/*
 * mail_imap.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_MAIL_IMAP

#include "ndpi_api.h"

static void ndpi_int_mail_imap_add_connection(struct ndpi_detection_module_struct *ndpi_struct, struct ndpi_flow_struct *flow)
{
    ndpi_set_detected_protocol(ndpi_struct, flow, NDPI_PROTOCOL_MAIL_IMAP);
}

void ndpi_search_mail_imap_tcp(struct ndpi_detection_module_struct *ndpi_struct, struct ndpi_flow_struct *flow)
{
    struct ndpi_packet_struct *packet = &flow->packet;
    u_int16_t i = 0;
    u_int16_t space_pos = 0;
    u_int16_t command_start = 0;
    u_int8_t saw_command = 0;
    /* const u_int8_t *command = 0; */

    NDPI_LOG_DBG(ndpi_struct, "search IMAP_IMAP\n");

    if (flow->l4.tcp.mail_imap_starttls == 2) {
        NDPI_LOG_DBG2(ndpi_struct, "starttls detected\n");
        NDPI_ADD_PROTOCOL_TO_BITMASK(flow->excluded_protocol_bitmask, NDPI_PROTOCOL_MAIL_IMAP);
        NDPI_DEL_PROTOCOL_FROM_BITMASK(flow->excluded_protocol_bitmask, NDPI_PROTOCOL_SSL);
        return;
    }

    if (packet->payload_packet_len >= 4 && ntohs(get_u_int16_t(packet->payload, packet->payload_packet_len - 2)) == 0x0d0a) {
        // the DONE command appears without a tag
        if (packet->payload_packet_len == 6 && ((packet->payload[0] == 'D' || packet->payload[0] == 'd')
                    && (packet->payload[1] == 'O' || packet->payload[1] == 'o')
                    && (packet->payload[2] == 'N' || packet->payload[2] == 'n')
                    && (packet->payload[3] == 'E' || packet->payload[3] == 'e'))) {
            flow->l4.tcp.mail_imap_stage += 1;
            saw_command = 1;
        } else {

            if (flow->l4.tcp.mail_imap_stage < 4) {
                // search for the first space character (end of the tag)
                while (i < 20 && i < packet->payload_packet_len) {
                    if (i > 0 && packet->payload[i] == ' ') {
                        space_pos = i;
                        break;
                    }
                    if (!((packet->payload[i] >= 'a' && packet->payload[i] <= 'z') ||
                                (packet->payload[i] >= 'A' && packet->payload[i] <= 'Z') ||
                                (packet->payload[i] >= '0' && packet->payload[i] <= '9') || packet->payload[i] == '*' || packet->payload[i] == '.')) {
                        goto imap_excluded;
                    }
                    i++;
                }
                if (space_pos == 0 || space_pos == (packet->payload_packet_len - 1)) {
                    goto imap_excluded;
                }
                // now walk over a possible mail number to the next space
                i++;
                if (i < packet->payload_packet_len && (packet->payload[i] >= '0' && packet->payload[i] <= '9')) {
                    while (i < 20 && i < packet->payload_packet_len) {
                        if (i > 0 && packet->payload[i] == ' ') {
                            space_pos = i;
                            break;
                        }
                        if (!(packet->payload[i] >= '0' && packet->payload[i] <= '9')) {
                            goto imap_excluded;
                        }
                        i++;
                    }
                    if (space_pos == 0 || space_pos == (packet->payload_packet_len - 1)) {
                        goto imap_excluded;
                    }
                }
                command_start = space_pos + 1;
                /* command = &(packet->payload[command_start]); */
            } else {
                command_start = 0;
                /* command = &(packet->payload[command_start]); */
            }

