Publishing messages to topics

This document provides information about publishing messages.

A publisher application creates and sends messages to a topic. Pub/Sub offers at-least-once message delivery and best-effort ordering to existing subscribers, as explained in the Subscriber Overview.

The general flow for a publisher application is:

  1. Create a message containing your data.
  2. Send a request to the Pub/Sub Server to publish the message to the desired topic.

Message format

A message consists of fields with the message data and metadata. Specify at least one of the following in the message:

If you're using the REST API, the message data must be base64-encoded.

The Pub/Sub service adds the following fields to the message:

  • A message ID unique to the topic
  • A timestamp for when the Pub/Sub service receives the message

Publishing messages

You can publish messages with the gcloud command-line tool or the Pub/Sub API. The client libraries can asynchronously publish messages.

Console

To publish a message, follow these steps:

  1. In the Cloud Console, go to the Pub/Sub topics page.

    Go to the Pub/Sub topics page

  2. Click the topic ID.

  3. In the Topic details page, click Publish messages.

  4. In the Message body field, enter the message data.

  5. Optional: Add message attributes.

    1. Click Add message attribute.

    2. Enter a key and a value for the attribute.

  6. Click Publish.

gcloud

To publish a message, use the gcloud pubsub topics publish command:

gcloud pubsub topics publish TOPIC_ID \
  --message=MESSAGE_DATA \
  [--attribute=KEY="VALUE",...]

Replace the following:

  • TOPIC_ID: the ID of the topic
  • MESSAGE_DATA: a string with the message data
  • KEY: the key of a message attribute
  • VALUE: the value for the key of the message attribute

REST

To publish a message, send a POST request like the following:

POST  https://pubsub.googleapis.com/v1/projects/PROJECT_ID/topics/TOPIC_ID:publish
Content-Type: application/json
Authorization: Bearer $(gcloud auth application-default print-access-token)

Replace the following:

  • PROJECT_ID: the project ID of the project with the topic
  • TOPIC_ID: the ID of the topic

Specify the following fields in the request body:

{
  "messages": [
    {
      "attributes": {
        "KEY": "VALUE",
        ...
      },
      "data": "MESSAGE_DATA",
    }
  ]
}

Replace the following:

  • KEY: the key of a message attribute
  • VALUE: the value for the key of the message attribute
  • MESSAGE_DATA: a base64-encoded string with the message data

The message must contain either a non-empty data field or at least one attribute.

If the request is successful, the response is a JSON object with the message ID. The following example is a response with a message ID:

{
  "messageIds": [
    "19916711285",
  ]
}

C++

Before trying this sample, follow the C++ setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub C++ API reference documentation. 

namespace pubsub = ::google::cloud::pubsub;
using ::google::cloud::future;
using ::google::cloud::StatusOr;
[](pubsub::Publisher publisher) {
  auto message_id = publisher.Publish(
      pubsub::MessageBuilder{}.SetData("Hello World!").Build());
  auto done = message_id.then([](future<StatusOr<std::string>> f) {
    auto id = f.get();
    if (!id) throw std::runtime_error(id.status().message());
    std::cout << "Hello World! published with id=" << *id << "\n";
  });
  // Block until the message is published
  done.get();
}

C#

Before trying this sample, follow the C# setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub C# API reference documentation. 


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

Before trying this sample, follow the Go setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Go API reference documentation. 

import (
	"context"
	"fmt"
	"io"
	"strconv"
	"sync"
	"sync/atomic"

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

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

	var wg sync.WaitGroup
	var totalErrors uint64
	t := client.Topic(topicID)

	for i := 0; i < n; i++ {
		result := t.Publish(ctx, &pubsub.Message{
			Data: []byte("Message " + strconv.Itoa(i)),
		})

		wg.Add(1)
		go func(i int, res *pubsub.PublishResult) {
			defer wg.Done()
			// The Get method blocks until a server-generated ID or
			// an error is returned for the published message.
			id, err := res.Get(ctx)
			if err != nil {
				// Error handling code can be added here.
				fmt.Fprintf(w, "Failed to publish: %v", err)
				atomic.AddUint64(&totalErrors, 1)
				return
			}
			fmt.Fprintf(w, "Published message %d; msg ID: %v\n", i, id)
		}(i, result)
	}

	wg.Wait()

	if totalErrors > 0 {
		return fmt.Errorf("%d of %d messages did not publish successfully", totalErrors, n)
	}
	return nil
}

Java

Before trying this sample, follow the Java setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Java API reference documentation. 


import com.google.api.core.ApiFuture;
import com.google.api.core.ApiFutureCallback;
import com.google.api.core.ApiFutures;
import com.google.api.gax.rpc.ApiException;
import com.google.cloud.pubsub.v1.Publisher;
import com.google.common.util.concurrent.MoreExecutors;
import com.google.protobuf.ByteString;
import com.google.pubsub.v1.PubsubMessage;
import com.google.pubsub.v1.TopicName;
import java.io.IOException;
import java.util.Arrays;
import java.util.List;
import java.util.concurrent.TimeUnit;

public class PublishWithErrorHandlerExample {

  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";

    publishWithErrorHandlerExample(projectId, topicId);
  }

  public static void publishWithErrorHandlerExample(String projectId, String topicId)
      throws IOException, 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();

      List<String> messages = Arrays.asList("first message", "second message");

      for (final String message : messages) {
        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> future = publisher.publish(pubsubMessage);

        // Add an asynchronous callback to handle success / failure
        ApiFutures.addCallback(
            future,
            new ApiFutureCallback<String>() {

              @Override
              public void onFailure(Throwable throwable) {
                if (throwable instanceof ApiException) {
                  ApiException apiException = ((ApiException) throwable);
                  // details on the API exception
                  System.out.println(apiException.getStatusCode().getCode());
                  System.out.println(apiException.isRetryable());
                }
                System.out.println("Error publishing message : " + message);
              }

              @Override
              public void onSuccess(String messageId) {
                // Once published, returns server-assigned message ids (unique within the topic)
                System.out.println("Published message ID: " + messageId);
              }
            },
            MoreExecutors.directExecutor());
      }
    } finally {
      if (publisher != null) {
        // When finished with the publisher, shutdown to free up resources.
        publisher.shutdown();
        publisher.awaitTermination(1, TimeUnit.MINUTES);
      }
    }
  }
}

Node.js

Before trying this sample, follow the Node.js setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Node.js API reference documentation. 

/**
 * 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

Before trying this sample, follow the PHP setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub PHP API reference documentation. 

use Google\Cloud\PubSub\MessageBuilder;
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);
    $topic->publish((new MessageBuilder)->setData($message)->build());

    print('Message published' . PHP_EOL);
}

Python

Before trying this sample, follow the Python setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Python API reference documentation. 

"""Publishes multiple messages to a Pub/Sub topic with an error handler."""
from concurrent import futures
from google.cloud import pubsub_v1

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

publisher = pubsub_v1.PublisherClient()
topic_path = publisher.topic_path(project_id, topic_id)
publish_futures = []

def get_callback(
    publish_future: pubsub_v1.publisher.futures.Future, data: str
) -> Callable[[pubsub_v1.publisher.futures.Future], None]:
    def callback(publish_future: pubsub_v1.publisher.futures.Future) -> None:
        try:
            # Wait 60 seconds for the publish call to succeed.
            print(publish_future.result(timeout=60))
        except futures.TimeoutError:
            print(f"Publishing {data} timed out.")

    return callback

for i in range(10):
    data = str(i)
    # When you publish a message, the client returns a future.
    publish_future = publisher.publish(topic_path, data.encode("utf-8"))
    # Non-blocking. Publish failures are handled in the callback function.
    publish_future.add_done_callback(get_callback(publish_future, data))
    publish_futures.append(publish_future)

# Wait for all the publish futures to resolve before exiting.
futures.wait(publish_futures, return_when=futures.ALL_COMPLETED)

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

Ruby

Before trying this sample, follow the Ruby setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Ruby API reference documentation. 

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

pubsub = Google::Cloud::Pubsub.new

topic = pubsub.topic topic_id

begin
  topic.publish_async "This is a test message." do |result|
    raise "Failed to publish the message." unless result.succeeded?
    puts "Message published asynchronously."
  end

  # Stop the async_publisher to send all queued messages immediately.
  topic.async_publisher.stop.wait!
rescue StandardError => e
  puts "Received error while publishing: #{e.message}"
end

After you publish a message, the Pub/Sub service returns the message ID to the publisher.

Using attributes

You can embed custom attributes as metadata in Pub/Sub messages. Attributes can be text strings or byte strings. The message schema can be represented as follows: 

{
  "data": string,
  "attributes": {
    string: string,
    ...
  },
  "messageId": string,
  "publishTime": string,
  "orderingKey": string
}

The PubsubMessage JSON schema is published as part of the REST and RPC documentation.

gcloud

gcloud pubsub topics publish my-topic --message="hello" \
  --attribute="origin=gcloud-sample,username=gcp"

C++

Before trying this sample, follow the C++ setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub C++ API reference documentation. 

namespace pubsub = ::google::cloud::pubsub;
using ::google::cloud::future;
using ::google::cloud::StatusOr;
[](pubsub::Publisher publisher) {
  std::vector<future<void>> done;
  for (int i = 0; i != 10; ++i) {
    auto message_id = publisher.Publish(
        pubsub::MessageBuilder{}
            .SetData("Hello World! [" + std::to_string(i) + "]")
            .SetAttribute("origin", "cpp-sample")
            .SetAttribute("username", "gcp")
            .Build());
    done.push_back(message_id.then([i](future<StatusOr<std::string>> f) {
      auto id = f.get();
      if (!id) throw std::runtime_error(id.status().message());
      std::cout << "Message " << i << " published with id=" << *id << "\n";
    }));
  }
  publisher.Flush();
  // Block until all the messages are published (optional)
  for (auto& f : done) f.get();
}

C#

Before trying this sample, follow the C# setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub C# API reference documentation. 


using Google.Cloud.PubSub.V1;
using Google.Protobuf;
using System;
using System.Threading.Tasks;

public class PublishMessageWithCustomAttributesAsyncSample
{
    public async Task PublishMessageWithCustomAttributesAsync(string projectId, string topicId, string messageText)
    {
        TopicName topicName = TopicName.FromProjectTopic(projectId, topicId);
        PublisherClient publisher = await PublisherClient.CreateAsync(topicName);

        var pubsubMessage = new PubsubMessage
        {
            // The data is any arbitrary ByteString. Here, we're using text.
            Data = ByteString.CopyFromUtf8(messageText),
            // The attributes provide metadata in a string-to-string dictionary.
            Attributes =
            {
                { "year", "2020" },
                { "author", "unknown" }
            }
        };
        string message = await publisher.PublishAsync(pubsubMessage);
        Console.WriteLine($"Published message {message}");
    }
}

Go

Before trying this sample, follow the Go setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Go API reference documentation. 

import (
	"context"
	"fmt"
	"io"

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

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

	t := client.Topic(topicID)
	result := t.Publish(ctx, &pubsub.Message{
		Data: []byte("Hello world!"),
		Attributes: map[string]string{
			"origin":   "golang",
			"username": "gcp",
		},
	})
	// 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 message with custom attributes; msg ID: %v\n", id)
	return nil
}

Java

Before trying this sample, follow the Java setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Java API reference documentation. 


import com.google.api.core.ApiFuture;
import com.google.cloud.pubsub.v1.Publisher;
import com.google.common.collect.ImmutableMap;
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 PublishWithCustomAttributesExample {
  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";

    publishWithCustomAttributesExample(projectId, topicId);
  }

  public static void publishWithCustomAttributesExample(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 = "first message";
      ByteString data = ByteString.copyFromUtf8(message);
      PubsubMessage pubsubMessage =
          PubsubMessage.newBuilder()
              .setData(data)
              .putAllAttributes(ImmutableMap.of("year", "2020", "author", "unknown"))
              .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 a message with custom attributes: " + messageId);

    } finally {
      if (publisher != null) {
        // When finished with the publisher, shutdown to free up resources.
        publisher.shutdown();
        publisher.awaitTermination(1, TimeUnit.MINUTES);
      }
    }
  }
}

Node.js

Before trying this sample, follow the Node.js setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Node.js API reference documentation. 

