Hice un Token con Fees en Balancer
Published: 2022-10-20 17:56:40

---
title: Hice un Token con Fees en Balancer
published: true
description: 
tags: 
cover_image: https://dev-to-uploads.s3.amazonaws.com/uploads/articles/vijt84oul24568knha8t.png
---

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.

{% youtube khnzvH781iw %}

## Antes de comenzar

Para este tutorial ocuparás [Metamask](https://metamask.io/) u otra wallet compatible con fondos en Goerli que puedes obtener desde un [faucet](https://goerlifaucet.com/).

## Smart contracts con fees de transacción en Balancer

```solidity
// 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](https://www.youtube.com/channel/UCNRB4tgwp09z4391JRjEsRA) para todo lo relacionado al desarrollo en Blockchain en Español.