Una manera de mantener con oxígeno a nuestros tokens o ecosistemas es mediante los fees por transacción, o sea cobrar una comisión cada vez que se mueven fondos. Esta comisión puede ir a una billetera de los creadores o a una bóveda. Solidity y las librerías de OpenZeppelin nos dan todas las herramientas necesarias para hacerlo. En este video exploramos diferentes formas de lograrlo, para ambos principiantes y avanzados.
Dependencias
Para este tutorial ocuparás Metamask con fondos de Rinkeby Testnet que puedes conseguir desde el Faucet. También necesitarás conectar tu wallet a Polygon Mainnet y conseguir MATIC desde algún exchange.
1. Fee fijo por transacción simple
Los contratos ERC-20 de OpenZeppelin exponen la función _afterTokenTransfer
que nos hacen muy conveniente implementar tax fees.
// SPDX-License-Identifier: MIT
pragma solidity 0.8.12;
import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
contract MyToken is ERC20
{
address public vault_address;
uint public fee;
bool private is_in_fee_transfer;
constructor () ERC20("My Token", "TKN")
{
// Edit here
vault_address = 0xb6F5414bAb8d5ad8F33E37591C02f7284E974FcB;
fee = 1 ether;
_mint(msg.sender, 1_000_000 ether);
// End edit
}
function _afterTokenTransfer(
address from,
address to,
uint amount
) internal virtual override(ERC20)
{
require(amount >= fee, "Amount must be greater than fee");
super._afterTokenTransfer(from, to, amount);
if(!is_in_fee_transfer)
{
is_in_fee_transfer = true;
_transfer(to, vault_address, fee);
is_in_fee_transfer = false;
}
}
}
2. Método avanzado de capturas de fees
- Con ayuda del Router de Uniswap podemos capturar un porcentaje diferente de fees en caso de Buy, Sell y P2P: Compra, Venta y transacción normal a otra billetera
- Esta vez capturamos un porcentaje de la tansacción, no un valor fijo
- Además agragamos addresses operadores como Taxless, exemptos de fees
Recuerda ajustar la dirección del router dependiendo de tu network:
- Polygon Quickswap:
0xa5E0829CaCEd8fFDD4De3c43696c57F7D7A678ff
- Ethereum Uniswap V2:
0x10ED43C718714eb63d5aA57B78B54704E256024E
- BSC Mainnet Pancake:
0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D
- BSC Testnet Pancake:
0xD99D1c33F9fC3444f8101754aBC46c52416550D1
// SPDX-License-Identifier: MIT
pragma solidity 0.8.12;
import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
interface IUniswapV2Factory {
function createPair(address tokenA, address tokenB) external returns (address pair);
}
interface IUniswapV2Router02 {
function factory() external pure returns (address);
function WETH() external pure returns (address);
}
contract MyToken is ERC20
{
address public vault_address;
address public pair;
uint public fee_decimal = 2;
enum FeesIndex{ BUY, SELL, P2P }
uint[] public fee_percentages;
mapping(address => bool) public is_taxless;
bool private is_in_fee_transfer;
constructor () ERC20("My Token", "TKN")
{
IUniswapV2Router02 _uniswapV2Router = IUniswapV2Router02(0xa5E0829CaCEd8fFDD4De3c43696c57F7D7A678ff);
pair = IUniswapV2Factory(_uniswapV2Router.factory()).createPair(address(this), _uniswapV2Router.WETH());
// Edit here
vault_address = 0xb6F5414bAb8d5ad8F33E37591C02f7284E974FcB;
fee_percentages.push(1000); // Buy fee is 10.00%
fee_percentages.push(1500); // Sell fee is 15.00%
fee_percentages.push(500); // Buy fee is 5.00%
// End edit
is_taxless[msg.sender] = true;
is_taxless[vault_address] = true;
is_taxless[address(this)] = true;
is_taxless[address(0)] = true;
_mint(msg.sender, 1_000_000 ether);
}
function _afterTokenTransfer(
address from,
address to,
uint amount
) internal virtual override(ERC20)
{
super._afterTokenTransfer(from, to, amount);
if(!is_in_fee_transfer)
{
uint fees_collected;
if (!is_taxless[from] && !is_taxless[to]) {
bool sell = to == pair;
bool p2p = from != pair && to != pair;
uint fee = calculateFee(p2p ? FeesIndex.P2P : sell ? FeesIndex.SELL : FeesIndex.BUY, amount);
fees_collected += fee;
}
if(fees_collected > 0)
{
is_in_fee_transfer = true;
_transfer(to, vault_address, fees_collected);
is_in_fee_transfer = false;
}
}
}
function calculateFee(FeesIndex fee_index, uint amount) internal view returns(uint) {
