write.c revision 28794 
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
37#ifndef lint
38static const char copyright[] =
39"@(#) Copyright (c) 1989, 1993\n\
40	The Regents of the University of California.  All rights reserved.\n";
41#endif /* not lint */
42
43#ifndef lint
44#if 0
45static char sccsid[] = "@(#)write.c	8.1 (Berkeley) 6/6/93";
46#endif
47static const char rcsid[] =
48	"$Id$";
49#endif /* not lint */
50
51#include <sys/param.h>
52#include <sys/signal.h>
53#include <sys/stat.h>
54#include <sys/file.h>
55#include <sys/time.h>
56#include <ctype.h>
57#include <err.h>
58#include <paths.h>
59#include <pwd.h>
60#include <stdio.h>
61#include <string.h>
62#include <unistd.h>
63#include <utmp.h>
64
65void done __P((void));
66void do_write __P((char *, char *, uid_t));
67static void usage __P((void));
68int term_chk __P((char *, int *, time_t *, int));
69void wr_fputs __P((unsigned char *s));
70void search_utmp __P((char *, char *, char *, uid_t));
71int utmp_chk __P((char *, char *));
72
73int
74main(argc, argv)
75	int argc;
76	char **argv;
77{
78	register char *cp;
79	time_t atime;
80	uid_t myuid;
81	int msgsok, myttyfd;
82	char tty[MAXPATHLEN], *mytty;
83
84	/* check that sender has write enabled */
85	if (isatty(fileno(stdin)))
86		myttyfd = fileno(stdin);
87	else if (isatty(fileno(stdout)))
88		myttyfd = fileno(stdout);
89	else if (isatty(fileno(stderr)))
90		myttyfd = fileno(stderr);
91	else
92		errx(1, "can't find your tty");
93	if (!(mytty = ttyname(myttyfd)))
94		errx(1, "can't find your tty's name");
95	if ((cp = rindex(mytty, '/')))
96		mytty = cp + 1;
97	if (term_chk(mytty, &msgsok, &atime, 1))
98		exit(1);
99	if (!msgsok)
100		errx(1, "you have write permission turned off");
101
102	myuid = getuid();
103
104	/* check args */
105	switch (argc) {
106	case 2:
107		search_utmp(argv[1], tty, mytty, myuid);
108		do_write(tty, mytty, myuid);
109		break;
110	case 3:
111		if (!strncmp(argv[2], _PATH_DEV, strlen(_PATH_DEV)))
112			argv[2] += strlen(_PATH_DEV);
113		if (utmp_chk(argv[1], argv[2]))
114			errx(1, "%s is not logged in on %s", argv[1], argv[2]);
115		if (term_chk(argv[2], &msgsok, &atime, 1))
116			exit(1);
117		if (myuid && !msgsok)
118			errx(1, "%s has messages disabled on %s", argv[1], argv[2]);
119		do_write(argv[2], mytty, myuid);
120		break;
121	default:
122		usage();
123	}
124	done();
125	return (0);
126}
127
128static void
129usage()
130{
131	(void)fprintf(stderr, "usage: write user [tty]\n");
132	exit(1);
133}
134
135/*
136 * utmp_chk - checks that the given user is actually logged in on
137 *     the given tty
138 */
139int
140utmp_chk(user, tty)
141	char *user, *tty;
142{
143	struct utmp u;
144	int ufd;
145
146	if ((ufd = open(_PATH_UTMP, O_RDONLY)) < 0)
147		return(0);	/* ignore error, shouldn't happen anyway */
148
149	while (read(ufd, (char *) &u, sizeof(u)) == sizeof(u))
150		if (strncmp(user, u.ut_name, sizeof(u.ut_name)) == 0 &&
151		    strncmp(tty, u.ut_line, sizeof(u.ut_line)) == 0) {
152			(void)close(ufd);
153			return(0);
154		}
155
156	(void)close(ufd);
157	return(1);
158}
159
160/*
161 * search_utmp - search utmp for the "best" terminal to write to
162 *
163 * Ignores terminals with messages disabled, and of the rest, returns
164 * the one with the most recent access time.  Returns as value the number
165 * of the user's terminals with messages enabled, or -1 if the user is
166 * not logged in at all.
167 *
168 * Special case for writing to yourself - ignore the terminal you're
169 * writing from, unless that's the only terminal with messages enabled.