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

  // Add two custom attributes, origin and username, to the message
  const customAttributes = {
    origin: 'nodejs-sample',
    username: 'gcp',
  };

  const messageId = await pubSubClient
    .topic(topicName)
    .publish(dataBuffer, customAttributes);
  console.log(`Message ${messageId} published.`);
}

publishMessageWithCustomAttributes().catch(console.error);

Python

Before trying this sample, follow the Python setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Python API reference documentation. 

from google.cloud import pubsub_v1

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

publisher = pubsub_v1.PublisherClient()
topic_path = publisher.topic_path(project_id, topic_id)

for n in range(1, 10):
    data = f"Message number {n}"
    # Data must be a bytestring
    data = data.encode("utf-8")
    # Add two attributes, origin and username, to the message
    future = publisher.publish(
        topic_path, data, origin="python-sample", username="gcp"
    )
    print(future.result())

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

Ruby

Before trying this sample, follow the Ruby setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Ruby API reference documentation. 

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

pubsub = Google::Cloud::Pubsub.new

topic = pubsub.topic topic_id
# Add two attributes, origin and username, to the message
topic.publish_async "This is a test message.",
                    origin:   "ruby-sample",
                    username: "gcp" do |result|
  raise "Failed to publish the message." unless result.succeeded?
  puts "Message with custom attributes published asynchronously."
end

# Stop the async_publisher to send all queued messages immediately.
topic.async_publisher.stop.wait!

Using ordering keys

If messages have the same ordering key and you publish the messages to the same region, subscribers can receive the messages in order. Publishing messages with ordering keys might increase latency. To publish messages to the same region, use a regional endpoint.

You can publish messages with ordering keys using the Cloud Console, the gcloud command-line tool, or the Pub/Sub API.

Console

  1. In the Cloud Console, go to the Pub/Sub topics page.

    Go to the Pub/Sub topics page

  2. Click the topic ID.

  3. In the Topic details page, click Publish messages.

  4. In the Message body field, enter the message data.

  5. In the Ordering key field, enter an ordering key.

  6. Click Publish.

gcloud

To publish a message with an ordering key, use the gcloud pubsub topics publish command and the --ordering-key flag:

gcloud pubsub topics publish TOPIC_ID \
  --message=MESSAGE_DATA \
  --ordering-key=ORDERING_KEY

Replace the following:

  • TOPIC_ID: the ID of the topic
  • MESSAGE_DATA: a string with the message data
  • ORDERING_KEY: a string with an ordering key

REST

To publish a message with an ordering key, send a POST request like the following:

POST  https://pubsub.googleapis.com/v1/projects/PROJECT_ID/topics/TOPIC_ID:publish
Content-Type: application/json
Authorization: Bearer $(gcloud auth application-default print-access-token)

Replace the following:

  • PROJECT_ID: the project ID of the project with the topic
  • TOPIC_ID: the ID of the topic

Specify the following fields in the request body:

{
  "messages": [
    {
      "attributes": {
        "KEY": "VALUE",
        ...
      },
      "data": "MESSAGE_DATA",
      "ordering_key": "ORDERING_KEY",
    }
  ]
}

Replace the following:

  • KEY: the key of a message attribute
  • VALUE: the value for the key of the message attribute
  • MESSAGE_DATA: a base64-encoded string with the message data
  • ORDERING_KEY: a string with an ordering key

The message must contain either a non-empty data field or at least one attribute.

If the request is successful, the response is a JSON object with the message ID. The following example is a response with a message ID:

{
  "messageIds": [
    "19916711285",
  ]
}

C++

Before trying this sample, follow the C++ setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub C++ API reference documentation. 

namespace pubsub = ::google::cloud::pubsub;
using ::google::cloud::future;
using ::google::cloud::StatusOr;
[](pubsub::Publisher publisher) {
  struct SampleData {
    std::string ordering_key;
    std::string data;
  } data[] = {
      {"key1", "message1"}, {"key2", "message2"}, {"key1", "message3"},
      {"key1", "message4"}, {"key1", "message5"},
  };
  std::vector<future<void>> done;
  for (auto const& datum : data) {
    auto message_id =
        publisher.Publish(pubsub::MessageBuilder{}
                              .SetData("Hello World! [" + datum.data + "]")
                              .SetOrderingKey(datum.ordering_key)
                              .Build());
    std::string ack_id = datum.ordering_key + "#" + datum.data;
    done.push_back(message_id.then([ack_id](future<StatusOr<std::string>> f) {
      auto id = f.get();
      if (!id) throw std::runtime_error(id.status().message());
      std::cout << "Message " << ack_id << " published with id=" << *id
                << "\n";
    }));
  }
  publisher.Flush();
  // Block until all the messages are published (optional)
  for (auto& f : done) f.get();
}

C#

Before trying this sample, follow the C# setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub C# API reference documentation. 


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

public class PublishOrderedMessagesAsyncSample
{
    public async Task<int> PublishOrderedMessagesAsync(string projectId, string topicId, IEnumerable<(string, string)> keysAndMessages)
    {
        TopicName topicName = TopicName.FromProjectTopic(projectId, topicId);

        var customSettings = new PublisherClient.Settings
        {
            EnableMessageOrdering = true
        };

        // Sending messages to the same region ensures they are received in order even when multiple publishers are used.
        var clientCreationSettings = new PublisherClient.ClientCreationSettings(serviceEndpoint: "us-east1-pubsub.googleapis.com:443");
        PublisherClient publisher = await PublisherClient.CreateAsync(topicName, clientCreationSettings, customSettings);

        int publishedMessageCount = 0;
        var publishTasks = keysAndMessages.Select(async keyAndMessage =>
        {
            try
            {
                string message = await publisher.PublishAsync(keyAndMessage.Item1, keyAndMessage.Item2);
                Console.WriteLine($"Published message {message}");
                Interlocked.Increment(ref publishedMessageCount);
            }
            catch (Exception exception)
            {
                Console.WriteLine($"An error occurred when publishing message {keyAndMessage.Item2}: {exception.Message}");
            }
        });
        await Task.WhenAll(publishTasks);
        return publishedMessageCount;
    }
}

Go

Before trying this sample, follow the Go setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Go API reference documentation. 

import (
	"context"
	"fmt"
	"io"
	"sync"
	"sync/atomic"

	"cloud.google.com/go/pubsub"
	"google.golang.org/api/option"
)

func publishWithOrderingKey(w io.Writer, projectID, topicID string) {
	// projectID := "my-project-id"
	// topicID := "my-topic"
	ctx := context.Background()

	// Sending messages to the same region ensures they are received in order
	// even when multiple publishers are used.
	client, err := pubsub.NewClient(ctx, projectID,
		option.WithEndpoint("us-east1-pubsub.googleapis.com:443"))
	if err != nil {
		fmt.Fprintf(w, "pubsub.NewClient: %v", err)
		return
	}
	defer client.Close()

	var wg sync.WaitGroup
	var totalErrors uint64
	t := client.Topic(topicID)
	t.EnableMessageOrdering = true

	messages := []struct {
		message     string
		orderingKey string
	}{
		{
			message:     "message1",
			orderingKey: "key1",
		},
		{
			message:     "message2",
			orderingKey: "key2",
		},
		{
			message:     "message3",
			orderingKey: "key1",
		},
		{
			message:     "message4",
			orderingKey: "key2",
		},
	}

	for _, m := range messages {
		res := t.Publish(ctx, &pubsub.Message{
			Data:        []byte(m.message),
			OrderingKey: m.orderingKey,
		})

		wg.Add(1)
		go func(res *pubsub.PublishResult) {
			defer wg.Done()
			// The Get method blocks until a server-generated ID or
			// an error is returned for the published message.
			_, err := res.Get(ctx)
			if err != nil {
				// Error handling code can be added here.
				fmt.Printf("Failed to publish: %s\n", err)
				atomic.AddUint64(&totalErrors, 1)
				return
			}
		}(res)
	}

	wg.Wait()

	if totalErrors > 0 {
		fmt.Fprintf(w, "%d of 4 messages did not publish successfully", totalErrors)
		return
	}

	fmt.Fprint(w, "Published 4 messages with ordering keys successfully\n")
}

Java

Before trying this sample, follow the Java setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Java API reference documentation. 

import com.google.api.core.ApiFuture;
import com.google.api.core.ApiFutureCallback;
import com.google.api.core.ApiFutures;
import com.google.api.gax.rpc.ApiException;
import com.google.cloud.pubsub.v1.Publisher;
import com.google.common.util.concurrent.MoreExecutors;
import com.google.protobuf.ByteString;
import com.google.pubsub.v1.PubsubMessage;
import com.google.pubsub.v1.TopicName;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.TimeUnit;

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

    publishWithOrderingKeysExample(projectId, topicId);
  }

  public static void publishWithOrderingKeysExample(String projectId, String topicId)
      throws IOException, InterruptedException {
    TopicName topicName = TopicName.of(projectId, topicId);
    // Create a publisher and set message ordering to true.
    Publisher publisher =
        Publisher.newBuilder(topicName)
            // Sending messages to the same region ensures they are received in order
            // even when multiple publishers are used.
            .setEndpoint("us-east1-pubsub.googleapis.com:443")
            .setEnableMessageOrdering(true)
            .build();

    try {
      Map<String, String> messages = new HashMap<String, String>();
      messages.put("message1", "key1");
      messages.put("message2", "key2");
      messages.put("message3", "key1");
      messages.put("message4", "key2");

      for (Map.Entry<String, String> entry : messages.entrySet()) {
        ByteString data = ByteString.copyFromUtf8(entry.getKey());
        PubsubMessage pubsubMessage =
            PubsubMessage.newBuilder().setData(data).setOrderingKey(entry.getValue()).build();
        ApiFuture<String> future = publisher.publish(pubsubMessage);

        // Add an asynchronous callback to handle publish success / failure.
        ApiFutures.addCallback(
            future,
            new ApiFutureCallback<String>() {

              @Override
              public void onFailure(Throwable throwable) {
                if (throwable instanceof ApiException) {
                  ApiException apiException = ((ApiException) throwable);
                  // Details on the API exception.
                  System.out.println(apiException.getStatusCode().getCode());
                  System.out.println(apiException.isRetryable());
                }
                System.out.println("Error publishing message : " + pubsubMessage.getData());
              }

              @Override
              public void onSuccess(String messageId) {
                // Once published, returns server-assigned message ids (unique within the topic).
                System.out.println(pubsubMessage.getData() + " : " + messageId);
              }
            },
            MoreExecutors.directExecutor());
      }
    } finally {
      // When finished with the publisher, shutdown to free up resources.
      publisher.shutdown();
      publisher.awaitTermination(1, TimeUnit.MINUTES);
    }
  }
}

Node.js

Before trying this sample, follow the Node.js setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Node.js API reference documentation. 

