xref: /freebsd/usr.bin/talk/get_iface.c (revision 1e413cf93298b5b97441a21d9a50fdcd0ee9945e)
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 
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 
49 int
50 get_iface(dst, iface)
51 	struct in_addr *dst;
52 	struct in_addr *iface;
53 {
54 	static struct sockaddr_in local;
55 	struct sockaddr_in remote;
56 	socklen_t namelen;
57 	int s, rv;
58 
59 	memcpy(&remote.sin_addr, dst, sizeof remote.sin_addr);
60 	remote.sin_port = htons(60000);
61 	remote.sin_family = AF_INET;
62 	remote.sin_len = sizeof remote;
63 
64 	local.sin_addr.s_addr = htonl(INADDR_ANY);
65 	local.sin_port = htons(60000);
66 	local.sin_family = AF_INET;
67 	local.sin_len = sizeof local;
68 
69 	s = socket(PF_INET, SOCK_DGRAM, 0);
70 	if (s < 0)
71 		return -1;
72 
73 	do {
74 		rv = bind(s, (struct sockaddr *)&local, sizeof local);
75 		local.sin_port = htons(ntohs(local.sin_port) + 1);
76 	} while(rv < 0 && errno == EADDRINUSE);
77 
78 	if (rv < 0) {
79 		close(s);
80 		return -1;
81 	}
82 
83 	do {
84 		rv = connect(s, (struct sockaddr *)&remote, sizeof remote);
85 		remote.sin_port = htons(ntohs(remote.sin_port) + 1);
86 	} while(rv < 0 && errno == EADDRINUSE);
87 
88 	if (rv < 0) {
89 		close(s);
90 		return -1;
91 	}
92 
93 	namelen = sizeof local;
94 	rv = getsockname(s, (struct sockaddr *)&local, &namelen);
95 	close(s);
96 	if (rv < 0)
97 		return -1;
98 
99 	memcpy(iface, &local.sin_addr, sizeof local.sin_addr);
100 	return 0;
101 }
102