From: Daniel Berger <djberg96@...>
Date: 2007-07-19T00:25:17+09:00
Subject: Listing all IP addresses on an multihomed system

Hi all,

I'm wondering if there's a way to list all IP addresses on a
multihomed system using Ruby's Socket API. I actually want this for
the sys-host library (at http://www.rubyforge.org/projects/sysutils).
It's C, but I figure I can reverse engineer the Ruby code back to C.

Here's the equivalent of what I'm currently doing (in C):

#include <unistd.h>
#include <netdb.h>
#include <stdio.h>
#include <arpa/inet.h>

#define BUF 256

int main(){
   struct hostent* h;
   char hostname[BUF];
   char ip[BUF];

   if(gethostname(hostname, BUF) != 0){
      printf("gethostbyname failed\n");
      return -1;
   }

   printf("Hostname: %s\n", hostname);

   h = gethostbyname(hostname);

   if(!h){
      printf("gethostbyname failed\n");
      return -1;
   }

   while(*h->h_addr_list){
      printf("Addr: %s\n", inet_ntop(h->h_addrtype, *h->h_addr_list,
ip, BUF));
      *h->h_addr_list++;
   }

   return 0;
}

But, at least one user has reported that he has eth0 configured with a
LAN IP and eth1 that has 5 attached IP addresses. The above code
doesn't pick them up.

Is there a pure Ruby solution? Is it just a matter of
Socket.getaddrinfo(Socket.gethostname, 80)? Or, does anyone happen to
know the C solution?

Thanks,

Dan