The Pulsar Node.js client

The Pulsar Node.js client can be used to create Pulsar producers, consumers, and readers in Node.js.

All the methods in producers, consumers, and readers of a Node.js client are thread-safe.

Installation

You can install the pulsar-client library via npm.

Requirements

Pulsar Node.js client library is based on the C++ client library. Follow these instructions and install the Pulsar C++ client library.

Compatibility

Compatibility between each version of the Node.js client and the C++ client is as follows:

Node.js client	C++ client
1.0.0	2.3.0 or later
1.1.0	2.4.0 or later
1.2.0	2.5.0 or later

If an incompatible version of the C++ client is installed, you may fail to build or run this library.

Installation using npm

Install the pulsar-client library via npm:

$ npm install pulsar-client

note

Also, this library works only in Node.js 10.x or later because it uses the node-addon-api module to wrap the C++ library.

Connection URLs

To connect to Pulsar using client libraries, you need to specify a Pulsar protocol URL.

Pulsar protocol URLs are assigned to specific clusters, use the pulsar scheme and have a default port of 6650. Here is an example for localhost:

pulsar://localhost:6650

A URL for a production Pulsar cluster may look something like this:

pulsar://pulsar.us-west.example.com:6650

If you are using TLS encryption or TLS Authentication, the URL will look like something like this:

pulsar+ssl://pulsar.us-west.example.com:6651

Create a client

In order to interact with Pulsar, you will first need a client object. You can create a client instance using a new operator and the Client method, passing in a client options object (more on configuration below).

Here is an example:

const Pulsar = require('pulsar-client');

(async () => {
  const client = new Pulsar.Client({
    serviceUrl: 'pulsar://localhost:6650',
  });

  await client.close();
})();

Client configuration

The following configurable parameters are available for Pulsar clients:

Parameter	Description	Default
`serviceUrl`	The connection URL for the Pulsar cluster. See above for more info.
`authentication`	Configure the authentication provider. (default: no authentication). See TLS Authentication for more info.
`operationTimeoutSeconds`	The timeout for Node.js client operations (creating producers, subscribing to and unsubscribing from topics). Retries will occur until this threshold is reached, at which point the operation will fail.	30
`ioThreads`	The number of threads to use for handling connections to Pulsar brokers.	1
`messageListenerThreads`	The number of threads used by message listeners (consumers and readers).	1
`concurrentLookupRequest`	The number of concurrent lookup requests that can be sent on each broker connection. Setting a maximum helps to keep from overloading brokers. You should set values over the default of 50000 only if the client needs to produce and/or subscribe to thousands of Pulsar topics.	50000
`tlsTrustCertsFilePath`	The file path for the trusted TLS certificate.
`tlsValidateHostname`	The boolean value of setup whether to enable TLS hostname verification.	`false`
`tlsAllowInsecureConnection`	The boolean value of setup whether the Pulsar client accepts untrusted TLS certificate from broker.	`false`
`statsIntervalInSeconds`	Interval between each stat info. Stats is activated with positive statsInterval. The value should be set to 1 second at least	600
`log`	A function that is used for logging.	`console.log`

Producers

Pulsar producers publish messages to Pulsar topics. You can configure Node.js producers using a producer configuration object.

Here is an example:

const producer = await client.createProducer({
  topic: 'my-topic', // or 'my-tenant/my-namespace/my-topic' to specify topic's tenant and namespace
});

await producer.send({
  data: Buffer.from("Hello, Pulsar"),
});

await producer.close();

Promise operation

When you create a new Pulsar producer, the operation will return Promise object and get producer instance or an error through executor function. In this example, using await operator instead of executor function.

