#!/usr/bin/perl

use Net::DNS;
  
my $separator=':';
my $res=Net::DNS::Resolver->new;

while (<>){
 chomp;
 my ($host,$port) = split(/$separator/o,$_);
 if ($host=~m/^(\d+)\.(\d+)\.(\d+)\.(\d+)$/o){
  my $dnspack = $res->query("$4.$3.$2.$1.in-addr.arpa",'PTR');
  if ($dnspack){
   foreach my $rdata ($dnspack->answer){
    my $rstr=$rdata->rdatastr;
    $rstr=~s/\.$//o;
    print "$rstr$separator$port\n";
   }
  } else {
   print "$host$separator$port\n";
  }
 } else {
  print "$host$separator$port\n";
 }
}

__END__

=head1 NAME

ip2dns convert proxy list from IP:PORT fromat to HOST:PORT format

=head1 SYNOPSIS

ip2dns < ip_port.txt > host_port.txt