main.go

package main

import (
	"context"
	"log"
	"net"
	"net/http"

	"google.golang.org/grpc/codes"

	"github.com/grpc-ecosystem/grpc-gateway/v2/runtime"
	"google.golang.org/grpc"
	"google.golang.org/grpc/credentials/insecure"

	pb "github.com/iamrajiv/basic-arithmetic-grpc-server/proto/arithmetic"
)

type server struct {
	Result *pb.Response
}

func (*server) Add(_ context.Context, request *pb.Request) (*pb.Response, error) {
	a, b := request.GetA(), request.GetB()

	result := a + b

	return &pb.Response{Result: result}, nil
}

func (*server) Divide(_ context.Context, request *pb.Request) (*pb.Response, error) {
	a, b := request.GetA(), request.GetB()

	if b == 0 {
		return nil, grpc.Errorf(codes.InvalidArgument, "Division by zero error")
	}

	result := a / b

	return &pb.Response{Result: result}, nil
}

func (*server) Multiply(_ context.Context, request *pb.Request) (*pb.Response, error) {
	a, b := request.GetA(), request.GetB()

	result := a * b

	return &pb.Response{Result: result}, nil
}

func (*server) Subtract(_ context.Context, request *pb.Request) (*pb.Response, error) {
	a, b := request.GetA(), request.GetB()

	result := a - b

	return &pb.Response{Result: result}, nil
}

func main() {
	// Create a listener on TCP port
	lis, err := net.Listen("tcp", ":8080")
	if err != nil {
		log.Fatalln("Failed to listen:", err)
	}

	// Create a gRPC server object
	s := grpc.NewServer()
	// Attach the Arithmetic service to the server
	pb.RegisterArithmeticServer(s, &server{})
	// Serve gRPC server
	log.Println("Serving gRPC on 0.0.0.0:8080")
	go func() {
		log.Fatalln(s.Serve(lis))
	}()

	// Create a client connection to the gRPC server we just started
	// This is where the gRPC-Gateway proxies the requests
	conn, err := grpc.DialContext(
		context.Background(),
		"0.0.0.0:8080",
		grpc.WithBlock(),
		grpc.WithTransportCredentials(insecure.NewCredentials()),
	)
	if err != nil {
		log.Fatalln("Failed to dial server:", err)
	}

	gwmux := runtime.NewServeMux()
	// Register Arithmetic
	err = pb.RegisterArithmeticHandler(context.Background(), gwmux, conn)
	if err != nil {
		log.Fatalln("Failed to register gateway:", err)
	}

	gwServer := &http.Server{
		Addr:    ":8090",
		Handler: gwmux,
	}

	log.Println("Serving gRPC-Gateway on http://0.0.0.0:8090")
	log.Fatalln(gwServer.ListenAndServe())
}