/**
 * TODO(developer): Uncomment these variables before running the sample.
 */
// const topicName = 'YOUR_TOPIC_NAME';
// const data = JSON.stringify({foo: 'bar'});
// const orderingKey = 'key1';

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

// Creates a client; cache this for further use
const pubSubClient = new PubSub({
  // Sending messages to the same region ensures they are received in order
  // even when multiple publishers are used.
  apiEndpoint: 'us-east1-pubsub.googleapis.com:443',
});

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

  // Be sure to set an ordering key that matches other messages
  // you want to receive in order, relative to each other.
  const message = {
    data: dataBuffer,
    orderingKey: orderingKey,
  };

  // Publishes the message
  const messageId = await pubSubClient
    .topic(topicName, {enableMessageOrdering: true})
    .publishMessage(message);

  console.log(`Message ${messageId} published.`);

  return messageId;
}

return await publishOrderedMessage();

Python

Before trying this sample, follow the Python setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Python API reference documentation. 

from google.cloud import pubsub_v1

# TODO(developer): Choose an existing topic.
# project_id = "your-project-id"
# topic_id = "your-topic-id"

publisher_options = pubsub_v1.types.PublisherOptions(enable_message_ordering=True)
# Sending messages to the same region ensures they are received in order
# even when multiple publishers are used.
client_options = {"api_endpoint": "us-east1-pubsub.googleapis.com:443"}
publisher = pubsub_v1.PublisherClient(
    publisher_options=publisher_options, client_options=client_options
)
# 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 message in [
    ("message1", "key1"),
    ("message2", "key2"),
    ("message3", "key1"),
    ("message4", "key2"),
]:
    # Data must be a bytestring
    data = message[0].encode("utf-8")
    ordering_key = message[1]
    # When you publish a message, the client returns a future.
    future = publisher.publish(topic_path, data=data, ordering_key=ordering_key)
    print(future.result())

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

Ruby

Before trying this sample, follow the Ruby setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Ruby API reference documentation. 

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

pubsub = Google::Cloud::Pubsub.new

# Start sending messages in one request once the size of all queued messages
# reaches 1 MB or the number of queued messages reaches 20
topic = pubsub.topic topic_id, async: {
  max_bytes:    1_000_000,
  max_messages: 20
}
topic.enable_message_ordering!
10.times do |i|
  topic.publish_async "This is message \##{i}.",
                      ordering_key: "ordering-key"
end

# Stop the async_publisher to send all queued messages immediately.
topic.async_publisher.stop!
puts "Messages published with ordering key."

Using schema

You can publish messages to topics with schema associated with them. To learn more, see Creating and managing schemas. Messages should be encoded in the schema and format specified when you created the topic.

C++

Before trying this sample, follow the C++ setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub C++ API reference documentation.

Avro 
namespace pubsub = ::google::cloud::pubsub;
using ::google::cloud::future;
using ::google::cloud::StatusOr;
[](pubsub::Publisher publisher) {
  auto constexpr kNewYork =
      R"js({ "name": "New York", "post_abbr": "NY" })js";
  auto constexpr kPennsylvania =
      R"js({ "name": "Pennsylvania", "post_abbr": "PA" })js";
  std::vector<future<void>> done;
  auto handler = [](future<StatusOr<std::string>> f) {
    auto id = f.get();
    if (!id) throw std::runtime_error(id.status().message());
  };
  for (auto const* data : {kNewYork, kPennsylvania}) {
    done.push_back(
        publisher.Publish(pubsub::MessageBuilder{}.SetData(data).Build())
            .then(handler));
  }
  // Block until all messages are published.
  for (auto& d : done) d.get();
}
Proto 
namespace pubsub = ::google::cloud::pubsub;
using ::google::cloud::future;
using ::google::cloud::StatusOr;
[](pubsub::Publisher publisher) {
  std::vector<std::pair<std::string, std::string>> states{
      {"New York", "NY"},
      {"Pennsylvania", "PA"},
  };
  std::vector<future<void>> done;
  auto handler = [](future<StatusOr<std::string>> f) {
    auto id = f.get();
    if (!id) throw std::runtime_error(id.status().message());
  };
  for (auto const& data : states) {
    google::cloud::pubsub::samples::State state;
    state.set_name(data.first);
    state.set_post_abbr(data.second);
    done.push_back(publisher
                       .Publish(pubsub::MessageBuilder{}
                                    .SetData(state.SerializeAsString())
                                    .Build())
                       .then(handler));
  }
  // Block until all messages are published.
  for (auto& d : done) d.get();
}

C#

Before trying this sample, follow the C# setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub C# API reference documentation.

Avro 

using Avro.IO;
using Avro.Specific;
using Google.Cloud.PubSub.V1;
using Newtonsoft.Json;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;

public class PublishAvroMessagesAsyncSample
{
    public async Task<int> PublishAvroMessagesAsync(string projectId, string topicId, IEnumerable<AvroUtilities.State> messageStates)
    {
        TopicName topicName = TopicName.FromProjectTopic(projectId, topicId);
        PublisherClient publisher = await PublisherClient.CreateAsync(topicName);

        PublisherServiceApiClient publishApi = PublisherServiceApiClient.Create();
        var topic = publishApi.GetTopic(topicName);

        int publishedMessageCount = 0;
        var publishTasks = messageStates.Select(async state =>
        {

            try
            {
                string messageId = null;
                switch (topic.SchemaSettings.Encoding)
                {
                    case Encoding.Binary:
                        using (var ms = new MemoryStream())
                        {
                            var encoder = new BinaryEncoder(ms);
                            var writer = new SpecificDefaultWriter(state.Schema);
                            writer.Write(state, encoder);
                            messageId = await publisher.PublishAsync(ms.ToArray());
                        }
                        break;
                    case Encoding.Json:
                        var jsonMessage = AvroUtilities.StateUtils.StateToJsonString(state);
                        messageId = await publisher.PublishAsync(jsonMessage);
                        break;
                }
                Console.WriteLine($"Published message {messageId}");
                Interlocked.Increment(ref publishedMessageCount);
            }
            catch (Exception exception)
            {
                Console.WriteLine($"An error ocurred when publishing message {state}: {exception.Message}");
            }
        });
        await Task.WhenAll(publishTasks);
        return publishedMessageCount;
    }
}
Proto 

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

public class PublishProtoMessagesAsyncSample
{
    public async Task<int> PublishProtoMessagesAsync(string projectId, string topicId, IEnumerable<Utilities.State> messageStates)
    {
        TopicName topicName = TopicName.FromProjectTopic(projectId, topicId);
        PublisherClient publisher = await PublisherClient.CreateAsync(topicName);

        PublisherServiceApiClient publishApi = PublisherServiceApiClient.Create();
        var topic = publishApi.GetTopic(topicName);

        int publishedMessageCount = 0;
        var publishTasks = messageStates.Select(async state =>
        {
            try
            {
                string messageId = null;
                switch (topic.SchemaSettings.Encoding)
                {
                    case Encoding.Binary:
                        var binaryMessage = state.ToByteString();
                        messageId = await publisher.PublishAsync(binaryMessage);
                        break;
                    case Encoding.Json:
                        var jsonMessage = JsonFormatter.Default.Format(state);
                        messageId = await publisher.PublishAsync(jsonMessage);
                        break;
                }
                Console.WriteLine($"Published message {messageId}");
                Interlocked.Increment(ref publishedMessageCount);
            }
            catch (Exception exception)
            {
                Console.WriteLine($"An error ocurred when publishing message {state}: {exception.Message}");
            }
        });
        await Task.WhenAll(publishTasks);
        return publishedMessageCount;
    }
}

Go

Before trying this sample, follow the Go setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Go API reference documentation.

Avro 
import (
	"context"
	"fmt"
	"io"
	"io/ioutil"

	"cloud.google.com/go/pubsub"
	"github.com/linkedin/goavro/v2"
)

func publishAvroRecords(w io.Writer, projectID, topicID, avscFile string) error {
	// projectID := "my-project-id"
	// topicID := "my-topic"
	// avscFile = "path/to/an/avro/schema/file(.avsc)/formatted/in/json"
	ctx := context.Background()
	client, err := pubsub.NewClient(ctx, projectID)
	if err != nil {
		return fmt.Errorf("pubsub.NewClient: %v", err)
	}

	avroSource, err := ioutil.ReadFile(avscFile)
	if err != nil {
		return fmt.Errorf("ioutil.ReadFile err: %v", err)
	}
	codec, err := goavro.NewCodec(string(avroSource))
	if err != nil {
		return fmt.Errorf("goavro.NewCodec err: %v", err)
	}
	record := map[string]interface{}{"name": "Alaska", "post_abbr": "AK"}

	// Get the topic encoding type.
	t := client.Topic(topicID)
	cfg, err := t.Config(ctx)
	if err != nil {
		return fmt.Errorf("topic.Config err: %v", err)
	}
	encoding := cfg.SchemaSettings.Encoding

	var msg []byte
	switch encoding {
	case pubsub.EncodingBinary:
		msg, err = codec.BinaryFromNative(nil, record)
		if err != nil {
			return fmt.Errorf("codec.BinaryFromNative err: %v", err)
		}
	case pubsub.EncodingJSON:
		msg, err = codec.TextualFromNative(nil, record)
		if err != nil {
			return fmt.Errorf("codec.TextualFromNative err: %v", err)
		}
	default:
		return fmt.Errorf("invalid encoding: %v", encoding)
	}

	result := t.Publish(ctx, &pubsub.Message{
		Data: msg,
	})
	_, err = result.Get(ctx)
	if err != nil {
		return fmt.Errorf("result.Get: %v", err)
	}
	fmt.Fprintf(w, "Published avro record: %s\n", string(msg))
	return nil
}
Proto 
import (
	"context"
	"fmt"
	"io"

	"cloud.google.com/go/pubsub"
	statepb "github.com/GoogleCloudPlatform/golang-samples/internal/pubsub/schemas"
	"google.golang.org/protobuf/encoding/protojson"
	"google.golang.org/protobuf/proto"
)

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

	state := &statepb.State{
		Name:     "Alaska",
		PostAbbr: "AK",
	}

	// Get the topic encoding type.
	t := client.Topic(topicID)
	cfg, err := t.Config(ctx)
	if err != nil {
		return fmt.Errorf("topic.Config err: %v", err)
	}
	encoding := cfg.SchemaSettings.Encoding

	var msg []byte
	switch encoding {
	case pubsub.EncodingBinary:
		msg, err = proto.Marshal(state)
		if err != nil {
			return fmt.Errorf("proto.Marshal err: %v", err)
		}
	case pubsub.EncodingJSON:
		msg, err = protojson.Marshal(state)
		if err != nil {
			return fmt.Errorf("protojson.Marshal err: %v", err)
		}
	default:
		return fmt.Errorf("invalid encoding: %v", encoding)
	}

	result := t.Publish(ctx, &pubsub.Message{
		Data: msg,
	})
	_, err = result.Get(ctx)
	if err != nil {
		return fmt.Errorf("result.Get: %v", err)
	}
	fmt.Fprintf(w, "Published proto message with %#v encoding: %s\n", encoding, string(msg))
	return nil
}

Java

Before trying this sample, follow the Java setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Java API reference documentation.

