/*

 * telegram.c

 *

 * Copyright (C) 2012-22 - ntop.org

 * Copyright (C) 2014 by Gianluca Costa xplico.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_TELEGRAM

#include "ndpi_api.h"

#include "ndpi_private.h"

static void ndpi_int_telegram_add_connection(struct ndpi_detection_module_struct

                                             *ndpi_struct, struct ndpi_flow_struct *flow,

               ndpi_confidence_t confidence) {

  ndpi_set_detected_protocol(ndpi_struct, flow, NDPI_PROTOCOL_TELEGRAM, NDPI_PROTOCOL_UNKNOWN, confidence);

  NDPI_LOG_INFO(ndpi_struct, "found telegram\n");

}

static u_int8_t is_telegram_port_range(u_int16_t port) {

  if((port >= 500) && (port <= 600))

    return(1);

  return(0);

}

static void ndpi_search_telegram(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 telegram\n");

  if(packet->tcp != NULL) {

    /* With MTProto 2.0 telegram via app is no longer TLS-based (althought based on TCP/443) so

       we need to detect it with Telegram IPs.

       Basically, we want a fast classification by ip. Note that, real Telegram traffic over

       TLS (i.e. Telegram Web) is correctly classified as TLS/Telegram because TLS dissector

       already kicked in.

       Let's check every port for the time being */

    if(flow->guessed_protocol_id_by_ip == NDPI_PROTOCOL_TELEGRAM) {

      ndpi_int_telegram_add_connection(ndpi_struct, flow, NDPI_CONFIDENCE_MATCH_BY_IP);

      return;

    }

  } else if(packet->udp != NULL) {

    /*

      The latest telegram protocol

      - contains a sequence of 12 consecutive 0xFF packets

      - it uses low UDP ports in the 500 range

     */

    if(packet->payload_packet_len >= 40) {

      u_int16_t sport = ntohs(packet->udp->source), dport = ntohs(packet->udp->dest);

      if(is_telegram_port_range(sport) || is_telegram_port_range(dport)) {

  u_int i, found = 0;

  for(i=0; i<packet->payload_packet_len; i++) {

    if(packet->payload[i] == 0xFF) {

      found = 1;

      break;

    }

  }

  if(!found) return;

  for(i += 1; i<packet->payload_packet_len; i++) {

    if(packet->payload[i] == 0xFF)

      found++;

    else

      break;

  }

  if(found == 12)  {

    ndpi_int_telegram_add_connection(ndpi_struct, flow, NDPI_CONFIDENCE_DPI);

    /* It seems this kind of traffic is used:

             * for "normal" stuff (at least years ago... and now? TODO)

             * for calls, as a custom encapsulation of STUN/DTLS/RTP packets

             Since we are not able to tell the former from the latter, always

             switch to STUN dissection. If we find STUN/DTLS/RTP stuff we will

             update the classification to something like STUN/Telegram_voip,

             otherwise it will remain Telegram */

    switch_extra_dissection_to_stun(ndpi_struct, flow, 0);

    return;

  }

      }

    }

  }

  NDPI_EXCLUDE_DISSECTOR(ndpi_struct, flow);

}

void init_telegram_dissector(struct ndpi_detection_module_struct *ndpi_struct)

{

  register_dissector("Telegram", ndpi_struct,

                     ndpi_search_telegram,

                     NDPI_SELECTION_BITMASK_PROTOCOL_V4_V6_TCP_OR_UDP_WITH_PAYLOAD_WITHOUT_RETRANSMISSION,

                     1, NDPI_PROTOCOL_TELEGRAM);

}