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Início rápido: como usar bibliotecas de cliente

O serviço Pub/Sub permite que os aplicativos troquem mensagens de maneira confiável, rápida e assíncrona. Para que isso aconteça, um produtor de dados publica uma mensagem em um tópico do Pub/Sub. Depois, um cliente assina o tópico para então começar a consumir as mensagens da assinatura. O Pub/Sub preserva as mensagens que não puderam ser entregues de maneira confiável por até sete dias. Veja nesta página como começar a publicar mensagens com o Pub/Sub usando bibliotecas de cliente.

Antes de começar

  1. Faça login na sua conta do Google.

    Se você ainda não tiver uma, inscreva-se.

  2. Configure um projeto do Console do Cloud.

    Configurar um projeto

    Clique para:

    • Crie ou selecione um projeto.
    • ativar a API Pub/Sub para esse projeto;
    • criar uma conta de serviço;
    • fazer o download de uma chave privada como JSON.

    É possível visualizar e gerenciar esses recursos a qualquer momento no Console do Cloud.

  3. Defina a variável de ambiente GOOGLE_APPLICATION_CREDENTIALS como o caminho do arquivo JSON que contém a chave da conta de serviço. Essa variável só se aplica à sessão de shell atual. Dessa maneira, se você abrir uma nova sessão, defina a variável novamente.

  4. Instale e inicialize o SDK do Cloud..

Como instalar bibliotecas de cliente

Os exemplos a seguir mostram como instalar as bibliotecas de cliente:

Python

Para mais informações sobre a configuração do ambiente de desenvolvimento Python, consulte o Guia de configuração do ambiente de desenvolvimento Python. 

# ensure that you are using virtualenv
# as described in the python dev setup guide

pip install --upgrade google-cloud-pubsub

C++

Para mais informações sobre como instalar a biblioteca C++, consulte o README do GitHub.

C#

Install-Package Google.Cloud.PubSub.V1 -Pre

Go

go get -u cloud.google.com/go/pubsub

Java

Se você estiver usando o Maven, adicione o código abaixo ao arquivo pom.xml. Para mais informações sobre BOMs, consulte BOM das bibliotecas do Google Cloud Platform.

<dependencyManagement>
  <dependencies>
    <dependency>
      <groupId>com.google.cloud</groupId>
      <artifactId>libraries-bom</artifactId>
      <version>17.0.0</version>
      <type>pom</type>
      <scope>import</scope>
    </dependency>
  </dependencies>
</dependencyManagement>

<dependencies>
  <dependency>
    <groupId>com.google.cloud</groupId>
    <artifactId>google-cloud-pubsub</artifactId>
  </dependency>

Se você estiver usando o Gradle, adicione isto às dependências:

implementation platform('com.google.cloud:libraries-bom:16.4.0')

compile 'com.google.cloud:google-cloud-pubsub'

Se você estiver usando o sbt, adicione o seguinte às suas dependências:

libraryDependencies += "com.google.cloud" % "google-cloud-pubsub" % "1.111.0"

Caso você esteja usando o IntelliJ ou o Eclipse, poderá adicionar bibliotecas de cliente ao seu projeto usando estes plug-ins de ambiente de desenvolvimento integrado:

Os plug-ins também oferecem outras funcionalidades, como gerenciamento de chaves de contas de serviço. Consulte a documentação de cada plug-in para mais detalhes.

Node.js

npm install --save @google-cloud/pubsub

PHP

composer require google/cloud-pubsub

Ruby

gem install google-cloud-pubsub

Como criar um tópico e uma assinatura

Depois de criar um tópico, é possível assiná-lo ou publicar nele.

Use o comando gcloud pubsub topics create para criar um tópico:

gcloud pubsub topics create my-topic

Use o comando gcloud pubsub subscriptions create para criar uma assinatura. Somente mensagens publicadas no tópico após a criação da assinatura estarão disponíveis para aplicativos do assinante.

gcloud pubsub subscriptions create my-sub --topic my-topic

Para mais informações sobre como nomear tópicos e assinaturas, consulte Nomes dos recursos.

