api.go

    package main

    import (
    	"log"
    	"net/http"

    	"golang.org/x/net/context"
    	"google.golang.org/grpc"

    	"github.com/gin-gonic/gin"
    )

    const (
    	address     = "localhost:50051"
    	defaultName = "world"
    )

    func main() {
    	r := gin.Default()
    	r.GET("/ping", func(c *gin.Context) {

    		conn, err := grpc.Dial(address, grpc.WithInsecure())
    		if err != nil {
    			log.Fatalf("did not connect: %v", err)
    		}
    		defer conn.Close()

    		client := NewProductServiceClient(conn)
    		result, err := client.List(context.Background(), &Params{})
    		if err != nil {
    			c.Status(http.StatusInternalServerError)
    			return
    		}

    		c.JSON(http.StatusOK, result)

    	})
    	r.Run(":8888")
    }

main.proto

syntax = "proto3";

package main;

service ProductService {
    rpc List (Params) returns (ProductList) {}
}

message ProductList {
    repeated Product product = 1;
}

message Product {
    int32 id = 1;
    string name = 2;
}

message Params {

}

productService.go

package main

import (
	"log"
	"net"

	"golang.org/x/net/context"

	"google.golang.org/grpc"
	"google.golang.org/grpc/reflection"
)

const (
	port = ":50051"
)

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

func (s *server) List(ctx context.Context, in *Params) (*ProductList, error) {
	return &ProductList{
		Product: []*Product{
			&Product{
				Id:   1,
				Name: "product-1",
			},
			&Product{
				Id:   2,
				Name: "product-2",
			},
		},
	}, nil
}
func main() {
	lis, err := net.Listen("tcp", port)
	if err != nil {
		log.Fatalf("failed to listen: %v", err)
	}
	s := grpc.NewServer()
	RegisterProductServiceServer(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)
	}
}