xva2img.sh

#!/usr/bin/env python3
#
# Carlos Albornoz <[email protected]>
#

RELATIVE = 1
BLOCK_SIZE = 2**20

import tarfile
import os
import sys

(xva_filename, ref, blocks, output) = tuple(sys.argv[1:])
blocks = int(blocks)
xva = tarfile.open(xva_filename)

def get_block(ref, n):
    try:
        b = xva.extractfile(f"{ref}/{n:08d}").read()
        return b
    except KeyError:
        return None

with open(output, 'wb') as fd:
    for n in range(0, blocks + 1):
        if n % 123 == 0:
            print(f'\r{n}', end='', flush=True)
        block = get_block(ref, n)
        if block is not None:
            fd.write(block)
        else:
            fd.seek(BLOCK_SIZE, RELATIVE)

print('\rDone.          ')