def detect_mimetype(file_data)
      if file_data.content_type.strip == "application/octet-stream"
        return File.mime_type?(file_data.original_filename)
      else
        return file_data.content_type
      end
    end
def detect_mimetype(file_data)
      if file_data.content_type.strip == "application/octet-stream"
        return File.mime_type?(file_data.original_filename)
      else
        return file_data.content_type
      end
    end
Detects the mime-type if content_type is 'application/octet-stream'