/*
 * mdns.c
 *
 * Copyright (C) 2016-18 - 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_MDNS

#include "ndpi_api.h"

#define NDPI_MAX_MDNS_REQUESTS  128

PACK_ON
struct mdns_header {
    u_int16_t transaction_id, flags, questions, answers, authority_rr, additional_rr;
} PACK_OFF;

/**
  MDNS header is similar to dns header

  0  1  2  3  4  5  6  7  8  9  0  1  2  3  4  5
  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
  |                  ID = 0x0000                  |
  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
  |                     FLAGS                     |
  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
  |                    QDCOUNT                    |
  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
  |                    ANCOUNT                    |
  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
  |                    NSCOUNT                    |
  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
  |                    ARCOUNT                    |
  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
  */

static void ndpi_int_mdns_add_connection(struct ndpi_detection_module_struct
        *ndpi_struct, struct ndpi_flow_struct *flow) {
    ndpi_set_detected_protocol(ndpi_struct, flow, NDPI_PROTOCOL_MDNS);
}

static int ndpi_int_check_mdns_payload(struct ndpi_detection_module_struct
        *ndpi_struct, struct ndpi_flow_struct *flow) {
    struct ndpi_packet_struct *packet = &flow->packet;
    struct mdns_header *h = (struct mdns_header*)packet->payload;
    u_int16_t questions = ntohs(h->questions), answers = ntohs(h->answers);

    if((questions > NDPI_MAX_MDNS_REQUESTS)
            || (answers > NDPI_MAX_MDNS_REQUESTS))
        return(0);

    if((packet->payload[2] & 0x80) == 0) {
        NDPI_LOG_INFO(ndpi_struct, "found MDNS with question query\n");
        return 1;
    } else if((packet->payload[2] & 0x80) != 0) {
        char answer[256];
        int i, j, len;

        for(i=13, j=0; (i < packet->payload_packet_len) && (i < (sizeof(answer)-1)) && (packet->payload[i] != 0); i++)
            answer[j++] = (packet->payload[i] < 13) ? '.' : packet->payload[i];

        answer[j] = '\0';

        /* printf("==> [%d] %s\n", j, answer);  */

        if(!ndpi_struct->disable_metadata_export) {
            len = ndpi_min(sizeof(flow->protos.mdns.answer)-1, j);
            strncpy(flow->protos.mdns.answer, (const char *)answer, len);
            flow->protos.mdns.answer[len] = '\0';
        }

        NDPI_LOG_INFO(ndpi_struct, "found MDNS with answer query\n");
        return 1;
    }

    return 0;
}

void ndpi_search_mdns(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 MDNS\n");

    /**
      information from http://www.it-administrator.de/lexikon/multicast-dns.html
      */

    /* check if UDP packet */
    if(packet->udp != NULL) {
        /* read destination port */
        u_int16_t sport = ntohs(packet->udp->source);
        u_int16_t dport = ntohs(packet->udp->dest);

        /* check standard MDNS ON port 5353 */
        if(((dport == 5353) || (sport == 5353))
                && (packet->payload_packet_len >= 12)) {
            if(packet->iph != NULL) {
                if(ndpi_int_check_mdns_payload(ndpi_struct, flow) == 1) {
                    ndpi_int_mdns_add_connection(ndpi_struct, flow);
                    return;
                }
            }
#ifdef NDPI_DETECTION_SUPPORT_IPV6
            if(packet->iphv6 != NULL) {
                const u_int32_t *daddr = packet->iphv6->ip6_dst.u6_addr.u6_addr32;
                if(daddr[0] == htonl(0xff020000) /* && daddr[1] == 0 && daddr[2] == 0 && daddr[3] == htonl(0xfb) */) {

                    NDPI_LOG_INFO(ndpi_struct, "found MDNS with destination address ff02::fb\n");

                    if(ndpi_int_check_mdns_payload(ndpi_struct, flow) == 1) {
                        ndpi_int_mdns_add_connection(ndpi_struct, flow);
                        return;
                    }
                }
            }
#endif
        }
    }

    NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
}


void init_mdns_dissector(struct ndpi_detection_module_struct *ndpi_struct, u_int32_t *id, NDPI_PROTOCOL_BITMASK *detection_bitmask)
{
    ndpi_set_bitmask_protocol_detection("MDNS", ndpi_struct, detection_bitmask, *id,
            NDPI_PROTOCOL_MDNS,
            ndpi_search_mdns,
            NDPI_SELECTION_BITMASK_PROTOCOL_V4_V6_UDP_WITH_PAYLOAD,
            SAVE_DETECTION_BITMASK_AS_UNKNOWN,
            ADD_TO_DETECTION_BITMASK);

    *id += 1;
}

