grpc订阅发布 grpc 消息推送

通讯模式简介

gRPC应用程序提供四种基础的通讯模式，这四种通信模式基本能满足绝大多数应用场景。得益于底层HTTP2长连接以及消息推送的机制，gRPC也把推送的能力进行抽象形成开发可调用的API。

如上图，四种通信模式为：

• Unary RPC - 也叫做 Simple RPC 简单的请求-响应，一问一答式的RPC请求，类似本地方法调用
• Server-side streaming RPC - 服务端流RPC模式，服务端在接收到客户请求后 主动推送数据。应用场景：APP消息推送、股票动态数据
• Client-side streaming RPC - 客户端流RPC模式，在该模式下客户端会发送多次请求，服务端则会发送最终响应给客户端。需要注意的是服务端并不一定要等到从客户端接收所有消息后，才发送响应。基于此，可以在接收到流中的一条或者几条消息之后就发送响应。也可以在等到所有消息后再发送响应。
• Bidirectional streaming RPC - 全双工流RPC模式，即数据在客户端、服务端双向流动。但是发起方必须是客户端。感觉可以使用这种方式进行IM聊天，哈哈。

Proto 文件定义

下面从完整的demo、不同模式的语法上展开讲一讲每一种模式实现的细节，以及底层的协议。创建route_guide.proto文件，内容如下：

// protobuf 语法
syntax = "proto3";

option go_package = "google.golang.org/grpc/examples/route_guide/routeguide";
// 我们使用golang做测试 以下代码不用考虑 
option java_multiple_files = true;
option java_package = "io.grpc.examples.routeguide";
option java_outer_classname = "RouteGuideProto";

package routeguide;

// Interface exported by the server.
service RouteGuide {
  // A simple RPC. 
  rpc GetFeature(Point) returns (Feature) {}

  // A server-to-client streaming RPC.
  // 跟 Simple RPC 相比，返回类型从对象 变成了 stream 
  rpc ListFeatures(Rectangle) returns (stream Feature) {}

  // A client-to-server streaming RPC.
  // 由于客户端发送多次数据 因此 参数前面加上 stream 关键字
  rpc RecordRoute(stream Point) returns (RouteSummary) {}

  // A Bidirectional streaming RPC.
  // 双向流模式 参数、返回 前面都加上 stream 关键字
  rpc RouteChat(stream RouteNote) returns (stream RouteNote) {}
}

// 以下定义 RPC service 需要的对象 不做过多讲解
// Points are represented as latitude-longitude pairs in the E7 representation
// (degrees multiplied by 10**7 and rounded to the nearest integer).
// Latitudes should be in the range +/- 90 degrees and longitude should be in
// the range +/- 180 degrees (inclusive).
message Point {
  int32 latitude = 1;
  int32 longitude = 2;
}

// A latitude-longitude rectangle, represented as two diagonally opposite
// points "lo" and "hi".
message Rectangle {
  // One corner of the rectangle.
  Point lo = 1;

  // The other corner of the rectangle.
  Point hi = 2;
}

// A feature names something at a given point.
//
// If a feature could not be named, the name is empty.
message Feature {
  // The name of the feature.
  string name = 1;

  // The point where the feature is detected.
  Point location = 2;
}

// A RouteNote is a message sent while at a given point.
message RouteNote {
  // The location from which the message is sent.
  Point location = 1;

  // The message to be sent.
  string message = 2;
}

// A RouteSummary is received in response to a RecordRoute rpc.
//
// It contains the number of individual points received, the number of
// detected features, and the total distance covered as the cumulative sum of
// the distance between each point.
message RouteSummary {
  // The number of points received.
  int32 point_count = 1;

  // The number of known features passed while traversing the route.
  int32 feature_count = 2;

  // The distance covered in metres.
  int32 distance = 3;

  // The duration of the traversal in seconds.
  int32 elapsed_time = 4;
}

自动生成代码

protoc --go_out=. --go_opt=paths=source_relative \
    --go-grpc_out=. --go-grpc_opt=paths=source_relative \
    route_guide.proto

执行以上指令会在相应的目录下生成两个文件

• route_guide.pb.go - 包含所有proto文件中message定义的数据对象，以及自动生成的对用编码、解码方法
• route_guide_grpc.pb.go - 包含两部分内容

• 在proto文件内部定义，需要被客户端实现的接口- RouteGuideClient
• 在proto文件内部定义，需要被服务端实现的接口- RouteGuideServer

完整代码

鉴于代码篇幅过大，文章中完整的代码在 通信模式完整代码

#拉取代码
git clone https://github.com/grpc/grpc-go.git

#下载依赖
cd grpc-go
go mod tidy

#代码目录
cd examples/route_guide

下面按照不同的通信模式，讲解一下其中核心的代码逻辑

Simple(Unary) RPC

服务端

// GetFeature returns the feature at the given point.
func (s *routeGuideServer) GetFeature(ctx context.Context, point *pb.Point) (*pb.Feature, error) {
	for _, feature := range s.savedFeatures {
		if proto.Equal(feature.Location, point) {
			return feature, nil
		}
	}
	// No feature was found, return an unnamed feature
	return &pb.Feature{Location: point}, nil
}

客户端

// printFeature gets the feature for the given point.
func printFeature(client pb.RouteGuideClient, point *pb.Point) {
	log.Printf("Getting feature for point (%d, %d)", point.Latitude, point.Longitude)
	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()
	feature, err := client.GetFeature(ctx, point)
	if err != nil {
		log.Fatalf("client.GetFeature failed: %v", err)
	}
	log.Println(feature)
}

Server-side streaming RPC

服务端

func (s *routeGuideServer) ListFeatures(rect *pb.Rectangle, stream pb.RouteGuide_ListFeaturesServer) error {
	for _, feature := range s.savedFeatures {
		if inRange(feature.Location, rect) {
			if err := stream.Send(feature); err != nil {
				return err
			}
		}
	}
	return nil
}

