ERC20 two feature: 1. Fee 2. Callback

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1

Hello,

I want to create new contract, which will have: 1. Transaction fee; 2. Callback URL

Now my example code looks like this:

pragma solidity 0.5.16;

interface IERC20 {

  function totalSupply() external view returns (uint256);
  function decimals() external view returns (uint8);
  function symbol() external view returns (string memory);
  function name() external view returns (string memory);
  function getOwner() external view returns (address);
  function balanceOf(address account) external view returns (uint256);
  function transfer(address recipient, 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 sender, address recipient, 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);
}

contract Context {
  function _msgSender() internal view returns (address payable) {
    return msg.sender;
  }

  function _msgData() internal view returns (bytes memory) {
    this;
    return msg.data;
  }
}

library SafeMath {

  function add(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a + b;
    require(c >= a, "SafeMath: addition overflow");

    return c;
  }
  
  function sub(uint256 a, uint256 b) internal pure returns (uint256) {
    return sub(a, b, "SafeMath: subtraction overflow");
  }

  function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
    require(b <= a, errorMessage);
    uint256 c = a - b;

    return c;
  }

  function mul(uint256 a, uint256 b) internal pure returns (uint256) {
    if (a == 0) {
      return 0;
    }

    uint256 c = a * b;
    require(c / a == b, "SafeMath: multiplication overflow");

    return c;
  }

  function div(uint256 a, uint256 b) internal pure returns (uint256) {
    return div(a, b, "SafeMath: division by zero");
  }

  function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
    require(b > 0, errorMessage);
    uint256 c = a / b;
    return c;
  }
 
  function mod(uint256 a, uint256 b) internal pure returns (uint256) {
    return mod(a, b, "SafeMath: modulo by zero");
  }

  function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
    require(b != 0, errorMessage);
    return a % b;
  }
}

contract Ownable is Context {
  address private _owner;

  event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

  constructor () internal {
    address msgSender = _msgSender();
    _owner = msgSender;
    emit OwnershipTransferred(address(0), msgSender);
  }

  function owner() public view returns (address) {
    return _owner;
  }

  modifier onlyOwner() {
    require(_owner == _msgSender(), "Ownable: caller is not the owner");
    _;
  }

  function renounceOwnership() public onlyOwner {
    emit OwnershipTransferred(_owner, address(0));
    _owner = address(0);
  }

  function transferOwnership(address newOwner) public onlyOwner {
    _transferOwnership(newOwner);
  }

  function _transferOwnership(address newOwner) internal {
    require(newOwner != address(0), "Ownable: new owner is the zero address");
    emit OwnershipTransferred(_owner, newOwner);
    _owner = newOwner;
  }
}

contract ERC20Token is Context, IERC20, Ownable {
  using SafeMath for uint256;

  mapping (address => uint256) private _balances;

  mapping (address => mapping (address => uint256)) private _allowances;

  uint256 private _totalSupply;
  uint8 private _decimals;
  string private _symbol;
  string private _name;

  constructor() public {
    _name = "Bulia";
    _symbol = "BULI";
    _decimals = 18;
    _totalSupply = 1000000000000000000000000000;
    _balances[msg.sender] = _totalSupply;

    emit Transfer(address(0), msg.sender, _totalSupply);
  }

  function getOwner() external view returns (address) {
    return owner();
  }

  function decimals() external view returns (uint8) {
    return _decimals;
  }

  function symbol() external view returns (string memory) {
    return _symbol;
  }

  function name() external view returns (string memory) {
    return _name;
  }

  function totalSupply() external view returns (uint256) {
    return _totalSupply;
  }

  function balanceOf(address account) external view returns (uint256) {
    return _balances[account];
  }

  function transfer(address recipient, uint256 amount) external returns (bool) {
    _transfer(_msgSender(), recipient, amount);
    return true;
  }

  function allowance(address owner, address spender) external view returns (uint256) {
    return _allowances[owner][spender];
  }

  function approve(address spender, uint256 amount) external returns (bool) {
    _approve(_msgSender(), spender, amount);
    return true;
  }

  function transferFrom(address sender, address recipient, uint256 amount) external returns (bool) {
    _transfer(sender, recipient, amount);
    _approve(sender, _msgSender(), _allowances[sender][_msgSender()].sub(amount, "ERC20: transfer amount exceeds allowance"));
    return true;
  }

  function increaseAllowance(address spender, uint256 addedValue) public returns (bool) {
    _approve(_msgSender(), spender, _allowances[_msgSender()][spender].add(addedValue));
    return true;
  }

  function decreaseAllowance(address spender, uint256 subtractedValue) public returns (bool) {
    _approve(_msgSender(), spender, _allowances[_msgSender()][spender].sub(subtractedValue, "ERC20: decreased allowance below zero"));
    return true;
  }

  function mint(uint256 amount) public onlyOwner returns (bool) {
    _mint(_msgSender(), amount);
    return true;
  }

  function _transfer(address sender, address recipient, uint256 amount) internal {
    require(sender != address(0), "ERC20: transfer from the zero address");
    require(recipient != address(0), "ERC20: transfer to the zero address");

    _balances[sender] = _balances[sender].sub(amount, "ERC20: transfer amount exceeds balance");
    _balances[recipient] = _balances[recipient].add(amount);
    emit Transfer(sender, recipient, amount);
  }

  function _mint(address account, uint256 amount) internal {
    require(account != address(0), "ERC20: mint to the zero address");

    _totalSupply = _totalSupply.add(amount);
    _balances[account] = _balances[account].add(amount);
    emit Transfer(address(0), account, amount);
  }

  function _burn(address account, uint256 amount) internal {
    require(account != address(0), "ERC20: burn from the zero address");

    _balances[account] = _balances[account].sub(amount, "ERC20: burn amount exceeds balance");
    _totalSupply = _totalSupply.sub(amount);
    emit Transfer(account, address(0), amount);
  }

  function _approve(address owner, address spender, uint256 amount) internal {
    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 _burnFrom(address account, uint256 amount) internal {
    _burn(account, amount);
    _approve(account, _msgSender(), _allowances[account][_msgSender()].sub(amount, "ERC20: burn amount exceeds allowance"));
  }
}

How there is a possible to add transaction fee, need to know 2 examples: a) 1% b) 1 token
And how there is a possible to every transaction connect to this URL: example.com/callback/{transaction_id}

Thanks

2

Hello, for the fee part you'd want to modify the _transfer function to something like this

  function _transfer(address sender, address recipient, uint256 amount) internal {
    require(sender != address(0), "ERC20: transfer from the zero address");
    require(recipient != address(0), "ERC20: transfer to the zero address");
	uint256 taxAmount = amount.div(100) // thats 1%, for 1 token you'd do taxAmount = 1 * 10 ** 18
    _balances[sender] = _balances[sender].sub(amount, "ERC20: transfer amount exceeds balance");
    _balances[recipient] = _balances[recipient].add(amount).sub(taxAmount);
	_balances[yourTaxWallet] = _balances[yourTaxWallet].add(taxAmount); // you can send the tax to the address you want
    emit Transfer(sender, recipient, amount);
  }

And im not too sure about what you mean by callback. If you just want to record that a transfer has been done you can do that by listening for transfer events for your contract using any tool that watches the blockchain such as tenderly. If you want to redirect the user to a website thats completely impossible.

1 Like
3

Nova, Thank you!

For Callback I think I need alternative method, buy API.

Thank you again!