Question

I have a (from what I can tell) perfectly working Linux setup (Ubuntu 8.04) where all tools (nslookup, curl, wget, firefox, etc) are able to resolve addresses. Yet, the following code fails:

$s = new IO::Socket::INET(     PeerAddr => 'stackoverflow.com',     PeerPort => 80,     Proto => 'tcp', );  die 'Error: $!\n' unless $s; 

I verified the following things:

• Perl is able to resolve addresses with gethostbyname (ie the code below works):

  my $ret = gethostbyname('stackoverflow.com'); print inet_ntoa($ret);

• The original source code works under Windows

• This is how it supposed to work (ie. it should resolve hostnames), since LWP tries to use this behavior (in fact I stumbled uppon the problem by trying to debug why LWP wasn’t working for me)
• Running the script doesn’t emit DNS requests (so it doesn’t even try to resolve the name). Verified with Wireshark

Answer 1

From a quick look, the following code from IO::Socket::INET

sub _get_addr {     my($sock,$addr_str, $multi) = @_;     my @addr;     if ($multi && $addr_str !~ /^\d+(?:\.\d+){3}$/) {         (undef, undef, undef, undef, @addr) = gethostbyname($addr_str);     } else {         my $h = inet_aton($addr_str);         push(@addr, $h) if defined $h;     }     @addr; } 

suggests (if you look at the caller of this code) the work-around of adding MultiHomed => 1, to your code.

Without that work-around, the above code appears to try to call inet_aton('hostname.com') using the inet_aton() from Socket.pm. That works for me in both Win32 and Unix, so I guess that is where the breakage lies for you.

See Socket.xs for the source code of inet_aton:

void inet_aton(host)     char *  host     CODE:     {         struct in_addr ip_address;         struct hostent * phe;          if (phe = gethostbyname(host)) {             Copy( phe->h_addr, &ip_address, phe->h_length, char );         } else {             ip_address.s_addr = inet_addr(host);         }          ST(0) = sv_newmortal();         if(ip_address.s_addr != INADDR_NONE) {             sv_setpvn( ST(0), (char *)&ip_address, sizeof ip_address );         }     } 

It appears that the Perl gethostbyname() works better than the C gethostbyname() for you.