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Use the null buffer's own offset when validating its length #10709

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Use the null buffer's own offset when validating its length #10709

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32 changes: 31 additions & 1 deletion arrow-data/src/data.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -965,7 +965,8 @@ impl ArrayData {
}

let actual_len = nulls.validity().len();
let needed_len = bit_util::ceil(len_plus_offset, 8);
// ArrayData::offset does not apply to the null buffer, which carries its own offset
let needed_len = bit_util::ceil(nulls.offset() + nulls.len(), 8);
if actual_len < needed_len {

@Jefffrey Jefffrey Aug 17, 2026

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i wonder if we should instead remove this validation; its brought up in the original issue:

Furthermore, this validation is currently redundant. There is no way to create an invalid BooleanBuffer today. I don't think it's necessarily a problem to have the validation (if fixed) since there may be a way to create an invalid BooleanBuffer in the future. I just mention this to point out that only the "false error" case (and not the "potentially unsafe" case) can be encountered.

and the way this fix handles it, its just validating that the NullBuffer contains enough bytes for its bits, which sounds like something NullBuffer itself should guarantee/check, and not ArrayData here. perhaps its a holdover from some old code that was refactored

return Err(ArrowError::InvalidArgumentError(format!(
"null_bit_buffer size too small. got {actual_len} needed {needed_len}",
Expand Down Expand Up @@ -3246,6 +3247,35 @@ mod tests {
ArrayData::new_null(&dt, 1).validate_full().unwrap();
}

#[test]
fn null_buffer_offset_is_independent_of_data_offset() {
// 100 values sliced down to the last 50, so the data has offset 50.
let int_data = ArrayData::builder(DataType::UInt32)
.offset(50)
.len(50)
.add_buffer(Buffer::from_vec(vec![0_u32; 100]))
.build()
.unwrap();
int_data.validate().unwrap();

// A null buffer that happens to share the data's offset.
let nulls = NullBuffer::new(BooleanBuffer::from(vec![false; 100]).slice(0, 50));
let with_sliced_nulls = int_data
.clone()
.into_builder()
.nulls(Some(nulls))
.build()
.unwrap();
with_sliced_nulls.validate().unwrap();

// The same 50 nulls at offset 0. ArrayData::offset does not apply to the
// null buffer, so this is just as valid and must not be rejected.
let nulls = NullBuffer::new(BooleanBuffer::from(vec![false; 50]));
let with_unsliced_nulls = int_data.into_builder().nulls(Some(nulls)).build().unwrap();
with_unsliced_nulls.validate().unwrap();
assert_eq!(with_unsliced_nulls.null_count(), 50);
}

fn test_both_builder_and_array_data(
data_type: DataType,
len: usize,
Expand Down
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