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write.c

/*
 * Copyright (c) 1989, 1993
 *    The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Jef Poskanzer and Craig Leres of the Lawrence Berkeley Laboratory.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *    This product includes software developed by the University of
 *    California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * Modified for Linux, Mon Mar  8 18:16:24 1993, faith@cs.unc.edu
 * Wed Jun 22 21:41:56 1994, faith@cs.unc.edu:
 *      Added fix from Mike Grupenhoff (kashmir@umiacs.umd.edu)
 * Mon Jul  1 17:01:39 MET DST 1996, janl@math.uio.no:
 *      - Added fix from David.Chapell@mail.trincoll.edu enabeling daemons
 *      to use write.
 *      - ANSIed it since I was working on it anyway.
 * 1999-02-22 Arkadiusz Mi¶kiewicz <misiek@pld.ORG.PL>
 * - added Native Language Support
 *
 */

#include <stdio.h>
#include <unistd.h>
#include <utmp.h>
#include <errno.h>
#include <ctype.h>
#include <time.h>
#include <pwd.h>
#include <string.h>
#include <stdlib.h>
#include <locale.h>
#include <signal.h>
#include <sys/param.h>
#include <sys/signal.h>
#include <sys/stat.h>
#include <sys/file.h>
#include <sys/time.h>
#include <paths.h>
#include "pathnames.h"
#include "carefulputc.h"
#include "nls.h"
 
void search_utmp(char *, char *, char *, uid_t);
void do_write(char *, char *, uid_t);
void wr_fputs(char *);
static void done(int);
int term_chk(char *, int *, time_t *, int);
int utmp_chk(char *, char *);

int
main(int argc, char **argv) {
      time_t atime;
      uid_t myuid;
      int msgsok, myttyfd;
      char tty[MAXPATHLEN], *mytty;

      setlocale(LC_ALL, "");
      bindtextdomain(PACKAGE, LOCALEDIR);
      textdomain(PACKAGE);

      /* check that sender has write enabled */
      if (isatty(fileno(stdin)))
            myttyfd = fileno(stdin);
      else if (isatty(fileno(stdout)))
            myttyfd = fileno(stdout);
      else if (isatty(fileno(stderr)))
            myttyfd = fileno(stderr);
      else {
            myttyfd = -1;
      }
      if (myttyfd != -1) {
        if (!(mytty = ttyname(myttyfd))) {
            (void)fprintf(stderr, _("write: can't find your tty's name\n"));
            exit(1);
        }
        /* We may have /dev/ttyN but also /dev/pts/xx.
           Below, term_chk() will put "/dev/" in front, so remove that part. */
        if (!strncmp(mytty, "/dev/", 5))
            mytty += 5;
        if (term_chk(mytty, &msgsok, &atime, 1))
            exit(1);
        if (!msgsok) {
            (void)fprintf(stderr,
                _("write: you have write permission turned off.\n"));
            exit(1);
        }
      
      } else {
          mytty = "<no tty>";
      }

      myuid = getuid();

      /* check args */
      switch (argc) {
      case 2:
            search_utmp(argv[1], tty, mytty, myuid);
            do_write(tty, mytty, myuid);
            break;
      case 3:
            if (!strncmp(argv[2], "/dev/", 5))
                  argv[2] += 5;
            if (utmp_chk(argv[1], argv[2])) {
                  (void)fprintf(stderr,
                      _("write: %s is not logged in on %s.\n"),
                      argv[1], argv[2]);
                  exit(1);
            }
            if (term_chk(argv[2], &msgsok, &atime, 1))
                  exit(1);
            if (myuid && !msgsok) {
                  (void)fprintf(stderr,
                      _("write: %s has messages disabled on %s\n"),
                      argv[1], argv[2]);
                  exit(1);
            }
            do_write(argv[2], mytty, myuid);
            break;
      default:
            (void)fprintf(stderr, _("usage: write user [tty]\n"));
            exit(1);
      }
      done(0);
      /* NOTREACHED */
      return 0;
}


/*
 * utmp_chk - checks that the given user is actually logged in on
 *     the given tty
 */
int utmp_chk(char *user, char *tty)

{
      struct utmp u;
      struct utmp *uptr;
      int res = 1;

      utmpname(_PATH_UTMP);
      setutent();

      while ((uptr = getutent())) {
            memcpy(&u, uptr, sizeof(u));
            if (strncmp(user, u.ut_name, sizeof(u.ut_name)) == 0 &&
                strncmp(tty, u.ut_line, sizeof(u.ut_line)) == 0) {
                  res = 0;
                  break;
            }
      }

      endutent();
      return(res);
}

/*
 * search_utmp - search utmp for the "best" terminal to write to
 *
 * Ignores terminals with messages disabled, and of the rest, returns
 * the one with the most recent access time.  Returns as value the number
 * of the user's terminals with messages enabled, or -1 if the user is
 * not logged in at all.
 *
 * Special case for writing to yourself - ignore the terminal you're
 * writing from, unless that's the only terminal with messages enabled.
 */
void search_utmp(char *user, char *tty, char *mytty, uid_t myuid)

