Topic

class

A Topic object allows you to interact with a Cloud Pub/Sub topic.

Constructor

Topic

new Topic(pubsub, name)

Parameter

pubsub

PubSub

PubSub object.

name

string

Name of the topic.

Example 

const {PubSub} = require('@google-cloud/pubsub');
const pubsub = new PubSub();

const topic = pubsub.topic('my-topic');

Properties

iam

IAM (Identity and Access Management) allows you to set permissions on individual resources and offers a wider range of roles: editor, owner, publisher, subscriber, and viewer. This gives you greater flexibility and allows you to set more fine-grained access control.

The IAM access control features described in this document are Beta, including the API methods to get and set IAM policies, and to test IAM permissions. Cloud Pub/Sub's use of IAM features is not covered by any SLA or deprecation policy, and may be subject to backward-incompatible changes.

Mixes in
IAM
See also

Access Control Overview

What is Cloud IAM?

Example 

const {PubSub} = require('@google-cloud/pubsub');
const pubsub = new PubSub();

const topic = pubsub.topic('my-topic');

//-
// Get the IAM policy for your topic.
//-
topic.iam.getPolicy((err, policy) => {
  console.log(policy);
});

//-
// If the callback is omitted, we'll return a Promise.
//-
topic.iam.getPolicy().then((data) => {
  const policy = data[0];
  const apiResponse = data[1];
});

name

string

The fully qualified name of this topic.

parent

PubSub

The parent PubSub instance of this topic instance.

pubsub

PubSub

The parent PubSub instance of this topic instance.

Methods

create

create(gaxOpts, callback) returns Promise containing CreateTopicResponse

Create a topic.

Parameter

gaxOpts

Optional

object

Request configuration options, outlined here: https://googleapis.github.io/gax-nodejs/CallSettings.html.

callback

Optional

CreateTopicCallback

Callback function.
Returns

Promise containing CreateTopicResponse 

Example 

const {PubSub} = require('@google-cloud/pubsub');
const pubsub = new PubSub();

const topic = pubsub.topic('my-topic');

topic.create((err, topic, apiResponse) => {
  if (!err) {
    // The topic was created successfully.
  }
});

//-
// If the callback is omitted, we'll return a Promise.
//-
topic.create().then((data) => {
  const topic = data[0];
  const apiResponse = data[1];
});

createSubscription

createSubscription(name, options, callback) returns Promise containing CreateSubscriptionResponse

Create a subscription to this topic.

Parameter

name

string

The name of the subscription.

options

Optional

CreateSubscriptionRequest

See a Subscription resource.

callback

Optional

CreateSubscriptionCallback

Callback function.
See also

Subscriptions: create API Documentation

Throws

Error 

If subscription name is omitted.

Returns

Promise containing CreateSubscriptionResponse 

Example 

const {PubSub} = require('@google-cloud/pubsub');
const pubsub = new PubSub();

const topic = pubsub.topic('my-topic');
const callback = function(err, subscription, apiResponse) {};

// Without specifying any options.
topic.createSubscription('newMessages', callback);

// With options.
topic.createSubscription('newMessages', {
  ackDeadlineSeconds: 90
}, callback);

//-
// If the callback is omitted, we'll return a Promise.
//-
topic.createSubscription('newMessages').then((data) => {
  const subscription = data[0];
  const apiResponse = data[1];
});

delete

delete(gaxOpts, callback)

Delete the topic. This will not delete subscriptions to this topic.

Parameter

gaxOpts

Optional

object

Request configuration options, outlined here: https://googleapis.github.io/gax-nodejs/CallSettings.html.

callback

Optional

function()

The callback function.

Values in callback have the following properties:

Parameter

err

error

An error returned while making this request.

Value may be null.

apiResponse

object

Raw API response.
See also

Topics: delete API Documentation

Example 

const {PubSub} = require('@google-cloud/pubsub');
const pubsub = new PubSub();

const topic = pubsub.topic('my-topic');

topic.delete((err, apiResponse) => {});

//-
// If the callback is omitted, we'll return a Promise.
//-
topic.delete().then((data) => {
  const apiResponse = data[0];
});

exists

exists(callback) returns Promise containing TopicExistsResponse

Check if a topic exists.

