How to obfuscate Flutter apps?

Question

Flutter's wiki mentions obfuscation is an opt-in in release mode.
And yet, the flutter build command has no relevant option - see:
flutter help -v build apk

Am I missing something here?
Did they make obfuscation the default?
Is obfuscation even relevant for flutter?

Any pointers on this would be very appreciated.

Answer 1

At the moment obfuscation is not directly exposed via the flutter CLI.

You can try to explicitly pass arguements to the gen_snapshot like this:

flutter build --extra-gen-snapshot-options=--obfuscate,--save-obfuscation-map=build/symbols.json --release

Note: that obfuscation support is not very well tested and might not work at the moment.

Answer 2

Obfuscation is needed - a flutter app knows its function names, which can be shown using Dart's StackTrace class. There's under-tested support for obfuscation. To enable it:

---

For Android:
Add to the file [ProjectRoot]/android/gradle.properties :

extra-gen-snapshot-options=--obfuscate

---

For iOS:
First, edit [FlutterRoot]/packages/flutter_tools/bin/xcode_backend.sh:
Locate the build aot call, and add a flag to it,

${extra_gen_snapshot_options_or_none}

defined as:

local extra_gen_snapshot_options_or_none=""
if [[ -n "$EXTRA_GEN_SNAPSHOT_OPTIONS" ]]; then
  extra_gen_snapshot_options_or_none="--extra-gen-snapshot-options=$EXTRA_GEN_SNAPSHOT_OPTIONS"
fi

To apply your changes, in [FlutterRoot], run

git commit -am "Enable obfuscation on iOS"  
flutter  

(Running "flutter" after the commit rebuilds flutter tools.)

Next, in your project, add following to [ProjectRoot]/ios/Flutter/Release.xcconfig file:

EXTRA_GEN_SNAPSHOT_OPTIONS=--obfuscate

---

PS: Haven't tried the --save-obfuscation-map flag mentioned at https://github.com/dart-lang/sdk/issues/30524
Again, obfuscation isn't very well tested, as mentioned by @mraleph.