/*
 * mail_pop.c
 *
 * Copyright (C) 2011-22 - ntop.org
 * Copyright (C) 2009-11 - 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_MAIL_POP

#include "ndpi_api.h"


#define POP_BIT_AUTH		0x0001
#define POP_BIT_APOP		0x0002
#define POP_BIT_USER		0x0004
#define POP_BIT_PASS		0x0008
#define POP_BIT_CAPA		0x0010
#define POP_BIT_LIST		0x0020
#define POP_BIT_STAT		0x0040
#define POP_BIT_UIDL		0x0080
#define POP_BIT_RETR		0x0100
#define POP_BIT_DELE		0x0200
#define POP_BIT_STLS		0x0400


static void ndpi_int_mail_pop_add_connection(struct ndpi_detection_module_struct
					     *ndpi_struct, struct ndpi_flow_struct *flow) {

  flow->guessed_protocol_id = NDPI_PROTOCOL_UNKNOWN; /* Avoid POP3S to be used s sub-protocol */
  ndpi_set_detected_protocol(ndpi_struct, flow, NDPI_PROTOCOL_MAIL_POP, NDPI_PROTOCOL_UNKNOWN, NDPI_CONFIDENCE_DPI);
}

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

static void popInitExtraPacketProcessing(struct ndpi_flow_struct *flow);

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

static int ndpi_int_mail_pop_check_for_client_commands(struct ndpi_detection_module_struct
						       *ndpi_struct, struct ndpi_flow_struct *flow) {
  struct ndpi_packet_struct *packet = &ndpi_struct->packet;
	
  if(packet->payload_packet_len > 4) {
    if((packet->payload[0] == 'A' || packet->payload[0] == 'a')
	&& (packet->payload[1] == 'U' || packet->payload[1] == 'u')
	&& (packet->payload[2] == 'T' || packet->payload[2] == 't')
	&& (packet->payload[3] == 'H' || packet->payload[3] == 'h')) {
      flow->l4.tcp.pop_command_bitmask |= POP_BIT_AUTH;
      return 1;
    } else if((packet->payload[0] == 'A' || packet->payload[0] == 'a')
	       && (packet->payload[1] == 'P' || packet->payload[1] == 'p')
	       && (packet->payload[2] == 'O' || packet->payload[2] == 'o')
	       && (packet->payload[3] == 'P' || packet->payload[3] == 'p')) {
      flow->l4.tcp.pop_command_bitmask |= POP_BIT_APOP;
      return 1;
    } else if((packet->payload[0] == 'U' || packet->payload[0] == 'u')
	       && (packet->payload[1] == 'S' || packet->payload[1] == 's')
	       && (packet->payload[2] == 'E' || packet->payload[2] == 'e')
	       && (packet->payload[3] == 'R' || packet->payload[3] == 'r')) {
      ndpi_user_pwd_payload_copy((u_int8_t*)flow->l4.tcp.ftp_imap_pop_smtp.username,
				 sizeof(flow->l4.tcp.ftp_imap_pop_smtp.username), 5,
				 packet->payload, packet->payload_packet_len);

      ndpi_set_risk(ndpi_struct, flow, NDPI_CLEAR_TEXT_CREDENTIALS);
      flow->l4.tcp.pop_command_bitmask |= POP_BIT_USER;
      return 1;
    } else if((packet->payload[0] == 'P' || packet->payload[0] == 'p')
	      && (packet->payload[1] == 'A' || packet->payload[1] == 'a')
	      && (packet->payload[2] == 'S' || packet->payload[2] == 's')
	      && (packet->payload[3] == 'S' || packet->payload[3] == 's')) {
      ndpi_user_pwd_payload_copy((u_int8_t*)flow->l4.tcp.ftp_imap_pop_smtp.password,
				 sizeof(flow->l4.tcp.ftp_imap_pop_smtp.password), 5,
				 packet->payload, packet->payload_packet_len);

