usr.bin/talk/get_iface.c

   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  * $FreeBSD: src/usr.bin/talk/get_iface.c,v 1.7 1999/08/28 01:06:12 peter Exp $
  33  */
  34
  35 #include <errno.h>
  36 #include <string.h>
  37 #include "talk.h"
  38
  39 /*
  40  * Try to find the interface address that is used to route an IP
  41  * packet to a remote peer.
  42  */
  43
  44 int
  45 get_iface(struct in_addr *dst, struct in_addr *iface)
  46 {
  47         static struct sockaddr_in local;
  48         struct sockaddr_in remote;
  49         int s, rv, namelen;
  50
  51         memcpy(&remote.sin_addr, dst, sizeof remote.sin_addr);
  52         remote.sin_port = htons(60000);
  53         remote.sin_family = AF_INET;
  54         remote.sin_len = sizeof remote;
  55
  56         local.sin_addr.s_addr = htonl(INADDR_ANY);
  57         local.sin_port = htons(60000);
  58         local.sin_family = AF_INET;
  59         local.sin_len = sizeof local;
  60
  61         s = socket(PF_INET, SOCK_DGRAM, 0);
  62         if (s < 0)
  63                 return -1;
  64
  65         do {
  66                 rv = bind(s, (struct sockaddr *)&local, sizeof local);
  67                 local.sin_port = htons(ntohs(local.sin_port) + 1);
  68         } while(rv < 0 && errno == EADDRINUSE);
  69
  70         if (rv < 0) {
  71                 close(s);
  72                 return -1;
  73         }
  74
  75         do {
  76                 rv = connect(s, (struct sockaddr *)&remote, sizeof remote);
  77                 remote.sin_port = htons(ntohs(remote.sin_port) + 1);
  78         } while(rv < 0 && errno == EADDRINUSE);
  79
  80         if (rv < 0) {
  81                 close(s);
  82                 return -1;
  83         }
  84
  85         namelen = sizeof local;
  86         rv = getsockname(s, (struct sockaddr *)&local, &namelen);
  87         close(s);
  88         if (rv < 0)
  89                 return -1;
  90
  91         memcpy(iface, &local.sin_addr, sizeof local.sin_addr);
  92         return 0;
  93 }