get_iface.c revision 178642 
1/*
2 * Copyright 1994, 1995 Massachusetts Institute of Technology
3 *
4 * Permission to use, copy, modify, and distribute this software and
5 * its documentation for any purpose and without fee is hereby
6 * granted, provided that both the above copyright notice and this
7 * permission notice appear in all copies, that both the above
8 * copyright notice and this permission notice appear in all
9 * supporting documentation, and that the name of M.I.T. not be used
10 * in advertising or publicity pertaining to distribution of the
11 * software without specific, written prior permission.  M.I.T. makes
12 * no representations about the suitability of this software for any
13 * purpose.  It is provided "as is" without express or implied
14 * warranty.
15 *
16 * THIS SOFTWARE IS PROVIDED BY M.I.T. ``AS IS''.  M.I.T. DISCLAIMS
17 * ALL EXPRESS OR IMPLIED WARRANTIES WITH REGARD TO THIS SOFTWARE,
18 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
19 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT
20 * SHALL M.I.T. BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
21 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
22 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
23 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
24 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
25 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
26 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
27 * SUCH DAMAGE.
28 */
29
30#include <sys/cdefs.h>
31
32__FBSDID("$FreeBSD: head/usr.bin/talk/get_iface.c 178642 2008-04-28 21:08:42Z delphij $");
33
34/*
35 * From:
36 *  Id: find_interface.c,v 1.1 1995/08/14 16:08:39 wollman Exp
37 */
38
39#include <errno.h>
40#include <string.h>
41
42#include "talk.h"
43
44/*
45 * Try to find the interface address that is used to route an IP
46 * packet to a remote peer.
47 */
48
49int
50get_iface(struct in_addr *dst, struct in_addr *iface)
51{
52	static struct sockaddr_in local;
53	struct sockaddr_in remote;
54	socklen_t namelen;
55	int s, rv;
56
57	memcpy(&remote.sin_addr, dst, sizeof remote.sin_addr);
58	remote.sin_port = htons(60000);
59	remote.sin_family = AF_INET;
60	remote.sin_len = sizeof remote;
61
62	local.sin_addr.s_addr = htonl(INADDR_ANY);
63	local.sin_port = htons(60000);
64	local.sin_family = AF_INET;
65	local.sin_len = sizeof local;
66
67	s = socket(PF_INET, SOCK_DGRAM, 0);
68	if (s < 0)
69		return -1;
70
71	do {
72		rv = bind(s, (struct sockaddr *)&local, sizeof local);
73		local.sin_port = htons(ntohs(local.sin_port) + 1);
74	} while(rv < 0 && errno == EADDRINUSE);
75
76	if (rv < 0) {
77		close(s);
78		return -1;
79	}
80
81	do {
82		rv = connect(s, (struct sockaddr *)&remote, sizeof remote);
83		remote.sin_port = htons(ntohs(remote.sin_port) + 1);
84	} while(rv < 0 && errno == EADDRINUSE);
85
86	if (rv < 0) {
87		close(s);
88		return -1;
89	}
90
91	namelen = sizeof local;
92	rv = getsockname(s, (struct sockaddr *)&local, &namelen);
93	close(s);
94	if (rv < 0)
95		return -1;
96
97	memcpy(iface, &local.sin_addr, sizeof local.sin_addr);
98	return 0;
99}
100