Bust CDN cache on media deletion (#31353)

app/models/media_attachment.rb

@@ -276,6 +276,9 @@ class MediaAttachment < ApplicationRecord
   before_create :set_unknown_type
   before_create :set_processing
 
+  before_destroy :prepare_cache_bust!, prepend: true
+  after_destroy :bust_cache!
+
   after_commit :enqueue_processing, on: :create
   after_commit :reset_parent_cache, on: :update
 
@@ -410,4 +413,29 @@ class MediaAttachment < ApplicationRecord
   def reset_parent_cache
     Rails.cache.delete("v3:statuses/#{status_id}") if status_id.present?
   end
+
+  # Record the cache keys to burst before the file get actually deleted
+  def prepare_cache_bust!
+    return unless Rails.configuration.x.cache_buster_enabled
+
+    @paths_to_cache_bust = MediaAttachment.attachment_definitions.keys.flat_map do |attachment_name|
+      attachment = public_send(attachment_name)
+      styles = DEFAULT_STYLES | attachment.styles.keys
+      styles.map { |style| attachment.path(style) }
+    end
+  rescue => e
+    # We really don't want any error here preventing media deletion
+    Rails.logger.warn "Error #{e.class} busting cache: #{e.message}"
+  end
+
+  # Once Paperclip has deleted the files, we can't recover the cache keys,
+  # so use the previously-saved ones
+  def bust_cache!
+    return unless Rails.configuration.x.cache_buster_enabled
+
+    CacheBusterWorker.push_bulk(@paths_to_cache_bust) { |path| [path] }
+  rescue => e
+    # We really don't want any error here preventing media deletion
+    Rails.logger.warn "Error #{e.class} busting cache: #{e.message}"
+  end
 end

spec/models/media_attachment_spec.rb

@@ -292,6 +292,25 @@ RSpec.describe MediaAttachment, :attachment_processing do
     end
   end
 
+  describe 'cache deletion hooks' do
+    let(:media) { Fabricate(:media_attachment) }
+
+    before do
+      allow(Rails.configuration.x).to receive(:cache_buster_enabled).and_return(true)
+    end
+
+    it 'queues CacheBusterWorker jobs' do
+      original_path = media.file.path(:original)
+      small_path = media.file.path(:small)
+      thumbnail_path = media.thumbnail.path(:original)
+
+      expect { media.destroy }
+        .to enqueue_sidekiq_job(CacheBusterWorker).with(original_path)
+        .and enqueue_sidekiq_job(CacheBusterWorker).with(small_path)
+        .and enqueue_sidekiq_job(CacheBusterWorker).with(thumbnail_path)
+    end
+  end
+
   private
 
   def media_metadata