libsodium integration on android

Question

I'm trying to integrate libsodium library on Android project. I'm using Android Studio (0.5.8) with gradle (0.9) and android build tools (19.1). I compiled libsodium with scripts that can be found in the library. I get four preBuild libs (.so files) for different architectures (arm, arm-v7a, mips & x86). I put this files inside the jniLibs folder. I declare in my build.gradle file that I'm using NDK and configure the path on local.properties file.

In this version of gradle, it's not necessary to write a makefile (http://ph0b.com/android-studio-gradle-and-ndk-integration/)

I declare some native functions in my activity after do a static call:

static {
    System.loadLibrary("sodium");
}

public final static native String sodium_version_string();

onCreate() {
    ...
    Log.d(getClass().getName(), "Sodium version:" + sodium_version_string());
}

Logcat output is:

05-29 23:14:10.538     481-1569/system_process I/ActivityManager﹕ Start proc com.example.myapplication2.app.x86 for activity com.example.myapplication2.app.x86/com.example.myapplication2.app.MainActivity: pid=1584 uid=10056 gids={50056, 1028}
05-29 23:14:10.554    1584-1584/com.example.myapplication2.app.x86 D/dalvikvm﹕ Trying to load lib /data/app-lib/com.example.myapplication2.app.x86-2/libsodium.so 0xa4ed8520
05-29 23:14:10.562    1584-1584/com.example.myapplication2.app.x86 D/dalvikvm﹕ Added shared lib /data/app-lib/com.example.myapplication2.app.x86-2/libsodium.so 0xa4ed8520
05-29 23:14:10.562    1584-1584/com.example.myapplication2.app.x86 D/dalvikvm﹕ No JNI_OnLoad found in /data/app-lib/com.example.myapplication2.app.x86-2/libsodium.so 0xa4ed8520, skipping init
05-29 23:14:10.578    1584-1584/com.example.myapplication2.app.x86 W/dalvikvm﹕ No implementation found for native Lcom/example/myapplication2/app/MainActivity;.sodium_version_string:()Ljava/lang/String;
05-29 23:14:10.578    1584-1584/com.example.myapplication2.app.x86 D/AndroidRuntime﹕ Shutting down VM
05-29 23:14:10.578    1584-1584/com.example.myapplication2.app.x86 W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0xa4c46648)
05-29 23:14:10.578    1584-1584/com.example.myapplication2.app.x86 E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.UnsatisfiedLinkError: Native method not found: com.example.myapplication2.app.MainActivity.sodium_version_string:()Ljava/lang/String;
        at com.example.myapplication2.app.MainActivity.sodium_version_string(Native Method)
        at com.example.myapplication2.app.MainActivity.onCreate(MainActivity.java:28)

Do I missing to declare something in another file? Is it really necessary kalium-JNI ? How can this lib be included in the project?

Thanks.

Answer 1

Right now your Java code has no way to know how to use your native library. You need to do the JNI part, either by using Kalium-JNI or implementing only the parts you need.

In the case of sodium_version_string(), this should work:

jstring java_com_example_myapplication2_app_MainActivity_sodium_version_string(JNIEnv* env, jclass cls)
{
    return (env*)->NewStringUTF(env, sodium_version_string());
}

Here java_com_example_myapplication2_app_MainActivity_sodium_version_string implementation will be automatically associated to your static native String sodium_version_string() thanks to JNI convention.

You can use JNI_Onload() instead to manually declare such association, but you still need to deal with JNI environment and objects inside the implementations.