Account Abstraction

Introduction

Account Abstraction simplifies blockchain interactions by allowing smart contracts to serve as user accounts, merging contract capabilities with account management. The Titan upgrade opens the door for Account Abstraction to become reality on Cronos Testnet. Account Abstraction opens up possibilities for numerous use cases such as multi-signature transactions, social recovery, contract whitelisting, custom gas tokens, subsidizing gas fees, and much more. It expands the use-case potential of DApps and enables a more intuitive user experience. \

Key components are provided to support Account Abstraction development:

• User Operations: A new transaction object type that includes additional data, allowing for custom transaction and security configurations.

• JSON-RPC API debug_traceCall: Enables simulation of User Operations before they are executed on-chain.

• Bundlers: Crucial nodes that bundle unsigned User Operations into a single package for signing and subsequent publication on the mainnet. Bundlers estimate transaction fees.

• Entry Point Contract: an audited and trusted singleton contract, is functional and can process the execution and validating User Operations.

Account Abstraction is natively supported on Cronos, and developers can leverage these features for their own use cases. There are also application-level account abstraction solutions available for developers who need Account Abstraction functionality now, such as Cometh. Please contact Cronos Labs if you would like to be introduced to the relevant developer tool platforms.

Send a UserOperation using userop.js

In this guide, we will go through how to send a userop transaction with subsidized gas fee. Here we are using userop.js to send UserOperations but you can use any library you like, even using curl .

We will create a new project for sending transactions

mkdir userop-test
cd userop-test
yarn init -y
yarn add userop
yarn add dotenv

In the root directory, create a new file .env

ENTRY_POINTS=0x5FF137D4b0FDCD49DcA30c7CF57E578a026d2789
ACCOUNT_FACTORY=0x9406Cc6185a346906296840746125a0E44976454
NODE_RPC_URL=http://localhost:8545
BUNDLER_RPC_URL=http://localhost:3000
SIGNER_PKEY=0x0000000000000000000000000000000000000000000000000000000000000003

Create a new index.mjs

import { ethers,Wallet,Contract } from "ethers";
import { Presets,Client } from "userop";

import { config } from "dotenv";
config();

const NODE_RPC_URL = process.env.NODE_RPC_URL;
const BUNDLER_RPC_URL = process.env.BUNDLER_RPC_URL;
const SIGNER_PKEY = process.env.SIGNER_PKEY;
const ENTRY_POINTS = process.env.ENTRY_POINTS;
const ACCOUNT_FACTORY = process.env.ACCOUNT_FACTORY;

async function main() {

  // signer is the owner of the smart account
  const signer = new ethers.Wallet(SIGNER_PKEY)

  // Initialize userop builder
  var builder = await Presets.Builder.SimpleAccount.init(
    signer,
    NODE_RPC_URL,
    {
      overrideBundlerRpc: BUNDLER_RPC_URL,
      entryPoint: ENTRY_POINTS,
      factory: ACCOUNT_FACTORY,
    }
  );
  
  // these two addresses are different
  // need to fund the smart account before running this script
  console.log(`Signer  address: ${signer.address}`);
  console.log(`Account address: ${builder.getSender()}`);

  // build a tranfer transaction
  builder = builder
    .execute(
      "0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266",
      "100",
      ethers.utils.hexlify("0x")
    )

  // create the client
  const client = await Client.init(
    NODE_RPC_URL,
    {
      overrideBundlerRpc: BUNDLER_RPC_URL,
      entryPoint: ENTRY_POINTS,
      factory: ACCOUNT_FACTORY,
    }
  );

  // send the useroperation to the bundler node
  const res = await client.sendUserOperation(builder, {
    onBuild: (op) => {
      console.log("Signed UserOperation:",op);
    },
  });

  console.log(`UserOpHash: ${res.userOpHash}`);

  // !!! this step can get stuck in a local geth dev setup
  // because the bundler node is waiting for new block event to bundle the userops
  // try to send a new tx in the local geth dev setup to trigger bundle
  console.log("Waiting for transaction...");
  const ev = await res.wait();

  console.log(`Transaction hash: ${ev?.transactionHash ?? null}`);
}

main().then();

Now send the userop by running:

$ node index.mjs

Signer  address: 0x6813Eb9362372EE...19671cBA69
Account address: 0xF249baC852124B9...1b6907FcAD
verification gas limit: 70000
verification gas limit: 1000000
Signed UserOperation: {
  sender: '0x6813Eb9362372EE...19671cBA69',
  nonce: '0xb',
  initCode: '0x',
  callData: '0xb61d27f6000000000000000000000000f39fd6e51aad88f6f...27279cfffb92266000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000000000000000000000000000000000000000600000000000000000000000000000000000000000000000000000000000000000',
  callGasLimit: '0x4443',
  verificationGasLimit: '0xaba7',
  preVerificationGas: '0xbfb1',
  maxFeePerGas: '0x925761c3500',
  maxPriorityFeePerGas: '0xd27a99500',
  paymasterAndData: '0x',
  signature: '0xd42139cf71d00cd7ff...5461bbd949df9500413948fd06a284029e4a777247d6dd609e72b538d60d51b'
}
UserOpHash: 0xdc07e08d601ff82dd509c...34c7262ccf22463f10fb2191
Waiting for transaction...
Transaction hash: 0xcd54434b8c949...2580930cf14045cc3829ef09feb73ec9a

If successful, you will see the above logs including transaction hash and userOpHash printed out.

We can now verify with this tx hash on the block explorer, that we have successfully sent out a TX, and the gas fees were funded by the account address 0x6813Eb9362372EE...19671cBA69.