ScalaPB（2）： 在scala中用gRPC实现微服务详解编程语言

   gRPC是google开源提供的一个RPC软件框架，它的特点是极大简化了传统RPC的开发流程和代码量，使用户可以免除许多陷阱并聚焦于实际应用逻辑中。作为一种google的最新RPC解决方案，gRPC具备了以下这些强项：

1、gRPC在HTTP/2协议上用protobuf取代了json实现了最佳效率

2、用IDL（Interface Definition Language），一种简单的描述语言来自动产生RPC的api源代码

3、支持blocking/non-blocking双向数据流交互，适合程序的流程控制

gRPC的使用非常简单，具体流程如下：

1、在一个.proto字符类文件中用IDL来描述用户自定义的数据类型和服务

2、用protoc编译器编译文件并产生自定义数据类型和服务的api源代码

3、在server端实现.proto中定义的服务函数

4、在client端通过自动产生的stub来调用服务

下面我们就来示范gRPC的编程流程。gRPC支持下面这几种服务类型：

1、Unary：独立的一对client-request/server-response，是我们常用的http交互模式

2、Server-Streaming：client发出一个request后从server端接收一串多个response

3、Client-Streaming：client向server发送一串多个request后从server接收一个response

4、Bidirectional-Streaming：由client首先发送request启动连接，然后在这个连接上两端可以不断交互信息。

在本篇讨论中我们先示范Unary-service的编程流程，下面是.proto文件内容：

syntax = "proto3"; 

import "google/protobuf/wrappers.proto"; 

import "scalapb/scalapb.proto"; 

package learn.grpc.services; 

 * Returns a greeting for the given person optionally including a custom message. 

service HelloWorld { 

 rpc SayHello(ToBeGreeted) returns (Greeting) {} 

message Person { 

 string name = 1; 

message ToBeGreeted { 

 Person person = 1; 

 google.protobuf.StringValue msg = 2; 

message Greeting { 

 string message = 1; 

}

这段IDL描述了一个HelloWorld服务，包括了一个服务函数SayHello。三种数据类型：Person,ToBeGreeted,Greeting。通过对.proto文件进行编译后产生文件中包括一个HelloWorldGrpc.scala文件，里面提供了一些重要的api：

trait HelloWorld - 用于实现HelloWorld服务的trait 

trait HelloWorldBlockingClient - 用于实现客户端stub 

class HelloWorldBlockingStub - blocking客户端stub 

class HelloWorldStub - non-blocking客户端stub 

def bindService - 服务类型绑带方法

我们先实现HelloWorld服务：

 class HelloService extends HelloWorldGrpc.HelloWorld { 

 override def sayHello(request: ToBeGreeted): Future[Greeting] = { 

 val greeter = request.person match { 

 case Some(p) = p.name 

 case None = "friendo" 

 Future.successful(Greeting(message = s"Hello $greeter, ${request.msg}")) 

 }

可以看到我们直接使用了IDL描述的自定义数据类型如：ToBeGreeted,Greeting。在客户端调用服务并输出返回结果response：

 //build connection channel 

 val channel = io.grpc.ManagedChannelBuilder 

 .forAddress("LocalHost",50051) 

 .usePlaintext(true) 

 .build() 

 //construct requestHelloService 

 val greeter = ToBeGreeted() 

 .withMsg("remote greetings!") 

 .withPerson(ToBeGreeted.Person("mickey")) 

 //async call 

 val asyncStub: HelloWorldGrpc.HelloWorldStub = HelloWorldGrpc.stub(channel) 

 val futResponse: Future[Greeting] = asyncStub.sayHello(greeter) 

 import scala.concurrent.ExecutionContext.Implicits.global 

 futResponse.foreach(greeting = println(greeting.message)) 

 val greeter2 = ToBeGreeted(person = Some(Person("jacky")),msg = Some("how are you?")) 

 //sync call 

 val syncStub: HelloWorldGrpc.HelloWorldBlockingClient = HelloWorldGrpc.blockingStub(channel) 

 val response: Greeting = syncStub.sayHello(greeter2) 

 println(s"${response.message}")

下面是bindService方法的使用示范：

 def main(args: Array[String]): Unit = { 

 val service = HelloWorldGrpc.bindService(new HelloService,ExecutionContext.global) 

 runServer(service) 

 }

runServer函数定义如下：

package learn.grpc.server 

import io.grpc.{ServerBuilder,ServerServiceDefinition} 

trait gRPCServer { 

 def runServer(service: ServerServiceDefinition): Unit = { 

 val server = ServerBuilder 

 .forPort(50051) 

 .addService(service) 

