Protocol Buffers 3 学习

时间：2023-02-23 11:07:44

如果您最近有学习 gRPC 如何使用的打算，那么您第一步其实应该学习 Protocol Buffers。

废话不多说，我们开始学习：

一、定义消息

1、首先看一个简单的例子：

1 syntax = "proto3";
2 
3 message SearchRequest {
4   string query = 1;
5   int32 page_number = 2;
6   int32 result_per_page = 3;
7 }

第一行 syntax 用于声明版本，如果不声明则默认使用版本2。

第三行 message 用于声明消息结构体。

第四到第六行每个字段后面都有一个数值，用于标识消息在二进制格式中的位置。值从1到15采用1个字节编码。

值从16到2047采用两个字节编码，最小的值是1，最大的值是2的29次方减1，另外19000到19999你也不可以使用，这些是保留值。

1 message SearchRequest {
2   string query = 1;
3   int32 page_number = 2;
4   int32 result_per_page = 3;
5 }
6 
7 message SearchResponse {
8  ...
9 }

另外，多个消息类型是可以定义在一个以 .proto 为后缀的文件的，如果你想要添加注释的话，同注释代码一样。

值得注意的是，如果您要修改消息类型，比如删除字段，或者注释字段，那么以后有可能有人在你删除字段的位置添加了一个新字段，并使用原删除字段相同的数值编号。如果此时有别的服务还在使用老版本的话，那么会导致数据被破坏。此时你可以使用 reserved 关键字来预占编号或者预占字段名称，如下所示：

message Foo {
  reserved 2, 15, 9 to 11, 40 to max;
  reserved "foo", "bar";
}

另外，在同一个 reserved 语句中不能同时预占编号和字段名称。

2、Protocol Buffers 同样支持枚举与结构嵌套。

enum Corpus {
  CORPUS_UNSPECIFIED = 0;
  CORPUS_UNIVERSAL = 1;
  CORPUS_WEB = 2;
  CORPUS_IMAGES = 3;
  CORPUS_LOCAL = 4;
  CORPUS_NEWS = 5;
  CORPUS_PRODUCTS = 6;
  CORPUS_VIDEO = 7;
}

message SearchRequest {
  string query = 1;
  int32 page_number = 2;
  int32 result_per_page = 3;
  Corpus corpus = 4;
}

枚举的第一个值为0，另外也支持键值对类型 map<key_type, value_type> map_field = N;

3、再来看另外一个语句

message SearchResponse {
  repeated Result results = 1;
}

message Result {
  optional string url = 1;
  string title = 2;
  repeated string snippets = 3;
}

optional 关键字
字面意思是可选的意思，具体protobuf里面怎么处理这个字段呢，就是protobuf处理的时候另外加了一个bool的变量，用来标记这个optional字段是否有值，发送方在发送的时候，如果这个字段有值，那么就给bool变量标记为true，否则就标记为false，接收方在收到这个字段的同时，也会收到发送方同时发送的bool变量，拿着bool变量就知道这个字段是否有值了，这就是option的意思。

repeated 关键字
字面意思大概是重复的意思，其实protobuf处理这个字段的时候，也是optional字段一样，另外加了一个count计数变量，用于标明这个字段有多少个，这样发送方发送的时候，同时发送了count计数变量和这个字段的起始地址，接收方在接受到数据之后，按照count来解析对应的数据即可。

4、导入

如果你想导入别的 proto 文件里的消息类型，同样也可以使用 import 导入：

import "myproject/other_protos.proto";

默认情况下，只能使用直接导入的 .proto 文件中的定义。然而，有时您可能需要将 .proto 文件移动到新的位置。您可以在旧位置放置一个占位符的.proto文件，使用 import public 将所有导入转发到新位置，而不是直接移动 .proto 文件并在一次更改中更新所有调用站点。

Protocol Buffers 3 学习

5、包

您可以向.proto文件添加可选的包说明符，以防止协议消息类型之间的名称冲突。

package foo.bar;
message Open { ... }
message Foo {
  ...
  foo.bar.Open open = 1;
  ...
}

为了生成Go代码，可以为提供编译后的输出路径。

option go_package = "example.com/project/protos/fizz";

