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
31/*
32 * From:
33 *  Id: find_interface.c,v 1.1 1995/08/14 16:08:39 wollman Exp
34 */
35
36#include <errno.h>
37#include <string.h>
38#include <unistd.h>
39
40#include "talk.h"
41
42/*
43 * Try to find the interface address that is used to route an IP
44 * packet to a remote peer.
45 */
46
47int
48get_iface(struct in_addr *dst, struct in_addr *iface)
49{
50	static struct sockaddr_in local;
51	struct sockaddr_in remote;
52	socklen_t namelen;
53	int s, rv;
54
55	memcpy(&remote.sin_addr, dst, sizeof remote.sin_addr);
56	remote.sin_port = htons(60000);
57	remote.sin_family = AF_INET;
58	remote.sin_len = sizeof remote;
59
60	local.sin_addr.s_addr = htonl(INADDR_ANY);
61	local.sin_port = htons(60000);
62	local.sin_family = AF_INET;
63	local.sin_len = sizeof local;
64
65	s = socket(PF_INET, SOCK_DGRAM, 0);
66	if (s < 0)
67		return -1;
68
69	do {
70		rv = bind(s, (struct sockaddr *)&local, sizeof local);
71		local.sin_port = htons(ntohs(local.sin_port) + 1);
72	} while(rv < 0 && errno == EADDRINUSE);
73
74	if (rv < 0) {
75		close(s);
76		return -1;
77	}
78
79	do {
80		rv = connect(s, (struct sockaddr *)&remote, sizeof remote);
81		remote.sin_port = htons(ntohs(remote.sin_port) + 1);
82	} while(rv < 0 && errno == EADDRINUSE);
83
84	if (rv < 0) {
85		close(s);
86		return -1;
87	}
88
89	namelen = sizeof local;
90	rv = getsockname(s, (struct sockaddr *)&local, &namelen);
91	close(s);
92	if (rv < 0)
93		return -1;
94
95	memcpy(iface, &local.sin_addr, sizeof local.sin_addr);
96	return 0;
97}
98