Gasless Transactions

In this guide we will look at executing a gasless transaction utilizing our sponsorship paymaster.

info

This guide assumes you have already initialized the Biconomy SDK and just need to understand how to execute a user paid transaction. See our tutorials for step by step setups.

Before using these code snippets make sure to set up a paymaster and register any smart contracts for sponsorship.

Imports

These are the imports needed for the code snippets below:

import { ethers } from "ethers";
import abi from "some abi location";
import {
  IHybridPaymaster,
  SponsorUserOperationDto,
  PaymasterMode,
} from "@biconomy/paymaster";

Additionally an Instance of the BiconomySmartAccount is needed as mentioned above.

Connect to Contract

Connect to an instance of a contract, below is an example of using ethers JS to connect to an NFT contract.

const nftAddress = "0x0a7755bDfb86109D9D403005741b415765EAf1Bc";

const contract = new ethers.Contract(nftAddress, abi, provider);

Build Useroperation

Using an instance of the smart account use the buildUserOp method to create a userOp.

// use the ethers populateTransaction method to create a raw transaction
const minTx = await contract.populateTransaction.safeMint(address);
const tx1 = {
  to: nftAddress,
  data: minTx.data,
};
let userOp = await smartAccount.buildUserOp([tx1]);

Request Paymaster Data

We now need to construct the paymasterAndData field of our userOp. This is done by making a request to the paymaster with the Paymaster mode set to sponsored and updating the userOp with the returned paymasterAndData response.

  const biconomyPaymaster = smartAccount.paymaster as IHybridPaymaster<SponsorUserOperationDto>;
      let paymasterServiceData: SponsorUserOperationDto = {
        mode: PaymasterMode.SPONSORED,
        smartAccountInfo: {
          name: 'BICONOMY',
          version: '2.0.0'
        },
      };
      const paymasterAndDataResponse = await biconomyPaymaster.getPaymasterAndData(
          userOp,
          paymasterServiceData
        );
      userOp.paymasterAndData = paymasterAndDataResponse.paymasterAndData;

Send UserOperation

Send your userOp to our Bundler which will send the userOp to the entry point contract to handle executing it as a transaction on chain.

const userOpResponse = await smartAccount.sendUserOp(userOp);
console.log("userOpHash", userOpResponse);
const { receipt } = await userOpResponse.wait(1);
console.log("txHash", receipt.transactionHash);

Mint NFT Function

 const handleMint = async () => {
    const contract = new ethers.Contract(
      nftAddress,
      abi,
      provider,
    )
    try {
      const minTx = await contract.populateTransaction.safeMint(address);
      const tx1 = {
        to: nftAddress,
        data: minTx.data,
      };
      let userOp = await smartAccount.buildUserOp([tx1]);
      const biconomyPaymaster =
        smartAccount.paymaster as IHybridPaymaster<SponsorUserOperationDto>;
      let paymasterServiceData: SponsorUserOperationDto = {
        mode: PaymasterMode.SPONSORED,
        smartAccountInfo: {
          name: 'BICONOMY',
          version: '2.0.0'
        },
      };
      const paymasterAndDataResponse =
        await biconomyPaymaster.getPaymasterAndData(
          userOp,
          paymasterServiceData
        );

      userOp.paymasterAndData = paymasterAndDataResponse.paymasterAndData;
      const userOpResponse = await smartAccount.sendUserOp(userOp);
      console.log("userOpHash", userOpResponse);
      const { receipt } = await userOpResponse.wait(1);
      console.log("txHash", receipt.transactionHash);
    } catch (err: any) {
      console.error(err);
      console.log(err)
    }
  }