write.c revision 200160 
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
42
43#if 0
44#ifndef lint
45static char sccsid[] = "@(#)write.c	8.1 (Berkeley) 6/6/93";
46#endif
47#endif
48
49#include <sys/cdefs.h>
50__FBSDID("$FreeBSD: head/usr.bin/write/write.c 200160 2009-12-05 20:22:26Z ed $");
51
52#include <sys/param.h>
53#include <sys/signal.h>
54#include <sys/stat.h>
55#include <sys/file.h>
56#include <sys/time.h>
57#include <ctype.h>
58#include <err.h>
59#include <locale.h>
60#include <paths.h>
61#include <pwd.h>
62#include <stdio.h>
63#include <stdlib.h>
64#include <string.h>
65#define	_ULOG_POSIX_NAMES
66#include <ulog.h>
67#include <unistd.h>
68
69void done(int);
70void do_write(char *, char *, uid_t);
71static void usage(void);
72int term_chk(char *, int *, time_t *, int);
73void wr_fputs(unsigned char *s);
74void search_utmp(char *, char *, char *, uid_t);
75int utmp_chk(char *, char *);
76
77int
78main(int argc, char **argv)
79{
80	time_t atime;
81	uid_t myuid;
82	int msgsok, myttyfd;
83	char tty[MAXPATHLEN], *mytty;
84
85	(void)setlocale(LC_CTYPE, "");
86
87	while (getopt(argc, argv, "") != -1)
88		usage();
89	argc -= optind;
90	argv += optind;
91
92	/* check that sender has write enabled */
93	if (isatty(fileno(stdin)))
94		myttyfd = fileno(stdin);
95	else if (isatty(fileno(stdout)))
96		myttyfd = fileno(stdout);
97	else if (isatty(fileno(stderr)))
98		myttyfd = fileno(stderr);
99	else
100		errx(1, "can't find your tty");
101	if (!(mytty = ttyname(myttyfd)))
102		errx(1, "can't find your tty's name");
103	if (!strncmp(mytty, _PATH_DEV, strlen(_PATH_DEV)))
104		mytty += strlen(_PATH_DEV);
105	if (term_chk(mytty, &msgsok, &atime, 1))
106		exit(1);
107	if (!msgsok)
108		errx(1, "you have write permission turned off");
109
110	myuid = getuid();
111
112	/* check args */
113	switch (argc) {
114	case 1:
115		search_utmp(argv[0], tty, mytty, myuid);
116		do_write(tty, mytty, myuid);
117		break;
118	case 2:
119		if (!strncmp(argv[1], _PATH_DEV, strlen(_PATH_DEV)))
120			argv[1] += strlen(_PATH_DEV);
121		if (utmp_chk(argv[0], argv[1]))
122			errx(1, "%s is not logged in on %s", argv[0], argv[1]);
123		if (term_chk(argv[1], &msgsok, &atime, 1))
124			exit(1);
125		if (myuid && !msgsok)
126			errx(1, "%s has messages disabled on %s", argv[0], argv[1]);
127		do_write(argv[1], mytty, myuid);
128		break;
129	default:
130		usage();
131	}
132	done(0);
133	return (0);
134}
135
136static void
137usage(void)
138{
139	(void)fprintf(stderr, "usage: write user [tty]\n");
140	exit(1);
141}
142
143/*
144 * utmp_chk - checks that the given user is actually logged in on
145 *     the given tty
146 */
147int
148utmp_chk(char *user, char *tty)
149{
150	struct utmpx lu, *u;
151
152	strncpy(lu.ut_line, tty, sizeof lu.ut_line);
153	setutxent();
154	while ((u = getutxline(&lu)) != NULL)
155		if (u->ut_type == USER_PROCESS &&
156		    strcmp(user, u->ut_user) == 0) {
157			endutxent();
158			return(0);
159		}
160	endutxent();
161	return(1);
162}
163
164/*
165 * search_utmp - search utmp for the "best" terminal to write to
166 *
167 * Ignores terminals with messages disabled, and of the rest, returns
168 * the one with the most recent access time.  Returns as value the number
169 * of the user's terminals with messages enabled, or -1 if the user is
170 * not logged in at all.
171 *
172 * Special case for writing to yourself - ignore the terminal you're
173 * writing from, unless that's the only terminal with messages enabled.
