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ERC-4337 Safe SDK

Safe accounts with the Safe4337Module

In this guide, you will learn how to create and execute multiple Safe transactions grouped in a batch from a Safe account that is not yet deployed and where the executor may or may not have funds to pay for the transaction fees. This can be achieved by supporting the ERC-4337 execution flow, which is supported by the Safe4337Module and exposed via the Relay Kit from the Safe{Core} SDK.

Pimlico (opens in a new tab) is used in this guide as the service provider, but any other provider compatible with the ERC-4337 can be used.

Read the Safe4337Module documentation to understand its benefits and flows better.

Prerequisites

Install dependencies


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yarn add @safe-global/relay-kit

Steps

Imports

Here are all the necessary imports for the script we implement in this guide.


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import { Safe4337Pack } from '@safe-global/relay-kit'

Create a signer

Firstly, we need to get a signer, which will be the owner of a Safe account after it's deployed.

In this example, we use a private key, but any way to get an EIP-1193 compatible signer can be used.


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const SIGNER_ADDRESS = // ...
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const SIGNER_PRIVATE_KEY = // ...
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const RPC_URL = 'https://rpc.ankr.com/eth_sepolia'

Initialize the Safe4337Pack

The Safe4337Pack class is exported from the Relay Kit and implements the ERC-4337 to create, sign, and submit Safe user operations.

To instantiate this class, the static init() method allows connecting existing Safe accounts (as long as they have the Safe4337Module enabled) or setting a custom configuration to deploy a new Safe account at the time where the first Safe transaction is submitted.

When deploying a new Safe account, we need to pass the configuration of the Safe in the options property. In this case, we are configuring a Safe account that will have our signer as the only owner.


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const safe4337Pack = await Safe4337Pack.init({
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provider: RPC_URL,
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signer: SIGNER_PRIVATE_KEY,
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rpcUrl: RPC_URL,
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bundlerUrl: `https://api.pimlico.io/v1/sepolia/rpc?apikey=${PIMLICO_API_KEY}`,
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options: {
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owners: [SIGNER_ADDRESS],
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threshold: 1
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},
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// ...
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})

By default, the transaction fees will be paid in the native token and extracted from the Safe account, so there must be enough funds in the Safe address. However, depending on how we want the transactions to be paid, there are two other ways we can initialize the Safe4337Pack.

A paymaster will execute the transactions and get reimbursed from the Safe account, which must have enough funds in the Safe address in advance.

Payment of transaction fees is made using an ERC-20 token specified with the paymasterTokenAddress property. If an ERC-20 token is used, the Safe must approve that token to the paymaster. If no balance is approved, it can be specified using the amountToApprove property.


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const safe4337Pack = await Safe4337Pack.init({
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// ...
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paymasterOptions: {
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paymasterAddress: '0x...'
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paymasterTokenAddress: '0x...',
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amountToApprove // Optional
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}
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})

Create a user operation

To create a Safe user operation, use the createTransaction() method, which takes the array of transactions to execute and returns a SafeOperation object.


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// Define the transactions to execute
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const transaction1 = { to, data, value }
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const transaction2 = { to, data, value }
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// Build the transaction array
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const transactions = [transaction1, transaction2]
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// Create the SafeOperation with all the transactions
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const safeOperation = await safe4337Pack.createTransaction({ transactions })

The safeOperation object has the data and signatures properties, which contain all the information about the transaction batch and the signatures of the Safe owners, respectively.

Sign the user operation

Before sending the user operation to the bundler, it's required to sign the safeOperation object with the connected signer. The signSafeOperation() method, which receives a SafeOperation object, generates a signature that will be checked when the Safe4337Module validates the user operation.


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const signedSafeOperation = await safe4337Pack.signSafeOperation(safeOperation)

Submit the user operation

Once the safeOperation object is signed, we can call the executeTransaction() method to submit the user operation to the bundler.


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const userOperationHash = await safe4337Pack.executeTransaction({
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executable: signedSafeOperation
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})

This method returns the hash of the user operation. With it, we can monitor the transaction status using a block explorer or the bundler's API.

Check the transaction status

To check the transaction status, we can use the getTransactionReceipt() method, which returns the transaction receipt after it's executed.


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let userOperationReceipt = null
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while (!userOperationReceipt) {
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// Wait 2 seconds before checking the status again
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await new Promise((resolve) => setTimeout(resolve, 2000))
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userOperationReceipt = await safe4337Pack.getUserOperationReceipt(
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userOperationHash
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)
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}

In addition, we can use the getUserOperationByHash() method with the returned hash to retrieve the user operation object we sent to the bundler.


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const userOperationPayload = await safe4337Pack.getUserOperationByHash(
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userOperationHash
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)

Recap and further reading

After following this guide, we are able to deploy new Safe accounts and create, sign, and execute Safe transactions in a batch without the executor needing to have funds to pay for the transaction fees.

Learn more about the ERC-4337 standard and the Safe4337Module contract following these links:

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