Parameter

callback

Optional

TopicExistsCallback

Callback function.
Returns

Promise containing TopicExistsResponse 

Example 

const {PubSub} = require('@google-cloud/pubsub');
const pubsub = new PubSub();

const topic = pubsub.topic('my-topic');

topic.exists((err, exists) => {});

//-
// If the callback is omitted, we'll return a Promise.
//-
topic.exists().then((data) => {
  const exists = data[0];
});

get

get(gaxOpts, callback) returns Promise containing GetTopicResponse

Get a topic if it exists.

Parameter

gaxOpts

Optional

object

Request configuration options, outlined here: https://googleapis.github.io/gax-nodejs/CallSettings.html.

Values in gaxOpts have the following properties:

Parameter

autoCreate

Optional

boolean

Automatically create the topic does not already exist.

callback

Optional

GetTopicCallback

Callback function.
Returns

Promise containing GetTopicResponse 

Example 

const {PubSub} = require('@google-cloud/pubsub');
const pubsub = new PubSub();

const topic = pubsub.topic('my-topic');

topic.get((err, topic, apiResponse) => {
  // The `topic` data has been populated.
});

//-
// If the callback is omitted, we'll return a Promise.
//-
topic.get().then((data) => {
  const topic = data[0];
  const apiResponse = data[1];
});

getMetadata

getMetadata(gaxOpts, callback) returns Promise containing GetTopicMetadataResponse

Get the official representation of this topic from the API.

Parameter

gaxOpts

Optional

object

Request configuration options, outlined here: https://googleapis.github.io/gax-nodejs/CallSettings.html.

callback

Optional

GetTopicMetadataCallback

Callback function.
See also

Topics: get API Documentation

Returns

Promise containing GetTopicMetadataResponse 

Example 

const {PubSub} = require('@google-cloud/pubsub');
const pubsub = new PubSub();

const topic = pubsub.topic('my-topic');

topic.getMetadata((err, apiResponse) => {});

//-
// If the callback is omitted, we'll return a Promise.
//-
topic.getMetadata().then((data) => {
  const apiResponse = data[0];
});

getSubscriptions

getSubscriptions(query, callback) returns Promise containing GetSubscriptionsResponse

Get a list of the subscriptions registered to this topic. You may optionally provide a query object as the first argument to customize the response.

Your provided callback will be invoked with an error object if an API error occurred or an array of {module:pubsub/subscription} objects.

Parameter

query

Optional

GetSubscriptionsRequest

Query object for listing subscriptions.

callback

Optional

GetSubscriptionsCallback

Callback function.
See also

Subscriptions: list API Documentation

Returns

Promise containing GetSubscriptionsResponse 

Example 

const {PubSub} = require('@google-cloud/pubsub');
const pubsub = new PubSub();

const topic = pubsub.topic('my-topic');

topic.getSubscriptions((err, subscriptions) => {
  // subscriptions is an array of `Subscription` objects.
});

// Customize the query.
topic.getSubscriptions({
  pageSize: 3
}, callback);

//-
// If the callback is omitted, we'll return a Promise.
//-
topic.getSubscriptions().then((data) => {
  const subscriptions = data[0];
});

publish

publish(data, attributes, callback) returns Promise containing PublishResponse

Publish the provided message.

Parameter

data

buffer

The message data. This must come in the form of a Buffer object.

attributes

Optional

Object with string properties

Attributes for this message.

callback

Optional

PublishCallback

Callback function.
Throws

TypeError 

If data is not a Buffer object.

TypeError 

If any value in attributes object is not a string.

