brunal opened a new pull request, #46408:
URL: https://github.com/apache/arrow/pull/46408
### Rationale for this change
Arrow C++ slices arrays by bumping the top-level `offset` value.
However, Arrow Rust slices list arrays by slicing the `value_offsets`
buffer. When receiving a Rust Arrow Array in C++ (via the C data
interface), its IPC serialization fails to notice that the
`value_offsets` buffer needed to be updated, but it still updates the
`values` buffer. This leads to a corrupt array on deserialization, with
an `value_offsets` buffer that points past the end of the values array.
This PR fixes the IPC serialization by looking at value_offset(0) to
determine whether the `value_offsets` buffer needs reconstructing,
instead of just looking at offset(). This works because
value_offset(int) is value_offset buffer + top-level offset (through
ArrayData::GetValuesSafe(int)).
Additionally, I update the comment surrounding the logic, as
it had 2 issues:
1. It hints that offset > 0 and value_offsets[0] > 0 happen together,
when they actually tend to be exclusive (... unless you slice twice,
once in Rust and once in C++).
2. It mentions slicing the values, when that does not happen in the
function where the comment appears (GetZeroBasedValueOffsets), but at
call site (Visit(Array)).
### What changes are included in this PR?
The fix, as well as a small cleanup of the function:
* Extend the loop to cover i == array.length() instead of a dedicated
statement.
* Avoid copying the `offsets_buffer` shared_ptr (avoid refcount ++ then
--).
Note: I am not sure that the logic covered by the
[ARROW-6046](https://issues.apache.org/jira/browse/ARROW-6046) tag does
anything. I don't think it should trigger lest the offsets buffer is
invalid, and removing it does not cause any test to fail.
### Are these changes tested?
Yep
### Are there any user-facing changes?
Nope (well, unless they are affected by the bug)
**This PR contains a "Critical Fix".** (the changes fix (a) a security
vulnerability, (b) a bug that caused incorrect or invalid data to be produced)
: valid operations on valid data produce invalid data.
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