💬 Real-Time Chat App Backend (Socket.IO + Express + MongoDB)

Welcome to the backend of a full-fledged real-time chat system — built from scratch using Node.js, Express, MongoDB, and Socket.IO 🚀

📢 From real-time messaging, offline delivery, read receipts, profile editing, admin tools, and even a chatbot — this backend is loaded.
✅ Tested purely with Postman & Socket.IO Client Tool — no frontend needed.

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⚙️ Tech Stack

• Node.js + Express – API and server logic
• MongoDB + Mongoose – Database and models
• Socket.IO – Real-time messaging, delivery, typing, read events
• Postman + Socket.IO Client Tool – API and event testing
• JWT Auth – Secure user endpoints
• Nodemon – Auto-reload during dev

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✨ Features

✅ Auth (JWT)

• POST /register – New user registration
• POST /login – Login and receive JWT token
• JWT-protected routes for profile and admin

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✅ Real-Time Chat Engine

🔌 register

• On socket connect, emit register
• Backend:
  • Stores username ↔ socketId in memory
  • Marks user as online
  • Pushes undelivered messages

💬 sendMessage

• Instantly delivers if receiver online
• Saves to DB regardless
• Handles delivered status

📤 Offline Delivery

• When a user connects:
  • All delivered: false messages are pushed
  • Status updated in DB

👁️ messageSeen

• Mark messages as seen: true
• Notifies original sender via seenAck event

✍️ Typing Indicators

• typing and stop-typing events supported

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📡 Online Status

• Emits onlineStatus updates to all users
• GET /api/users/online returns list of active users

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🤖 Auto-Reply Bot (Fun Feature)

• Send messages to Bot like:
  • "hello", "who are you", "joke", "bye"
• Bot responds with hardcoded replies

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🔐 Admin Panel Features

JWT role-based admin with these routes:

Route	Description
DELETE /admin/users/:id	Delete any user
DELETE /admin/messages/:id	Delete any message
POST /admin/freeze/:id	Freeze a user (disable sending)
POST /admin/unfreeze/:id	Unfreeze a user

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🧾 Profile Management

• GET /api/users/profile/me – Get your profile
• PUT /api/users/profile/me – Edit bio or avatar
• GET /api/users/profile/:username – View others' profiles
• GET /api/users/ – List all users (except self)

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📊 Analytics & Export

• GET /api/messages/analytics
  → Returns:

  {
    "totalMessages": 145,
    "delivered": 140,
    "seen": 100,
    "undelivered": 5
  }

• GET /api/messages/export
  → Download all your messages in .txt format

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🧪 Testing Instructions

Socket.IO Client Tool:

• Emit register → "mehul"
• Emit sendMessage → { sender, receiver, message }
• Emit messageSeen → { sender, receiver }
• Emit typing → { to }, then stop-typing

Postman:

• Auth: POST /register, POST /login
• Protected routes (use Bearer token in header):
  • GET /api/users/
  • GET /api/users/profile/me
  • PUT /api/users/profile/me
  • GET /api/messages/history?user1=A&user2=B
  • Admin routes (/admin/...)
  • Bot via regular sendMessage with receiver: "Bot"

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🗂️ Project Structure

chat-backend/
├── server.js
├── config/
│   └── db.js
├── models/
│   ├── User.js
│   └── Message.js
├── routes/
│   ├── messageRoutes.js
│   ├── userRoutes.js
│   ├── statusRoutes.js
│   ├── adminRoutes.js
│   └── onlineRoute.js
├── sockets/
│   └── chat.js
├── utils/
│   └── userStore.js
├── middleware/
│   └── auth.js
├── .env
├── package.json
└── README.md

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🧑‍💻 Author

Mehul Khanna
Backend Developer Intern · 2025
Passionate about building real-time scalable systems 💻🔥

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⭐️ If you like this project

Don’t forget to star ⭐ the repo and fork if you'd like to build on top of it!