usr.bin/write/write.c

   1 /*
   2  * Copyright (c) 1989, 1993
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * This code is derived from software contributed to Berkeley by
   6  * Jef Poskanzer and Craig Leres of the Lawrence Berkeley Laboratory.
   7  *
   8  * Redistribution and use in source and binary forms, with or without
   9  * modification, are permitted provided that the following conditions
  10  * are met:
  11  * 1. Redistributions of source code must retain the above copyright
  12  *    notice, this list of conditions and the following disclaimer.
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in the
  15  *    documentation and/or other materials provided with the distribution.
  16  * 3. All advertising materials mentioning features or use of this software
  17  *    must display the following acknowledgement:
  18  *      This product includes software developed by the University of
  19  *      California, Berkeley and its contributors.
  20  * 4. Neither the name of the University nor the names of its contributors
  21  *    may be used to endorse or promote products derived from this software
  22  *    without specific prior written permission.
  23  *
  24  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  25  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  26  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  27  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  28  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  29  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  30  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  31  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  32  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  33  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  34  * SUCH DAMAGE.
  35  *
  36  * @(#) Copyright (c) 1989, 1993 The Regents of the University of California.  All rights reserved.
  37  * @(#)write.c  8.1 (Berkeley) 6/6/93
  38  * $FreeBSD: src/usr.bin/write/write.c,v 1.12 1999/08/28 01:07:48 peter Exp $
  39  * $DragonFly: src/usr.bin/write/write.c,v 1.7 2005/08/30 22:02:36 liamfoy Exp $
  40  */
  41
  42 #include <sys/param.h>
  43 #include <sys/stat.h>
  44 #include <sys/file.h>
  45
  46 #include <ctype.h>
  47 #include <err.h>
  48 #include <locale.h>
  49 #include <paths.h>
  50 #include <pwd.h>
  51 #include <stdio.h>
  52 #include <stdlib.h>
  53 #include <string.h>
  54 #include <signal.h>
  55 #include <time.h>
  56 #include <unistd.h>
  57 #include <utmp.h>
  58
  59 static void     done(int);
  60 static void     do_write(const char *, const char *, uid_t, int *);
  61 static void     usage(void);
  62 static int      term_chk(const char *, int *, time_t *, int);
  63 static void     wr_fputs(unsigned char *s);
  64 static void     search_utmp(const char *, char *, size_t, const char *, uid_t);
  65 static int      utmp_chk(const char *, const char *);
  66
  67 int
  68 main(int argc, char **argv)
  69 {
  70         char *cp;
  71         time_t atime;
  72         uid_t myuid;
  73         int msgsok, mymsgok, myttyfd;
  74         char tty[MAXPATHLEN], *mytty;
  75
  76         setlocale(LC_CTYPE, "");
  77
  78         /* check that sender has write enabled */
  79         if (isatty(fileno(stdin)))
  80                 myttyfd = fileno(stdin);
  81         else if (isatty(fileno(stdout)))
  82                 myttyfd = fileno(stdout);
  83         else if (isatty(fileno(stderr)))
  84                 myttyfd = fileno(stderr);
  85         else
  86                 errx(1, "can't find your tty");
  87         if (!(mytty = ttyname(myttyfd)))
  88                 errx(1, "can't find your tty's name");
  89         if ((cp = strrchr(mytty, '/')))
  90                 mytty = cp + 1;
  91         if (term_chk(mytty, &mymsgok, &atime, 1))
  92                 exit(1);
  93         if (!mymsgok)
  94                 warnx("you have write permission turned off (man mesg)");
  95
