Why does Prefab NDK Dependencies not work?

Question

I have some native code that depends on OpenSSL. In the beginning, I tried manually compiling OpenSSL for Android, but it simply wouldn't find the definitions. Then I decided to move on and try using Prefabs instead. I followed the example Android NDK Prefab example, but it just doesn't work.

My CMakeLists contains the following

find_package(openssl REQUIRED CONFIG)

target_link_libraries(
    testproject
    openssl::openssl)

My build.gradle:

android {
compileSdk 31

defaultConfig {
    minSdk 21
    targetSdk 32
    versionCode 1
    versionName "1.0"

    testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    consumerProguardFiles "consumer-rules.pro"
    externalNativeBuild {
        cmake {
            cppFlags ""
        }
    }
}

buildTypes {
    release {
        minifyEnabled false
        proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
    }
}

buildFeatures {
    prefab true
}
externalNativeBuild {
    cmake {
        path "src/main/cpp/CMakeLists.txt"
        version "3.10.2"
    }
}
compileOptions {
    sourceCompatibility JavaVersion.VERSION_1_8
    targetCompatibility JavaVersion.VERSION_1_8
}
}

dependencies {

implementation 'androidx.appcompat:appcompat:1.4.0'
implementation 'com.google.android.material:material:1.4.0'
implementation 'com.android.ndk.thirdparty:openssl:1.1.1l-beta-1'
testImplementation 'junit:junit:4.+'
androidTestImplementation 'androidx.test.ext:junit:1.1.3'
androidTestImplementation 'androidx.test.espresso:espresso-core:3.4.0'
}

But whenever I compile, I get

  Could not find a package configuration file provided by "openssl" with any
  of the following names:

opensslConfig.cmake
openssl-config.cmake

Looking into the downloaded data, I see the openSSL folder under cmake only contains opensslConfigVersion.cmake and not opensslConfig.cmake, as it does with curl, for example.

What is going on? Why is this not working? Any help is appreiciated.

Answer 1

The curl-ssl example in the [ndk samples](gitclo https://github.com/android/ndk-samples) only builds because it allows C++ and STL. But openssl is C only.

The maven repo ndk thirdparty links to the sources for the prefab package for openssl and curl among others, i.e. ndkports.

There is no reference to C++ there for openssl. It seems the problem is by prefab.

I found this issues: OpenSSL forces c++_shared – why?

Judging from this and other issues there is a high chance that prefab might just not fit your and my project as of yet.

You don't get an according curl message, because curl depends on openssl, which makes the latter build first. If you remove openssl you get:

  Error: curl depends on unknown dependency openssl

I first did have no ndkVersion defined, as you. Only afterward I got more error messages:

... //openssl/crypto. Rejected the following libraries:
C/C++: prefabandroid.arm64-v8a: User is targeting armeabi-v7a but library is for arm64-v8a

Removing armeabi-v7a from

        ndk.abiFilters 'x86', 'x86_64', 'armeabi-v7a', 'arm64-v8a'

I got

... //openssl/ssl. Rejected the following libraries:
C/C++: prefabandroid.arm64-v8a: User requested no STL but library requires libc++
C/C++: prefabandroid.armeabi-v7a: User is targeting arm64-v8a but library is for armeabi-v7a

Another sign that prefab is ealily getting confused.

And because it was not built finally:

    Could not find a package configuration file provided by "openssl" with any
    of the following names:
··
      opensslConfig.cmake
      openssl-config.cmake

The file refers to

app/.cxx/cmake/debug/prefab/arm64-v8a/prefab/lib/aarch64-linux-android/cmake/openssl/opensslConfig.cmake

This has links that point to ~/.gradle. So the include and link directories are somewhere deep down in ~/.gradle and not under the project directory.

One can include native code directly via cmake. The ndkports are a starting point for to configuration.