RPC介绍

Remote Procedure Call，远程过程调用

解决问题

而一旦踏入公司尤其是大型互联网公司就会发现，公司的系统都由成千上万大大小小的服务组成，各服务部署在不同的机器上，由不同的团队负责。这时就会遇到两个问题：
1）要搭建一个新服务，免不了需要依赖他人的服务，而现在他人的服务都在远端，怎么调用？
2）其它团队要使用我们的服务，我们的服务该怎么发布以便他人调用？

过程

1. 服务消费方（client）调用以本地调用方式调用服务；
2. client stub接收到调用后负责将方法、参数等组装成能够进行网络传输的消息体；
3. client stub找到服务地址，并将消息发送到服务端；
4. server stub收到消息后进行解码；
5. server stub根据解码结果调用本地的服务；
6. 本地服务执行并将结果返回给server stub；
7. server stub将返回结果打包成消息并发送至消费方；
8. client stub接收到消息，并进行解码；
9. 服务消费方得到最终结果。

RPC的目标就是要2~8这些步骤都封装起来，让用户对这些细节透明。

实现方式

RPC可以通过HTTP来实现（grpc基于http2.0）,也可以通过Socket自己实现一套协议来实现.

grpc框架

4种通信方式

• 简单rpc：一个请求对象对应一个返回对象

rpc simpleHello(Person) returns (Result) {}

• 服务端流式rpc ：一个请求对象，服务端可以传回多个结果对象

rpc serverStreamHello(Person) returns (stream Result) {}

• 客户端流式rpc：客户端传入多个请求对象，服务端返回一个响应结果

rpc clientStreamHello(stream Person) returns (Result) {}

• 双向流式rpc：可以传入多个对象，返回多个响应对象

rpc biStreamHello(stream Person) returns (stream Result) {}

案例

simple.proto

syntax = "proto3";
package testRPC;service testRPC {rpc simple (emit) returns (on) {}rpc serverStream (emit) returns (stream on){}rpc clientStream (stream emit) returns (on){}rpc bothStream (stream emit) returns (stream on){}
}message emit{string type = 1;string name = 2;
}message on{string type = 1;int32 age = 2;
}

service

package mainimport ("net""google.golang.org/grpc"pb "google.golang.org/grpc/examples/test/proto""google.golang.org/grpc/reflection""fmt""golang.org/x/net/context""io"
)const (port = ":50051"
)type server struct {
}func (s *server) Simple(ctx context.Context, in *pb.Emit) (*pb.On, error) {return &pb.On{Type: "Hello " + in.Type, Age: 10}, nil
}
func (s *server) ServerStream(in *pb.Emit, stream pb.TestRPC_ServerStreamServer) (error) {for i := 1; i < 10; i++ {if err := stream.Send(&pb.On{Type: "Hello " + in.Type, Age: int32(i)}); err != nil {return err}}return nil
}
func (s *server) ClientStream(stream pb.TestRPC_ClientStreamServer) (error) {var pointCount int32for {_, err := stream.Recv()if err == io.EOF {return stream.SendAndClose(&pb.On{Type: "end",Age:  pointCount,})}pointCount++}
}func (s *server) BothStream(stream pb.TestRPC_BothStreamServer) (error) {for {emit, err := stream.Recv()if err == io.EOF {return nil}fmt.Println(string(emit.Type))for i := 1; i < 3; i++ {if err := stream.Send(&pb.On{Type: emit.Type, Age: int32(i)}); err != nil {return err}}}return nil
}func main() {lis, _ := net.Listen("tcp", port)s := grpc.NewServer()pb.RegisterTestRPCServer(s, &server{})reflection.Register(s)if err := s.Serve(lis); err != nil {fmt.Println("error")}
}

client

package mainimport ("google.golang.org/grpc"pb "google.golang.org/grpc/examples/test/proto""golang.org/x/net/context""time""log""io"
)const (address = "localhost:50051"
)func main() {conn, _ := grpc.Dial(address, grpc.WithInsecure())defer conn.Close()rpcClient := pb.NewTestRPCClient(conn)testSimple(rpcClient)testServerStream(rpcClient)testClientStream(rpcClient)testBothStream(rpcClient)}func testSimple(client pb.TestRPCClient) {ctx, cancel := context.WithTimeout(context.Background(), time.Second)defer cancel()// simpler, _ := client.Simple(ctx, &pb.Emit{Type: "11"})log.Printf("Greeting: %s", r)
}func testServerStream(client pb.TestRPCClient) {ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)defer cancel()stream, err := client.ServerStream(ctx, &pb.Emit{Type: "Hello "})if err != nil {log.Fatalf("%v.ListFeatures(_) = _, %v", client, err)}for {feature, err := stream.Recv()if err == io.EOF {break}if err != nil {log.Fatalf("%v.ListFeatures(_) = _, %v", client, err)}log.Println(feature)}
}func testClientStream(client pb.TestRPCClient) {ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)defer cancel()stream, err := client.ClientStream(ctx)if err != nil {log.Fatalf("%v.RecordRoute(_) = _, %v", client, err)}var points []pb.Emitfor i := 0; i < 10; i++ {points = append(points, pb.Emit{Type: "t", Name: string(i)})}for _, point := range points {if err := stream.Send(&point); err != nil {log.Fatalf("%v.Send(%v) = %v", stream, point, err)}}reply, err := stream.CloseAndRecv()if err != nil {log.Fatalf("%v.CloseAndRecv() got error %v, want %v", stream, err, nil)}log.Printf("Route summary: %v", reply)
}func testBothStream(client pb.TestRPCClient) {ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)defer cancel()stream, err := client.BothStream(ctx)if err != nil {log.Fatalf("%v.RecordRoute(_) = _, %v", client, err)}var points []pb.Emitfor i := 0; i < 10; i++ {points = append(points, pb.Emit{Type: "xiaoming"+string(i), Name: "xiaohong"})}waitc := make(chan struct{})go func() {for {on, err := stream.Recv()if err == io.EOF {// read done.close(waitc)return}if err != nil {log.Fatalf("Failed to receive a note : %v", err)}log.Printf("Got message %s = %d)", on.Type, on.Age)}}()for _, point := range points {if err := stream.Send(&point); err != nil {log.Fatalf("Failed to send a note: %v", err)}}stream.CloseSend()<-waitc
}