code: func NewUpgradeAwareHandler(location *url.URL, transport http.RoundTripper, wrapTransport, upgradeRequired bool, responder ErrorResponder) *UpgradeAwareHandler {
  	return &UpgradeAwareHandler{
  		Location:        normalizeLocation(location),
  		Transport:       transport,
  		WrapTransport:   wrapTransport,
  		UpgradeRequired: upgradeRequired,
  		FlushInterval:   defaultFlushInterval,
  		Responder:       responder,
  	}
  }
docs: // NewUpgradeAwareHandler creates a new proxy handler with a default flush interval. Responder is required for returning
  // errors to the caller.