android-go/examples/dex/dex_android.go

package main

/*
#cgo LDFLAGS: -landroid -llog

#include <stdlib.h>
#include <jni.h>
#include <android/log.h>

static jobject gClassLoader;
static jmethodID gFindClassMethod;

jobject
CreateObject(JNIEnv* env, jclass cls) {
        jmethodID init = (*env)->GetMethodID(env, cls, "<init>", "()V");
        return (*env)->NewObject(env, cls, init);
}

jmethodID GetMethodID(JNIEnv *env, jclass cls, const char *name, const char *sig) {
	return (*env)->GetMethodID(env, cls, name, sig);
}

jclass
FindClass(JNIEnv* env, char* name) {
	jstring strClassName = (*env)->NewStringUTF(env, name);
	return (*env)->CallObjectMethod(env, gClassLoader, gFindClassMethod, strClassName);
}

void
SetupJVM(JNIEnv* env, jobject context, void* buf, int len) {
	jclass cls = (*env)->GetObjectClass(env, context);
	jmethodID mid = (*env)->GetMethodID(env, cls, "getClassLoader", "()Ljava/lang/ClassLoader;");
	jobject loader = (*env)->CallObjectMethod(env, context, mid);
	gClassLoader = (*env)->NewGlobalRef(env, loader);
	cls = (*env)->GetObjectClass(env, loader);
	gFindClassMethod = (*env)->GetMethodID(env, cls, "findClass", "(Ljava/lang/String;)Ljava/lang/Class;");

	__android_log_write(ANDROID_LOG_DEBUG, "gio", "Looking for InMemoryDexClassLoader");
	cls = (*env)->FindClass(env, "dalvik/system/InMemoryDexClassLoader");
	if (cls == NULL) {
		__android_log_write(ANDROID_LOG_DEBUG, "gio", "not found");
		return;
	}
	__android_log_write(ANDROID_LOG_DEBUG, "gio", "NewDirectByteBuffer");
	jobject bbuf = (*env)->NewDirectByteBuffer(env, buf, (jlong)len);
	if (bbuf == NULL) {
		__android_log_write(ANDROID_LOG_DEBUG, "gio", "failed");
		return;
	}

	__android_log_write(ANDROID_LOG_DEBUG, "gio", "looking for <init>");
	mid = (*env)->GetMethodID(env, cls, "<init>", "(Ljava/nio/ByteBuffer;Ljava/lang/ClassLoader;)V");
	if (mid == NULL) {
		__android_log_write(ANDROID_LOG_DEBUG, "gio", "not found");
		return;
	}
	__android_log_write(ANDROID_LOG_DEBUG, "gio", "calling <init>");
	jobject dexLoader = (*env)->NewObject(env, cls, mid, bbuf, gClassLoader);
	// make the dexLoader our new class loader
	gClassLoader = (*env)->NewGlobalRef(env, dexLoader);
}

//	__android_log_write(ANDROID_LOG_DEBUG, "gio", "looking for AClass");
//	cls = FindClass(env, "st/wow/git/dex/AClass");
//	if (cls == NULL) {
//		__android_log_write(ANDROID_LOG_DEBUG, "gio", "not found");
//		return;
//	}
//
//	__android_log_write(ANDROID_LOG_DEBUG, "gio", "calling CreateObject");
//	jobject obj = CreateObject(env, cls);
//	if (obj == NULL) {
//		__android_log_write(ANDROID_LOG_DEBUG, "gio", "failed");
//		return;
//	}
//
//	__android_log_write(ANDROID_LOG_DEBUG, "gio", "looking for <init>");
//	mid = (*env)->GetMethodID(env, cls, "<init>", "()V");
//	if (mid == NULL) {
//		__android_log_write(ANDROID_LOG_DEBUG, "gio", "not found");
//		return;
//	}
//	__android_log_write(ANDROID_LOG_DEBUG, "gio", "creating object");
//	obj = (*env)->NewObject(env, cls, mid);
//	if (obj == NULL) {
//		__android_log_write(ANDROID_LOG_DEBUG, "gio", "failed");
//		return;
//	}
//
//	__android_log_write(ANDROID_LOG_DEBUG, "gio", "looking for Num");
//	mid = (*env)->GetMethodID(env, cls, "Num", "()I");
//	if (mid == NULL) {
//		__android_log_write(ANDROID_LOG_DEBUG, "gio", "not found");
//		return;
//	}
//	jint val = (*env)->CallIntMethod(env, obj, mid);
//	__android_log_print(ANDROID_LOG_DEBUG, "gio", "value = %d", val);


