fix: harden vortex.zoned metadata parsing against malformed input; decimal sum fallback (#197)#224
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…cimal sum fallback (#197) The aggregate-spec zone-map decoder added in #197 (commit 9e20edc) had two post-merge review findings. Overflow class: ProtoCursor guarded reads with `pos + len > bound`. A varint length up to Long.MAX_VALUE overflows `pos + len` to negative, so the `> bound` check is false and the guard passes — then `new byte[(int) len]` throws NegativeArraySizeException, or `pos` advances negative and the next segment read throws IndexOutOfBoundsException. This is untrusted file metadata (ADR 0003), so it must never surface a raw JDK exception. Every length/offset check (readAggregateSpecId message descent, readString, advance/skipField) is rewritten overflow-safe: the invariant pos <= bound holds throughout, so `bound - pos >= 0` never overflows and the guard becomes `len < 0 || len > bound - pos`. Malformed metadata now falls back to per-chunk stats. Decimal divergence: Rust's default_zoned_aggregate_fns (vortex-layout zoned/writer.rs) emits a `sum` column whenever Sum.return_dtype is Some — which is Some(Decimal(precision + 10)) for a Decimal column (sum/mod.rs) — while our sumDtype returns null for Decimal. Dropping that field with `continue` reconstructs {max,min,null_count} for an encoded {max,min,sum,null_count} table, so the positional decode reads null_count out of the sum buffer. The reconstructor now distinguishes "Rust also omits this" (nan_count over non-float per nan_count/mod.rs, min/max over an unsupported column per min_max minmax_supported_dtype — safe skip) from "Rust keeps a field we cannot map" (decimal sum, bounded_max/min nested state — return null so the whole column falls back to correct-but-unpruned per-chunk stats). Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Post-merge review follow-up to #197. The hand-rolled protobuf cursor added there had two defects:
Crash on untrusted input (ADR 0003). The bounds guards used
pos + len > bound, which integer-overflows when a malformed varint length is nearLong.MAX_VALUE— the guard passes and the code then doesnew byte[(int) len](NegativeArraySizeException) or advancesposnegative (IndexOutOfBoundsException). Empirically confirmed by the reviewer against crafted metadata. Rewritten overflow-safe aslen < 0 || len > bound - pos(invariantpos <= boundholds, sobound - posnever overflows) acrossreadAggregateSpecId,readString, andadvance/skipField.Latent wrong answer for decimal columns. Rust's zoned schema emits a
sumcolumn wheneverSum::return_dtypeisSome— which isSome(Decimal)for a decimal column — but ourstatDtype(SUM, decimal)returns null, so we silently dropped the field and the positional decode readnull_countout of thesumbuffer. Now anull-resolving mapped aggregate that Rust would still emit (decimal sum) makes the whole column fall back to per-chunk stats (correct, unpruned); only aggregates Rust also omits (nan_count on non-float, min/max on unsupported types) are skipped, via a newrustAlsoOmitshelper. Drop-vs-keep enumeration verified againstvortex-layout/src/layouts/zoned/writer.rs+ the aggregatereturn_dtype/state_dtypeimpls.Malformed-metadata contract: null → per-chunk fallback (consistent with the existing
bailsOn*cases and thedecodeZoneTablecaller), never a raw JDK exception.Validation:
ZonedStatsSchemaTest26 (newMalformedAggregateMetadatagroup covering truncated varint, oversized string/skip length, unknown wire type, message past end; plus decimal-sum fallback); reader 1150 green;RustWritesJavaReadsIntegrationTest13/13 (zone-map ground truth still green). docs/explanation.md zoned row updated.Refs #197
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