Returns

Promise containing PublishResponse 

Example 

const {PubSub} = require('@google-cloud/pubsub');
const pubsub = new PubSub();

const topic = pubsub.topic('my-topic');
const data = Buffer.from('Hello, world!');

const callback = (err, messageId) => {
  if (err) {
    // Error handling omitted.
  }
};

topic.publish(data, callback);

//-
// Optionally you can provide an object containing attributes for the
// message. Note that all values in the object must be strings.
//-
const attributes = {
  key: 'value'
};

topic.publish(data, attributes, callback);

//-
// If the callback is omitted, we'll return a Promise.
//-
topic.publish(data).then((messageId) => {});

publishJSON

publishJSON(json, attributes, callback) returns Promise containing PublishResponse

Publish the provided JSON. It should be noted that all messages published are done so in the form of a Buffer. This is simply a convenience method that will transform JSON into a Buffer before publishing. Subscription objects will always return message data in the form of a Buffer, so any JSON published will require manual deserialization.

Parameter

json

object

The JSON data to publish.

attributes

Optional

object

Attributes for this message.

callback

Optional

PublishCallback

Callback function.
See also
Topic#publish
Throws

Error 

If non-object data is provided.

Returns

Promise containing PublishResponse 

Example 

const {PubSub} = require('@google-cloud/pubsub');
const pubsub = new PubSub();
const topic = pubsub.topic('my-topic');

const data = {
  foo: 'bar'
};

const callback = (err, messageId) => {
  if (err) {
    // Error handling omitted.
  }
};

topic.publishJSON(data, callback);

//-
// Optionally you can provide an object containing attributes for the
// message. Note that all values in the object must be strings.
//-
const attributes = {
  key: 'value'
};

topic.publishJSON(data, attributes, callback);

//-
// If the callback is omitted, we'll return a Promise.
//-
topic.publishJSON(data).then((messageId) => {});

setMetadata

setMetadata(metadata, gaxOpts, callback) returns Promise containing SetTopicMetadataResponse

Updates the topic.

Parameter

metadata

object

The fields to update. This should be structured like a Topic object.

gaxOpts

Optional

object

Request configuration options, outlined here: https://googleapis.github.io/gax-nodejs/CallSettings.html.

callback

Optional

SetTopicMetadataCallback

Callback function.
See also

UpdateTopicRequest API Documentation

Returns

Promise containing SetTopicMetadataResponse 

Examples 

const {PubSub} = require('@google-cloud/pubsub');
const pubsub = new PubSub();

const topic = pubsub.topic('my-topic');
const metadata = {
  labels: {foo: 'bar'}
};

topic.setMetadata(metadata, err => {
  if (err) {
    // Error handling omitted.
  }
});
<caption>If the callback is omitted, we'll return a
Promise.</caption>
topic.setMetadata(metadata).then((data) => {
  const apiResponse = data[0];
});

setPublishOptions

setPublishOptions(options)

Set the publisher options.

Parameter

options

PublishOptions

The publisher options.

Example 

const {PubSub} = require('@google-cloud/pubsub');
const pubsub = new PubSub();

const topic = pubsub.topic('my-topic');

topic.setPublishOptions({
  batching: {
    maxMilliseconds: 10
  }
});

subscription

subscription(name, options) returns Subscription

Create a Subscription object. This command by itself will not run any API requests. You will receive a {module:pubsub/subscription} object, which will allow you to interact with a subscription.

Parameter

name

string

Name of the subscription.

options

Optional

object

Configuration object.

Values in options have the following properties:

Parameter

flowControl

Optional

object

Flow control configurations for receiving messages. Note that these options do not persist across subscription instances.

flowControl.maxBytes

Optional

number

The maximum number of bytes in un-acked messages to allow before the subscription pauses incoming messages. Defaults to 20% of free memory.

flowControl.maxMessages

Optional

number

The maximum number of un-acked messages to allow before the subscription pauses incoming messages.

maxConnections

Optional

number

Use this to limit the number of connections to be used when sending and receiving messages.
Throws

Error 

If subscription name is omitted.

Returns

Subscription 

Example 

const {PubSub} = require('@google-cloud/pubsub');
const pubsub = new PubSub();

const topic = pubsub.topic('my-topic');
const subscription = topic.subscription('my-subscription');

// Register a listener for `message` events.
subscription.on('message', (message) => {
  // Called every time a message is received.
  // message.id = ID of the message.
  // message.ackId = ID used to acknowledge the message receival.
  // message.data = Contents of the message.
  // message.attributes = Attributes of the message.
  // message.publishTime = Timestamp when Pub/Sub received the message.
});