84 lines
3.5 KiB
Python
84 lines
3.5 KiB
Python
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#!/usr/bin/env python3
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"""Extract one file from a digest-pinned public OCI image without docker (NK-WP-0058-T02). Read-only.
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python3 tools/contract-tests/oci_extract.py --image forgejo.coulomb.social/coulomb/key-cape@sha256:<64 hex> \
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--file keycape --out DIR/keycape
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The manifest must hash to the pinned digest, and every layer read must hash to its manifest digest, so the file
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is exactly the one in the pinned image. The pull token is the registry's anonymous one; no credential is used.
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The newest layer holding the file wins, as in the image's own filesystem. Exit 0 when the file is written.
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"""
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import argparse
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import hashlib
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import io
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import json
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import re
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import sys
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import tarfile
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import urllib.parse
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import urllib.request
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from pathlib import Path
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ACCEPT = ', '.join(('application/vnd.oci.image.manifest.v1+json',
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'application/vnd.docker.distribution.manifest.v2+json'))
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class ExtractError(Exception):
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pass
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def get(url, token=None, accept=None, opener=urllib.request.urlopen):
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headers = {**({'Authorization': 'Bearer ' + token} if token else {}), **({'Accept': accept} if accept else {})}
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with opener(urllib.request.Request(url, headers=headers), timeout=120) as response:
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return response.read()
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def pull_token(host, repository, opener=urllib.request.urlopen):
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query = urllib.parse.urlencode({'service': 'container_registry', 'scope': f'repository:{repository}:pull'})
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return json.loads(get(f'https://{host}/v2/token?{query}', opener=opener))['token']
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def extract(image, wanted, out, opener=urllib.request.urlopen):
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match = re.fullmatch(r'([^/]+)/(.+)@(sha256:[0-9a-f]{64})', image)
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if not match:
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raise ExtractError('image must be host/repository@sha256:<64 hex>')
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host, repository, digest = match.groups()
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token = pull_token(host, repository, opener)
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raw = get(f'https://{host}/v2/{repository}/manifests/{digest}', token, ACCEPT, opener)
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if 'sha256:' + hashlib.sha256(raw).hexdigest() != digest:
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raise ExtractError('manifest_digest_mismatch')
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manifest = json.loads(raw)
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if 'layers' not in manifest:
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raise ExtractError('not_a_single_platform_manifest')
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for layer in reversed(manifest['layers']):
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blob = get(f"https://{host}/v2/{repository}/blobs/{layer['digest']}", token, opener=opener)
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if 'sha256:' + hashlib.sha256(blob).hexdigest() != layer['digest']:
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raise ExtractError('layer_digest_mismatch')
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with tarfile.open(fileobj=io.BytesIO(blob), mode='r:*') as archive:
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for member in archive.getmembers():
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if member.isfile() and member.name.lstrip('./') == wanted.lstrip('/'):
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out.parent.mkdir(parents=True, exist_ok=True)
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out.write_bytes(archive.extractfile(member).read())
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out.chmod(0o755)
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return {'image': digest, 'layer': layer['digest'], 'file': wanted,
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'sha256': hashlib.sha256(out.read_bytes()).hexdigest()}
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raise ExtractError('file_not_in_image')
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def main(argv=None):
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p = argparse.ArgumentParser(description=__doc__, formatter_class=argparse.RawDescriptionHelpFormatter)
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p.add_argument('--image', required=True)
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p.add_argument('--file', required=True)
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p.add_argument('--out', required=True, type=Path)
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a = p.parse_args(argv)
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try:
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print(json.dumps(extract(a.image, a.file, a.out)))
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except ExtractError as error:
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print(json.dumps({'status': 'refused', 'reason': str(error)}))
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return 1
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return 0
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if __name__ == '__main__':
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sys.exit(main())
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