To flutter: to move in quick, irregular motions, to beat rapidly, to be agitated.
Doldrums: a period of stagnation.

Doldrums is a reverse engineering tool for Flutter apps targetting Android. Concretely, it is a parser and information extractor for the Flutter/Dart Android binary, conventionally named libapp.so, for all Dart version 2.10 releases. When run, it outputs a full dump of all classes present in the isolate snapshot.

The tool is currently in beta, and missing some deserialization routines and class information. If it does not work out-of-the-box, please let me know.

Doldrums requires pyelftools to parse the ELF format. You can install it with

pip3 install pyelftools

To use, simply run the following command, substituting libapp.so for the appropriate binary, and output for the desired output file.

python3 src/main.py libapp.so output

The expected output is a dump of all classes, in the following format:

class MyApp extends StatelessWidget {
    Widget build(DynamicType, DynamicType) {
        Code at absolute offset: 0xec85c
    }

    String myPrint(DynamicType, DynamicType) {
        Code at absolute offset: 0xeca80
    }
}

The absolute code offset indicates the offset into the libapp.so file where the native function may be found.

For a detailed write-up on the format, please check my blog post.

darter is a fully implemented and fully tested parser for Dart version 2.5 releases.