Producer operations

Pulsar Node.js producers have the following methods available:

Method	Description	Return type
`send(Object)`	Publishes a message to the producer's topic. When the message is successfully acknowledged by the Pulsar broker, or an error will be thrown, the Promise object run executor function.	`Promise<null>`
`flush()`	Sends message from send queue to Pulsar broker. When the message is successfully acknowledged by the Pulsar broker, or an error will be thrown, the Promise object run executor function.	`Promise<null>`
`close()`	Closes the producer and releases all resources allocated to it. If `close()` is called then no more messages will be accepted from the publisher. This method will return Promise object, and when all pending publish requests have been persisted by Pulsar then run executor function. If an error is thrown, no pending writes will be retried.	`Promise<null>`

Producer configuration

Parameter	Description	Default
`topic`	The Pulsar topic to which the producer publishes messages. The topic format is `<topic-name>` or `<tenant-name>/<namespace-name>/<topic-name>`. For example, `sample/ns1/my-topic`.
`producerName`	A name for the producer. If you do not explicitly assign a name, Pulsar will automatically generate a globally unique name. If you choose to explicitly assign a name, it will need to be unique across all Pulsar clusters, otherwise the creation operation will throw an error.
`sendTimeoutMs`	When publishing a message to a topic, the producer will wait for an acknowledgment from the responsible Pulsar broker. If a message is not acknowledged within the threshold set by this parameter, an error will be thrown. If you set `sendTimeoutMs` to -1, the timeout will be set to infinity (and thus removed). Removing the send timeout is recommended when using Pulsar's message de-duplication feature.	30000
`initialSequenceId`	The initial sequence ID of the message. When producer send message, add sequence ID to message. The ID is increased each time to send.
`maxPendingMessages`	The maximum size of the queue holding pending messages (i.e. messages waiting to receive an acknowledgment from the broker). By default, when the queue is full all calls to the `send` method will fail unless `blockIfQueueFull` is set to `true`.	1000
`maxPendingMessagesAcrossPartitions`	The maximum size of the sum of partition's pending queue.	50000
`blockIfQueueFull`	If set to `true`, the producer's `send` method will wait when the outgoing message queue is full rather than failing and throwing an error (the size of that queue is dictated by the `maxPendingMessages` parameter); if set to `false` (the default), `send` operations will fail and throw a error when the queue is full.	`false`
`messageRoutingMode`	The message routing logic (for producers on partitioned topics). This logic is applied only when no key is set on messages. The available options are: round robin (`RoundRobinDistribution`), or publishing all messages to a single partition (`UseSinglePartition`, the default).	`UseSinglePartition`
`hashingScheme`	The hashing function that determines the partition on which a particular message is published (partitioned topics only). The available options are: `JavaStringHash` (the equivalent of `String.hashCode()` in Java), `Murmur3_32Hash` (applies the Murmur3 hashing function), or `BoostHash` (applies the hashing function from C++'s Boost library).	`BoostHash`
`compressionType`	The message data compression type used by the producer. The available options are `LZ4`, and `Zlib`.	Compression None
`batchingEnabled`	If set to `true`, the producer send message as batch.	`true`
`batchingMaxPublishDelayMs`	The maximum time of delay sending message in batching.	10
`batchingMaxMessages`	The maximum size of sending message in each time of batching.	1000
`properties`	The metadata of producer.

Producer example

This example creates a Node.js producer for the my-topic topic and sends 10 messages to that topic:

const Pulsar = require('pulsar-client');

(async () => {
  // Create a client
  const client = new Pulsar.Client({
    serviceUrl: 'pulsar://localhost:6650',
  });

  // Create a producer
  const producer = await client.createProducer({
    topic: 'my-topic',
  });

  // Send messages
  for (let i = 0; i < 10; i += 1) {
    const msg = `my-message-${i}`;
    producer.send({
      data: Buffer.from(msg),
    });
    console.log(`Sent message: ${msg}`);
  }
  await producer.flush();

  await producer.close();
  await client.close();
})();

Consumers

Pulsar consumers subscribe to one or more Pulsar topics and listen for incoming messages produced on that topic/those topics. You can configure Node.js consumers using a consumer configuration object.

Here is an example:

const consumer = await client.subscribe({
  topic: 'my-topic',
  subscription: 'my-subscription',
});

const msg = await consumer.receive();
console.log(msg.getData().toString());
consumer.acknowledge(msg);

await consumer.close();

Promise operation

When you create a new Pulsar consumer, the operation will return Promise object and get consumer instance or an error through executor function. In this example, using await operator instead of executor function.