jint
CallIntMethod(JNIEnv *env, jobject obj, jmethodID methodID) {
	return (*env)->CallIntMethod(env, obj, methodID);
}

jint
GetEnv(JavaVM *vm, JNIEnv **env, jint version) {
	return (*vm)->GetEnv(vm, (void **)env, version);
}

jint
AttachCurrentThread(JavaVM *vm, JNIEnv **p_env, void *thr_args) {
	return (*vm)->AttachCurrentThread(vm, p_env, thr_args);
}

jint
DetachCurrentThread(JavaVM *vm) {
	return (*vm)->DetachCurrentThread(vm);
}

*/
import "C"

import (
	"errors"
	"fmt"
	"runtime"
	"unsafe"

	"gioui.org/app"
)

var theJVM *C.JavaVM

func SetJVM() {
	h := app.PlatformHandle()
	theJVM = (*C.JavaVM)(unsafe.Pointer(h.JVM))
	dex := MustAsset("java/classes.dex")
	RunInJVM(func(env *C.JNIEnv) {
		labchan <- "Set up JVM"
		C.SetupJVM(
			env,
			(C.jobject)(h.Context),
			unsafe.Pointer(&dex[0]),
			C.int(len(dex)),
		)
	})
}

func CallJNI() {
	labchan <- "Call JNI"
	RunInJVM(func(env *C.JNIEnv) {
		labchan <- "FindClass"
		cls := JniFindClass(env, "st/wow/git/dex/AClass")
		labchan <- "GetMethodID"
		mid := JniGetMethodID(env, cls, "Num", "()I")
		labchan <- "CreateObject"
		obj := JniCreateObject(env, cls)
		val := JniCallIntMethod(env, obj, mid)
		labchan <- fmt.Sprintf("val = %d", val)
	})
}

func JniFindClass(env *C.JNIEnv, name string) C.jclass {
	cname := C.CString(name)
	defer C.free(unsafe.Pointer(cname))
	return C.FindClass((*C.JNIEnv)(env), cname)
}

func JniCreateObject(env *C.JNIEnv, cls C.jclass) C.jobject {
	return C.CreateObject(env, (C.jclass)(cls))
}

func JniCallIntMethod(env *C.JNIEnv, obj C.jobject, methodID C.jmethodID) int {
	return (int)(C.CallIntMethod(env, obj, methodID))
}

func JniGetMethodID(env *C.JNIEnv, cls C.jclass, name, sig string) C.jmethodID {
	cname := C.CString(name)
	defer C.free(unsafe.Pointer(cname))
	csig := C.CString(sig)
	defer C.free(unsafe.Pointer(csig))
	return C.GetMethodID(env, cls, cname, csig)
}

func RunInJVM(f func(env *C.JNIEnv)) {
        runtime.LockOSThread()
        defer runtime.UnlockOSThread()
        var env *C.JNIEnv
        var detach bool
        if res := C.GetEnv(theJVM, &env, C.JNI_VERSION_1_6); res != C.JNI_OK {
                if res != C.JNI_EDETACHED {
                        panic(fmt.Errorf("JNI GetEnv failed with error %d", res))
                }
                if C.AttachCurrentThread(theJVM, &env, nil) != C.JNI_OK {
                        panic(errors.New("runInJVM: AttachCurrentThread failed"))
                }
                detach = true
        }

        if detach {
                defer func() {
                        C.DetachCurrentThread(theJVM)
                }()
        }
        f(env)
}