adjust preview cache

app/controllers/preview_document_page_controller.rb

@@ -5,6 +5,10 @@ class PreviewDocumentPageController < ActionController::API
 
   FORMAT = Templates::ProcessDocument::FORMAT
 
+  TMPFILE_PREFIX = 'attachment-'
+  TMPFILE_TTL = 5.minutes
+  TMPFILE_MAX_TOTAL_SIZE = Docuseal.multitenant? ? 400.megabytes : 1.gigabyte
+
   def show
     result_data =
       ApplicationRecord.signed_id_verifier.verified(params[:signed_key], purpose: :attachment)
@@ -30,34 +34,63 @@ class PreviewDocumentPageController < ActionController::API
                          allow_other_host: true
     end
 
-    file_path =
-      if attachment.service.name == :disk
-        ActiveStorage::Blob.service.path_for(attachment.key)
-      else
-        find_or_create_document_tempfile_path(attachment)
-      end
-
     preview_image =
-      Templates::ProcessDocument.generate_pdf_preview_from_file(attachment, file_path, params[:id].to_i)
+      open_attachment_io(attachment) do |io|
+        Templates::ProcessDocument.generate_pdf_preview_from_io(attachment, io, params[:id].to_i)
+      end
 
     redirect_to preview_image.url(time: ActiveStorage::Attachment.service_url_time), allow_other_host: true
   end
 
-  def find_or_create_document_tempfile_path(attachment)
-    file_path = "#{Dir.tmpdir}/attachment-#{Digest::SHA1.hexdigest("#{attachment.id}-#{attachment.uuid}")}"
+  def open_attachment_io(attachment, &)
+    return File.open(ActiveStorage::Blob.service.path_for(attachment.key), 'rb', &) if attachment.service.name == :disk
 
-    File.open(file_path, File::RDWR | File::CREAT, 0o644) do |f|
-      f.flock(File::LOCK_EX)
+    file_name = "#{TMPFILE_PREFIX}#{Digest::SHA1.hexdigest("#{attachment.id}-#{attachment.uuid}")}"
+
+    file_path = File.join(Dir.tmpdir, file_name)
+
+    File.open(file_path, File::RDWR | File::CREAT, 0o644) do |file|
+      file.flock(File::LOCK_EX)
 
       # rubocop:disable Style/ZeroLengthPredicate
-      if f.size.zero?
-        f.binmode
+      if file.size.zero?
+        cleanup_stale_tempfiles
 
-        f.write(attachment.download)
+        file.binmode
+
+        file.write(attachment.download)
+      else
+        FileUtils.touch(file_path)
       end
       # rubocop:enable Style/ZeroLengthPredicate
-    end
 
-    file_path
+      file.flock(File::LOCK_UN)
+
+      yield file
+    end
+  end
+
+  def cleanup_stale_tempfiles
+    entries =
+      Dir.glob(File.join(Dir.tmpdir, "#{TMPFILE_PREFIX}*")).filter_map do |path|
+        stat = File.stat(path)
+
+        [path, stat.mtime, stat.size]
+      rescue Errno::ENOENT
+        nil
+      end
+
+    total_size = entries.sum(&:last)
+    stale_time = TMPFILE_TTL.ago
+
+    entries.sort_by(&:second).each do |path, mtime, size|
+      break if mtime > stale_time && total_size <= TMPFILE_MAX_TOTAL_SIZE
+
+      File.unlink(path)
+
+      total_size -= size
+    rescue Errno::ENOENT
+      nil
+    end
   end
 end