不通过grpc stub，直接发起grpc请求

call_grpc.go

package main

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

	"google.golang.org/grpc"
	"google.golang.org/grpc/credentials/insecure"
	"google.golang.org/grpc/encoding"
	pb "google.golang.org/grpc/examples/helloworld/helloworld"
	"google.golang.org/protobuf/types/known/emptypb"

	_ "google.golang.org/grpc/encoding/proto"
)

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()

	req := &pb.HelloRequest{Name: *name}
	input, err := toEmpty(req)
	if err != nil {
		panic(err)
	}

	output := &emptypb.Empty{}
	if err := conn.Invoke(context.Background(), "/helloworld.Greeter/SayHello", input, output); err != nil {
		panic(err)
	}

	resp := &pb.HelloReply{}
	if err := fromEmpty(output, resp); err != nil {
		panic(err)
	}
	fmt.Println(resp.Message)

	fmt.Println("done")
}

func toEmpty(v any) (*emptypb.Empty, error) {
	data, err := encoding.GetCodec("proto").Marshal(v)
	if err != nil {
		return nil, err
	}

	result := &emptypb.Empty{}
	if err := encoding.GetCodec("proto").Unmarshal(data, result); err != nil {
		return nil, err
	}
	return result, nil
}

func fromEmpty(src *emptypb.Empty, dst any) error {
	data, err := encoding.GetCodec("proto").Marshal(src)
	if err != nil {
		return err
	}

	return encoding.GetCodec("proto").Unmarshal(data, dst)
}