How to Send a Gasless Transaction

Learn how to send gasless transactions using a paymaster.

If you are coming from the previous guide, you only need one additional step. Skip directly to step 5.

Quickstart

If you need, you can fork and run this tutorial directly on Github

Prerequisites

• Node and a package manager (yarn or npm)
• Bundler API key from the Candide Dashboard
• An API key from the dashboard
• A Gas Policy, private or public, created on the dashboard

Step 1: Get setup

1. Create a new directory for your project:

mkdir smart-wallet-send-gasless-tx
cd smart-wallet-send-gasless-tx
yarn init

2. Install required dependencies

yarn add abstractionkit dotenv

3. Configure Environment Variables

• Create a .env file in ./src and add the following environment variables with your own values
• We will be using Sepolia Testnet for this example

.env

CHAIN_ID=11155111
BUNDLER_URL=https://api.candide.dev/bundler/version/network/YOUR_API_KEY
JSON_RPC_NODE_PROVIDER=NODE_PROVIDER_URL

# API key for Sepolia
PAYMASTER_RPC=https://api.candide.dev/paymaster/$version/sepolia/$APY_KEY

# Private gas policy ID 
SPONSORSHIP_POLICY_ID=

#account owner pub & private key
PRIVATE_KEY=YOUR_PRIVATE_KEY
PUBLIC_ADDRESS=YOUR_PUBLIC_KEY

4. Create a empty file and a function to run our script

index.ts

async function main(): Promise<void> {
  // Rest of the code will go here...
}

main();

Step 2: Generate Account Address

Let's open up index.ts

To generate an account address, we will be using the Safe Module/Fallback as our base smart account. An extension to the Safe contract that implements the ERC4337 interface. We will control the Account with a single EOA owner.

Since this is our first transaction, we will need to deploy the account in the same transaction

index.ts

import * as dotenv from "dotenv";
import { SafeAccountV0_3_0 as SafeAccount } from "abstractionkit";
  
async function main(): Promise<void> {
  //get values from .env
  dotenv.config();

  const ownerPublicAddress = process.env.PUBLIC_ADDRESS as string
  const smartAccount = SafeAccount.initializeNewAccount(
      [ownerPublicAddress],
  )
  console.log("Account address(sender) : " + smartAccount.accountAddress);
}

main();

Let's run this code

Terminal

npx ts-node index.ts

If everything worked, you will get the calculate address of the account in the console.

Result example

Account address(sender): 0x32afdcfa1e3bfe70d03ecb55b5c8045c26515c9d

Step 3: Generate the callData

We will be creating two transactions to mint 2 NFTs. You can use your fav library (like ethers or viem) to construct the calldata.

index.ts

import {
  SafeAccountV0_3_0 as SafeAccount
  MetaTransaction,
  getFunctionSelector,
  createCallData,
} from "abstractionkit";

const nftContractAddress = "0x9a7af758aE5d7B6aAE84fe4C5Ba67c041dFE5336";
const mintFunctionSignature =  'mint(address)';
const mintFunctionSelector =  getFunctionSelector(mintFunctionSignature);
const mintTransactionCallData = createCallData(
  mintFunctionSelector, 
  ["address"], 
  [smartAccount.accountAddress]
);

const transaction1 :MetaTransaction ={
    to: nftContractAddress,
    value: 0n,
    data: mintTransactionCallData, 
}

const transaction2 :MetaTransaction ={
    to: nftContractAddress, 
    value: 0n,
    data: mintTransactionCallData,
}

Step 4: Create UserOperation

Now the fun part. Call createUserOperation, which will determine the nonce, fetch the gas prices, estimate gas limits and return a userop to be signed.

index.ts

const jsonRpcNodeProvider = process.env.JSON_RPC_NODE_PROVIDER as string
const bundlerUrl = process.env.BUNDLER_URL as string

let userOperation = await smartAccount.createUserOperation(
  [transaction1, transaction2], // you can batch multiple transactions to be executed in one userop
  jsonRpcNodeProvider, // the node rpc is used to fetch the current nonce and fetch gas prices.
  bundlerUrl, // the bundler rpc is used to estimate the gas limits
)

Step 5: Get Paymaster Data

Sponsor gas for a user operation by first checking for publicly available gas policies set up by third parties. If no matching public gas policy is found for the user operation, you can fall back to a private gas policy.

