gRPCによるマイクロサービス間通信：効率性とパフォーマンス向上の実践

syntax = "proto3";

package payment;

service PaymentService {
  rpc ProcessPayment(PaymentRequest) returns (PaymentResponse);
  rpc GetPaymentStatus(PaymentStatusRequest) returns (stream PaymentStatusResponse);
}

message PaymentRequest {
  string payment_id = 1;
  double amount = 2;
  string currency = 3;
  string method = 4;
}

message PaymentResponse {
  string transaction_id = 1;
  bool success = 2;
  string error_message = 3;
}

message PaymentStatusRequest {
  string transaction_id = 1;
}

message PaymentStatusResponse {
  string transaction_id = 1;
  string status = 2;
  string updated_at = 3;
}

// コード生成後のサーバー実装例
package main

import (
	"context"
	"log"
	"net"
	"time"

	pb "dx-media.example/payment"
	"google.golang.org/grpc"
)

type server struct {
	pb.UnimplementedPaymentServiceServer
}

func (s *server) ProcessPayment(ctx context.Context, req *pb.PaymentRequest) (*pb.PaymentResponse, error) {
	// 決済処理のロジック
	return &pb.PaymentResponse{
		TransactionId: "txn_" + req.PaymentId,
		Success:      true,
	}, nil
}

func (s *server) GetPaymentStatus(req *pb.PaymentStatusRequest, stream pb.PaymentService_GetPaymentStatusServer) error {
	// ステータス更新をストリーミング
	statuses := []string{"pending", "processing", "completed"}
	
	for _, status := range statuses {
		response := &pb.PaymentStatusResponse{
			TransactionId: req.TransactionId,
			Status:       status,
			UpdatedAt:    time.Now().Format(time.RFC3339),
		}
		
		if err := stream.Send(response); err != nil {
			return err
		}
		
		time.Sleep(1 * time.Second)
	}
	
	return nil
}

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

// Javaクライアント実装例
import io.grpc.ManagedChannel;
import io.grpc.ManagedChannelBuilder;
import payment.PaymentServiceGrpc;
import payment.Payment.PaymentRequest;
import payment.Payment.PaymentResponse;
import payment.Payment.PaymentStatusRequest;
import payment.Payment.PaymentStatusResponse;

public class PaymentClient {
    public static void main(String[] args) {
        // チャネルを作成
        ManagedChannel channel = ManagedChannelBuilder.forAddress("localhost", 50051)
                .usePlaintext()
                .build();

        // Stubを作成
        PaymentServiceGrpc.PaymentServiceBlockingStub blockingStub = 
            PaymentServiceGrpc.newBlockingStub(channel);
        
        // 決済処理リクエスト
        PaymentRequest request = PaymentRequest.newBuilder()
                .setPaymentId("payment_123")
                .setAmount(100.50)
                .setCurrency("JPY")
                .setMethod("credit_card")
                .build();
        
        // 同期呼び出し
        PaymentResponse response = blockingStub.processPayment(request);
        System.out.println("Transaction ID: " + response.getTransactionId());
        System.out.println("Success: " + response.getSuccess());
        
        // ステータス監視
        PaymentStatusRequest statusRequest = PaymentStatusRequest.newBuilder()
                .setTransactionId(response.getTransactionId())
                .build();
        
        // ストリーミングレスポンスを処理
        blockingStub.getPaymentStatus(statusRequest).forEachRemaining(statusResponse -> {
            System.out.println("Status: " + statusResponse.getStatus() + 
                               " at " + statusResponse.getUpdatedAt());
        });
        
        channel.shutdown();
    }
}