based on https://github.com/grpc/grpc-go/tree/master/examples/helloworld

main.go

/*
 *
 * Copyright 2015 gRPC authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

//go:generate protoc -I ../helloworld --go_out=plugins=grpc:../helloworld ../helloworld/helloworld.proto

package main

import (
	"context"
	"fmt"
	"log"
	"net"
	"os"
	"time"

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

const (
	port = ":50051"
)

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

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

func doStuff(ctx context.Context) {
	select {
	case <-time.After(1 * time.Second):
		fmt.Fprintln(os.Stderr, "beep")
	case <-ctx.Done():
		fmt.Fprintln(os.Stderr, "context cancelled")
	}
}

func main() {
	lis, err := net.Listen("tcp", port)
	if err != nil {
		log.Fatalf("failed to listen: %v", err)
	}
	s := grpc.NewServer()
	pb.RegisterGreeterServer(s, &server{})
	// Register reflection service on gRPC server.
	reflection.Register(s)
	if err := s.Serve(lis); err != nil {
		log.Fatalf("failed to serve: %v", err)
	}
}

output client

$ grpcurl -plaintext 127.0.0.1:50051 helloworld.Greeter/SayHello
{
  "message": "Hello "
}

output server

$ go run greeter_server/main.go
2019/06/06 10:56:01 Received:
context cancelled