/*
 * telnet.c
 *
 * Copyright (C) 2011-20 - ntop.org
 * Copyright (C) 2009-2011 by ipoque GmbH
 *
 * 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_TELNET

#include "ndpi_api.h"

/* #define TELNET_DEBUG 1 */

/* ************************************************************************ */

static int search_telnet_again(struct ndpi_detection_module_struct *ndpi_struct,
        struct ndpi_flow_struct *flow) {
    struct ndpi_packet_struct *packet = &flow->packet;
    int i;

#ifdef TELNET_DEBUG
    printf("==> %s() [%s][direction: %u]\n", __FUNCTION__, packet->payload, packet->packet_direction);
#endif

    if((packet->payload == NULL)
            || (packet->payload_packet_len == 0)
            || (packet->payload[0] == 0xFF))
        return(1);

    if(flow->protos.telnet.username_detected) {
        if((!flow->protos.telnet.password_found)
                && (packet->payload_packet_len > 9)) {

            if(strncasecmp((char*)packet->payload, "password:", 9) == 0) {
                flow->protos.telnet.password_found = 1;
            }

            return(1);
        }

        if(packet->payload[0] == '\r') {
            if(!flow->protos.telnet.password_found)
                return(1);

            flow->protos.telnet.password_detected = 1;
            flow->protos.telnet.password[flow->protos.telnet.character_id] = '\0';
            return(0);
        }

        if(packet->packet_direction == 0) /* client -> server */ {
            for(i=0; i<packet->payload_packet_len; i++) {
                if(flow->protos.telnet.character_id < (sizeof(flow->protos.telnet.password)-1))
                    flow->protos.telnet.password[flow->protos.telnet.character_id++] = packet->payload[i];
            }
        }

        return(1);
    }

    if((!flow->protos.telnet.username_found)
            && (packet->payload_packet_len > 6)) {

        if(strncasecmp((char*)packet->payload, "login:", 6) == 0) {
            flow->protos.telnet.username_found = 1;
        }

        return(1);
    }

    if(packet->payload[0] == '\r') {
        flow->protos.telnet.username_detected = 1;
        flow->protos.telnet.username[flow->protos.telnet.character_id] = '\0';
        flow->protos.telnet.character_id = 0;
        return(1);
    }

    for(i=0; i<packet->payload_packet_len; i++) {
        if(packet->packet_direction == 0) /* client -> server */ {
            if(flow->protos.telnet.character_id < (sizeof(flow->protos.telnet.username)-1))
                flow->protos.telnet.username[flow->protos.telnet.character_id++] = packet->payload[i];
        }
    }

    /* Possibly more processing */
    return(1);
}

/* ************************************************************************ */

static void ndpi_int_telnet_add_connection(struct ndpi_detection_module_struct
        *ndpi_struct, struct ndpi_flow_struct *flow) {
    flow->guessed_host_proto_id = flow->guessed_proto_id = NDPI_PROTOCOL_TELNET;

    /* This is necessary to inform the core to call this dissector again */
    flow->check_extra_packets = 1;
    flow->max_extra_packets_to_check = 64;
    flow->extra_packets_func = search_telnet_again;

    ndpi_set_detected_protocol(ndpi_struct, flow, NDPI_PROTOCOL_TELNET);
}

/* ************************************************************************ */

#if !defined(WIN32)
static inline
#elif defined(MINGW_GCC)
__mingw_forceinline static
#else
__forceinline static
#endif
u_int8_t search_iac(struct ndpi_detection_module_struct *ndpi_struct,
        struct ndpi_flow_struct *flow) {
    struct ndpi_packet_struct *packet = &flow->packet;

    u_int16_t a;

#ifdef TELNET_DEBUG
    printf("==> %s()\n", __FUNCTION__);
#endif

    if(packet->payload_packet_len < 3)
        return(0);

    if(!((packet->payload[0] == 0xff)
                && (packet->payload[1] > 0xf9)
                && (packet->payload[1] != 0xff)
                && (packet->payload[2] < 0x28)))
        return(0);

    a = 3;

    while (a < packet->payload_packet_len - 2) {
        // commands start with a 0xff byte followed by a command byte >= 0xf0 and < 0xff
        // command bytes 0xfb to 0xfe are followed by an option byte <= 0x28
        if(!(packet->payload[a] != 0xff ||
                    (packet->payload[a] == 0xff && (packet->payload[a + 1] >= 0xf0) && (packet->payload[a + 1] <= 0xfa)) ||
                    (packet->payload[a] == 0xff && (packet->payload[a + 1] >= 0xfb) && (packet->payload[a + 1] != 0xff)
                     && (packet->payload[a + 2] <= 0x28))))
            return(0);

        a++;
    }

    return 1;
}

/* ************************************************************************ */

/* this detection also works asymmetrically */
void ndpi_search_telnet_tcp(struct ndpi_detection_module_struct *ndpi_struct,
        struct ndpi_flow_struct *flow) {
    NDPI_LOG_DBG(ndpi_struct, "search telnet\n");

    if(search_iac(ndpi_struct, flow) == 1) {
        if(flow->l4.tcp.telnet_stage == 2) {
            NDPI_LOG_INFO(ndpi_struct, "found telnet\n");
            ndpi_int_telnet_add_connection(ndpi_struct, flow);
            return;
        }

        flow->l4.tcp.telnet_stage++;
        NDPI_LOG_DBG2(ndpi_struct, "telnet stage %u\n", flow->l4.tcp.telnet_stage);
        return;
    }

    if(((flow->packet_counter < 12) && (flow->l4.tcp.telnet_stage > 0)) || (flow->packet_counter < 6)) {
#ifdef TELNET_DEBUG
        printf("==> [%s:%d] %s()\n", __FILE__, __LINE__, __FUNCTION__);
#endif
        return;
    } else {
#ifdef TELNET_DEBUG
        printf("==> [%s:%d] %s()\n", __FILE__, __LINE__, __FUNCTION__);
#endif
        NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
    }

    return;
}


void init_telnet_dissector(struct ndpi_detection_module_struct *ndpi_struct, u_int32_t *id, NDPI_PROTOCOL_BITMASK *detection_bitmask)
{
    ndpi_set_bitmask_protocol_detection("Telnet", ndpi_struct, detection_bitmask, *id,
            NDPI_PROTOCOL_TELNET,
            ndpi_search_telnet_tcp,
            NDPI_SELECTION_BITMASK_PROTOCOL_V4_V6_TCP_WITH_PAYLOAD_WITHOUT_RETRANSMISSION,
            SAVE_DETECTION_BITMASK_AS_UNKNOWN,
            ADD_TO_DETECTION_BITMASK);
    *id += 1;
}