• Public Gas Policies: These are gas policies provided by third parties that do not require a sponsorship policy ID.
• Private Gas Policies: These require a sponsorship policy ID and can be used if no public gas policy matches the user operation.

1. Create a new app on the dashboard, and copy the paymaster RPC URL in your .env
2. Setup a Private Gas Policy on the dashboard, and copy its sponsor policy ID in your .env
3. Import CandidePaymaster and call the method createsponsorpaymasteruseroperation

index.ts

import {
  CandidePaymaster,
} from "abstractionkit";

const paymasterRPC = process.env.PAYMASTER_RPC as string;
const paymaster: CandidePaymaster = new CandidePaymaster(paymasterRPC);
const sponsorshipPolicyId = process.env.SPONSORSHIP_POLICY_ID;

let paymasterUserOperation;
let sponsorMetadata;
try {
  [paymasterUserOperation, sponsorMetadata] =
    await paymaster.createSponsorPaymasterUserOperation(
      userOperation,
      bundlerUrl,
    );
} catch (error) {
  try {
    [paymasterUserOperation, sponsorMetadata] =
      await paymaster.createSponsorPaymasterUserOperation(
        userOperation,
        bundlerUrl,
        sponsorshipPolicyId,
      );
  } catch (finalError) {
    // Last fallback to propose to the user the option to pay gas in erc-20 tokens 
    throw finalError;
  }
}

userOperation = paymasterUserOperation;

.env

PAYMASTER_RPC=https://api.candide.dev/paymaster/$version/$network/$apikey
SPONSORSHIP_POLICY_ID=

Step 6: Sign and Submit

1. Call signUserOperation, which will create a signature for the private key provided of the owner of the Safe.

index.ts

const chainId = BigInt(process.env.CHAIN_ID as string);
const privateKey = process.env.PRIVATE_KEY as string;

userOperation.signature = smartAccount.signUserOperation(
  userOperation,
  [privateKey],
  chainId,
)

2. Use the Bundler RPC to send the userop to the bundler with sendUserOperation, and await the return SendUseroperationResponse object to confirm the on-chain inclusion of the user operation.

index.ts

const sendUserOperationResponse = await smartAccount.sendUserOperation(userOperation, bundlerUrl)

console.log("UserOperation sent. Waiting to be included ......")

3. Track the userOperation and wait for its inclusion onchain

let userOperationReceiptResult = await sendUserOperationResponse.included()

console.log("Useroperation receipt received.")
console.log(userOperationReceiptResult)

if (userOperationReceiptResult.success) {
    console.log("Two Nfts were minted. The transaction hash is : " + userOperationReceiptResult.receipt.transactionHash)
} else {
    console.log("Useroperation execution failed")
}

Now let's run this code again

Terminal

npx ts-node index.ts

You've now sent your first sponsored userOperation! If everything went well, you should see the bundler returning a receipt

