write.c revision 139718 
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 139718 2005-01-05 11:52:40Z cognet $");
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#include <unistd.h>
66#include <utmp.h>
67
68void done(int);
69void do_write(char *, char *, uid_t);
70static void usage(void);
71int term_chk(char *, int *, time_t *, int);
72void wr_fputs(unsigned char *s);
73void search_utmp(char *, char *, char *, uid_t);
74int utmp_chk(char *, char *);
75
76int
77main(int argc, char **argv)
78{
79	char *cp;
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 ((cp = rindex(mytty, '/')))
104		mytty = cp + 1;
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 utmp u;
151	int ufd;
152
153	if ((ufd = open(_PATH_UTMP, O_RDONLY)) < 0)
154		return(0);	/* ignore error, shouldn't happen anyway */
155
156	while (read(ufd, (char *) &u, sizeof(u)) == sizeof(u))
157		if (strncmp(user, u.ut_name, sizeof(u.ut_name)) == 0 &&
158		    strncmp(tty, u.ut_line, sizeof(u.ut_line)) == 0) {
159			(void)close(ufd);
160			return(0);
161		}
162
163	(void)close(ufd);
164	return(1);
165}
166
167/*
168 * search_utmp - search utmp for the "best" terminal to write to
169 *
170 * Ignores terminals with messages disabled, and of the rest, returns
171 * the one with the most recent access time.  Returns as value the number
172 * of the user's terminals with messages enabled, or -1 if the user is
173 * not logged in at all.
174 *
175 * Special case for writing to yourself - ignore the terminal you're
176 * writing from, unless that's the only terminal with messages enabled.
177 */
178void
179search_utmp(char *user, char *tty, char *mytty, uid_t myuid)
180{
181	struct utmp u;
182	time_t bestatime, atime;
183	int ufd, nloggedttys, nttys, msgsok, user_is_me;
184	char atty[UT_LINESIZE + 1];
185
186	if ((ufd = open(_PATH_UTMP, O_RDONLY)) < 0)
187		err(1, "utmp");
188
189	nloggedttys = nttys = 0;
190	bestatime = 0;
191	user_is_me = 0;
192	while (read(ufd, (char *) &u, sizeof(u)) == sizeof(u))
193		if (strncmp(user, u.ut_name, sizeof(u.ut_name)) == 0) {
194			++nloggedttys;
195			(void)strncpy(atty, u.ut_line, UT_LINESIZE);
196			atty[UT_LINESIZE] = '\0';
197			if (term_chk(atty, &msgsok, &atime, 0))
198				continue;	/* bad term? skip */
199			if (myuid && !msgsok)
200				continue;	/* skip ttys with msgs off */
201			if (strcmp(atty, mytty) == 0) {
202				user_is_me = 1;
203				continue;	/* don't write to yourself */
204			}
205			++nttys;
206			if (atime > bestatime) {
207				bestatime = atime;
208				(void)strcpy(tty, atty);
209			}
210		}
211
212	(void)close(ufd);
213	if (nloggedttys == 0)
214		errx(1, "%s is not logged in", user);
215	if (nttys == 0) {
216		if (user_is_me) {		/* ok, so write to yourself! */
217			(void)strcpy(tty, mytty);
218			return;
219		}
220		errx(1, "%s has messages disabled", user);
221	} else if (nttys > 1) {
222		warnx("%s is logged in more than once; writing to %s", user, tty);
223	}
224}
225
226/*
227 * term_chk - check that a terminal exists, and get the message bit
228 *     and the access time
229 */
230int
231term_chk(char *tty, int *msgsokP, time_t *atimeP, int showerror)
232{
233	struct stat s;
234	char path[MAXPATHLEN];
235
236	(void)snprintf(path, sizeof(path), "%s%s", _PATH_DEV, tty);
237	if (stat(path, &s) < 0) {
238		if (showerror)
239			warn("%s", path);
240		return(1);
241	}
242	*msgsokP = (s.st_mode & (S_IWRITE >> 3)) != 0;	/* group write bit */
243	*atimeP = s.st_atime;
244	return(0);
245}
246
247/*
248 * do_write - actually make the connection
249 */
250void
251do_write(char *tty, char *mytty, uid_t myuid)
252{
253	const char *login;
254	char *nows;
255	struct passwd *pwd;
256	time_t now;
257	char path[MAXPATHLEN], host[MAXHOSTNAMELEN], line[512];
258
259	/* Determine our login name before we reopen() stdout */
260	if ((login = getlogin()) == NULL) {
261		if ((pwd = getpwuid(myuid)))
262			login = pwd->pw_name;
263		else
264			login = "???";
265	}
266
267	(void)snprintf(path, sizeof(path), "%s%s", _PATH_DEV, tty);
268	if ((freopen(path, "w", stdout)) == NULL)
269		err(1, "%s", path);
270
271	(void)signal(SIGINT, done);
272	(void)signal(SIGHUP, done);
273
274	/* print greeting */
275	if (gethostname(host, sizeof(host)) < 0)
276		(void)strcpy(host, "???");
277	now = time((time_t *)NULL);
278	nows = ctime(&now);
279	nows[16] = '\0';
280	(void)printf("\r\n\007\007\007Message from %s@%s on %s at %s ...\r\n",
281	    login, host, mytty, nows + 11);
282
283	while (fgets(line, sizeof(line), stdin) != NULL)
284		wr_fputs(line);
285}
286
287/*
288 * done - cleanup and exit
289 */
290void
291done(int n __unused)
292{
293	(void)printf("EOF\r\n");
294	exit(0);
295}
296
297/*
298 * wr_fputs - like fputs(), but makes control characters visible and
299 *     turns \n into \r\n
300 */
301void
302wr_fputs(unsigned char *s)
303{
304
305#define	PUTC(c)	if (putchar(c) == EOF) err(1, NULL);
306
307	for (; *s != '\0'; ++s) {
308		if (*s == '\n') {
309			PUTC('\r');
310		} else if (((*s & 0x80) && *s < 0xA0) ||
311			   /* disable upper controls */
312			   (!isprint(*s) && !isspace(*s) &&
313			    *s != '\a' && *s != '\b')
314			  ) {
315			if (*s & 0x80) {
316				*s &= ~0x80;
317				PUTC('M');
318				PUTC('-');
319			}
320			if (iscntrl(*s)) {
321				*s ^= 0x40;
322				PUTC('^');
323			}
324		}
325		PUTC(*s);
326	}
327	return;
328#undef PUTC
329}
330