gRPC & High Performance APIs · 강의

서버 스트리밍 이해

서버가 하나의 클라이언트 요청에 여러 응답을 보내는 서버 측 스트리밍을 이해하고 구현합니다.

서버 스트리밍 이해은(는) CoddyKit의 무료 gRPC & High Performance APIs 강의입니다. 이것은 4개 중 1번째 강의입니다. 아래에서 전체 강의를 무료로 읽을 수 있으며, 내장 코드 에디터와 24/7 AI 튜터와 함께 브라우저에서 직접 실습할 수 있습니다. 이 강의는 gRPC & High Performance APIs 학습 경로의 일부이며, 진행 상황이 웹과 CoddyKit 앱에 동기화됩니다. gRPC & High Performance APIs 강의에는 총 4개의 강의가 포함되어 있습니다.

이 강의의 일부는 아직 번역되지 않았으며 영어로 표시됩니다.

Server Streaming Basics

In gRPC, a server-side streaming call is when a client sends a single request, but the server responds with a sequence of messages.

Think of it like subscribing to a newsletter: you send one request (subscribe), and the server sends you many updates over time (newsletters).

Use Cases for Streaming

Server streaming is perfect for scenarios where the server needs to push updates or a large amount of data to the client over time. Common uses include:

Real-time data feeds: Stock prices, sensor readings.
Notifications: Alerts, chat messages.
Large data downloads: Breaking a big file into smaller chunks.

Protobuf for Server Streaming

To define a server-side streaming method in your .proto file, you simply add the stream keyword before the response type.

This tells gRPC that the server will send multiple messages for each client request, not just one.

Streaming Protobuf Example

Here's how you define a service that streams messages from the server:

syntax = "proto3";

option java_package = "com.coddykit.grpc";
option java_outer_classname = "StreamingProto";

service NotifierService {
  rpc SubscribeToNotifications (SubscriptionRequest) returns (stream Notification);
}

message SubscriptionRequest {
  string userId = 1;
}

message Notification {
  string message = 1;
  int64 timestamp = 2;
}

Implementing the Server Stream

On the server side, your streaming method will receive a single request object, just like a unary call. However, instead of returning a single response, you'll use a StreamObserver to send multiple responses back to the client.

You'll typically loop and send messages, then call onCompleted() when done.

Server Method Structure

The server method for a streaming call takes the request and a StreamObserver. You send responses via responseObserver.onNext() and signal completion with responseObserver.onCompleted().

// Example (Java)
public void subscribeToNotifications(SubscriptionRequest request,
    io.grpc.stub.StreamObserver<Notification> responseObserver) {

  String userId = request.getUserId();
  System.out.println("Client " + userId + " subscribed.");

  // Simulate sending multiple notifications
  for (int i = 0; i < 3; i++) {
    Notification notification = Notification.newBuilder()
        .setMessage("Update " + (i + 1) + " for " + userId)
        .setTimestamp(System.currentTimeMillis())
        .build();
    responseObserver.onNext(notification); // Send a message
    try {
      Thread.sleep(1000); // Wait a bit
    } catch (InterruptedException e) { /* handle */ }
  }

  responseObserver.onCompleted(); // Signal completion
  System.out.println("Finished sending notifications to " + userId);
}

Receiving Streamed Responses

The client makes a single call, but then it needs to wait and process multiple responses. It provides a StreamObserver to handle the incoming messages, errors, and the completion signal from the server.

This observer will have onNext(), onError(), and onCompleted() methods.

Client Stream Observer

The client's StreamObserver defines how it reacts to each event from the server stream. It processes each onNext message until onCompleted is called.

// Example (Java)
StreamObserver<Notification> responseObserver = new StreamObserver<Notification>() {
  @Override
  public void onNext(Notification notification) {
    System.out.println("Received: " + notification.getMessage());
  }

  @Override
  public void onError(Throwable t) {
    System.err.println("Error: " + t.getMessage());
  }

  @Override
  public void onCompleted() {
    System.out.println("Server stream completed.");
  }
};

// Call the streaming method
// asyncStub.subscribeToNotifications(request, responseObserver);

Complete Server Stream Service

Here's a complete gRPC server that implements the SubscribeToNotifications server-side streaming method. Run this first, then the client!

import io.grpc.Server;
import io.grpc.ServerBuilder;
import io.grpc.stub.StreamObserver;
import com.coddykit.grpc.StreamingProto.SubscriptionRequest;
import com.coddykit.grpc.StreamingProto.Notification;
import com.coddykit.grpc.NotifierServiceGrpc.NotifierServiceImplBase;

public class StreamingServer {

  private Server server;

  private void start() throws Exception {
    int port = 50051;
    server = ServerBuilder.forPort(port)
        .addService(new NotifierServiceImpl())
        .build()
        .start();
    System.out.println("Server started, listening on " + port);

    Runtime.getRuntime().addShutdownHook(new Thread() {
      @Override
      public void run() {
        System.err.println("*** shutting down gRPC server since JVM is shutting down");
        StreamingServer.this.stop();
        System.err.println("*** server shut down");
      }
    });
  }

  private void stop() {
    if (server != null) {
      server.shutdown();
    }
  }

  private void blockUntilShutdown() throws InterruptedException {
    if (server != null) {
      server.awaitTermination();
    }
  }

  public static void main(String[] args) throws Exception {
    final StreamingServer server = new StreamingServer();
    server.start();
    server.blockUntilShutdown();
  }

  static class NotifierServiceImpl extends NotifierServiceImplBase {
    @Override
    public void subscribeToNotifications(SubscriptionRequest request,
        StreamObserver<Notification> responseObserver) {

