fauria has asked for the wisdom of the Perl Monks concerning the following question:

Hi all!

Ive got a problem performing IP address operations using Net::IP.

Here is what i need: I have to translate an IP address (for example, 10.0.1.3) into an integer value (for example, 167772419), and translate an integer value to an ip (167772419 to 10.0.1.3). I did:

use Net::IP qw(:PROC);

my $ipaddr = '10.0.1.3';
my $ip = new Net::IP($ipaddr) or die (Net::IP::Error());
my $int = $ip->intip();

print "Integer value of IP $ipaddr: $int\n";

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And it prints:
Integer value of IP 10.0.1.3: 167772419

Which is correct. But the reverse operation:

use Net::IP qw(:PROC);
                                                                      
+                                                                     
+      
my $intaddr = 167772419;
my $binaddr;
eval{
     $binaddr = ip_inttobin($intaddr);
};
die "Error: $@" if($@);

!defined($binaddr) and print "Binary not defined\n";
print "Binary value of integer $intaddr: $binaddr\n";

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Prints:

Binary not defined
Binary value of integer 167772419:

Thus, i dont know how to transform an integer into a binary, and a binary into an ip, which is the only way i currently know.

Any idea on how to deal with this?
Thank you

Replies are listed 'Best First'.
Re: IP operation trouble
by gellyfish (Monsignor) on Jan 12, 2005 at 14:07 UTC

    It's probably a lot easier than this: 

    use Socket;
                                                                      
+          
my $ip = '127.0.0.1';
                                                                      
+          
my $int = ip_to_int($ip);
                                                                      
+          
print $int,"\n";
                                                                      
+          
print int_to_ip($int);
                                                                      
+          
sub int_to_ip
{
   my ($int) = @_;
   return inet_ntoa(pack('N', $int));
}
                                                                      
+          
sub ip_to_int
{
   my ($ip) = @_;
   return unpack('N', inet_aton($ip));
}

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    Note the use of pack and unpack here.

    /J\

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Re: IP operation trouble
by borisz (Canon) on Jan 12, 2005 at 14:16 UTC
    without testing, your my $binaddr inside the eval is out of scope. try: 
    my $intaddr = 167772419;
my $binaddr;
eval{
     $binaddr = ip_inttobin($intaddr);
};
die "Error: $@" if($@);

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    Boris
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Re: IP operation trouble
by naChoZ (Curate) on Jan 12, 2005 at 14:08 UTC

    It's because $binaddr only lives within the eval block. Ditch the eval block and you should be ok.

    Update:
    I fiddled with it a little just because I've never really messed with binary operations. 

    #!/usr/local/bin/perl -w 
  
use strict;
  
use Net::IP qw/:PROC/;
  
#
# create your Net::IP object
#
my $ip_addr = Net::IP->new( "192.168.0.20" );
  
#
# $ip_int becomes a Math::BigInt object
#
my $ip_int = ip_bintoint( $ip_addr->binip );

print "IP Address: ", $ip_addr->ip,
      "\nBin: ", $ip_addr->binip,
      "\nInt: ", $ip_int->numify(),
      "\n";

#
# turn the Integer into a vanilla scalar
#
my $int_ip = $ip_int->numify();
  
#
# Now start from the integer and go backwards
#

my $bin_from_int = sprintf( "%b", $int_ip);
my $ip_from_bin = ip_bintoip( $bin_from_int, 4);

print "\n\nInt: $int_ip\n",
      "Bin: $bin_from_int\n",
      "IP:  ", $ip_from_bin, "\n";

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    --
    "This alcoholism thing, I think it's just clever propaganda produced by people who want you to buy more bottled water." -- pedestrianwolf

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      Hi there, The purpose of the eval block was to ensure there was not any error in the function, without it there happens the same. Thanks anyway
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Re: IP operation trouble
by DrHyde (Prior) on Jan 13, 2005 at 10:14 UTC
    I'm not familiar with that module, so here's what I would have written: 
    sub ipv4_to_int {
    my $int = 0;
    foreach (split(/\./, $_[0]) {
        $int <<= 8;
        $int += $_;
    }
    return $int;
}

sub int_to_ipv4 {
    my $ip = '';
    my $int = shift;
    while($int) {
        $ip = ($int & 255).".$ip";
        $int >>= 8;
    }
    chop($ip);
    return $ip;
}

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    Untested, season with error-checking to taste.

    You hardly ever see the >> and << bit-shifting operators in perl, and bitwise AND (&) is rare too, but they behave exactly the same as they do in C.

    And while I normally disapprove of "magic numbers" like the 8 and 255, I think that in this case their meaning is sufficiently obvious.

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