带入gRPC:gRPC Streaming, Client and Server原文地址:带入gRPC:gRPC Streaming, Client and Server前言本章节将介绍 gRPC 的流式,分为三种类型:Server-side streaming RPC:服务器端流式 RPCClient-side streaming RPC:客户端流式 RPCBidirectional streaming RPC:双向流式 RPC流任何技术,因为有痛点,所以才有了存在的必要性。如果您想要了解 gRPC 的流式调用,请继续图gRPC Streaming 是基于 HTTP/2 的,后续章节再进行详细讲解为什么不用 Simple RPC流式为什么要存在呢,是 Simple RPC 有什么问题吗?通过模拟业务场景,可得知在使用 Simple RPC 时,有如下问题:数据包过大造成的瞬时压力接收数据包时,需要所有数据包都接受成功且正确后,才能够回调响应,进行业务处理(无法客户端边发送,服务端边处理)为什么用 Streaming RPC大规模数据包实时场景模拟场景每天早上 6 点,都有一批百万级别的数据集要同从 A 同步到 B,在同步的时候,会做一系列操作(归档、数据分析、画像、日志等)。这一次性涉及的数据量确实大在同步完成后,也有人马上会去查阅数据,为了新的一天筹备。也符合实时性。两者相较下,这个场景下更适合使用 Streaming RPCgRPC在讲解具体的 gRPC 流式代码时,会着重在第一节讲解,因为三种模式其实是不同的组合。希望你能够注重理解,举一反三,其实都是一样的知识点 ????目录结构$ tree go-grpc-example go-grpc-example├── client│ ├── simple_client│ │ └── client.go│ └── stream_client│ └── client.go├── proto│ ├── search.proto│ └── stream.proto└── server ├── simple_server │ └── server.go └── stream_server └── server.go增加 stream_server、stream_client 存放服务端和客户端文件,proto/stream.proto 用于编写 IDLIDL在 proto 文件夹下的 stream.proto 文件中,写入如下内容:syntax = “proto3”;package proto;service StreamService { rpc List(StreamRequest) returns (stream StreamResponse) {}; rpc Record(stream StreamRequest) returns (StreamResponse) {}; rpc Route(stream StreamRequest) returns (stream StreamResponse) {};}message StreamPoint { string name = 1; int32 value = 2;}message StreamRequest { StreamPoint pt = 1;}message StreamResponse { StreamPoint pt = 1;}注意关键字 stream,声明其为一个流方法。这里共涉及三个方法,对应关系为List:服务器端流式 RPCRecord:客户端流式 RPCRoute:双向流式 RPC基础模板 + 空定义Serverpackage mainimport ( “log” “net” “google.golang.org/grpc” pb “github.com/EDDYCJY/go-grpc-example/proto” )type StreamService struct{}const ( PORT = “9002”)func main() { server := grpc.NewServer() pb.RegisterStreamServiceServer(server, &StreamService{}) lis, err := net.Listen(“tcp”, “:"+PORT) if err != nil { log.Fatalf(“net.Listen err: %v”, err) } server.Serve(lis)}func (s *StreamService) List(r *pb.StreamRequest, stream pb.StreamService_ListServer) error { return nil}func (s *StreamService) Record(stream pb.StreamService_RecordServer) error { return nil}func (s *StreamService) Route(stream pb.StreamService_RouteServer) error { return nil}写代码前,建议先将 gRPC Server 的基础模板和接口给空定义出来。若有不清楚可参见上一章节的知识点Clientpackage mainimport ( “log” “google.golang.org/grpc” pb “github.com/EDDYCJY/go-grpc-example/proto”)const ( PORT = “9002”)func main() { conn, err := grpc.Dial(”:"+PORT, grpc.WithInsecure()) if err != nil { log.Fatalf(“grpc.Dial err: %v”, err) } defer conn.Close() client := pb.NewStreamServiceClient(conn) err = printLists(client, &pb.StreamRequest{Pt: &pb.StreamPoint{Name: “gRPC Stream Client: List”, Value: 2018}}) if err != nil { log.Fatalf(“printLists.err: %v”, err) } err = printRecord(client, &pb.StreamRequest{Pt: &pb.StreamPoint{Name: “gRPC Stream Client: Record”, Value: 2018}}) if err != nil { log.Fatalf(“printRecord.err: %v”, err) } err = printRoute(client, &pb.StreamRequest{Pt: &pb.StreamPoint{Name: “gRPC Stream Client: Route”, Value: 2018}}) if err != nil { log.Fatalf(“printRoute.err: %v”, err) }}func printLists(client pb.StreamServiceClient, r *pb.StreamRequest) error { return nil}func printRecord(client pb.StreamServiceClient, r *pb.StreamRequest) error { return nil}func printRoute(client pb.StreamServiceClient, r *pb.StreamRequest) error { return nil}一、Server-side streaming RPC:服务器端流式 RPC服务器端流式 RPC,显然是单向流,并代指 Server 为 Stream 而 Client 为普通 RPC 请求简单来讲就是客户端发起一次普通的 RPC 请求,服务端通过流式响应多次发送数据集,客户端 Recv 接收数据集。