A Topic object allows you to interact with a Cloud Pub/Sub topic.
Package
@google-cloud/pubsub
Examples
const {PubSub} = require('@google-cloud/pubsub');
const pubsub = new PubSub();
const topic = pubsub.topic('my-topic');
To enable message ordering, set enableMessageOrdering to true. Please note that this does not persist to an actual topic.
const topic = pubsub.topic('ordered-topic', {enableMessageOrdering: true});
Constructors
(constructor)(pubsub, name, options)
constructor(pubsub: PubSub, name: string, options?: PublishOptions);
Constructs a new instance of the Topic class
Properties
getSubscriptionsStream
getSubscriptionsStream: () => ObjectStream<Subscription>;
iam
metadata?: TopicMetadata;
name
parent
publisher
pubsub
request
request: typeof PubSub.prototype.request;
Methods
create(gaxOpts)
create(gaxOpts?: CallOptions): Promise<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];
});
create(callback)
create(callback: CreateTopicCallback): void;
| Returns |
| Type |
Description |
void |
|
create(gaxOpts, callback)
create(gaxOpts: CallOptions, callback: CreateTopicCallback): void;
| Returns |
| Type |
Description |
void |
|
createSubscription(name, callback)
createSubscription(name: string, callback: CreateSubscriptionCallback): void;
Create a subscription to this topic.
| Returns |
| Type |
Description |
void |
{Promise
|
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];
});
createSubscription(name, options)
createSubscription(name: string, options?: CreateSubscriptionOptions): Promise<CreateSubscriptionResponse>;
createSubscription(name, options, callback)
createSubscription(name: string, options: CreateSubscriptionOptions, callback: CreateSubscriptionCallback): void;
| Returns |
| Type |
Description |
void |
|
delete(callback)
delete(callback: EmptyCallback): void;
Delete the topic. This will not delete subscriptions to this topic.
| Parameter |
| Name |
Description |
callback |
EmptyCallback
The callback function.
|
| Returns |
| Type |
Description |
void |
|
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];
});
delete(gaxOpts)
delete(gaxOpts?: CallOptions): Promise<EmptyResponse>;
| Parameter |
| Name |
Description |
gaxOpts |
CallOptions
|
delete(gaxOpts, callback)
delete(gaxOpts: CallOptions, callback: EmptyCallback): void;
| Parameters |
| Name |
Description |
gaxOpts |
CallOptions
|
callback |
EmptyCallback
|
| Returns |
| Type |
Description |
void |
|
exists()
exists(): Promise<ExistsResponse>;
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];
});
exists(callback)
exists(callback: ExistsCallback): void;
| Returns |
| Type |
Description |
void |
|
flowControlled()
flowControlled(): FlowControlledPublisher;
Creates a FlowControlledPublisher for this Topic.
FlowControlledPublisher is a helper that lets you control how many messages are simultaneously queued to send, to avoid ballooning memory usage on a low bandwidth connection to Pub/Sub.
Note that it's perfectly fine to create more than one on the same Topic. The actual flow control settings on the Topic will apply across all FlowControlledPublisher objects on that Topic.
| Returns |
| Type |
Description |
FlowControlledPublisher |
{FlowControlledPublisher} The flow control helper.
|
flush()
Immediately sends all remaining queued data. This is mostly useful if you are planning to call close() on the PubSub object that holds the server connections.
| Returns |
| Type |
Description |
Promise<void> |
{Promise
|
flush(callback)
flush(callback: EmptyCallback): void;
| Returns |
| Type |
Description |
void |
|
static formatName_(projectId: string, name: string): string;
Format the name of a topic. A Topic's full name is in the format of 'projects/{projectId}/topics/{topicName}'.
{string}
| Parameters |
| Name |
Description |
projectId |
string
|
name |
string
|
| Returns |
| Type |
Description |
string |
|
get(callback)
get(callback: GetTopicCallback): void;
Get a topic if it exists.
| Returns |
| Type |
Description |
void |
{Promise
|
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];
});
get(gaxOpts)
get(gaxOpts?: GetTopicOptions): Promise<GetTopicResponse>;
get(gaxOpts, callback)
get(gaxOpts: GetTopicOptions, callback: GetTopicCallback): void;
| Returns |
| Type |
Description |
void |
|
getMetadata(callback: GetTopicMetadataCallback): void;
Get the official representation of this topic from the API.
| Returns |
| Type |
Description |
void |
{Promise
|
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];
});
getMetadata(gaxOpts: CallOptions, callback: GetTopicMetadataCallback): void;
| Returns |
| Type |
Description |
void |
|
getMetadata(gaxOpts?: CallOptions): Promise<GetTopicMetadataResponse>;
| Parameter |
| Name |
Description |
gaxOpts |
CallOptions
|
getPublishOptionDefaults()
getPublishOptionDefaults(): PublishOptions;
Get the default publisher options. These may be modified and passed back into .
