/* GNU Mailutils -- a suite of utilities for electronic mail
   Copyright (C) 1999, 2000, 2001, 2002, 2005 Free Software Foundation, Inc.

   GNU Mailutils 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, or (at your option)
   any later version.

   GNU Mailutils 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 General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with GNU Mailutils; if not, write to the Free Software
   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
   MA 02110-1301 USA */

#include "comsat.h"

#ifndef PATH_DEV
# define PATH_DEV "/dev"
#endif
#ifndef PATH_TTY_PFX
# define PATH_TTY_PFX PATH_DEV
#endif

#ifdef HAVE_UTMP_H
# include <utmp.h>
#endif

#ifndef HAVE_GETUTENT_CALLS
extern void setutent __P((void));
extern struct utmp *getutent __P((void));
#endif

#ifdef UTMPX
# ifdef HAVE_UTMPX_H
#  include <utmpx.h>
# endif
typedef struct utmpx UTMP;
# define SETUTENT() setutxent()
# define GETUTENT() getutxent()
# define ENDUTENT() endutxent()
#else
typedef struct utmp UTMP;
# define SETUTENT() setutent()
# define GETUTENT() getutent()
# define ENDUTENT() endutent()
#endif

#define MAX_TTY_SIZE (sizeof (PATH_TTY_PFX) + sizeof (((UTMP*)0)->ut_line))

const char *program_version = "comsatd (" PACKAGE_STRING ")";
static char doc[] = "GNU comsatd";

static struct argp_option options[] = 
{
  {"config", 'c', N_("FILE"), 0, N_("Read configuration from FILE"), 0},
  { NULL, 0, NULL, 0, NULL, 0 }
};

static error_t comsatd_parse_opt (int key, char *arg, struct argp_state *state);

static struct argp argp = {
  options,
  comsatd_parse_opt,
  NULL, 
  doc,
  NULL,
  NULL, NULL
};

static const char *comsat_argp_capa[] = {
  "daemon",
  "common",
  "logging",
  "mailbox",
  "license",
  NULL
};

#define SUCCESS 0
#define NOT_HERE 1
#define PERMISSION_DENIED 2

#ifndef MAXHOSTNAMELEN
# define MAXHOSTNAMELEN 64
#endif

struct daemon_param daemon_param = {
  MODE_INTERACTIVE,     /* Start in interactive (inetd) mode */
  20,                   /* Default maximum number of children.
			   Currently unused */
  512,                  /* Default biff port */
  0,                    /* Default timeout */
};
int maxlines = 5;
char hostname[MAXHOSTNAMELEN];
const char *username;

static void comsat_init (void);
static void comsat_daemon_init (void);
static void comsat_daemon (int _port);
static int comsat_main (int fd);
static void notify_user (const char *user, const char *device, const char *path, off_t offset);
static int find_user (const char *name, char *tty);
static char *mailbox_path (const char *user);
static void change_user (const char *user);

static int xargc;
static char **xargv;
char *config_file = NULL;

static error_t
comsatd_parse_opt (int key, char *arg, struct argp_state *state)
{
  switch (key)
    {
    case ARGP_KEY_INIT:
      state->child_inputs[0] = state->input;
      break;
      
    case 'c':
      config_file = arg;
      break;
      
    default:
      return ARGP_ERR_UNKNOWN;
    }
  return 0;
}


int
main(int argc, char **argv)
{
  int c;

  /* Native Language Support */
  mu_init_nls ();

  mu_argp_init (program_version, NULL);
  mu_argp_parse (&argp, &argc, &argv, 0, comsat_argp_capa,
		 NULL, &daemon_param);

  if (daemon_param.timeout > 0 && daemon_param.mode == MODE_DAEMON)
    {
      fprintf (stderr, _("--timeout and --daemon are incompatible\n"));
      exit (EXIT_FAILURE);
    }

  comsat_init ();

  if (daemon_param.mode == MODE_DAEMON)
    {
      /* Preserve invocation arguments */
      xargc = argc;
      xargv = argv;
      comsat_daemon_init ();
    }