Result

Useroperation sent. Waiting to be included ......
Useroperation receipt received.
{
  userOpHash: '0x1acede61123ab7116eb29c797aeaec3c03615c37732ba66428524aebdb4b4514',
  entryPoint: '0x5FF137D4b0FDCD49DcA30c7CF57E578a026d2789',
  sender: '0xb8741a449d50ed0dcfe395287f85be152884c8d9',
  nonce: 0n,
  paymaster: '0x3fe285dcd76bcce4ac92d38a6f2f8e964041e020',
  actualGasCost: 8078496n,
  actualGasUsed: 504906n,
  success: true,
  logs: '[{"address":"0x5ff137d4b0fdcd49dca30c7cf57e578a026d2789","blockHash":"0xe19e52b4c222c1cdbc765f1a4e196ff4bf40c5550926e02974570e1845e88e2c","blockNumber":"0x9efe5f","data":"0x0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000000000000000000000000000000000007b44a0000000000000000000000000000000000000000000000000000000000007b44a","logIndex":"0x9a","removed":false,"topics":["0x49628fd1471006c1482da88028e9ce4dbb080b815c9b0344d39e5a8e6ec1419f","0x1acede61123ab7116eb29c797aeaec3c03615c37732ba66428524aebdb4b4514","0x000000000000000000000000b8741a449d50ed0dcfe395287f85be152884c8d9","0x0000000000000000000000003fe285dcd76bcce4ac92d38a6f2f8e964041e020"],"transactionHash":"0xf43576a07f39660737a342c99a187eb70ac59d89bc0df92ff3c1bb8a8da370aa","transactionIndex":"0x1d"}]',
  receipt: {
    blockHash: '0xe19e52b4c222c1cdbc765f1a4e196ff4bf40c5550926e02974570e1845e88e2c',
    blockNumber: 10419807n,
    from: '0x3cfdc212769c890907bce93d3d8c2c53de6a7a89',
    cumulativeGasUsed: 6978990n,
    gasUsed: 507053n,
    logs: '[{"address":"0xb8741a449d50ed0dcfe395287f85be152884c8d9","blockHash":"0xe19e52b4c222c1cdbc765f1a4e196ff4bf40c5550926e02974570e1845e88e2c","blockNumber":"0x9efe5f","data":"0x","logIndex":"0x90","removed":false,"topics":["0xecdf3a3effea5783a3c4c2140e677577666428d44ed9d474a0b3a4c9943f8440","0x000000000000000000000000a581c4a4db7175302464ff3c06380bc3270b4037"],"transactionHash":"0xf43576a07f39660737a342c99a187eb70ac59d89bc0df92ff3c1bb8a8da370aa","transactionIndex":"0x1d"},{"address":"0xb8741a449d50ed0dcfe395287f85be152884c8d9","blockHash":"0xe19e52b4c222c1cdbc765f1a4e196ff4bf40c5550926e02974570e1845e88e2c","blockNumber":"0x9efe5f","data":"0x000000000000000000000000000000000000000000000000000000000000008000000000000000000000000000000000000000000000000000000000000000010000000000000000000000008ecd4ec46d4d2a6b64fe960b3d64e8b94b2234eb000000000000000000000000a581c4a4db7175302464ff3c06380bc3270b40370000000000000000000000000000000000000000000000000000000000000001000000000000000000000000bdbc5fbc9ca8c3f514d073ec3de840ac84fc6d31","logIndex":"0x91","removed":false,"topics":["0x141df868a6331af528e38c83b7aa03edc19be66e37ae67f9285bf4f8e3c6a1a8","0x0000000000000000000000004e1dcf7ad4e460cfd30791ccc4f9c8a4f820ec67"],"transactionHash":"0xf43576a07f39660737a342c99a187eb70ac59d89bc0df92ff3c1bb8a8da370aa","transactionIndex":"0x1d"},{"address":"0x4e1dcf7ad4e460cfd30791ccc4f9c8a4f820ec67","blockHash":"0xe19e52b4c222c1cdbc765f1a4e196ff4bf40c5550926e02974570e1845e