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 \
  [--attributes=KEY="VALUE",...]

Replace the following:

  • TOPIC_ID: the ID of the topic
  • MESSAGE_DATA: a base64-encoded 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
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

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.


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)
	}

	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() {
  /**
   * TODO(developer): Uncomment the following lines to run the sample.
   */
  // const topicName = 'my-topic';

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

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

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

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."""
import time

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)

futures = dict()

def get_callback(f, data):
    def callback(f):
        try:
            print(f.result())
            futures.pop(data)
        except:  # noqa
            print("Please handle {} for {}.".format(f.exception(), data))

    return callback

for i in range(10):
    data = str(i)
    futures.update({data: None})
    # When you publish a message, the client returns a future.
    future = publisher.publish(
        topic_path, data=data.encode("utf-8")  # data must be a bytestring.
    )
    futures[data] = future
    # Publish failures shall be handled in the callback function.
    future.add_done_callback(get_callback(future, data))

# Wait for all the publish futures to resolve before exiting.
while futures:
    time.sleep(5)

print("Published message with error handler.")

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.

# project_id = "Your Google Cloud Project ID"
# topic_name = "Your Pubsub topic name"
require "google/cloud/pubsub"

pubsub = Google::Cloud::Pubsub.new project: project_id

topic = pubsub.topic topic_name
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!

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
}

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"

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)
	}

	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 = u"Message number {}".format(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("Published messages with custom attributes.")

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.

# project_id = "Your Google Cloud Project ID"
# topic_name = "Your Pubsub topic name"
require "google/cloud/pubsub"

pubsub = Google::Cloud::Pubsub.new project: project_id

topic = pubsub.topic topic_name
# 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 base64-encoded 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
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

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"
]
}

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)
            .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);
    }
  }
}

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.


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)
	}
	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 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 is ten messages,
# one kilobyte of data, or one second has passed.
batch_settings = pubsub_v1.types.BatchSettings(
    max_messages=10,  # default 100
    max_bytes=1024,  # default 1 MB
    max_latency=1,  # default 10 ms
)
publisher = pubsub_v1.PublisherClient(batch_settings)
topic_path = publisher.topic_path(project_id, topic_id)

# Resolve the publish future in a separate thread.
def callback(future):
    message_id = future.result()
    print(message_id)

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

print("Published messages with batch settings.")

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.

# project_id = "Your Google Cloud Project ID"
# topic_name = "Your Pubsub topic name"
require "google/cloud/pubsub"

pubsub = Google::Cloud::Pubsub.new project: project_id

topic = pubsub.topic topic_name
topic.publish do |batch|
  10.times do |i|
    batch.publish "This is message \##{i}."
  end
end

puts "Messages published in batch."
# project_id = "Your Google Cloud Project ID"
# topic_name = "Your Pubsub topic name"
require "google/cloud/pubsub"

pubsub = Google::Cloud::Pubsub.new project: project_id

# 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_name, 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):

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
  const retrySettings = {
    retryCodes: [
      10, // 'ABORTED'
      1, // 'CANCELLED',
      4, // 'DEADLINE_EXCEEDED'
      13, // 'INTERNAL'
      8, // 'RESOURCE_EXHAUSTED'
      14, // 'UNAVAILABLE'
      2, // 'UNKNOWN'
    ],
    backoffSettings: {
      initialRetryDelayMillis: 100,
      retryDelayMultiplier: 1.3,
      maxRetryDelayMillis: 60000,
      initialRpcTimeoutMillis: 5000,
      rpcTimeoutMultiplier: 1.0,
      maxRpcTimeoutMillis: 600000,
      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.cloud import pubsub_v1

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

# Configure the retry settings. Defaults will be overwritten.
retry_settings = {
    "interfaces": {
        "google.pubsub.v1.Publisher": {
            "retry_codes": {
                "publish": [
                    "ABORTED",
                    "CANCELLED",
                    "DEADLINE_EXCEEDED",
                    "INTERNAL",
                    "RESOURCE_EXHAUSTED",
                    "UNAVAILABLE",
                    "UNKNOWN",
                ]
            },
            "retry_params": {
                "messaging": {
                    "initial_retry_delay_millis": 100,  # default: 100
                    "retry_delay_multiplier": 1.3,  # default: 1.3
                    "max_retry_delay_millis": 60000,  # default: 60000
                    "initial_rpc_timeout_millis": 5000,  # default: 25000
                    "rpc_timeout_multiplier": 1.0,  # default: 1.0
                    "max_rpc_timeout_millis": 600000,  # default: 30000
                    "total_timeout_millis": 600000,  # default: 600000
                }
            },
            "methods": {
                "Publish": {
                    "retry_codes_name": "publish",
                    "retry_params_name": "messaging",
                }
            },
        }
    }
}

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

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

print("Published messages with retry settings.")

Retry settings control both the total number of retries and exponential backoff (how long the client waits between subsequent retries). The initial RPC timeout is the time the client waits for the initial RPC to succeed before retrying. The total timeout is the time the client waits before it stops retrying. To retry publish requests, the initial RPC timeout should be shorter than the total timeout.

Once the first RPC fails or times out, the exponential backoff logic determines when the subsequent retries occur. On each retry, the RPC timeout increases by this multiplier, up to the maximum RPC timeout. In addition, the retry delay settings determine how long the client waits between getting an error or timeout and initiating the next request.

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.

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);
    }
  }
}

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:

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)
	}

	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.

# project_id = "Your Google Cloud Project ID"
# topic_name = "Your Pubsub topic name"
require "google/cloud/pubsub"

pubsub = Google::Cloud::Pubsub.new project: project_id

topic = pubsub.topic topic_name, 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!