grpc 入门（二）-- 服务接口类型

本节是继上一章节Hello world的进一步深入挖掘;

一、grpc服务接口类型

　　在godoc的网站上对grpc的端口类型进行了简单的介绍，总共有下面4种类型[1]：

gRPC lets you define four kinds of service method:

    Unary RPCs where the client sends a single request to the server and gets a single response back, just like a normal function call.

　　rpc SayHello(HelloRequest) returns (HelloResponse){
　　}

    Server streaming RPCs where the client sends a request to the server and gets a stream to read a sequence of messages back. The client reads from the returned stream until there are no more messages.

　　rpc LotsOfReplies(HelloRequest) returns (stream HelloResponse){
　　}

    Client streaming RPCs where the client writes a sequence of messages and sends them to the server, again using a provided stream. Once the client has finished writing the messages, it waits for the server to read them and return its response.

　　rpc LotsOfGreetings(stream HelloRequest) returns (HelloResponse) {
　　}

    Bidirectional streaming RPCs where both sides send a sequence of messages using a read-write stream. The two streams operate independently, so clients and servers can read and write in whatever order they like: for example, the server could wait to receive all the client messages before writing its responses, or it could alternately read a message then write a message, or some other combination of reads and writes. The order of messages in each stream is preserved.

　　rpc BidiHello(stream HelloRequest) returns (stream HelloResponse){
　　}

　　We’ll look at the different types of RPC in more detail in the RPC life cycle section below.

　　上面是从官网摘抄过来的，简单的来讲客户端和服务发送数据有两种形式：Unary和Streaming。Unary （一元）一次只发送一个包; Streaming（流）一次可以发送多个包。两种方式组合一下就形成了4种类型：

	服务端	客户端
1	Unary	Unary
2	Streaming	Streaming
3	Unary	Streaming
4	Streaming	Unary

　

　　在上一篇Hello world文章里面的示例就是第一种类型接口，它最终声明了一个需要开发者去实习具体业务逻辑的接口：

// Server API for Greeter service

type GreeterServer interface {
    // Sends a greeting
    SayHello(context.Context, *HelloRequest) (*HelloReply, error)
}

　　开发者需要根据业务需求来考虑使用不同的grpc服务接口类型 。

参考网址

[1] https://grpc.io/docs/guides/concepts.html#service-definition