/*
 * ntp.c
 *
 * Copyright (C) 2009-11 - ipoque GmbH
 * Copyright (C) 2011-22 - ntop.org
 *
 * This file is part of nDPI, an open source deep packet inspection
 * library based on the OpenDPI and PACE technology by ipoque GmbH
 *
 * nDPI is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * nDPI is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with nDPI.  If not, see <http://www.gnu.org/licenses/>.
 * 
 */

#include "ndpi_protocol_ids.h"

#define NDPI_CURRENT_PROTO NDPI_PROTOCOL_NTP

#include "ndpi_api.h"
#include "ndpi_private.h"

static void ndpi_int_ntp_add_connection(struct ndpi_detection_module_struct
					*ndpi_struct, struct ndpi_flow_struct *flow)
{
  ndpi_set_detected_protocol(ndpi_struct, flow, NDPI_PROTOCOL_NTP, NDPI_PROTOCOL_UNKNOWN, NDPI_CONFIDENCE_DPI);
}

static void ndpi_search_ntp_udp(struct ndpi_detection_module_struct *ndpi_struct, struct ndpi_flow_struct *flow)
{
  struct ndpi_packet_struct *packet = &ndpi_struct->packet;
  
  NDPI_LOG_DBG(ndpi_struct, "search NTP\n");

  if (packet->udp->dest == htons(123) || packet->udp->source == htons(123)) {
  
    NDPI_LOG_DBG2(ndpi_struct, "NTP port and length detected\n");
  
    if ((((packet->payload[0] & 0x38) >> 3) <= 4)) {
    
      // 38 in binary representation is 00111000 
      flow->protos.ntp.version = (packet->payload[0] & 0x38) >> 3;
    
      if (packet->payload_packet_len > 3 && flow->protos.ntp.version == 2) {
        flow->protos.ntp.request_code = packet->payload[3];
      }
    
      NDPI_LOG_INFO(ndpi_struct, "found NTP\n");
      ndpi_int_ntp_add_connection(ndpi_struct, flow);
      return;
    }
  }

  NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
}


void init_ntp_dissector(struct ndpi_detection_module_struct *ndpi_struct, u_int32_t *id)
{
  ndpi_set_bitmask_protocol_detection("NTP", ndpi_struct, *id,
				      NDPI_PROTOCOL_NTP,
				      ndpi_search_ntp_udp,
				      NDPI_SELECTION_BITMASK_PROTOCOL_V4_V6_UDP_WITH_PAYLOAD,
				      SAVE_DETECTION_BITMASK_AS_UNKNOWN,
				      ADD_TO_DETECTION_BITMASK);

  *id += 1;
}