# File lib/sinatra/rack_etag.rb, line 41
    def call(env)
      status, headers, body = @app.call(env)

      if etag_status?(status) && etag_body?(body) && !http_caching?(headers)
        digest, body = digest_body(body)
        headers['ETag'] = %("#{digest}") if digest
      end

      if not headers['Cache-Control'] and digest
        headers['Cache-Control'] = digest ? @cache_control : @no_cache_control
      end

      [status, headers, body]
    end