170 */
171void
172search_utmp(user, tty, mytty, myuid)
173	char *user, *tty, *mytty;
174	uid_t myuid;
175{
176	struct utmp u;
177	time_t bestatime, atime;
178	int ufd, nloggedttys, nttys, msgsok, user_is_me;
179	char atty[UT_LINESIZE + 1];
180
181	if ((ufd = open(_PATH_UTMP, O_RDONLY)) < 0)
182		err(1, "utmp");
183
184	nloggedttys = nttys = 0;
185	bestatime = 0;
186	user_is_me = 0;
187	while (read(ufd, (char *) &u, sizeof(u)) == sizeof(u))
188		if (strncmp(user, u.ut_name, sizeof(u.ut_name)) == 0) {
189			++nloggedttys;
190			(void)strncpy(atty, u.ut_line, UT_LINESIZE);
191			atty[UT_LINESIZE] = '\0';
192			if (term_chk(atty, &msgsok, &atime, 0))
193				continue;	/* bad term? skip */
194			if (myuid && !msgsok)
195				continue;	/* skip ttys with msgs off */
196			if (strcmp(atty, mytty) == 0) {
197				user_is_me = 1;
198				continue;	/* don't write to yourself */
199			}
200			++nttys;
201			if (atime > bestatime) {
202				bestatime = atime;
203				(void)strcpy(tty, atty);
204			}
205		}
206
207	(void)close(ufd);
208	if (nloggedttys == 0)
209		errx(1, "%s is not logged in", user);
210	if (nttys == 0) {
211		if (user_is_me) {		/* ok, so write to yourself! */
212			(void)strcpy(tty, mytty);
213			return;
214		}
215		errx(1, "%s has messages disabled", user);
216	} else if (nttys > 1) {
217		warnx("%s is logged in more than once; writing to %s", user, tty);
218	}
219}
220
221/*
222 * term_chk - check that a terminal exists, and get the message bit
223 *     and the access time
224 */
225int
226term_chk(tty, msgsokP, atimeP, showerror)
227	char *tty;
228	int *msgsokP, showerror;
229	time_t *atimeP;
230{
231	struct stat s;
232	char path[MAXPATHLEN];
233
234	(void)snprintf(path, sizeof(path), "%s%s", _PATH_DEV, tty);
235	if (stat(path, &s) < 0) {
236		if (showerror)
237			warn("%s", path);
238		return(1);
239	}
240	*msgsokP = (s.st_mode & (S_IWRITE >> 3)) != 0;	/* group write bit */
241	*atimeP = s.st_atime;
242	return(0);
243}
244
245/*
246 * do_write - actually make the connection
247 */
248void
249do_write(tty, mytty, myuid)
250	char *tty, *mytty;
251	uid_t myuid;
252{
253	register char *login, *nows;
254	register struct passwd *pwd;
255	time_t now;
256	char path[MAXPATHLEN], host[MAXHOSTNAMELEN], line[512];
257
258	/* Determine our login name before the we reopen() stdout */
259	if ((login = getlogin()) == NULL)
260		if ((pwd = getpwuid(myuid)))
261			login = pwd->pw_name;
262		else
263			login = "???";
264
265	(void)snprintf(path, sizeof(path), "%s%s", _PATH_DEV, tty);
266	if ((freopen(path, "w", stdout)) == NULL)
267		err(1, "%s", path);
268
269	(void)signal(SIGINT, done);
270	(void)signal(SIGHUP, done);
271
272	/* print greeting */
273	if (gethostname(host, sizeof(host)) < 0)
274		(void)strcpy(host, "???");
275	now = time((time_t *)NULL);
276	nows = ctime(&now);
277	nows[16] = '\0';
278	(void)printf("\r\n\007\007\007Message from %s@%s on %s at %s ...\r\n",
279	    login, host, mytty, nows + 11);
280
281	while (fgets(line, sizeof(line), stdin) != NULL)
282		wr_fputs(line);
283}
284
285/*
286 * done - cleanup and exit
287 */
288void
289done()
290{
291	(void)printf("EOF\r\n");
292	exit(0);
293}
294
295/*
296 * wr_fputs - like fputs(), but makes control characters visible and
297 *     turns \n into \r\n
298 */
299void
300wr_fputs(s)
301	register unsigned char *s;
302{
303
304#define	PUTC(c)	if (putchar(c) == EOF) err(1, NULL);
305
306	for (; *s != '\0'; ++s) {
307		if (*s == '\n') {
308			PUTC('\r');
309		} else if (!isprint(*s) && !isspace(*s) && *s != '\007') {
310			if (*s & 0x80) {
311				*s &= ~0x80;
312				PUTC('M');
313				PUTC('-');
314			}
315			if (iscntrl(*s)) {
316				*s ^= 0x40;
317				PUTC('^');
318			}
319		}
320		PUTC(*s);
321	}
322	return;
323#undef PUTC
324}
325