use warnings;
use 5.012; # for "package BLOCK" syntax

BEGIN { $INC{'MyUtils.pm'}=__FILE__; # emulate "use"
	package MyUtils {
		use Exporter 'import';
		our @EXPORT_OK = qw/ binread /;
		
		sub binread { # helper function for read+unpack
			my ($fh, $bytes, $templ) = @_;
			read($fh, my $data, $bytes) == $bytes
				or die "failed to read $bytes bytes";
			return unpack($templ, $data);
		}
	}
}

package Packet {
	use Moo;
	use MyUtils qw/binread/;
	
	has type => ( is => 'ro' );
	has length => ( is => 'ro' );
	
	my %packet_types = ( 0x01 => 'MainHeader', 0x02 => 'ExtHeader',
		0x13 => 'Section' );
	sub parse {
		my ($class, $fh) = @_;
		my ($type, $length) = binread($fh, 2, "CC");
		die "Unknown packet type $type" unless $packet_types{$type};
		return $packet_types{$type}
			->new( type=>$type, length=>$length )->parse($fh);
	}
}

package MainHeader {
	use Moo;
	use MyUtils qw/binread/;
	extends 'Packet';
	
	has foo => ( is => 'rwp' );
	
	sub parse {
		my ($self, $fh) = @_;
		my ($foo) = binread($fh, $self->length, 'Z*');
		$self->_set_foo($foo);
		return $self;
	}
}

package ExtHeader {
	use Moo;
	use MyUtils qw/binread/;
	extends 'Packet';
	
	has bar => ( is => 'rwp' );
	
	sub parse {
		my ($self, $fh) = @_;
		my ($bar) = binread($fh, $self->length, 'N');
		$self->_set_bar($bar);
		return $self;
	}
}

package Section {
	use Moo;
	use MyUtils qw/binread/;
	extends 'Packet';
	
	has quz => ( is => 'rwp' );
	
	sub parse {
		my ($self, $fh) = @_;
		my ($quz) = binread($fh, $self->length, 'n');
		$self->_set_quz($quz);
		return $self;
	}
}

sub parsefile {
	my $file = shift;
	open my $fh, '<:raw', $file or die $!;
	my @pkts;
	while (!eof($fh)) {
		push @pkts, Packet->parse($fh);
	}
	close $fh;
	return @pkts;
}

my $binfile =
	 "\x01\x06Hello\0"
	."\x02\x04\0\x12\x34\x56"
	."\x13\x02\xBE\xEF";
my @packets = parsefile(\$binfile);

use Data::Dump;
dd @packets;
__END__
(
  bless({ foo => "Hello", length => 6, type => 1 }, "MainHeader"),
  bless({ bar => 1193046, length => 4, type => 2 }, "ExtHeader"),
  bless({ length => 2, quz => 48879, type => 19 }, "Section"),
)