public static boolean isRequestTimeoutResponse(HttpResponse httpResponse) {
        return httpResponse.status().code() == HttpResponseStatus.REQUEST_TIMEOUT.code() &&
               "close".equalsIgnoreCase(httpResponse.headers().get(HttpHeaderNames.CONNECTION));
    }
A 408 Request Timeout response can be received even without a request.
More details can be found at <a href="https://github.com/line/armeria/issues/3055">#3055</a>.
core/src/main/java/com/linecorp/armeria/internal/common/ArmeriaHttpUtil.java