Possible bug in GZipCodec decode with dictionary

[chocolatkey]

Dart SDK version: 2.12.0 (stable) (Thu Feb 25 19:50:53 2021 +0100) on "windows_x64" used to reproduce and test, but also an issue on Flutter (Android ARM64).

When decoding gzip data compressed with a custom dictionary using another language (go)'s implementation, Dart returns Filter error, bad data. However, the same content compressed using the custom dictionary in Dart works fine. That lead me to believe that it's a bug in my go code, however I then wrote an implementation in python, which is able to decode both the go and dart versions. This leads me to believe there is a bug in Dart's implementation. Strangely Dart sets the gzip flag for the OS to TOPS-20 (10) as well (although this is not a bug just strange behavior that maybe has to do with the issue).

I have managed to consistently reproduce this issue on Windows, and have attached a ZIP with some example files for testing/debugging. The files are as follows:

• [pgd]: contains the python gzip module modified to support reading gzip files with custom dictionaries (just adds to the zlib call)
• gdict.bin: the custom dictionary used
• test.dart: the dart script used to create testpart.html.dart.gz and which also fails to decompress testpart.html.go.gz
• test.py: the python script which can successfully decompress both .gz files
• testpart.html: the test plaintext
• testpart.html.dart.gz: the dictionary-compressed file created by test.dart
• testpart.html.go.gz: the dictionary-compressed file created by the go backend

Please let me know if there's anything else I can provide anything else that may help, I'm eager to get this resolved.

[chocolatkey]

test_case.zip

[chocolatkey]

Hello, has there been any update for this potential bug?

[chocolatkey]

Has there been any update on this?

[chocolatkey]

Have there been any updates on this issue?