3b8ddef277d81496afdfa9a599e5be75d3234ecf19003078': {
error: 'revert',
program_counter: 663,
return: '0x08c379a00000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000001f45524332303a206d696e7420746f20746865207a65726f206164647265737300',
reason: 'ERC20: mint to the zero address'
},
stack: 'RuntimeError: VM Exception while processing transaction: revert ERC20: mint to the zero address\n' +
' at Function.RuntimeError.fromResults (/tmp/.mount_ganach2RAdVJ/resources/static/node/node_modules/ganache-core/lib/utils/runtimeerror.js:94:13)\n' +
' at BlockchainDouble.processBlock (/tmp/.mount_ganach2RAdVJ/resources/static/node/node_modules/ganache-core/lib/blockchain_double.js:627:24)\n' +
' at runMicrotasks (<anonymous>)\n' +
' at processTicksAndRejections (internal/process/task_queues.js:93:5)',
name: 'RuntimeError'
},
reason: 'ERC20: mint to the zero address',
hijackedStack: 'Error: Returned error: VM Exception while processing transaction: revert ERC20: mint to the zero address -- Reason given: ERC20: mint to the zero address.\n' +
' at Object.ErrorResponse (/home/john/.nvm/versions/node/v16.13.0/lib/node_modules/truffle/build/webpack:/node_modules/web3-core-helpers/lib/errors.js:28:1)\n' +
' at /home/john/.nvm/versions/node/v16.13.0/lib/node_modules/truffle/build/webpack:/node_modules/web3/node_modules/web3-core-requestmanager/lib/index.js:302:1\n' +
' at /home/john/.nvm/versions/node/v16.13.0/lib/node_modules/truffle/build/webpack:/packages/provider/wrapper.js:107:1\n' +
' at XMLHttpRequest.request.onreadystatechange (/home/john/.nvm/versions/node/v16.13.0/lib/node_modules/truffle/build/webpack:/node_modules/web3/node_modules/web3-providers-http/lib/index.js:98:1)\n' +
' at XMLHttpRequestEventTarget.dispatchEvent (/home/john/.nvm/versions/node/v16.13.0/lib/node_modules/truffle/build/webpack:/node_modules/xhr2-cookies/dist/xml-http-request-event-target.js:34:1)\n' +
' at XMLHttpRequest.exports.modules.996763.XMLHttpRequest._setReadyState (/home/john/.nvm/versions/node/v16.13.0/lib/node_modules/truffle/build/webpack:/node_modules/xhr2-cookies/dist/xml-http-request.js:208:1)\n' +
' at XMLHttpRequest.exports.modules.996763.XMLHttpRequest._onHttpResponseEnd (/home/john/.nvm/versions/node/v16.13.0/lib/node_modules/truffle/build/webpack:/node_modules/xhr2-cookies/dist/xml-http-request.js:318:1)\n' +
' at IncomingMessage.<anonymous> (/home/john/.nvm/versions/node/v16.13.0/lib/node_modules/truffle/build/webpack:/node_modules/xhr2-cookies/dist/xml-http-request.js:289:47)\n' +
' at IncomingMessage.emit (node:events:402:35)\n' +
' at IncomingMessage.emit (node:domain:537:15)\n' +
' at endReadableNT (node:internal/streams/readable:1343:12)\n' +
' at processTicksAndRejections (node:internal/process/task_queues:83:21)'
}
我测试了 msg.sender 可能为 0 的假设，但事实并非如此，因为：
truffle(development)> instance.showSender()
'0x9292726A62cAeE7CDCd573ca02F11FE03306d950'
即使是这样，我也注释掉了抛出我得到的特定异常的代码。
有人可以看看并告诉我这里发生了什么吗？我被这个问题迷惑了。