C++ on Android example client and server

22 files changed, 949 insertions, 0 deletions

diff --git a/examples/android/helloworld/.gitignore b/examples/android/helloworld/.gitignore
new file mode 100644
index 0000000000..39fb081a42
--- /dev/null
+++ b/examples/android/helloworld/.gitignore
@@ -0,0 +1,9 @@
+*.iml
+.gradle
+/local.properties
+/.idea/workspace.xml
+/.idea/libraries
+.DS_Store
+/build
+/captures
+.externalNativeBuild
diff --git a/examples/android/helloworld/README.md b/examples/android/helloworld/README.md
new file mode 100644
index 0000000000..ebb16d136b
--- /dev/null
+++ b/examples/android/helloworld/README.md
@@ -0,0 +1,24 @@
+gRPC on Android
+==============
+
+Note: Building the protobuf dependency for Android requires
+https://github.com/google/protobuf/pull/3878. This fix will be in the next
+protobuf release, but until then must be manually patched in to
+`third_party/protobuf` to build gRPC for Android.
+
+PREREQUISITES
+-------------
+
+- Android SDK
+- Android NDK
+- `protoc` and `grpc_cpp_plugin` binaries on the host system
+
+INSTALL
+-------
+
+The example application can be built via Android Studio or on the command line
+using `gradle`:
+
+  ```sh
+  $ ./gradlew installDebug
+  ```
diff --git a/examples/android/helloworld/app/.gitignore b/examples/android/helloworld/app/.gitignore
new file mode 100644
index 0000000000..796b96d1c4
--- /dev/null
+++ b/examples/android/helloworld/app/.gitignore
@@ -0,0 +1 @@
+/build
diff --git a/examples/android/helloworld/app/CMakeLists.txt b/examples/android/helloworld/app/CMakeLists.txt
new file mode 100644
index 0000000000..6ee18daaab
--- /dev/null
+++ b/examples/android/helloworld/app/CMakeLists.txt
@@ -0,0 +1,123 @@
+cmake_minimum_required(VERSION 3.4.1)
+
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
+
+set(helloworld_PROTOBUF_PROTOC_EXECUTABLE "/usr/local/bin/protoc" CACHE STRING "Protoc binary on host")
+set(helloworld_GRPC_CPP_PLUGIN_EXECUTABLE "/usr/local/bin/grpc_cpp_plugin" CACHE STRING "gRPC CPP plugin binary on host")
+
+set(GRPC_SRC_DIR ../../../../)
+
+set(GRPC_BUILD_DIR ../grpc/outputs/${ANDROID_ABI})
+file(MAKE_DIRECTORY ${GRPC_BUILD_DIR})
+
+add_subdirectory(${GRPC_SRC_DIR} ${GRPC_BUILD_DIR})
+
+include_directories(${GRPC_SRC_DIR}/include)
+
+add_library(libgrpc STATIC IMPORTED)
+set_target_properties(libgrpc PROPERTIES IMPORTED_LOCATION
+  ${GRPC_BUILD_DIR}/libgrpc.a)
+
+add_library(libgrpc++ STATIC IMPORTED)
+set_target_properties(libgrpc++ PROPERTIES IMPORTED_LOCATION
+  ${GRPC_BUILD_DIR}/libgrpc++.a)
+
+add_library(libgpr STATIC IMPORTED)
+set_target_properties(libgpr PROPERTIES IMPORTED_LOCATION
+  ${GRPC_BUILD_DIR}/libgpr.a)
+
+add_library(libcares STATIC IMPORTED)
+set_target_properties(libcares PROPERTIES IMPORTED_LOCATION
+  ${GRPC_BUILD_DIR}/third_party/cares/cares/lib/libcares.a)
+
+add_library(libzlib STATIC IMPORTED)
+set_target_properties(libzlib PROPERTIES IMPORTED_LOCATION
+  ${GRPC_BUILD_DIR}/third_party/zlib/libz.a)
+
+add_library(libcrypto STATIC IMPORTED)
+set_target_properties(libcrypto PROPERTIES IMPORTED_LOCATION
+  ${GRPC_BUILD_DIR}/third_party/boringssl/crypto/libcrypto.a)
+
+add_library(libssl STATIC IMPORTED)
+set_target_properties(libssl PROPERTIES IMPORTED_LOCATION
+  ${GRPC_BUILD_DIR}/third_party/boringssl/ssl/libssl.a)
+
+set(GRPC_PROTO_GENS_DIR ${CMAKE_BINARY_DIR}/gens)
+file(MAKE_DIRECTORY ${GRPC_PROTO_GENS_DIR})
+include_directories(${GRPC_PROTO_GENS_DIR})
+
+function(android_protobuf_grpc_generate_cpp SRC_FILES HDR_FILES INCLUDE_ROOT)
+  if(NOT ARGN)
+    message(SEND_ERROR "Error: android_protobuf_grpc_generate_cpp() called without any proto files")
+    return()
+  endif()
+
+  set(${SRC_FILES})
+  set(${HDR_FILES})
+  set(PROTOBUF_INCLUDE_PATH -I ${INCLUDE_ROOT})
+  foreach(FIL ${ARGN})
+    get_filename_component(ABS_FIL ${FIL} ABSOLUTE)
+    get_filename_component(FIL_WE ${FIL} NAME_WE)
+    file(RELATIVE_PATH REL_FIL ${CMAKE_CURRENT_SOURCE_DIR}/${INCLUDE_ROOT} ${ABS_FIL})
