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
47 int
get_iface(struct in_addr * dst,struct in_addr * iface)48 get_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