大致如图:Serverfunc (s *StreamService) List(r *pb.StreamRequest, stream pb.StreamService_ListServer) error { for n := 0; n <= 6; n++ { err := stream.Send(&pb.StreamResponse{ Pt: &pb.StreamPoint{ Name: r.Pt.Name, Value: r.Pt.Value + int32(n), }, }) if err != nil { return err } } return nil}在 Server,主要留意 stream.Send 方法。它看上去能发送 N 次?有没有大小限制?type StreamService_ListServer interface { Send(*StreamResponse) error grpc.ServerStream}func (x *streamServiceListServer) Send(m *StreamResponse) error { return x.ServerStream.SendMsg(m)}通过阅读源码,可得知是 protoc 在生成时,根据定义生成了各式各样符合标准的接口方法。最终再统一调度内部的 SendMsg 方法,该方法涉及以下过程:消息体(对象)序列化压缩序列化后的消息体对正在传输的消息体增加 5 个字节的 header判断压缩+序列化后的消息体总字节长度是否大于预设的 maxSendMessageSize(预设值为 math.MaxInt32),若超出则提示错误写入给流的数据集Clientfunc printLists(client pb.StreamServiceClient, r *pb.StreamRequest) error { stream, err := client.List(context.Background(), r) if err != nil { return err } for { resp, err := stream.Recv() if err == io.EOF { break } if err != nil { return err } log.Printf(“resp: pj.name: %s, pt.value: %d”, resp.Pt.Name, resp.Pt.Value) } return nil}在 Client,主要留意 stream.Recv() 方法。什么情况下 io.EOF ?什么情况下存在错误信息呢?type StreamService_ListClient interface { Recv() (*StreamResponse, error) grpc.ClientStream}func (x *streamServiceListClient) Recv() (*StreamResponse, error) { m := new(StreamResponse) if err := x.ClientStream.RecvMsg(m); err != nil { return nil, err } return m, nil}通过阅读源码,可得知:当流结束(调用了 Close)时,会出现 io.EOF。而错误信息(err)基本都由另一侧反馈过来,因此进行日常处理和标记即可验证运行 stream_server/server.go:$ go run server.go运行 stream_client/client.go:$ go run client.go 2018/09/24 16:18:25 resp: pj.name: gRPC Stream Client: List, pt.value: 20182018/09/24 16:18:25 resp: pj.name: gRPC Stream Client: List, pt.value: 20192018/09/24 16:18:25 resp: pj.name: gRPC Stream Client: List, pt.value: 20202018/09/24 16:18:25 resp: pj.name: gRPC Stream Client: List, pt.value: 20212018/09/24 16:18:25 resp: pj.name: gRPC Stream Client: List, pt.value: 20222018/09/24 16:18:25 resp: pj.name: gRPC Stream Client: List, pt.value: 20232018/09/24 16:18:25 resp: pj.name: gRPC Stream Client: List, pt.value: 2024二、Client-side streaming RPC:客户端流式 RPC客户端流式 RPC,单向流,客户端通过流式发起多次 RPC 请求给服务端,服务端发起一次响应给客户端,大致如图:Serverfunc (s *StreamService) Record(stream pb.StreamService_RecordServer) error { for { r, err := stream.Recv() if err == io.EOF { return stream.SendAndClose(&pb.StreamResponse{Pt: &pb.StreamPoint{Name: “gRPC Stream Server: Record”, Value: 1}}) } if err != nil { return err } log.Printf(“stream.Recv pt.name: %s, pt.value: %d”, r.Pt.Name, r.Pt.Value) } return nil}多了一个从未见过的方法 stream.SendAndClose,它是做什么用的呢?