fix(parquet/encoding): reject invalid delta byte prefixes - #1014
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zeroshade merged 2 commits intoJul 27, 2026
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Verified two distinct real bugs here:
- `SetData` never reset `lastVal`, so a decoder reused across pages skipped first-value initialization and consumed `prefixLengths[0]` as a continuation, corrupting the first value of the second page. Column readers do reuse decoders across pages, so this is reachable.
- `d.lastVal[:prefixLen:prefixLen]` panicked on a negative prefix or one longer than the previous value, and the loop could index an empty `prefixLengths`.
Requiring the first prefix to be zero matches the DELTA_BYTE_ARRAY spec, and the validation is applied consistently to both the decode and discard paths. LGTM.
Note: #1013 modifies the same `SetData` and will need a rebase now that this has landed.
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Rationale for this change
DELTA_BYTE_ARRAY prefix lengths are used directly as slice bounds. Negative prefixes or prefixes longer than the previous value therefore panic. The decoder also retains its previous value when reused for a new page, even though each page starts an independent delta sequence.
What changes are included in this PR?
SetData.Are these changes tested?
Yes. Focused tests cover decoder reuse, negative prefixes, and prefixes longer than the previous value.