+    get_filename_component(REL_DIR ${REL_FIL} DIRECTORY)
+    set(RELFIL_WE "${REL_DIR}/${FIL_WE}")
+
+    list(APPEND ${SRC_FILES} "${GRPC_PROTO_GENS_DIR}/${RELFIL_WE}.pb.cc")
+    list(APPEND ${HDR_FILES} "${GRPC_PROTO_GENS_DIR}/${RELFIL_WE}.pb.h")
+    list(APPEND ${SRC_FILES} "${GRPC_PROTO_GENS_DIR}/${RELFIL_WE}.grpc.pb.cc")
+    list(APPEND ${HDR_FILES} "${GRPC_PROTO_GENS_DIR}/${RELFIL_WE}.grpc.pb.h")
+
+    add_custom_command(
+      OUTPUT "${GRPC_PROTO_GENS_DIR}/${RELFIL_WE}.grpc.pb.cc"
+             "${GRPC_PROTO_GENS_DIR}/${RELFIL_WE}.grpc.pb.h"
+             "${GRPC_PROTO_GENS_DIR}/${RELFIL_WE}.pb.cc"
+             "${GRPC_PROTO_GENS_DIR}/${RELFIL_WE}.pb.h"
+      COMMAND ${helloworld_PROTOBUF_PROTOC_EXECUTABLE}
+      ARGS --grpc_out=${GRPC_PROTO_GENS_DIR}
+        --cpp_out=${GRPC_PROTO_GENS_DIR}
+        --plugin=protoc-gen-grpc=${helloworld_GRPC_CPP_PLUGIN_EXECUTABLE}
+        ${PROTOBUF_INCLUDE_PATH}
+        ${REL_FIL}
+      WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
+      DEPENDS ${helloworld_PROTOBUF_PROTOC_EXECUTABLE} ${helloworld_GRPC_CPP_PLUGIN_EXECUTABLE} ${ABS_FIL} )
+  endforeach()
+
+  set_source_files_properties(${${SRC_FILES}} ${${HDR_FILES}} PROPERTIES GENERATED TRUE)
+  set(${SRC_FILES} ${${SRC_FILES}} PARENT_SCOPE)
+  set(${HDR_FILES} ${${HDR_FILES}} PARENT_SCOPE)
+endfunction()
+
+set(PROTO_BASE_DIR ${GRPC_SRC_DIR}/examples/protos)
+
+android_protobuf_grpc_generate_cpp(
+  HELLOWORLD_PROTO_SRCS HELLOWORLD_PROTO_HDRS ${PROTO_BASE_DIR} ${PROTO_BASE_DIR}/helloworld.proto)
+
+add_library(helloworld_proto_lib
+  SHARED ${HELLOWORLD_PROTO_HDRS} ${HELLOWORLD_PROTO_SRCS})
+
+target_link_libraries(helloworld_proto_lib
+  libprotobuf
+  libgrpc++
+  android
+  log)
+
+find_library(log-lib
+ log)
+
+add_library(grpc-helloworld
+  SHARED src/main/cpp/grpc-helloworld.cc)
+
+target_include_directories(grpc-helloworld
+  PRIVATE ${HELLOWORLD_PROTO_HEADERS})
+
+target_link_libraries(grpc-helloworld
+  libgrpc++
+  libgrpc
+  libzlib
+  libcares
+  libssl
+  libcrypto
+  helloworld_proto_lib
+  libgpr
+  android
+  ${log-lib})
diff --git a/examples/android/helloworld/app/build.gradle b/examples/android/helloworld/app/build.gradle
new file mode 100644
index 0000000000..c6ab7308ae
--- /dev/null
+++ b/examples/android/helloworld/app/build.gradle
@@ -0,0 +1,53 @@
+apply plugin: 'com.android.application'
+
+android {
+    compileSdkVersion 26
+    defaultConfig {
+        applicationId "io.grpc.android.cpp.helloworldexample"
+        minSdkVersion 14
+        targetSdkVersion 26
+        versionCode 1
+        versionName "1.0"
+        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
+        externalNativeBuild {
+            cmake {
+                cppFlags "-std=c++14 -frtti -fexceptions"
+                arguments '-DANDROID_STL=c++_static'
+                arguments '-DRUN_HAVE_POSIX_REGEX=0'
+                arguments '-DRUN_HAVE_STD_REGEX=0'
+                arguments '-DRUN_HAVE_STEADY_CLOCK=0'
+                arguments '-Dprotobuf_BUILD_PROTOC_BINARIES=off'
+                arguments '-DgRPC_BUILD_CODEGEN=off'
+                // Set this to the path to the protoc binary on the host system (codegen is not
+                // cross-compiled to Android)
+                arguments '-Dhelloworld_PROTOBUF_PROTOC_EXECUTABLE=/usr/local/bin/protoc'
+                // Set this to the path to the gRPC C++ protoc plugin binary on the host system
+                // (codegen is not cross-compiled to Android)
+                arguments '-Dhelloworld_GRPC_CPP_PLUGIN_EXECUTABLE=/usr/local/bin/grpc_cpp_plugin'
+            }
+        }
+        ndk.abiFilters 'x86'
+    }
+    buildTypes {
+        debug {
+            minifyEnabled false
+        }
+        release {
+            minifyEnabled true
+            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
+        }
+    }
+    externalNativeBuild {
