`tarfile.open()` does not forward keyword arguments to the underlying `_Stream` object for zstd in stream mode

[beavailable]

Bug report

Bug description:

I found the bug when I was browsing the source code, so I just put the source code here:

    @classmethod
    def open(cls, name=None, mode="r", fileobj=None, bufsize=RECORDSIZE, **kwargs):
        # irrevalent code...
        elif "|" in mode:
            # irrevalent code...
            compresslevel = kwargs.pop("compresslevel", 6)
            preset = kwargs.pop("preset", None)
            stream = _Stream(name, filemode, comptype, fileobj, bufsize,
                             compresslevel, preset)
            # irrevalent code...

But the doc says that:

For modes 'w:zst', 'x:zst' and 'w|zst', tarfile.open() accepts the keyword argument level to specify the compression level of the file. The keyword argument options may also be passed, providing advanced Zstandard compression parameters described by CompressionParameter. The keyword argument zstd_dict can be passed to provide a ZstdDict, a Zstandard dictionary used to improve compression of smaller amounts of data.

So there're three keyword arguments: level, options and zstd_dict that need to pass to _Stream constructor, and the constructor needs to change to accept these keyword arguments.

I'll open a PR to fix this soon.

CPython versions tested on:

3.14

Operating systems tested on:

No response

Linked PRs

• gh-139821: Make tarfile.open correctly forward keyword arguments for zstd in stream mode. #139822

[emmatyping]

This was left intentionally absent due to time constraints and concerns about how to handle all the different compression formats. Please see https://github.com/python/cpython/pull/139822/files#r2422059990 where I propose a solution and also why it is absent. I have moved this to a feature rather than a bug.

[grossag]

@emmatyping I was going to file a bug that may be related but wanted to confirm before doing so. I have a .tar.zst file that I can't extract in stream mode or I get error EOFError: Already at the end of a Zstandard frame.. If I open it in regular mode it works fine. I have a reproducer .tar.zst and script if it helps. Would you like me to file a separate bug about it, post the archive and script here, or no?

[emmatyping]

@grossag that does seem like a different issue. Please open another issue, thanks!