Is it possible to check the gas fees for a contract before executing the contract itself?

Question

Is it possible to check the overall gas price of a transaction before executing the contract? I'm trying to implement some arbitrage trade through a smart contract that would find me price discrepancies between sushiswap and uniswap. But I need to check before running the swap if the profit - the gas fees would be in the green, and if it's not, just do not run the transaction. Any advice would be greatly appreciated

Answer 1

You can use a library like ethers.js or web3.js to estimate the gas usage and cost of the transaction.

A sample code to achieve that using ethers.js:

Using ethers.js v5:

const { ethers } = require('ethers');

const contractAddress = "YOUR_CONTRACT_ADDRESS";

const contractAbi = [
    /* YOUR_CONTRACT_ABI */
];

const provider = new ethers.providers.JsonRpcProvider("YOUR_RPC_URL");
const privateKey = "YOUR_ACCOUNT_PRIVATE_KEY";
const wallet = new ethers.Wallet(privateKey, provider);

const contract = new ethers.Contract(contractAddress, contractAbi, wallet);

contract.estimateGas.yourMethod(params).then(async (gasEstimate) => {

    console.log('Gas Usage Estimate In Wei: ', parseFloat(gasEstimate.toString()));

    const gasEstimateInEther = ethers.utils.formatUnits(gasEstimate);

    console.log('Gas Usage Estimate In Ether: ', gasEstimateInEther);

    const gasData = await wallet.getFeeData();

    const estimatedCostInWei = (gasData.maxFeePerGas.sub(gasData.lastBaseFeePerGas)).mul(gasEstimate);

    console.log('Tx Cost Estimate In Wei: ', parseFloat(estimatedCostInWei.toString()));

    const estimatedCostInEth = ethers.utils.formatUnits(estimatedCostInWei);

    console.log('Tx Cost Estimate In Ether: ', estimatedCostInEth);

    // Actual call to the contract function
    contract.yourMethod(params, {
        gasPrice: gasData.gasPrice,
        gasLimit: gasEstimate
    }).then(async (tx) => {
         const receipt = await tx.wait();
         console.log(receipt.hash)
    });

});

Using ethers.js v6:

const { ethers } = require('ethers');

const contractAddress = "YOUR_CONTRACT_ADDRESS";

const contractAbi = [
    /* YOUR_CONTRACT_ABI */
];

const provider = new ethers.JsonRpcProvider("YOUR_RPC_URL");
const privateKey = "YOUR_ACCOUNT_PRIVATE_KEY";
const wallet = new ethers.Wallet(privateKey, provider);

const contract = new ethers.Contract(contractAddress, contractAbi, wallet);

contract.yourMethod.estimateGas(params).then(async (gasEstimate) => {

    console.log('Gas Usage Estimate In Wei: ', parseFloat(gasEstimate.toString()));

    const gasEstimateInEther = ethers.formatUnits(gasEstimate);

    console.log('Gas Usage Estimate In Ether: ', gasEstimateInEther);

    const gasData = await provider.getFeeData();

    const estimatedCostInWei = gasData.gasPrice * gasEstimate;

    console.log('Tx Cost Estimate In Wei: ', parseFloat(estimatedCostInWei.toString()));

    const estimatedCostInEth = ethers.formatUnits(estimatedCostInWei);

    console.log('Tx Cost Estimate In Ether: ', estimatedCostInEth);

    // Actual call to the contract function
    contract.yourMethod(params, {
        gasPrice: gasData.gasPrice,
        gasLimit: gasEstimate
    }).then(async (tx) => {
         const receipt = await tx.wait();
         console.log(receipt.hash)
    });

});