Como publicar mensagens

Nos exemplos a seguir, use my-topic para o ID do tópico.

Python

samples/snippets/publisher.py 
from google.cloud import pubsub_v1

# TODO(developer)
# project_id = "your-project-id"
# topic_id = "your-topic-id"

publisher = pubsub_v1.PublisherClient()
# The `topic_path` method creates a fully qualified identifier
# in the form `projects/{project_id}/topics/{topic_id}`
topic_path = publisher.topic_path(project_id, topic_id)

for n in range(1, 10):
    data = "Message number {}".format(n)
    # Data must be a bytestring
    data = data.encode("utf-8")
    # When you publish a message, the client returns a future.
    future = publisher.publish(topic_path, data)
    print(future.result())

print(f"Published messages to {topic_path}.")

C++

#include "google/cloud/pubsub/publisher.h"
#include <iostream>
#include <stdexcept>

int main(int argc, char* argv[]) try {
  if (argc != 3) {
    std::cerr << "Usage: " << argv[0] << " <project-id> <topic-id>\n";
    return 1;
  }

  std::string const project_id = argv[1];
  std::string const topic_id = argv[2];

  // Create a namespace alias to make the code easier to read.
  namespace pubsub = google::cloud::pubsub;
  auto publisher = pubsub::Publisher(
      pubsub::MakePublisherConnection(pubsub::Topic(project_id, topic_id), {}));
  auto id =
      publisher
          .Publish(pubsub::MessageBuilder{}.SetData("Hello World!").Build())
          .get();
  if (!id) throw std::runtime_error(id.status().message());
  std::cout << "Hello World published with id=" << *id << "\n";

  return 0;
} catch (std::exception const& ex) {
  std::cerr << "Standard exception raised: " << ex.what() << "\n";
  return 1;
}

C#


using Google.Cloud.PubSub.V1;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;

public class PublishMessagesAsyncSample
{
    public async Task<int> PublishMessagesAsync(string projectId, string topicId, IEnumerable<string> messageTexts)
    {
        TopicName topicName = TopicName.FromProjectTopic(projectId, topicId);
        PublisherClient publisher = await PublisherClient.CreateAsync(topicName);

        int publishedMessageCount = 0;
        var publishTasks = messageTexts.Select(async text =>
        {
            try
            {
                string message = await publisher.PublishAsync(text);
                Console.WriteLine($"Published message {message}");
                Interlocked.Increment(ref publishedMessageCount);
            }
            catch (Exception exception)
            {
                Console.WriteLine($"An error ocurred when publishing message {text}: {exception.Message}");
            }
        });
        await Task.WhenAll(publishTasks);
        return publishedMessageCount;
    }
}

Go

pubsub/topics/publish.go 
import (
	"context"
	"fmt"
	"io"

	"cloud.google.com/go/pubsub"
)

func publish(w io.Writer, projectID, topicID, msg string) error {
	// projectID := "my-project-id"
	// topicID := "my-topic"
	// msg := "Hello World"
	ctx := context.Background()
	client, err := pubsub.NewClient(ctx, projectID)
	if err != nil {
		return fmt.Errorf("pubsub.NewClient: %v", err)
	}

	t := client.Topic(topicID)
	result := t.Publish(ctx, &pubsub.Message{
		Data: []byte(msg),
	})
	// Block until the result is returned and a server-generated
	// ID is returned for the published message.
	id, err := result.Get(ctx)
	if err != nil {
		return fmt.Errorf("Get: %v", err)
	}
	fmt.Fprintf(w, "Published a message; msg ID: %v\n", id)
	return nil
}

Java

samples/snippets/src/main/java/pubsub/PublisherExample.java 

import com.google.api.core.ApiFuture;
import com.google.cloud.pubsub.v1.Publisher;
import com.google.protobuf.ByteString;
import com.google.pubsub.v1.PubsubMessage;
import com.google.pubsub.v1.TopicName;
import java.io.IOException;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeUnit;

public class PublisherExample {
  public static void main(String... args) throws Exception {
    // TODO(developer): Replace these variables before running the sample.
    String projectId = "your-project-id";
    String topicId = "your-topic-id";

    publisherExample(projectId, topicId);
  }

  public static void publisherExample(String projectId, String topicId)
      throws IOException, ExecutionException, InterruptedException {
    TopicName topicName = TopicName.of(projectId, topicId);