+        cmake {
+            path "CMakeLists.txt"
+        }
+    }
+}
+
+dependencies {
+    implementation fileTree(dir: 'libs', include: ['*.jar'])
+    implementation 'com.android.support:appcompat-v7:26.1.0'
+    testImplementation 'junit:junit:4.12'
+    androidTestImplementation 'com.android.support.test:runner:1.0.1'
+    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.1'
+}
diff --git a/examples/android/helloworld/app/proguard-rules.pro b/examples/android/helloworld/app/proguard-rules.pro
new file mode 100644
index 0000000000..f1b424510d
--- /dev/null
+++ b/examples/android/helloworld/app/proguard-rules.pro
@@ -0,0 +1,21 @@
+# Add project specific ProGuard rules here.
+# You can control the set of applied configuration files using the
+# proguardFiles setting in build.gradle.
+#
+# For more details, see
+#   http://developer.android.com/guide/developing/tools/proguard.html
+
+# If your project uses WebView with JS, uncomment the following
+# and specify the fully qualified class name to the JavaScript interface
+# class:
+#-keepclassmembers class fqcn.of.javascript.interface.for.webview {
+#   public *;
+#}
+
+# Uncomment this to preserve the line number information for
+# debugging stack traces.
+#-keepattributes SourceFile,LineNumberTable
+
+# If you keep the line number information, uncomment this to
+# hide the original source file name.
+#-renamesourcefileattribute SourceFile
diff --git a/examples/android/helloworld/app/src/main/AndroidManifest.xml b/examples/android/helloworld/app/src/main/AndroidManifest.xml
new file mode 100644
index 0000000000..8109da9e96
--- /dev/null
+++ b/examples/android/helloworld/app/src/main/AndroidManifest.xml
@@ -0,0 +1,22 @@
+<?xml version="1.0" encoding="utf-8"?>
+<manifest xmlns:android="http://schemas.android.com/apk/res/android"
+    package="io.grpc.helloworldexample.cpp" >
+
+    <uses-permission android:name="android.permission.INTERNET" />
+
+    <application
+        android:allowBackup="false"
+        android:icon="@mipmap/ic_launcher"
+        android:label="@string/app_name"
+        android:theme="@style/Base.V7.Theme.AppCompat.Light" >
+        <activity
+            android:name=".HelloworldActivity"
+            android:label="@string/app_name" >
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN" />
+                <category android:name="android.intent.category.LAUNCHER" />
+            </intent-filter>
+        </activity>
+    </application>
+
+</manifest>
diff --git a/examples/android/helloworld/app/src/main/cpp/grpc-helloworld.cc b/examples/android/helloworld/app/src/main/cpp/grpc-helloworld.cc
new file mode 100644
index 0000000000..7a31b783c4
--- /dev/null
+++ b/examples/android/helloworld/app/src/main/cpp/grpc-helloworld.cc
@@ -0,0 +1,142 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include <atomic>
+
+#include <grpc++/grpc++.h>
+#include <jni.h>
+
+#include "helloworld.grpc.pb.h"
+
+using grpc::Channel;
+using grpc::ClientContext;
+using grpc::Server;
+using grpc::ServerBuilder;
+using grpc::ServerContext;
+using grpc::Status;
+using helloworld::Greeter;
+using helloworld::HelloReply;
+using helloworld::HelloRequest;
+
+std::atomic<bool> stop_server(false);
+
+// Logic and data behind the server's behavior.
+class GreeterServiceImpl final : public Greeter::Service {
+  Status SayHello(ServerContext* context, const HelloRequest* request,
+                  HelloReply* reply) override {
+    std::string prefix("Hello ");
+    reply->set_message(prefix + request->name());
+    return Status::OK;
+  }
+};
+
+void StartServer(JNIEnv* env, jobject obj, jmethodID is_cancelled_mid,
+                 int port) {
+  const int host_port_buf_size = 1024;
+  char host_port[host_port_buf_size];
+  snprintf(host_port, host_port_buf_size, "0.0.0.0:%d", port);
+
+  GreeterServiceImpl service;
+  ServerBuilder builder;
+  // Listen on the given address without any authentication mechanism.