      ndpi_set_risk(ndpi_struct, flow, NDPI_CLEAR_TEXT_CREDENTIALS);
      flow->l4.tcp.pop_command_bitmask |= POP_BIT_PASS;
      return 1;
    } else if((packet->payload[0] == 'C' || packet->payload[0] == 'c')
	       && (packet->payload[1] == 'A' || packet->payload[1] == 'a')
	       && (packet->payload[2] == 'P' || packet->payload[2] == 'p')
	       && (packet->payload[3] == 'A' || packet->payload[3] == 'a')) {
      flow->l4.tcp.pop_command_bitmask |= POP_BIT_CAPA;
      return 1;
    } else if((packet->payload[0] == 'L' || packet->payload[0] == 'l')
	       && (packet->payload[1] == 'I' || packet->payload[1] == 'i')
	       && (packet->payload[2] == 'S' || packet->payload[2] == 's')
	       && (packet->payload[3] == 'T' || packet->payload[3] == 't')) {
      flow->l4.tcp.pop_command_bitmask |= POP_BIT_LIST;
      return 1;
    } else if((packet->payload[0] == 'S' || packet->payload[0] == 's')
	       && (packet->payload[1] == 'T' || packet->payload[1] == 't')
	       && (packet->payload[2] == 'A' || packet->payload[2] == 'a')
	       && (packet->payload[3] == 'T' || packet->payload[3] == 't')) {
      flow->l4.tcp.pop_command_bitmask |= POP_BIT_STAT;
      return 1;
    } else if((packet->payload[0] == 'U' || packet->payload[0] == 'u')
	       && (packet->payload[1] == 'I' || packet->payload[1] == 'i')
	       && (packet->payload[2] == 'D' || packet->payload[2] == 'd')
	       && (packet->payload[3] == 'L' || packet->payload[3] == 'l')) {
      flow->l4.tcp.pop_command_bitmask |= POP_BIT_UIDL;
      return 1;
    } else if((packet->payload[0] == 'R' || packet->payload[0] == 'r')
	       && (packet->payload[1] == 'E' || packet->payload[1] == 'e')
	       && (packet->payload[2] == 'T' || packet->payload[2] == 't')
	       && (packet->payload[3] == 'R' || packet->payload[3] == 'r')) {
      flow->l4.tcp.pop_command_bitmask |= POP_BIT_RETR;
      return 1;
    } else if((packet->payload[0] == 'D' || packet->payload[0] == 'd')
	       && (packet->payload[1] == 'E' || packet->payload[1] == 'e')
	       && (packet->payload[2] == 'L' || packet->payload[2] == 'l')
	       && (packet->payload[3] == 'E' || packet->payload[3] == 'e')) {
      flow->l4.tcp.pop_command_bitmask |= POP_BIT_DELE;
      return 1;
    } else if((packet->payload[0] == 'S' || packet->payload[0] == 's')
	       && (packet->payload[1] == 'T' || packet->payload[1] == 't')
	       && (packet->payload[2] == 'L' || packet->payload[2] == 'l')
	       && (packet->payload[3] == 'S' || packet->payload[3] == 's')) {
      flow->l4.tcp.pop_command_bitmask |= POP_BIT_STLS;
      return 1;
    }
  }
  return 0;
}



void ndpi_search_mail_pop_tcp(struct ndpi_detection_module_struct
			      *ndpi_struct, struct ndpi_flow_struct *flow)
{
  struct ndpi_packet_struct *packet = &ndpi_struct->packet;
  u_int8_t a = 0;
  u_int8_t bit_count = 0;

