Extract ActiveStorage::SetCurrent

Provide a handy concern for custom Active Storage controllers that can't inherit from ActiveStorage::BaseController.

activestorage/CHANGELOG.md

@@ -1,3 +1,8 @@
+*   Added the `ActiveStorage::SetCurrent` concern for custom Active Storage
+    controllers that can't inherit from `ActiveStorage::BaseController`.
+
+    *George Claghorn*
+
 *   Active Storage error classes like `ActiveStorage::IntegrityError` and
     `ActiveStorage::UnrepresentableError` now inherit from `ActiveStorage::Error`
     instead of `StandardError`. This permits rescuing `ActiveStorage::Error` to

activestorage/app/controllers/active_storage/base_controller.rb

@@ -1,10 +1,8 @@
 # frozen_string_literal: true
 
-# The base controller for all ActiveStorage controllers.
+# The base class for all Active Storage controllers.
 class ActiveStorage::BaseController < ActionController::Base
-  protect_from_forgery with: :exception
+  include ActiveStorage::SetCurrent
 
-  before_action do
+  protect_from_forgery with: :exception
-    ActiveStorage::Current.host = request.base_url
-  end
 end

activestorage/app/controllers/concerns/active_storage/set_current.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+# Sets the <tt>ActiveStorage::Current.host</tt> attribute, which the disk service uses to generate URLs.
+# Include this concern in custom controllers that call ActiveStorage::Blob#service_url,
+# ActiveStorage::Variant#service_url, or ActiveStorage::Preview#service_url so the disk service can
+# generate URLs using the same host, protocol, and base path as the current request.
+module ActiveStorage::SetCurrent
+  extend ActiveSupport::Concern
+
+  included do
+    before_action do
+      ActiveStorage::Current.host = request.base_url
+    end
+  end
+end