+  builder.AddListeningPort(host_port, grpc::InsecureServerCredentials());
+  // Register "service" as the instance through which we'll communicate with
+  // clients. In this case it corresponds to an *synchronous* service.
+  builder.RegisterService(&service);
+  // Finally assemble the server.
+  std::unique_ptr<Server> server(builder.BuildAndStart());
+  while (!stop_server.load()) {
+    // Check with the Java code to see if the user has requested the server stop or the app is no
+    // longer in the foreground.
+    jboolean is_cancelled = env->CallBooleanMethod(obj, is_cancelled_mid);
+    if (is_cancelled == JNI_TRUE) {
+      stop_server = true;
+    }
+  }
+}
+
+class GreeterClient {
+ public:
+  GreeterClient(std::shared_ptr<Channel> channel)
+      : stub_(Greeter::NewStub(channel)) {}
+
+  // Assembles the client's payload, sends it and presents the response back
+  // from the server.
+  std::string SayHello(const std::string& user) {
+    // Data we are sending to the server.
+    HelloRequest request;
+    request.set_name(user);
+
+    // Container for the data we expect from the server.
+    HelloReply reply;
+
+    // Context for the client. It could be used to convey extra information to
+    // the server and/or tweak certain RPC behaviors.
+    ClientContext context;
+    // The actual RPC.
+    Status status = stub_->SayHello(&context, request, &reply);
+
+    if (status.ok()) {
+      return reply.message();
+    } else {
+      return status.error_message();
+    }
+  }
+
+ private:
+  std::unique_ptr<Greeter::Stub> stub_;
+};
+
+// Send an RPC and return the response. Invoked from Java code.
+extern "C" JNIEXPORT jstring JNICALL
+Java_io_grpc_helloworldexample_cpp_HelloworldActivity_sayHello(
+    JNIEnv* env, jobject obj_unused, jstring host_raw, jint port_raw,
+    jstring message_raw) {
+  const char* host_chars = env->GetStringUTFChars(host_raw, (jboolean*)0);
+  std::string host(host_chars, env->GetStringUTFLength(host_raw));
+
+  int port = static_cast<int>(port_raw);
+
+  const char* message_chars = env->GetStringUTFChars(message_raw, (jboolean*)0);
+  std::string message(message_chars, env->GetStringUTFLength(message_raw));
+
+  const int host_port_buf_size = 1024;
+  char host_port[host_port_buf_size];
+  snprintf(host_port, host_port_buf_size, "%s:%d", host.c_str(), port);
+
+  GreeterClient greeter(
+      grpc::CreateChannel(host_port, grpc::InsecureChannelCredentials()));
+  std::string reply = greeter.SayHello(message);
+
+  return env->NewStringUTF(reply.c_str());
+}
+
+// Start the server. Invoked from Java code.
+extern "C" JNIEXPORT void JNICALL
+Java_io_grpc_helloworldexample_cpp_HelloworldActivity_startServer(
+    JNIEnv* env, jobject obj_this, jint port_raw) {
+  int port = static_cast<int>(port_raw);
+
+  jclass cls = env->GetObjectClass(obj_this);
+  jmethodID is_cancelled_mid =
+      env->GetMethodID(cls, "isRunServerTaskCancelled", "()Z");
+
+  stop_server = false;
+
+  StartServer(env, obj_this, is_cancelled_mid, port);
+}
diff --git a/examples/android/helloworld/app/src/main/java/io/grpc/helloworldexample/cpp/HelloworldActivity.java b/examples/android/helloworld/app/src/main/java/io/grpc/helloworldexample/cpp/HelloworldActivity.java
new file mode 100644
index 0000000000..ae5c88b208
--- /dev/null
+++ b/examples/android/helloworld/app/src/main/java/io/grpc/helloworldexample/cpp/HelloworldActivity.java
@@ -0,0 +1,167 @@
+/*
+ * Copyright 2018, gRPC Authors All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.grpc.helloworldexample.cpp;
+
+import android.content.Context;
+import android.os.AsyncTask;
+import android.os.Bundle;
+import android.support.v7.app.AppCompatActivity;
+import android.text.TextUtils;
+import android.text.method.ScrollingMovementMethod;
+import android.view.View;
+import android.view.inputmethod.InputMethodManager;
+import android.widget.Button;
+import android.widget.EditText;
+import android.widget.TextView;
+import android.widget.Toast;
+import java.lang.ref.WeakReference;
+
+public class HelloworldActivity extends AppCompatActivity {
+
+  static {
+    System.loadLibrary("grpc-helloworld");
+  }
+
+  private Button sendButton;
+  private Button serverButton;
