#!/usr/local/bin/perl -w
# $Id: cdbootget,v 1.2 2004/01/05 08:59:56 candy Exp candy $
use strict;
use Getopt::Std;

use vars qw($opt_c);
use vars qw($opt_o);
use vars qw($opt_v);
use vars qw($opt_V);

my $SECT = 2048;
my $BOOT_REC = 17;

sub myseek($$) {
	my($fd, $offset) = @_;
	my $pos = tell($fd);
	my $ret = 0;
	if ($offset < $pos) {
		$ret = seek($fd, $offset - $pos, 1);
	}
	else {
		$ret = seek($fd, $offset, 0);
	}
	return $ret;
}

sub read_boot_rec($) {
	my($fd) = @_;
	my $err = -1;
	my $lbuf = "";
	if (myseek($fd, $SECT * $BOOT_REC)) {
		if (read($fd, $lbuf, $SECT) == $SECT) {
			$err = 0;
		}
	}
	if ($err == -1) {
		printf(STDERR "Error in read_boot_rec: $!\n");
	}
	return $lbuf;
}

sub read_boot_catalog($$) {
	my($fd, $boot_sect) = @_;
	my $err = -1;
	my $lbuf = "";
	if (myseek($fd, $SECT * $boot_sect)) {
		if (read($fd, $lbuf, $SECT) == $SECT) {
			$err = 0;
		}
	}
	if ($err == -1) {
		printf(STDERR "Error in read_boot_catalog: $!\n");
	}
	return $lbuf;
}

sub get1($$) {
	my($s, $o) = @_;
	return ord(substr($s, $o, 1));
}

sub get2($$) {
	my($s, $o) = @_;
	return ord(substr($s, $o, 1)) + 
		ord(substr($s, $o + 1, 1)) * 0x100;
}

sub get4($$) {
	my($s, $o) = @_;
	return ord(substr($s, $o, 1)) + 
		ord(substr($s, $o + 1, 1)) * 0x100 +
		ord(substr($s, $o + 2, 1)) * 0x10000 +
		ord(substr($s, $o + 3, 1)) * 0x1000000;
}

sub read_boot_code($) {
	my($fd) = @_;
	my $err = -1;
	my $lbuf = "";
	my $boot_rec = read_boot_rec($fd);
	if ($boot_rec ne "") {
		my $boot_sect = get4($boot_rec, 0x47);
		$opt_v && printf(STDERR "bootsect = 0x%04x\n", $boot_sect);
		my $boot_catalog = read_boot_catalog($fd, $boot_sect);
		if ($boot_catalog ne "") {
			my $bootable = get1($boot_catalog, 0x20 + 0x00);
			my $boot_media_type = get1($boot_catalog, 0x20 + 0x01);
			my $sect_count = get2($boot_catalog, 0x20 + 0x06);
			my $load_RBA = get4($boot_catalog, 0x20 + 0x08);
			my $sect = $boot_media_type == 0 ? 0x200 : 0x800;
			my $bytes = $sect * $sect_count;
			$opt_v && printf(STDERR "bootable: 0x%02x\n", $bootable);
			$opt_v && printf(STDERR "boot_media_type: 0x%02x\n", $boot_media_type);
			$opt_v && printf(STDERR "sect_count: 0x%04x\n", $sect_count);
			$opt_v && printf(STDERR "load_RBA: 0x%08x\n", $load_RBA);
			$opt_v && printf(STDERR "bytes: 0x%04x\n", $bytes);
			if ($bootable == 0x88) {
				if (myseek($fd, $SECT * $load_RBA)) {
					if (read($fd, $lbuf, $bytes) == $bytes) {
						$err = 0;
					}
				}
				if ($err == -1) {
					printf(STDERR "$!\n");
				}
			}
			else {
				printf(STDERR "not bootable CD\n");
			}
		}
	}
	return $lbuf;
}

sub nain($) {
	my($fd) = @_;
	my $lbuf = read_boot_code($fd);
	if (!$opt_c) {
		if ($opt_o) {
			if (open(F, ">$opt_o")) {
				printf(F "%s", $lbuf);
				close(F);
			}
			else {
				printf(STDERR "%s: $!\n", $opt_o);
			}
		}
		else {
			printf("%s", $lbuf);
		}
	}
}

sub main() {
	my $ex = 1;
	getopts('co:vV');
	if ($opt_V) {
		printf(STDERR << "END");
usage: $0 [-cvV][-o output] [iso_image_file]
Read boot code of iso_image_file and write it to stdout.
	-c		Check only.
	-o output	Write to output instead of stdout.
	-v		verbose
	-V		usage
END
	}
	else {
		if ($#ARGV >= 0) {
			if (open(F, $ARGV[0])) {
				nain(\*F);
				close(F);
			}
			else {
				printf(STDERR "%s: $!\n", $ARGV[0]);
			}
		}
		else {
			nain(\*STDIN);
			$ex = 0;
		}
	}
	return $ex;
}

exit(main());