{
      struct utmp u;
      struct utmp *uptr;
      time_t bestatime, atime;
      int nloggedttys, nttys, msgsok, user_is_me;
      char atty[sizeof(u.ut_line) + 1];

      utmpname(_PATH_UTMP);
      setutent();

      nloggedttys = nttys = 0;
      bestatime = 0;
      user_is_me = 0;
      while ((uptr = getutent())) {
            memcpy(&u, uptr, sizeof(u));
            if (strncmp(user, u.ut_name, sizeof(u.ut_name)) == 0) {
                  ++nloggedttys;
                  (void)strncpy(atty, u.ut_line, sizeof(u.ut_line));
                  atty[sizeof(u.ut_line)] = '\0';
                  if (term_chk(atty, &msgsok, &atime, 0))
                        continue;   /* bad term? skip */
                  if (myuid && !msgsok)
                        continue;   /* skip ttys with msgs off */
                  if (strcmp(atty, mytty) == 0) {
                        user_is_me = 1;
                        continue;   /* don't write to yourself */
                  }
                        if (u.ut_type != USER_PROCESS)
                          continue;       /* it's not a valid entry */
                  ++nttys;
                  if (atime > bestatime) {
                        bestatime = atime;
                        (void)strcpy(tty, atty);
                  }
            }
      }

      endutent();
      if (nloggedttys == 0) {
            (void)fprintf(stderr, _("write: %s is not logged in\n"), user);
            exit(1);
      }
      if (nttys == 0) {
            if (user_is_me) {       /* ok, so write to yourself! */
                  (void)strcpy(tty, mytty);
                  return;
            }
            (void)fprintf(stderr,
                _("write: %s has messages disabled\n"), user);
            exit(1);
      } else if (nttys > 1) {
            (void)fprintf(stderr,
                _("write: %s is logged in more than once; writing to %s\n"),
                user, tty);
      }
}

/*
 * term_chk - check that a terminal exists, and get the message bit
 *     and the access time
 */
int term_chk(char *tty, int *msgsokP, time_t *atimeP, int showerror)

{
      struct stat s;
      char path[MAXPATHLEN];

      if (strlen(tty) + 6 > sizeof(path))
            return(1);
      (void)sprintf(path, "/dev/%s", tty);
      if (stat(path, &s) < 0) {
            if (showerror)
                  (void)fprintf(stderr,
                      "write: %s: %s\n", path, strerror(errno));
            return(1);
      }
      *msgsokP = (s.st_mode & (S_IWRITE >> 3)) != 0;  /* group write bit */
      *atimeP = s.st_atime;
      return(0);
}

/*
 * do_write - actually make the connection
 */
void do_write(char *tty, char *mytty, uid_t myuid) {
      char *login, *pwuid, *nows;
      struct passwd *pwd;
      time_t now;
      char path[MAXPATHLEN], host[MAXHOSTNAMELEN], line[512];

      /* Determine our login name(s) before the we reopen() stdout */
      if ((pwd = getpwuid(myuid)) != NULL)
            pwuid = pwd->pw_name;
      else
            pwuid = "???";
      if ((login = getlogin()) == NULL)
            login = pwuid;

      if (strlen(tty) + 6 > sizeof(path))
            exit(1);
      (void)sprintf(path, "/dev/%s", tty);
      if ((freopen(path, "w", stdout)) == NULL) {
            (void)fprintf(stderr, "write: %s: %s\n",
                        path, strerror(errno));
            exit(1);
      }

      (void)signal(SIGINT, done);
      (void)signal(SIGHUP, done);

      /* print greeting */
      if (gethostname(host, sizeof(host)) < 0)
            (void)strcpy(host, "???");
      now = time((time_t *)NULL);
      nows = ctime(&now);
      nows[16] = '\0';
      printf("\r\n\007\007\007");
      if (strcmp(login, pwuid))
            (void)printf(_("Message from %s@%s (as %s) on %s at %s ..."),
                       login, host, pwuid, mytty, nows + 11);
      else
            (void)printf(_("Message from %s@%s on %s at %s ..."),
                       login, host, mytty, nows + 11);
      printf("\r\n");

      while (fgets(line, sizeof(line), stdin) != NULL)
            wr_fputs(line);
}

/*
 * done - cleanup and exit
 */
static void
done(int dummy) {
      (void)printf("EOF\r\n");
      exit(0);
}

/*
 * wr_fputs - like fputs(), but makes control characters visible and
 *     turns \n into \r\n.
 */
void
wr_fputs(char *s) {
      char c;

#define     PUTC(c)     if (carefulputc(c,stdout) == EOF) goto err;

      while(*s) {
            c = *s++;
            if (c == '\n')
                  PUTC('\r');
            PUTC(c);
      }
      return;

err:
      fprintf(stderr, "write: %s\n", strerror(errno));
      exit(1);
#undef PUTC
}

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