http requests fail with cronetHttpNoPlay=true with error java.lang.ClassNotFoundException

[dreautall]

Hello.

I have an app that works fine with cronet_http with the GPS-Cronet. Trying to build the same app with --dart-define=cronetHttpNoPlay=true works, but the app is not usable and throws errors on http requests. The error message reads:

Exception in Java code called through JNI:
java.lang.ClassNotFoundException: Didn't find class "org/chromium/net/CronetEngine$Builder" on path:
DexPathList[[zip file "/data/app/~~xlxrt1ba2YAQ0amUKmEvNg==/com.dreautall.waterflyiii-AbxaklwneLCpq2CmygW_Jg==/base.apk"],nativeLibrary Directories=[/data/app/~~xlxrt1ba2YAQ0amUKmEvNg==/com.dreautall.waterflyiii-AbxaklwneLCpq2CmygW_Jg==/lib/arm64,/data/app/~~xlxrt1ba2YAQ0amUKmEvNg==/com.dreautall.waterflyiii-AbxaklwneLCpq2CmygW_Jg==/base.apk!/lib/arm64-v8a, /system/lib64,/system/system_ext/lib64]]

java.lang.ClassNotFoundException: Didn't find class "org/chromium/net/CronetEngine$Builder" on path:
DexPDexPathList[[zip file "/data/app/~~xlxrt1ba2YAQ0amUKmEvNg==/com.dreautall.waterflyiii-AbxaklwneLCpq2CmygW_Jg==/base.apk"],nativeLibrary Directories=[/data/app/~~xlxrt1ba2YAQ0amUKmEvNg==/com.dreautall.waterflyiii-AbxaklwneLCpq2CmygW_Jg==/lib/arm64,/data/app/~~xlxrt1ba2YAQ0amUKmEvNg==/com.dreautall.waterflyiii-AbxaklwneLCpq2CmygW_Jg==/base.apk!/lib/arm64-v8a, /system/lib64,/system/system_ext/lib64]]

at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:259)
at java.lang.ClassLoader.loadClass(ClassLoader.java:379)
at java.lang.ClassLoader.loadClass(ClassLoader.java:312)

pubspec.yaml defines cronet_http: ^1.2.0. As no other change is outlined in the documentation, there was no code change from my side anywhere - not sure if I would have to exclude/include something in the Android manifest, gradle build or similar.

The app was built with flutter build apk --split-debug-info=build/app/outputs/symbols/aab --release --dart-define=cronetHttpNoPlay=true, the test device of the error message is a Samsung Galaxy A52 running the stock OS, but it also fails on a Pixel 8.

[dreautall]

Additional information after some testing: The minimum example provided in https://github.com/dart-lang/http/tree/master/pkgs/cronet_http/example only works when you leave in the line https://github.com/dart-lang/http/blob/master/pkgs/cronet_http/example/android/app/build.gradle#L76

According to the comment in that file, this line should be removed in applications. If you remove that line and run the same example app built with --dart-define=cronetHttpNoPlay=true, the app will fail with the same error message as above:

[ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: Exception in Java code called through JNI: java.lang.ClassNotFoundException: Didn't find class "org/chromium/net/CronetEngine$Builder" on path: DexPathList[[zip file "/data/app/~~I8ItowLGsmVoQ2kI3h2Emg==/io.flutter.cronet_http_example-IyQ_FmWiOsAjp7272xKdUg==/base.apk"],nativeLibraryDirectories=[/data/app/~~I8ItowLGsmVoQ2kI3h2Emg==/io.flutter.cronet_http_example-IyQ_FmWiOsAjp7272xKdUg==/lib/arm64, /data/app/~~I8ItowLGsmVoQ2kI3h2Emg==/io.flutter.cronet_http_example-IyQ_FmWiOsAjp7272xKdUg==/base.apk!/lib/arm64-v8a, /system/lib64, /system_ext/lib64]]

java.lang.ClassNotFoundException: Didn't find class "org/chromium/net/CronetEngine$Builder" on path: DexPathList[[zip file "/data/app/~~I8ItowLGsmVoQ2kI3h2Emg==/io.flutter.cronet_http_example-IyQ_FmWiOsAjp7272xKdUg==/base.apk"],nativeLibraryDirectories=[/data/app/~~I8ItowLGsmVoQ2kI3h2Emg==/io.flutter.cronet_http_example-IyQ_FmWiOsAjp7272xKdUg==/lib/arm64, /data/app/~~I8ItowLGsmVoQ2kI3h2Emg==/io.flutter.cronet_http_example-IyQ_FmWiOsAjp7272xKdUg==/base.apk!/lib/arm64-v8a, /system/lib64, /system_ext/lib64]]
      at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:259)
      at java.lang.ClassLoader.loadClass(ClassLoader.java:379)
      at java.lang.ClassLoader.loadClass(ClassLoader.java:312)

I'm not sure if you're able to detect whether GPS-Cronet or No-Play-Cronet is then actually used by the application, I unfortunately don't have a test device without Play Services at hand.

[veloce]

I also reproduce this issue either using flutter build or flutter run command.

It seems that the cronetHttpNoPlay=true flag does not work in release mode.

The app works fine with flutter run --dart-define=cronetHttpNoPlay=true (I can see the cronet version in the logs), but it ceases to work if I append --release (same class not found issue).

[brianquinlan]

@AlexV525 Did you want to take a look at this?

[AlexV525]

It sounds like a obfuscate issue with native methods, but since they actually exported the same entryport the guess might be incorrect. Could anyone try with minifyEnabled disabled?

[AlexV525]

https://developer.android.com/build/multidex#multidexkeepproguard-property might be helpful too.

[KevinCFechtel]

With minifyEnabled and shrinkResources disabled, the error no longer occurs for me.
Unfortunately, the multiDexKeepProguard property file did not work for me.

[AlexV525]

So the solution we should try is providing the proguard rules that exclude the cronet library. I'll request changes later. Thanks for the feedback.

[dreautall]

Can confirm a proguard-rules.pro file with this content fixes the issue in release mode with minifyEnabled and shrinkResources enabled.

-keep class org.chromium.** { *; }
-keep class io.flutter.plugins.cronet_http.** { *; }

I'm no expert in proguard rules and have not tried to "trim it down" for now. Might be the second line is useless, for example.