Aghajari / Go-JNI-Android

A template project to use go as a native library in android projects

Go-JNI-Android

A template project to use go as a native library in android projects

1. First of all, you should add JNI support to your project. Official Tutorial
2. Create jni/cpp folder (New -> Folder -> JNI/CPP Folder)
3. Create a .c/.cpp file in jni/cpp for creating a c library (for example: c_android.c)
4. Create CMakeFiles.txt in jni/cpp

cmake_minimum_required(VERSION 3.4.1)

SET(C_LIB native-lib)

add_library(${C_LIB}
        SHARED
        c_android.c)

find_library(log-lib log)
target_link_libraries(${C_LIB} ${log-lib})

5. Add externalNativeBuild to build.gradle (Module: app)

buildTypes {
    ...
    
    externalNativeBuild {
        cmake {
            path "src/main/jni/CMakeLists.txt" // jni/cpp
        }
    }
}

6. You should be able to build and compile your project if you have done everything successfully!

7. Install Go (If you haven't done it already)

Verify that you've installed Go by opening a command prompt and typing the following command:

$ go version

8. Create a folder named go for go sources
9. Ceate makefile in go with following codes

NDK_GO_ARCH_x86 := 386
NDK_GO_ARCH_x86_64 := amd64
NDK_GO_ARCH_arm := arm
NDK_GO_ARCH_arm64 := arm64
NDK_GO_ARCH_mips := mipsx
NDK_GO_ARCH_mips64 := mips64x

CLANG_FLAGS := --target=$(ANDROID_LLVM_TRIPLE) --gcc-toolchain=$(ANDROID_TOOLCHAIN_ROOT) --sysroot=$(ANDROID_SYSROOT)
export CGO_CFLAGS := $(CLANG_FLAGS) $(CFLAGS)
export CGO_LDFLAGS := $(CLANG_FLAGS) $(LDFLAGS) -Wl,-soname=${SONAME}
export CC := $(ANDROID_C_COMPILER)
export GOARCH := $(NDK_GO_ARCH_$(ANDROID_ARCH_NAME))
export GOOS := android
export CGO_ENABLED := 1

$(BUILDDIR)/${SONAME}:
	go build -o "$(BUILDDIR)/${SONAME}" -buildmode c-shared

.DELETE_ON_ERROR:

10. Edit CMakeFiles.txt to include go as a target

cmake_minimum_required(VERSION 3.4.1)

SET(C_LIB native-lib)
SET(GO_LIB native-lib-go)

add_library(${C_LIB}
        SHARED
        c_android.c)

add_custom_target(${GO_LIB}
        WORKING_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}/go"
        COMMENT "Building ${GO_LIB}"
        VERBATIM COMMAND make
        ANDROID_ARCH_NAME=${ANDROID_ARCH_NAME}
        ANDROID_C_COMPILER=${ANDROID_C_COMPILER}
        ANDROID_TOOLCHAIN_ROOT=${ANDROID_TOOLCHAIN_ROOT}
        ANDROID_LLVM_TRIPLE=${ANDROID_LLVM_TRIPLE}
        ANDROID_SYSROOT=${ANDROID_SYSROOT}
        ANDROID_PACKAGE_NAME=${ANDROID_PACKAGE_NAME}
        GRADLE_USER_HOME=${GRADLE_USER_HOME}
        CFLAGS=${CMAKE_C_FLAGS}\ -Wno-unused-command-line-argument
        LDFLAGS=${CMAKE_SHARED_LINKER_FLAGS}\ -fuse-ld=gold
        BUILDDIR=${CMAKE_LIBRARY_OUTPUT_DIRECTORY}
        SONAME=lib${GO_LIB}.so)

add_dependencies(${C_LIB} ${GO_LIB})

find_library(log-lib log)
target_link_libraries(${C_LIB} ${log-lib})

11. Create a .go file in go folder

package main

import "C"

// export functionName => makes function accessible in c

//export goHelloWorld
func goHelloWorld() *C.char {
    return C.CString("Hello :)")
}

//export goInteger
func goInteger() int {
    return 24
}

func main() {}

12. Create a .c/.cpp file for connecting go to jni (I suggest you name it JNI.c)

#include <jni.h>

extern char *goHelloWorld();
extern int goInteger();

jstring Java_packagename_ClassName_helloWorld(JNIEnv *env, jclass clazz) {
    return (*env)->NewStringUTF(env, goHelloWorld());
}

jint Java_packagename_ClassName_integerTest(JNIEnv *env, jclass clazz) {
    return goInteger();
}

13. Create the java class

package packagename;

public class ClassName {
    static {
        System.loadLibrary("native-lib-go"); // CMakeLists.txt => ${GO_Lib}
    }
    
    public static native String helloWorld();
    public static native int integerTest();
}

14. And everything is done!

You can also directly link java & go function like this :

//export Java_packagename_ClassName_goTest
func Java_packagename_ClassName_goTest(env uintptr, clazz uintptr) int {
    return 100
}

public static native int goTest();