eth_subscribe

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Prerequisites

• Node.js Environment: You have Node.js installed on your system.
• Familiarity with JavaScript: You are comfortable with JavaScript and asynchronous programming (using async/await).
• WebSocket Connection: You will connect to a peaq network node via WebSocket (using wss://quicknode.peaq.xyz).
• Dependencies: The required packages (web3, dotenv, and web3-providers-ws) are installed.
• Basic Blockchain Knowledge: You understand the concepts of pending transactions, mempool, and real‑time event subscription.

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Instructions

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1. Setting Up the Environment

• Install Dependencies: Ensure you install the necessary packages:

npm install web3 dotenv web3-providers-ws

• Set ESM Module: Add the following to your package.json to allow for ESM modules.

"type": "module",

• Configure Environment Variables: Create a .env file with the following content:

PEAQ_WS_URL=wss://quicknode.peaq.xyz

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2. Understanding eth_subscribe

• Subscription Request: When you call web3.eth.subscribe('pendingTransactions'), the node sets up a listener for new pending transactions.
• Data Event: The subscription object returns a push-based stream of events. Each event provides the transaction hash of a pending transaction. The code attaches an event handler on the "data" event to process each incoming transaction hash.
• Error Handling: An "error" event is also attached to handle any issues (e.g., network errors or connection drops).

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3. Implementing the Boilerplate

• Initialize the Provider and Web3 Instance: A WebSocket provider is created using web3-providers-ws, connecting to the peaq network RPC endpoint.
• Subscribe to Pending Transactions: An asynchronous function is used to call web3.eth.subscribe('pendingTransactions'). Once the subscription is created, event handlers for "data" and "error" are attached.
• Graceful Shutdown: A signal handler for SIGINT (e.g., when pressing Ctrl+C) is registered. Upon receiving the shutdown signal, the code unsubscribes from pending transactions and disconnects the WebSocket provider to ensure a clean exit.

// eth_subscribe_pendingTx.js

import dotenv from 'dotenv';
dotenv.config();

import Web3 from 'web3';
import WSProvider from 'web3-providers-ws';

const WS_URL = process.env.PEAQ_WS_URL;
const provider = new WSProvider(WS_URL);
const web3 = new Web3(provider);

let pendingSubscription;

(async () => {
  try {
    pendingSubscription = await web3.eth.subscribe('pendingTransactions');
    pendingSubscription.on("data", (txHash) => {
      console.log("Pending Transaction Hash received:");
      console.log(txHash);
    });
    pendingSubscription.on("error", (error) => {
      console.error("Error in pendingTransactions subscription:", error);
    });
  } catch (err) {
    console.error("Error subscribing to pendingTransactions:", err);
  }
})();

// Graceful shutdown
process.on('SIGINT', async () => {
  console.log("\nGracefully shutting down...");
  try {
    if (pendingSubscription) {
      await pendingSubscription.unsubscribe();
      console.log("Unsubscribed from pendingTransactions.");
    }
  } catch (err) {
    console.error("Error unsubscribing from pendingTransactions:", err);
  }
  provider.disconnect();
  process.exit();
});

console.log("Listening for pending transactions on the peaq network (eth_subscribe)...");

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Conclusion