check_crc.py

#!/usr/bin/env python
import struct
import sys
import zlib

def check_archive(fragment_archive):
    with open(fragment_archive, 'rb') as fp:
        meta = fp.read(59)
        if len(meta) != 59:
            raise ValueError('Incomplete metadata!')
        if len(fp.read(8)) != 8:
            raise ValueError('Incomplete header! '
                             'Missing/incomplete magic/version')
        crc = fp.read(4)
        if len(crc) != 4:
            raise ValueError('Incomplete header! Missing/incomplete crc')

    meta_crc = zlib.crc32(meta) & 0xffffffff
    recorded_crc, = struct.unpack_from('I', crc)
    return meta_crc == recorded_crc

if __name__ == '__main__':
    if len(sys.argv) < 2:
        exit('Missing expected argument: fragment_archive')
    if len(sys.argv) == 2:
        if check_archive(sys.argv[1]):
            print 'first frag checksum OK'
        else:
            exit('checksum mismatch!')
    else:
        for frag_archive in sys.argv[1:]:
            if check_archive(frag_archive):
                print '%s: ok' % frag_archive
            else:
                print '%s: ERROR' % frag_archive