Unique docs

Contract Helpers

Address: 0x842899ecf380553e8a4de75bf534cdf6fbf64049

This precompiled contract allows the owner to manage the sponsorship of their contract.

In Unique Network, transactions can be sponsored, allowing for a gasless experience where the sponsor covers the transaction fees. This enables seamless and cost-free transfers of NFTs and the execution of smart contracts, even for accounts without native tokens.

Interface

Check the reference section for the complete interface details

Code examples

Below are examples of how to use this precompiled contract with ethers.js and hardhat.

If you're unfamiliar with setting up a Hardhat project, refer to the official documentation: https://hardhat.org/docs

Connect to contract

First, let's deploy the smart contract to be sponsored and connect to ContractHelpers precompile. We assume you have developed a contract called MyContract.sol and want to sponsor its calls.

import { ethers } from 'hardhat';
import { ContractHelpers__factory } from '@unique-nft/solidity-interfaces';

const [signer] = await ethers.getSigners();

const MyContractFactory = await ethers.getContractFactory('MyContract', seller);

// Contract to be sponsored
const myContract = await MyContractFactory.deploy();
myContract.waitForDeployment();

const contractHelpers = ContractHelpers__factory
  .connect("0x842899ecf380553e8a4de75bf534cdf6fbf64049", signer);

Choose sponsoring mode

Self-sponsoring

The simplest option is to sponsor transactions directly from the contract address itself.

await contractHelpers.selfSponsoredEnable(await myContract.getAddress());

const hasSponsor = await contractHelpers.hasSponsor(myContract.getAddress());
console.log("Self sponsoring enabled: ", hasSponsor); // true

External address sponsoring

You can also set up sponsorship from an arbitrary address. In this case, one additional step is required – the sponsor must confirm the sponsorship.

await contractHelpers.selfSponsoredEnable(await myContract.getAddress());

const hasSponsor = await contractHelpers.hasSponsor(myContract.getAddress());
console.log("Self sponsoring enabled: ", hasSponsor); // true

Enable sponsoring

There are a couple more steps to enable gasless transactions.

  1. There are three sponsoring modes:
  • 0: Disabled (default)
  • 1: Allowlisted (Only users from allowlist will be sponsored)
  • 2: Generous (All users will be sponsored)

Let's configure the contract to sponsor transactions for all users.

  1. By default, not every block is sponsored due to a timeout. Let's adjust this setting.
// Sponsoring is Disabled by default:
const sponsoringEnabled = await contractHelpers.sponsoringEnabled(myContract.getAddress());
console.log("Is sponsoring enabled?", sponsoringEnabled);

// Set to 2 - Generous mode
await contractHelpers.setSponsoringMode(myContract.getAddress(), 2);
// Set to 0 - Sponsor transactions in every block
await contractHelpers.setSponsoringRateLimit(myContract.getAddress(), 0);

// Optionally, you can limit the maximum fee amount you want to sponsor
// await contractHelpers.setSponsoringFeeLimit(myContract.getAddress(), ...);

const sponsoringEnabledAfter = await contractHelpers.sponsoringEnabled(myContract.getAddress());
console.log("Sponsoring enabled now:", sponsoringEnabledAfter);

Setting up Metamask

When sending transactions through Metamask, it initially verifies if the user has sufficient balance to cover gas fees. To enable sponsoring with Metamask, we need to bypass this gas check. Use the following libraryopen in new window.