Add BinderTransport example app (#26747)

This commit adds an app that will be served as BinderTransport example
later.

Currently the app simply calls C++ function when button is pressed. In
the future the C++ function will run BinderTransport gRPC example
instead.

Tests not included in this commit, later we will add a build test to
CI to make sure this apk is always build-able. (This app will also be
used to make sure our BinderTransport implementation is compile-able
with Android toolchain, on GitHub) For now we exclude this target in
bazel build test.

Changes are made to WORKSPACE file in order to support android builds.

Build instructions are documented at
examples/android/binder/java/io/grpc/binder/cpp/example/README.md

WORKSPACE

@@ -69,6 +69,27 @@ rbe_autoconfig(
 
 load("@bazel_toolchains//rules:environments.bzl", "clang_env")
 load("@bazel_skylib//lib:dicts.bzl", "dicts")
+load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
+
+http_archive(
+    name = "build_bazel_rules_android",
+    sha256 = "cd06d15dd8bb59926e4d65f9003bfc20f9da4b2519985c27e190cddc8b7a7806",
+    strip_prefix = "rules_android-0.1.1",
+    urls = ["https://github.com/bazelbuild/rules_android/archive/v0.1.1.zip"],
+)
+
+android_sdk_repository(
+    name = "androidsdk",
+    # version 31.0.0 won't work https://stackoverflow.com/a/68036845
+    build_tools_version = "30.0.3",
+)
+
+android_ndk_repository(
+    name = "androidndk",
+    # Note that Bazel does not support NDK 22 yet, and Bazel 3.7.1 only
+    # supports up to API level 29 for NDK 21
+    # https://github.com/bazelbuild/bazel/issues/13421
+)
 
 # Create msan toolchain configuration for remote execution.
 rbe_autoconfig(

examples/android/binder/java/io/grpc/binder/cpp/example/AndroidManifest.xml

@@ -0,0 +1,21 @@
+<manifest xmlns:android="http://schemas.android.com/apk/res/android"
+    package="io.grpc.binder.cpp.example"
+    android:versionCode="1"
+    android:versionName="1.0" >
+
+  <uses-sdk
+      android:minSdkVersion="29"
+      android:targetSdkVersion="30" />
+
+  <application
+      android:label="gRPC BinderTransport Cpp">
+    <activity
+        android:name=".MainActivity"
+        android:label="gRPC BinderTransport Cpp" >
+      <intent-filter>
+        <action android:name="android.intent.action.MAIN" />
+        <category android:name="android.intent.category.LAUNCHER" />
+      </intent-filter>
+    </activity>
+  </application>
+</manifest>

examples/android/binder/java/io/grpc/binder/cpp/example/BUILD

@@ -0,0 +1,48 @@
+# Copyright 2021 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.
+
+load("@build_bazel_rules_android//android:rules.bzl", "android_binary", "android_library")
+
+cc_library(
+    name = "jni_lib",
+    srcs = ["native.cc"],
+    linkopts = [
+        "-ldl",
+        "-llog",
+        "-Wl,--no-undefined",
+    ],
+    deps = [],
+    alwayslink = True,
+)
+
+android_library(
+    name = "activity",
+    srcs = [
+        "ButtonPressHandler.java",
+        "MainActivity.java",
+    ],
+    manifest = "AndroidManifest.xml",
+    resource_files = glob(["res/**"]),
+    deps = [
+        ":jni_lib",
+    ],
+)
+
+android_binary(
+    name = "app",
+    manifest = "AndroidManifest.xml",
+    deps = [
+        ":activity",
+    ],
+)

examples/android/binder/java/io/grpc/binder/cpp/example/ButtonPressHandler.java

@@ -0,0 +1,15 @@
+package io.grpc.binder.cpp.example;
+
+import android.app.Application;
+
+public class ButtonPressHandler {
+  static {
+    System.loadLibrary("app");
+  }
+
+  public native String native_entry(Application application);
+
+  public String onPressed(Application application) {
+    return native_entry(application);
+  }
+}

