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tarfile: Appending nothing to a TAR with PAX global headers corrupts it #149674
Description
Bug report
Bug description:
It appears that opening a TAR file with tarfile in append mode corrupts it, if it was created with global PAX headers. This works without PAX headers.
Might be related to #149578
Reproducer
import traceback
import tarfile
import sys
import io
for case, kwargs in dict(
without_pax_headers=dict(
mode='w'
),
with_pax_headers=dict(
mode='w', pax_headers=dict(abc="def")
),
).items():
filename = case + ".tar"
print(case, end=" ", file=sys.stderr)
try:
with tarfile.TarFile(filename, **kwargs) as tar:
contents = b"contents"
tarinfo = tarfile.TarInfo("file")
tarinfo.size = len(contents)
tar.addfile(tarinfo, io.BytesIO(contents))
with tarfile.TarFile(filename, mode='a'):
pass
with tarfile.TarFile(filename, mode='a'):
pass
print("PASS", file=sys.stderr)
except Exception:
print("FAIL", file=sys.stderr)
print(traceback.format_exc(), file=sys.stderr)The output I get from this is:
without_pax_headers PASS
with_pax_headers FAIL
Traceback (most recent call last):
File "<python-input-0>", line 24, in <module>
with tarfile.TarFile(filename, mode='a'):
~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^
File "/usr/local/lib/python3.15/tarfile.py", line 1834, in __init__
raise ReadError(str(e)) from None
tarfile.ReadError: end of file header
CPython versions tested on:
3.15
Operating systems tested on:
Linux
Activity
spbnick commentedon May 11, 2026
@ShadiBahaa ^^^ 😁
picnixz commentedon May 13, 2026
I sm going to consider them as related. Can you update the other issue description please and change the title to describe that degenerate tars with PAX headers do not work well?