174 */
175void
176search_utmp(char *user, char *tty, char *mytty, uid_t myuid)
177{
178	struct utmpx *u;
179	time_t bestatime, atime;
180	int nloggedttys, nttys, msgsok, user_is_me;
181
182	nloggedttys = nttys = 0;
183	bestatime = 0;
184	user_is_me = 0;
185
186	setutxent();
187	while ((u = getutxent()) != NULL)
188		if (u->ut_type == USER_PROCESS &&
189		    strcmp(user, u->ut_user) == 0) {
190			++nloggedttys;
191			if (term_chk(u->ut_line, &msgsok, &atime, 0))
192				continue;	/* bad term? skip */
193			if (myuid && !msgsok)
194				continue;	/* skip ttys with msgs off */
195			if (strcmp(u->ut_line, mytty) == 0) {
196				user_is_me = 1;
197				continue;	/* don't write to yourself */
198			}
199			++nttys;
200			if (atime > bestatime) {
201				bestatime = atime;
202				(void)strlcpy(tty, u->ut_line, MAXPATHLEN);
203			}
204		}
205	endutxent();
206
207	if (nloggedttys == 0)
208		errx(1, "%s is not logged in", user);
209	if (nttys == 0) {
210		if (user_is_me) {		/* ok, so write to yourself! */
211			(void)strlcpy(tty, mytty, MAXPATHLEN);
212			return;
213		}
214		errx(1, "%s has messages disabled", user);
215	} else if (nttys > 1) {
216		warnx("%s is logged in more than once; writing to %s", user, tty);
217	}
218}
219
220/*
221 * term_chk - check that a terminal exists, and get the message bit
222 *     and the access time
223 */
224int
225term_chk(char *tty, int *msgsokP, time_t *atimeP, int showerror)
226{
227	struct stat s;
228	char path[MAXPATHLEN];
229
230	(void)snprintf(path, sizeof(path), "%s%s", _PATH_DEV, tty);
231	if (stat(path, &s) < 0) {
232		if (showerror)
233			warn("%s", path);
234		return(1);
235	}
236	*msgsokP = (s.st_mode & (S_IWRITE >> 3)) != 0;	/* group write bit */
237	*atimeP = s.st_atime;
238	return(0);
239}
240
241/*
242 * do_write - actually make the connection
243 */
244void
245do_write(char *tty, char *mytty, uid_t myuid)
246{
247	const char *login;
248	char *nows;
249	struct passwd *pwd;
250	time_t now;
251	char path[MAXPATHLEN], host[MAXHOSTNAMELEN], line[512];
252
253	/* Determine our login name before we reopen() stdout */
254	if ((login = getlogin()) == NULL) {
255		if ((pwd = getpwuid(myuid)))
256			login = pwd->pw_name;
257		else
258			login = "???";
259	}
260
261	(void)snprintf(path, sizeof(path), "%s%s", _PATH_DEV, tty);
262	if ((freopen(path, "w", stdout)) == NULL)
263		err(1, "%s", path);
264
265	(void)signal(SIGINT, done);
266	(void)signal(SIGHUP, done);
267
268	/* print greeting */
269	if (gethostname(host, sizeof(host)) < 0)
270		(void)strcpy(host, "???");
271	now = time((time_t *)NULL);
272	nows = ctime(&now);
273	nows[16] = '\0';
274	(void)printf("\r\n\007\007\007Message from %s@%s on %s at %s ...\r\n",
275	    login, host, mytty, nows + 11);
276
277	while (fgets(line, sizeof(line), stdin) != NULL)
278		wr_fputs(line);
279}
280
281/*
282 * done - cleanup and exit
283 */
284void
285done(int n __unused)
286{
287	(void)printf("EOF\r\n");
288	exit(0);
289}
290
291/*
292 * wr_fputs - like fputs(), but makes control characters visible and
293 *     turns \n into \r\n
294 */
295void
296wr_fputs(unsigned char *s)
297{
298
299#define	PUTC(c)	if (putchar(c) == EOF) err(1, NULL);
300
301	for (; *s != '\0'; ++s) {
302		if (*s == '\n') {
303			PUTC('\r');
304		} else if (((*s & 0x80) && *s < 0xA0) ||
305			   /* disable upper controls */
306			   (!isprint(*s) && !isspace(*s) &&
307			    *s != '\a' && *s != '\b')
308			  ) {
309			if (*s & 0x80) {
310				*s &= ~0x80;
311				PUTC('M');
312				PUTC('-');
313			}
314			if (iscntrl(*s)) {
315				*s ^= 0x40;
316				PUTC('^');
317			}
318		}
319		PUTC(*s);
320	}
321	return;
322#undef PUTC
323}
324