    Publisher publisher = null;
    try {
      // Create a publisher instance with default settings bound to the topic
      publisher = Publisher.newBuilder(topicName).build();

      String message = "Hello World!";
      ByteString data = ByteString.copyFromUtf8(message);
      PubsubMessage pubsubMessage = PubsubMessage.newBuilder().setData(data).build();

      // Once published, returns a server-assigned message id (unique within the topic)
      ApiFuture<String> messageIdFuture = publisher.publish(pubsubMessage);
      String messageId = messageIdFuture.get();
      System.out.println("Published message ID: " + messageId);
    } finally {
      if (publisher != null) {
        // When finished with the publisher, shutdown to free up resources.
        publisher.shutdown();
        publisher.awaitTermination(1, TimeUnit.MINUTES);
      }
    }
  }
}

Node.js

samples/publishMessage.js 
/**
 * TODO(developer): Uncomment these variables before running the sample.
 */
// const topicName = 'YOUR_TOPIC_NAME';
// const data = JSON.stringify({foo: 'bar'});

// Imports the Google Cloud client library
const {PubSub} = require('@google-cloud/pubsub');

// Creates a client; cache this for further use
const pubSubClient = new PubSub();

async function publishMessage() {
  // Publishes the message as a string, e.g. "Hello, world!" or JSON.stringify(someObject)
  const dataBuffer = Buffer.from(data);

  try {
    const messageId = await pubSubClient.topic(topicName).publish(dataBuffer);
    console.log(`Message ${messageId} published.`);
  } catch (error) {
    console.error(`Received error while publishing: ${error.message}`);
    process.exitCode = 1;
  }
}

publishMessage();

PHP

pubsub/api/src/publish_message.php 
use Google\Cloud\PubSub\PubSubClient;

/**
 * Publishes a message for a Pub/Sub topic.
 *
 * @param string $projectId  The Google project ID.
 * @param string $topicName  The Pub/Sub topic name.
 * @param string $message  The message to publish.
 */
function publish_message($projectId, $topicName, $message)
{
    $pubsub = new PubSubClient([
        'projectId' => $projectId,
    ]);
    $topic = $pubsub->topic($topicName);
    $topic->publish(['data' => $message]);
    print('Message published' . PHP_EOL);
}

Ruby

pubsub/topics.rb 
# topic_id = "your-topic-id"
require "google/cloud/pubsub"

pubsub = Google::Cloud::Pubsub.new

topic = pubsub.topic topic_id
topic.publish "This is a test message."

puts "Message published."

Receber mensagens

Configure um assinante para solicitar as mensagens que você acabou de publicar. Todos os assinantes precisam confirmar o recebimento de cada mensagem dentro de um determinado período de tempo configurável. As mensagens não confirmadas serão reenviadas. Observe que o Pub/Sub de vez em quando entrega as mensagens mais de uma vez para garantir que todas as mensagens foram entregues ao assinante.

Nos exemplos a seguir, use my-sub para o ID de assinatura.

Python

samples/snippets/subscriber.py 
from concurrent.futures import TimeoutError
from google.cloud import pubsub_v1

# TODO(developer)
# project_id = "your-project-id"
# subscription_id = "your-subscription-id"
# Number of seconds the subscriber should listen for messages
# timeout = 5.0

subscriber = pubsub_v1.SubscriberClient()
# The `subscription_path` method creates a fully qualified identifier
# in the form `projects/{project_id}/subscriptions/{subscription_id}`
subscription_path = subscriber.subscription_path(project_id, subscription_id)

def callback(message):
    print(f"Received {message}.")
    message.ack()

streaming_pull_future = subscriber.subscribe(subscription_path, callback=callback)
print(f"Listening for messages on {subscription_path}..\n")

