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Flux bidirectionnel

Maîtrisez le flux bidirectionnel, qui permet au client et au serveur d’envoyer simultanément une suite de messages.

Flux bidirectionnel est une leçon gRPC & High Performance APIs gratuite sur CoddyKit. Ceci est la leçon 3 sur 4. Tu peux lire la leçon complète ci-dessous gratuitement — puis la pratiquer en direct dans le navigateur avec un éditeur de code intégré et un tuteur IA 24/7. Elle fait partie du parcours d'apprentissage gRPC & High Performance APIs, et ta progression se synchronise sur le web et l'application CoddyKit. Le cours gRPC & High Performance APIs comprend 4 leçons au total.

Certaines parties de cette leçon n'ont pas encore été traduites et s'affichent en anglais.

Bidirectional Streaming: Two-Way Talk

What if both sides in a conversation could speak and listen at the same time? That's bidirectional streaming in gRPC! It allows both the client and server to send a sequence of messages to each other, concurrently.

Why Use Bidi Streaming?

Bidirectional streaming is perfect for applications needing real-time, interactive communication. Think of it like a phone call where both parties can talk and hear simultaneously.

  • Chat applications: Users send and receive messages instantly.
  • Live updates: Servers push data to clients as events happen.
  • Gaming: Synchronized game state updates between players and server.

Defining a Bidi Stream Service

To enable bidirectional streaming, you use the stream keyword for both the request and response types in your .proto file.

This tells gRPC that the method will handle a continuous flow of messages in both directions.

syntax = "proto3";

package chat;

message ChatMessage {
  string user = 1;
  string message = 2;
}

service ChatService {
  rpc Chat(stream ChatMessage) returns (stream ChatMessage);
}

Server: Receiving Client Messages

On the server, your service method will receive a StreamObserver for the incoming client messages. You'll implement its methods to process each message.

  • onNext(msg): Called for each message from the client.
  • onError(t): Called if the client stream encounters an error.
  • onCompleted(): Called when the client finishes sending messages.

Server: Sending Back Responses

The server also gets a StreamObserver (usually named responseObserver) to send messages back to the client. This allows the server to push multiple responses.

  • responseObserver.onNext(resp): Sends a message to the client.
  • responseObserver.onError(t): Signals an error to the client.
  • responseObserver.onCompleted(): Closes the server's outgoing stream.

Client: Starting the Conversation

On the client, you'll use an asynchronous (non-blocking) stub to call the streaming method. This call immediately returns a StreamObserver.

This returned observer is what the client uses to send messages to the server.

Client: Two-Way Communication

The client needs two main parts for bidirectional streaming:

  1. An observer for outgoing messages: This is used to onNext() messages to the server.
  2. An observer for incoming messages: This is passed to the gRPC call to handle responses from the server.

Both streams operate independently and concurrently.

Full Server Bidi Stream Example

Here's a simplified gRPC server that echoes messages received from the client. Remember to compile your .proto file and include gRPC dependencies.

Try running this example:

import io.grpc.Server;
import io.grpc.ServerBuilder;
import io.grpc.stub.StreamObserver;

// Assuming ChatServiceGrpc and ChatMessage are generated
// from the proto definition.
import chat.ChatServiceGrpc;
import chat.ChatMessage;

public class ChatServer {

  public static void main(String[] args) throws Exception {
    Server server = ServerBuilder.forPort(50051)
        .addService(new ChatServiceImpl())
        .build();

    server.start();
    System.out.println("Server started on port 50051");
    server.awaitTermination();
  }

  static class ChatServiceImpl extends ChatServiceGrpc.ChatServiceImplBase {
    @Override
    public StreamObserver<ChatMessage> chat(
        final StreamObserver<ChatMessage> responseObserver) {

      return new StreamObserver<ChatMessage>() {
        @Override
        public void onNext(ChatMessage request) {
          // Received a message from the client
          System.out.println("Server received: " + request.getMessage());
          // Echo it back to the client
          ChatMessage response = ChatMessage.newBuilder()
              .setUser("Server")
              .setMessage("Echo: " + request.getMessage())
              .build();
          responseObserver.onNext(response);
        }

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

        @Override
        public void onCompleted() {
          System.out.println("Client stream completed.");
          responseObserver.onCompleted(); // Close server stream
        }
      };
    }
  }
}

Full Client Bidi Stream Example

This client sends a few messages and listens for responses. Run the server first, then this client. The client will send messages and print the server's echoes.

