fix: raise UnsupportedOperation exception in fsspec.BufferedFile impl

[RacleRay]

• zipfile.ZipFile.init only catch OSError
• io.UnsupportedOperation inherits OSError and ValueError, may be helpful

[kylebarron]

Can you provide some rationale for this change? Is this something that fsspec expects?

[RacleRay]

Yes, the rationale:

Problem: A file opened via obstore-fsspec crashes zipfile.ZipFile in write mode:

from obstore.fsspec import register
register("s3")

fs = fsspec.filesystem("s3", config=config)

with fs.open(url) as filelike, zipfile.ZipFile(filelike, "w") as zf:  # ValueError raised here
    ...

Root cause: our tell() raises a bare ValueError on non-seekable files, but ZipFile.init only catches (AttributeError, OSError) when probing fp.tell(), so the _Tellable fallback never kicks in (CPython 3.12, zipfile init.py:1352–1391):

try:
    self.start_dir = self.fp.tell()
except (AttributeError, OSError):  # ValueError is NOT caught here
    self.fp = _Tellable(self.fp)
    self.start_dir = 0
    self._seekable = False

Fix: io.UnsupportedOperation inherits from both OSError and ValueError

Thanks for your reply.

[kylebarron]

Ok, could you add a test case to this PR that previously errored and now works?

[RacleRay]

Done, added test_zipfile_write_mode in tests/test_fsspec.py. It reproduces the original scenario that wrapping a write-mode file with zipfile.ZipFile.