write.c revision 216370 
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 * 4. Neither the name of the University nor the names of its contributors
17 *    may be used to endorse or promote products derived from this software
18 *    without specific prior written permission.
19 *
20 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30 * SUCH DAMAGE.
31 */
32
33#ifndef lint
34static const char copyright[] =
35"@(#) Copyright (c) 1989, 1993\n\
36	The Regents of the University of California.  All rights reserved.\n";
37#endif
38
39#if 0
40#ifndef lint
41static char sccsid[] = "@(#)write.c	8.1 (Berkeley) 6/6/93";
42#endif
43#endif
44
45#include <sys/cdefs.h>
46__FBSDID("$FreeBSD: head/usr.bin/write/write.c 216370 2010-12-11 08:32:16Z joel $");
47
48#include <sys/param.h>
49#include <sys/signal.h>
50#include <sys/stat.h>
51#include <sys/file.h>
52#include <sys/time.h>
53#include <ctype.h>
54#include <err.h>
55#include <locale.h>
56#include <paths.h>
57#include <pwd.h>
58#include <stdio.h>
59#include <stdlib.h>
60#include <string.h>
61#include <unistd.h>
62#include <utmpx.h>
63
64void done(int);
65void do_write(char *, char *, uid_t);
66static void usage(void);
67int term_chk(char *, int *, time_t *, int);
68void wr_fputs(unsigned char *s);
69void search_utmp(char *, char *, char *, uid_t);
70int utmp_chk(char *, char *);
71
72int
73main(int argc, char **argv)
74{
75	time_t atime;
76	uid_t myuid;
77	int msgsok, myttyfd;
78	char tty[MAXPATHLEN], *mytty;
79
80	(void)setlocale(LC_CTYPE, "");
81
82	while (getopt(argc, argv, "") != -1)
83		usage();
84	argc -= optind;
85	argv += optind;
86
87	/* check that sender has write enabled */
88	if (isatty(fileno(stdin)))
89		myttyfd = fileno(stdin);
90	else if (isatty(fileno(stdout)))
91		myttyfd = fileno(stdout);
92	else if (isatty(fileno(stderr)))
93		myttyfd = fileno(stderr);
94	else
95		errx(1, "can't find your tty");
96	if (!(mytty = ttyname(myttyfd)))
97		errx(1, "can't find your tty's name");
98	if (!strncmp(mytty, _PATH_DEV, strlen(_PATH_DEV)))
99		mytty += strlen(_PATH_DEV);
100	if (term_chk(mytty, &msgsok, &atime, 1))
101		exit(1);
102	if (!msgsok)
103		errx(1, "you have write permission turned off");
104
105	myuid = getuid();
106
107	/* check args */
108	switch (argc) {
109	case 1:
110		search_utmp(argv[0], tty, mytty, myuid);
111		do_write(tty, mytty, myuid);
112		break;
113	case 2:
114		if (!strncmp(argv[1], _PATH_DEV, strlen(_PATH_DEV)))
115			argv[1] += strlen(_PATH_DEV);
116		if (utmp_chk(argv[0], argv[1]))
117			errx(1, "%s is not logged in on %s", argv[0], argv[1]);
118		if (term_chk(argv[1], &msgsok, &atime, 1))
119			exit(1);
120		if (myuid && !msgsok)
121			errx(1, "%s has messages disabled on %s", argv[0], argv[1]);
122		do_write(argv[1], mytty, myuid);
123		break;
124	default:
125		usage();
126	}
127	done(0);
128	return (0);
129}
130
131static void
132usage(void)
133{
134	(void)fprintf(stderr, "usage: write user [tty]\n");
135	exit(1);
136}
137
138/*
139 * utmp_chk - checks that the given user is actually logged in on
140 *     the given tty
141 */
142int
143utmp_chk(char *user, char *tty)
144{
145	struct utmpx lu, *u;
146
147	strncpy(lu.ut_line, tty, sizeof lu.ut_line);
148	setutxent();
149	while ((u = getutxline(&lu)) != NULL)
150		if (u->ut_type == USER_PROCESS &&
151		    strcmp(user, u->ut_user) == 0) {
152			endutxent();
153			return(0);
154		}
155	endutxent();
156	return(1);
157}
158
159/*
160 * search_utmp - search utmp for the "best" terminal to write to
161 *
162 * Ignores terminals with messages disabled, and of the rest, returns
163 * the one with the most recent access time.  Returns as value the number
164 * of the user's terminals with messages enabled, or -1 if the user is
165 * not logged in at all.
166 *
167 * Special case for writing to yourself - ignore the terminal you're
168 * writing from, unless that's the only terminal with messages enabled.
