Publish-Subscribe Messaging System

This project implements a Publish-Subscribe (Pub-Sub) messaging system using Python sockets. The system consists of three main components:

• Broker: Manages subscriptions and forwards published messages to subscribers.
• Publisher: Sends messages to a specific topic.
• Subscriber: Receives messages for topics it has subscribed to.

Quickstart Guide

Running the Broker

1. Copy all the contents from this repository.
2. Open a terminal and navigate to the folder containing broker.py.
3. Start the broker by running:

   python broker.py

4. The broker will listen on port 9000 for connections from publishers and subscribers.

Running a Publisher

1. Open another terminal and navigate to the same folder.
2. Start a publisher instance by running:

   python publisher.py <PUBLISHER_ID>

3. The publisher can send messages using the format:

   <TOPIC> <MESSAGE>
   

Running a Subscriber

1. Open another terminal and navigate to the same folder.
2. Start a subscriber instance by running:

   python subscriber.py <SUBSCRIBER_ID>

3. The subscriber can use the following commands:

   subscribe <TOPIC>
   unsubscribe <TOPIC>
   

Core Concepts

• Message Routing: The broker delivers published messages to all subscribed clients.
• Topic-Based Filtering: Messages are categorized by topics, allowing targeted delivery.
• Real-Time Communication: Messages are sent instantly between publishers and subscribers.

Preview of Pub-Sub System

Example Usage

# Terminal 1 - Start the broker
python broker.py

# Terminal 2 - Start a subscriber
python subscriber.py sub1
> subscribe weather

# Terminal 3 - Start a publisher
python publisher.py pub1
> weather Rainy day ahead!

Example Output

# Subscriber Output
>> DELIVER weather Rainy day ahead! pub1 2025-03-14 10:30:00

Notes:

• Multiple subscribers and publishers can run simultaneously.
• The system is event-driven, meaning messages are forwarded as soon as they arrive.
• The broker ensures message delivery to all active subscribers of a given topic.

Future Enhancements

• Implement message persistence for disconnected subscribers.
• Add QoS levels for guaranteed message delivery.
• Support distributed brokers for scalability.