二、定义服务

如果您想在RPC(远程过程调用)系统中使用您的消息类型，您可以在 .proto 文件中定义RPC服务接口，protocol buffer compiler将用您选择的语言生成服务接口代码。因此，如果你想用一个方法定义一个RPC服务，它接受你的SearchRequest并返回一个SearchResponse，你可以在你的 .proto 文件中定义它，如下所示:

service SearchService {
  rpc Search(SearchRequest) returns (SearchResponse);
}

三、编译 protocol buffer

现在运行编译器，指定源目录(应用程序源代码所在的目录-如果不提供值，则使用当前目录)和目标目录(您希望生成的代码存放的目录;通常与$SRC_DIR相同)，以及你的 .proto 的路径。在这种情况下，您将调用:

protoc -I=$SRC_DIR --go_out=$DST_DIR $SRC_DIR/addressbook.proto

 假如您输入以下命令进行编译，并且 proto 文件使用了 option go_package = "/path2";

protoc --go_out=./path1 ./test.proto

那么输出目录就在当前目录的 /path1/paht2 目录下。

举个例子：

syntax = "proto3";

package test;

option go_package = "order/service";

message SearchRequest {
  string requestParam1 = 1;
  string requestParam2 = 2;
  int32 requestParam3 = 3;
}

message SearchResponse {
  int32 code = 1;
  string msg = 2;
}

service SearchService {
  rpc SearchOrder(SearchRequest) returns (SearchResponse);
}

使用如下命令进行编译：

protoc --go_out=./gen ./test.proto

编译之后的文件在 ./gen/order/service/ 目录下，文件名为 test.pb.go:

// Code generated by protoc-gen-go. DO NOT EDIT.
// versions:
//     protoc-gen-go v1.28.1
//     protoc        v4.22.0
// source: test.proto

package service

import (
    protoreflect "google.golang.org/protobuf/reflect/protoreflect"
    protoimpl "google.golang.org/protobuf/runtime/protoimpl"
    reflect "reflect"
    sync "sync"
)

const (
    // Verify that this generated code is sufficiently up-to-date.
    _ = protoimpl.EnforceVersion(20 - protoimpl.MinVersion)
    // Verify that runtime/protoimpl is sufficiently up-to-date.
    _ = protoimpl.EnforceVersion(protoimpl.MaxVersion - 20)
)

type SearchRequest struct {
    state         protoimpl.MessageState
    sizeCache     protoimpl.SizeCache
    unknownFields protoimpl.UnknownFields

    RequestParam1 string `protobuf:"bytes,1,opt,name=requestParam1,proto3" json:"requestParam1,omitempty"`
    RequestParam2 string `protobuf:"bytes,2,opt,name=requestParam2,proto3" json:"requestParam2,omitempty"`
    RequestParam3 int32  `protobuf:"varint,3,opt,name=requestParam3,proto3" json:"requestParam3,omitempty"`
}

func (x *SearchRequest) Reset() {
    *x = SearchRequest{}
    if protoimpl.UnsafeEnabled {
        mi := &file_test_proto_msgTypes[0]
        ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
        ms.StoreMessageInfo(mi)
    }
}

func (x *SearchRequest) String() string {
    return protoimpl.X.MessageStringOf(x)
}

func (*SearchRequest) ProtoMessage() {}

func (x *SearchRequest) ProtoReflect() protoreflect.Message {
    mi := &file_test_proto_msgTypes[0]
    if protoimpl.UnsafeEnabled && x != nil {
        ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
        if ms.LoadMessageInfo() == nil {
            ms.StoreMessageInfo(mi)
        }
        return ms
    }
    return mi.MessageOf(x)
}

// Deprecated: Use SearchRequest.ProtoReflect.Descriptor instead.
func (*SearchRequest) Descriptor() ([]byte, []int) {
    return file_test_proto_rawDescGZIP(), []int{0}
}

func (x *SearchRequest) GetRequestParam1() string {
    if x != nil {
        return x.RequestParam1
    }
    return ""
}

func (x *SearchRequest) GetRequestParam2() string {
    if x != nil {
        return x.RequestParam2
    }
    return ""
}

func (x *SearchRequest) GetRequestParam3() int32 {
    if x != nil {
        return x.RequestParam3
    }
    return 0
}

type SearchResponse struct {
    state         protoimpl.MessageState
    sizeCache     protoimpl.SizeCache
    unknownFields protoimpl.UnknownFields

    Code int32  `protobuf:"varint,1,opt,name=code,proto3" json:"code,omitempty"`
    Msg  string `protobuf:"bytes,2,opt,name=msg,proto3" json:"msg,omitempty"`
}

func (x *SearchResponse) Reset() {
    *x = SearchResponse{}
    if protoimpl.UnsafeEnabled {
        mi := &file_test_proto_msgTypes[1]
        ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
        ms.StoreMessageInfo(mi)
    }
}

func (x *SearchResponse) String() string {
    return protoimpl.X.MessageStringOf(x)
}

func (*SearchResponse) ProtoMessage() {}

func (x *SearchResponse) ProtoReflect() protoreflect.Message {
    mi := &file_test_proto_msgTypes[1]
    if protoimpl.UnsafeEnabled && x != nil {
        ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
        if ms.LoadMessageInfo() == nil {
            ms.StoreMessageInfo(mi)
        }
        return ms
    }
    return mi.MessageOf(x)
}

