UerOp-SDK Usage

This document introduces the use of userop-sdk, how dapp assembles userop, and the process of obtaining gas solutions by calling paymaster-rpc, and bundling on-chain.

Install package from github

npm install github:nerochain/aa-userop-sdk

Import into dapp project

import {Client, Presets} from 'userop';

Init build

const builder = await Presets.Builder.SimpleAccount.init(
    accountSigner,    //aa wallet owner provider
    RPC_ENDPOINT,     //nerochain rpc
    {
      overrideBundlerRpc: bundlerRpc,    //bundler rpc
      entryPoint: entryPointAddress,    //entrypoint contract
      factory: accountFactoryAddr,    //SimpleAccountFactory contract
    }
);

Set platform apikey to paymaster

builder.setPaymasterOptions({
    apikey: apiKey,    //platform api-key
    rpc: payMasterRpc  //paymaster rpc
});

Init client(parameters same as build)

const client = await Client.init(RPC_ENDPOINT, {
    overrideBundlerRpc: bundlerRpc,
    entryPoint: entryPointAddress,
});

Construct builder's transaction data on actual business scenarios

const callData = [
      defaultTokenContract.interface.encodeFunctionData('approve', [
        state.toAddress,
        ethers.parseEther(state.tranNum.toString())
      ]),
      defaultTokenContract.interface.encodeFunctionData('transfer', [
        state.toAddress,
        ethers.parseEther(state.tranNum.toString())
      ])
    ];
    const callTo = [testTokenAddr, testTokenAddr];
    builder.executeBatch(callTo, callData);
    //builder.execute(..) for single calldata

Now get supported tokens

const supportedTokens = await client.getSupportedTokens(builder);

The above data depends on the strategies set by developers on the platform. The dapp analyzes tokens for users to choose gas options:

• type=0 freegas. Developer sponsors gas fees, users do not need to pay ERC20.

• type=1 prefund erc20. During the verification phase, the system first deducts the full amount of ERC20 from the user, and then returns the excess portion after executing the user operation.

• type=2 postfund erc20. After the userop is executed, the system deducts the ERC20 from the user in one go. However, it’s possible that the deduction may fail due to the specific nature of the userop code.

builder.setPaymasterOptions({ type: selectedMode.value }); //type: 0/free 1/prepay 2/postpay

then regenerates the transaction data, requests a signature from the paymaster and submits to the bundler for packaging and uploading to the blockchain.

const res = await client.sendUserOperation(builder)