Avro 

import com.google.api.core.ApiFuture;
import com.google.cloud.pubsub.v1.Publisher;
import com.google.cloud.pubsub.v1.TopicAdminClient;
import com.google.protobuf.ByteString;
import com.google.pubsub.v1.Encoding;
import com.google.pubsub.v1.PubsubMessage;
import com.google.pubsub.v1.TopicName;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeUnit;
import org.apache.avro.io.Encoder;
import org.apache.avro.io.EncoderFactory;
import utilities.State;

public class PublishAvroRecordsExample {

  public static void main(String... args) throws Exception {
    // TODO(developer): Replace these variables before running the sample.
    String projectId = "your-project-id";
    // Use a topic created with an Avro schema.
    String topicId = "your-topic-id";

    publishAvroRecordsExample(projectId, topicId);
  }

  public static void publishAvroRecordsExample(String projectId, String topicId)
      throws IOException, ExecutionException, InterruptedException {

    Encoding encoding = null;

    TopicName topicName = TopicName.of(projectId, topicId);

    // Get the topic encoding type.
    try (TopicAdminClient topicAdminClient = TopicAdminClient.create()) {
      encoding = topicAdminClient.getTopic(topicName).getSchemaSettings().getEncoding();
    }

    // Instantiate an avro-tools-generated class defined in `us-states.avsc`.
    State state = State.newBuilder().setName("Alaska").setPostAbbr("AK").build();

    Publisher publisher = null;

    block:
    try {
      publisher = Publisher.newBuilder(topicName).build();

      // Prepare to serialize the object to the output stream.
      ByteArrayOutputStream byteStream = new ByteArrayOutputStream();

      Encoder encoder = null;

      // Prepare an appropriate encoder for publishing to the topic.
      switch (encoding) {
        case BINARY:
          System.out.println("Preparing a BINARY encoder...");
          encoder = EncoderFactory.get().directBinaryEncoder(byteStream, /*reuse=*/ null);
          break;

        case JSON:
          System.out.println("Preparing a JSON encoder...");
          encoder = EncoderFactory.get().jsonEncoder(State.getClassSchema(), byteStream);
          break;

        default:
          break block;
      }

      // Encode the object and write it to the output stream.
      state.customEncode(encoder);
      encoder.flush();

      // Publish the encoded object as a Pub/Sub message.
      ByteString data = ByteString.copyFrom(byteStream.toByteArray());
      PubsubMessage message = PubsubMessage.newBuilder().setData(data).build();
      System.out.println("Publishing message: " + message);

      ApiFuture<String> future = publisher.publish(message);
      System.out.println("Published message ID: " + future.get());

    } finally {
      if (publisher != null) {
        publisher.shutdown();
        publisher.awaitTermination(1, TimeUnit.MINUTES);
      }
    }
  }
}
Proto 

import com.google.api.core.ApiFuture;
import com.google.cloud.pubsub.v1.Publisher;
import com.google.cloud.pubsub.v1.TopicAdminClient;
import com.google.protobuf.ByteString;
import com.google.protobuf.util.JsonFormat;
import com.google.pubsub.v1.Encoding;
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;
import utilities.StateProto.State;

public class PublishProtobufMessagesExample {

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

    publishProtobufMessagesExample(projectId, topicId);
  }

  public static void publishProtobufMessagesExample(String projectId, String topicId)
      throws IOException, ExecutionException, InterruptedException {

    Encoding encoding = null;

    TopicName topicName = TopicName.of(projectId, topicId);

    // Get the topic encoding type.
    try (TopicAdminClient topicAdminClient = TopicAdminClient.create()) {
      encoding = topicAdminClient.getTopic(topicName).getSchemaSettings().getEncoding();
    }

    Publisher publisher = null;

    // Instantiate a protoc-generated class defined in `us-states.proto`.
    State state = State.newBuilder().setName("Alaska").setPostAbbr("AK").build();

    block:
    try {
      publisher = Publisher.newBuilder(topicName).build();

      PubsubMessage.Builder message = PubsubMessage.newBuilder();

      // Prepare an appropriately formatted message based on topic encoding.
      switch (encoding) {
        case BINARY:
          message.setData(state.toByteString());
          System.out.println("Publishing a BINARY-formatted message:\n" + message);
          break;

        case JSON:
          String jsonString = JsonFormat.printer().omittingInsignificantWhitespace().print(state);
          message.setData(ByteString.copyFromUtf8(jsonString));
          System.out.println("Publishing a JSON-formatted message:\n" + message);
          break;

        default:
          break block;
      }

      // Publish the message.
      ApiFuture<String> future = publisher.publish(message.build());
      System.out.println("Published message ID: " + future.get());

    } finally {
      if (publisher != null) {
        publisher.shutdown();
        publisher.awaitTermination(1, TimeUnit.MINUTES);
      }
    }
  }
}

Node.js

Before trying this sample, follow the Node.js setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Node.js API reference documentation.

Avro 
/**
 * TODO(developer): Uncomment this variable before running the sample.
 */
// const topicName = 'YOUR_TOPIC_NAME';

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

// And the Apache Avro library
const avro = require('avro-js');
const fs = require('fs');

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

async function publishAvroRecords(topicName) {
  // Get the topic metadata to learn about its schema encoding.
  const topic = pubSubClient.topic(topicName);
  const [topicMetadata] = await topic.getMetadata();
  const topicSchemaMetadata = topicMetadata.schemaSettings;

  if (!topicSchemaMetadata) {
    console.log(`Topic ${topicName} doesn't seem to have a schema.`);
    return;
  }
  const schemaEncoding = topicSchemaMetadata.encoding;

  // Make an encoder using the official avro-js library.
  const definition = fs
    .readFileSync('system-test/fixtures/provinces.avsc')
    .toString();
  const type = avro.parse(definition);

  // Encode the message.
  const province = {
    name: 'Ontario',
    post_abbr: 'ON',
  };
  let dataBuffer;
  switch (schemaEncoding) {
    case Encodings.Binary:
      dataBuffer = type.toBuffer(province);
      break;
    case Encodings.Json:
      dataBuffer = Buffer.from(type.toString(province));
      break;
    default:
      console.log(`Unknown schema encoding: ${schemaEncoding}`);
      break;
  }
  if (!dataBuffer) {
    console.log(`Invalid encoding ${schemaEncoding} on the topic.`);
    return;
  }

  const messageId = await topic.publish(dataBuffer);
  console.log(`Avro record ${messageId} published.`);
}
Protocol Buffer 
/**
 * TODO(developer): Uncomment this variable before running the sample.
 */
// const topicName = 'YOUR_TOPIC_NAME';

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

// And the protobufjs library
const protobuf = require('protobufjs');

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

async function publishProtobufMessages(topicName) {
  // Get the topic metadata to learn about its schema.
  const topic = pubSubClient.topic(topicName);
  const [topicMetadata] = await topic.getMetadata();
  const topicSchemaMetadata = topicMetadata.schemaSettings;

  if (!topicSchemaMetadata) {
    console.log(`Topic ${topicName} doesn't seem to have a schema.`);
    return;
  }
  const schemaEncoding = topicSchemaMetadata.encoding;

  // Encode the message.
  const province = {
    name: 'Ontario',
    postAbbr: 'ON',
  };

  // Make an encoder using the protobufjs library.
  //
  // Since we're providing the test message for a specific schema here, we'll
  // also code in the path to a sample proto definition.
  const root = await protobuf.load('system-test/fixtures/provinces.proto');
  const Province = root.lookupType('utilities.Province');
  const message = Province.create(province);

  let dataBuffer;
  switch (schemaEncoding) {
    case Encodings.Binary:
      dataBuffer = Buffer.from(Province.encode(message).finish());
      break;
    case Encodings.Json:
      dataBuffer = Buffer.from(JSON.stringify(message.toJSON()));
      break;
    default:
      console.log(`Unknown schema encoding: ${schemaEncoding}`);
      break;
  }
  if (!dataBuffer) {
    console.log(`Invalid encoding ${schemaEncoding} on the topic.`);
    return;
  }

  const messageId = await topic.publish(dataBuffer);
  console.log(`Protobuf message ${messageId} published.`);
}

PHP

Before trying this sample, follow the PHP setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub PHP API reference documentation.

Avro 
use Google\Cloud\PubSub\PubSubClient;
use Google\Cloud\PubSub\V1\Encoding;

use AvroStringIO;
use AvroSchema;
use AvroIODatumWriter;
use AvroDataIOWriter;

/**
 * Publish a message using an AVRO schema.
 *
 * This sample uses `wikimedia/avro` for AVRO encoding.
 *
 * @param string $projectId
 * @param string $topicId
 * @param string $definitionFile
 * @return void
 */
function publish_avro_records($projectId, $topicId, $definitionFile)
{
    $pubsub = new PubSubClient([
        'projectId' => $projectId,
    ]);

    $definition = file_get_contents($definitionFile);

    $messageData = [
        'name' => 'Alaska',
        'post_abbr' => 'AK',
    ];

    $topic = $pubsub->topic($topicId);

    // get the encoding type.
    $topicInfo = $topic->info();
    $encoding = '';
    if (isset($topicInfo['schemaSettings']['encoding'])) {
        $encoding = $topicInfo['schemaSettings']['encoding'];
    }

    // if encoding is not set, we can't continue.
    if ($encoding === '') {
        printf('Topic %s does not have schema enabled', $topicId);
        return;
    }

    // If you are using gRPC, encoding may be an integer corresponding to an
    // enum value on Google\Cloud\PubSub\V1\Encoding.
    if (!is_string($encoding)) {
        $encoding = Encoding::name($encoding);
    }

    $encodedMessageData = '';
    if ($encoding == 'BINARY') {
        // encode as AVRO binary.
        $io = new AvroStringIO();
        $schema = AvroSchema::parse($definition);
        $writer = new AvroIODatumWriter($schema);
        $dataWriter = new AvroDataIOWriter($io, $writer, $schema);

        $dataWriter->append($messageData);

        $dataWriter->close();

        // AVRO binary data must be base64-encoded.
        $encodedMessageData = base64_encode($io->string());
    } else {
        // encode as JSON.
        $encodedMessageData = json_encode($messageData);
    }

    $topic->publish(['data' => $encodedMessageData]);

    printf('Published message with %s encoding', $encoding);
}
Protocol Buffer 
use Google\Cloud\PubSub\PubSubClient;
use Google\Cloud\PubSub\V1\Encoding;

use Utilities\StateProto;

/**
 * Publish a message using a protocol buffer schema.
 *
 * Relies on a proto message of the following form:
 * ```
 * syntax = "proto3";
 *
 * package utilities;
 *
 * message StateProto {
 *   string name = 1;
 *   string post_abbr = 2;
 * }
 * ```
 *
 * @param string $projectId
 * @param string $topicId
 * @return void
 */
function publish_proto_messages($projectId, $topicId)
{
    $pubsub = new PubSubClient([
        'projectId' => $projectId,
    ]);

    $messageData = new StateProto([
        'name' => 'Alaska',
        'post_abbr' => 'AK',
    ]);

    $topic = $pubsub->topic($topicId);

    // get the encoding type.
    $topicInfo = $topic->info();
    $encoding = '';
    if (isset($topicInfo['schemaSettings']['encoding'])) {
        $encoding = $topicInfo['schemaSettings']['encoding'];
    }

    // if encoding is not set, we can't continue.
    if ($encoding === '') {
        printf('Topic %s does not have schema enabled', $topicId);
        return;
    }

    // If you are using gRPC, encoding may be an integer corresponding to an
    // enum value on Google\Cloud\PubSub\V1\Encoding.
    if (!is_string($encoding)) {
        $encoding = Encoding::name($encoding);
    }

    $encodedMessageData = '';
    if ($encoding == 'BINARY') {
        // encode as protobuf binary.
        $encodedMessageData = $messageData->serializeToString();
    } else {
        // encode as JSON.
        $encodedMessageData = $messageData->serializeToJsonString();
    }

    $topic->publish(['data' => $encodedMessageData]);

    printf('Published message with %s encoding', $encoding);
}

Python

Before trying this sample, follow the Python setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Python API reference documentation.