在这段程序中,我们对每一个 Recv 都进行了处理,当发现 io.EOF (流关闭) 后,需要将最终的响应结果发送给客户端,同时关闭正在另外一侧等待的 RecvClientfunc printRecord(client pb.StreamServiceClient, r *pb.StreamRequest) error { stream, err := client.Record(context.Background()) if err != nil { return err } for n := 0; n < 6; n++ { err := stream.Send(r) if err != nil { return err } } resp, err := stream.CloseAndRecv() if err != nil { return err } log.Printf(“resp: pj.name: %s, pt.value: %d”, resp.Pt.Name, resp.Pt.Value) return nil}stream.CloseAndRecv 和 stream.SendAndClose 是配套使用的流方法,相信聪明的你已经秒懂它的作用了验证重启 stream_server/server.go,再次运行 stream_client/client.go:stream_client:$ go run client.go2018/09/24 16:23:03 resp: pj.name: gRPC Stream Server: Record, pt.value: 1stream_server:$ go run server.go2018/09/24 16:23:03 stream.Recv pt.name: gRPC Stream Client: Record, pt.value: 20182018/09/24 16:23:03 stream.Recv pt.name: gRPC Stream Client: Record, pt.value: 20182018/09/24 16:23:03 stream.Recv pt.name: gRPC Stream Client: Record, pt.value: 20182018/09/24 16:23:03 stream.Recv pt.name: gRPC Stream Client: Record, pt.value: 20182018/09/24 16:23:03 stream.Recv pt.name: gRPC Stream Client: Record, pt.value: 20182018/09/24 16:23:03 stream.Recv pt.name: gRPC Stream Client: Record, pt.value: 2018三、Bidirectional streaming RPC:双向流式 RPC双向流式 RPC,顾名思义是双向流。由客户端以流式的方式发起请求,服务端同样以流式的方式响应请求首个请求一定是 Client 发起,但具体交互方式(谁先谁后、一次发多少、响应多少、什么时候关闭)根据程序编写的方式来确定(可以结合协程)因此图示也千变万化,这里就不放出来了Serverfunc (s *StreamService) Route(stream pb.StreamService_RouteServer) error { n := 0 for { err := stream.Send(&pb.StreamResponse{ Pt: &pb.StreamPoint{ Name: “gPRC Stream Client: Route”, Value: int32(n), }, }) if err != nil { return err } r, err := stream.Recv() if err == io.EOF { return nil } if err != nil { return err } n++ log.Printf(“stream.Recv pt.name: %s, pt.value: %d”, r.Pt.Name, r.Pt.Value) } return nil}Clientfunc printRoute(client pb.StreamServiceClient, r *pb.StreamRequest) error { stream, err := client.Route(context.Background()) if err != nil { return err } for n := 0; n <= 6; n++ { err = stream.Send(r) if err != nil { return err } resp, err := stream.Recv() if err == io.EOF { break } if err != nil { return err } log.Printf(“resp: pj.name: %s, pt.value: %d”, resp.Pt.Name, resp.Pt.Value) } stream.CloseSend() return nil}验证重启 stream_server/server.go,再次运行 stream_client/client.go:stream_server$ go run server.go2018/09/24 16:29:43 stream.Recv pt.name: gRPC Stream Client: Route, pt.value: 20182018/09/24 16:29:43 stream.Recv pt.name: gRPC Stream Client: Route, pt.value: 20182018/09/24 16:29:43 stream.Recv pt.name: gRPC Stream Client: Route, pt.value: 20182018/09/24 16:29:43 stream.Recv pt.name: gRPC Stream Client: Route, pt.value: 20182018/09/24 16:29:43 stream.Recv pt.name: gRPC Stream Client: Route, pt.value: 20182018/09/24 16:29:43 stream.Recv pt.name: gRPC Stream Client: Route, pt.value: 2018stream_client$ go run client.go2018/09/24 16:29:43 resp: pj.name: gPRC Stream Client: Route, pt.value: 02018/09/24 16:29:43 resp: pj.name: gPRC Stream Client: Route, pt.value: 12018/09/24 16:29:43 resp: pj.name: gPRC Stream Client: Route, pt.value: 22018/09/24 16:29:43 resp: pj.name: gPRC Stream Client: Route, pt.value: 32018/09/24 16:29:43 resp: pj.name: gPRC Stream Client: Route, pt.value: 42018/09/24 16:29:43 resp: pj.name: gPRC Stream Client: Route, pt.value: 52018/09/24 16:29:43 resp: pj.name: gPRC Stream Client: Route, pt.value: 6总结在本文共介绍了三类流的交互方式,可以根据实际的业务场景去选择合适的方式。会事半功倍哦 ????系列目录带入gRPC:gRPC及相关介绍带入gRPC:gRPC Client and Server带入gRPC:gRPC Streaming, Client and Server