Moonchain Transaction Agents

The Moonchain Transaction Agents libraries are designed for proxying transactions on Moonchain or other chains, allowing users to send contract transactions without paying gas fees.

It consists of the following components:

• Next Api Agents: Servers that proxy the sending of transactions, reading the RPC address and private key from the .env file and broadcasting transaction requests to the network.
• Contracts Utils: Contracts used for proxying transactions, ensuring and verifying that transactions are sent only by the proxy or the user themselves.

Install

pnpm install @moonchain/agents

Add API route

Create a .env file with the following two parameters:

• NETWORK_RPC: Your Network RPC url
• PRIVATE_KEY: The private key address of the proxy

Configure routing in the pages/api/agents directory of your Next.js project. The API route will be used to send transactions to the proxy server.

// pages/api/agents/[...path].ts
import { TransactionAgents } from '@moonchain/agents'

export default TransactionAgents({
  NETWORK_RPC: process.env.NETWORK_RPC!,
  PRIVATE_KEY: process.env.PRIVATE_KEY!
})
// or
export default TransactionAgents({
  NETWORK_RPC: req => '...',
  PRIVATE_KEY: req => '...'
})

Please ensure that the proxy's private key address has sufficient balance to cover transaction fees, and keep the private key secure to prevent theft.

Contracts

The contracts are located in the contracts directory of this repository. You can reference them in your contract project using npm.

• ProxyForward.sol: A contract for proxying transactions, ensuring and verifying that transactions are sent only by the proxy or the user themselves.
• ProxyForwardUpgradeable.sol: A contract for proxying transactions that supports upgradeable contracts.

import "@moonchain/agents/contracts/ProxyForward.sol";

contract Counter is ProxyForward {
  constructor(address _agent) ProxyForward(_agent) {}

  uint256 public count;

  function add(address sender, uint256 num) public proxy(sender) {
    count += num;
  }

  function sub(address sender, uint256 num) public proxy(sender) {
    count -= num;
  }
}

Usage

This example uses the Counter.sol contract written above and utilizes the Agents Servers to proxy the sending of transactions.

import { agent, proof } from '@moonchain/agents'
import { Contract, JsonRpcProvider, Transaction, Wallet } from 'ethers'
import abi from './Counter.json'

const provider = new JsonRpcProvider('URL_ADDRESS')
const user = new Wallet('264a...3492', provider)
const counter = new Contract('COUNTER_ADDRESS', abi, user)

// 1. Assemble the transaction
const populateTransaction = await counter.add.populateTransaction(user.address, 10)

// 2. Get the signed message generated by the proxy server
const message = await proof(counter.add.fragment, populateTransaction)

/**
 * message
 *
 *
 * from: ...
 * contract: ...
 * method: 0xa9059cbb | add(uint256)
 * params:
 *   to: ...
 *   value: 400
 * nonce: 4673
 */

// 3. Sign the message with the user's private key
const signedMessage = await user.signMessage(message)

// 4. Send the transaction to the proxy server and get the transaction information
const transaction = await agent(counter.add.fragment, {
  ...populateTransaction,
  signature: signedMessage,
})

// 5. Wait for the transaction broadcast to complete
const receipt = await provider.waitForTransaction(transaction.hash)

Limitations

Moonchain Transaction Agents do not support the direct sending of native tokens and are only applicable to contract-related transactions.

If you need to support the sending of ERC20 tokens, please modify the ERC20 contract to allow the proxy contract to perform user approvals.

import "@moonchain/agents/contracts/ProxyForward.sol";

contract ERC20 is ProxyForward {
  constructor(address _agent) ProxyForward(_agent) {}

  function approveProxy(address sender, address spender, uint256 amount) public proxy(sender) {
    _approve(sender, spender, amount);
  }
}