Avro 
from avro.io import BinaryEncoder, DatumWriter
import avro
import io
import json
from google.api_core.exceptions import NotFound
from google.cloud.pubsub import PublisherClient
from google.pubsub_v1.types import Encoding

# TODO(developer): Replace these variables before running the sample.
# project_id = "your-project-id"
# topic_id = "your-topic-id"
# avsc_file = "path/to/an/avro/schema/file/(.avsc)/formatted/in/json"

publisher_client = PublisherClient()
topic_path = publisher_client.topic_path(project_id, topic_id)

# Prepare to write Avro records to the binary output stream.
avro_schema = avro.schema.parse(open(avsc_file, "rb").read())
writer = DatumWriter(avro_schema)
bout = io.BytesIO()

# Prepare some data using a Python dictionary that matches the Avro schema
record = {"name": "Alaska", "post_abbr": "AK"}

try:
    # Get the topic encoding type.
    topic = publisher_client.get_topic(request={"topic": topic_path})
    encoding = topic.schema_settings.encoding

    # Encode the data according to the message serialization type.
    if encoding == Encoding.BINARY:
        encoder = BinaryEncoder(bout)
        writer.write(record, encoder)
        data = bout.getvalue()
        print(f"Preparing a binary-encoded message:\n{data}")
    elif encoding == Encoding.JSON:
        data = json.dumps(record).encode("utf-8")
        print(f"Preparing a JSON-encoded message:\n{data}")
    else:
        print(f"No encoding specified in {topic_path}. Abort.")
        exit(0)

    future = publisher_client.publish(topic_path, data)
    print(f"Published message ID: {future.result()}")

except NotFound:
    print(f"{topic_id} not found.")
Protocol Buffer 
from google.api_core.exceptions import NotFound
from google.cloud.pubsub import PublisherClient
from google.protobuf.json_format import MessageToJson
from google.pubsub_v1.types import Encoding

from utilities import us_states_pb2

# TODO(developer): Replace these variables before running the sample.
# project_id = "your-project-id"
# topic_id = "your-topic-id"

publisher_client = PublisherClient()
topic_path = publisher_client.topic_path(project_id, topic_id)

try:
    # Get the topic encoding type.
    topic = publisher_client.get_topic(request={"topic": topic_path})
    encoding = topic.schema_settings.encoding

    # Instantiate a protoc-generated class defined in `us-states.proto`.
    state = us_states_pb2.StateProto()
    state.name = "Alaska"
    state.post_abbr = "AK"

    # Encode the data according to the message serialization type.
    if encoding == Encoding.BINARY:
        data = state.SerializeToString()
        print(f"Preparing a binary-encoded message:\n{data}")
    elif encoding == Encoding.JSON:
        json_object = MessageToJson(state)
        data = str(json_object).encode("utf-8")
        print(f"Preparing a JSON-encoded message:\n{data}")
    else:
        print(f"No encoding specified in {topic_path}. Abort.")
        exit(0)

    future = publisher_client.publish(topic_path, data)
    print(f"Published message ID: {future.result()}")

except NotFound:
    print(f"{topic_id} not found.")

Ruby

Before trying this sample, follow the Ruby setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Ruby API reference documentation.

Avro 
# topic_id = "your-topic-id"
# avsc_file = "path/to/an/avro/schema/file/(.avsc)/formatted/in/json"
require "google/cloud/pubsub"

pubsub = Google::Cloud::Pubsub.new

topic = pubsub.topic topic_id

record = { "name" => "Alaska", "post_abbr" => "AK" }

if topic.message_encoding_binary?
  require "avro"
  avro_schema = Avro::Schema.parse File.read(avsc_file)
  writer = Avro::IO::DatumWriter.new avro_schema
  buffer = StringIO.new
  encoder = Avro::IO::BinaryEncoder.new buffer
  writer.write record, encoder
  topic.publish buffer
  puts "Published binary-encoded AVRO message."
elsif topic.message_encoding_json?
  require "json"
  topic.publish record.to_json
  puts "Published JSON-encoded AVRO message."
else
  raise "No encoding specified in #{topic.name}."
end
Protocol Buffer 
# topic_id = "your-topic-id"
require "google/cloud/pubsub"
require_relative "utilities/us-states_pb"

pubsub = Google::Cloud::Pubsub.new

topic = pubsub.topic topic_id

state = Utilities::StateProto.new name: "Alaska", post_abbr: "AK"

if topic.message_encoding_binary?
  topic.publish Utilities::StateProto.encode(state)
  puts "Published binary-encoded protobuf message."
elsif topic.message_encoding_json?
  topic.publish Utilities::StateProto.encode_json(state)
  puts "Published JSON-encoded protobuf message."
else
  raise "No encoding specified in #{topic.name}."
end

Batching messages

The Pub/Sub client libraries batch multiple messages into a single call to the service. Larger batch sizes increase message throughput (rate of messages sent per CPU). The cost of batching is latency for individual messages, which are queued in memory until their corresponding batch is filled and ready to be sent over the network. To minimize latency, batching should be turned off. This is particularly important for applications that publish a single message as part of a request-response sequence. A common example of this pattern is encountered in serverless, event-driven applications using Cloud Functions or App Engine.

Messages can be batched based on request size (in bytes), number of messages, and time. You can override the default settings as shown in this sample:

C++

Before trying this sample, follow the C++ setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub C++ API reference documentation. 

namespace pubsub = ::google::cloud::pubsub;
using ::google::cloud::future;
using ::google::cloud::StatusOr;
[](std::string project_id, std::string topic_id) {
  auto topic = pubsub::Topic(std::move(project_id), std::move(topic_id));
  // By default the publisher will flush a batch after 10ms, after it contains
  // more than 100 message, or after it contains more than 1MiB of data,
  // whichever comes first. This changes those defaults.
  auto publisher = pubsub::Publisher(pubsub::MakePublisherConnection(
      std::move(topic),
      pubsub::PublisherOptions{}
          .set_maximum_hold_time(std::chrono::milliseconds(20))
          .set_maximum_batch_bytes(4 * 1024 * 1024L)
          .set_maximum_batch_message_count(200),
      pubsub::ConnectionOptions{}));

  std::vector<future<void>> ids;
  for (char const* data : {"1", "2", "3", "go!"}) {
    ids.push_back(
        publisher.Publish(pubsub::MessageBuilder().SetData(data).Build())
            .then([data](future<StatusOr<std::string>> f) {
              auto s = f.get();
              if (!s) return;
              std::cout << "Sent '" << data << "' (" << *s << ")\n";
            }));
  }
  publisher.Flush();
  // Block until they are actually sent.
  for (auto& id : ids) id.get();
}

C#

Before trying this sample, follow the C# setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub C# API reference documentation. 


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

public class PublishBatchedMessagesAsyncSample
{
    public async Task<int> PublishBatchMessagesAsync(string projectId, string topicId, IEnumerable<string> messageTexts)
    {
        TopicName topicName = TopicName.FromProjectTopic(projectId, topicId);

        // Default Settings:
        // byteCountThreshold: 1000000
        // elementCountThreshold: 100
        // delayThreshold: 10 milliseconds
        var customSettings = new PublisherClient.Settings
        {
            BatchingSettings = new BatchingSettings(
                elementCountThreshold: 50,
                byteCountThreshold: 10240,
                delayThreshold: TimeSpan.FromMilliseconds(500))
        };

        PublisherClient publisher = await PublisherClient.CreateAsync(topicName, settings: customSettings);

        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 occurred when publishing message {text}: {exception.Message}");
            }
        });
        await Task.WhenAll(publishTasks);
        return publishedMessageCount;
    }
}

Go

Before trying this sample, follow the Go setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Go API reference documentation. 

import (
	"context"
	"fmt"
	"io"
	"strconv"
	"time"

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

func publishWithSettings(w io.Writer, projectID, topicID string) error {
	// projectID := "my-project-id"
	// topicID := "my-topic"
	ctx := context.Background()
	client, err := pubsub.NewClient(ctx, projectID)
	if err != nil {
		return fmt.Errorf("pubsub.NewClient: %v", err)
	}
	defer client.Close()
	var results []*pubsub.PublishResult
	var resultErrors []error
	t := client.Topic(topicID)
	t.PublishSettings.ByteThreshold = 5000
	t.PublishSettings.CountThreshold = 10
	t.PublishSettings.DelayThreshold = 100 * time.Millisecond

	for i := 0; i < 10; i++ {
		result := t.Publish(ctx, &pubsub.Message{
			Data: []byte("Message " + strconv.Itoa(i)),
		})
		results = append(results, result)
	}
	// The Get method blocks until a server-generated ID or
	// an error is returned for the published message.
	for i, res := range results {
		id, err := res.Get(ctx)
		if err != nil {
			resultErrors = append(resultErrors, err)
			fmt.Fprintf(w, "Failed to publish: %v", err)
			continue
		}
		fmt.Fprintf(w, "Published message %d; msg ID: %v\n", i, id)
	}
	if len(resultErrors) != 0 {
		return fmt.Errorf("Get: %v", resultErrors[len(resultErrors)-1])
	}
	fmt.Fprintf(w, "Published messages with batch settings.")
	return nil
}

Java

Before trying this sample, follow the Java setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Java API reference documentation. 


import com.google.api.core.ApiFuture;
import com.google.api.core.ApiFutures;
import com.google.api.gax.batching.BatchingSettings;
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.ArrayList;
import java.util.List;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeUnit;
import org.threeten.bp.Duration;

public class PublishWithBatchSettingsExample {
  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";

    publishWithBatchSettingsExample(projectId, topicId);
  }

  public static void publishWithBatchSettingsExample(String projectId, String topicId)
      throws IOException, ExecutionException, InterruptedException {
    TopicName topicName = TopicName.of(projectId, topicId);
    Publisher publisher = null;
    List<ApiFuture<String>> messageIdFutures = new ArrayList<>();

    try {
      // Batch settings control how the publisher batches messages
      long requestBytesThreshold = 5000L; // default : 1 byte
      long messageCountBatchSize = 100L; // default : 1 message

      Duration publishDelayThreshold = Duration.ofMillis(100); // default : 1 ms

      // Publish request get triggered based on request size, messages count & time since last
      // publish, whichever condition is met first.
      BatchingSettings batchingSettings =
          BatchingSettings.newBuilder()
              .setElementCountThreshold(messageCountBatchSize)
              .setRequestByteThreshold(requestBytesThreshold)
              .setDelayThreshold(publishDelayThreshold)
              .build();

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

      // schedule publishing one message at a time : messages get automatically batched
      for (int i = 0; i < 100; i++) {
        String message = "message " + i;
        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);
        messageIdFutures.add(messageIdFuture);
      }
    } finally {
      // Wait on any pending publish requests.
      List<String> messageIds = ApiFutures.allAsList(messageIdFutures).get();

      System.out.println("Published " + messageIds.size() + " messages with batch settings.");

      if (publisher != null) {
        // When finished with the publisher, shutdown to free up resources.
        publisher.shutdown();
        publisher.awaitTermination(1, TimeUnit.MINUTES);
      }
    }
  }
}

Node.js

Before trying this sample, follow the Node.js setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Node.js API reference documentation. 