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

  if((packet->payload_packet_len > 3
       && (packet->payload[0] == '+' && (packet->payload[1] == 'O' || packet->payload[1] == 'o')
	   && (packet->payload[2] == 'K' || packet->payload[2] == 'k')))
      || (packet->payload_packet_len > 4
	  && (packet->payload[0] == '-' && (packet->payload[1] == 'E' || packet->payload[1] == 'e')
	      && (packet->payload[2] == 'R' || packet->payload[2] == 'r')
	      && (packet->payload[3] == 'R' || packet->payload[3] == 'r')))) {
    // +OK or -ERR seen
    flow->l4.tcp.mail_pop_stage += 1;
  } else if(!ndpi_int_mail_pop_check_for_client_commands(ndpi_struct, flow)) {
    goto maybe_split_pop;
  }

  if(packet->payload_packet_len > 2 && ntohs(get_u_int16_t(packet->payload, packet->payload_packet_len - 2)) == 0x0d0a) {
    // count the bits set in the bitmask
    if(flow->l4.tcp.pop_command_bitmask != 0) {
      for (a = 0; a < 16; a++) {
	bit_count += (flow->l4.tcp.pop_command_bitmask >> a) & 0x01;
      }
    }

    NDPI_LOG_DBG2(ndpi_struct,
		  "mail_pop +OK/-ERR responses: %u, unique commands: %u\n",
		  flow->l4.tcp.mail_pop_stage, bit_count);

    if((bit_count + flow->l4.tcp.mail_pop_stage) >= 3) {
      if(flow->l4.tcp.mail_pop_stage > 0) {
	NDPI_LOG_INFO(ndpi_struct, "mail_pop identified\n");
	
	if((flow->l4.tcp.ftp_imap_pop_smtp.password[0] != '\0')
	   || (flow->l4.tcp.mail_pop_stage > 3)) {
	  ndpi_int_mail_pop_add_connection(ndpi_struct, flow);
	  popInitExtraPacketProcessing(flow);
	}
      }
      
      return;      
    } else
      return;    
  } else {
    // first part of a split packet
    NDPI_LOG_DBG2(ndpi_struct,
		  "mail_pop command without line ending -> skip\n");
    return;
  }


 maybe_split_pop:

  if(((packet->payload_packet_len > 2 && ntohs(get_u_int16_t(packet->payload, packet->payload_packet_len - 2)) == 0x0d0a)
       || flow->l4.tcp.pop_command_bitmask != 0 || flow->l4.tcp.mail_pop_stage != 0) && flow->packet_counter < 12) {
    // maybe part of a split pop packet
    NDPI_LOG_DBG2(ndpi_struct,
		  "maybe part of split mail_pop packet -> skip\n");
    return;
  }

  NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
}


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

int ndpi_extra_search_mail_pop_tcp(struct ndpi_detection_module_struct *ndpi_struct,
				    struct ndpi_flow_struct *flow) {
  int rc;
  
  ndpi_search_mail_pop_tcp(ndpi_struct, flow);

  rc = (flow->l4.tcp.ftp_imap_pop_smtp.password[0] == '\0') ? 1 : 0;
  
#ifdef POP_DEBUG
  printf("**** %s() [rc: %d]\n", __FUNCTION__, rc);
#endif  

  return(rc);
}

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

static void popInitExtraPacketProcessing(struct ndpi_flow_struct *flow) {
#ifdef POP_DEBUG
  printf("**** %s()\n", __FUNCTION__);
#endif
  
  flow->check_extra_packets = 1;
  /* At most 7 packets should almost always be enough */
  flow->max_extra_packets_to_check = 7;
  flow->extra_packets_func = ndpi_extra_search_mail_pop_tcp;
}

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

void init_mail_pop_dissector(struct ndpi_detection_module_struct *ndpi_struct,
			     u_int32_t *id, NDPI_PROTOCOL_BITMASK *detection_bitmask) {
  ndpi_set_bitmask_protocol_detection("MAIL_POP", ndpi_struct, detection_bitmask, *id,
				      NDPI_PROTOCOL_MAIL_POP,
				      ndpi_search_mail_pop_tcp,
				      NDPI_SELECTION_BITMASK_PROTOCOL_V4_V6_TCP_WITH_PAYLOAD_WITHOUT_RETRANSMISSION,
				      SAVE_DETECTION_BITMASK_AS_UNKNOWN,
				      ADD_TO_DETECTION_BITMASK);

  *id += 1;
}