const {PubSub} = require('@google-cloud/pubsub');
const pubsub = new PubSub();
const topic = pubsub.topic('my-topic');
const defaults = topic.getPublishOptionDefaults();
defaults.batching.maxMilliseconds = 10;
topic.setPublishOptions(defaults);
getSubscriptions(callback)
getSubscriptions(callback: GetTopicSubscriptionsCallback): void;
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.
| Returns |
| Type |
Description |
void |
{Promise
|
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];
});
getSubscriptions(options, callback)
getSubscriptions(options: PageOptions, callback: GetTopicSubscriptionsCallback): void;
| Returns |
| Type |
Description |
void |
|
getSubscriptions(options)
getSubscriptions(options?: PageOptions): Promise<GetTopicSubscriptionsResponse>;
publish(data, attributes)
publish(data: Buffer, attributes?: Attributes): Promise<string>;
Publish the provided message.
| Parameters |
| Name |
Description |
data |
Buffer
The message data. This must come in the form of a Buffer object.
|
attributes |
Attributes
Attributes for this message.
|
| Returns |
| Type |
Description |
Promise<string> |
{Promise
|
Examples
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) => {});
publish(data, callback)
publish(data: Buffer, callback: PublishCallback): void;
| Returns |
| Type |
Description |
void |
|
publish(data, attributes, callback)
publish(data: Buffer, attributes: Attributes, callback: PublishCallback): void;
| Returns |
| Type |
Description |
void |
|
publishJSON(json, attributes)
publishJSON(json: object, attributes?: Attributes): Promise<string>;
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. objects will always return message data in the form of a Buffer, so any JSON published will require manual deserialization.
| Parameters |
| Name |
Description |
json |
object
The JSON data to publish.
|
attributes |
Attributes
Attributes for this message.
|
| Returns |
| Type |
Description |
Promise<string> |
{Promise
|
Examples
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) => {});
publishJSON(json, callback)
publishJSON(json: object, callback: PublishCallback): void;
| Returns |
| Type |
Description |
void |
|
publishJSON(json, attributes, callback)
publishJSON(json: object, attributes: Attributes, callback: PublishCallback): void;
| Returns |
| Type |
Description |
void |
|
publishMessage(message)
publishMessage(message: MessageOptions): Promise<string>;
Publish the provided message.
| Parameter |
| Name |
Description |
message |
MessageOptions
Message object.
|
| Returns |
| Type |
Description |
Promise<string> |
{Promise
|
Examples
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.publishMessage({data}, callback);
Publish JSON message data.
const json = {foo: 'bar'};
topic.publishMessage({json}, callback);
To publish messages in order (this is still experimental), make sure message ordering is enabled and provide an ordering key
const topic = pubsub.topic('ordered-topic', {messageOrdering: true});
const orderingKey = 'my-key';
topic.publishMessage({data, orderingKey}, callback);
If the callback is omitted, we'll return a Promise.
const messageId = await topic.publishMessage({data});
publishMessage(message, callback)
publishMessage(message: MessageOptions, callback: PublishCallback): void;
| Parameters |
| Name |
Description |
message |
MessageOptions
|
callback |
PublishCallback
|
| Returns |
| Type |
Description |
void |
|
resumePublishing(orderingKey)
resumePublishing(orderingKey: string): void;
In the event that the client fails to publish an ordered message, all subsequent publish calls using the same ordering key will fail. Calling this method will disregard the publish failure, allowing the supplied ordering key to be used again in the future.
| Parameter |
| Name |
Description |
orderingKey |
string
The ordering key in question.
|
| Returns |
| Type |
Description |
void |
|
Example
const {PubSub} = require('@google-cloud/pubsub');
const pubsub = new PubSub();
const topic = pubsub.topic('my-topic', {messageOrdering: true});
const orderingKey = 'foo';
const data = Buffer.from('Hello, order!');
topic.publishMessage({data, orderingKey}, err => {
if (err) {
topic.resumePublishing(orderingKey);
}
});
setMetadata(options: TopicMetadata, gaxOpts?: CallOptions): Promise<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.
}
});
If the callback is omitted, we'll return a Promise.
topic.setMetadata(metadata).then((data) => {
const apiResponse = data[0];
});
setMetadata(options: TopicMetadata, callback: SetTopicMetadataCallback): void;
| Returns |
| Type |
Description |
void |
|
setMetadata(options: TopicMetadata, gaxOpts: CallOptions, callback: SetTopicMetadataCallback): void;
| Returns |
| Type |
Description |
void |
|
setPublishOptions(options)
setPublishOptions(options: PublishOptions): void;
Set the publisher options.
| Parameter |
| Name |
Description |
options |
PublishOptions
The publisher options.
|
| Returns |
| Type |
Description |
void |
|
Example
const {PubSub} = require('@google-cloud/pubsub');
const pubsub = new PubSub();
const topic = pubsub.topic('my-topic');
topic.setPublishOptions({
batching: {
maxMilliseconds: 10
}
});
subscription(name, options)
subscription(name: string, options?: SubscriptionOptions): 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.
| Parameters |
| Name |
Description |
name |
string
Name of the subscription.
|
options |
SubscriptionOptions
Configuration object. {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.
});
