#!/usr/bin/perl -w

use strict;
use warnings;
use Fcntl;

if ($#ARGV != 1) {
  die "$0 converts a vtar to a tar file\n" .
      "usage: $0 <srcfile> <dstfile>";
}
my ($src, $dst) = @ARGV;

open(SRC, $src) || die "$src: $!";
binmode SRC;

my $boundary = "";
for (my $i = 0; $i < 512 * 8; $i++) {
  vec($boundary, $i, 1) = 0;
}

my @entries;
for (;;) {
  my $entry;
  read(SRC, $entry, 512);
  last if ($entry eq $boundary);
  push @entries, $entry;
}

my $pos = $#entries * 512 + 1024;

open(DST, ">$dst") || die "$dst: $!";
binmode DST;

foreach my $entry(@entries) {
  print DST $entry;
  my $size = int((oct(substr($entry, 124, 12)) + 511) / 512) * 512;
  if ($size) {
    seek(SRC, $pos, Fcntl::SEEK_SET);
    my $buf;
    read(SRC, $buf, $size);
    print DST $buf;
    $pos += $size;
  }
}

print DST substr($boundary, 0, 512 - ($pos % 512)) if ($pos % 512);
print DST $boundary;
print DST $boundary;

close(DST);
close(SRC);