mhd.io — Real-Time Chat Application

A full-stack real-time chat app built with Node.js / Express / Socket.io / Prisma / PostgreSQL on the backend and React Native (Expo) on the frontend.

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Project Structure

mhd.io/
├── backend/               # Node.js API + Socket.io server
│   ├── prisma/
│   │   └── schema.prisma  # User & Message models
│   ├── src/
│   │   ├── auth.js        # JWT auth helpers + middleware
│   │   └── validation.js  # Zod schemas + Express validate() middleware
│   ├── server.js          # Express app + Socket.io server
│   ├── .env.example
│   └── package.json
└── frontend/              # React Native (Expo) app
    ├── src/
    │   ├── api/
    │   │   └── client.js          # Axios instance with auth interceptor
    │   ├── context/
    │   │   └── SocketContext.js   # Socket.io provider + useSocket hook
    │   └── screens/
    │       ├── LoginScreen.js
    │       ├── ChatListScreen.js  # User list with online indicators
    │       └── ChatScreen.js      # Message history + real-time chat
    ├── App.js             # Root navigator + session bootstrap
    ├── app.json
    └── package.json

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Backend Setup

1 — Prerequisites

• Node.js >= 18
• PostgreSQL database running locally (or a connection string)

2 — Install dependencies

cd backend
npm install

3 — Configure environment

cp .env.example .env
# Edit .env and fill in DATABASE_URL and JWT_SECRET

4 — Run migrations & generate Prisma client

npx prisma migrate dev --name init

5 — Start the server

npm run dev   # development (nodemon)
npm start     # production

The server starts on http://localhost:4000 by default.

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Frontend Setup

1 — Install dependencies

cd frontend
npm install

2 — Configure environment

cp .env.example .env
# Set EXPO_PUBLIC_API_URL to your backend URL

3 — Start the Expo dev server

npm start

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API Reference

Method	Path	Auth	Description
POST	/api/auth/register	—	Register a new user
POST	/api/auth/login	—	Login; returns JWT
GET	/api/users	yes	List all other users
GET	/api/messages/:userId	yes	Fetch message history with a user

Socket.io events

Client -> Server	Payload	Description
send_message	{ receiverId, content }	Send a message

Server -> Client	Payload	Description
new_message	Message object	A message was received
user_status	{ userId, isOnline }	A user's online status changed

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Features

• JWT authentication — register/login with bcrypt-hashed passwords
• Real-time messaging — Socket.io delivers messages instantly to the recipient
• Message history — cursor-based paginated REST endpoint
• Online/offline presence — DB flag + broadcast on connect/disconnect
• Input validation — Zod schemas on all auth and message inputs
• Rate limiting — 10 login attempts / 15 min; 5 registrations / hour per IP
• React Native UI — sent/received bubble styles, keyboard-avoiding, FlatList pagination