  96         myuid = getuid();
  97
  98         /* check args */
  99         switch (argc) {
 100         case 2:
 101                 search_utmp(argv[1], tty, sizeof tty, mytty, myuid);
 102                 do_write(tty, mytty, myuid, &mymsgok);
 103                 break;
 104         case 3:
 105                 if (!strncmp(argv[2], _PATH_DEV, strlen(_PATH_DEV)))
 106                         argv[2] += strlen(_PATH_DEV);
 107                 if (utmp_chk(argv[1], argv[2]))
 108                         errx(1, "%s is not logged in on %s", argv[1], argv[2]);
 109                 if (term_chk(argv[2], &msgsok, &atime, 1))
 110                         exit(1);
 111                 if (myuid && !msgsok)
 112                         errx(1, "%s has messages disabled on %s", argv[1], argv[2]);
 113                 do_write(argv[2], mytty, myuid, &mymsgok);
 114                 break;
 115         default:
 116                 usage();
 117         }
 118         done(0);
 119         return (0);
 120 }
 121
 122 static void
 123 usage(void)
 124 {
 125         fprintf(stderr, "usage: write user [tty]\n");
 126         exit(1);
 127 }
 128
 129 /*
 130  * utmp_chk - checks that the given user is actually logged in on
 131  *     the given tty
 132  */
 133 static int
 134 utmp_chk(const char *user, const char *tty)
 135 {
 136         struct utmp u;
 137         int ufd;
 138
 139         if ((ufd = open(_PATH_UTMP, O_RDONLY)) < 0)
 140                 err(1, "open failed: %s\n", _PATH_UTMP);
 141
 142         while (read(ufd, (char *) &u, sizeof(u)) == sizeof(u)) {
 143                 if (strncmp(user, u.ut_name, sizeof(u.ut_name)) == 0 &&
 144                     strncmp(tty, u.ut_line, sizeof(u.ut_line)) == 0) {
 145                         close(ufd);
 146                         return(0);
 147                 }
 148         }
 149
 150         close(ufd);
 151         return(1);
 152 }
 153
 154 /*
 155  * search_utmp - search utmp for the "best" terminal to write to
 156  *
 157  * Ignores terminals with messages disabled, and of the rest, returns
 158  * the one with the most recent access time.  Returns as value the number
 159  * of the user's terminals with messages enabled, or -1 if the user is
 160  * not logged in at all.
 161  *
 162  * Special case for writing to yourself - ignore the terminal you're
 163  * writing from, unless that's the only terminal with messages enabled.
 164  */
 165 static void
 166 search_utmp(const char *user, char *tty, size_t ttyl, const char *mytty, uid_t myuid)
 167 {
 168         struct utmp u;
 169         time_t bestatime, atime;
 170         int ufd, nloggedttys, nttys, msgsok, user_is_me;
 171         char atty[UT_LINESIZE + 1];
 172
 173         if ((ufd = open(_PATH_UTMP, O_RDONLY)) < 0)
 174                 err(1, "open failed: %s", _PATH_UTMP);
 175
 176         nloggedttys = nttys = 0;
 177         bestatime = 0;
 178         user_is_me = 0;
 179         while (read(ufd, (char *) &u, sizeof(u)) == sizeof(u))
 180                 if (strncmp(user, u.ut_name, sizeof(u.ut_name)) == 0) {
 181                         ++nloggedttys;
 182                         strlcpy(atty, u.ut_line, ttyl);
 183                         if (term_chk(atty, &msgsok, &atime, 0))
 184                                 continue;       /* bad term? skip */
 185                         if (myuid && !msgsok)
 186                                 continue;       /* skip ttys with msgs off */
 187                         if (strcmp(atty, mytty) == 0) {
 188                                 user_is_me = 1;
 189                                 continue;       /* don't write to yourself */
 190                         }
 191                         ++nttys;
 192                         if (atime > bestatime) {
 193                                 bestatime = atime;
 194                                 strlcpy(tty, atty, ttyl);
 195                         }
 196                 }
 197
 198         close(ufd);
