ziyziy89 opened a new pull request, #777:
URL: https://github.com/apache/datasketches-java/pull/777
`FrequentLongsSketch.getInstance(String)` builds the hash map from the
length and numActive tokens in the string without checking either against the
map. The probe loops in `ReversePurgeLongHashMap` (`adjustOrPutValue`,
`hashProbe`) only stop at an empty slot, and the only guard is an `assert`, so
once every slot is taken a probe for a new key spins forever.
`getInstance("1,10,3,0,3,0,3,2,1,1,2,1,3,1")` never returns, and an empty image
that claims a map length of 2 (`"1,10,3,5,0,0,0,2"`) deserializes fine but
hangs on the third distinct `update()`, because `curMapCap` is computed from
the 8-slot minimum while the map only has 2 slots. With assertions off this is
an unbounded CPU loop from a ~30 byte input in any service that deserializes
sketch strings it receives.
Reject a map length below `1 << LG_MIN_MAP_SIZE` and a numActive outside
`[0, capacity]` in `getInstance(String)`, next to the existing "Possible
Corruption" checks. `serializeToString()` never produces either, so valid
images are unaffected; the `MemorySegment` path already goes through `update()`
and resizes/purges, so it does not need the same check. Added two tests to
`LongsSketchTest` (with a timeout so a regression fails instead of hanging the
suite); `mvn clean verify` passes.
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