+  private EditText hostEdit;
+  private EditText portEdit;
+  private EditText messageEdit;
+  private EditText serverPortEdit;
+  private TextView resultText;
+  private GrpcTask grpcTask;
+  private RunServerTask runServerTask;
+
+  @Override
+  protected void onCreate(Bundle savedInstanceState) {
+    super.onCreate(savedInstanceState);
+    setContentView(R.layout.activity_helloworld);
+    sendButton = (Button) findViewById(R.id.send_button);
+    serverButton = (Button) findViewById(R.id.server_button);
+    hostEdit = (EditText) findViewById(R.id.host_edit_text);
+    portEdit = (EditText) findViewById(R.id.port_edit_text);
+    messageEdit = (EditText) findViewById(R.id.message_edit_text);
+    serverPortEdit = (EditText) findViewById(R.id.server_port_edit_text);
+    resultText = (TextView) findViewById(R.id.grpc_response_text);
+    resultText.setMovementMethod(new ScrollingMovementMethod());
+  }
+
+  @Override
+  protected void onPause() {
+    super.onPause();
+    if (runServerTask != null) {
+      runServerTask.cancel(true);
+      runServerTask = null;
+      serverButton.setText("Start gRPC Server");
+    }
+    if (grpcTask != null) {
+      grpcTask.cancel(true);
+      grpcTask = null;
+    }
+  }
+
+  public void sendMessage(View view) {
+    ((InputMethodManager) getSystemService(Context.INPUT_METHOD_SERVICE))
+        .hideSoftInputFromWindow(hostEdit.getWindowToken(), 0);
+    sendButton.setEnabled(false);
+    resultText.setText("");
+    grpcTask = new GrpcTask(this);
+    grpcTask.executeOnExecutor(
+        AsyncTask.THREAD_POOL_EXECUTOR,
+        hostEdit.getText().toString(),
+        messageEdit.getText().toString(),
+        portEdit.getText().toString());
+  }
+
+  public void startOrStopServer(View view) {
+    if (runServerTask != null) {
+      runServerTask.cancel(true);
+      runServerTask = null;
+      serverButton.setText("Start gRPC Server");
+      Toast.makeText(this, "Server stopped", Toast.LENGTH_SHORT).show();
+    } else {
+      runServerTask = new RunServerTask(this);
+      String portStr = serverPortEdit.getText().toString();
+      int port = TextUtils.isEmpty(portStr) ? 50051 : Integer.valueOf(portStr);
+      runServerTask.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, port);
+      serverButton.setText("Stop gRPC Server");
+      Toast.makeText(this, "Server started on port " + port, Toast.LENGTH_SHORT).show();
+    }
+  }
+
+  private static class RunServerTask extends AsyncTask<Integer, Void, Void> {
+    private final WeakReference<HelloworldActivity> activityReference;
+
+    private RunServerTask(HelloworldActivity activity) {
+      this.activityReference = new WeakReference<HelloworldActivity>(activity);
+    }
+
+    @Override
+    protected Void doInBackground(Integer... params) {
+      int port = params[0];
+      HelloworldActivity activity = activityReference.get();
+      if (activity != null) {
+        activity.startServer(port);
+      }
+      return null;
+    }
+  }
+
+  private static class GrpcTask extends AsyncTask<String, Void, String> {
+    private final WeakReference<HelloworldActivity> activityReference;
+
+    private GrpcTask(HelloworldActivity activity) {
+      this.activityReference = new WeakReference<HelloworldActivity>(activity);
+    }
+
+    @Override
+    protected String doInBackground(String... params) {
+      String host = params[0];
+      String message = params[1];
+      String portStr = params[2];
+      int port = TextUtils.isEmpty(portStr) ? 50051 : Integer.valueOf(portStr);
+      return sayHello(host, port, message);
+    }
+
+    @Override
+    protected void onPostExecute(String result) {
+      HelloworldActivity activity = activityReference.get();
+      if (activity == null || isCancelled()) {
+        return;
+      }
+      TextView resultText = (TextView) activity.findViewById(R.id.grpc_response_text);
+      Button sendButton = (Button) activity.findViewById(R.id.send_button);
+      resultText.setText(result);
+      sendButton.setEnabled(true);
+    }
+  }
+
+  /**
+   * Invoked by native code to stop server when RunServerTask has been canceled, either by user
+   * request or upon app moving to background.
