[Python] `pa.output_stream()` aborts the process on a read-only buffer

[marinelay]

Describe the bug, including details regarding any error messages, version, and platform.

I've been fuzzing Python C extension modules for a small research project, and this one came up. It reproduces with the binary wheel from a plain pip install pyarrow.

Versions

pyarrow 25.0.0, CPython 3.12.3, Ubuntu 24.04 x86_64.

Reproducer

import pyarrow as pa

pa.output_stream(pa.py_buffer(b'x'))

The process aborts (SIGABRT, exit 134) after printing:

/arrow/cpp/src/arrow/io/memory.cc:165:  Check failed: buffer->is_mutable() Must pass mutable buffer
[1]    3911118 IOT instruction (core dumped)  python

memoryview(b'') and an empty py_buffer do the same:

pa.output_stream(memoryview(b''))       # SIGABRT
pa.output_stream(pa.py_buffer(b''))     # SIGABRT

What does work

A mutable buffer, a path, and BufferOutputStream are all fine:

>>> b = pa.allocate_buffer(16)
>>> b.is_mutable
True
>>> type(pa.output_stream(b))
<class 'pyarrow.lib.FixedSizeBufferWriter'>
>>> type(pa.output_stream('/tmp/o.bin'))
<class 'pyarrow.lib.OSFile'>

And pa.py_buffer is documented to produce a read-only buffer:

>>> pa.py_buffer(b'x').is_mutable
False

Why I think it is worth reporting

output_stream's own docstring lists buffer among the accepted source types:

source : str, Path, buffer, file-like object
    The source to open for writing.

so passing a buffer is the documented usage, and a read-only one terminates the interpreter rather than raising.

---

This looks to me like a bug, but I'm not certain it is one, so I'm filing an issue.

Component(s)

Python