// Deprecated: Use SearchResponse.ProtoReflect.Descriptor instead.
func (*SearchResponse) Descriptor() ([]byte, []int) {
    return file_test_proto_rawDescGZIP(), []int{1}
}

func (x *SearchResponse) GetCode() int32 {
    if x != nil {
        return x.Code
    }
    return 0
}

func (x *SearchResponse) GetMsg() string {
    if x != nil {
        return x.Msg
    }
    return ""
}

var File_test_proto protoreflect.FileDescriptor

var file_test_proto_rawDesc = []byte{
    0x0a, 0x0a, 0x74, 0x65, 0x73, 0x74, 0x2e, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x12, 0x04, 0x74, 0x65,
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    0x6f, 0x33,
}

var (
    file_test_proto_rawDescOnce sync.Once
    file_test_proto_rawDescData = file_test_proto_rawDesc
)

func file_test_proto_rawDescGZIP() []byte {
    file_test_proto_rawDescOnce.Do(func() {
        file_test_proto_rawDescData = protoimpl.X.CompressGZIP(file_test_proto_rawDescData)
    })
    return file_test_proto_rawDescData
}

var file_test_proto_msgTypes = make([]protoimpl.MessageInfo, 2)
var file_test_proto_goTypes = []interface{}{
    (*SearchRequest)(nil),  // 0: test.SearchRequest
    (*SearchResponse)(nil), // 1: test.SearchResponse
}
var file_test_proto_depIdxs = []int32{
    0, // 0: test.SearchService.SearchOrder:input_type -> test.SearchRequest
    1, // 1: test.SearchService.SearchOrder:output_type -> test.SearchResponse
    1, // [1:2] is the sub-list for method output_type
    0, // [0:1] is the sub-list for method input_type
    0, // [0:0] is the sub-list for extension type_name
    0, // [0:0] is the sub-list for extension extendee
    0, // [0:0] is the sub-list for field type_name
}

func init() { file_test_proto_init() }
func file_test_proto_init() {
    if File_test_proto != nil {
        return
    }
    if !protoimpl.UnsafeEnabled {
        file_test_proto_msgTypes[0].Exporter = func(v interface{}, i int) interface{} {
            switch v := v.(*SearchRequest); i {
            case 0:
                return &v.state
            case 1:
                return &v.sizeCache
            case 2:
                return &v.unknownFields
            default:
                return nil
            }
        }
        file_test_proto_msgTypes[1].Exporter = func(v interface{}, i int) interface{} {
            switch v := v.(*SearchResponse); i {
            case 0:
                return &v.state
            case 1:
                return &v.sizeCache
            case 2:
                return &v.unknownFields
            default:
                return nil
            }
        }
    }
    type x struct{}
    out := protoimpl.TypeBuilder{
        File: protoimpl.DescBuilder{
            GoPackagePath: reflect.TypeOf(x{}).PkgPath(),
            RawDescriptor: file_test_proto_rawDesc,
            NumEnums:      0,
            NumMessages:   2,
            NumExtensions: 0,
            NumServices:   1,
        },
        GoTypes:           file_test_proto_goTypes,
        DependencyIndexes: file_test_proto_depIdxs,
        MessageInfos:      file_test_proto_msgTypes,
    }.Build()
    File_test_proto = out.File
    file_test_proto_rawDesc = nil
    file_test_proto_goTypes = nil
    file_test_proto_depIdxs = nil
}

如果你要使用的消息结构的话，可以看如下示例：

package main

import (
    "fmt"
    "github.com/golang/protobuf/proto"
    pb "study.com/study-user/api/proto/gen/order/service"
)

func main() {
    request := &pb.SearchRequest{
        RequestParam1: "aaa",
        RequestParam2: "bbb",
        RequestParam3: 0,
    }
    fmt.Printf("编码前: %v \n", request)
    marshal, err := proto.Marshal(request)
    fmt.Printf("编码后: %v \n", marshal)
    if err == nil {
        newRequest := &pb.SearchRequest{}
        proto.Unmarshal(marshal, newRequest)
        fmt.Printf("解码后: %v \n", newRequest)
    }