169 */
170void
171search_utmp(char *user, char *tty, char *mytty, uid_t myuid)
172{
173	struct utmpx *u;
174	time_t bestatime, atime;
175	int nloggedttys, nttys, msgsok, user_is_me;
176
177	nloggedttys = nttys = 0;
178	bestatime = 0;
179	user_is_me = 0;
180
181	setutxent();
182	while ((u = getutxent()) != NULL)
183		if (u->ut_type == USER_PROCESS &&
184		    strcmp(user, u->ut_user) == 0) {
185			++nloggedttys;
186			if (term_chk(u->ut_line, &msgsok, &atime, 0))
187				continue;	/* bad term? skip */
188			if (myuid && !msgsok)
189				continue;	/* skip ttys with msgs off */
190			if (strcmp(u->ut_line, mytty) == 0) {
191				user_is_me = 1;
192				continue;	/* don't write to yourself */
193			}
194			++nttys;
195			if (atime > bestatime) {
196				bestatime = atime;
197				(void)strlcpy(tty, u->ut_line, MAXPATHLEN);
198			}
199		}
200	endutxent();
201
202	if (nloggedttys == 0)
203		errx(1, "%s is not logged in", user);
204	if (nttys == 0) {
205		if (user_is_me) {		/* ok, so write to yourself! */
206			(void)strlcpy(tty, mytty, MAXPATHLEN);
207			return;
208		}
209		errx(1, "%s has messages disabled", user);
210	} else if (nttys > 1) {
211		warnx("%s is logged in more than once; writing to %s", user, tty);
212	}
213}
214
215/*
216 * term_chk - check that a terminal exists, and get the message bit
217 *     and the access time
218 */
219int
220term_chk(char *tty, int *msgsokP, time_t *atimeP, int showerror)
221{
222	struct stat s;
223	char path[MAXPATHLEN];
224
225	(void)snprintf(path, sizeof(path), "%s%s", _PATH_DEV, tty);
226	if (stat(path, &s) < 0) {
227		if (showerror)
228			warn("%s", path);
229		return(1);
230	}
231	*msgsokP = (s.st_mode & (S_IWRITE >> 3)) != 0;	/* group write bit */
232	*atimeP = s.st_atime;
233	return(0);
234}
235
236/*
237 * do_write - actually make the connection
238 */
239void
240do_write(char *tty, char *mytty, uid_t myuid)
241{
242	const char *login;
243	char *nows;
244	struct passwd *pwd;
245	time_t now;
246	char path[MAXPATHLEN], host[MAXHOSTNAMELEN], line[512];
247
248	/* Determine our login name before we reopen() stdout */
249	if ((login = getlogin()) == NULL) {
250		if ((pwd = getpwuid(myuid)))
251			login = pwd->pw_name;
252		else
253			login = "???";
254	}
255
256	(void)snprintf(path, sizeof(path), "%s%s", _PATH_DEV, tty);
257	if ((freopen(path, "w", stdout)) == NULL)
258		err(1, "%s", path);
259
260	(void)signal(SIGINT, done);
261	(void)signal(SIGHUP, done);
262
263	/* print greeting */
264	if (gethostname(host, sizeof(host)) < 0)
265		(void)strcpy(host, "???");
266	now = time((time_t *)NULL);
267	nows = ctime(&now);
268	nows[16] = '\0';
269	(void)printf("\r\n\007\007\007Message from %s@%s on %s at %s ...\r\n",
270	    login, host, mytty, nows + 11);
271
272	while (fgets(line, sizeof(line), stdin) != NULL)
273		wr_fputs(line);
274}
275
276/*
277 * done - cleanup and exit
278 */
279void
280done(int n __unused)
281{
282	(void)printf("EOF\r\n");
283	exit(0);
284}
285
286/*
287 * wr_fputs - like fputs(), but makes control characters visible and
288 *     turns \n into \r\n
289 */
290void
291wr_fputs(unsigned char *s)
292{
293
294#define	PUTC(c)	if (putchar(c) == EOF) err(1, NULL);
295
296	for (; *s != '\0'; ++s) {
297		if (*s == '\n') {
298			PUTC('\r');
299		} else if (((*s & 0x80) && *s < 0xA0) ||
300			   /* disable upper controls */
301			   (!isprint(*s) && !isspace(*s) &&
302			    *s != '\a' && *s != '\b')
303			  ) {
304			if (*s & 0x80) {
305				*s &= ~0x80;
306				PUTC('M');
307				PUTC('-');
308			}
309			if (iscntrl(*s)) {
310				*s ^= 0x40;
311				PUTC('^');
312			}
313		}
314		PUTC(*s);
315	}
316	return;
317#undef PUTC
318}
319