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("$FreeBSD$");
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#include <unistd.h>
42
43#include "talk.h"
44
45/*
46 * Try to find the interface address that is used to route an IP
47 * packet to a remote peer.
48 */
49
50int
51get_iface(struct in_addr *dst, struct in_addr *iface)
52{
53	static struct sockaddr_in local;
54	struct sockaddr_in remote;
55	socklen_t namelen;
56	int s, rv;
57
58	memcpy(&remote.sin_addr, dst, sizeof remote.sin_addr);
59	remote.sin_port = htons(60000);
60	remote.sin_family = AF_INET;
61	remote.sin_len = sizeof remote;
62
63	local.sin_addr.s_addr = htonl(INADDR_ANY);
64	local.sin_port = htons(60000);
65	local.sin_family = AF_INET;
66	local.sin_len = sizeof local;
67
68	s = socket(PF_INET, SOCK_DGRAM, 0);
69	if (s < 0)
70		return -1;
71
72	do {
73		rv = bind(s, (struct sockaddr *)&local, sizeof local);
74		local.sin_port = htons(ntohs(local.sin_port) + 1);
75	} while(rv < 0 && errno == EADDRINUSE);
76
77	if (rv < 0) {
78		close(s);
79		return -1;
80	}
81
82	do {
83		rv = connect(s, (struct sockaddr *)&remote, sizeof remote);
84		remote.sin_port = htons(ntohs(remote.sin_port) + 1);
85	} while(rv < 0 && errno == EADDRINUSE);
86
87	if (rv < 0) {
88		close(s);
89		return -1;
90	}
91
92	namelen = sizeof local;
93	rv = getsockname(s, (struct sockaddr *)&local, &namelen);
94	close(s);
95	if (rv < 0)
96		return -1;
97
98	memcpy(iface, &local.sin_addr, sizeof local.sin_addr);
99	return 0;
100}
101