give me a golang grpc demo code

Sure! Here is a simple gRPC demo code written in Go:

package main

import (
    "context"
    "log"
    "net"

    "google.golang.org/grpc"
    pb "path/to/your/protobuf/package" // import your protobuf package
)

type server struct {
    pb.UnimplementedYourServiceServer // implement your service interface generated by protobuf
}

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

func main() {
    lis, err := net.Listen("tcp", ":50051")
    if err != nil {
        log.Fatalf("failed to listen: %v", err)
    }
    s := grpc.NewServer()
    pb.RegisterYourServiceServer(s, &server{})
    log.Println("Starting server on port :50051")
    if err := s.Serve(lis); err != nil {
        log.Fatalf("failed to serve: %v", err)
    }
}

In this example, we define a `server` struct that implements the `YourServiceServer` interface generated by protobuf. We then define a `SayHello` function which receives a `HelloRequest` and returns a `HelloResponse`.

We then create a new gRPC server, register our `server` with it, and start serving on port 50051.

You will need to replace `path/to/your/protobuf/package` with the actual import path of your protobuf package, and `YourServiceServer` with the name of the service interface generated by protobuf.