}

细心的你可能发现，我没有调用函数，毕竟也没有定义函数，你就算用 pb. 后面也找不到函数名，可以先看看gRPC，这里会告诉你答案。

四、gRPC介绍

当你来到gRPC官网Go语言时，他会要求你提前准备如下：

1、安装 Go

2、安装 Protocol Buffer 编译器

3、安装编译插件

$ go install google.golang.org/protobuf/cmd/protoc-gen-go@v1.28
$ go install google.golang.org/grpc/cmd/protoc-gen-go-grpc@v1.2

4、配置 Protocol Buffer 环境变量

$ export PATH="$PATH:$(go env GOPATH)/bin"

5、下载测试用例

git clone -b v1.53.0 --depth 1 https://github.com/grpc/grpc-go

6、运行示例

go run greeter_server/main.go
go run greeter_client/main.go

6、生成 gRPC代码

$ protoc --go_out=. --go_opt=paths=source_relative \
    --go-grpc_out=. --go-grpc_opt=paths=source_relative \
    helloworld/helloworld.proto

这个我们拿之前的例子来举例，go_opt 选项你可以在源文件中使用 option go_package 来替代。

protoc --go_out=./gen --go-grpc_out=./gen ./test.proto

这时可以看到生成了两个文件：test.pb.go、test_grpc.pb.go，我们来看一下生成的 grpc 代码：

// Code generated by protoc-gen-go-grpc. DO NOT EDIT.
// versions:
// - protoc-gen-go-grpc v1.2.0
// - protoc             v4.22.0
// source: test.proto

package service

import (
    context "context"
    grpc "google.golang.org/grpc"
    codes "google.golang.org/grpc/codes"
    status "google.golang.org/grpc/status"
)

// This is a compile-time assertion to ensure that this generated file
// is compatible with the grpc package it is being compiled against.
// Requires gRPC-Go v1.32.0 or later.
const _ = grpc.SupportPackageIsVersion7

// SearchServiceClient is the client API for SearchService service.
//
// For semantics around ctx use and closing/ending streaming RPCs, please refer to https://pkg.go.dev/google.golang.org/grpc/?tab=doc#ClientConn.NewStream.
type SearchServiceClient interface {
    SearchOrder(ctx context.Context, in *SearchRequest, opts ...grpc.CallOption) (*SearchResponse, error)
}

type searchServiceClient struct {
    cc grpc.ClientConnInterface
}

func NewSearchServiceClient(cc grpc.ClientConnInterface) SearchServiceClient {
    return &searchServiceClient{cc}
}

func (c *searchServiceClient) SearchOrder(ctx context.Context, in *SearchRequest, opts ...grpc.CallOption) (*SearchResponse, error) {
    out := new(SearchResponse)
    err := c.cc.Invoke(ctx, "/test.SearchService/SearchOrder", in, out, opts...)
    if err != nil {
        return nil, err
    }
    return out, nil
}

// SearchServiceServer is the server API for SearchService service.
// All implementations must embed UnimplementedSearchServiceServer
// for forward compatibility
type SearchServiceServer interface {
    SearchOrder(context.Context, *SearchRequest) (*SearchResponse, error)
    mustEmbedUnimplementedSearchServiceServer()
}

// UnimplementedSearchServiceServer must be embedded to have forward compatible implementations.
type UnimplementedSearchServiceServer struct {
}

func (UnimplementedSearchServiceServer) SearchOrder(context.Context, *SearchRequest) (*SearchResponse, error) {
    return nil, status.Errorf(codes.Unimplemented, "method SearchOrder not implemented")
}
func (UnimplementedSearchServiceServer) mustEmbedUnimplementedSearchServiceServer() {}

// UnsafeSearchServiceServer may be embedded to opt out of forward compatibility for this service.
// Use of this interface is not recommended, as added methods to SearchServiceServer will
// result in compilation errors.
type UnsafeSearchServiceServer interface {
    mustEmbedUnimplementedSearchServiceServer()
}

func RegisterSearchServiceServer(s grpc.ServiceRegistrar, srv SearchServiceServer) {
    s.RegisterService(&SearchService_ServiceDesc, srv)
}

func _SearchService_SearchOrder_Handler(srv interface{}, ctx context.Context, dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
    in := new(SearchRequest)
    if err := dec(in); err != nil {
        return nil, err
    }
    if interceptor == nil {
        return srv.(SearchServiceServer).SearchOrder(ctx, in)
    }
    info := &grpc.UnaryServerInfo{
        Server:     srv,
        FullMethod: "/test.SearchService/SearchOrder",
    }
    handler := func(ctx context.Context, req interface{}) (interface{}, error) {
        return srv.(SearchServiceServer).SearchOrder(ctx, req.(*SearchRequest))
    }
    return interceptor(ctx, in, info, handler)
}

