Publisher Subscriber Notification System

This project implements a simple Publisher-Subscriber Notification System using Node.js for the backend and React.js for the frontend.

Features

1. Subscribe to a Topic: Subscribers can subscribe to a topic.
2. Notify Subscribers: Send notifications to all subscribers of a topic.
3. Unsubscribe from a Topic: Subscribers can unsubscribe from a topic.

Backend

The backend is implemented using Node.js and Express.

APIs

1. Subscribe

   • Endpoint: /subscribe
   • Method: POST
   • Body: { "topicId": "string", "subscriberId": "string" }
   • Description: Adds a subscriber to a topic.

2. Notify

   • Endpoint: /notify
   • Method: POST
   • Body: { "topicId": "string" }
   • Description: Sends notifications to all subscribers of a topic.

3. Unsubscribe

   • Endpoint: /unsubscribe
   • Method: POST
   • Body: { "topicId": "string", "subscriberId": "string" }
   • Description: Removes a subscriber from a topic.

Internal Data Structures

• JavaScript Object (topics): Stores topics and their corresponding subscribers.

  • Key: topicId (string)
  • Value: Set of subscriberIds (Set of strings)

• Set: Ensures unique subscribers for each topic.

Edge Cases

1. Non-existent Topic Notification: Attempting to notify subscribers of a non-existent topic returns a 404 error.
2. Duplicate Subscription: Subscribing a subscriber to a topic they are already subscribed to does not create duplicate entries due to the use of a Set.
3. Unsubscribe Non-existent Subscriber: Attempting to unsubscribe a subscriber who is not subscribed to the topic returns a 404 error.

Frontend

The frontend is implemented using React.js.

Features

• Subscribe: Enter a topic ID and subscriber ID to subscribe to a topic.
• Notify: Enter a topic ID to notify all subscribers.
• Unsubscribe: Enter a topic ID and subscriber ID to unsubscribe from a topic.

Running the Project

Backend

1. Navigate to the pubsub-system directory.
2. Install the required packages:

   npm install express body-parser cors axios

3. Start the backend server:

   node index.js

Frontend

1. Navigate to the pubsub-client directory.
2. Install the required packages:

   npm install

3. Start the React development server:

   npm start

Driver Script

1. Ensure the backend server is running.
2. Run the driver script to demonstrate the flow of the application:

   node driver_functionn.js

Example Flow

1. Subscribe subscriber1 and subscriber2 to topic1.
2. Notify subscribers of topic1.
3. Unsubscribe subscriber1 from topic1.
4. Notify subscribers of topic1 after unsubscription.

The driver script will output the results of each operation.

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## Postman Documentation

The API endpoints for the Publisher-Subscriber Notification System are documented in Postman. You can import the collection to view and test the endpoints.

Shareable Link

Importing the JSON Collection

If the shareable link is not available, you can import the Postman collection using the JSON file included in the repository.

1. Download the PubSubSystem.postman_collection.json file from the repository.
2. Open Postman and click on Import in the top left.
3. Select the Upload Files tab.
4. Choose the downloaded JSON file and click Import.

This will import all the API endpoints into your Postman workspace.

You Can also find shared valid json config for postman collection which is uploaded on repo along with code

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### Screenshots

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Conclusion

This project demonstrates a simple implementation of a Publisher-Subscriber Notification System using Node.js and React.js. The internal data structures ensure efficient and correct handling of subscriptions, notifications, and unsubscriptions.