mirror of
https://github.com/Abdess/retroarch_system.git
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92 lines
3.0 KiB
Python
92 lines
3.0 KiB
Python
"""Deterministic ZIP rebuilding for arcade BIOS and sample archives.
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A ZIP's hash depends on entry order, timestamps, compression level, and
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permission bits as much as on content. Packs ship archives rebuilt with
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all of that fixed, so the same ROMs always produce the same pack hash
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regardless of how the source set was assembled.
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Usage:
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from deterministic_zip import rebuild_zip_deterministic
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sha1 = rebuild_zip_deterministic("neogeo.zip", "out/neogeo.zip")
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"""
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from __future__ import annotations
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import hashlib
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import os
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import shutil
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import tempfile
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import zipfile
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from pathlib import Path
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# Fixed metadata for deterministic ZIPs
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_FIXED_DATE_TIME = (1980, 1, 1, 0, 0, 0) # minimum ZIP timestamp
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_FIXED_CREATE_SYSTEM = 0 # FAT/DOS (most compatible)
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_FIXED_EXTERNAL_ATTR = 0o100644 << 16 # -rw-r--r--
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_COMPRESS_LEVEL = 9 # deflate level 9 for determinism
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_COPY_CHUNK = 1024 * 1024
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def _sha1_file(path: str | Path) -> str:
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sha1 = hashlib.sha1()
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with open(path, "rb") as f:
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for chunk in iter(lambda: f.read(65536), b""):
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sha1.update(chunk)
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return sha1.hexdigest()
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def rebuild_zip_deterministic(
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source_zip: str | Path,
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output_zip: str | Path,
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) -> str:
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"""Rebuild a ZIP with fixed metadata and entries sorted by name.
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Copies one chunk at a time rather than loading the archive: arcade
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sample sets reach 279 MB, and holding a whole set plus its rebuilt
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copy in memory costs hundreds of megabytes per pack for no benefit.
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Reading through ZipFile.open verifies each entry against the CRC
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recorded in the source archive, so a corrupt entry raises
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BadZipFile instead of being copied through.
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Returns the SHA1 of the new ZIP.
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"""
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with zipfile.ZipFile(str(source_zip)) as src:
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entries = sorted(
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(i for i in src.infolist() if not i.is_dir()),
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key=lambda i: i.filename,
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)
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with zipfile.ZipFile(
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str(output_zip),
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"w",
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zipfile.ZIP_DEFLATED,
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compresslevel=_COMPRESS_LEVEL,
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) as dst:
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for info in entries:
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out_info = zipfile.ZipInfo(
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filename=info.filename, date_time=_FIXED_DATE_TIME
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)
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out_info.compress_type = zipfile.ZIP_DEFLATED
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out_info.create_system = _FIXED_CREATE_SYSTEM
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out_info.external_attr = _FIXED_EXTERNAL_ATTR
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with src.open(info) as fsrc, dst.open(out_info, "w") as fdst:
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shutil.copyfileobj(fsrc, fdst, _COPY_CHUNK)
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return _sha1_file(output_zip)
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def verify_zip_determinism(zip_path: str | Path) -> tuple[bool, str, str]:
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"""Check whether a ZIP already matches its deterministic rebuild.
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Returns (is_deterministic, original_sha1, rebuilt_sha1).
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"""
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original = _sha1_file(zip_path)
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fd, tmp_path = tempfile.mkstemp(suffix=".zip")
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os.close(fd)
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try:
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rebuilt = rebuild_zip_deterministic(zip_path, tmp_path)
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finally:
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Path(tmp_path).unlink(missing_ok=True)
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return original == rebuilt, original, rebuilt
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