class Object

# File research/debug1/tarfix.rb, line 1
def tarfix ifp, ofp
  zeroblk = "\0" * 512
  nreset = 0
  nskip = 0
  while true
    pos = ifp.pos
    bpos = pos / 512
    blk = ifp.read(512)
    break if blk.nil?
    if blk == zeroblk then
      nskip += 1
      next
    end
    if nskip > 0 then
      printf("%u: reset nskip %u\n", bpos, nskip)
      nreset += nskip
      nskip = 0
    end
    # check the header
    hdr = blk[0, 500]
    magic = hdr[257, 5]
    cksum = hdr[148, 8].unpack('A*').first.to_i(8)
    hdr[148, 8] = ' ' * 8
    s = 0
    hdr.each_byte{|c| s += c}
    if s != cksum
      printf("%d: checksum %d != %d\n", bpos, cksum, s)
      exit 1
    else
      bsize = size = hdr[124, 12].unpack('A*').first.to_i(8)
      size -= 1
      size -= size % 512
      size += 512
      ofp.write(blk)
      ofp.write(ifp.read(size))
    end
  end
  printf("%u: nreset %u nskip %u\n", bpos, nreset, nskip)
  (nreset + nskip).times { ofp.write(zeroblk) }
end

# File research/debug1/tardump.rb, line 1
def tartest fp
  while true
    pos = fp.pos
    bpos = pos / 512
    blk = fp.read(512)
    break if blk.nil?
    hdr = blk[0, 500]
    magic = hdr[257, 5]
    printf("%d: magic=%s\n", bpos, magic.inspect)
    cksum = hdr[148, 8].unpack('A*').first.to_i(8)
    hdr[148, 8] = ' ' * 8
    s = 0
    hdr.each_byte{|c| s += c}
    printf("%d: checksum %d != %d\n", bpos, cksum, s) if s != cksum
    bsize = size = hdr[124, 12].unpack('A*').first.to_i(8)
    size -= 1
    size -= size % 512
    size += 512
    printf("%d: bytesize=%d size=%d\n", bpos, bsize, size / 512)
    fp.pos = pos + size + 512
  end
end