tenthirtyone / stackup-paymaster

Stackup Paymaster

A proof of concept for sending gasless transactions on the Polygon Mumbai testnet using the ERC-4337 implementation provided by StackUp. Transactions sent by the integration test in this repo will send 0.001 MATIC back to itself and the account balance will remain unchanged -> no gas fees will be charged.

The data value of the transactions are currently hardcoded to 0x, but you may perform any transaction an externally owned account is permitted to perform including launching and interacting with smart contracts.

The userop library will create a smart contract on the first transaction. This contract is used to verify the offchain data signed by the signingkey and execute the transactions. Effectively, it is a proxy for the external account that takes actions on behalf of the user, and its transaction gas is paid by the paymaster controlled by StackUp.

Prerequisites

1. This code requires a developer API key from Stackup. A free account will not have access to the paymaster API and transactions will fail. The paymaster API allows for gasless transactions. A gasless transaction allows for the end user to hold no ETH/MATIC in their wallet and still transact on the EVM compatible network.

See .env-template

2. The Signing Key used by this must have a balance. Visit the Polygon Faucet and fund your signing key's address. Transactions sent from this address will appear under the "Internal Txns" tab.

Example

You can generate a signing key using the ethers library:

const wallet = new ethers.Wallet(ethers.utils.randomBytes(32));

console.log(wallet.address); // fund this
console.log(wallet.privateKey); // this is STACKUP_SIGNING_KEY in .env

Installation

Use the package manager yarn to install the required dependencies for this project. For now, the userops package requires yarn for typescript-y things.

yarn install

Usage

1. Make a copy of the .env.example file and name it .env:

cp .env.example .env

2. Update the .env file with the required API keys and other configuration options.

3. Import the Server class and use it as needed:

const server = new Server();

(async () => {
  const address = await server.getAddress();
  console.log(`Address: ${address}`);

  const amount = "0.001";
  const transactionHash = await server.sendTransaction(address, amount);
  console.log(`Transaction hash: ${transactionHash}`);
})();

Testing

To run the unit and integration tests, execute the following command:

npm test