Log stack traces from exceptions thrown by calls from native into Java (#4346)

fml/platform/android/jni_util.cc

@@ -123,5 +123,47 @@ bool ClearException(JNIEnv* env) {
   return true;
 }
 
+std::string GetJavaExceptionInfo(JNIEnv* env, jthrowable java_throwable) {
+  ScopedJavaLocalRef<jclass> throwable_clazz(
+      env, env->FindClass("java/lang/Throwable"));
+  jmethodID throwable_printstacktrace = env->GetMethodID(
+      throwable_clazz.obj(), "printStackTrace", "(Ljava/io/PrintStream;)V");
+
+  // Create an instance of ByteArrayOutputStream.
+  ScopedJavaLocalRef<jclass> bytearray_output_stream_clazz(
+      env, env->FindClass("java/io/ByteArrayOutputStream"));
+  jmethodID bytearray_output_stream_constructor =
+      env->GetMethodID(bytearray_output_stream_clazz.obj(), "<init>", "()V");
+  jmethodID bytearray_output_stream_tostring = env->GetMethodID(
+      bytearray_output_stream_clazz.obj(), "toString", "()Ljava/lang/String;");
+  ScopedJavaLocalRef<jobject> bytearray_output_stream(
+      env, env->NewObject(bytearray_output_stream_clazz.obj(),
+                          bytearray_output_stream_constructor));
+
+  // Create an instance of PrintStream.
+  ScopedJavaLocalRef<jclass> printstream_clazz(
+      env, env->FindClass("java/io/PrintStream"));
+  jmethodID printstream_constructor = env->GetMethodID(
+      printstream_clazz.obj(), "<init>", "(Ljava/io/OutputStream;)V");
+  ScopedJavaLocalRef<jobject> printstream(
+      env, env->NewObject(printstream_clazz.obj(), printstream_constructor,
+                          bytearray_output_stream.obj()));
+
+  // Call Throwable.printStackTrace(PrintStream)
+  env->CallVoidMethod(java_throwable, throwable_printstacktrace,
+                      printstream.obj());
+
+  // Call ByteArrayOutputStream.toString()
+  ScopedJavaLocalRef<jstring> exception_string(
+      env,
+      static_cast<jstring>(env->CallObjectMethod(
+          bytearray_output_stream.obj(), bytearray_output_stream_tostring)));
+  if (ClearException(env)) {
+    return "Java OOM'd in exception handling, check logcat";
+  }
+
+  return JavaStringToString(env, exception_string.obj());
+}
+
 }  // namespace jni
 }  // namespace fml

fml/platform/android/jni_util.h

@@ -36,6 +36,8 @@ bool HasException(JNIEnv* env);
 
 bool ClearException(JNIEnv* env);
 
+std::string GetJavaExceptionInfo(JNIEnv* env, jthrowable java_throwable);
+
 }  // namespace jni
 }  // namespace fml
 

shell/platform/android/platform_view_android_jni.cc

@@ -18,6 +18,21 @@
 
 namespace shell {
 
+namespace {
+
+bool CheckException(JNIEnv* env) {
+  if (env->ExceptionCheck() == JNI_FALSE)
+    return true;
+
+  jthrowable exception = env->ExceptionOccurred();
+  env->ExceptionClear();
+  FXL_LOG(INFO) << fml::jni::GetJavaExceptionInfo(env, exception);
+  env->DeleteLocalRef(exception);
+  return false;
+}
+
+}  // anonymous namespace
+
 static fml::jni::ScopedJavaGlobalRef<jclass>* g_flutter_view_class = nullptr;
 static fml::jni::ScopedJavaGlobalRef<jclass>* g_flutter_native_view_class =
     nullptr;
@@ -33,7 +48,7 @@ void FlutterViewHandlePlatformMessage(JNIEnv* env,
                                       jint responseId) {
   env->CallVoidMethod(obj, g_handle_platform_message_method, channel, message,
                       responseId);
-  FXL_CHECK(env->ExceptionCheck() == JNI_FALSE);
+  FXL_CHECK(CheckException(env));
 }
 
 static jmethodID g_handle_platform_message_response_method = nullptr;
@@ -43,7 +58,7 @@ void FlutterViewHandlePlatformMessageResponse(JNIEnv* env,
                                               jobject response) {
   env->CallVoidMethod(obj, g_handle_platform_message_response_method,
                       responseId, response);
-  FXL_CHECK(env->ExceptionCheck() == JNI_FALSE);
+  FXL_CHECK(CheckException(env));
 }
 
 static jmethodID g_update_semantics_method = nullptr;
@@ -52,34 +67,34 @@ void FlutterViewUpdateSemantics(JNIEnv* env,
                                 jobject buffer,
                                 jobjectArray strings) {
   env->CallVoidMethod(obj, g_update_semantics_method, buffer, strings);
-  FXL_CHECK(env->ExceptionCheck() == JNI_FALSE);
+  FXL_CHECK(CheckException(env));
 }
 
 static jmethodID g_on_first_frame_method = nullptr;
 void FlutterViewOnFirstFrame(JNIEnv* env, jobject obj) {
   env->CallVoidMethod(obj, g_on_first_frame_method);
-  FXL_CHECK(env->ExceptionCheck() == JNI_FALSE);
+  FXL_CHECK(CheckException(env));
 }
 
 static jmethodID g_attach_to_gl_context_method = nullptr;
 void SurfaceTextureAttachToGLContext(JNIEnv* env, jobject obj, jint textureId) {
   ASSERT_IS_GPU_THREAD;
   env->CallVoidMethod(obj, g_attach_to_gl_context_method, textureId);
-  FXL_CHECK(env->ExceptionCheck() == JNI_FALSE);
+  FXL_CHECK(CheckException(env));
 }
 
 static jmethodID g_update_tex_image_method = nullptr;
 void SurfaceTextureUpdateTexImage(JNIEnv* env, jobject obj) {
   ASSERT_IS_GPU_THREAD;
   env->CallVoidMethod(obj, g_update_tex_image_method);
-  FXL_CHECK(env->ExceptionCheck() == JNI_FALSE);
+  FXL_CHECK(CheckException(env));
 }
 
 static jmethodID g_detach_from_gl_context_method = nullptr;
 void SurfaceTextureDetachFromGLContext(JNIEnv* env, jobject obj) {
   ASSERT_IS_GPU_THREAD;
   env->CallVoidMethod(obj, g_detach_from_gl_context_method);
-  FXL_CHECK(env->ExceptionCheck() == JNI_FALSE);
+  FXL_CHECK(CheckException(env));
 }
 
 // Called By Java