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#!/usr/bin/python3
# Copyright 2024 Helmut Grohne <helmut@subdivi.de>
# SPDX-License-Identifier: GPL-3
"""Extensions to the tarfile module.
* ZstdTarFile extends TarFile to deal with zstd-compressed archives.
* get_comptype guesses the compression used for an open TarFile.
"""
import tarfile
import typing
class ZstdTarFile(tarfile.TarFile):
"""Subclass of tarfile.TarFile that can read zstd compressed archives."""
OPEN_METH = {"zst": "zstopen"} | tarfile.TarFile.OPEN_METH
@classmethod
def zstopen(
cls,
name: str,
mode: typing.Literal["r", "w", "x"] = "r",
fileobj: typing.BinaryIO | None = None,
**kwargs: typing.Any,
) -> tarfile.TarFile:
if mode not in ("r", "w", "x"):
raise ValueError("mode must be 'r', 'w' or 'x'")
openobj: str | typing.BinaryIO = name if fileobj is None else fileobj
try:
import zstandard
except ImportError as err:
raise tarfile.CompressionError(
"zstandard module not available"
) from err
if mode == "r":
zfobj = zstandard.open(openobj, "rb")
else:
zfobj = zstandard.open(
openobj,
mode + "b",
cctx=zstandard.ZstdCompressor(write_checksum=True, threads=-1),
)
try:
tarobj = cls.taropen(name, mode, zfobj, **kwargs)
except (OSError, EOFError, zstandard.ZstdError) as exc:
zfobj.close()
if mode == "r":
raise tarfile.ReadError("not a zst file") from exc
raise
except:
zfobj.close()
raise
# Setting the _extfileobj attribute is important to signal a need to
# close this object and thus flush the compressed stream.
# Unfortunately, tarfile.pyi doesn't know about it.
tarobj._extfileobj = False # type: ignore
return tarobj
def get_comptype(tarobj: tarfile.TarFile) -> str:
"""Return the compression type used to compress the given TarFile."""
# The tarfile module does not expose the compression method selected
# for open mode "r:*" in any way. We can guess it from the module that
# implements the fileobj.
compmodule = tarobj.fileobj.__class__.__module__
try:
return {
"bz2": "bz2",
"gzip": "gz",
"lzma": "xz",
"_io": "tar",
"zstd": "zst",
}[compmodule]
except KeyError:
# pylint: disable=raise-missing-from # no value in chaining
raise ValueError(f"cannot guess comptype for module {compmodule}")
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