            if ((command_start + 3) < packet->payload_packet_len) {
                if ((packet->payload[command_start] == 'O' || packet->payload[command_start] == 'o')
                        && (packet->payload[command_start + 1] == 'K' || packet->payload[command_start + 1] == 'k')
                        && packet->payload[command_start + 2] == ' ') {
                    flow->l4.tcp.mail_imap_stage += 1;
                    if (flow->l4.tcp.mail_imap_starttls == 1)
                        flow->l4.tcp.mail_imap_starttls = 2;
                    saw_command = 1;
                } else if ((packet->payload[command_start] == 'U' || packet->payload[command_start] == 'u')
                        && (packet->payload[command_start + 1] == 'I' || packet->payload[command_start + 1] == 'i')
                        && (packet->payload[command_start + 2] == 'D' || packet->payload[command_start + 2] == 'd')) {
                    flow->l4.tcp.mail_imap_stage += 1;
                    saw_command = 1;
                }
            }
            if ((command_start + 10) < packet->payload_packet_len) {
                if ((packet->payload[command_start] == 'C' || packet->payload[command_start] == 'c')
                        && (packet->payload[command_start + 1] == 'A' || packet->payload[command_start + 1] == 'a')
                        && (packet->payload[command_start + 2] == 'P' || packet->payload[command_start + 2] == 'p')
                        && (packet->payload[command_start + 3] == 'A' || packet->payload[command_start + 3] == 'a')
                        && (packet->payload[command_start + 4] == 'B' || packet->payload[command_start + 4] == 'b')
                        && (packet->payload[command_start + 5] == 'I' || packet->payload[command_start + 5] == 'i')
                        && (packet->payload[command_start + 6] == 'L' || packet->payload[command_start + 6] == 'l')
                        && (packet->payload[command_start + 7] == 'I' || packet->payload[command_start + 7] == 'i')
                        && (packet->payload[command_start + 8] == 'T' || packet->payload[command_start + 8] == 't')
                        && (packet->payload[command_start + 9] == 'Y' || packet->payload[command_start + 9] == 'y')) {
                    flow->l4.tcp.mail_imap_stage += 1;
                    saw_command = 1;
                }
            }
            if ((command_start + 8) < packet->payload_packet_len) {
                if ((packet->payload[command_start] == 'S' || packet->payload[command_start] == 's')
                        && (packet->payload[command_start + 1] == 'T' || packet->payload[command_start + 1] == 't')
                        && (packet->payload[command_start + 2] == 'A' || packet->payload[command_start + 2] == 'a')
                        && (packet->payload[command_start + 3] == 'R' || packet->payload[command_start + 3] == 'r')
                        && (packet->payload[command_start + 4] == 'T' || packet->payload[command_start + 4] == 't')
                        && (packet->payload[command_start + 5] == 'T' || packet->payload[command_start + 5] == 't')
                        && (packet->payload[command_start + 6] == 'L' || packet->payload[command_start + 6] == 'l')
                        && (packet->payload[command_start + 7] == 'S' || packet->payload[command_start + 7] == 's')) {
                    flow->l4.tcp.mail_imap_stage += 1;
                    flow->l4.tcp.mail_imap_starttls = 1;
                    flow->detected_protocol = NDPI_PROTOCOL_MAIL_IMAPS;
                    saw_command = 1;
                }
            }
            if ((command_start + 5) < packet->payload_packet_len) {
                if ((packet->payload[command_start] == 'L' || packet->payload[command_start] == 'l')
                        && (packet->payload[command_start + 1] == 'O' || packet->payload[command_start + 1] == 'o')
                        && (packet->payload[command_start + 2] == 'G' || packet->payload[command_start + 2] == 'g')
                        && (packet->payload[command_start + 3] == 'I' || packet->payload[command_start + 3] == 'i')
                        && (packet->payload[command_start + 4] == 'N' || packet->payload[command_start + 4] == 'n')) {
                    flow->l4.tcp.mail_imap_stage += 1;
                    saw_command = 1;
                } else if ((packet->payload[command_start] == 'F' || packet->payload[command_start] == 'f')
                        && (packet->payload[command_start + 1] == 'E' || packet->payload[command_start + 1] == 'e')
                        && (packet->payload[command_start + 2] == 'T' || packet->payload[command_start + 2] == 't')
                        && (packet->payload[command_start + 3] == 'C' || packet->payload[command_start + 3] == 'c')
                        && (packet->payload[command_start + 4] == 'H' || packet->payload[command_start + 4] == 'h')) {
                    flow->l4.tcp.mail_imap_stage += 1;
                    saw_command = 1;
                } else if ((packet->payload[command_start] == 'F' || packet->payload[command_start] == 'f')
                        && (packet->payload[command_start + 1] == 'L' || packet->payload[command_start + 1] == 'l')
                        && (packet->payload[command_start + 2] == 'A' || packet->payload[command_start + 2] == 'a')
                        && (packet->payload[command_start + 3] == 'G' || packet->payload[command_start + 3] == 'g')
                        && (packet->payload[command_start + 4] == 'S' || packet->payload[command_start + 4] == 's')) {
                    flow->l4.tcp.mail_imap_stage += 1;
                    saw_command = 1;
                } else if ((packet->payload[command_start] == 'C' || packet->payload[command_start] == 'c')
                        && (packet->payload[command_start + 1] == 'H' || packet->payload[command_start + 1] == 'h')
                        && (packet->payload[command_start + 2] == 'E' || packet->payload[command_start + 2] == 'e')
                        && (packet->payload[command_start + 3] == 'C' || packet->payload[command_start + 3] == 'c')
                        && (packet->payload[command_start + 4] == 'K' || packet->payload[command_start + 4] == 'k')) {
                    flow->l4.tcp.mail_imap_stage += 1;
                    saw_command = 1;
                } else if ((packet->payload[command_start] == 'S' || packet->payload[command_start] == 's')
                        && (packet->payload[command_start + 1] == 'T' || packet->payload[command_start + 1] == 't')
                        && (packet->payload[command_start + 2] == 'O' || packet->payload[command_start + 2] == 'o')
                        && (packet->payload[command_start + 3] == 'R' || packet->payload[command_start + 3] == 'r')
                        && (packet->payload[command_start + 4] == 'E' || packet->payload[command_start + 4] == 'e')) {
                    flow->l4.tcp.mail_imap_stage += 1;
                    saw_command = 1;
                }
            }
            if ((command_start + 12) < packet->payload_packet_len) {
                if ((packet->payload[command_start] == 'A' || packet->payload[command_start] == 'a')
                        && (packet->payload[command_start + 1] == 'U' || packet->payload[command_start + 1] == 'u')
