How to call internal _burn function of already deployed smart contract?

Question

i have started to work on ethereum project.

i have a customer who owns his own token and he wants to burn some tokens.

i have seen that the smart contract has as an internal _burn function but this is never called and there is no public function for _burn

Now my question.

Is there a way i can upgrade his contract so i can add a public burn function? or is there i way i can execute the never called _burn internal function in other way?

Answer 1

Contracts are not upgradable on Ethereum, if not explicitly being developed in such a way.

If the token of your customer uses a Proxy pattern then this is possible.

Otherwise you will not be able to make your internal function accessible if it was not accessible before.

A common pattern to burn tokens is to sent them to the zero-address. This also triggers the Transfer event that is associated to burning. This is also the reason why you can see that the zero-address on Etherscan holds quite a large amount of tokens: https://etherscan.io/address/0x0000000000000000000000000000000000000000

Answer 2

Based on your claim that you have seen internal _burn function. I will assume the function in question is something like this

 /**
 * @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 {
    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);
}

The function above is usually found in ERC20.sol contract that is used in conjunction with ERC20Burnable.sol

ERC20Burnable.sol contains a function burn() that will call the _burn() from ERC20.sol

/**
 * @dev Destroys `amount` tokens from the caller.
 *
 * See {ERC20-_burn}.
 */
function burn(uint256 amount) public {
    _burn(_msgSender(), amount);
}

I assume this is the case with the contracts you are looking at the moment. Therefore, there is probably no need to upgrade the contract. But I would need more info to help you here if that is not the case.