+   */
+  public boolean isRunServerTaskCancelled() {
+    if (runServerTask != null) {
+      return runServerTask.isCancelled();
+    }
+    return false;
+  }
+
+  public static native String sayHello(String host, int port, String message);
+
+  public native void startServer(int port);
+}
diff --git a/examples/android/helloworld/app/src/main/res/layout/activity_helloworld.xml b/examples/android/helloworld/app/src/main/res/layout/activity_helloworld.xml
new file mode 100644
index 0000000000..52804697a3
--- /dev/null
+++ b/examples/android/helloworld/app/src/main/res/layout/activity_helloworld.xml
@@ -0,0 +1,86 @@
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+              xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
+              android:layout_height="match_parent"
+              tools:context=".HelloworldActivity"
+              android:orientation="vertical" >
+
+    <TextView
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:paddingTop="12dp"
+        android:paddingBottom="12dp"
+        android:textSize="16sp"
+        android:text="gRPC Client Configuration"
+        android:textStyle="bold" />
+
+    <LinearLayout
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:orientation="horizontal">
+        <EditText
+                android:id="@+id/host_edit_text"
+                android:layout_weight="2"
+                android:layout_width="0dp"
+                android:layout_height="wrap_content"
+                android:hint="Enter Host" />
+        <EditText
+                android:id="@+id/port_edit_text"
+                android:layout_weight="1"
+                android:layout_width="0dp"
+                android:layout_height="wrap_content"
+                android:inputType="numberDecimal"
+                android:hint="Enter Port" />
+    </LinearLayout>
+
+
+    <EditText
+            android:id="@+id/message_edit_text"
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:hint="Enter message to send" />
+
+    <Button
+            android:id="@+id/send_button"
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:onClick="sendMessage"
+            android:text="Send gRPC Request" />
+
+    <TextView
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:paddingTop="12dp"
+        android:paddingBottom="12dp"
+        android:textSize="16sp"
+        android:text="Response:" />
+
+    <TextView
+        android:id="@+id/grpc_response_text"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:scrollbars = "vertical"
+        android:textSize="16sp" />
+
+    <TextView
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:paddingTop="12dp"
+        android:paddingBottom="12dp"
+        android:textSize="16sp"
+        android:text="gRPC Server Configuration"
+        android:textStyle="bold" />
+
+    <EditText
+        android:id="@+id/server_port_edit_text"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:hint="Server port" />
+
+    <Button
+        android:id="@+id/server_button"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:onClick="startOrStopServer"
+        android:text="Start gRPC Server" />
+
+</LinearLayout>
diff --git a/examples/android/helloworld/app/src/main/res/mipmap-hdpi/ic_launcher.png b/examples/android/helloworld/app/src/main/res/mipmap-hdpi/ic_launcher.png
new file mode 100644
index 0000000000..cde69bccce
--- /dev/null
+++ b/examples/android/helloworld/app/src/main/res/mipmap-hdpi/ic_launcher.png
diff --git a/examples/android/helloworld/app/src/main/res/mipmap-mdpi/ic_launcher.png b/examples/android/helloworld/app/src/main/res/mipmap-mdpi/ic_launcher.png
new file mode 100644
index 0000000000..c133a0cbd3
--- /dev/null
+++ b/examples/android/helloworld/app/src/main/res/mipmap-mdpi/ic_launcher.png
diff --git a/examples/android/helloworld/app/src/main/res/mipmap-xhdpi/ic_launcher.png b/examples/android/helloworld/app/src/main/res/mipmap-xhdpi/ic_launcher.png
new file mode 100644
index 0000000000..bfa42f0e7b
--- /dev/null
+++ b/examples/android/helloworld/app/src/main/res/mipmap-xhdpi/ic_launcher.png
diff --git a/examples/android/helloworld/app/src/main/res/mipmap-xxhdpi/ic_launcher.png b/examples/android/helloworld/app/src/main/res/mipmap-xxhdpi/ic_launcher.png
new file mode 100644
index 0000000000..324e72cdd7
--- /dev/null
+++ b/examples/android/helloworld/app/src/main/res/mipmap-xxhdpi/ic_launcher.png
diff --git a/examples/android/helloworld/app/src/main/res/values/strings.xml b/examples/android/helloworld/app/src/main/res/values/strings.xml
new file mode 100644
index 0000000000..7e916e348c
--- /dev/null
+++ b/examples/android/helloworld/app/src/main/res/values/strings.xml
@@ -0,0 +1,3 @@
+<resources>
+    <string name="app_name">GrpcHelloworldCppExample</string>
+</resources>
diff --git a/examples/android/helloworld/build.gradle b/examples/android/helloworld/build.gradle
new file mode 100644
index 0000000000..bd5f337f01
--- /dev/null
+++ b/examples/android/helloworld/build.gradle
@@ -0,0 +1,24 @@
+// Top-level build file where you can add configuration options common to all sub-projects/modules.
+
+buildscript {
+    repositories {
+        google()
+        jcenter()
+    }
+    dependencies {
+        classpath 'com.android.tools.build:gradle:3.0.1'
+        // NOTE: Do not place your application dependencies here; they belong
+        // in the individual module build.gradle files
+    }
+}
+
+allprojects {
+    repositories {
+        google()
+        jcenter()
+    }
+}
+
+task clean(type: Delete) {
+    delete rootProject.buildDir
+}
diff --git a/examples/android/helloworld/gradle.properties b/examples/android/helloworld/gradle.properties
new file mode 100644
index 0000000000..aac7c9b461
--- /dev/null
+++ b/examples/android/helloworld/gradle.properties
@@ -0,0 +1,17 @@
+# Project-wide Gradle settings.