/**
 * TODO(developer): Uncomment these variables before running the sample.
 */
// const topicName = 'YOUR_TOPIC_NAME';
// const data = JSON.stringify({foo: 'bar'});
// const maxMessages = 10;
// const maxWaitTime = 10;

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

  const batchPublisher = pubSubClient.topic(topicName, {
    batching: {
      maxMessages: maxMessages,
      maxMilliseconds: maxWaitTime * 1000,
    },
  });

  for (let i = 0; i < 10; i++) {
    (async () => {
      const messageId = await batchPublisher.publish(dataBuffer);
      console.log(`Message ${messageId} published.`);
    })();
  }
}

publishBatchedMessages().catch(console.error);

PHP

Before trying this sample, follow the PHP setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub PHP API reference documentation. 

use Google\Cloud\PubSub\PubSubClient;

/**
 * Publishes a message for a Pub/Sub topic.
 *
 * The publisher should be used in conjunction with the `google-cloud-batch`
 * daemon, which should be running in the background.
 *
 * To start the daemon, from your project root call `vendor/bin/google-cloud-batch daemon`.
 *
 * @param string $projectId  The Google project ID.
 * @param string $topicName  The Pub/Sub topic name.
 * @param string $message    The message to publish.
 */
function publish_message_batch($projectId, $topicName, $message)
{
    // Check if the batch daemon is running.
    if (getenv('IS_BATCH_DAEMON_RUNNING') !== 'true') {
        trigger_error(
            'The batch daemon is not running. Call ' .
            '`vendor/bin/google-cloud-batch daemon` from ' .
            'your project root to start the daemon.',
            E_USER_NOTICE
        );
    }

    $batchOptions = [
        'batchSize' => 100, // Max messages for each batch.
        'callPeriod' => 0.01, // Max time in seconds between each batch publish.
    ];

    $pubsub = new PubSubClient([
        'projectId' => $projectId,
    ]);
    $topic = $pubsub->topic($topicName);
    $publisher = $topic->batchPublisher([
        'batchOptions' => $batchOptions
    ]);

    for ($i = 0; $i < 10; $i++) {
        $publisher->publish(['data' => $message]);
    }

    print('Messages enqueued for publication.' . PHP_EOL);
}

Python

Before trying this sample, follow the Python setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Python API reference documentation. 

from concurrent import futures
from google.cloud import pubsub_v1

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

# Configure the batch to publish as soon as there are 10 messages
# or 1 KiB of data, or 1 second has passed.
batch_settings = pubsub_v1.types.BatchSettings(
    max_messages=10,  # default 100
    max_bytes=1024,  # default 1 MiB
    max_latency=1,  # default 10 ms
)
publisher = pubsub_v1.PublisherClient(batch_settings)
topic_path = publisher.topic_path(project_id, topic_id)
publish_futures = []

# Resolve the publish future in a separate thread.
def callback(future: pubsub_v1.publisher.futures.Future) -> None:
    message_id = future.result()
    print(message_id)

for n in range(1, 10):
    data = f"Message number {n}"
    # Data must be a bytestring
    data = data.encode("utf-8")
    publish_future = publisher.publish(topic_path, data)
    # Non-blocking. Allow the publisher client to batch multiple messages.
    publish_future.add_done_callback(callback)
    publish_futures.append(publish_future)

futures.wait(publish_futures, return_when=futures.ALL_COMPLETED)

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

Ruby

Before trying this sample, follow the Ruby setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Ruby API reference documentation. 

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

pubsub = Google::Cloud::Pubsub.new

# Start sending messages in one request once the size of all queued messages
# reaches 1 MB or the number of queued messages reaches 20
topic = pubsub.topic topic_id, async: {
  max_bytes:    1_000_000,
  max_messages: 20
}
10.times do |i|
  topic.publish_async "This is message \##{i}."
end

# Stop the async_publisher to send all queued messages immediately.
topic.async_publisher.stop.wait!
puts "Messages published asynchronously in batch."

Retrying requests

Publishing failures are automatically retried, except for errors that do not warrant retries. This sample code demonstrates creating a publisher with custom retry settings (note that not all client libraries support custom retry settings; see the API Reference documentation for your chosen language):

C++

Before trying this sample, follow the C++ setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub C++ API reference documentation. 

namespace pubsub = ::google::cloud::pubsub;
using ::google::cloud::future;
using ::google::cloud::StatusOr;
[](std::string project_id, std::string topic_id) {
  auto topic = pubsub::Topic(std::move(project_id), std::move(topic_id));
  // By default a publisher will retry for 60 seconds, with an initial backoff
  // of 100ms, a maximum backoff of 60 seconds, and the backoff will grow by
  // 30% after each attempt. This changes those defaults.
  auto publisher = pubsub::Publisher(pubsub::MakePublisherConnection(
      std::move(topic), pubsub::PublisherOptions{}, {},
      pubsub::LimitedTimeRetryPolicy(
          /*maximum_duration=*/std::chrono::minutes(10))
          .clone(),
      pubsub::ExponentialBackoffPolicy(
          /*initial_delay=*/std::chrono::milliseconds(200),
          /*maximum_delay=*/std::chrono::seconds(45),
          /*scaling=*/2.0)
          .clone()));

  std::vector<future<bool>> done;
  for (char const* data : {"1", "2", "3", "go!"}) {
    done.push_back(
        publisher.Publish(pubsub::MessageBuilder().SetData(data).Build())
            .then([](future<StatusOr<std::string>> f) {
              return f.get().ok();
            }));
  }
  publisher.Flush();
  int count = 0;
  for (auto& f : done) {
    if (f.get()) ++count;
  }
  std::cout << count << " messages sent successfully\n";
}

C#

Before trying this sample, follow the C# setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub C# API reference documentation. 


using Google.Api.Gax.Grpc;
using Google.Cloud.PubSub.V1;
using Grpc.Core;
using System;
using System.Threading.Tasks;

public class PublishMessageWithRetrySettingsAsyncSample
{
    public async Task PublishMessageWithRetrySettingsAsync(string projectId, string topicId, string messageText)
    {
        TopicName topicName = TopicName.FromProjectTopic(projectId, topicId);
        // Retry settings control how the publisher handles retry-able failures
        var maxAttempts = 3;
        var initialBackoff = TimeSpan.FromMilliseconds(110); // default: 100 ms
        var maxBackoff = TimeSpan.FromSeconds(70); // default : 60 seconds
        var backoffMultiplier = 1.3; // default: 1.0
        var totalTimeout = TimeSpan.FromSeconds(100); // default: 600 seconds

        var publisher = await PublisherClient.CreateAsync(topicName,
               clientCreationSettings: new PublisherClient.ClientCreationSettings(
                   publisherServiceApiSettings: new PublisherServiceApiSettings
                   {
                       PublishSettings = CallSettings.FromRetry(RetrySettings.FromExponentialBackoff(
                               maxAttempts: maxAttempts,
                               initialBackoff: initialBackoff,
                               maxBackoff: maxBackoff,
                               backoffMultiplier: backoffMultiplier,
                               retryFilter: RetrySettings.FilterForStatusCodes(StatusCode.Unavailable)))
                       .WithTimeout(totalTimeout)
                   }
               )).ConfigureAwait(false);
        string message = await publisher.PublishAsync(messageText);
        Console.WriteLine($"Published message {message}");
    }
}

Java

Before trying this sample, follow the Java setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Java API reference documentation. 


import com.google.api.core.ApiFuture;
import com.google.api.gax.retrying.RetrySettings;
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;
import org.threeten.bp.Duration;

public class PublishWithRetrySettingsExample {
  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";

    publishWithRetrySettingsExample(projectId, topicId);
  }

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

    try {
      // Retry settings control how the publisher handles retry-able failures
      Duration initialRetryDelay = Duration.ofMillis(100); // default: 100 ms
      double retryDelayMultiplier = 2.0; // back off for repeated failures, default: 1.3
      Duration maxRetryDelay = Duration.ofSeconds(60); // default : 60 seconds
      Duration initialRpcTimeout = Duration.ofSeconds(1); // default: 5 seconds
      double rpcTimeoutMultiplier = 1.0; // default: 1.0
      Duration maxRpcTimeout = Duration.ofSeconds(600); // default: 600 seconds
      Duration totalTimeout = Duration.ofSeconds(600); // default: 600 seconds

      RetrySettings retrySettings =
          RetrySettings.newBuilder()
              .setInitialRetryDelay(initialRetryDelay)
              .setRetryDelayMultiplier(retryDelayMultiplier)
              .setMaxRetryDelay(maxRetryDelay)
              .setInitialRpcTimeout(initialRpcTimeout)
              .setRpcTimeoutMultiplier(rpcTimeoutMultiplier)
              .setMaxRpcTimeout(maxRpcTimeout)
              .setTotalTimeout(totalTimeout)
              .build();

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

      String message = "first message";
      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 a message with retry settings: " + messageId);

    } finally {
      if (publisher != null) {
        // When finished with the publisher, shutdown to free up resources.
        publisher.shutdown();
        publisher.awaitTermination(1, TimeUnit.MINUTES);
      }
    }
  }
}

Node.js

Before trying this sample, follow the Node.js setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Node.js API reference documentation. 

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

// Imports the Google Cloud client library. v1 is for the lower level
// proto access.
const {v1} = require('@google-cloud/pubsub');

// Creates a publisher client.
const publisherClient = new v1.PublisherClient({
  // optional auth parameters
});

async function publishWithRetrySettings() {
  const formattedTopic = publisherClient.projectTopicPath(
    projectId,
    topicName
  );

  // Publishes the message as a string, e.g. "Hello, world!" or JSON.stringify(someObject)
  const dataBuffer = Buffer.from(data);
  const messagesElement = {
    data: dataBuffer,
  };
  const messages = [messagesElement];

  // Build the request
  const request = {
    topic: formattedTopic,
    messages: messages,
  };

  // Retry settings control how the publisher handles retryable failures. Default values are shown.
  // The `retryCodes` array determines which grpc errors will trigger an automatic retry.
  // The `backoffSettings` object lets you specify the behaviour of retries over time.
  const retrySettings = {
    retryCodes: [
      10, // 'ABORTED'
      1, // 'CANCELLED',
      4, // 'DEADLINE_EXCEEDED'
      13, // 'INTERNAL'
      8, // 'RESOURCE_EXHAUSTED'
      14, // 'UNAVAILABLE'
      2, // 'UNKNOWN'
    ],
    backoffSettings: {
      // The initial delay time, in milliseconds, between the completion
      // of the first failed request and the initiation of the first retrying request.
      initialRetryDelayMillis: 100,
      // The multiplier by which to increase the delay time between the completion
      // of failed requests, and the initiation of the subsequent retrying request.
      retryDelayMultiplier: 1.3,
      // The maximum delay time, in milliseconds, between requests.
      // When this value is reached, retryDelayMultiplier will no longer be used to increase delay time.
      maxRetryDelayMillis: 60000,
      // The initial timeout parameter to the request.
      initialRpcTimeoutMillis: 5000,
      // The multiplier by which to increase the timeout parameter between failed requests.
      rpcTimeoutMultiplier: 1.0,
      // The maximum timeout parameter, in milliseconds, for a request. When this value is reached,
      // rpcTimeoutMultiplier will no longer be used to increase the timeout.
      maxRpcTimeoutMillis: 600000,
      // The total time, in milliseconds, starting from when the initial request is sent,
      // after which an error will be returned, regardless of the retrying attempts made meanwhile.
      totalTimeoutMillis: 600000,
    },
  };

  const [response] = await publisherClient.publish(request, {
    retry: retrySettings,
  });
  console.log(`Message ${response.messageIds} published.`);
}

publishWithRetrySettings().catch(console.error);

