/*
 * gtp.c
 *
 * Copyright (C) 2011-18 - 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_GTP

#include "ndpi_api.h"

struct gtp_header_generic {
    u_int8_t flags, message_type;
    u_int16_t message_len;
    u_int32_t teid;
};

static void ndpi_check_gtp(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((packet->udp != NULL) && (payload_len > sizeof(struct gtp_header_generic))) {
        u_int32_t gtp_u  = ntohs(2152);
        u_int32_t gtp_c  = ntohs(2123);
        u_int32_t gtp_v0 = ntohs(3386);

        if((packet->udp->source == gtp_u) || (packet->udp->dest == gtp_u)
                || (packet->udp->source == gtp_c) || (packet->udp->dest == gtp_c)
                || (packet->udp->source == gtp_v0) || (packet->udp->dest == gtp_v0)
          ) {
            struct gtp_header_generic *gtp = (struct gtp_header_generic*)packet->payload;
            u_int8_t gtp_version = (gtp->flags & 0xE0) >> 5;

            if((gtp_version == 0) || (gtp_version == 1) || (gtp_version == 2)) {
                u_int16_t message_len = ntohs(gtp->message_len);

                if(message_len <= (payload_len-sizeof(struct gtp_header_generic))) {
                    NDPI_LOG_INFO(ndpi_struct, "found gtp\n");
                    ndpi_set_detected_protocol(ndpi_struct, flow, NDPI_PROTOCOL_GTP);
                    return;
                }
            }
        }
    }

    NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
    return;
}

void ndpi_search_gtp(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 gtp\n");

    /* skip marked packets */
    if(packet->detected_protocol != NDPI_PROTOCOL_GTP)
        ndpi_check_gtp(ndpi_struct, flow);
}


void init_gtp_dissector(struct ndpi_detection_module_struct *ndpi_struct, u_int32_t *id, NDPI_PROTOCOL_BITMASK *detection_bitmask)
{
    ndpi_set_bitmask_protocol_detection("GTP", ndpi_struct, detection_bitmask, *id,
            NDPI_PROTOCOL_GTP,
            ndpi_search_gtp,
            NDPI_SELECTION_BITMASK_PROTOCOL_V4_V6_UDP_WITH_PAYLOAD,
            SAVE_DETECTION_BITMASK_AS_UNKNOWN,
            ADD_TO_DETECTION_BITMASK);

    *id += 1;
}
