Balancer es un proyecto que me ha llamado la atención por estar innovando en el espacio DeFi. Balancer permite a inversionistas obtener ingresos pasivos por mantener un portafolio a su medida, a traders hacer swaps con gas fees bajos y protegidos contra el MEV, a bots de arbitraje buenas oportunidades entre otras cosas. Todo esto ofreciendo una moderna interfaz de usuario y de smart contracts.
En este video lanzamos un token que cobra fees de transacción por cada swap en las piscinas de Balancer.
Antes de comenzar
Para este tutorial ocuparás Metamask u otra wallet compatible con fondos en Goerli que puedes obtener desde un faucet.
Smart contracts con fees de transacción en Balancer
// SPDX-License-Identifier: MIT
pragma solidity 0.8.17;
abstract contract Context {
function _msgSender() internal view virtual returns (address) {
return msg.sender;
}
function _msgData() internal view virtual returns (bytes calldata) {
return msg.data;
}
}
interface IERC20 {
function totalSupply() external view returns (uint256);
function balanceOf(address account) external view returns (uint256);
function transfer(address to, uint256 amount) external returns (bool);
function allowance(address owner, address spender) external view returns (uint256);
function approve(address spender, uint256 amount) external returns (bool);
function transferFrom(
address from,
address to,
uint256 amount
) external returns (bool);
event Transfer(address indexed from, address indexed to, uint256 value);
event Approval(address indexed owner, address indexed spender, uint256 value);
}
interface IERC20Metadata is IERC20 {
function name() external view returns (string memory);
function symbol() external view returns (string memory);
function decimals() external view returns (uint8);
}
contract BalancerToken is Context, IERC20, IERC20Metadata {
// Openzeppelin variables
mapping(address => uint256) private _balances;
mapping(address => mapping(address => uint256)) private _allowances;
uint256 private _totalSupply;
string private _name;
string private _symbol;
// My variables
address public balancerVault = 0xBA12222222228d8Ba445958a75a0704d566BF2C8;
address public feeWallet;
uint public _feeDecimal = 2;
// index 0 = buy fee, index 1 = sell fee, index 2 = p2p fee
uint[] public fees;
mapping(address => bool) public isTaxless;
// Openzeppelin functions
constructor() {
_name = "My Balancer Token";
_symbol = "BT";
feeWallet = 0x0000000000000000000000000000000000000000;
fees.push(100); // 1% buy fee
fees.push(200); // 2% sell fee
fees.push(0); // 0% p2p fee
isTaxless[msg.sender] = true;
isTaxless[address(this)] = true;
isTaxless[feeWallet] = true;
isTaxless[address(0)] = true;
_mint(msg.sender, 1_000_000 ether);
}
function name() public view virtual override returns (string memory) {
return _name;
}
function symbol() public view virtual override returns (string memory) {
return _symbol;
}
function decimals() public view virtual override returns (uint8) {
return 18;
}
function totalSupply() public view virtual override returns (uint256) {
return _totalSupply;
}
function balanceOf(address account) public view virtual override returns (uint256) {
return _balances[account];
}
function transfer(address to, uint256 amount) public virtual override returns (bool) {
address owner = _msgSender();
_transfer(owner, to, amount);
return true;
}
function allowance(address owner, address spender) public view virtual override returns (uint256) {
return _allowances[owner][spender];
}
function approve(address spender, uint256 amount) public virtual override returns (bool) {
address owner = _msgSender();
_approve(owner, spender, amount);
return true;
}
function transferFrom(
address from,
address to,
uint256 amount
) public virtual override returns (bool) {
address spender = _msgSender();
_spendAllowance(from, spender, amount);
_transfer(from, to, amount);
return true;
}
function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
address owner = _msgSender();
_approve(owner, spender, _allowances[owner][spender] + addedValue);
return true;
}
function decreaseAllowance(address spender, uint256 subtractedValue) public virtual returns (bool) {
address owner = _msgSender();
uint256 currentAllowance = _allowances[owner][spender];
require(currentAllowance >= subtractedValue, "ERC20: decreased allowance below zero");
unchecked {
_approve(owner, spender, currentAllowance - subtractedValue);
}
return true;
}
function _transfer(
address from,
address to,
uint256 amount
) internal virtual {
require(from != address(0), "ERC20: transfer from the zero address");
require(to != address(0), "ERC20: transfer to the zero address");
_beforeTokenTransfer(from, to, amount);
// My implementation
uint256 feesCollected;
if (!isTaxless[from] && !isTaxless[to]) {
bool sell = to == balancerVault;
bool p2p = from != balancerVault && to != balancerVault;
uint feeIndex = p2p ? 2 : sell ? 1 : 0;
feesCollected = (amount * fees[feeIndex]) / (10**(_feeDecimal + 2));
}
amount -= feesCollected;
_balances[from] -= feesCollected;
_balances[feeWallet] += feesCollected;
// End my implementation
uint256 fromBalance = _balances[from];
require(fromBalance >= amount, "ERC20: transfer amount exceeds balance");
unchecked {
_balances[from] = fromBalance - amount;
}
_balances[to] += amount;
emit Transfer(from, to, amount);
_afterTokenTransfer(from, to, amount);
}
function _mint(address account, uint256 amount) internal virtual {
require(account != address(0), "ERC20: mint to the zero address");
_beforeTokenTransfer(address(0), account, amount);
_totalSupply += amount;
_balances[account] += amount;
emit Transfer(address(0), account, amount);
_afterTokenTransfer(address(0), account, amount);
}
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);
}
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);
}
function _spendAllowance(
address owner,
address spender,
uint256 amount
) internal virtual {
uint256 currentAllowance = allowance(owner, spender);
if (currentAllowance != type(uint256).max) {
require(currentAllowance >= amount, "ERC20: insufficient allowance");
unchecked {
_approve(owner, spender, currentAllowance - amount);
}
}
}
function _beforeTokenTransfer(
address from,
address to,
uint256 amount
) internal virtual {}
function _afterTokenTransfer(
address from,
address to,
uint256 amount
) internal virtual {}
}
Gracias por ver este video!
Sígannos en dev.to y en Youtube para todo lo relacionado al desarrollo en Blockchain en Español.
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