friendlymatthew commented on code in PR #7906:
URL: https://github.com/apache/arrow-rs/pull/7906#discussion_r2201515136
##########
parquet-variant/src/variant/list.rs:
##########
@@ -216,28 +216,19 @@ impl<'m, 'v> VariantList<'m, 'v> {
self.header.first_offset_byte() as _..self.first_value_byte as
_,
)?;
- let offsets =
- map_bytes_to_offsets(offset_buffer,
self.header.offset_size).collect::<Vec<_>>();
-
- // Validate offsets are in-bounds and monotonically increasing.
- // Since shallow verification checks whether the first and last
offsets are in-bounds,
- // we can also verify all offsets are in-bounds by checking if
offsets are monotonically increasing.
- let are_offsets_monotonic = offsets.is_sorted_by(|a, b| a < b);
- if !are_offsets_monotonic {
- return Err(ArrowError::InvalidArgumentError(
- "offsets are not monotonically increasing".to_string(),
- ));
- }
-
let value_buffer = slice_from_slice(self.value,
self.first_value_byte as _..)?;
// Validate whether values are valid variant objects
- for i in 1..offsets.len() {
- let start_offset = offsets[i - 1];
- let end_offset = offsets[i];
-
- let value_bytes = slice_from_slice(value_buffer,
start_offset..end_offset)?;
+ //
+ // Since we use offsets to slice into the value buffer, we can
also verify all offsets are in-bounds
+ // and monotonically increasing
Review Comment:
Yes, here was how I thought about it.
`slice_from_slice` will err if the slice range is invalid. A slice range is
invalid when the start offset is greater than the end offset.
So when we iterate through the offsets, we build our slice range
`offsets[i]..offsets[i + 1]`. If every slice attempt is successful, we can
guarantee offsets are non-decreasing.
We still need to check if `offsets[i] != offsets[i + 1]` for any `i`. This
is still a valid range and `slice_from_slice` will return a valid slice (empty
bytes).
This is when the `Variant::try_new_with_metadata` will err.
```rs
#[test]
fn foo() {
let metadata = VariantMetadata::try_new(&[]).unwrap();
// the following will panic:
// called `Result::unwrap()` on an `Err` value:
InvalidArgumentError("Received empty bytes")
let v = Variant::try_new_with_metadata(metadata, &[]).unwrap();
}
```
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