      String userId = request.getUserId();
      System.out.println("Server received subscription from: " + userId);

      for (int i = 0; i < 3; i++) {
        Notification notification = Notification.newBuilder()
            .setMessage("Update " + (i + 1) + " for " + userId)
            .setTimestamp(System.currentTimeMillis())
            .build();
        responseObserver.onNext(notification);
        try {
          Thread.sleep(1000); // Simulate some work
        } catch (InterruptedException e) {
          Thread.currentThread().interrupt();
          responseObserver.onError(e);
          return;
        }
      }
      responseObserver.onCompleted();
      System.out.println("Server finished sending notifications to: " + userId);
    }
  }
}

Complete Client Stream Receiver

Now, run this client code. It will connect to the server and receive the stream of notifications.

import io.grpc.ManagedChannel;
import io.grpc.ManagedChannelBuilder;
import io.grpc.stub.StreamObserver;
import com.coddykit.grpc.StreamingProto.SubscriptionRequest;
import com.coddykit.grpc.StreamingProto.Notification;
import com.coddykit.grpc.NotifierServiceGrpc;

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;

public class StreamingClient {

  public static void main(String[] args) throws InterruptedException {
    ManagedChannel channel = ManagedChannelBuilder.forAddress("localhost", 50051)
        .usePlaintext() // For local testing, no TLS
        .build();

    NotifierServiceGrpc.Stub asyncStub = NotifierServiceGrpc.newStub(channel);

    CountDownLatch latch = new CountDownLatch(1);

    System.out.println("Client sending subscription request...");
    SubscriptionRequest request = SubscriptionRequest.newBuilder()
        .setUserId("user123")
        .build();

    asyncStub.subscribeToNotifications(request, new StreamObserver<Notification>() {
      @Override
      public void onNext(Notification notification) {
        System.out.println("Client received notification: " + notification.getMessage());
      }

      @Override
      public void onError(Throwable t) {
        System.err.println("Client received error: " + t.getMessage());
        latch.countDown();
      }

      @Override
      public void onCompleted() {
        System.out.println("Client stream completed.");
        latch.countDown();
      }
    });

    latch.await(5, TimeUnit.SECONDS); // Wait for stream to complete
    System.out.println("Client finished.");

    channel.shutdown().awaitTermination(5, TimeUnit.SECONDS);
  }
}

Stream Method Check

You're building a gRPC service where a client requests a list of recent log entries, and the server continuously sends new entries as they occur. Which Protobuf definition correctly sets up the GetLogStream method for this?

Streaming Recap

Great job! In this lesson, you've learned about server-side streaming in gRPC.

It allows a server to send multiple responses for a single client request.
It's defined using the stream keyword on the response type in Protobuf.
You implemented both server and client logic to handle these continuous data flows.

Next, we'll explore client-side streaming, where the client sends multiple requests!

자주 묻는 질문

“서버 스트리밍 이해” 강의는 무료인가요?

네 — “서버 스트리밍 이해” 전체 내용을 이 웹사이트에서 무료로 읽을 수 있습니다. 인터랙티브하게 실습하려면(내장 코드 에디터와 24/7 AI 튜터), CoddyKit PRO로 업그레이드하면 gRPC & High Performance APIs 강의 전체를 잠금 해제할 수 있습니다. gRPC & High Performance APIs 강의에는 총 4개의 강의가 포함되어 있습니다.

“서버 스트리밍 이해”에서 뭘 배우나요?

서버가 하나의 클라이언트 요청에 여러 응답을 보내는 서버 측 스트리밍을 이해하고 구현합니다. 브라우저에서 직접 실행하는 실습 코드로 gRPC & High Performance APIs을(를) 배우며, 24/7 AI 튜터가 강의를 진행하면서 질문에 답변해줍니다.

gRPC & High Performance APIs을(를) 시작하는 데 경험이 필요한가요?

사전 경험은 필요하지 않습니다. CoddyKit의 gRPC & High Performance APIs은(는) 초급자부터 고급 학습자까지를 위해 구성되어 있으므로, 여기서 시작하거나 처음부터 시작할 수 있으며 자신의 속도대로 진행할 수 있습니다. 이것은 4개 중 1번째 강의입니다.

“서버 스트리밍 이해” 강의는 얼마나 걸리나요?

대부분의 CoddyKit 강의는 약 5~10분이 소요됩니다. 각 강의는 간결하고 인터랙티브하여 꾸준한 진행이 가능하며, 웹과 앱에서 중단한 부분부터 바로 시작할 수 있습니다.

이 gRPC & High Performance APIs 강의에서 코드를 작성하고 실행할 수 있나요?

네. 모든 gRPC & High Performance APIs 강의에는 내장 코드 에디터가 포함되어 있으므로, 브라우저에서 바로 실제 코드를 작성하고 실행한 후 즉시 AI 피드백을 받을 수 있습니다 — 로컬 설정이 필요 없습니다.

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