Consumer operations

Pulsar Node.js consumers have the following methods available:

Method	Description	Return type
`receive()`	Receives a single message from the topic. When the message is available, the Promise object run executor function and get message object.	`Promise<Object>`
`receive(Number)`	Receives a single message from the topic with specific timeout in milliseconds.	`Promise<Object>`
`acknowledge(Object)`	Acknowledges a message to the Pulsar broker by message object.	`void`
`acknowledgeId(Object)`	Acknowledges a message to the Pulsar broker by message ID object.	`void`
`acknowledgeCumulative(Object)`	Acknowledges all the messages in the stream, up to and including the specified message. The `acknowledgeCumulative` method will return void, and send the ack to the broker asynchronously. After that, the messages will not be redelivered to the consumer. Cumulative acking can not be used with a shared subscription type.	`void`
`acknowledgeCumulativeId(Object)`	Acknowledges all the messages in the stream, up to and including the specified message ID.	`void`
`negativeAcknowledge(Message)`	Negatively acknowledges a message to the Pulsar broker by message object.	`void`
`negativeAcknowledgeId(MessageId)`	Negatively acknowledges a message to the Pulsar broker by message ID object.	`void`
`close()`	Closes the consumer, disabling its ability to receive messages from the broker.	`Promise<null>`

Consumer configuration

Parameter	Description	Default
`topic`	The Pulsar topic on which the consumer will establish a subscription and listen for messages.
`subscription`	The subscription name for this consumer.
`subscriptionType`	Available options are `Exclusive`, `Shared`, `Key_Shared`, and `Failover`.	`Exclusive`
`subscriptionInitialPosition`	Initial position at which to set cursor when subscribing to a topic at first time.	`SubscriptionInitialPosition.Latest`
`ackTimeoutMs`	Acknowledge timeout in milliseconds.	0
`nAckRedeliverTimeoutMs`	Delay to wait before redelivering messages that failed to be processed.	60000
`receiverQueueSize`	Sets the size of the consumer's receiver queue, i.e. the number of messages that can be accumulated by the consumer before the application calls `receive`. A value higher than the default of 1000 could increase consumer throughput, though at the expense of more memory utilization.	1000
`receiverQueueSizeAcrossPartitions`	Set the max total receiver queue size across partitions. This setting will be used to reduce the receiver queue size for individual partitions if the total exceeds this value.	50000
`consumerName`	The name of consumer. Currently(v2.4.1), failover mode use consumer name in ordering.
`properties`	The metadata of consumer.
`listener`	A listener that is called for a message received.
`readCompacted`	If enabling `readCompacted`, a consumer reads messages from a compacted topic rather than reading a full message backlog of a topic. A consumer only sees the latest value for each key in the compacted topic, up until reaching the point in the topic message when compacting backlog. Beyond that point, send messages as normal. `readCompacted` can only be enabled on subscriptions to persistent topics, which have a single active consumer (like failure or exclusive subscriptions). Attempting to enable it on subscriptions to non-persistent topics or on shared subscriptions leads to a subscription call throwing a `PulsarClientException`.	false

Consumer example

This example creates a Node.js consumer with the my-subscription subscription on the my-topic topic, receives messages, prints the content that arrive, and acknowledges each message to the Pulsar broker for 10 times:

const Pulsar = require('pulsar-client');

(async () => {
  // Create a client
  const client = new Pulsar.Client({
    serviceUrl: 'pulsar://localhost:6650',
  });

  // Create a consumer
  const consumer = await client.subscribe({
    topic: 'my-topic',
    subscription: 'my-subscription',
    subscriptionType: 'Exclusive',
  });

  // Receive messages
  for (let i = 0; i < 10; i += 1) {
    const msg = await consumer.receive();
    console.log(msg.getData().toString());
    consumer.acknowledge(msg);
  }

  await consumer.close();
  await client.close();
})();

Instead a consumer can be created with listener to process messages.

// Create a consumer
const consumer = await client.subscribe({
  topic: 'my-topic',
  subscription: 'my-subscription',
  subscriptionType: 'Exclusive',
  listener: (msg, msgConsumer) => {
    console.log(msg.getData().toString());
    msgConsumer.acknowledge(msg);
  },
});

Readers

Pulsar readers process messages from Pulsar topics. Readers are different from consumers because with readers you need to explicitly specify which message in the stream you want to begin with (consumers, on the other hand, automatically begin with the most recently unacked message). You can configure Node.js readers using a reader configuration object.

