How to distinguish between adding liquidity and swapping tokens

Smart Contracts
1

Hi,

I'm adding fees to a token and I want to distinguish buys and sells when swapping.
I don't want to include fees when the token is transferred or liquidity is added. While testing, I realized that adding liquidity takes fees from the user as well.

How can I make sure fees are only accounted for when swapping and not when adding liquidity?

Some code:


function _transfer(address sender, address recipient, uint amount) internal override virtual{
        requires(...)

        variables(...)

        if (isExcludedFromFee[sender]) {
            takeFee = false;
        }

        bool Buy = getLPStatus(sender) || getRouterStatus(sender);
        bool Sell = getLPStatus(recipient) || getRouterStatus(recipient);

        taxes = (Buy) ? amount.mul(buyFeePercentage).div(10000) : taxes;
        taxes = (Sell) ? amount.mul(sellFeePercentage).div(10000) : taxes;

        if (!takeFee || taxes == 0){
            _realTransfer(sender, recipient, amount);
        } else {

            amount = amount.sub(taxes);
            _realTransfer(sender, recipient, amount);

            uint taxD = taxAmount.mul(devpercent).div(10000);
            uint taxBurn = taxAmount.sub(taxD).mul(burnpercent).div(10000);
            uint taxlps = taxAmount.sub(taxD).sub(taxBurn);
            _realTransfers(...)
        }
    }

Also, I'm making transfers to another smart contract/wallet because I'm not sure how to prevent sandwich attacks unless I hardcode a low slippage but sounds like a pretty bad choice. Sending the funds to another smart contract will allow me to change it in the future once it's properly optimized.

Thank you,

2

This is an internal function, you could create different external functions that call this one for each case, like a addLiquidity function that sends a parameter to _transfer indicating if a fee is to be charge.

3

I'm assuming you mean uniswap or pancakeswap. I think the router handles the liquidity events and only calls transfer on the token contract. So i dont think its possible to distinguish between a normal transfer and a liquidity event. You could exclude the router address from the tax event, but that would probably also exclude all swap events.