/*
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program 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 Library General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *
 *       $Id: fake-pop3.c,v 1.2 2012/02/05 17:38:14 james.stevenson Exp $
 *
 * Author:
 *       NAME:   James Stevenson
 *       WWW:    http://www.stev.org
 *
 */

#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <string.h>
#include <errno.h>
#include <syslog.h>
#include <unistd.h>
#include <signal.h>

#include <arpa/inet.h>
#include <netinet/in.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/wait.h>

int use_syslog = 0;
int verbose = 0;
int backlog = 5;
int max_attempts = 5;
int delay = 0;
int auth_delay = 3;

void print_help(FILE *fp, char *app) {

  fprintf(fp, "Usage: %s [<options>]\n", app);
  fprintf(fp, "\n");
  fprintf(fp, "   -a <delay>   Failed auth delay\n");
  fprintf(fp, "   -p <port>    Port to listen on\n");
  fprintf(fp, "   -s           Use syslog\n");
  fprintf(fp, "   -v           Verbose. Repeat for more info\n");
  fprintf(fp, "   -m <n>       Maximum number attempts\n");
  fprintf(fp, "   -w <delay>   Delay until banner is sent to client\n");
  fprintf(fp, "\n");
}

void logger(const char *fmt, ...) {
  va_list ap;
  va_start(ap, fmt);
  vprintf(fmt, ap);
  printf("\n");

  if (use_syslog)
  vsyslog(LOG_NOTICE, fmt, ap);

  va_end(ap);
}

void handle_sigchild(int signum) {
    int status = -1;
    int pid = 0;

    do {
        pid = waitpid(-1, &status, WNOHANG);
        if (verbose > 0)
            logger("Process %d Exited", pid);
    } while(pid > 0);
}

void strip(char *str) {
  while(*str != 0) {
    if (*str == '\r'
      || *str == '\n') {
      *str = 0;
      return;
    }
    str++;
  }
}

void start(int fd, struct sockaddr_in *client) {
  FILE *fp = fdopen(fd, "r+");
  char *buf = 0;
  size_t buflen = 0;
  char *user = 0, *pass = 0;
  char *client_ip = inet_ntoa(client->sin_addr);
  int attempts = 0;
  
  logger("Connection From %s:%d", client_ip, client->sin_port);

  if (!fp) {
    logger("fdopen: %s", strerror(errno));
    return;    
  }

  if (delay)
    sleep(delay);

  fprintf(fp, "+OK POP3 Server Reader\r\n");
  fflush(fp);

  while(getline(&buf, &buflen, fp) >= 0) {
    strip(buf);
    
    if (verbose >= 2)
      logger("%s", buf);


    if (strncasecmp("QUIT", buf, 4) == 0) {
      fprintf(fp, "+OK Closing Connection\r\n");
      fflush(fp);
      break;
    } else if (strncasecmp("USER", buf, 4) == 0) {
      char *tmp = strchr(buf, ' ');
      if (tmp == NULL) {
        fprintf(fp, "-ERR Invalid\r\n");
        fflush(fp);
      } else {
        if (user != NULL)
          free(user);
        tmp++;
        user = strdup(tmp);
        fprintf(fp, "+OK Send Password\r\n");
        fflush(fp);
      }
    } else if (strncasecmp("PASS", buf, 4) == 0) {
      char *tmp = strchr(buf, ' ');
      if (tmp == NULL || user == NULL) {
        fprintf(fp, "-ERR Invalid\r\n");
        fflush(fp);
      } else {
        if (pass != NULL)
          free(pass);
        tmp++;
        pass = strdup(tmp);

        logger("IP: %s USER: %s PASS: %s", client_ip, user, pass);

        fprintf(fp, "-ERR Invalid login\r\n");
        fflush(fp);
        if (auth_delay)
          sleep(auth_delay);

        attempts++;
        if (attempts > max_attempts)
          break;
      }
    
    } else {
      logger("Unknown Command: %s", buf);
      fprintf(fp, "-ERR Invalid\r\n");
      fflush(fp);
    }
  }

  logger("Closed Connection From %s:%d", client_ip, client->sin_port);

  if (user)
    free(user);

  if (pass)
    free(pass);

  if (fp)
    fclose(fp);
  if (buf)
    free(buf);
  close(fd);
}


int main(int argc, char **argv) {
  struct sockaddr_in server, client;
  socklen_t addr_len = sizeof(client);
  int port = 110;
  int c;
  int sockfd;
  int one = 1;

  while( (c = getopt(argc, argv, "a:hp:svm:w:")) != -1) {
    switch(c) {
      case 'a':
        auth_delay = atoi(optarg);
        break;
      case 'h':
        print_help(stdout, argv[0]);
        exit(EXIT_SUCCESS);
        break;
      case 'p':
        port = atoi(optarg);
        break;
      case 's':
        use_syslog = 1;
        break;
      case 'v':
        verbose++;
        break;
      case 'm':
        max_attempts = atoi(optarg);
        break;
      case 'w':
        delay = atoi(optarg);
      default:
        break;
    }

  }

  signal(SIGCHLD, &handle_sigchild);

  sockfd = socket(AF_INET, SOCK_STREAM, 0);
  if (sockfd < 0) {
    perror("socket");
    exit(EXIT_FAILURE);
  }

  memset(&server, 0, sizeof(server));

  server.sin_family = AF_INET;
  server.sin_port = htons(port);
  server.sin_addr.s_addr = INADDR_ANY;

  if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one)) < 0) {
    perror("setsockopt");
  }

  if (bind(sockfd, (struct sockaddr *) &server, sizeof(server)) < 0) {
    perror("bind");
    exit(EXIT_FAILURE);
  }

  if (listen(sockfd, backlog) < 0) {
    perror("listen");
    exit(EXIT_FAILURE);
  }

  while(1) {
    int fd = accept(sockfd, (struct sockaddr *) &client, &addr_len);
    if (fd < 0) {
      logger("accept: %s", strerror(errno));
      continue;  
    }

    int ret = fork();
    if (ret < 0) {
      logger("fork: %s", strerror(errno));
      close(fd);
      continue;
    }

    if (ret == 0) {
      start(fd, &client);
      exit(EXIT_SUCCESS);
    } else {
      if (verbose > 0)
        logger("Started Process %d", ret);
      close(fd);
    }
  }

  return 0;
}