Introduction to Form Validation & Sanitization

1. Introduction

Form validation and sanitization are crucial components of web security that ensure the integrity and safety of user input before it is processed by the server. This lesson covers the basics of these processes.

2. Why Validation & Sanitization?

• Protect against malicious input.
• Ensure data integrity.
• Improve user experience by providing immediate feedback.

3. Form Validation

Form validation is the process of checking user input against predefined rules before submission. This can be done on both the client and server sides.

3.1 Client-Side Validation

Client-side validation is important for providing immediate feedback. Here’s an example using HTML5 attributes:

<form>
    <input type="text" name="username" required minlength="3">
    <input type="email" name="email" required>
    <input type="submit" value="Submit">
</form>

3.2 Server-Side Validation

Server-side validation is essential for security, as it cannot be bypassed by the user. Here’s a simple example in JavaScript:

function validateForm(data) {
    if (!data.username || data.username.length < 3) {
        throw new Error("Username must be at least 3 characters long.");
    }
    if (!data.email || !validateEmail(data.email)) {
        throw new Error("Invalid email format.");
    }
    return true;
}

4. Form Sanitization

Sanitization is the process of cleaning user input to remove any potentially harmful content. This is typically done on the server side.

4.1 Example of Sanitization

Here’s how you might sanitize user input in a Node.js application:

const sanitizeHtml = require('sanitize-html');

function sanitizeInput(input) {
    return sanitizeHtml(input, {
        allowedTags: [],
        allowedAttributes: {}
    });
}

5. Best Practices

• Always validate on the server side.
• Use prepared statements for database queries to prevent SQL Injection.
• Escape output to prevent XSS.
• Implement comprehensive error handling.
• Keep libraries and dependencies updated.

6. FAQ