[CP] Fix zlib inflation to ignore data past the ADLER32 trailer.

[brianquinlan]

trafficstars

Commit(s) to merge

https://dart-review.googlesource.com/c/sdk/+/380861

Target

stable

Prepared changelist for beta/stable

https://dart-review.googlesource.com/c/sdk/+/381389

Issue Description

Fixes a regression where ZLibDecoder would attempt to read data past the compressed data's trailer. This happens on all platforms. See https://github.com/dart-lang/sdk/issues/56481

What is the fix

The fix is to modify the ZLibDecoder to have two modes:

1. one that stops decompression after the first compression block (this is the default and the behavior prior to Dart 3.5)
2. one that decompresses concatenated decompression blocks (required for gzip decompression)

and to modify the gzip decompressor to use (2)

Why cherry-pick

The full impact of the ZLibDecoder regression is unknown. It broke at least one Flutter project: https://github.com/GitJournal/GitJournal/issues/962

Risk

Low. The cherry pick reverts the default behavior of ZLibDecoder to what it was before Dart 3.5, while preserving the ability to decompress gzip files that was added in Dart 3.5.

Issue link(s)

https://github.com/dart-lang/sdk/issues/56481

Extra Info

No response

[dart-github-bot]

Summary: The ZLibDecoder in Dart 3.5 incorrectly attempted to read data past the compressed data's trailer, causing a regression. This fix modifies the ZLibDecoder to have two modes, one that stops decompression after the first block and one that decompresses concatenated blocks, and uses the latter for gzip decompression.

[a-siva]

lgtm