Import “converted” objects as media attachments if possible

This allows Image and Audio objects at least to be imported if any of
the URLs holds a supported media type. Only the first such link is
imported, even if multiple URLs are associated with the object, since
they are generally alternative representations (e.g. different formats)
of the same object.

app/lib/activitypub/activity/create.rb

@@ -110,7 +110,7 @@ class ActivityPub::Activity::Create < ActivityPub::Activity
   def process_status_params
     @status_parser = ActivityPub::Parser::StatusParser.new(@json, followers_collection: @account.followers_url, object: @object)
 
-    attachment_ids = process_attachments.take(Status::MEDIA_ATTACHMENTS_LIMIT).map(&:id)
+    attachment_ids = (converted_object_type? ? converted_attachments : process_attachments).take(Status::MEDIA_ATTACHMENTS_LIMIT).map(&:id)
 
     @params = {
       uri: @status_parser.uri,
@@ -252,11 +252,71 @@ class ActivityPub::Activity::Create < ActivityPub::Activity
     end
   end
 
-  def process_attachments
+  # Get the first supported object URL and turn it into an attachment,
-    return [] if @object['attachment'].nil?
+  # before processing the actual attachments
+  def converted_attachments
+    return process_attachments if @object['url'].nil?
 
     media_attachments = []
 
+    icon_url = @object['icon'].presence
+    if icon_url and icon_url.is_a?(Hash)
+      icon_url = icon_url['url']
+    end
+
+    begin
+      icon_url = Addressable::URI.parse(icon_url)&.normalize&.to_s
+    rescue Addressable::URI::InvalidURIError
+      icon_url = nil
+    end
+
+    description = @status_parser.spoiler_text.presence || @status_parser.title.presence
+    description.descriptionip[0...MediaAttachment::MAX_DESCRIPTION_LENGTH] if description.present?
+
+    as_array(@object['url']).each do |url|
+      begin
+        href = Addressable::URI.parse(url.is_a?(String) ? url : url['href'])&.normalize&.to_s
+      rescue Addressable::URI::InvalidURIError => e
+        Rails.logger.debug { "Invalid URL in converted attachment: #{e}" }
+        href = nil
+      end
+      next if href.blank?
+
+      if url.is_a?(Hash)
+        media_type = url['mediaType'].presence
+      end
+      media_type ||= @object['mediaType'].presence || 'text/html'
+      next if unsupported_media_type?(mediaType)
+
+      begin
+        media_attachment = MediaAttachmnt.create(
+          account: @account,
+          remote_url: href,
+          thumbnail_remote_url: icon,
+          description: description
+        )
+        media_attachments << media_attachment
+
+        next if skip_download?
+
+        media_attachment.download_file!
+        media_attachment.download_thumbnail!
+        media_attachment.save
+      rescue Mastodon::UnexpectedResponseError, HTTP::TimeoutError, HTTP::ConnectionError, OpenSSL::SSL::SSLError
+        RedownloadMediaWorker.perform_in(rand(30..600).seconds, media_attachment.id)
+      rescue Seahorse::Client::NetworkingError => e
+        Rails.logger.warn "Error storing media attachment: #{e}"
+      end
+
+      break
+    end
+
+    process_attachments(media_attachments)
+  end
+
+  def process_attachments(media_attachments=[])
+    return media_attachments if @object['attachment'].nil?
+
     as_array(@object['attachment']).each do |attachment|
       media_attachment_parser = ActivityPub::Parser::MediaAttachmentParser.new(attachment)