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traittrait HelloWorldBlockingClIEnt -> 用于实现客户端stubclass HelloWorldBlockingStub -> blocking客户端stubclass HelloWorldStub -> non-blocking客户端stubdef 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.serverimport 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.scalapbVersionimport scalapb.compiler.Version.grpcJavaVersionname := "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.serverimport 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.serverimport learn.grpc.services.hello._import learn.grpc.server.gRPCServerimport 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.clIEntimport learn.grpc.services.hello.ToBeGreeted.Personimport learn.grpc.services.hello._import scala.concurrent.Futureobject HelloClIEnt { def main(args: Array[String]): Unit = { //build connection channel val channel = io.grpc.ManagedChannelBuilder .forAddress("LocalHost",msg = Some("how are you?")) //sync call val syncStub: HelloWorldGrpc.HelloWorldBlockingClIEnt = HelloWorldGrpc.blockingStub(channel) val response: Greeting = syncStub.sayHello(greeter2) println(s"${response.message}") }}总结
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