Python

Before trying this sample, follow the Python setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Python API reference documentation. 

from google import api_core
from google.cloud import pubsub_v1

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

# Configure the retry settings. Defaults shown in comments are values applied
# by the library by default, instead of default values in the Retry object.
custom_retry = api_core.retry.Retry(
    initial=0.250,  # seconds (default: 0.1)
    maximum=90.0,  # seconds (default: 60.0)
    multiplier=1.45,  # default: 1.3
    deadline=300.0,  # seconds (default: 60.0)
    predicate=api_core.retry.if_exception_type(
        api_core.exceptions.Aborted,
        api_core.exceptions.DeadlineExceeded,
        api_core.exceptions.InternalServerError,
        api_core.exceptions.ResourceExhausted,
        api_core.exceptions.ServiceUnavailable,
        api_core.exceptions.Unknown,
        api_core.exceptions.Cancelled,
    ),
)

publisher = pubsub_v1.PublisherClient()
topic_path = publisher.topic_path(project_id, topic_id)

for n in range(1, 10):
    data = f"Message number {n}"
    # Data must be a bytestring
    data = data.encode("utf-8")
    future = publisher.publish(topic=topic_path, data=data, retry=custom_retry)
    print(future.result())

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

Retry settings control how the Pub/Sub client libraries retry publish requests. The client libraries have any of the following retry settings:

  • Initial request timeout: the amount of time before a client library stops waiting for the initial publish request to complete.
  • Retry delay: the amount of time after a request times out that a client library waits to retry the request.
  • Total timeout: the amount of time after a client library stops retrying publish requests.

To retry publish requests, the initial request timeout must be shorter than the total timeout. For example, if you're using exponential backoff, the client libraries compute the request timeout and retry delay as follows:

  • After each publish request, the request timeout increases by the request timeout multiplier, up to the maximum request timeout.
  • After each retry, the retry delay increases by the retry delay multiplier, up to the maximum retry delay.

When a client library retries a request and the message has an ordering key, the client library repeatedly retries the request, regardless of the retry settings.

If a non-retryable error occurs, the client library doesn't publish the message and stops publishing other messages with the same ordering key. For example, when a publisher sends a message to a topic that doesn't exist, a non-retryable error occurs. To continue publishing messages with the same ordering key, call a method to resume publishing and then start publishing again.

The following sample shows you how to resume publishing messages with the same ordering key.

C++

Before trying this sample, follow the C++ setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub C++ API reference documentation. 

namespace pubsub = ::google::cloud::pubsub;
using ::google::cloud::future;
using ::google::cloud::StatusOr;
[](pubsub::Publisher publisher) {
  struct SampleData {
    std::string ordering_key;
    std::string data;
  } data[] = {
      {"key1", "message1"}, {"key2", "message2"}, {"key1", "message3"},
      {"key1", "message4"}, {"key1", "message5"},
  };
  std::vector<future<void>> done;
  for (auto const& datum : data) {
    auto const& da = datum;  // workaround MSVC lambda capture confusion
    auto handler = [da, publisher](future<StatusOr<std::string>> f) mutable {
      auto const msg = da.ordering_key + "#" + da.data;
      auto id = f.get();
      if (!id) {
        std::cout << "An error has occurred publishing " << msg << "\n";
        publisher.ResumePublish(da.ordering_key);
        return;
      }
      std::cout << "Message " << msg << " published as id=" << *id << "\n";
    };
    done.push_back(
        publisher
            .Publish(pubsub::MessageBuilder{}
                         .SetData("Hello World! [" + datum.data + "]")
                         .SetOrderingKey(datum.ordering_key)
                         .Build())
            .then(handler));
  }
  publisher.Flush();
  // Block until all the messages are published (optional)
  for (auto& f : done) f.get();
}

C#

Before trying this sample, follow the C# setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub C# API reference documentation. 


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

public class ResumePublishSample
{
    public async Task<int> PublishOrderedMessagesAsync(string projectId, string topicId, IEnumerable<(string, string)> keysAndMessages)
    {
        TopicName topicName = TopicName.FromProjectTopic(projectId, topicId);

        var customSettings = new PublisherClient.Settings
        {
            EnableMessageOrdering = true
        };

        PublisherClient publisher = await PublisherClient.CreateAsync(topicName, settings: customSettings);

        int publishedMessageCount = 0;
        var publishTasks = keysAndMessages.Select(async keyAndMessage =>
        {
            try
            {
                string message = await publisher.PublishAsync(keyAndMessage.Item1, keyAndMessage.Item2);
                Console.WriteLine($"Published message {message}");
                Interlocked.Increment(ref publishedMessageCount);
            }
            catch (Exception exception)
            {
                Console.WriteLine($"An error occurred when publishing message {keyAndMessage.Item2}: {exception.Message}");
                publisher.ResumePublish(keyAndMessage.Item1);
            }
        });
        await Task.WhenAll(publishTasks);
        return publishedMessageCount;
    }
}

Go

Before trying this sample, follow the Go setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Go API reference documentation. 

import (
	"context"
	"fmt"
	"io"

	"cloud.google.com/go/pubsub"
	"google.golang.org/api/option"
)

func resumePublishWithOrderingKey(w io.Writer, projectID, topicID string) {
	// projectID := "my-project-id"
	// topicID := "my-topic"
	ctx := context.Background()

	// Sending messages to the same region ensures they are received in order
	// even when multiple publishers are used.
	client, err := pubsub.NewClient(ctx, projectID,
		option.WithEndpoint("us-east1-pubsub.googleapis.com:443"))
	if err != nil {
		fmt.Fprintf(w, "pubsub.NewClient: %v", err)
		return
	}
	defer client.Close()

	t := client.Topic(topicID)
	t.EnableMessageOrdering = true
	key := "some-ordering-key"

	res := t.Publish(ctx, &pubsub.Message{
		Data:        []byte("some-message"),
		OrderingKey: key,
	})
	_, err = res.Get(ctx)
	if err != nil {
		// Error handling code can be added here.
		fmt.Printf("Failed to publish: %s\n", err)

		// Resume publish on an ordering key that has had unrecoverable errors.
		// After such an error publishes with this ordering key will fail
		// until this method is called.
		t.ResumePublish(key)
	}

	fmt.Fprint(w, "Published a message with ordering key successfully\n")
}

Java

Before trying this sample, follow the Java setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Java API reference documentation. 

import com.google.api.core.ApiFuture;
import com.google.api.core.ApiFutureCallback;
import com.google.api.core.ApiFutures;
import com.google.api.gax.rpc.ApiException;
import com.google.cloud.pubsub.v1.Publisher;
import com.google.common.util.concurrent.MoreExecutors;
import com.google.protobuf.ByteString;
import com.google.pubsub.v1.PubsubMessage;
import com.google.pubsub.v1.TopicName;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.TimeUnit;

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

    resumePublishWithOrderingKeysExample(projectId, topicId);
  }

  public static void resumePublishWithOrderingKeysExample(String projectId, String topicId)
      throws IOException, InterruptedException {
    TopicName topicName = TopicName.of(projectId, topicId);
    // Create a publisher and set message ordering to true.
    Publisher publisher =
        Publisher.newBuilder(topicName)
            .setEnableMessageOrdering(true)
            .setEndpoint("us-east1-pubsub.googleapis.com:443")
            .build();

    try {
      Map<String, String> messages = new HashMap<String, String>();
      messages.put("message1", "key1");
      messages.put("message2", "key2");
      messages.put("message3", "key1");
      messages.put("message4", "key2");

      for (Map.Entry<String, String> entry : messages.entrySet()) {
        ByteString data = ByteString.copyFromUtf8(entry.getKey());
        PubsubMessage pubsubMessage =
            PubsubMessage.newBuilder().setData(data).setOrderingKey(entry.getValue()).build();
        ApiFuture<String> future = publisher.publish(pubsubMessage);

        // Add an asynchronous callback to handle publish success / failure.
        ApiFutures.addCallback(
            future,
            new ApiFutureCallback<String>() {

              @Override
              public void onFailure(Throwable throwable) {
                if (throwable instanceof ApiException) {
                  ApiException apiException = ((ApiException) throwable);
                  // Details on the API exception.
                  System.out.println(apiException.getStatusCode().getCode());
                  System.out.println(apiException.isRetryable());
                }
                System.out.println("Error publishing message : " + pubsubMessage.getData());
                // (Beta) Must call resumePublish to reset key and continue publishing with order.
                publisher.resumePublish(pubsubMessage.getOrderingKey());
              }

              @Override
              public void onSuccess(String messageId) {
                // Once published, returns server-assigned message ids (unique within the topic).
                System.out.println(pubsubMessage.getData() + " : " + messageId);
              }
            },
            MoreExecutors.directExecutor());
      }
    } finally {
      publisher.shutdown();
      publisher.awaitTermination(1, TimeUnit.MINUTES);
    }
  }
}

Node.js

Before trying this sample, follow the Node.js setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Node.js API reference documentation. 

/**
 * TODO(developer): Uncomment these variables before running the sample.
 */
// const topicName = 'YOUR_TOPIC_NAME';
// const data = JSON.stringify({foo: 'bar'});
// const orderingKey = 'key1';

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

  // Publishes the message
  const publisher = pubSubClient.topic(topicName, {
    enableMessageOrdering: true,
  });
  try {
    const message = {
      data: dataBuffer,
      orderingKey: orderingKey,
    };
    const messageId = await publisher.publishMessage(message);
    console.log(`Message ${messageId} published.`);

    return messageId;
  } catch (e) {
    console.log(`Could not publish: ${e}`);
    publisher.resumePublishing(orderingKey);
    return null;
  }
}

return await resumePublish();

Python

Before trying this sample, follow the Python setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Python API reference documentation. 

from google.cloud import pubsub_v1

# TODO(developer): Choose an existing topic.
# project_id = "your-project-id"
# topic_id = "your-topic-id"

publisher_options = pubsub_v1.types.PublisherOptions(enable_message_ordering=True)
# Sending messages to the same region ensures they are received in order
# even when multiple publishers are used.
client_options = {"api_endpoint": "us-east1-pubsub.googleapis.com:443"}
publisher = pubsub_v1.PublisherClient(
    publisher_options=publisher_options, client_options=client_options
)
# 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 message in [
    ("message1", "key1"),
    ("message2", "key2"),
    ("message3", "key1"),
    ("message4", "key2"),
]:
    # Data must be a bytestring
    data = message[0].encode("utf-8")
    ordering_key = message[1]
    # When you publish a message, the client returns a future.
    future = publisher.publish(topic_path, data=data, ordering_key=ordering_key)
    try:
        print(future.result())
    except RuntimeError:
        # Resume publish on an ordering key that has had unrecoverable errors.
        publisher.resume_publish(topic_path, ordering_key)

print(f"Resumed publishing messages with ordering keys to {topic_path}.")