+
+# IDE (e.g. Android Studio) users:
+# Gradle settings configured through the IDE *will override*
+# any settings specified in this file.
+
+# For more details on how to configure your build environment visit
+# http://www.gradle.org/docs/current/userguide/build_environment.html
+
+# Specifies the JVM arguments used for the daemon process.
+# The setting is particularly useful for tweaking memory settings.
+org.gradle.jvmargs=-Xmx1536m
+
+# When configured, Gradle will run in incubating parallel mode.
+# This option should only be used with decoupled projects. More details, visit
+# http://www.gradle.org/docs/current/userguide/multi_project_builds.html#sec:decoupled_projects
+# org.gradle.parallel=true
diff --git a/examples/android/helloworld/gradle/wrapper/gradle-wrapper.jar b/examples/android/helloworld/gradle/wrapper/gradle-wrapper.jar
new file mode 100644
index 0000000000..13372aef5e
--- /dev/null
+++ b/examples/android/helloworld/gradle/wrapper/gradle-wrapper.jar
diff --git a/examples/android/helloworld/gradle/wrapper/gradle-wrapper.properties b/examples/android/helloworld/gradle/wrapper/gradle-wrapper.properties
new file mode 100644
index 0000000000..4c81831f53
--- /dev/null
+++ b/examples/android/helloworld/gradle/wrapper/gradle-wrapper.properties
@@ -0,0 +1,6 @@
+#Thu Jan 25 11:45:30 PST 2018
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-4.1-all.zip
diff --git a/examples/android/helloworld/gradlew b/examples/android/helloworld/gradlew
new file mode 100755
index 0000000000..9d82f78915
--- /dev/null
+++ b/examples/android/helloworld/gradlew
@@ -0,0 +1,160 @@
+#!/usr/bin/env bash
+
+##############################################################################
+##
+##  Gradle start up script for UN*X
+##
+##############################################################################
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS=""
+
+APP_NAME="Gradle"
+APP_BASE_NAME=`basename "$0"`
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD="maximum"
+
+warn ( ) {
+    echo "$*"
+}
+
+die ( ) {
+    echo
+    echo "$*"
+    echo
+    exit 1
+}
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+case "`uname`" in
+  CYGWIN* )
+    cygwin=true
+    ;;
+  Darwin* )
+    darwin=true
+    ;;
+  MINGW* )
+    msys=true
+    ;;
+esac
+
+# Attempt to set APP_HOME
+# Resolve links: $0 may be a link
+PRG="$0"
+# Need this for relative symlinks.
+while [ -h "$PRG" ] ; do
+    ls=`ls -ld "$PRG"`
+    link=`expr "$ls" : '.*-> \(.*\)$'`
+    if expr "$link" : '/.*' > /dev/null; then
+        PRG="$link"
+    else
+        PRG=`dirname "$PRG"`"/$link"
+    fi
+done
+SAVED="`pwd`"
+cd "`dirname \"$PRG\"`/" >/dev/null
+APP_HOME="`pwd -P`"
+cd "$SAVED" >/dev/null
+
+CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+        # IBM's JDK on AIX uses strange locations for the executables
+        JAVACMD="$JAVA_HOME/jre/sh/java"
+    else
+        JAVACMD="$JAVA_HOME/bin/java"
+    fi
+    if [ ! -x "$JAVACMD" ] ; then
+        die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+else
+    JAVACMD="java"
+    which java >/dev/null 2>&1 || die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+fi
+
+# Increase the maximum file descriptors if we can.