88e2c","blockNumber":"0x9efe5f","data":"0x00000000000000000000000029fcb43b46531bca003ddc8fcb67ffe91900c762","logIndex":"0x92","removed":false,"topics":["0x4f51faf6c4561ff95f067657e43439f0f856d97c04d9ec9070a6199ad418e235","0x000000000000000000000000b8741a449d50ed0dcfe395287f85be152884c8d9"],"transactionHash":"0xf43576a07f39660737a342c99a187eb70ac59d89bc0df92ff3c1bb8a8da370aa","transactionIndex":"0x1d"},{"address":"0x5ff137d4b0fdcd49dca30c7cf57e578a026d2789","blockHash":"0xe19e52b4c222c1cdbc765f1a4e196ff4bf40c5550926e02974570e1845e88e2c","blockNumber":"0x9efe5f","data":"0x0000000000000000000000004e1dcf7ad4e460cfd30791ccc4f9c8a4f820ec670000000000000000000000003fe285dcd76bcce4ac92d38a6f2f8e964041e020","logIndex":"0x93","removed":false,"topics":["0xd51a9c61267aa6196961883ecf5ff2da6619c37dac0fa92122513fb32c032d2d","0x1acede61123ab7116eb29c797aeaec3c03615c37732ba66428524aebdb4b4514","0x000000000000000000000000b8741a449d50ed0dcfe395287f85be152884c8d9"],"transactionHash":"0xf43576a07f39660737a342c99a187eb70ac59d89bc0df92ff3c1bb8a8da370aa","transactionIndex":"0x1d"},{"address":"0x5ff137d4b0fdcd49dca30c7cf57e578a026d2789","blockHash":"0xe19e52b4c222c1cdbc765f1a4e196ff4bf40c5550926e02974570e1845e88e2c","blockNumber":"0x9efe5f","data":"0x","logIndex":"0x94","removed":false,"topics":["0xbb47ee3e183a558b1a2ff0874b079f3fc5478b7454eacf2bfc5af2ff5878f972"],"transactionHash":"0xf43576a07f39660737a342c99a187eb70ac59d89bc0df92ff3c1bb8a8da370aa","transactionIndex":"0x1d"},{"address":"0xb8741a449d50ed0dcfe395287f85be152884c8d9","blockHash":"0xe19e52b4c222c1cdbc765f1a4e196ff4bf40c5550926e02974570e1845e88e2c","blockNumber":"0x9efe5f","data":"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","logIndex":"0x95","removed":false,"topics":["0xb648d3644f584ed1c2232d53c46d87e693586486ad0d1175f8656013110b714e"],"transactionHash":"0xf43576a07f39660737a342c99a187eb70ac59d89bc0df92ff3c1bb8a8da370aa","transactionIndex":"0x1d"},{"address":"0xd9de104e3386d9a45a61bce269c43e48b534e4e7","blockHash":"0xe19e52b4c222c1cdbc765f1a4e196ff4bf40c5550926e02974570e1845e88e2c","blockNumber":"0x9efe5f","data":"0x","logIndex":"0x96","removed":false,"topics":["0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef","0x0000000000000000000000000000000000000000000000000000000000000000","0x000000000000000000000000b8741a449d50ed0dcfe395287f85be152884c8d9","0x0000000000000000000000000000000000000000000000000000000000000056"],"transactionHash":"0xf43576a07f39660737a342c99a187eb70ac59d89bc0df92ff3c1bb8a8da370aa","transactionIndex":"0x1d"},{"address":"0xd9de104e3386d9a45a61bce269c43e48b534e4e7","blockHash":"0xe19e52b4c222c1cdbc765f1a4e196ff4bf40c5550926e02974570e1845e88e2c","blockNumber":"0x9efe5f","data":"0x","logIndex":"0x97","removed":false,"topics":["0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef","0x0000000000000000000000000000000000000000000000000000000000000000","0x000000000000000000000000b8741a449d50ed0dcfe395