 199         if (nloggedttys == 0)
 200                 errx(1, "%s is not logged in", user);
 201         if (nttys == 0) {
 202                 if (user_is_me) {               /* ok, so write to yourself! */
 203                         strlcpy(tty, mytty, ttyl);
 204                         return;
 205                 }
 206                 errx(1, "%s has messages disabled", user);
 207         } else if (nttys > 1) {
 208                 warnx("%s is logged in more than once; writing to %s", user, tty);
 209         }
 210 }
 211
 212 /*
 213  * term_chk - check that a terminal exists, and get the message bit
 214  *     and the access time
 215  */
 216 static int
 217 term_chk(const char *tty, int *msgsokP, time_t *atimeP, int showerror)
 218 {
 219         struct stat s;
 220         char path[MAXPATHLEN];
 221
 222         snprintf(path, sizeof(path), "%s%s", _PATH_DEV, tty);
 223         if (stat(path, &s) < 0) {
 224                 if (showerror)
 225                         warn("%s", path);
 226                 return(1);
 227         }
 228         *msgsokP = (s.st_mode & S_IWGRP) != 0;  /* group write bit */
 229         *atimeP = s.st_atime;
 230         return(0);
 231 }
 232
 233 /*
 234  * do_write - actually make the connection
 235  */
 236 static void
 237 do_write(const char *tty, const char *mytty, uid_t myuid, int *mymsgok)
 238 {
 239         const char *login;
 240         char *nows;
 241         struct passwd *pwd;
 242         time_t now;
 243         char path[MAXPATHLEN], host[MAXHOSTNAMELEN], line[512];
 244
 245         /* Determine our login name before we reopen() stdout */
 246         if ((login = getlogin()) == NULL) {
 247                 if ((pwd = getpwuid(myuid)))
 248                         login = pwd->pw_name;
 249                 else
 250                         login = "???";
 251         }
 252
 253         snprintf(path, sizeof(path), "%s%s", _PATH_DEV, tty);
 254         if ((freopen(path, "w", stdout)) == NULL)
 255                 err(1, "%s", path);
 256
 257         signal(SIGINT, done);
 258         signal(SIGHUP, done);
 259
 260         /* print greeting */
 261         if (gethostname(host, sizeof(host)) < 0)
 262                 strlcpy(host, "???", sizeof host);
 263         now = time((time_t *)NULL);
 264         nows = ctime(&now);
 265         nows[16] = '\0';
 266         printf("\r\n\007\007\007Message from %s@%s on %s at %s (%s %s replies)...\r\n",
 267             login, host, mytty, nows + 11, login, *mymsgok == 0 ? "does not accept" : "accepts");
 268
 269         while (fgets(line, sizeof(line), stdin) != NULL)
 270                 wr_fputs(line);
 271 }
 272
 273 /*
 274  * done - cleanup and exit
 275  */
 276 static void
 277 done(__unused int n)
 278 {
 279         printf("EOF\r\n");
 280         exit(0);
 281 }
 282
 283 /*
 284  * wr_fputs - like fputs(), but makes control characters visible and
 285  *     turns \n into \r\n
 286  */
 287 static void
 288 wr_fputs(unsigned char *s)
 289 {
 290
 291 #define PUTC(c) if (putchar(c) == EOF) err(1, NULL);
 292
 293         for (; *s != '\0'; ++s) {
 294                 if (*s == '\n') {
 295                         PUTC('\r');
 296                 } else if (((*s & 0x80) && *s < 0xA0) ||
 297                            /* disable upper controls */
 298                            (!isprint(*s) && !isspace(*s) &&
 299                             *s != '\a' && *s != '\b')
 300                           ) {
 301                         if (*s & 0x80) {
 302                                 *s &= ~0x80;
 303                                 PUTC('M');
 304                                 PUTC('-');
 305                         }
 306                         if (iscntrl(*s)) {
 307                                 *s ^= 0x40;
 308                                 PUTC('^');
 309                         }
 310                 }
 311                 PUTC(*s);
 312         }
 313         return;
 314 #undef PUTC
 315 }