Protobuf Grpc使用异常 类型有未导出的方法，并且是在不同的软件包中定义

Grpc使用异常

类型有未导出的方法，并且是在不同的软件包中定义

• 导致原因:

  导出的pb.go 文件中 GretterServer interface中有私有变量导致的。

  // GreeterServer is the server API for Greeter service.
  // All implementations must embed UnimplementedGreeterServer
  // for forward compatibility
  type GreeterServer interface {
         
  	SayHello(context.Context, *HelloRequest) (*HelloReply, error)
  	mustEmbedUnimplementedGreeterServer()
  }
  
  

  proto文件内容：

  syntax = "proto3";
  
  package helloworld;
  option go_package = "./helloworld";
  
  service Greeter {
         
    rpc SayHello (HelloRequest) returns (HelloReply) {
         }
  }
  
  message HelloRequest {
         
    string name = 1;
  }
  
  message HelloReply {
         
    string message = 1;
  }
  

• 异常提示：

  无法将 ‘&GreeterServer{}’ (类型 *GreeterServer) 用作类型 GreeterServer 类型无法实现 ‘GreeterServer’，因为类型有未导出的方法，并且是在不同的软件包中定义

  

• 运行异常：

  .\server.go:33:35: cannot use &GreeterServer{} (value of type *GreeterServer) as type helloworld.GreeterServer in argument to pb.RegisterGreeterServer:
  *GreeterServer does not implement helloworld.GreeterServer (missing mustEmbedUnimplementedGreeterServer method)

  

• protobuf 和 grpc 版本:

  google.golang.org/grpc v1.48.0
  google.golang.org/protobuf v1.28.0

• 修复方式: 增加第15行代码内容：*pb.UnimplementedXxxxxServer Xxxxx为proto文件中定义的service名称

  package main
  
  import (
  	pb "GoRpc/proto/helloworld"
  	"context"
  	"flag"
  	"google.golang.org/grpc"
  	"net"
  )
  
  var port string
  
  type GreeterServer struct {
        
  	// 增加此行代码
  	*pb.UnimplementedGreeterServer
  }
  
  func init() {
        
  	flag.StringVar(&port, "p", "8001", "port to connect to")
  	flag.Parse()
  }
  
  func (s *GreeterServer) SayHello(ctx context.Context, r *pb.HelloRequest) (*pb.HelloReply, error) {
        
  	return &pb.HelloReply{
        Message: "Hello.world"}, nil
  }
  
  func main() {
        
  	server := grpc.NewServer()
  	pb.RegisterGreeterServer(server, &GreeterServer{
        })
  	lis, _ := net.Listen("tcp", ":"+port)
  	server.Serve(lis)
  }
  

• 修复问题的原因，查看helloworld_grpc.pb.go 文件。 实际SayHello由UnimplementedGreeterServer 结构实现

  // GreeterServer is the server API for Greeter service.
  // All implementations must embed UnimplementedGreeterServer
  // for forward compatibility
  type GreeterServer interface {
        
  	SayHello(context.Context, *HelloRequest) (*HelloReply, error)
  	mustEmbedUnimplementedGreeterServer()
  }
  
  // UnimplementedGreeterServer must be embedded to have forward compatible implementations.
  type UnimplementedGreeterServer struct {
        
  }
  
  func (UnimplementedGreeterServer) SayHello(context.Context, *HelloRequest) (*HelloReply, error) {
        
  	return nil, status.Errorf(codes.Unimplemented, "method SayHello not implemented")
  }