token decimals on getAmountsOut

[IronSight87]

Hy there,

is there a more simple way to consider tokens with varying in decimals places when determining max output amount?

The funny part: When the decimals of token0 and token1 differ the transaction fails with "Fail with error 'ds-math-sub-underflow'" and
tx.await() times out.

// WBNB
let token0 = "0xbb4CdB9CBd36B01bD1cBaEBF2De08d9173bc095c";
let precision0 = 18

// BabyFlokiCoin
let token1 = "0x808fac147a9c02723d0be300ac4753eaf93c0e1f";
let precision1 = 9

let provider = new ethers.providers.WebSocketProvider('wss://bsc-ws-node.nariox.org:443');
let wallet = new ethers.Wallet('PRIVATE KEY', provider);
let account = wallet.address;

let router = new ethers.Contract(
    '0x10ED43C718714eb63d5aA57B78B54704E256024E',
    [
        'function getAmountsOut(uint amountIn, address[] calldata path) external view returns (uint[] memory amounts)',
        'function swapETHForExactTokens(uint amountOut, address[] calldata path, address to, uint deadline) external payable returns (uint[] memory amounts)'
    ],
    wallet
);

let bnbVal = 0.5;
let amountIn = ethers.utils.parseUnits(`${bnbVal}`, precision0);
let amounts = await router.getAmountsOut(amountIn, [token0, token1]);
// consider precision of token1 and append 0s
let maxOutputAmount = amounts[1].mul(10 ** (precision0 - precision1));

let tx = await .swapETHForExactTokens(
    maxOutputAmount, // ignore slippage in this sample
    [token0, token1],
    account,
    Date.now() + 1000 * 60 * 5, //5 minutes
    {
    'gasLimit': 250000, 
    'gasPrice': ethers.utils.parseUnits('5', 'gwei'),
    'nonce' : null,
    'value' : amountIn
});
let receipt = await tx.wait();

[zemse]

You should be using BigNumber because for a larger difference in decimals would cause an error.

let maxOutputAmount = amounts[1].mul(ethers.BigNumber.from(10).pow(precision0 - precision1));

Also the time is not what you is intending for, Date.now() gives you in milliseconds.

Math.floor(Date.now()/1000) + 1000 * 60 * 5, //5 minutes

If it's still a problem, can you give a transaction hash, I can try to help

[IronSight87]

@zemse Thank you for you reply. Unfortunately the error still occurs. The corresponding transaction hash is 0xbe28a9808e7f2d0ee057e2d71e157fe6860078a55c4bb3c9b96fceac728544db

[zemse]

I just used tenderly to check. It seems that there aren't enough reserves in the pool that you're trying to do the swap.