Fix media attachment order of remote posts (#28469)

app/lib/activitypub/activity/create.rb

@@ -110,6 +110,8 @@ class ActivityPub::Activity::Create < ActivityPub::Activity
   def process_status_params
     @status_parser = ActivityPub::Parser::StatusParser.new(@json, followers_collection: @account.followers_url)
 
+    attachment_ids = process_attachments.take(4).map(&:id)
+
     @params = {
       uri: @status_parser.uri,
       url: @status_parser.url || @status_parser.uri,
@@ -125,7 +127,8 @@ class ActivityPub::Activity::Create < ActivityPub::Activity
       visibility: @status_parser.visibility,
       thread: replied_to_status,
       conversation: conversation_from_uri(@object['conversation']),
-      media_attachment_ids: process_attachments.take(4).map(&:id),
+      media_attachment_ids: attachment_ids,
+      ordered_media_attachment_ids: attachment_ids,
       poll: process_poll,
     }
   end

app/models/status.rb

@@ -277,7 +277,9 @@ class Status < ApplicationRecord
 
   def ordered_media_attachments
     if ordered_media_attachment_ids.nil?
-      media_attachments
+      # NOTE: sort Ruby-side to avoid hitting the database when the status is
+      # not persisted to database yet
+      media_attachments.sort_by(&:id)
     else
       map = media_attachments.index_by(&:id)
       ordered_media_attachment_ids.filter_map { |media_attachment_id| map[media_attachment_id] }

spec/lib/activitypub/activity/create_spec.rb

@@ -532,15 +532,21 @@ RSpec.describe ActivityPub::Activity::Create do
                 mediaType: 'image/png',
                 url: 'http://example.com/attachment.png',
               },
+              {
+                type: 'Document',
+                mediaType: 'image/png',
+                url: 'http://example.com/emoji.png',
+              },
             ],
           }
         end
 
-        it 'creates status' do
+        it 'creates status with correctly-ordered media attachments' do
           status = sender.statuses.first
 
           expect(status).to_not be_nil
-          expect(status.media_attachments.map(&:remote_url)).to include('http://example.com/attachment.png')
+          expect(status.ordered_media_attachments.map(&:remote_url)).to eq ['http://example.com/attachment.png', 'http://example.com/emoji.png']
+          expect(status.ordered_media_attachment_ids).to be_present
         end
       end