287f85be152884c8d9","0x0000000000000000000000000000000000000000000000000000000000000057"],"transactionHash":"0xf43576a07f39660737a342c99a187eb70ac59d89bc0df92ff3c1bb8a8da370aa","transactionIndex":"0x1d"},{"address":"0xb8741a449d50ed0dcfe395287f85be152884c8d9","blockHash":"0xe19e52b4c222c1cdbc765f1a4e196ff4bf40c5550926e02974570e1845e88e2c","blockNumber":"0x9efe5f","data":"0x","logIndex":"0x98","removed":false,"topics":["0x6895c13664aa4f67288b25d7a21d7aaa34916e355fb9b6fae0a139a9085becb8","0x000000000000000000000000a581c4a4db7175302464ff3c06380bc3270b4037"],"transactionHash":"0xf43576a07f39660737a342c99a187eb70ac59d89bc0df92ff3c1bb8a8da370aa","transactionIndex":"0x1d"},{"address":"0x3fe285dcd76bcce4ac92d38a6f2f8e964041e020","blockHash":"0xe19e52b4c222c1cdbc765f1a4e196ff4bf40c5550926e02974570e1845e88e2c","blockNumber":"0x9efe5f","data":"0x0000000000000000000000000000000000000000000000000000000000000000","logIndex":"0x99","removed":false,"topics":["0xa050a122b4c0e369e3385eb6b7cccd8019638b2764de67bec0af99130ddf8471","0x1acede61123ab7116eb29c797aeaec3c03615c37732ba66428524aebdb4b4514","0x000000000000000000000000b8741a449d50ed0dcfe395287f85be152884c8d9","0x0000000000000000000000000000000000000000000000000000000000000000"],"transactionHash":"0xf43576a07f39660737a342c99a187eb70ac59d89bc0df92ff3c1bb8a8da370aa","transactionIndex":"0x1d"},{"address":"0x5ff137d4b0fdcd49dca30c7cf57e578a026d2789","blockHash":"0xe19e52b4c222c1cdbc765f1a4e196ff4bf40c5550926e02974570e1845e88e2c","blockNumber":"0x9efe5f","data":"0x0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000000000000000000000000000000000007b44a0000000000000000000000000000000000000000000000000000000000007b44a","logIndex":"0x9a","removed":false,"topics":["0x49628fd1471006c1482da88028e9ce4dbb080b815c9b0344d39e5a8e6ec1419f","0x1acede61123ab7116eb29c797aeaec3c03615c37732ba66428524aebdb4b4514","0x000000000000000000000000b8741a449d50ed0dcfe395287f85be152884c8d9","0x0000000000000000000000003fe285dcd76bcce4ac92d38a6f2f8e964041e020"],"transactionHash":"0xf43576a07f39660737a342c99a187eb70ac59d89bc0df92ff3c1bb8a8da370aa","transactionIndex":"0x1d"}]',
    logsBloom: '0x0000040000009000000000000000010080000000000000000000000000000000000800000000000000020001000004040010000000000000800002000000000000001000000000000000000c0002000000000000010000080040000000000000020000000a0000000500002000000800008000000100000000000014000000000800010020000200008000000040000000000200000400000000000000000000000004000000000000500000000004000210000000000000000002001000000020200082000000000001000008000000000000002060000000100000000026000000082000010000000000000008100220000000000000000000000010000200',
    transactionHash: '0xf43576a07f39660737a342c99a187eb70ac59d89bc0df92ff3c1bb8a8da370aa',
    transactionIndex: 29n,
    effectiveGasPrice: 16n
  }
}
Two Nfts were minted. The transaction hash is : 0xf43576a07f39660737a342c99a187eb70ac59d89bc0df92ff3c1bb8a8da370aa