# Wrap subscriber in a 'with' block to automatically call close() when done.
with subscriber:
    try:
        # When `timeout` is not set, result() will block indefinitely,
        # unless an exception is encountered first.
        streaming_pull_future.result(timeout=timeout)
    except TimeoutError:
        streaming_pull_future.cancel()

C++

google/cloud/pubsub/samples/samples.cc 
namespace pubsub = google::cloud::pubsub;
using google::cloud::future;
using google::cloud::StatusOr;
[](pubsub::Subscriber subscriber) {
  std::mutex mu;
  std::condition_variable cv;
  int message_count = 0;
  auto session = subscriber.Subscribe(
      [&](pubsub::Message const& m, pubsub::AckHandler h) {
        std::cout << "Received message " << m << "\n";
        std::unique_lock<std::mutex> lk(mu);
        ++message_count;
        lk.unlock();
        cv.notify_one();
        std::move(h).ack();
      });
  // Wait until at least one message has been received.
  std::unique_lock<std::mutex> lk(mu);
  cv.wait(lk, [&message_count] { return message_count > 0; });
  lk.unlock();
  // Cancel the subscription session.
  session.cancel();
  // Wait for the session to complete, no more callbacks can happen after this
  // point.
  auto status = session.get();
  // Report any final status, blocking.
  std::cout << "Message count: " << message_count << ", status: " << status
            << "\n";
}

C#

pubsub/api/Pubsub.Samples/PullMessagesAsync.cs 

using Google.Cloud.PubSub.V1;
using System;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

public class PullMessagesAsyncSample
{
    public async Task<int> PullMessagesAsync(string projectId, string subscriptionId, bool acknowledge)
    {
        SubscriptionName subscriptionName = SubscriptionName.FromProjectSubscription(projectId, subscriptionId);
        SubscriberClient subscriber = await SubscriberClient.CreateAsync(subscriptionName);
        // SubscriberClient runs your message handle function on multiple
        // threads to maximize throughput.
        int messageCount = 0;
        Task startTask = subscriber.StartAsync((PubsubMessage message, CancellationToken cancel) =>
        {
            string text = Encoding.UTF8.GetString(message.Data.ToArray());
            Console.WriteLine($"Message {message.MessageId}: {text}");
            Interlocked.Increment(ref messageCount);
            return Task.FromResult(acknowledge ? SubscriberClient.Reply.Ack : SubscriberClient.Reply.Nack);
        });
        // Run for 5 seconds.
        await Task.Delay(5000);
        await subscriber.StopAsync(CancellationToken.None);
        // Lets make sure that the start task finished successfully after the call to stop.
        await startTask;
        return messageCount;
    }
}

Go

pubsub/subscriptions/async_pull.go 
import (
	"context"
	"fmt"
	"io"
	"sync"

	"cloud.google.com/go/pubsub"
)

func pullMsgs(w io.Writer, projectID, subID string) error {
	// projectID := "my-project-id"
	// subID := "my-sub"
	ctx := context.Background()
	client, err := pubsub.NewClient(ctx, projectID)
	if err != nil {
		return fmt.Errorf("pubsub.NewClient: %v", err)
	}

	// Consume 10 messages.
	var mu sync.Mutex
	received := 0
	sub := client.Subscription(subID)
	cctx, cancel := context.WithCancel(ctx)
	err = sub.Receive(cctx, func(ctx context.Context, msg *pubsub.Message) {
		mu.Lock()
		defer mu.Unlock()
		fmt.Fprintf(w, "Got message: %q\n", string(msg.Data))
		msg.Ack()
		received++
		if received == 10 {
			cancel()
		}
	})
	if err != nil {
		return fmt.Errorf("Receive: %v", err)
	}
	return nil
}

