public static String parseInternalErrorCode(final ResponseFlags responseFlags) {
        if (responseFlags != null) {
            if (responseFlags.getFailedLocalHealthcheck()) {
                return "failed_local_healthcheck";
            } else if (responseFlags.getNoHealthyUpstream()) {
                return "no_healthy_upstream";
            } else if (responseFlags.getUpstreamRequestTimeout()) {
                return "upstream_request_timeout";
            } else if (responseFlags.getLocalReset()) {
                return "local_reset";
            } else if (responseFlags.getUpstreamConnectionFailure()) {
                return "upstream_connection_failure";
            } else if (responseFlags.getUpstreamConnectionTermination()) {
                return "upstream_connection_termination";
            } else if (responseFlags.getUpstreamOverflow()) {
                return "upstream_overflow";
            } else if (responseFlags.getNoRouteFound()) {
                return "no_route_found";
            } else if (responseFlags.getDelayInjected()) {
                return "delay_injected";
            } else if (responseFlags.getFaultInjected()) {
                return "fault_injected";
            } else if (responseFlags.getRateLimited()) {
                return "rate_limited";
            } else if (responseFlags.hasUnauthorizedDetails()) {
                return "unauthorized_details";
            } else if (responseFlags.getRateLimitServiceError()) {
                return "rate_limit_service_error";
            } else if (responseFlags.getDownstreamConnectionTermination()) {
                return "downstream_connection_termination";
            } else if (responseFlags.getUpstreamRetryLimitExceeded()) {
                return "upstream_retry_limit_exceeded";
            } else if (responseFlags.getStreamIdleTimeout()) {
                return "stream_idle_timeout";
            } else if (responseFlags.getInvalidEnvoyRequestHeaders()) {
                return "invalid_envoy_request_headers";
            } else if (responseFlags.getDownstreamProtocolError()) {
                return "downstream_protocol_error";
            }
        }
        return "";
    }
Refer to https://www.envoyproxy.io/docs/envoy/latest/api-v2/data/accesslog/v2/accesslog.proto#data-accesslog-v2-responseflags

@param responseFlags in the ALS v2
@return empty string if no internal error code, or literal string representing the code.
oap-server/server-receiver-plugin/envoy-metrics-receiver-plugin/src/main/java/org/apache/skywalking/oap/server/receiver/envoy/als/LogEntry2MetricsAdapter.java