/*
 * skype.c
 *
 * Copyright (C) 2017-18 - 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"

#define NDPI_CURRENT_PROTO NDPI_PROTOCOL_SKYPE

#include "ndpi_api.h"

int is_port(u_int16_t a, u_int16_t b, u_int16_t c) {
    return(((a == c) || (b == c)) ? 1 : 0);
}

static void ndpi_skype_report_protocol(
        struct ndpi_detection_module_struct *ndpi_struct,
        struct ndpi_flow_struct *flow) {

    /* printf("[SKYPE] payload_len=%u\n", flow->packet.payload_packet_len); */

    NDPI_LOG_INFO(ndpi_struct, "found skype\n");
    ndpi_set_detected_protocol(ndpi_struct, flow, NDPI_PROTOCOL_SKYPE);
}

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

            /* skype-to-skype */
            if(is_port(sport, dport, 1119) /* It can be confused with battle.net */
                    || is_port(sport, dport, 80) /* No HTTP-like protocols UDP/80 */
              ) {
                ;
            } else {
                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_skype_report_protocol(ndpi_struct, flow);
                }
            }
        }

        NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
        return;

        // TCP check
    } else if((packet->tcp != NULL)
            /* As the TCP skype heuristic is weak, we need to make sure no other protocols overlap */
            && (flow->guessed_host_proto_id == NDPI_PROTOCOL_UNKNOWN)
            && (flow->guessed_proto_id == NDPI_PROTOCOL_UNKNOWN)) {
        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_skype_report_protocol(ndpi_struct, flow);
            } 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 != 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;
}