  /* Set up error messaging  */
  openlog ("gnu-comsat", LOG_PID, log_facility);
  mu_error_set_print (mu_syslog_error_printer);

  if (config_file)
    read_config (config_file);

  chdir ("/");

  if (daemon_param.mode == MODE_DAEMON)
    comsat_daemon (daemon_param.port);
  else
    c = comsat_main (0);

  return c != 0;
}

static RETSIGTYPE
sig_hup (int sig)
{
  syslog (LOG_NOTICE, _("Restarting"));

  if (xargv[0][0] != '/')
    syslog (LOG_ERR, _("Cannot restart: program must be invoked using absolute pathname"));
  else
    execvp (xargv[0], xargv);

  signal (sig, sig_hup);
}

void
comsat_init ()
{
  registrar_record (path_record);

  gethostname (hostname, sizeof hostname);

  /* Set signal handlers */
  signal (SIGTTOU, SIG_IGN);
  signal (SIGCHLD, SIG_IGN);
  signal (SIGHUP, SIG_IGN);	/* Ignore SIGHUP.  */
}

/* Set up for daemon mode.  */
static void
comsat_daemon_init (void)
{
  extern int daemon (int, int);

  /* Become a daemon. Take care to close inherited fds and to hold
     first three one, in, out, err.  Do not do the chdir("/").   */
  if (daemon (1, 0) < 0)
    {
      perror (_("Failed to become a daemon"));
      exit (EXIT_FAILURE);
    }
}

int allow_biffrc = 1;            /* Allow per-user biffrc files */
unsigned maxrequests = 16;       /* Maximum number of request allowed per
			            control interval */
time_t request_control_interval = 10;  /* Request control interval */
time_t overflow_control_interval = 10; /* Overflow control interval */
time_t overflow_delay_time = 5;


void
comsat_daemon (int port)
{
  int fd;
  struct sockaddr_in local_sin;
  time_t last_request_time;    /* Timestamp of the last received request */
  unsigned reqcount = 0;       /* Number of request received in the
				  current control interval */
  time_t last_overflow_time;   /* Timestamp of last overflow */
  unsigned overflow_count = 0; /* Number of overflows achieved during
				  the current interval */
  time_t now;

  fd = socket (PF_INET, SOCK_DGRAM, 0);
  if (fd == -1)
    {
      syslog (LOG_CRIT, "socket: %m");
      exit (1);
    }

  memset (&local_sin, 0, sizeof local_sin);
  local_sin.sin_family = AF_INET;
  local_sin.sin_addr.s_addr = INADDR_ANY; /*FIXME*/
  local_sin.sin_port = htons (port);

  if (bind (fd, (struct sockaddr *) &local_sin, sizeof local_sin) < 0)
    {
      syslog (LOG_CRIT, "bind: %m");
      exit (1);
    }

  syslog (LOG_NOTICE, _("GNU comsat started"));

  last_request_time = last_overflow_time = time (NULL);
  while (1)
    {
      fd_set fdset;
      int rc;

      FD_ZERO (&fdset);
      FD_SET (fd, &fdset);
      rc = select (fd+1, &fdset, NULL, NULL, NULL);
      if (rc == -1)
	{
	  if (errno != EINTR)
	    syslog (LOG_ERR, "select: %m");
	  continue;
	}

      /* Control the request flow */
      if (maxrequests != 0)
	{
	  now = time (NULL);
	  if (reqcount > maxrequests)
	    {
	      unsigned delay;

	      delay = overflow_delay_time << (overflow_count + 1);
	      syslog (LOG_NOTICE,
		      ngettext ("Too many requests: pausing for %u second",
				"Too many requests: pausing for %u seconds",
				delay),
		      delay);
	      sleep (delay);
	      reqcount = 0;
	      if (now - last_overflow_time <= overflow_control_interval)
		{
		  if ((overflow_delay_time << (overflow_count + 2)) >
		      overflow_delay_time)
		    ++overflow_count;
		}
	      else
		overflow_count = 0;
	      last_overflow_time = time (NULL);
	    }

