xref: /freebsd/usr.bin/talk/get_iface.c (revision 952d112864d8008aa87278a30a539d888a8493cd)
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  * From:
30  *  Id: find_interface.c,v 1.1 1995/08/14 16:08:39 wollman Exp
31  *
32  * $Id$
33  */
34 
35 #include <unistd.h>
36 #include <stdlib.h>
37 #include <string.h>
38 #include <errno.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 
47 int
48 get_iface(dst, iface)
49 	struct in_addr *dst;
50 	struct in_addr *iface;
51 {
52 	static struct sockaddr_in local;
53 	struct sockaddr_in remote;
54 	struct hostent *hp;
55 	int s, rv, namelen;
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