Java

samples/snippets/src/main/java/pubsub/SubscribeAsyncExample.java 

import com.google.cloud.pubsub.v1.AckReplyConsumer;
import com.google.cloud.pubsub.v1.MessageReceiver;
import com.google.cloud.pubsub.v1.Subscriber;
import com.google.pubsub.v1.ProjectSubscriptionName;
import com.google.pubsub.v1.PubsubMessage;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;

public class SubscribeAsyncExample {
  public static void main(String... args) throws Exception {
    // TODO(developer): Replace these variables before running the sample.
    String projectId = "your-project-id";
    String subscriptionId = "your-subscription-id";

    subscribeAsyncExample(projectId, subscriptionId);
  }

  public static void subscribeAsyncExample(String projectId, String subscriptionId) {
    ProjectSubscriptionName subscriptionName =
        ProjectSubscriptionName.of(projectId, subscriptionId);

    // Instantiate an asynchronous message receiver.
    MessageReceiver receiver =
        (PubsubMessage message, AckReplyConsumer consumer) -> {
          // Handle incoming message, then ack the received message.
          System.out.println("Id: " + message.getMessageId());
          System.out.println("Data: " + message.getData().toStringUtf8());
          consumer.ack();
        };

    Subscriber subscriber = null;
    try {
      subscriber = Subscriber.newBuilder(subscriptionName, receiver).build();
      // Start the subscriber.
      subscriber.startAsync().awaitRunning();
      System.out.printf("Listening for messages on %s:\n", subscriptionName.toString());
      // Allow the subscriber to run for 30s unless an unrecoverable error occurs.
      subscriber.awaitTerminated(30, TimeUnit.SECONDS);
    } catch (TimeoutException timeoutException) {
      // Shut down the subscriber after 30s. Stop receiving messages.
      subscriber.stopAsync();
    }
  }
}

Node.js

samples/listenForMessages.js 
/**
 * TODO(developer): Uncomment these variables before running the sample.
 */
// const subscriptionName = 'YOUR_SUBSCRIPTION_NAME';
// const timeout = 60;

// Imports the Google Cloud client library
const {PubSub} = require('@google-cloud/pubsub');

// Creates a client; cache this for further use
const pubSubClient = new PubSub();

function listenForMessages() {
  // References an existing subscription
  const subscription = pubSubClient.subscription(subscriptionName);

  // Create an event handler to handle messages
  let messageCount = 0;
  const messageHandler = message => {
    console.log(`Received message ${message.id}:`);
    console.log(`\tData: ${message.data}`);
    console.log(`\tAttributes: ${message.attributes}`);
    messageCount += 1;

    // "Ack" (acknowledge receipt of) the message
    message.ack();
  };

  // Listen for new messages until timeout is hit
  subscription.on('message', messageHandler);

  setTimeout(() => {
    subscription.removeListener('message', messageHandler);
    console.log(`${messageCount} message(s) received.`);
  }, timeout * 1000);
}

listenForMessages();

PHP

pubsub/api/src/pull_messages.php 
use Google\Cloud\PubSub\PubSubClient;

/**
 * Pulls all Pub/Sub messages for a subscription.
 *
 * @param string $projectId  The Google project ID.
 * @param string $subscriptionName  The Pub/Sub subscription name.
 */
function pull_messages($projectId, $subscriptionName)
{
    $pubsub = new PubSubClient([
        'projectId' => $projectId,
    ]);
    $subscription = $pubsub->subscription($subscriptionName);
    foreach ($subscription->pull() as $message) {
        printf('Message: %s' . PHP_EOL, $message->data());
        // Acknowledge the Pub/Sub message has been received, so it will not be pulled multiple times.
        $subscription->acknowledge($message);
    }
}

Ruby

pubsub/subscriptions.rb 
# subscription_id = "your-subscription-id"
require "google/cloud/pubsub"

pubsub = Google::Cloud::Pubsub.new

subscription = pubsub.subscription subscription_id
subscriber   = subscription.listen do |received_message|
  puts "Received message: #{received_message.data}"
  received_message.acknowledge!
end

subscriber.start
# Let the main thread sleep for 60 seconds so the thread for listening
# messages does not quit
sleep 60
subscriber.stop.wait!

Como foi?

Limpar (opcional)

Para evitar que os recursos usados neste guia sejam cobrados na conta do Google Cloud Platform, use a linha de comando para excluir o tópico e a assinatura. 

  gcloud pubsub subscriptions delete my-sub
  gcloud pubsub topics delete my-topic

A seguir