/*
 * skype.c
 *
 * Copyright (C) 2017 - ntop.org
 *
 * 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"

#ifdef NDPI_PROTOCOL_SKYPE

#define NDPI_CURRENT_PROTO NDPI_PROTOCOL_SKYPE

#include "ndpi_api.h"


static void ndpi_check_skype(struct ndpi_detection_module_struct *ndpi_struct, struct ndpi_flow_struct *flow)
{
  struct ndpi_packet_struct *packet = &flow->packet;
  // const u_int8_t *packet_payload = packet->payload;
  u_int32_t payload_len = packet->payload_packet_len;


  if(flow->host_server_name[0] != '\0')
    return;

  // UDP check
  if(packet->udp != NULL) {
    flow->l4.udp.skype_packet_id++;

    if(flow->l4.udp.skype_packet_id < 5) {
      u_int16_t dport = ntohs(packet->udp->dest);

      /* skype-to-skype */
      if(dport != 1119) /* It can be confused with battle.net */ {
	if(((payload_len == 3) && ((packet->payload[2] & 0x0F)== 0x0d)) ||
	   ((payload_len >= 16)
	    && (packet->payload[0] != 0x30) /* Avoid invalid SNMP detection */
	    && (packet->payload[2] == 0x02))) {
	  NDPI_LOG_INFO(ndpi_struct, "found skype\n");
	  ndpi_set_detected_protocol(ndpi_struct, flow, NDPI_PROTOCOL_SKYPE, NDPI_PROTOCOL_UNKNOWN);
	}
      }
      return;
    }
    NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
    return;

    // TCP check
  } else if(packet->tcp != NULL) {
    flow->l4.tcp.skype_packet_id++;

    if(flow->l4.tcp.skype_packet_id < 3) {
      ; /* Too early */
    } else if((flow->l4.tcp.skype_packet_id == 3)
	      /* We have seen the 3-way handshake */
	      && flow->l4.tcp.seen_syn
	      && flow->l4.tcp.seen_syn_ack
	      && flow->l4.tcp.seen_ack) {

      if((payload_len == 8) || (payload_len == 3) || (payload_len == 17)) {
	// printf("[SKYPE] payload_len=%u\n", payload_len);
	/* printf("[SKYPE] %u/%u\n", ntohs(packet->tcp->source), ntohs(packet->tcp->dest)); */

	NDPI_LOG_INFO(ndpi_struct, "found skype\n");
	ndpi_set_detected_protocol(ndpi_struct, flow, NDPI_PROTOCOL_SKYPE, NDPI_PROTOCOL_UNKNOWN);
      } else {
	// printf("NO [SKYPE] payload_len=%u\n", payload_len);
      }

      /* printf("[SKYPE] [id: %u][len: %d]\n", flow->l4.tcp.skype_packet_id, payload_len);  */
    } else {
      NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
    }

    return;
  }
}

void ndpi_search_skype(struct ndpi_detection_module_struct *ndpi_struct, struct ndpi_flow_struct *flow)
{
  struct ndpi_packet_struct *packet = &flow->packet;

  NDPI_LOG_DBG(ndpi_struct, "search skype\n");

  /* skip marked packets */
  if(packet->detected_protocol_stack[0] != NDPI_PROTOCOL_SKYPE)
    ndpi_check_skype(ndpi_struct, flow);
}


void init_skype_dissector(struct ndpi_detection_module_struct *ndpi_struct, u_int32_t *id, NDPI_PROTOCOL_BITMASK *detection_bitmask)
{
  ndpi_set_bitmask_protocol_detection("Skype", ndpi_struct, detection_bitmask, *id,
				      NDPI_PROTOCOL_SKYPE,
				      ndpi_search_skype,
				      NDPI_SELECTION_BITMASK_PROTOCOL_TCP_OR_UDP_WITH_PAYLOAD,
				      SAVE_DETECTION_BITMASK_AS_UNKNOWN,
				      ADD_TO_DETECTION_BITMASK);

  *id += 1;
}

#endif