Realtime Chat Application

A production-ready realtime messaging application built using Node.js, Express.js, MongoDB, Socket.IO, React.js, and JWT Authentication.

---

Features

Authentication

• User Registration
• User Login
• JWT Access Token Authentication
• Refresh Token Support
• Protected API Routes
• Socket Authentication
• Email OTP Verification

---

Realtime Messaging

• One-to-One Chat
• Instant Message Delivery
• Realtime Message Updates
• Online/Offline Presence
• Typing Indicators
• Seen Status
• Delivered Status
• Multi-Tab Support
• Automatic Reconnection

---

Chat History

• Persistent Message Storage
• Encrypted Messages in Database
• Pagination Support
• Infinite Scroll Ready
• Fast Conversation Loading
• Optimized Query Structure

---

File Sharing

• Image Uploads
• Document Uploads
• File Preview Support
• Download Support
• Secure Upload Validation
• File Size Restrictions

---

Security

• Password Hashing (bcrypt)
• JWT Authentication
• Refresh Token Validation
• Socket Authentication Middleware
• Protected Routes
• Input Validation
• File Validation
• Encrypted Message Storage

---

Tech Stack

Backend

• Node.js
• Express.js
• MongoDB
• Mongoose
• Socket.IO
• JWT
• bcryptjs
• Multer

Frontend

• React.js
• Vite
• Tailwind CSS
• Socket.IO Client
• Zustand
• Axios
• Framer Motion

---

Project Structure

Backend

backend/
│
├── src/
│   ├── controllers/
│   │   ├── auth.controller.js
│   │   ├── conversation.controller.js
│   │   ├── message.controller.js
│   │   └── upload.controller.js
│   │
│   ├── middleware/
│   │   ├── auth.middleware.js
│   │   └── upload.middleware.js
│   │
│   ├── models/
│   │   ├── user.model.js
│   │   ├── conversation.model.js
│   │   ├── message.model.js
│   │   └── otp.model.js
│   │
│   ├── repositories/
│   │   ├── conversation.repository.js
│   │   └── message.repository.js
│   │
│   ├── routes/
│   │   ├── auth.routes.js
│   │   ├── conversation.routes.js
│   │   ├── message.routes.js
│   │   ├── upload.routes.js
│   │   └── user.routes.js
│   │
│   ├── services/
│   │   └── otp.service.js
│   │
│   ├── socket/
│   │   ├── middleware/
│   │   │   └── socketAuth.js
│   │   │
│   │   ├── managers/
│   │   │   └── onlineUsers.manager.js
│   │   │
│   │   └── socket.js
│   │
│   ├── utils/
│   │   ├── encryption.js
│   │   └── token.js
│   │
│   └── app.js
│
└── uploads/

---

Database Design

User Collection

{
  name,
  email,
  password,
  avatar,
  isVerified,
  refreshToken
}

Conversation Collection

{
  participants,
  lastMessage,
  lastMessageSender,
  lastMessageAt,
  unreadCounts
}

Message Collection

{
  conversationId,
  senderId,
  receiverId,
  message,
  messageType,
  fileUrl,
  fileName,
  fileSize,
  mimeType,
  status
}

---

API Documentation

Authentication

Register User

POST /api/auth/register

Request

{
  "name": "John",
  "email": "john@example.com",
  "password": "123456"
}

---

Login User

POST /api/auth/login

Request

{
  "email": "john@example.com",
  "password": "123456"
}

---

Get Current User

GET /api/auth/me

Headers

Authorization: Bearer <token>

---

Refresh Access Token

POST /api/auth/refresh-token

---

Conversations

Get Conversations

GET /api/conversations

---

Start Conversation

POST /api/conversations/start

Request

{
  "userId": "receiver_user_id"
}

---

Messages

Get Messages

GET /api/messages/:conversationId?page=1&limit=20

---

Upload

Upload File

POST /api/upload

Body

form-data

file: <file>

---

Socket Events

Client → Server

join_conversation

send_message

typing_start

typing_stop

message_seen

mark_conversation_read

---

Server → Client

receive_message

message_sent

typing_start

typing_stop

message_seen

online_users

conversations_updated

---

Environment Variables

Create a .env file in backend directory.

PORT=5000

MONGO_URI=your_mongodb_connection_string

JWT_SECRET=your_access_token_secret

JWT_REFRESH_SECRET=your_refresh_token_secret

FRONTEND_URL=http://localhost:8080

---

Installation

Backend

cd backend

npm install

npm run dev

---

Frontend

cd frontend

npm install

npm run dev

---

Architectural Decisions

Why JWT?

JWT provides stateless authentication and simplifies API authorization.

Why Socket.IO?

Socket.IO provides realtime bidirectional communication, automatic reconnection, and room-based messaging.

Why Separate Conversations and Messages?

Messages grow rapidly over time. Keeping them separate improves scalability and query performance.

Why Store Last Message in Conversation?

It enables fast sidebar rendering without querying the Messages collection repeatedly.

Why Use Repository Pattern?

Repositories isolate database logic from business logic and improve maintainability.

Why Encrypt Messages?

Messages are encrypted before storage to improve data security.

Why Use Pagination?

Pagination prevents loading large chat histories at once and improves performance.

---

Scalability Considerations

The current architecture supports future improvements such as:

• Redis Adapter for Socket.IO
• Horizontal Scaling
• Message Queue Integration
• CDN-Based File Storage
• AWS S3 File Uploads
• Distributed Caching
• Microservice Migration

---

Future Enhancements

• Group Chats
• Voice Messages
• Video Calling
• Push Notifications
• Read Receipts Analytics
• Message Reactions
• End-to-End Encryption
• Cloud File Storage
• Redis Caching
• Admin Dashboard

---

Author

Jeet Ahirwar

Realtime Messaging System Backend Assessment Project