Stop setting a shortcode to newly-created media attachments (#16730)

* Stop setting a shortcode to newly-created media attachments

The WebUI has stopped using the “short media URL” in ages. This isn't used
anywhere except for mail notifications.

Deprecating it would allow us to eventually get rid of at least a database
column and corruption-prone index, as well as a controller.

* Fix tests

app/models/media_attachment.rb

@@ -255,7 +255,7 @@ class MediaAttachment < ApplicationRecord
   after_commit :reset_parent_cache, on: :update
 
   before_create :prepare_description, unless: :local?
-  before_create :set_shortcode
+  before_create :set_unknown_type
   before_create :set_processing
 
   after_post_process :set_meta
@@ -298,15 +298,8 @@ class MediaAttachment < ApplicationRecord
 
   private
 
-  def set_shortcode
+  def set_unknown_type
     self.type = :unknown if file.blank? && !type_changed?
-
-    return unless local?
-
-    loop do
-      self.shortcode = SecureRandom.urlsafe_base64(14)
-      break if MediaAttachment.find_by(shortcode: shortcode).nil?
-    end
   end
 
   def prepare_description

app/serializers/rest/media_attachment_serializer.rb

@@ -40,7 +40,7 @@ class REST::MediaAttachmentSerializer < ActiveModel::Serializer
   end
 
   def text_url
-    object.local? ? medium_url(object) : nil
+    object.local? && object.shortcode.present? ? medium_url(object) : nil
   end
 
   def meta

app/views/notification_mailer/_status.html.haml

@@ -37,7 +37,7 @@
                                   %p
                                     - status.media_attachments.each do |a|
                                       - if status.local?
-                                        = link_to medium_url(a), medium_url(a)
+                                        = link_to full_asset_url(a.file.url(:original)), full_asset_url(a.file.url(:original))
                                       - else
                                         = link_to a.remote_url, a.remote_url
 

spec/controllers/media_controller_spec.rb

@@ -8,14 +8,14 @@ describe MediaController do
   describe '#show' do
     it 'redirects to the file url when attached to a status' do
       status = Fabricate(:status)
-      media_attachment = Fabricate(:media_attachment, status: status)
+      media_attachment = Fabricate(:media_attachment, status: status, shortcode: 'foo')
       get :show, params: { id: media_attachment.to_param }
 
       expect(response).to redirect_to(media_attachment.file.url(:original))
     end
 
     it 'responds with missing when there is not an attached status' do
-      media_attachment = Fabricate(:media_attachment, status: nil)
+      media_attachment = Fabricate(:media_attachment, status: nil, shortcode: 'foo')
       get :show, params: { id: media_attachment.to_param }
 
       expect(response).to have_http_status(404)
@@ -29,7 +29,7 @@ describe MediaController do
 
     it 'raises when not permitted to view' do
       status = Fabricate(:status, visibility: :direct)
-      media_attachment = Fabricate(:media_attachment, status: status)
+      media_attachment = Fabricate(:media_attachment, status: status, shortcode: 'foo')
       get :show, params: { id: media_attachment.to_param }
 
       expect(response).to have_http_status(404)