/*
 * modbus.c
 *
 * Copyright (C) 2018 - 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"
#include "ndpi_api.h"

#define NDPI_CURRENT_PROTO NDPI_PROTOCOL_MODBUS

void ndpi_search_modbus_tcp(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 Modbus\n");
    u_int16_t modbus_port = htons(502); // port used by modbus

    /* Check connection over TCP */

    if(packet->tcp) {
        /* The payload of Modbus-TCP segment must be at least 8 bytes (7 bytes of header application
           packet plus 1 byte of minimum payload of application packet)
           */
        if((packet->payload_packet_len >= 8)
                &&((packet->tcp->dest == modbus_port) || (packet->tcp->source == modbus_port))) {
            // Modbus uses the port 502
            u_int16_t modbus_len = htons(*((u_int16_t*)&packet->payload[4]));

            // the fourth parameter of the payload is the length of the segment
            if((modbus_len-1) == (packet->payload_packet_len - 7 /* ModbusTCP header len */)) {
                NDPI_LOG_INFO(ndpi_struct, "found MODBUS\n");
                ndpi_set_detected_protocol(ndpi_struct, flow, NDPI_PROTOCOL_MODBUS);
                return;
            }
        }
    }
    NDPI_EXCLUDE_PROTO(ndpi_struct, flow);

}



void init_modbus_dissector(struct ndpi_detection_module_struct *ndpi_struct,
        u_int32_t *id, NDPI_PROTOCOL_BITMASK *detection_bitmask) {

    ndpi_set_bitmask_protocol_detection("Modbus", ndpi_struct, detection_bitmask, *id,
            NDPI_PROTOCOL_MODBUS,
            ndpi_search_modbus_tcp,
            NDPI_SELECTION_BITMASK_PROTOCOL_V4_V6_TCP_WITH_PAYLOAD_WITHOUT_RETRANSMISSION,
            SAVE_DETECTION_BITMASK_AS_UNKNOWN,
            ADD_TO_DETECTION_BITMASK);
    *id += 1;
}