You can lookup the hash on explorers that supports user operations like Blockscout.

In the next guides, we will show how to allow users to pay gas in erc-20s using a paymaster.

Full Example

Below is the complete example code that you can copy directly to implement the functionality described in the tutorial.

index.js

import * as dotenv from 'dotenv'

import {
    SafeAccountV0_3_0 as SafeAccount,
    MetaTransaction,
    calculateUserOperationMaxGasCost,
    CandidePaymaster,
    UserOperationV7,
    getFunctionSelector,
    createCallData,
} from "abstractionkit";

async function main(): Promise<void> {
    //get values from .env
    dotenv.config()
    const chainId = BigInt(process.env.CHAIN_ID as string)
    const bundlerUrl = process.env.BUNDLER_URL as string
    const jsonRpcNodeProvider = process.env.JSON_RPC_NODE_PROVIDER as string
    const ownerPublicAddress = process.env.PUBLIC_ADDRESS as string
    const ownerPrivateKey = process.env.PRIVATE_KEY as string
    const paymasterRPC = process.env.PAYMASTER_RPC as string;
    
    //initializeNewAccount only needed when the smart account
    //have not been deployed yet for its first useroperation.
    //You can store the accountAddress to use it to initialize 
    //the SafeAccount object for the following useroperations
    let smartAccount = SafeAccount.initializeNewAccount(
        [ownerPublicAddress],
    )

    //After the account contract is deployed, no need to call initializeNewAccount
    //let smartAccount = new SafeAccount(accountAddress)

    console.log("Account address(sender) : " + smartAccount.accountAddress)

    //create two meta transaction to mint two NFTs
    //you can use favorite method (like ethers.js) to construct the call data 
    const nftContractAddress = "0x9a7af758aE5d7B6aAE84fe4C5Ba67c041dFE5336";
    const mintFunctionSignature =  'mint(address)';
    const mintFunctionSelector =  getFunctionSelector(mintFunctionSignature);
    const mintTransactionCallData = createCallData(
        mintFunctionSelector, 
        ["address"],
        [smartAccount.accountAddress]
    );
    const transaction1 :MetaTransaction ={
        to: nftContractAddress,
        value: 0n,
        data: mintTransactionCallData,
    }

    const transaction2 :MetaTransaction ={
        to: nftContractAddress,
        value: 0n,
        data: mintTransactionCallData,
    }

    //createUserOperation will determine the nonce, fetch the gas prices,
    //estimate gas limits and return a useroperation to be signed.
    //you can override all these values using the overrides parameter.
    let userOperation = await smartAccount.createUserOperation(
        [
            //You can batch multiple transactions to be executed in one useroperation.
            transaction1, transaction2,
        ],
        jsonRpcNodeProvider, //the node rpc is used to fetch the current nonce and fetch gas prices.
        bundlerUrl, //the bundler rpc is used to estimate the gas limits.
    )

  

    let paymaster: CandidePaymaster = new CandidePaymaster(paymasterRPC)

    let [paymasterUserOperation, _sponsorMetadata] =
      await paymaster.createSponsorPaymasterUserOperation(
        userOperation,
        bundlerUrl
      );
    userOperation = paymasterUserOperation as UserOperationV7;

    const cost = calculateUserOperationMaxGasCost(userOperation)
    console.log("This useroperation may cost upto : " + cost + " wei")
    console.log("This example uses a Candide paymaster to sponsor the useroperation, so there is not need to fund the sender account.")
    console.log("Get early access to Candide's sponsor paymaster by visiting our Discord")

    //Safe is a multisig that can have multiple owners/signers
    //signUserOperation will create a signature for the provided
    //privateKeys
    userOperation.signature = smartAccount.signUserOperation(
        userOperation,
        [ownerPrivateKey],
        chainId,
    )
    console.log(userOperation)

    //use the bundler rpc to send a userOperation
    //sendUserOperation will return a SendUseroperationResponse object
    //that can be awaited for the useroperation to be included onchain
    const sendUserOperationResponse = await smartAccount.sendUserOperation(
        userOperation, bundlerUrl
    )

    console.log("Useroperation sent. Waiting to be included ......")
    //included will return a UserOperationReceiptResult when 
    //useroperation is included onchain
    let userOperationReceiptResult = await sendUserOperationResponse.included()

    console.log("Useroperation receipt received.")
    console.log(userOperationReceiptResult)
    if(userOperationReceiptResult.success){
        console.log("Two Nfts were minted. The transaction hash is : " + userOperationReceiptResult.receipt.transactionHash)
    }else{
        console.log("Useroperation execution failed")
    }
}

main()