	  if (now - last_request_time <= request_control_interval)
	    reqcount++;
	  else
	    {
	      last_request_time = now;
	      reqcount = 1;
	    }
	}
      comsat_main (fd);
    }
}

int
comsat_main (int fd)
{
  int rdlen;
  int len;
  struct sockaddr_in sin_from;
  char buffer[216]; /*FIXME: Arbitrary size */
  pid_t pid;
  char tty[MAX_TTY_SIZE];
  char *p, *endp;
  size_t offset;
  char *path = NULL;

  len = sizeof sin_from;
  rdlen = recvfrom (fd, buffer, sizeof buffer, 0,
		    (struct sockaddr*)&sin_from, &len);
  if (rdlen <= 0)
    {
      if (errno == EINTR)
	return 0;
      syslog (LOG_ERR, "recvfrom: %m");
      return 1;
    }

  if (acl_match (&sin_from))
    {
      syslog (LOG_ALERT, _("DENIED attempt to connect from %s"),
	      inet_ntoa (sin_from.sin_addr));
      return 1;
    }

  syslog (LOG_INFO,
	  ngettext ("Received %d byte from %s",
		    "Received %d bytes from %s", rdlen),
	  rdlen, inet_ntoa (sin_from.sin_addr));

  buffer[rdlen] = 0;

  /* Parse the buffer */
  p = strchr (buffer, '@');
  if (!p)
    {
      syslog (LOG_ERR, _("Malformed input: %s"), buffer);
      return 1;
    }
  *p++ = 0;

  offset = strtoul (p, &endp, 0);
  switch (*endp)
    {
    case 0:
      break;
    case ':':
      path = endp+1;
      break;
    default:
      if (!isspace (*endp))
	syslog (LOG_ERR, _("Malformed input: %s@%s (near %s)"), buffer, p, endp);
    }

  if (find_user (buffer, tty) != SUCCESS)
    return 0;

  /* All I/O is done by child process. This is to avoid various blocking
     problems. */

  pid = fork ();

  if (pid == -1)
    {
      syslog (LOG_ERR, "fork: %m");
      return 1;
    }

  if (pid > 0)
    {
      struct timeval tv;
      tv.tv_sec = 0;
      tv.tv_usec = 100000;
      select (0, NULL, NULL, NULL, &tv);
      kill (pid, SIGKILL); /* Just in case the child is hung */
      return 0;
    }

  /* Child: do actual I/O */
  notify_user (buffer, tty, path, offset);
  exit (0);
}

static const char *
get_newline_str (FILE *fp)
{
#if defined(OPOST) && defined(ONLCR)
  struct termios tbuf;

  tcgetattr (fileno (fp), &tbuf);
  if ((tbuf.c_oflag & OPOST) && (tbuf.c_oflag & ONLCR))
    return "\n";
  else
    return "\r\n";
#else
  return "\r\n"; /* Just in case */
#endif
}

/* NOTE: Do not bother to free allocated memory, as the program exits
   immediately after executing this */
static void
notify_user (const char *user, const char *device, const char *path, off_t offset)
{
  FILE *fp;
  const char *cr;
  char *blurb;
  mailbox_t mbox = NULL, tmp = NULL;
  message_t msg;
  stream_t stream = NULL;
  int status;
  off_t size;
  size_t count, n;

  change_user (user);
  if ((fp = fopen (device, "w")) == NULL)
    {
      syslog (LOG_ERR, _("Cannot open device %s: %m"), device);
      exit (0);
    }

  cr = get_newline_str (fp);

  if (!path)
    {
      path = mailbox_path (user);
      if (!path)
	return;
    }

  if ((status = mailbox_create (&mbox, path)) != 0
      || (status = mailbox_open (mbox, MU_STREAM_READ)) != 0)
    {
      syslog (LOG_ERR, _("Cannot open mailbox %s: %s"),
	      path, mu_strerror (status));
      return;
    }

  if ((status = mailbox_get_stream (mbox, &stream)))
    {
      syslog (LOG_ERR, _("Cannot get stream for mailbox %s: %s"),
	      path, mu_strerror (status));
      return;
    }

  if ((status = stream_size (stream, &size)))
    {
      syslog (LOG_ERR, _("Cannot get stream size (mailbox %s): %s"),
	      path, mu_strerror (status));
      return;
    }

