Add helloworld example. (#59)

This will be used in the quickstart docs, similar to the other
languages.

example/helloworld/README.md

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+# Description
+The hello world server and client demonstrate how to use Dart gRPC libraries to
+perform unary RPCs.
+
+See the definition of the hello world service in `protos/helloworld.proto`.
+
+# Run the sample code
+To compile and run the example, assuming you are in the root of the helloworld
+folder, i.e., .../example/helloworld/, first get the dependencies by running:
+
+```sh
+$ pub get
+```
+
+Then, to run the server:
+
+```sh
+$ dart bin/server.dart
+```
+
+Likewise, to run the client:
+
+```sh
+$ dart bin/client.dart
+```
+
+# Regenerate the stubs
+
+If you have made changes to the message or service definition in
+`protos/helloworld.proto` and need to regenerate the corresponding Dart files,
+you will need to have protoc version 3.0.0 or higher and the Dart protoc plugin
+version 0.7.9 or higher on your PATH.
+
+To install protoc, see the instructions on
+[the Protocol Buffers website](https://developers.google.com/protocol-buffers/).
+
+The easiest way to get the Dart protoc plugin is by running
+
+```sh
+$ pub global activate protoc_plugin
+```
+
+and follow the directions to add `~/.pub-cache/bin` to your PATH, if you haven't
+already done so.
+
+You can now regenerate the Dart files by running
+
+```sh
+$ protoc --dart_out=grpc:lib/src/generated -Iprotos protos/helloworld.proto
+```

example/helloworld/bin/client.dart

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+// Copyright (c) 2018, the gRPC project authors. Please see the AUTHORS file
+// for details. 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.
+
+/// Dart implementation of the gRPC helloworld.Greeter client.
+import 'dart:async';
+
+import 'package:grpc/grpc.dart';
+
+import 'package:helloworld/src/generated/helloworld.pb.dart';
+import 'package:helloworld/src/generated/helloworld.pbgrpc.dart';
+
+Future<Null> main(List<String> args) async {
+  final channel = new ClientChannel('localhost',
+      port: 50051, options: const ChannelOptions.insecure());
+  final stub = new GreeterClient(channel);
+
+  final name = args.isNotEmpty ? args[0] : 'world';
+
+  try {
+    final response = await stub.sayHello(new HelloRequest()..name = name);
+    print('Greeter client received: ${response.message}');
+  } catch (e) {
+    print('Caught error: $e');
+  }
+  await channel.shutdown();
+}

example/helloworld/bin/server.dart

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+// Copyright (c) 2018, the gRPC project authors. Please see the AUTHORS file
+// for details. 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.
+
+/// Dart implementation of the gRPC helloworld.Greeter server.
+import 'dart:async';
+
+import 'package:grpc/grpc.dart';
+
+import 'package:helloworld/src/generated/helloworld.pb.dart';
+import 'package:helloworld/src/generated/helloworld.pbgrpc.dart';
+
+class GreeterService extends GreeterServiceBase {
+  @override
+  Future<HelloReply> sayHello(ServiceCall call, HelloRequest request) async {
+    return new HelloReply()..message = 'Hello, ${request.name}!';
+  }
+}
+
+Future<Null> main(List<String> args) async {
+  final server = new Server.insecure([new GreeterService()], port: 50051);
+  await server.serve();
+  print('Server listening...');
+}

example/helloworld/lib/src/generated/helloworld.pb.dart

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+///
+//  Generated code. Do not modify.
+///
+// ignore_for_file: non_constant_identifier_names,library_prefixes
+library helloworld_helloworld;
+
+// ignore: UNUSED_SHOWN_NAME
+import 'dart:core' show int, bool, double, String, List, override;
+
+import 'package:protobuf/protobuf.dart';
+
+class HelloRequest extends GeneratedMessage {
+  static final BuilderInfo _i = new BuilderInfo('HelloRequest')
+    ..aOS(1, 'name')
+    ..hasRequiredFields = false;
+
+  HelloRequest() : super();
+  HelloRequest.fromBuffer(List<int> i,
+      [ExtensionRegistry r = ExtensionRegistry.EMPTY])
+      : super.fromBuffer(i, r);
+  HelloRequest.fromJson(String i,
+      [ExtensionRegistry r = ExtensionRegistry.EMPTY])
+      : super.fromJson(i, r);
+  HelloRequest clone() => new HelloRequest()..mergeFromMessage(this);
+  BuilderInfo get info_ => _i;
+  static HelloRequest create() => new HelloRequest();
+  static PbList<HelloRequest> createRepeated() => new PbList<HelloRequest>();
+  static HelloRequest getDefault() {
+    if (_defaultInstance == null)
+      _defaultInstance = new _ReadonlyHelloRequest();
+    return _defaultInstance;
+  }
+
+  static HelloRequest _defaultInstance;
+  static void $checkItem(HelloRequest v) {
+    if (v is! HelloRequest) checkItemFailed(v, 'HelloRequest');
+  }
+
+  String get name => $_getS(0, '');
+  set name(String v) {
+    $_setString(0, v);
+  }
+
+  bool hasName() => $_has(0);
+  void clearName() => clearField(1);
+}
+
+class _ReadonlyHelloRequest extends HelloRequest with ReadonlyMessageMixin {}
+
+class HelloReply extends GeneratedMessage {
+  static final BuilderInfo _i = new BuilderInfo('HelloReply')
+    ..aOS(1, 'message')
+    ..hasRequiredFields = false;
+
+  HelloReply() : super();
+  HelloReply.fromBuffer(List<int> i,
+      [ExtensionRegistry r = ExtensionRegistry.EMPTY])
+      : super.fromBuffer(i, r);
+  HelloReply.fromJson(String i, [ExtensionRegistry r = ExtensionRegistry.EMPTY])
+      : super.fromJson(i, r);
+  HelloReply clone() => new HelloReply()..mergeFromMessage(this);
+  BuilderInfo get info_ => _i;
+  static HelloReply create() => new HelloReply();
+  static PbList<HelloReply> createRepeated() => new PbList<HelloReply>();
+  static HelloReply getDefault() {
+    if (_defaultInstance == null) _defaultInstance = new _ReadonlyHelloReply();
+    return _defaultInstance;
+  }
+
+  static HelloReply _defaultInstance;
+  static void $checkItem(HelloReply v) {
+    if (v is! HelloReply) checkItemFailed(v, 'HelloReply');
+  }
+
+  String get message => $_getS(0, '');
+  set message(String v) {
+    $_setString(0, v);
+  }
+
+  bool hasMessage() => $_has(0);
+  void clearMessage() => clearField(1);
+}
+
+class _ReadonlyHelloReply extends HelloReply with ReadonlyMessageMixin {}