// SearchService_ServiceDesc is the grpc.ServiceDesc for SearchService service.
// It's only intended for direct use with grpc.RegisterService,
// and not to be introspected or modified (even as a copy)
var SearchService_ServiceDesc = grpc.ServiceDesc{
    ServiceName: "test.SearchService",
    HandlerType: (*SearchServiceServer)(nil),
    Methods: []grpc.MethodDesc{
        {
            MethodName: "SearchOrder",
            Handler:    _SearchService_SearchOrder_Handler,
        },
    },
    Streams:  []grpc.StreamDesc{},
    Metadata: "test.proto",
}

我们重点关注如下：

// SearchServiceServer is the server API for SearchService service.
// All implementations must embed UnimplementedSearchServiceServer
// for forward compatibility
type SearchServiceServer interface {
    SearchOrder(context.Context, *SearchRequest) (*SearchResponse, error)
    mustEmbedUnimplementedSearchServiceServer()
}

SearchServiceServer 是 SearchService 服务的 api，所有的实现必须组合 mustEmbedUnimplementedSearchServiceServer 为了向前兼容。

7、官方helloworld使用示例

proto 文件：

syntax = "proto3";

option go_package = "google.golang.org/grpc/examples/helloworld/helloworld";
option java_multiple_files = true;
option java_package = "io.grpc.examples.helloworld";
option java_outer_classname = "HelloWorldProto";

package helloworld;

// The greeting service definition.
service Greeter {
  // Sends a greeting
  rpc SayHello (HelloRequest) returns (HelloReply) {}
}

// The request message containing the user's name.
message HelloRequest {
  string name = 1;
}

// The response message containing the greetings
message HelloReply {
  string message = 1;
}

服务端：

package main

import (
    "context"
    "flag"
    "fmt"
    "log"
    "net"

    "google.golang.org/grpc"
    pb "google.golang.org/grpc/examples/helloworld/helloworld"
)

var (
    port = flag.Int("port", 50051, "The server port")
)

// server is used to implement helloworld.GreeterServer.
type server struct {
    pb.UnimplementedGreeterServer
}

// SayHello implements helloworld.GreeterServer
func (s *server) SayHello(ctx context.Context, in *pb.HelloRequest) (*pb.HelloReply, error) {
    log.Printf("Received: %v", in.GetName())
    return &pb.HelloReply{Message: "Hello " + in.GetName()}, nil
}

func main() {
    flag.Parse()
    lis, err := net.Listen("tcp", fmt.Sprintf(":%d", *port))
    if err != nil {
        log.Fatalf("failed to listen: %v", err)
    }
    s := grpc.NewServer()
    pb.RegisterGreeterServer(s, &server{})
    log.Printf("server listening at %v", lis.Addr())
    if err := s.Serve(lis); err != nil {
        log.Fatalf("failed to serve: %v", err)
    }
}

官方使用 server 组合了 pb.UnimplementedGreeterServer，然后 server 实现了 SayHello 的方法。

在 main 方法里对某个端口号进行监听，并注册了 SayHello 服务，因为只有一个 rpc 方法，然后服务端进行服务。

客户端：

package main

import (
    "context"
    "flag"
    "log"
    "time"

    "google.golang.org/grpc"
    "google.golang.org/grpc/credentials/insecure"
    pb "google.golang.org/grpc/examples/helloworld/helloworld"
)

const (
    defaultName = "world"
)

var (
    addr = flag.String("addr", "localhost:50051", "the address to connect to")
    name = flag.String("name", defaultName, "Name to greet")
)

func main() {
    flag.Parse()
    // Set up a connection to the server.
    conn, err := grpc.Dial(*addr, grpc.WithTransportCredentials(insecure.NewCredentials()))
    if err != nil {
        log.Fatalf("did not connect: %v", err)
    }
    defer conn.Close()
    c := pb.NewGreeterClient(conn)

    // Contact the server and print out its response.
    ctx, cancel := context.WithTimeout(context.Background(), time.Second)
    defer cancel()
    r, err := c.SayHello(ctx, &pb.HelloRequest{Name: *name})
    if err != nil {
        log.Fatalf("could not greet: %v", err)
    }
    log.Printf("Greeting: %s", r.GetMessage())
}

客户端连接服务端gRPC服务地址，调用服务端的 SayHello 方法，拿到结果后返回。

如果想要详细了解的话，可以看看 gRPC 官方文档哈，如果有帮助可以帮忙点个赞哈！

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