1. Introduction

1.1 Goal of the Tutorial

This tutorial aims to guide you through the process of setting up secure file downloads in a Django application. We'll discuss how to ensure the secure delivery of user-uploaded files.

1.2 Learning Outcomes

By the end of this tutorial, you will be able to:
- Understand how Django handles file downloads
- Implement secure file download in your Django application
- Understand best practices for secure file handling

1.3 Prerequisites

Before starting, you should have:
- Basic knowledge of Python
- Basic understanding of Django framework
- A running Django application to implement the examples

2. Step-by-Step Guide

2.1 Concepts

In Django, files for download are typically stored in MEDIA_ROOT and served at MEDIA_URL. However, serving user-uploaded files directly can lead to security issues. Hence, it's crucial to implement measures to ensure that only authorized users can download the files.

2.2 Best Practices

• Always validate and sanitize filename to prevent directory traversal attacks.
• Use Django's built-in FileField for handling file uploads, which automatically validates file data.
• Use sendfile() for sending files to the user. It checks user permissions and handles large files efficiently.

3. Code Examples

3.1 Example: Secure File Download

from django.core.files.storage import default_storage
from django.http import FileResponse

def download(request, filename):
    # Check if user has permission
    if request.user.is_authenticated:
        file = default_storage.open(filename, 'rb')
        response = FileResponse(file)
        return response
    else:
        return HttpResponseForbidden("You don't have permission to access this file.")

In this example, the download view function checks if the user is authenticated before serving the file. It uses Django's FileResponse which streams the file out of Django in small chunks, allowing you to serve large files efficiently.

4. Summary

4.1 Key Points Covered

• Django handles file downloads using the FileField and FileResponse
• It's crucial to check user permissions before serving files
• Always sanitize filenames to prevent directory traversal attacks

4.2 Next Steps

Continue learning about Django's file handling capabilities, such as handling file uploads and storing files using Django's storage API.

4.3 Additional resources

• Django's official documentation on file handling
• Securing Django File Downloads

5. Practice Exercises

5.1 Exercise 1

Create a Django view that allows only admin users to download a file.

5.2 Solution

def admin_download(request, filename):
    if request.user.is_staff:
        file = default_storage.open(filename, 'rb')
        response = FileResponse(file)
        return response
    else:
        return HttpResponseForbidden("You don't have permission to access this file.")

In this solution, we check if the user is an admin (request.user.is_staff) before serving the file.

5.3 Exercise 2

Create a Django view that allows file download only if the user has a specific permission (assume the permission is can_download_files).

5.4 Solution

def download_with_permission(request, filename):
    if request.user.has_perm('app_name.can_download_files'):
        file = default_storage.open(filename, 'rb')
        response = FileResponse(file)
        return response
    else:
        return HttpResponseForbidden("You don't have permission to access this file.")

In this solution, we check if the user has the can_download_files permission before serving the file. Remember to replace app_name with the name of your Django app.

5.5 Tips for further practice

Try implementing file download restrictions based on other user attributes (like user groups) or based on file attributes (like file size or file type).