examples/android/binder/java/io/grpc/binder/cpp/example/MainActivity.java

@@ -0,0 +1,26 @@
+package io.grpc.binder.cpp.example;
+
+import android.app.Activity;
+import android.os.Bundle;
+import android.util.Log;
+import android.widget.Button;
+import android.widget.TextView;
+
+/** Main class for the example app. */
+public class MainActivity extends Activity {
+  @Override
+  public void onCreate(Bundle savedInstanceState) {
+    super.onCreate(savedInstanceState);
+    Log.v("Example", "hello, world");
+
+    setContentView(R.layout.activity_main);
+
+    Button clickMeButton = findViewById(R.id.clickMeButton);
+    TextView exampleTextView = findViewById(R.id.exampleTextView);
+
+    ButtonPressHandler h = new ButtonPressHandler();
+
+    clickMeButton.setOnClickListener(
+        v -> exampleTextView.setText(h.onPressed(getApplication())));
+  }
+}

examples/android/binder/java/io/grpc/binder/cpp/example/README.md

@@ -0,0 +1,18 @@
+# gRPC-core BinderTransport example app
+
+WIP.
+
+## Build Instruction
+
+1. Install Android SDK and NDK. Currently we only support SDK version 30.0.3 and
+   NDK version 21.4.7075529 . Make sure you get these exact versions otherwise
+   Bazel might complain.
+
+2. Point environment variables to install locations of SDK and NDK
+    ```
+    export ANDROID_HOME=$HOME/Android/Sdk/
+    export ANDROID_NDK_HOME=$HOME/Android/Sdk/ndk/21.4.7075529
+    ```
+3. `bazel build //examples/android/binder/java/io/grpc/binder/cpp/example:app`
+4. `adb install
+   bazel-bin/examples/android/binder/java/io/grpc/binder/cpp/example/app.apk`

examples/android/binder/java/io/grpc/binder/cpp/example/native.cc

@@ -0,0 +1,30 @@
+// Copyright 2021 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 <android/log.h>
+#include <jni.h>
+
+extern "C" JNIEXPORT jstring JNICALL
+Java_io_grpc_binder_cpp_example_ButtonPressHandler_native_1entry(
+    JNIEnv* env, jobject /*this*/, jobject /*application*/) {
+  static bool first = true;
+  __android_log_print(ANDROID_LOG_INFO, "Demo", "Line number %d", __LINE__);
+  if (first) {
+    first = false;
+    return env->NewStringUTF("Clicked 1 time");
+  } else {
+    return env->NewStringUTF("Clicked more than 1 time");
+  }
+}

examples/android/binder/java/io/grpc/binder/cpp/example/res/layout/activity_main.xml

@@ -0,0 +1,24 @@
+<?xml version="1.0" encoding="utf-8"?>
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    android:padding="16dp"
+    android:orientation="vertical"
+    android:gravity="center_vertical"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent">
+
+  <TextView
+      android:id="@+id/exampleTextView"
+      android:layout_width="wrap_content"
+      android:layout_height="wrap_content"
+      android:layout_gravity="center_horizontal"
+      android:textSize="32dp"
+      android:text="@string/thinking_face"/>
+
+  <Button
+      android:id="@+id/clickMeButton"
+      android:layout_width="wrap_content"
+      android:layout_height="wrap_content"
+      android:layout_gravity="center_horizontal"
+      android:layout_marginTop="16dp"
+      android:text="@string/click_me_button"/>
+</LinearLayout>

examples/android/binder/java/io/grpc/binder/cpp/example/res/values/strings.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+  <string name="click_me_button">Run example</string>
+  <string name="thinking_face">🤔</string>
+</resources>

tools/internal_ci/linux/grpc_bazel_build_in_docker.sh

@@ -27,12 +27,16 @@ cd /var/local/git/grpc
 
 # Build all basic targets using the strict warning option which leverages the
 # clang compiler to check if sources can pass a set of warning options.
+# For now //examples/android/binder/ are excluded because it needs Android
+# SDK/NDK to be installed to build
 bazel build --define=use_strict_warning=true \
+	-- \
 	:all \
 	//src/core/... \
 	//src/compiler/... \
 	//test/... \
-	//examples/...
+	//examples/... \
+	-//examples/android/binder/...
 
 # TODO(jtattersmusch): Adding a build here for --define=grpc_no_xds is not ideal
 # and we should find a better place for this. Refer