AWS CloudFront Signed URLs: A Guide to Enable Content Disposition Using Django and django-storages

Introduction

In the world of software architecture, AWS presents us with a myriad of tools that, when used effectively, can drastically streamline our processes. Among these is the CloudFront Signed URL. As proficient Django developers, we find ourselves needing to enable Content Disposition within these URLs. Our goal? Transforming original file URLs into downloadable links.

The Power of URLs and Content Disposition: A Brief Overview

AWS CloudFront service’s cornerstone is the Signed URL, a tool that opens up a realm of possibilities for online resources. But how do we demystify 'enabling Content Disposition' within these CloudFront Signed URLs?

Content Disposition, in essence, is a response header. It directs the desired action for a requested file. By enabling Content Disposition, we convert the original file URL into a downloadable link. The process involves passing a query string labeled 'Content Disposition Attachment'. While this might sound complex, it's a straightforward process once we break it down.

The Django Approach: Crafting Downloadable Links

Creating a downloadable link requires a nuanced understanding of how to manipulate CloudFront Signed URLs for optimal user experience. With Django and django-storages, this is made simpler. The django-storages package conveniently auto-signs URLs, and we can utilize this functionality to our advantage.

Detailed Steps to Enable Content Disposition on Cloudfront Signed URL Using Django

NOTE: This tutorial uses Django + django-storages and assumes you already have a working project that utilizes both.

1. Modify CloudFront Behaviour: Start by navigating to 'Cache key and origin requests' under CloudFront behaviour. Here, you need to create a new policy named 'AllowQueryStrings' and fill in the necessary values.

2. Create the AttachmentMediaStorage class: this will auto convert the file fields into downloadable links instead of simple signed links.

• 2.1. In your project root directory create a file named "storage_backends.py"
• 2.2 Add the script below to the new file

from abc import ABC
from storages.backends.s3boto3 import S3Boto3Storage
import os

class AttachmentMediaStorage(S3Boto3Storage, ABC):
    def url(self, name, parameters=None, expire=None, http_method=None):
        f_name = os.path.basename(name)
        extra = {
            'response-content-disposition': f'attachment; filename={f_name};'}
        if not parameters:
            parameters = extra
        else:
            parameters = {**parameters, **extra}
        url = super().url(name, parameters=parameters, expire=expire, http_method=http_method)
        return url

3. (Optional)Update Django Settings: Django's django-storages package automatically signs URLs. If you wish to make all file links to add the content disposition then go to your settings.py file and change the

DEFAULT_FILE_STORAGE=

to

DEFAULT_FILE_STORAGE = 'storage_backends.AttachmentMediaStorage'

. If not, then use it individually to your target file fields by going to step 4

4. Implement AttachmentMediaStorage Individually: Now,

AttachmentMediaStorage

can be used in model fields to override

DEFAULT_FILE_STORAGE

, allowing us to leverage Content Disposition functionality effectively on individual file fields. Here's an example of how you can do this:

    invoice = models.FileField(upload_to=file_upload_to, storage=AttachmentMediaStorage)

Further Reading

For a deeper dive into CloudFront URL signing, you can refer to this comprehensive guide: S3 CloudFront URL Signer.

Conclusion

AWS equips us with a wide range of tools that, with the right knowledge and application, can significantly enhance our workflow. By understanding how to enable Content Disposition in CloudFront Signed URLs using Django and django-storages, we can build efficient and user-friendly solutions. Stay tuned for more tips and tricks on mastering AWS.