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Filename : netent.pm
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package Net::netent;
use strict;

use 5.006_001;
our $VERSION = '1.01';
our(@EXPORT, @EXPORT_OK, %EXPORT_TAGS);
our (
    $n_name, @n_aliases,
    $n_addrtype, $n_net
);
 
BEGIN { 
    use Exporter   ();
    @EXPORT      = qw(getnetbyname getnetbyaddr getnet);
    @EXPORT_OK   = qw(
			$n_name	    	@n_aliases
			$n_addrtype 	$n_net
		   );
    %EXPORT_TAGS = ( FIELDS => [ @EXPORT_OK, @EXPORT ] );
}

# Class::Struct forbids use of @ISA
sub import { goto &Exporter::import }

use Class::Struct qw(struct);
struct 'Net::netent' => [
   name		=> '$',
   aliases	=> '@',
   addrtype	=> '$',
   net		=> '$',
];

sub populate (@) {
    return unless @_;
    my $nob = new();
    $n_name 	 =    $nob->[0]     	     = $_[0];
    @n_aliases	 = @{ $nob->[1] } = split ' ', $_[1];
    $n_addrtype  =    $nob->[2] 	     = $_[2];
    $n_net	 =    $nob->[3] 	     = $_[3];
    return $nob;
} 

sub getnetbyname ($)  { populate(CORE::getnetbyname(shift)) } 

sub getnetbyaddr ($;$) { 
    my ($net, $addrtype);
    $net = shift;
    require Socket if @_;
    $addrtype = @_ ? shift : Socket::AF_INET();
    populate(CORE::getnetbyaddr($net, $addrtype)) 
} 

sub getnet($) {
    if ($_[0] =~ /^\d+(?:\.\d+(?:\.\d+(?:\.\d+)?)?)?$/) {
	require Socket;
	&getnetbyaddr(Socket::inet_aton(shift));
    } else {
	&getnetbyname;
    } 
} 

1;
__END__

=head1 NAME

Net::netent - by-name interface to Perl's built-in getnet*() functions

=head1 SYNOPSIS

 use Net::netent qw(:FIELDS);
 getnetbyname("loopback") 		or die "bad net";
 printf "%s is %08X\n", $n_name, $n_net;

 use Net::netent;

 $n = getnetbyname("loopback") 		or die "bad net";
 { # there's gotta be a better way, eh?
     @bytes = unpack("C4", pack("N", $n->net));
     shift @bytes while @bytes && $bytes[0] == 0;
 }
 printf "%s is %08X [%d.%d.%d.%d]\n", $n->name, $n->net, @bytes;

=head1 DESCRIPTION

This module's default exports override the core getnetbyname() and
getnetbyaddr() functions, replacing them with versions that return
"Net::netent" objects.  This object has methods that return the similarly
named structure field name from the C's netent structure from F<netdb.h>;
namely name, aliases, addrtype, and net.  The aliases 
method returns an array reference, the rest scalars.  

You may also import all the structure fields directly into your namespace
as regular variables using the :FIELDS import tag.  (Note that this still
overrides your core functions.)  Access these fields as variables named
with a preceding C<n_>.  Thus, C<$net_obj-E<gt>name()> corresponds to
$n_name if you import the fields.  Array references are available as
regular array variables, so for example C<@{ $net_obj-E<gt>aliases()
}> would be simply @n_aliases.

The getnet() function is a simple front-end that forwards a numeric
argument to getnetbyaddr(), and the rest
to getnetbyname().

To access this functionality without the core overrides,
pass the C<use> an empty import list, and then access
function functions with their full qualified names.
On the other hand, the built-ins are still available
via the C<CORE::> pseudo-package.

=head1 EXAMPLES

The getnet() functions do this in the Perl core:

    sv_setiv(sv, (I32)nent->n_net);

The gethost() functions do this in the Perl core:

    sv_setpvn(sv, hent->h_addr, len);

That means that the address comes back in binary for the
host functions, and as a regular perl integer for the net ones.
This seems a bug, but here's how to deal with it:

 use strict;
 use Socket;
 use Net::netent;

 @ARGV = ('loopback') unless @ARGV;

 my($n, $net);

 for $net ( @ARGV ) {

     unless ($n = getnetbyname($net)) {
 	warn "$0: no such net: $net\n";
 	next;
     }

     printf "\n%s is %s%s\n", 
 	    $net, 
 	    lc($n->name) eq lc($net) ? "" : "*really* ",
 	    $n->name;

     print "\taliases are ", join(", ", @{$n->aliases}), "\n"
 		if @{$n->aliases};     

     # this is stupid; first, why is this not in binary?
     # second, why am i going through these convolutions
     # to make it looks right
     {
 	my @a = unpack("C4", pack("N", $n->net));
 	shift @a while @a && $a[0] == 0;
 	printf "\taddr is %s [%d.%d.%d.%d]\n", $n->net, @a;
     }

     if ($n = getnetbyaddr($n->net)) {
 	if (lc($n->name) ne lc($net)) {
 	    printf "\tThat addr reverses to net %s!\n", $n->name;
 	    $net = $n->name;
 	    redo;
 	} 
     }
 }

=head1 NOTE

While this class is currently implemented using the Class::Struct
module to build a struct-like class, you shouldn't rely upon this.

=head1 AUTHOR

Tom Christiansen