Implement Schema-Based Server-Side Input Validation with Joi in Node.js

const express = require('express');
const Joi = require('joi'); // Joi is a powerful schema description and validation library
const bodyParser = require('body-parser');

const app = express();
const port = 3000;

// Middleware to parse JSON request bodies
app.use(bodyParser.json());

// Define a Joi schema for user registration data
const userSchema = Joi.object({
  username: Joi.string().alphanum().min(3).max(30).required(),
  email: Joi.string().email({ tlds: { allow: ['com', 'net', 'org'] } }).required(),
  password: Joi.string().pattern(new RegExp('^[a-zA-Z0-9]{3,30}$')).required(), // Example: Alphanumeric 3-30 chars
  age: Joi.number().integer().min(18).max(120).optional(),
  role: Joi.string().valid('user', 'admin').default('user'),
});

// Validation middleware function
const validate = (schema) => (req, res, next) => {
  const { error } = schema.validate(req.body, { abortEarly: false }); // abortEarly: false to get all errors
  if (error) {
    const errors = error.details.map(err => err.message);
    return res.status(400).json({ errors: errors });
  }
  next();
};

// Route for user registration with validation
app.post('/register', validate(userSchema), (req, res) => {
  // If we reach here, the request body is valid
  const newUser = req.body;
  console.log('Validated User Data:', newUser);
  // In a real application, you would save newUser to a database
  res.status(201).json({ message: 'User registered successfully!', user: newUser });
});

// Example of another schema for updating user details
const updateUserSchema = Joi.object({
    email: Joi.string().email({ tlds: { allow: ['com', 'net', 'org'] } }).optional(),
    age: Joi.number().integer().min(18).max(120).optional(),
    role: Joi.string().valid('user', 'admin').optional(),
}).min(1); // At least one field must be provided for update

app.put('/users/:id', validate(updateUserSchema), (req, res) => {
    const userId = req.params.id;
    const updatedData = req.body;
    console.log(`Updating user ${userId} with data:`, updatedData);
    res.json({ message: `User ${userId} updated successfully!`, updated: updatedData });
});

app.get('/', (req, res) => {
  res.send('Welcome to the Joi validation example!');
});

app.listen(port, () => {
  console.log(`Server running on http://localhost:${port}`);
  console.log('Try POSTing to /register with valid and invalid JSON data.');
  console.log('e.g., {"username": "john_doe", "email": "[email protected]", "password": "MySecurePassword123", "age": 30}');
});

/*
Example invalid request (POST to /register):
{
  "username": "jo", // Too short
  "email": "invalid-email", // Invalid format
  "password": "123", // Too short
  "age": 10 // Too young
}
*/