Date: Mon, 7 Aug 1995 11:05:10 -0400 From: Garrett Wollman <wollman@halloran-eldar.lcs.mit.edu> To: freebsd-current@FreeBSD.org (FreeBSD-current users), joerg_wunsch@uriah.heep.sax.de (Joerg Wunsch) Subject: workaround for talk's address problem Message-ID: <9508071505.AA00541@halloran-eldar.lcs.mit.edu> In-Reply-To: <199508061603.SAA07779@uriah.heep.sax.de> References: <199508061603.SAA07779@uriah.heep.sax.de>
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<<On Sun, 6 Aug 1995 18:03:27 +0200 (MET DST), J Wunsch <j@uriah.heep.sax.de> said:
> The correct solution would be asking the routing socket to see which
> interface address must be used to get in contact with the remote
> peer.
Not necessarily. The following program figures out which address to
use to contact a host passed on the command line:
#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdlib.h>
#include <stdio.h>
#include <netdb.h>
#include <err.h>
#include <errno.h>
#include <string.h>
#include <sysexits.h>
int
main(int argc, char **argv)
{
struct sockaddr_in local, remote;
struct hostent *hp;
int s, rv, namelen;
argc--, argv++;
if (!*argv) {
errx(EX_USAGE, "must supply a hostname");
}
hp = gethostbyname(*argv);
if (!hp) {
errx(EX_NOHOST, "cannot resolve hostname: %s", *argv);
}
memcpy(&remote.sin_addr, hp->h_addr_list[0], sizeof remote.sin_addr);
remote.sin_port = htons(60000);
remote.sin_family = AF_INET;
remote.sin_len = sizeof remote;
local.sin_addr.s_addr = htonl(INADDR_ANY);
local.sin_port = htons(60000);
local.sin_family = AF_INET;
local.sin_len = sizeof local;
s = socket(PF_INET, SOCK_DGRAM, 0);
if (s < 0)
err(EX_OSERR, "socket");
do {
rv = bind(s, (struct sockaddr *)&local, sizeof local);
local.sin_port++;
} while(rv < 0 && errno == EADDRINUSE);
if (rv < 0)
err(EX_OSERR, "bind");
do {
rv = connect(s, (struct sockaddr *)&remote, sizeof remote);
remote.sin_port++;
} while(rv < 0 && errno == EADDRINUSE);
if (rv < 0)
err(EX_OSERR, "connect");
namelen = sizeof local;
rv = getsockname(s, (struct sockaddr *)&local, &namelen);
if (rv < 0)
err(EX_OSERR, "getsockname");
printf("Route to %s is out %s\n", *argv, inet_ntoa(local.sin_addr));
return 0;
}
-GAWollman
--
Garrett A. Wollman | Shashish is simple, it's discreet, it's brief. ...
wollman@lcs.mit.edu | Shashish is the bonding of hearts in spite of distance.
Opinions not those of| It is a bond more powerful than absence. We like people
MIT, LCS, ANA, or NSA| who like Shashish. - Claude McKenzie + Florent Vollant
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