#
# this program converts tar formats from old par to ustar on the fly.
# old tar is read from stdin and then, in ustar format, written to
# stdout.
#
# author: Dmitri
#
# $Id: tar2ustar,v 1.2 2001/03/15 13:19:39 dmitri Exp $
#
# $Log: tar2ustar,v $
# Revision 1.2  2001/03/15 13:19:39  dmitri
# Little clean-up.
#
# Revision 1.1  2001/03/14 17:33:53  dmitri
# Filter to conver tar archives from old format to the ustar format
# (POSIX 1003.1).
#

use integer;
use strict;

my $block;
my $blocksize = 512;
my $blknum = 0;

my @tar_field = (100, 8, 8, 8, 12, 12, 8, 1, 100);

my @tar_name = ('name', 'mode', 'uid', 'gid', 'size', 'mtime', 'chksum',
                'link', 'linkname');

sub checksum {
        my ($block) = @_;
        my $chksum = 0;

        substr $block, 148, 8, '        ';

        for (split '', $block) { $chksum += ord }
        $chksum = sprintf("%o%c ", $chksum, 0);
        $chksum = ' 'x(8 - length($chksum)) . $chksum;

        substr $block, 148, 8, $chksum;

        return $block;
}


sub parse_block {
        my ($block, $filename, $prefix) = @_;
        my %tar;
        
        my $off = 0;
        for (my $i = 0; $i < scalar @tar_field; ++$i) {
                ($tar{$tar_name[$i]} = substr $block, $off, $tar_field[$i]) =~
                        s/\000//g;
                $off += $tar_field[$i];
        }

        # this condition probably only applies at the end, where there's a
        # trailer (don't feel like detecting it).
        ++$blknum && return $block unless $tar{name};

        if ($tar{'name'} =~ m|^\./\./\@LongLink| && $tar{'link'} eq "L") {
                read(STDIN, $block, $blocksize);
                $block =~ s/\000.*$//;
                print STDERR $block, "\n";
                my ($filename, $prefix, $index);
                $index = index $block, "/", length($block) - 100;
                $filename = substr $block, $index + 1;
                $prefix = substr $block, 0, $index;

                read(STDIN, $block, $blocksize);

                return parse_block($block, $filename, $prefix);
        }

        if ($filename && $prefix) {
                substr $block, 0, 100, sprintf("%c", 0) x 100;
                substr $block, 0, length $filename, $filename;
                substr $block, 345, length $prefix, $prefix;
        }

        # mode
        substr $block, 100, 7, "       ";
        substr $block, 101, length $tar{'mode'}, $tar{'mode'};

        substr $block, 108, 7, "     0 ";       # uid
        substr $block, 116, 7, "     0 ";       # gid

        # size
        $tar{'size'} =~ s/^0+//;
        substr $block, 124, 12, "            ";
        substr  $block,
                135 - length $tar{'size'},
                length $tar{'size'},
                $tar{'size'};

        # mtime
        $tar{'mtime'} =~ s/^0+//;
        substr $block, 136, 12, "            ";
        substr  $block,
                147 - length $tar{'mtime'},
                length $tar{'mtime'},
                $tar{'mtime'};

        substr $block, 257, 5, "ustar";         # magic
        substr $block, 329, 7, "     0 ";       # devmajor
        substr $block, 337, 7, "     0 ";       # devminor

        if (oct $tar{'size'} != 0) {
                $blknum += (oct $tar{'size'}) / $blocksize;
                ++$blknum if (oct $tar{'size'}) % $blocksize;
        }
        ++$blknum;

        return checksum $block;
}
        

for (my $i = 0; read(STDIN, $block, $blocksize); ++$i) {
        if ($blknum == $i) {
                # if header block, convert.
                print parse_block $block;
        } else {
                print $block;
        }
}