Unpack files in a CoreOS ignition config file

unpack-ignitionconfig-files.py

#!/usr/bin/python3
#
# Unpack files in a CoreOS ignition config file.
#
# This is a quick hack just to help examine file contents.
# Ignores file ownership and permission attributes in the ignition config.
#
# e.g. $ ./unpack-ignitionconfig-files.py bootstrap.ign
#      creates ./bootstrap.ign.d directory tree with files decoded.

import json
import os
import sys

from urllib.request import urlopen

def unpack_filespec(basedir, filespec):
    path = basedir + filespec['path']
    os.makedirs(os.path.dirname(path), exist_ok=True)
    if 'contents' in filespec:
        data_uris = [filespec['contents']['source']]
    elif 'append' in filespec:
        data_uris = [item['source'] for item in filespec['append']]
    with open(path, 'wb') as outfile:
        for data_uri in data_uris:
            with urlopen(data_uri) as response:
                outfile.write(response.read())

def main(ign_files):
    for filename in ign_files:
        with open(filename) as ign_stream:
            rel_basedir = os.path.basename(filename) + '.d'
            abs_basedir = os.path.abspath(rel_basedir)
            ign_config = json.load(ign_stream)
            list_of_files = ign_config.get('storage', {}).get('files', [])
            for filespec in list_of_files:
                unpack_filespec(abs_basedir, filespec)

if __name__ == '__main__':
    if len(sys.argv) == 1:
        print('Usage: {} IGNFILES'.format(sys.argv[0]))
        sys.exit(1)
    main(sys.argv[1:])