                        && (packet->payload[command_start + 2] == 'T' || packet->payload[command_start + 2] == 't')
                        && (packet->payload[command_start + 3] == 'H' || packet->payload[command_start + 3] == 'h')
                        && (packet->payload[command_start + 4] == 'E' || packet->payload[command_start + 4] == 'e')
                        && (packet->payload[command_start + 5] == 'N' || packet->payload[command_start + 5] == 'n')
                        && (packet->payload[command_start + 6] == 'T' || packet->payload[command_start + 6] == 't')
                        && (packet->payload[command_start + 7] == 'I' || packet->payload[command_start + 7] == 'i')
                        && (packet->payload[command_start + 8] == 'C' || packet->payload[command_start + 8] == 'c')
                        && (packet->payload[command_start + 9] == 'A' || packet->payload[command_start + 9] == 'a')
                        && (packet->payload[command_start + 10] == 'T' || packet->payload[command_start + 10] == 't')
                        && (packet->payload[command_start + 11] == 'E' || packet->payload[command_start + 11] == 'e')) {
                    flow->l4.tcp.mail_imap_stage += 1;
                    saw_command = 1;
                }
            }
            if ((command_start + 9) < packet->payload_packet_len) {
                if ((packet->payload[command_start] == 'N' || packet->payload[command_start] == 'n')
                        && (packet->payload[command_start + 1] == 'A' || packet->payload[command_start + 1] == 'a')
                        && (packet->payload[command_start + 2] == 'M' || packet->payload[command_start + 2] == 'm')
                        && (packet->payload[command_start + 3] == 'E' || packet->payload[command_start + 3] == 'e')
                        && (packet->payload[command_start + 4] == 'S' || packet->payload[command_start + 4] == 's')
                        && (packet->payload[command_start + 5] == 'P' || packet->payload[command_start + 5] == 'p')
                        && (packet->payload[command_start + 6] == 'A' || packet->payload[command_start + 6] == 'a')
                        && (packet->payload[command_start + 7] == 'C' || packet->payload[command_start + 7] == 'c')
                        && (packet->payload[command_start + 8] == 'E' || packet->payload[command_start + 8] == 'e')) {
                    flow->l4.tcp.mail_imap_stage += 1;
                    saw_command = 1;
                }
            }
            if ((command_start + 4) < packet->payload_packet_len) {
                if ((packet->payload[command_start] == 'L' || packet->payload[command_start] == 'l')
                        && (packet->payload[command_start + 1] == 'S' || packet->payload[command_start + 1] == 's')
                        && (packet->payload[command_start + 2] == 'U' || packet->payload[command_start + 2] == 'u')
                        && (packet->payload[command_start + 3] == 'B' || packet->payload[command_start + 3] == 'b')) {
                    flow->l4.tcp.mail_imap_stage += 1;
                    saw_command = 1;
                } else if ((packet->payload[command_start] == 'L' || packet->payload[command_start] == 'l')
                        && (packet->payload[command_start + 1] == 'I' || packet->payload[command_start + 1] == 'i')
                        && (packet->payload[command_start + 2] == 'S' || packet->payload[command_start + 2] == 's')
                        && (packet->payload[command_start + 3] == 'T' || packet->payload[command_start + 3] == 't')) {
                    flow->l4.tcp.mail_imap_stage += 1;
                    saw_command = 1;
                } else if ((packet->payload[command_start] == 'N' || packet->payload[command_start] == 'n')
                        && (packet->payload[command_start + 1] == 'O' || packet->payload[command_start + 1] == 'o')
                        && (packet->payload[command_start + 2] == 'O' || packet->payload[command_start + 2] == 'o')
                        && (packet->payload[command_start + 3] == 'P' || packet->payload[command_start + 3] == 'p')) {
                    flow->l4.tcp.mail_imap_stage += 1;
                    saw_command = 1;
                } else if ((packet->payload[command_start] == 'I' || packet->payload[command_start] == 'i')
                        && (packet->payload[command_start + 1] == 'D' || packet->payload[command_start + 1] == 'd')
                        && (packet->payload[command_start + 2] == 'L' || packet->payload[command_start + 2] == 'l')
                        && (packet->payload[command_start + 3] == 'E' || packet->payload[command_start + 3] == 'e')) {
                    flow->l4.tcp.mail_imap_stage += 1;
                    saw_command = 1;
                }
            }
            if ((command_start + 6) < packet->payload_packet_len) {
                if ((packet->payload[command_start] == 'S' || packet->payload[command_start] == 's')
                        && (packet->payload[command_start + 1] == 'E' || packet->payload[command_start + 1] == 'e')
                        && (packet->payload[command_start + 2] == 'L' || packet->payload[command_start + 2] == 'l')
                        && (packet->payload[command_start + 3] == 'E' || packet->payload[command_start + 3] == 'e')
                        && (packet->payload[command_start + 4] == 'C' || packet->payload[command_start + 4] == 'c')
                        && (packet->payload[command_start + 5] == 'T' || packet->payload[command_start + 5] == 't')) {
                    flow->l4.tcp.mail_imap_stage += 1;
                    saw_command = 1;
                } else if ((packet->payload[command_start] == 'E' || packet->payload[command_start] == 'e')
                        && (packet->payload[command_start + 1] == 'X' || packet->payload[command_start + 1] == 'x')
                        && (packet->payload[command_start + 2] == 'I' || packet->payload[command_start + 2] == 'i')
                        && (packet->payload[command_start + 3] == 'S' || packet->payload[command_start + 3] == 's')
                        && (packet->payload[command_start + 4] == 'T' || packet->payload[command_start + 4] == 't')
                        && (packet->payload[command_start + 5] == 'S' || packet->payload[command_start + 5] == 's')) {
                    flow->l4.tcp.mail_imap_stage += 1;
                    saw_command = 1;
                } else if ((packet->payload[command_start] == 'A' || packet->payload[command_start] == 'a')
                        && (packet->payload[command_start + 1] == 'P' || packet->payload[command_start + 1] == 'p')
                        && (packet->payload[command_start + 2] == 'P' || packet->payload[command_start + 2] == 'p')
                        && (packet->payload[command_start + 3] == 'E' || packet->payload[command_start + 3] == 'e')
                        && (packet->payload[command_start + 4] == 'N' || packet->payload[command_start + 4] == 'n')
                        && (packet->payload[command_start + 5] == 'D' || packet->payload[command_start + 5] == 'd')) {
                    flow->l4.tcp.mail_imap_stage += 1;
                    saw_command = 1;
                }
            }