 .build 

 .start 

 // make sure our server is stopped when jvm is shut down 

 Runtime.getRuntime.addShutdownHook(new Thread() { 

 override def run(): Unit = server.shutdown() 

 server.awaitTermination() 

}

注意我们还使用了io.grpc库里的类型和方法，这是protobuf项目提供的一个标准库。在客户端也需要使用它来构建通道：

 //build connection channel 

 val channel = io.grpc.ManagedChannelBuilder 

 .forAddress("LocalHost",50051) 

 .usePlaintext(true) 

 .build()

我们将在后面的讨论里介绍gRPC的streaming编程方法。下面是本次示范的源代码：

project/scalapb.sbt

addSbtPlugin("com.thesamet" % "sbt-protoc" % "0.99.18") 

libraryDependencies += "com.thesamet.scalapb" %% "compilerplugin" % "0.7.1"

build.sbt

import scalapb.compiler.Version.scalapbVersion 

import scalapb.compiler.Version.grpcJavaVersion 

name := "learn-gRPC" 

version := "0.1" 

scalaVersion := "2.12.6" 

libraryDependencies ++= Seq( 

 "com.thesamet.scalapb" %% "scalapb-runtime" % scalapbVersion % "protobuf", 

 "io.grpc" % "grpc-netty" % grpcJavaVersion, 

 "com.thesamet.scalapb" %% "scalapb-runtime-grpc" % scalapbVersion 

PB.targets in Compile := Seq( 

 scalapb.gen() - (sourceManaged in Compile).value 

)

src/main/protobuf/hello.proto

syntax = "proto3"; 

import "google/protobuf/wrappers.proto"; 

import "scalapb/scalapb.proto"; 

package learn.grpc.services; 

 * Returns a greeting for the given person optionally including a custom message. 

service HelloWorld { 

 rpc SayHello(ToBeGreeted) returns (Greeting) {} 

message Person { 

 string name = 1; 

message ToBeGreeted { 

 Person person = 1; 

 google.protobuf.StringValue msg = 2; 

message Greeting { 

 string message = 1; 

}

src/main/scala/gRPCServer.scala

package learn.grpc.server 

import io.grpc.{ServerBuilder,ServerServiceDefinition} 

trait gRPCServer { 

 def runServer(service: ServerServiceDefinition): Unit = { 

 val server = ServerBuilder 

 .forPort(50051) 

 .addService(service) 

 .build 

 .start 

 // make sure our server is stopped when jvm is shut down 

 Runtime.getRuntime.addShutdownHook(new Thread() { 

 override def run(): Unit = server.shutdown() 

 server.awaitTermination() 

}

src/main/scala/HelloServer.scala

package learn.grpc.hello.server 

import learn.grpc.services.hello._ 

import learn.grpc.server.gRPCServer 

import scala.concurrent._ 

object HelloServer extends gRPCServer { 

 class HelloService extends HelloWorldGrpc.HelloWorld { 

 override def sayHello(request: ToBeGreeted): Future[Greeting] = { 

 val greeter = request.person match { 

 case Some(p) = p.name 

 case None = "friendo" 

 Future.successful(Greeting(message = s"Hello $greeter, ${request.msg}")) 

 def main(args: Array[String]): Unit = { 

 val service = HelloWorldGrpc.bindService(new HelloService,ExecutionContext.global) 

 runServer(service) 

}

src/main/scala/HelloClient.scala

package learn.grpc.hello.client 

import learn.grpc.services.hello.ToBeGreeted.Person 

import learn.grpc.services.hello._ 

import scala.concurrent.Future 

object HelloClient { 

 def main(args: Array[String]): Unit = { 

 //build connection channel 

 val channel = io.grpc.ManagedChannelBuilder 

 .forAddress("LocalHost",50051) 

 .usePlaintext(true) 

 .build() 

 //construct requestHelloService 

 val greeter = ToBeGreeted() 

 .withMsg("remote greetings!") 

 .withPerson(ToBeGreeted.Person("mickey")) 

 //async call 

 val asyncStub: HelloWorldGrpc.HelloWorldStub = HelloWorldGrpc.stub(channel) 

 val futResponse: Future[Greeting] = asyncStub.sayHello(greeter) 

 import scala.concurrent.ExecutionContext.Implicits.global 

 futResponse.foreach(greeting = println(greeting.message)) 

 val greeter2 = ToBeGreeted(person = Some(Person("jacky")),msg = Some("how are you?")) 

 //sync call 

 val syncStub: HelloWorldGrpc.HelloWorldBlockingClient = HelloWorldGrpc.blockingStub(channel) 

 val response: Greeting = syncStub.sayHello(greeter2) 

 println(s"${response.message}")