+if [ "$cygwin" = "false" -a "$darwin" = "false" ] ; then
+    MAX_FD_LIMIT=`ulimit -H -n`
+    if [ $? -eq 0 ] ; then
+        if [ "$MAX_FD" = "maximum" -o "$MAX_FD" = "max" ] ; then
+            MAX_FD="$MAX_FD_LIMIT"
+        fi
+        ulimit -n $MAX_FD
+        if [ $? -ne 0 ] ; then
+            warn "Could not set maximum file descriptor limit: $MAX_FD"
+        fi
+    else
+        warn "Could not query maximum file descriptor limit: $MAX_FD_LIMIT"
+    fi
+fi
+
+# For Darwin, add options to specify how the application appears in the dock
+if $darwin; then
+    GRADLE_OPTS="$GRADLE_OPTS \"-Xdock:name=$APP_NAME\" \"-Xdock:icon=$APP_HOME/media/gradle.icns\""
+fi
+
+# For Cygwin, switch paths to Windows format before running java
+if $cygwin ; then
+    APP_HOME=`cygpath --path --mixed "$APP_HOME"`
+    CLASSPATH=`cygpath --path --mixed "$CLASSPATH"`
+    JAVACMD=`cygpath --unix "$JAVACMD"`
+
+    # We build the pattern for arguments to be converted via cygpath
+    ROOTDIRSRAW=`find -L / -maxdepth 1 -mindepth 1 -type d 2>/dev/null`
+    SEP=""
+    for dir in $ROOTDIRSRAW ; do
+        ROOTDIRS="$ROOTDIRS$SEP$dir"
+        SEP="|"
+    done
+    OURCYGPATTERN="(^($ROOTDIRS))"
+    # Add a user-defined pattern to the cygpath arguments
+    if [ "$GRADLE_CYGPATTERN" != "" ] ; then
+        OURCYGPATTERN="$OURCYGPATTERN|($GRADLE_CYGPATTERN)"
+    fi
+    # Now convert the arguments - kludge to limit ourselves to /bin/sh
+    i=0
+    for arg in "$@" ; do
+        CHECK=`echo "$arg"|egrep -c "$OURCYGPATTERN" -`
+        CHECK2=`echo "$arg"|egrep -c "^-"`                                 ### Determine if an option
+
+        if [ $CHECK -ne 0 ] && [ $CHECK2 -eq 0 ] ; then                    ### Added a condition
+            eval `echo args$i`=`cygpath --path --ignore --mixed "$arg"`
+        else
+            eval `echo args$i`="\"$arg\""
+        fi
+        i=$((i+1))
+    done
+    case $i in
+        (0) set -- ;;
+        (1) set -- "$args0" ;;
+        (2) set -- "$args0" "$args1" ;;
+        (3) set -- "$args0" "$args1" "$args2" ;;
+        (4) set -- "$args0" "$args1" "$args2" "$args3" ;;
+        (5) set -- "$args0" "$args1" "$args2" "$args3" "$args4" ;;
+        (6) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" ;;
+        (7) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" ;;
+        (8) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" ;;
+        (9) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" "$args8" ;;
+    esac
+fi
+
+# Split up the JVM_OPTS And GRADLE_OPTS values into an array, following the shell quoting and substitution rules
+function splitJvmOpts() {
+    JVM_OPTS=("$@")
+}
+eval splitJvmOpts $DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS
+JVM_OPTS[${#JVM_OPTS[*]}]="-Dorg.gradle.appname=$APP_BASE_NAME"
+
+exec "$JAVACMD" "${JVM_OPTS[@]}" -classpath "$CLASSPATH" org.gradle.wrapper.GradleWrapperMain "$@"
diff --git a/examples/android/helloworld/gradlew.bat b/examples/android/helloworld/gradlew.bat
new file mode 100644
index 0000000000..8a0b282aa6
--- /dev/null
+++ b/examples/android/helloworld/gradlew.bat
@@ -0,0 +1,90 @@
+@if "%DEBUG%" == "" @echo off
+@rem ##########################################################################
+@rem
+@rem  Gradle startup script for Windows
+@rem
+@rem ##########################################################################
+
+@rem Set local scope for the variables with windows NT shell
+if "%OS%"=="Windows_NT" setlocal
+
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS=
+
+set DIRNAME=%~dp0
+if "%DIRNAME%" == "" set DIRNAME=.
+set APP_BASE_NAME=%~n0
+set APP_HOME=%DIRNAME%
+
+@rem Find java.exe
+if defined JAVA_HOME goto findJavaFromJavaHome
+
+set JAVA_EXE=java.exe
+%JAVA_EXE% -version >NUL 2>&1
+if "%ERRORLEVEL%" == "0" goto init
+
+echo.
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto init
+
+echo.
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME%
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:init
+@rem Get command-line arguments, handling Windowz variants
+
+if not "%OS%" == "Windows_NT" goto win9xME_args
+if "%@eval[2+2]" == "4" goto 4NT_args
+
+:win9xME_args
+@rem Slurp the command line arguments.
+set CMD_LINE_ARGS=
+set _SKIP=2
+
+:win9xME_args_slurp
+if "x%~1" == "x" goto execute
+
+set CMD_LINE_ARGS=%*
+goto execute
+
+:4NT_args
+@rem Get arguments from the 4NT Shell from JP Software
+set CMD_LINE_ARGS=%$
+
+:execute
+@rem Setup the command line
+
+set CLASSPATH=%APP_HOME%\gradle\wrapper\gradle-wrapper.jar
+
+@rem Execute Gradle
+"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" org.gradle.wrapper.GradleWrapperMain %CMD_LINE_ARGS%
+
+:end
+@rem End local scope for the variables with windows NT shell
+if "%ERRORLEVEL%"=="0" goto mainEnd
+
+:fail
+rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
+rem the _cmd.exe /c_ return code!
+if  not "" == "%GRADLE_EXIT_CONSOLE%" exit 1
+exit /b 1
+
+:mainEnd
+if "%OS%"=="Windows_NT" endlocal
+
+:omega
diff --git a/examples/android/helloworld/settings.gradle b/examples/android/helloworld/settings.gradle
new file mode 100644
index 0000000000..e7b4def49c
--- /dev/null
+++ b/examples/android/helloworld/settings.gradle
@@ -0,0 +1 @@
+include ':app'