Nexus – Real-Time Chat Application

Nexus is a full-stack real-time chat application built to demonstrate live communication, secure authentication, user presence tracking, and media handling using modern web technologies.

The project focuses on correctness, security, and real-time system behavior, rather than UI-heavy features.

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✨ Key Features

🔹 Real-Time Messaging

• Instant 1-to-1 message delivery using Socket.IO
• Typing indicators with smooth UI updates
• Automatic message ordering during concurrent sends

🔹 Live Presence & Last Seen

• Real-time online/offline user status
• Accurate lastSeen timestamps persisted in MongoDB
• Presence updates broadcast instantly across connected clients

🔹 Secure Authentication

• JWT-based authentication stored in HTTP-only cookies
• Protected Express routes using middleware-based authorization
• Persistent login via session validation

🔹 Media Support

• Profile images and inline chat media uploads via Cloudinary
• Optimized image URLs stored securely in the database

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🛠️ Tech Stack

Frontend

• React (Vite)
• Context API
• React Router
• Axios
• Socket.IO Client
• Tailwind CSS

Backend

• Node.js
• Express.js
• MongoDB & Mongoose
• Socket.IO
• JWT Authentication
• Cloudinary

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🧠 Architecture Overview

• REST APIs handle authentication, user management, and message history
• Socket.IO powers real-time messaging, typing indicators, and presence updates
• Server maintains a userId → socketId mapping to track active users
• On socket disconnect, the user’s lastSeen timestamp is updated in MongoDB

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🔐 Security & Design Decisions

• HTTP-only cookies are used instead of localStorage to mitigate XSS risks
• Authentication middleware protects all sensitive routes
• Media uploads are offloaded to Cloudinary to reduce backend load
• Route–controller separation improves maintainability and clarity

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🚀 Running Locally

Backend

cd backend
npm install
npm run dev