return (amount * fee_percentages[uint(fee_index)]) / (10**(fee_decimal + 2));
}
}
3. Método avanzado más completo
- Funciones editables
onlyOwner
- Split de fees a diferentes billeteras
// SPDX-License-Identifier: MIT
pragma solidity 0.8.12;
import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/access/Ownable.sol";
interface IUniswapV2Factory {
function createPair(address tokenA, address tokenB) external returns (address pair);
}
interface IUniswapV2Router02 {
function factory() external pure returns (address);
function WETH() external pure returns (address);
}
contract MyToken is ERC20, Ownable
{
uint internal wallet_a_collected;
uint internal wallet_b_collected;
address public wallet_a;
address public wallet_b;
address public pair;
enum FeesIndex{ BUY, SELL, P2P }
uint[] public wallet_a_fee_percentages;
uint[] public wallet_b_fee_percentages;
uint public fee_decimal = 2;
mapping(address => bool) public is_taxless;
bool private is_in_fee_transfer;
constructor () ERC20("My Token", "TKN")
{
IUniswapV2Router02 _uniswapV2Router = IUniswapV2Router02(0xa5E0829CaCEd8fFDD4De3c43696c57F7D7A678ff);
pair = IUniswapV2Factory(_uniswapV2Router.factory()).createPair(address(this), _uniswapV2Router.WETH());
// Edit here
wallet_a = 0xb6F5414bAb8d5ad8F33E37591C02f7284E974FcB;
wallet_a = 0xb6F5414bAb8d5ad8F33E37591C02f7284E974FcB;
wallet_a_fee_percentages.push(500); // Buy fee is 5.00%
wallet_a_fee_percentages.push(500); // Sell fee is 5.00%
wallet_a_fee_percentages.push(500); // Buy fee is 5.00%
wallet_b_fee_percentages.push(1000); // Buy fee is 10.00%
wallet_b_fee_percentages.push(1500); // Sell fee is 15.00%
wallet_b_fee_percentages.push(500); // Buy fee is 5.00%
// End edit
is_taxless[msg.sender] = true;
is_taxless[wallet_a] = true;
is_taxless[wallet_b] = true;
is_taxless[address(this)] = true;
is_taxless[address(0)] = true;
_mint(msg.sender, 1_000_000 ether);
}
function _afterTokenTransfer(
address from,
address to,
uint amount
) internal virtual override(ERC20)
{
super._afterTokenTransfer(from, to, amount);
if(!is_in_fee_transfer)
{
uint fees_collected;
if (!is_taxless[from] && !is_taxless[to]) {
uint wallet_a_fee;
uint wallet_b_fee;
bool sell = to == pair;
bool p2p = from != pair && to != pair;
(wallet_a_fee, wallet_b_fee) = calculateFee(p2p ? FeesIndex.P2P : sell ? FeesIndex.SELL : FeesIndex.BUY, amount);
wallet_a_collected += wallet_a_fee;
wallet_b_collected += wallet_b_fee;
fees_collected += wallet_a_fee + wallet_b_fee;
}
if(fees_collected > 0)
{
is_in_fee_transfer = true;
_transfer(to, address(this), fees_collected);
is_in_fee_transfer = false;
}
}
}
function calculateFee(FeesIndex fee_index, uint amount) internal view returns(uint, uint) {
uint wallet_a_fee = (amount * wallet_a_fee_percentages[uint(fee_index)]) / (10**(fee_decimal + 2));
uint wallet_b_fee = (amount * wallet_b_fee_percentages[uint(fee_index)]) / (10**(fee_decimal + 2));
return (wallet_a_fee, wallet_b_fee);
}
// Owner admin functions
function setWalletA(address wallet) external onlyOwner {
wallet_a = wallet;
}
function setWalletB(address wallet) external onlyOwner {
wallet_b = wallet;
}
function setWalletAFee(uint buy, uint sell, uint p2p) external onlyOwner {
wallet_a_fee_percentages[0] = buy;
wallet_a_fee_percentages[1] = sell;
wallet_a_fee_percentages[2] = p2p;
}
function setWalletBFee(uint buy, uint sell, uint p2p) external onlyOwner {
wallet_b_fee_percentages[0] = buy;
wallet_b_fee_percentages[1] = sell;
wallet_b_fee_percentages[2] = p2p;
}
function setIsTaxless(address _address, bool value) external onlyOwner {
is_taxless[_address] = value;
}
// Fee collector functions
function collectWalletAFee() external {
require(msg.sender == wallet_a, "Sender must be buy address");
wallet_a_collected = 0;
transfer(wallet_a, wallet_a_collected);
}
function collectWalletBFee() external {
require(msg.sender == wallet_b, "Sender must be buy address");
wallet_b_collected = 0;
transfer(wallet_b, wallet_b_collected);
}
}
¡Gracias por ver este tutorial!
Sígueme en dev.to y en Youtube para todo lo relacionado al desarrollo en Blockchain en Español.