Chatify – Real Time Scalable Chat Application

Chatify is a production-ready real-time chat application built using the MERN stack. It features instant messaging, reactions, OTP-based authentication, rate limiting, and a scalable architecture powered by Redis and Socket.IO.

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🚀 Features

🔐 Authentication

• OTP via Phone: Integrated with Twilio.
• OTP via Email: Integrated with SendGrid.
• Secure auth via header: Implemented using JWT (JSON Web Tokens).

💬 Messaging

• Real-Time: 1-to-1 chat using Socket.IO.
• Reactions: Full emoji support for messages.
• Presence: Online/Offline status.
• Anti-Spam: Redis-based message rate limiting.

⚡ Performance & Security

• Optimized Queries: MongoDB indexing for fast data retrieval.
• Scalability: Logic designed for scalable socket management. Implemented Cursor-based pagination.
• Security: Secure environment variable handling and middleware protection.

📜 Cursor-Based Pagination

• Efficient message loading using cursor-based pagination.
• Loads messages in chunks instead of fetching entire chat history.
• Uses MongoDB _id as a cursor for consistent ordering.

How it works:

• Messages are fetched in reverse chronological order.
• Each request returns:
  • messages
  • nextCursor
  • hasMore
• Older messages are loaded when the user scrolls up.

Benefits:

• Faster initial load
• Reduced database load
• Scales well for long conversations

🖼 Media Support

• File Handling: Image and file uploads via Multer.

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🛠 Tech Stack

Layer	Technologies
Frontend	React.js, Zustand, Tailwind CSS, Socket.IO Client, Yup
Backend	Node.js, Express.js, Socket.IO, Redis, JWT, Cloudinary (Media Storage)
Database	MongoDB + Mongoose
Services	Twilio (Phone), SendGrid (Email), Upstash (Cloud Redis)

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🚦 Rate Limiting Strategy

Chatify uses a two-layer Redis-based rate limiting system to prevent spam while keeping the chat experience smooth.

1️⃣ Per User Rate Limit (Global)

Limits how frequently a user can send messages overall.

• Purpose: Prevents abuse, bot behavior, and accidental message floods
• Key: msg:{senderID}
• Example: Max 30 messages in 60 seconds per user

2️⃣ Per User Per Conversation Rate Limit

Applies stricter limits within a single conversation.

• Purpose: Stops spamming in individual chats without blocking the user globally
• Key: msg:{senderId}:{conversationId}
• Example: Max 15 messages in 10 seconds per user per conversation

⚙️ Implementation

• Built using Redis INCR + EXPIRE
• Executed before message persistence
• Avoids unnecessary MongoDB writes and file uploads

✅ Benefits

• Fine-grained abuse control
• High performance (in-memory operations)
• Scales efficiently for real-time messaging

👨‍💻 Author

Aansh Malhotra (Full Stack Developer)

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📝 Final Note

Thank you for checking out Chatify! This project was built to demonstrate the power of real-time communication using the MERN stack and Redis.

If you have any questions or just want to connect, feel free to reach out.

Don't forget to give this project a ⭐ if you found it useful!