Simple Go Pub/Sub Server (Learning Example)

This project is a minimal, self-contained implementation of a Publish-Subscribe (Pub/Sub) messaging service built in Go. It uses Go's powerful concurrency primitives—Goroutines, Channels, and Mutexes—along with standard HTTP and WebSockets for network communication.

The primary goal of this repository is learning and experimentation!, please note it is not production-ready and lacks features like durable message persistence, scaling, backpressure management, advanced error handling etc...

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Overview

The service enables clients to subscribe to topics over WebSocket connections and receive real-time messages published to those topics.

• Publishers send messages to a specific topic via an HTTP endpoint.
• Subscribers connect via WebSockets and listen for messages on that topic.
• Synchronization is handled using sync.RWMutex to protect shared data while allowing concurrent operations.
• Channels ensure non-blocking message delivery between publishers and subscribers.

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Tri it out

1. Run the server:

   go run main.go

The server will start on port 8080.

2. Connect Subscribers (WebSockets)

Open your browser console or a WebSocket client like Postman and connect:

// Replace 'alerts' with the topic you want to test
const topic = "order_events";
const clientID = `client_${Math.floor(Math.random() * 1000)}`;

const ws = new WebSocket(`ws://localhost:8080/ws/sub/${topic}?id=${clientID}`);

ws.onopen = () =>
  console.log(`[${clientID}] Connected! Waiting for messages on '${topic}'.`);
ws.onmessage = (event) =>
  console.log(`[${clientID}] Received Message:`, JSON.parse(event.data));
ws.onclose = () => console.log(`[${clientID}] Connection closed.`);

// Connect a second client too
const ws2 = new WebSocket(
  `ws://localhost:8080/ws/sub/${topic}?id=second_client`
);
ws2.onmessage = (event) =>
  console.log(`[SECOND CLIENT] Received Message:`, JSON.parse(event.data));

3. Publish a Message (HTTP POST)

Use curl or any HTTP client to publish a message to the topic:

# Publish a message to the 'order_events' topic
curl -X POST http://localhost:8080/pub/order_events \
     -d "New Order: ORD-12345"

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