From: "Mr. Sunblade" <djberge@...>
Date: 2002-06-11T23:47:35+09:00
Subject: hostent extension problem - returning the ip address

Hi all,

Ruby 1.6.7 on Solaris 8

I'm writing an extension that simply returns the hostname or ip addresses
for a given host.  I'm having a problem with core dumps, however, and I
think it's because I'm not wrapping the return value from hptr->h_addr_list
(a pointer to an array of pointers that contain in_addr{}).  I've tried a
few things and though it will compile, it continues to core dump/seg fault.
Any ideas?  Here's my source (including extconf.rb source in comments):

/* my extconf.rb:
require 'mkmf'

# Solaris needs the socket lib to work
if RUBY_PLATFORM =~ /solaris/
   have_library('socket')
   have_library('nsl')
end

create_makefile('sys/host')
*/

#include "ruby.h"
#include <unistd.h>
#include <netdb.h>
#include <arpa/inet.h>

#ifdef __cplusplus
extern "C"
{
#endif

#ifndef MAXHOSTNAMELEN
#define MAXHOSTNAMELEN 256
#endif

VALUE cHost;

static void host_free(void* p)
{
   free(p);
}

static VALUE host_hostname()
{
   char h[MAXHOSTNAMELEN];
   int rv;
   rv = gethostname(h,sizeof(h));
   if(rv != 0){
      rb_exit(INT2NUM(rv));
   }
   return rb_str_new2(h);
}

static VALUE host_ip_addr()
{
   char h[MAXHOSTNAMELEN];
   char str[INET_ADDRSTRLEN];
   char **pptr;
   struct hostent* hp;
   int rv;

   Data_Wrap_Struct(cHost,0,host_free,hp);

   rv = gethostname(h,sizeof(h));
   if(rv != 0){
      rb_exit(INT2NUM(rv));
   }

   hp = gethostbyname(h);
   pptr = hp->h_addr_list;
   Data_Wrap_Struct(cHost,0,host_free,pptr); /* problem here? */

   if( rb_block_given() ){

rb_yield(rb_str_new2(inet_ntop(hp->h_addrtype,*pptr,str,sizeof(str))));
   }
   else{
      VALUE results = rb_ary_new();
      for( ; *pptr != NULL; pptr++){

rb_ary_push(results,rb_str_new2(inet_ntop(hp->h_addrtype,*pptr,str,sizeof(st
r))));
      }
      return results;
   }
}

void Init_host()
{

   VALUE sys_mSys;

   sys_mSys = rb_define_module("Sys");
   cHost = rb_define_class_under(sys_mSys, "Host", rb_cObject);

   rb_define_singleton_method(cHost, "hostname", host_hostname, 0);
   rb_define_singleton_method(cHost, "ip_addr", host_ip_addr, 0);
}

#ifdef __cplusplus
}
#endif

==============

Here's some equivalent C source code (that works, btw):

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

/* Compile with -lsocket option to gcc on Solaris or it will fail */

int main(){
   long addr;
   char *ptr, **pptr;
   char str[INET_ADDRSTRLEN];

   struct hostent* hp;

   hp = gethostbyname("v55host11.interprise.com");

   printf("Address length: %i\n", hp->h_length);
   printf("Name: %s\n", hp->h_name);

   pptr = hp->h_addr_list;
   for( ; *pptr != NULL; pptr++){
      printf("Address: %s\n", inet_ntop(hp->h_addrtype, *pptr, str,
sizeof(str)));
   }

   return 1;
}