Pay Gas in ERC-20

Learn how to offer the ability for users to pay gas in ERC-20s using a Paymaster.

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

Quickstart

Prerequisites

• Node and a package manager (yarn or npm)
• An API key to access Candide's Paymaster. Visit dashboard
• Some Candide Test Tokens (CTT). Request CTT on our Discord or telegram

info

You can find the full example of this tutorial on Github

Step 1: Get setup

1. Create a new directory for your project:

mkdir smart-wallet-pay-gas-erc20
cd smart-wallet-pay-gas-erc20

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
• yarn add dotenv to load environment variables from the .env file

.env

CHAIN_ID=11155111
BUNDLER_URL=https://sepolia.test.voltaire.candidewallet.com/rpc
JSON_RPC_NODE_PROVIDER=NODE_PROVIDER_URL

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

info

We host free bundlers endpoints, you do not need to create an account.

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_2_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 with npx ts-node index.ts

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

Terminal

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_2_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
)

info

You can override any of the returned values using the overrides parameter.

Step 5: Get Paymaster Data

1. Import CandidePaymaster, and initiate an instance with its URL. You can get a free API key on the dashboard.

index.ts

import {
  ...
  CandidePaymaster,
} from "abstractionkit";

const paymasterRPC = process.env.PAYMASTER_RPC as string;
const tokenAddress = process.env.TOKEN_ADDRESS as string;

const paymaster: CandidePaymaster = new CandidePaymaster(paymasterRPC)

const userOperation = await paymaster.createTokenPaymasterUserOperation(
    smartAccount,
    userOperation,
    tokenAddress,
    bundlerUrl,
)

const cost = await paymaster.calculateUserOperationErc20TokenMaxGasCost(
    userOperation,
    tokenAddress
)

console.log("This useroperation may cost upto : " + cost + " wei in CTT token")
console.log("Please fund the sender account : " + userOperation.sender +" with more than "+ cost + " wei CTT token")

.env

PAYMASTER_RPC=https://api.candide.dev/paymaster/$version/$network/$apikey
TOKEN_ADDRESS=0xFa5854FBf9964330d761961F46565AB7326e5a3b # CTT address on sepolia

info

Don't forget to fund the account with ERC-20s to pay for gas. We are using Candide Test Tokens (CTT). Request some on telegram or Discord.

Step 5: 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 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 with npx ts-node index.ts

You've now sent your first user operation with a token paymaster! If everything went well, you should see the bundler returning a user operation 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

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_2_0 as SafeAccount,
    MetaTransaction,
    CandidePaymaster,
    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;
    const paymasterTokenAddress = process.env.PAYMASTER_TOKEN_ADDRESS 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,
    )

    userOperation = await paymaster.createTokenPaymasterUserOperation(
        smartAccount,
        userOperation,
        paymasterTokenAddress,
        bundlerUrl,
    )

    const cost = await paymaster.calculateUserOperationErc20TokenMaxGasCost(
        userOperation,
        paymasterTokenAddress
    )
    console.log("This useroperation may cost upto : " + cost + " wei in CTT token")
    console.log(
        "Please fund the sender account : " + 
        userOperation.sender +
        " with more than "+ cost + " wei CTT token"
    )
    console.log("This example uses a Candide token paymaster.")
    console.log("Please visit https://dashboard.candide.dev/ to get a token paymaster url.")
    console.log("Please visit our Discord to get some CTT token for testing")

    //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()