Try running this example:

import io.grpc.ManagedChannel;
import io.grpc.ManagedChannelBuilder;
import io.grpc.stub.StreamObserver;

// Assuming ChatServiceGrpc and ChatMessage are generated
// from the proto definition.
import chat.ChatServiceGrpc;
import chat.ChatMessage;

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

public class ChatClient {

  public static void main(String[] args) throws Exception {
    ManagedChannel channel = ManagedChannelBuilder.forAddress("localhost", 50051)
        .usePlaintext() // For demonstration, use TLS in production
        .build();

    ChatServiceGrpc.ChatStub asyncStub = ChatServiceGrpc.newStub(channel);

    CountDownLatch finishLatch = new CountDownLatch(1);

    StreamObserver<ChatMessage> requestObserver = asyncStub.chat(
        new StreamObserver<ChatMessage>() {
          @Override
          public void onNext(ChatMessage response) {
            System.out.println("Client received: " + response.getMessage());
          }

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

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

    try {
      // Client sends messages
      for (int i = 0; i < 3; i++) {
        ChatMessage request = ChatMessage.newBuilder()
            .setUser("Client")
            .setMessage("Hello " + i)
            .build();
        requestObserver.onNext(request);
        Thread.sleep(500); // Simulate delay
      }
    } catch (RuntimeException | InterruptedException e) {
      requestObserver.onError(e);
      throw e;
    } finally {
      requestObserver.onCompleted(); // Client finishes sending
    }

    if (!finishLatch.await(1, TimeUnit.MINUTES)) {
      System.err.println("Client timed out waiting for server response.");
    }
    channel.shutdownNow().awaitTermination(5, TimeUnit.SECONDS);
  }
}

Bidirectional Stream Check

You've learned about bidirectional streaming. Which statement best describes how both client and server communicate in a gRPC bidirectional stream?

Bidirectional Streaming Recap

Great job! You've mastered bidirectional streaming in gRPC.

  • It enables both client and server to send sequences of messages.
  • Ideal for real-time, interactive applications like chat.
  • Defined using the stream keyword for both request and response in Protobuf.
  • Requires separate logic on both client and server to manage incoming and outgoing message streams.

This powerful pattern opens up many possibilities for highly responsive distributed systems.

Questions Fréquemment Posées

La leçon « Flux bidirectionnel » est-elle gratuite ?

Oui — le texte complet de « Flux bidirectionnel » est gratuit à lire ici sur le web. Pour la pratiquer de manière interactive (un éditeur de code intégré et un tuteur IA 24/7) et déverrouiller le reste du cours gRPC & High Performance APIs, passe à CoddyKit PRO. Le cours gRPC & High Performance APIs comprend 4 leçons au total.

Qu'est-ce que j'apprendrai dans « Flux bidirectionnel » ?

Maîtrisez le flux bidirectionnel, qui permet au client et au serveur d’envoyer simultanément une suite de messages. Tu pratiques gRPC & High Performance APIs avec du code pratique que tu exécutes directement dans le navigateur, et un tuteur IA 24/7 répond à tes questions au fur et à mesure que tu avances dans la leçon.

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Aucune expérience préalable n'est requise. gRPC & High Performance APIs sur CoddyKit est structuré pour les débutants jusqu'aux apprenants avancés, donc tu peux commencer ici ou depuis le début et avancer à ton rythme. Ceci est la leçon 3 sur 4.

Combien de temps prend la leçon « Flux bidirectionnel » ?

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Peux-tu écrire et exécuter du code dans cette leçon gRPC & High Performance APIs ?

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Toutes les leçons de ce cours

  1. Le flux serveur expliqué
  2. Le flux client expliqué
  3. Flux bidirectionnel
  4. Contrôle du flux et rétropression des flux
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