        }

        if (saw_command == 1) {
            if (flow->l4.tcp.mail_imap_stage == 3 || flow->l4.tcp.mail_imap_stage == 5) {
                NDPI_LOG_INFO(ndpi_struct, "found MAIL_IMAP\n");
                ndpi_int_mail_imap_add_connection(ndpi_struct, flow);
                return;
            }
        }
    }

    if (packet->payload_packet_len > 1 && packet->payload[packet->payload_packet_len - 1] == ' ') {
        NDPI_LOG_DBG2(ndpi_struct,
                "maybe a split imap command -> need next packet and imap_stage is set to 4.\n");
        flow->l4.tcp.mail_imap_stage = 4;
        return;
    }

imap_excluded:

    // skip over possible authentication hashes etc. that cannot be identified as imap commands or responses
    // if the packet count is low enough and at least one command or response was seen before
    if ((packet->payload_packet_len >= 2 && ntohs(get_u_int16_t(packet->payload, packet->payload_packet_len - 2)) == 0x0d0a)
            && flow->packet_counter < 6 && flow->l4.tcp.mail_imap_stage >= 1) {
        NDPI_LOG_DBG2(ndpi_struct,
                "no imap command or response but packet count < 6 and imap stage >= 1 -> skip\n");
        return;
    }

    NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
}


void init_mail_imap_dissector(struct ndpi_detection_module_struct *ndpi_struct, u_int32_t *id, NDPI_PROTOCOL_BITMASK *detection_bitmask)
{
    ndpi_set_bitmask_protocol_detection("MAIL_IMAP", ndpi_struct, detection_bitmask, *id,
            NDPI_PROTOCOL_MAIL_IMAP,
            ndpi_search_mail_imap_tcp,
            NDPI_SELECTION_BITMASK_PROTOCOL_V4_V6_TCP_WITH_PAYLOAD_WITHOUT_RETRANSMISSION,
            SAVE_DETECTION_BITMASK_AS_UNKNOWN,
            ADD_TO_DETECTION_BITMASK);

    *id += 1;
}
