if (priorResponse != null && priorResponse.code == HTTP_CLIENT_TIMEOUT) {
          // We attempted to retry and got another timeout. Give up.
          return null
        }

        if (retryAfter(userResponse, 0) > 0) {
          return null
        }

        return userResponse.request
      }

      HTTP_UNAVAILABLE -> {
        val priorResponse = userResponse.priorResponse

			// To indicate disable keep-alive, server is shutting down.
			w.Header().Set("Connection", "close")

			// Add 1 minute retry header, incase-client wants to honor it
			w.Header().Set(RetryAfter, "60")

			w.WriteHeader(http.StatusServiceUnavailable)
			w.Write([]byte(http.ErrServerClosed.Error()))
			return
		}

		atomic.AddInt32(&srv.requestCount, 1)

	ContentRange       = "Content-Range"
	Connection         = "Connection"
	AcceptRanges       = "Accept-Ranges"
	AmzBucketRegion    = "X-Amz-Bucket-Region"
	ServerInfo         = "Server"
	RetryAfter         = "Retry-After"
	Location           = "Location"
	CacheControl       = "Cache-Control"
	ContentDisposition = "Content-Disposition"
	Authorization      = "Authorization"
	Action             = "Action"

		xhttp.ContentRange,
		xhttp.ContentEncoding,
		xhttp.ContentLength,
		xhttp.ContentType,
		xhttp.ContentDisposition,
		xhttp.LastModified,
		xhttp.ContentLanguage,
		xhttp.CacheControl,
		xhttp.RetryAfter,
		xhttp.AmzBucketRegion,
		xhttp.Expires,
		"X-Amz*",
		"x-amz*",
		"*",
	}
	opts := cors.Options{
		AllowOriginFunc: func(origin string) bool {

		// Set retry-after header to indicate user-agents to retry request after 60 seconds.
		// https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Retry-After
		w.Header().Set(xhttp.RetryAfter, "60")
	}

	switch err.Code {
	case "InvalidRegion":
		err.Description = fmt.Sprintf("Region does not match; expecting '%s'.", globalSite.Region())
	case "AuthorizationHeaderMalformed":

        response.getWriter()
                .write("{\"response\":{\"status\":9,\"message\":\"Server is busy. Please retry after " + RETRY_AFTER_SECONDS
                        + " seconds.\",\"retry_after\":" + RETRY_AFTER_SECONDS + "}}");
    }

        response.getWriter()
                .write("{\"error\":\"rate_limit_exceeded\",\"message\":\"Too many requests. Please retry after " + retryAfterSeconds
                        + " seconds.\",\"retry_after\":" + retryAfterSeconds + "}");
    }

        assertEquals("60", mockResponse.getHeaderValue("Retry-After"));
        assertTrue(mockResponse.getWriterOutput().contains("\"status\":9"));
        assertTrue(mockResponse.getWriterOutput().contains("\"retry_after\":60"));
    }

    @Test
    public void test_doFilter_apiAtThreshold() throws IOException, ServletException {
        setConfig(100, 80);
        testableFilter.setCpuPercent((short) 80);

   *
   * @since 27.1
   */
  public static final String REPORT_TO = "Report-To";

  /** The HTTP {@code Retry-After} header field name. */
  public static final String RETRY_AFTER = "Retry-After";

  /** The HTTP {@code Server} header field name. */
  public static final String SERVER = "Server";

  /**