Using ActiveStorage in Rails API-apps

Rails 5.2 introduced ActiveStorage as one of its main features. Using it from Rails views is easy and well-documented - but how can you use it in a Rails API-app?In this short tutorial, you will learn how to use and test ActiveStorage in a Rails API-only app. While the integration of ActiveStorage into Rails is mainly very good, there are some pitfalls to consider.We will create a simple user model, consisting of a username and an attached avatar, and write a controller to create a user and download its avatar. We will use the command-line tool curl and the testing framework RSpec to test this controller. In the progress, we will discover two shortcomings of ActiveStorage and will show how to circumvent them.