Ruby

Before trying this sample, follow the Ruby setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Ruby API reference documentation. 

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

pubsub = Google::Cloud::Pubsub.new

# Start sending messages in one request once the size of all queued messages
# reaches 1 MB or the number of queued messages reaches 20
topic = pubsub.topic topic_id, async: {
  max_bytes:    1_000_000,
  max_messages: 20
}
topic.enable_message_ordering!
10.times do |i|
  topic.publish_async "This is message \##{i}.",
                      ordering_key: "ordering-key" do |result|
    if result.succeeded?
      puts "Message \##{i} successfully published."
    else
      puts "Message \##{i} failed to publish"
      # Allow publishing to continue on "ordering-key" after processing the
      # failure.
      topic.resume_publish "ordering-key"
    end
  end
end

# Stop the async_publisher to send all queued messages immediately.
topic.async_publisher.stop!

Flow control

A publisher client may attempt to publish messages faster than that client is capable of sending data to the Pub/Sub service. Clients are limited by many factors, including:

  • Machine CPU, RAM, and network capacity
  • Network settings, such as the number of outstanding requests and available bandwidth
  • The latency of each publish request, largely determined by the network connections between the Pub/Sub service, the client, and Google Cloud

If the publish request rate exceeds these limits, requests will accumulate in memory until they fail with a DEADLINE_EXCEEDED error. This is especially likely when tens of thousands of messages are published in a loop, generating thousands of requests in milliseconds.

You can diagnose this issue by checking the server side metrics in Monitoring. You won't be able to see the requests that have failed with DEADLINE_EXCEEDED, only the successful requests. The rate of successful requests tells you the throughput capacity of your client machines, providing a baseline for configuring flow control.

Go to the Monitoring page

To mitigate flow rate issues, configure your publisher client with flow control to limit the rate of publish requests. You can configure the maximum number of bytes allocated for outstanding requests, and the maximum number of outstanding messages permitted. Set these limits according to the throughput capacity of your client machines.

Publisher flow control is available via the Pub/Sub client libraries in the following languages:

C++

Before trying this sample, follow the C++ setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub C++ API reference documentation. 

namespace pubsub = ::google::cloud::pubsub;
using ::google::cloud::future;
using ::google::cloud::StatusOr;
[](std::string project_id, std::string topic_id) {
  auto topic = pubsub::Topic(std::move(project_id), std::move(topic_id));
  // Configure the publisher to block if either (1) 100 or more messages, or
  // (2) messages with 100MiB worth of data have not been acknowledged by the
  // service. By default the publisher never blocks, and its capacity is only
  // limited by the system's memory.
  auto publisher = pubsub::Publisher(pubsub::MakePublisherConnection(
      std::move(topic), pubsub::PublisherOptions{}
                            .set_maximum_pending_messages(100)
                            .set_maximum_pending_bytes(100 * 1024 * 1024L)
                            .set_full_publisher_blocks()));

  std::vector<future<void>> ids;
  for (char const* data : {"a", "b", "c"}) {
    ids.push_back(
        publisher.Publish(pubsub::MessageBuilder().SetData(data).Build())
            .then([data](future<StatusOr<std::string>> f) {
              auto s = f.get();
              if (!s) return;
              std::cout << "Sent '" << data << "' (" << *s << ")\n";
            }));
  }
  publisher.Flush();
  // Block until they are actually sent.
  for (auto& id : ids) id.get();
}

Java

Before trying this sample, follow the Java setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Java API reference documentation. 


import com.google.api.core.ApiFuture;
import com.google.api.core.ApiFutures;
import com.google.api.gax.batching.BatchingSettings;
import com.google.api.gax.batching.FlowControlSettings;
import com.google.api.gax.batching.FlowController.LimitExceededBehavior;
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.ArrayList;
import java.util.List;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeUnit;

public class PublishWithFlowControlExample {
  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";

    publishWithFlowControlExample(projectId, topicId);
  }

  public static void publishWithFlowControlExample(String projectId, String topicId)
      throws IOException, ExecutionException, InterruptedException {
    TopicName topicName = TopicName.of(projectId, topicId);
    Publisher publisher = null;
    List<ApiFuture<String>> messageIdFutures = new ArrayList<>();

    try {
      // Configure how many messages the publisher client can hold in memory
      // and what to do when messages exceed the limit.
      FlowControlSettings flowControlSettings =
          FlowControlSettings.newBuilder()
              // Block more messages from being published when the limit is reached. The other
              // options are Ignore (or continue publishing) and ThrowException (or error out).
              .setLimitExceededBehavior(LimitExceededBehavior.Block)
              .setMaxOutstandingRequestBytes(10 * 1024 * 1024L) // 10 MiB
              .setMaxOutstandingElementCount(100L) // 100 messages
              .build();

      // By default, messages are not batched.
      BatchingSettings batchingSettings =
          BatchingSettings.newBuilder().setFlowControlSettings(flowControlSettings).build();

      publisher = Publisher.newBuilder(topicName).setBatchingSettings(batchingSettings).build();

      // Publish 1000 messages in quick succession may be constrained by publisher flow control.
      for (int i = 0; i < 1000; i++) {
        String message = "message " + i;
        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);
        messageIdFutures.add(messageIdFuture);
      }
    } finally {
      // Wait on any pending publish requests.
      List<String> messageIds = ApiFutures.allAsList(messageIdFutures).get();

      System.out.println(
          "Published " + messageIds.size() + " messages with flow control settings.");

      if (publisher != null) {
        // When finished with the publisher, shut down to free up resources.
        publisher.shutdown();
        publisher.awaitTermination(1, TimeUnit.MINUTES);
      }
    }
  }
}

Python

Before trying this sample, follow the Python setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Python API reference documentation. 

from concurrent import futures
from google.cloud import pubsub_v1
from google.cloud.pubsub_v1.types import (
    LimitExceededBehavior,
    PublisherOptions,
    PublishFlowControl,
)

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

# Configure how many messages the publisher client can hold in memory
# and what to do when messages exceed the limit.
flow_control_settings = PublishFlowControl(
    message_limit=100,  # 100 messages
    byte_limit=10 * 1024 * 1024,  # 10 MiB
    limit_exceeded_behavior=LimitExceededBehavior.BLOCK,
)
publisher = pubsub_v1.PublisherClient(
    publisher_options=PublisherOptions(flow_control=flow_control_settings)
)
topic_path = publisher.topic_path(project_id, topic_id)
publish_futures = []

# Resolve the publish future in a separate thread.
def callback(publish_future: pubsub_v1.publisher.futures.Future) -> None:
    message_id = publish_future.result()
    print(message_id)

# Publish 1000 messages in quick succession may be constrained by
# publisher flow control.
for n in range(1, 1000):
    data = f"Message number {n}"
    # Data must be a bytestring
    data = data.encode("utf-8")
    publish_future = publisher.publish(topic_path, data)
    # Non-blocking. Allow the publisher client to batch messages.
    publish_future.add_done_callback(callback)
    publish_futures.append(publish_future)

futures.wait(publish_futures, return_when=futures.ALL_COMPLETED)

print(f"Published messages with flow control settings to {topic_path}.")

Concurrency control

Support for concurrency depends on your programming language. Refer to the API Reference documentation for more information.

The following sample illustrates how to control concurrency in a publisher:

C++

Before trying this sample, follow the C++ setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub C++ API reference documentation. 

namespace pubsub = ::google::cloud::pubsub;
using ::google::cloud::future;
using ::google::cloud::StatusOr;
[](std::string project_id, std::string topic_id) {
  auto topic = pubsub::Topic(std::move(project_id), std::move(topic_id));
  // Override the default number of background (I/O) threads. By default the
  // library uses `std::thread::hardware_concurrency()` threads.
  auto options =
      pubsub::ConnectionOptions{}.set_background_thread_pool_size(8);
  auto publisher = pubsub::Publisher(pubsub::MakePublisherConnection(
      std::move(topic), pubsub::PublisherOptions{}, std::move(options)));

  std::vector<future<void>> ids;
  for (char const* data : {"1", "2", "3", "go!"}) {
    ids.push_back(
        publisher.Publish(pubsub::MessageBuilder().SetData(data).Build())
            .then([data](future<StatusOr<std::string>> f) {
              auto s = f.get();
              if (!s) return;
              std::cout << "Sent '" << data << "' (" << *s << ")\n";
            }));
  }
  publisher.Flush();
  // Block until they are actually sent.
  for (auto& id : ids) id.get();
}

Go

Before trying this sample, follow the Go setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Go API reference documentation. 

import (
	"context"
	"fmt"
	"io"

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

func publishSingleGoroutine(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)
	}
	defer client.Close()

	t := client.Topic(topicID)
	t.PublishSettings.NumGoroutines = 1

	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

Before trying this sample, follow the Java setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Java API reference documentation. 


import com.google.api.core.ApiFuture;
import com.google.api.core.ApiFutures;
import com.google.api.gax.core.ExecutorProvider;
import com.google.api.gax.core.InstantiatingExecutorProvider;
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.ArrayList;
import java.util.List;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeUnit;

public class PublishWithConcurrencyControlExample {
  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";

    publishWithConcurrencyControlExample(projectId, topicId);
  }

  public static void publishWithConcurrencyControlExample(String projectId, String topicId)
      throws IOException, ExecutionException, InterruptedException {
    TopicName topicName = TopicName.of(projectId, topicId);
    Publisher publisher = null;
    List<ApiFuture<String>> messageIdFutures = new ArrayList<>();

    try {
      // Provides an executor service for processing messages. The default
      // `executorProvider` used by the publisher has a default thread count of
      // 5 * the number of processors available to the Java virtual machine.
      ExecutorProvider executorProvider =
          InstantiatingExecutorProvider.newBuilder().setExecutorThreadCount(4).build();

      // `setExecutorProvider` configures an executor for the publisher.
      publisher = Publisher.newBuilder(topicName).setExecutorProvider(executorProvider).build();

      // schedule publishing one message at a time : messages get automatically batched
      for (int i = 0; i < 100; i++) {
        String message = "message " + i;
        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);
        messageIdFutures.add(messageIdFuture);
      }
    } finally {
      // Wait on any pending publish requests.
      List<String> messageIds = ApiFutures.allAsList(messageIdFutures).get();

      System.out.println("Published " + messageIds.size() + " messages with concurrency control.");

      if (publisher != null) {
        // When finished with the publisher, shutdown to free up resources.
        publisher.shutdown();
        publisher.awaitTermination(1, TimeUnit.MINUTES);
      }
    }
  }
}

Ruby

Before trying this sample, follow the Ruby setup instructions in Quickstart: Using Client Libraries. For more information, see the Pub/Sub Ruby API reference documentation. 

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

pubsub = Google::Cloud::Pubsub.new

topic = pubsub.topic topic_id, async: {
  threads: {
    # Use exactly one thread for publishing message and exactly one thread
    # for executing callbacks
    publish:  1,
    callback: 1
  }
}
topic.publish_async "This is a test message." do |result|
  raise "Failed to publish the message." unless result.succeeded?
  puts "Message published asynchronously."
end

# Stop the async_publisher to send all queued messages immediately.
topic.async_publisher.stop.wait!