example/helloworld/lib/src/generated/helloworld.pbenum.dart

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+///
+//  Generated code. Do not modify.
+///
+// ignore_for_file: non_constant_identifier_names,library_prefixes
+library helloworld_helloworld_pbenum;

example/helloworld/lib/src/generated/helloworld.pbgrpc.dart

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+///
+//  Generated code. Do not modify.
+///
+// ignore_for_file: non_constant_identifier_names,library_prefixes
+library helloworld_helloworld_pbgrpc;
+
+import 'dart:async';
+
+import 'package:grpc/grpc.dart';
+
+import 'helloworld.pb.dart';
+export 'helloworld.pb.dart';
+
+class GreeterClient extends Client {
+  static final _$sayHello = new ClientMethod<HelloRequest, HelloReply>(
+      '/helloworld.Greeter/SayHello',
+      (HelloRequest value) => value.writeToBuffer(),
+      (List<int> value) => new HelloReply.fromBuffer(value));
+
+  GreeterClient(ClientChannel channel, {CallOptions options})
+      : super(channel, options: options);
+
+  ResponseFuture<HelloReply> sayHello(HelloRequest request,
+      {CallOptions options}) {
+    final call = $createCall(_$sayHello, new Stream.fromIterable([request]),
+        options: options);
+    return new ResponseFuture(call);
+  }
+}
+
+abstract class GreeterServiceBase extends Service {
+  String get $name => 'helloworld.Greeter';
+
+  GreeterServiceBase() {
+    $addMethod(new ServiceMethod<HelloRequest, HelloReply>(
+        'SayHello',
+        sayHello_Pre,
+        false,
+        false,
+        (List<int> value) => new HelloRequest.fromBuffer(value),
+        (HelloReply value) => value.writeToBuffer()));
+  }
+
+  Future<HelloReply> sayHello_Pre(
+      ServiceCall call, Future<HelloRequest> request) async {
+    return sayHello(call, await request);
+  }
+
+  Future<HelloReply> sayHello(ServiceCall call, HelloRequest request);
+}

example/helloworld/lib/src/generated/helloworld.pbjson.dart

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+///
+//  Generated code. Do not modify.
+///
+// ignore_for_file: non_constant_identifier_names,library_prefixes
+library helloworld_helloworld_pbjson;
+
+const HelloRequest$json = const {
+  '1': 'HelloRequest',
+  '2': const [
+    const {'1': 'name', '3': 1, '4': 1, '5': 9, '10': 'name'},
+  ],
+};
+
+const HelloReply$json = const {
+  '1': 'HelloReply',
+  '2': const [
+    const {'1': 'message', '3': 1, '4': 1, '5': 9, '10': 'message'},
+  ],
+};

example/helloworld/protos/helloworld.proto

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+// Copyright 2015 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.
+
+syntax = "proto3";
+
+option java_multiple_files = true;
+option java_package = "io.grpc.examples.helloworld";
+option java_outer_classname = "HelloWorldProto";
+option objc_class_prefix = "HLW";
+
+package helloworld;
+
+// The greeting service definition.
+service Greeter {
+  // Sends a greeting
+  rpc SayHello (HelloRequest) returns (HelloReply) {}
+}
+
+// The request message containing the user's name.
+message HelloRequest {
+  string name = 1;
+}
+
+// The response message containing the greetings
+message HelloReply {
+  string message = 1;
+}

example/helloworld/pubspec.yaml

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+name: helloworld
+description: Dart gRPC sample client and server.
+version: 0.0.1
+homepage: https://github.com/dart-lang/grpc-dart
+
+environment:
+  sdk: '>=1.24.3 <2.0.0'
+
+dependencies:
+  async: ^1.13.3
+  grpc:
+    path: ../../
+  protobuf: ^0.7.0
+
+dev_dependencies:
+  test: ^0.12.0