code: function shouldTransform (req, res) {
    var cacheControl = res.getHeader('Cache-Control')
  
    // Don't compress for Cache-Control: no-transform
    // https://tools.ietf.org/html/rfc7234#section-5.2.2.4
    return !cacheControl ||
      !cacheControlNoTransformRegExp.test(cacheControl)
  }
docs: Determine if the entity should be transformed.
  @private