# File lib/rack/etag.rb, line 22
    def call(env)
      status, headers, body = @app.call(env)

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

      unless headers['Cache-Control']
        headers['Cache-Control'] =
          (digest ? @cache_control : @no_cache_control) || []
      end

      [status, headers, body]
    end