class Rack::Directory

def entity_not_found(path_info)

Rack response to use for unreadable and non-file, non-directory entries. 
def entity_not_found(path_info)
  body = "Entity not found: #{path_info}\n"
  [404, { CONTENT_TYPE => "text/plain",
    CONTENT_LENGTH => body.bytesize.to_s,
    "x-cascade" => "pass" }, [body]]
end