read the zlib dictionary length once in CopyDictionary

[ubeddulla]

CopyDictionary in runtime/bin/filter.cc sizes the dictionary heap buffer from one Dart_ListLength call, and Filter_CreateZLibInflate / Filter_CreateZLibDeflate then call Dart_ListLength on the same object a second time to get the length they hand to the filter. For a user-defined class implementing List<int> that call dispatches to the Dart length getter, so the two reads can disagree, and a getter that returns a bigger value the second time leaves dictionary_length_ pointing past the end of the allocation that inflateSetDictionary / deflateSetDictionary later read from. ZLibCodec, ZLibEncoder and ZLibDecoder all pass the caller's List<int> straight through to these natives, so no copy happens on the Dart side first.

Having CopyDictionary report the number of bytes it actually copied keeps the buffer and the length in sync and drops the second lookup at both call sites.

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[ubeddulla]

any update?

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[ubeddulla]

Pushed an update for both comments.

The dictionary is now a Filter::Dictionary struct (a std::unique_ptr<uint8_t[]> plus its length) that gets moved into the filter, so the buffer and length are always in sync and the manual delete[] calls are gone. I put the struct on the base Filter so both the inflate and deflate filters can share it.

Also dropped the hand-rolled Dart_TypedDataAcquireData fast path in CopyDictionary and just call Dart_ListGetAsBytes, since it already handles the typed-data case internally.

[copybara-service]

https://dart-review.googlesource.com/c/sdk/+/526160 has been updated with the latest commits from this pull request.

[copybara-service]

https://dart-review.googlesource.com/c/sdk/+/526160 has been updated with the latest commits from this pull request.

[copybara-service]

CL has new comments, please view and respond to them in Gerrit.

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