客户端

func printFeatures(client pb.RouteGuideClient, rect *pb.Rectangle) {
	log.Printf("Looking for features within %v", rect)
	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()
	stream, err := client.ListFeatures(ctx, rect)
	if err != nil {
		log.Fatalf("client.ListFeatures failed: %v", err)
	}
	for {
		feature, err := stream.Recv()
		if err == io.EOF {
			break
		}
		if err != nil {
			log.Fatalf("client.ListFeatures failed: %v", err)
		}
		log.Printf("Feature: name: %q, point:(%v, %v)", feature.GetName(),
			feature.GetLocation().GetLatitude(), feature.GetLocation().GetLongitude())
	}
}

协议分析

同样屏蔽其它模式的调用代码，先后启动服务端、客户端程序，控制台输出结果请自行测试，就不一一展示了。这里需要说明的，当服务端通过多个流会送结果时，在协议上是如何进行数据通信的。

如上图，服务端在最后一个流输出时，会将该stream标记为 END 状态，从而结束数据传递。后续无论是客户端流RPC模式、全双工流RPC模式都是基于这种思路，将最后一个stream 标记为END状态，终止数据传输

Client-side streaming RPC

服务端

func (s *routeGuideServer) RecordRoute(stream pb.RouteGuide_RecordRouteServer) error {
	var pointCount, featureCount, distance int32
	var lastPoint *pb.Point
	startTime := time.Now()
	for {
		// 流结束 发送流关闭的请求
		point, err := stream.Recv()
		if err == io.EOF {
			endTime := time.Now()
			return stream.SendAndClose(&pb.RouteSummary{
				PointCount:   pointCount,
				FeatureCount: featureCount,
				Distance:     distance,
				ElapsedTime:  int32(endTime.Sub(startTime).Seconds()),
			})
		}
		// 数据计算
		if err != nil {
			return err
		}
		pointCount++
		for _, feature := range s.savedFeatures {
			if proto.Equal(feature.Location, point) {
				featureCount++
			}
		}
		if lastPoint != nil {
			distance += calcDistance(lastPoint, point)
		}
		lastPoint = point
	}
}

客户端

func runRecordRoute(client pb.RouteGuideClient) {
	// Create a random number of random points
	r := rand.New(rand.NewSource(time.Now().UnixNano()))
	pointCount := int(r.Int31n(100)) + 2 // Traverse at least two points
	var points []*pb.Point
	for i := 0; i < pointCount; i++ {
		points = append(points, randomPoint(r))
	}
	log.Printf("Traversing %d points.", len(points))
	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()
	stream, err := client.RecordRoute(ctx)
	if err != nil {
		log.Fatalf("client.RecordRoute failed: %v", err)
	}
	//多次发送
	for _, point := range points {
		if err := stream.Send(point); err != nil {
			log.Fatalf("client.RecordRoute: stream.Send(%v) failed: %v", point, err)
		}
	}
	reply, err := stream.CloseAndRecv()
	if err != nil {
		log.Fatalf("client.RecordRoute failed: %v", err)
	}
	log.Printf("Route summary: %v", reply)
}

Bidirectional streaming RPC

服务端

func (s *routeGuideServer) RouteChat(stream pb.RouteGuide_RouteChatServer) error {
	for {
		in, err := stream.Recv()
		if err == io.EOF {
			return nil
		}
		if err != nil {
			return err
		}
		key := serialize(in.Location)

		s.mu.Lock()
		s.routeNotes[key] = append(s.routeNotes[key], in)
		// Note: this copy prevents blocking other clients while serving this one.
		// We don't need to do a deep copy, because elements in the slice are
		// insert-only and never modified.
		rn := make([]*pb.RouteNote, len(s.routeNotes[key]))
		copy(rn, s.routeNotes[key])
		s.mu.Unlock()

		for _, note := range rn {
			if err := stream.Send(note); err != nil {
				return err
			}
		}
	}
}

客户端

func runRouteChat(client pb.RouteGuideClient) {
	notes := []*pb.RouteNote{
		{Location: &pb.Point{Latitude: 0, Longitude: 1}, Message: "First message"},
		{Location: &pb.Point{Latitude: 0, Longitude: 2}, Message: "Second message"},
		{Location: &pb.Point{Latitude: 0, Longitude: 3}, Message: "Third message"},
		{Location: &pb.Point{Latitude: 0, Longitude: 1}, Message: "Fourth message"},
		{Location: &pb.Point{Latitude: 0, Longitude: 2}, Message: "Fifth message"},
		{Location: &pb.Point{Latitude: 0, Longitude: 3}, Message: "Sixth message"},
	}
	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()
	stream, err := client.RouteChat(ctx)
	if err != nil {
		log.Fatalf("client.RouteChat failed: %v", err)
	}
	waitc := make(chan struct{})
	go func() {
		for {
			in, err := stream.Recv()
			if err == io.EOF {
				// read done.
				close(waitc)
				return
			}
			if err != nil {
				log.Fatalf("client.RouteChat failed: %v", err)
			}
			log.Printf("Got message %s at point(%d, %d)", in.Message, in.Location.Latitude, in.Location.Longitude)
		}
	}()
	for _, note := range notes {
		if err := stream.Send(note); err != nil {
			log.Fatalf("client.RouteChat: stream.Send(%v) failed: %v", note, err)
		}
	}
	stream.CloseSend()
	<-waitc
}

番外

代码中的服务端、客户端程序都支持TLS启动，默认不开启可以通过以下指令开启TLS

```sh
$ go run server/server.go -tls=true
```


```sh
$ go run client/client.go -tls=true
```