[Ethereum] Check valid slippage before sending transaction using web3

bscpancakeswapweb3js

I have a web3 script that buys and sells the token on Binance Smart Chain (BSC). Now let's say there is a token that has mentioned a mandatory 10% fee in their contract but I don't know about that at the time of swapping. Now if you perform a swap operation from pancakeswap with a slippage of 2% only, it will show an error message that something is wrong with your swap. This error is thrown before even sending the transaction. So I need to achieve a similar feature with my web3.js script. Any help is much appreciated.

Best Answer

Currently, ERC-20 tokens do not expose interface expose transaction fees. Only thing you can find these out is by checking them by hand.

Also, taking fee on transfer() does not fit to ERC-20 token model well at all. Usually the only tokens that do so are some sort of scam tokens from anon fly by the night teams, so my personal recommendation is stay away from all of them.

Related Solutions

[Ethereum] swapExactTokensForETHSupportingFeeOnTransferTokens fails for some tokens when called from script, but works when submitted from Pancakeswap

I had the same issue, the only solutions that I could think of are:

Get the price of the token and calculate the slippage on the fly
Set amountOutMin to 0, at first I thought it would give me 0 bnb but on all the tokens that I have used it, it only took the tax specified on the contract.

    token_tx = pancake.functions.swapExactTokensForETHSupportingFeeOnTransferTokens(tokens_amount,0 , path, reciever[0],expire ).buildTransaction(
        {
            'chainId':56,
            'gas': 500000,
            'gasPrice': web3.toWei(gas,'gwei'),
            'nonce':nonce,
        }
    )

My guess is that when you try to sell and the tokens received < amountOutMin it fails

[Ethereum] Is swapExactETHForTokens the right function for buying ? python, web3

swapExactTokensForETHSupportingFeeOnTransferTokens is used to sell fee on transfer tokens (e.g. Safemoon) for BNB (on the BSC of course). Its counterpart (swapExactETHForTokensSupportingFeeOnTransferTokens) is probably what you're looking for if you're trying to buy that kind of tokens with BNB (it also works with "normal" tokens but costs more gas IIRC, id love someone to confirm that as im not home rn and cant check the pancake router code)

Best Answer

Related Solutions

[Ethereum] swapExactTokensForETHSupportingFeeOnTransferTokens fails for some tokens when called from script, but works when submitted from Pancakeswap

[Ethereum] Is swapExactETHForTokens the right function for buying ? python, web3

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