  /* Read headers */
  size -= offset;
  blurb = malloc (size + 1);
  if (!blurb)
    return;

  stream_read (stream, blurb, size, offset, &n);
  blurb[size] = 0;

  if ((status = mailbox_create (&tmp, "/dev/null")) != 0
      || (status = mailbox_open (tmp, MU_STREAM_READ)) != 0)
    {
      syslog (LOG_ERR, _("Cannot create temporary mailbox: %s"),
	      mu_strerror (status));
      return;
    }

  if ((status = memory_stream_create (&stream, 0, 0)))
    {
      syslog (LOG_ERR, _("Cannot create temporary stream: %s"),
	      mu_strerror (status));
      return;
    }

  stream_write (stream, blurb, size, 0, &count);
  mailbox_set_stream (tmp, stream);
  mailbox_messages_count (tmp, &count);
  mailbox_get_message (tmp, 1, &msg);

  run_user_action (fp, cr, msg);
  fclose (fp);
}

/* Search utmp for the local user */
static int
find_user (const char *name, char *tty)
{
  UTMP *uptr;
  int status;
  struct stat statb;
  char ftty[MAX_TTY_SIZE];
  time_t last_time = 0;

  status = NOT_HERE;
  sprintf (ftty, "%s/", PATH_TTY_PFX);

  SETUTENT ();

  while ((uptr = GETUTENT ()) != NULL)
    {
#ifdef USER_PROCESS
      if (uptr->ut_type != USER_PROCESS)
	continue;
#endif
      if (!strncmp (uptr->ut_name, name, sizeof(uptr->ut_name)))
	{
	  /* no particular tty was requested */
	  strncpy (ftty + sizeof(PATH_DEV),
		   uptr->ut_line,
		   sizeof (ftty) - sizeof (PATH_DEV) - 2);
	  ftty[sizeof (ftty) - 1] = 0;

	  mu_normalize_path (ftty, "/");
	  if (strncmp (ftty, PATH_TTY_PFX, strlen (PATH_TTY_PFX)))
	    {
	      /* An attempt to break security... */
	      syslog (LOG_ALERT, _("Bad line name in utmp record: %s"), ftty);
	      return NOT_HERE;
	    }

	  if (stat (ftty, &statb) == 0)
	    {
	      if (!S_ISCHR (statb.st_mode))
		{
		  syslog (LOG_ALERT, _("Not a character device: %s"), ftty);
		  return NOT_HERE;
		}

	      if (!(statb.st_mode & S_IEXEC))
		{
		  if (status != SUCCESS)
		    status = PERMISSION_DENIED;
		  continue;
		}
	      if (statb.st_atime > last_time)
		{
		  last_time = statb.st_atime;
		  strcpy(tty, ftty);
		  status = SUCCESS;
		}
	      continue;
	    }
	}
    }

  ENDUTENT ();
  return status;
}

void
change_user (const char *user)
{
  struct passwd *pw;

  pw = getpwnam (user);
  if (!pw)
    {
      syslog (LOG_CRIT, _("No such user: %s"), user);
      exit (1);
    }

  setgid (pw->pw_gid);
  setuid (pw->pw_uid);
  chdir (pw->pw_dir);
  username = user;
}

char *
mailbox_path (const char *user)
{
  struct mu_auth_data *auth;
  char *mailbox_name;

  auth = mu_get_auth_by_name (user);

  if (!auth)
    {
      syslog (LOG_ALERT, _("User nonexistent: %s"), user);
      return NULL;
    }

  mailbox_name = strdup (auth->mailbox);
  mu_auth_data_free (auth);
  return mailbox_name;
}