Here is an example:

const reader = await client.createReader({
  topic: 'my-topic',
  startMessageId: Pulsar.MessageId.earliest(),
});

const msg = await reader.readNext();
console.log(msg.getData().toString());

await reader.close();

Reader operations

Pulsar Node.js readers have the following methods available:

Method	Description	Return type
`readNext()`	Receives the next message on the topic (analogous to the `receive` method for consumers). When the message is available, the Promise object run executor function and get message object.	`Promise<Object>`
`readNext(Number)`	Receives a single message from the topic with specific timeout in milliseconds.	`Promise<Object>`
`hasNext()`	Return whether the broker has next message in target topic.	`Boolean`
`close()`	Closes the reader, disabling its ability to receive messages from the broker.	`Promise<null>`

Reader configuration

Parameter	Description	Default
`topic`	The Pulsar topic on which the reader will establish a subscription and listen for messages.
`startMessageId`	The initial reader position, i.e. the message at which the reader begins processing messages. The options are `Pulsar.MessageId.earliest` (the earliest available message on the topic), `Pulsar.MessageId.latest` (the latest available message on the topic), or a message ID object for a position that is not earliest or latest.
`receiverQueueSize`	Sets the size of the reader's receiver queue, i.e. the number of messages that can be accumulated by the reader before the application calls `readNext`. A value higher than the default of 1000 could increase reader throughput, though at the expense of more memory utilization.	1000
`readerName`	The name of the reader.
`subscriptionRolePrefix`	The subscription role prefix.
`readCompacted`	If enabling `readCompacted`, a consumer reads messages from a compacted topic rather than reading a full message backlog of a topic. A consumer only sees the latest value for each key in the compacted topic, up until reaching the point in the topic message when compacting backlog. Beyond that point, send messages as normal. `readCompacted` can only be enabled on subscriptions to persistent topics, which have a single active consumer (like failure or exclusive subscriptions). Attempting to enable it on subscriptions to non-persistent topics or on shared subscriptions leads to a subscription call throwing a `PulsarClientException`.	`false`

Reader example

This example creates a Node.js reader with the my-topic topic, reads messages, and prints the content that arrive for 10 times:

const Pulsar = require('pulsar-client');

(async () => {
  // Create a client
  const client = new Pulsar.Client({
    serviceUrl: 'pulsar://localhost:6650',
    operationTimeoutSeconds: 30,
  });

  // Create a reader
  const reader = await client.createReader({
    topic: 'my-topic',
    startMessageId: Pulsar.MessageId.earliest(),
  });

  // read messages
  for (let i = 0; i < 10; i += 1) {
    const msg = await reader.readNext();
    console.log(msg.getData().toString());
  }

  await reader.close();
  await client.close();
})();

Messages

In Pulsar Node.js client, you have to construct producer message object for producer.

Here is an example message:

const msg = {
  data: Buffer.from('Hello, Pulsar'),
  partitionKey: 'key1',
  properties: {
    'foo': 'bar',
  },
  eventTimestamp: Date.now(),
  replicationClusters: [
    'cluster1',
    'cluster2',
  ],
}

await producer.send(msg);

The following keys are available for producer message objects:

Parameter	Description
`data`	The actual data payload of the message.
`properties`	A Object for any application-specific metadata attached to the message.
`eventTimestamp`	The timestamp associated with the message.
`sequenceId`	The sequence ID of the message.
`partitionKey`	The optional key associated with the message (particularly useful for things like topic compaction).
`replicationClusters`	The clusters to which this message will be replicated. Pulsar brokers handle message replication automatically; you should only change this setting if you want to override the broker default.

Message object operations

In Pulsar Node.js client, you can receive (or read) message object as consumer (or reader).

The message object have the following methods available:

Method	Description	Return type
`getTopicName()`	Getter method of topic name.	`String`
`getProperties()`	Getter method of properties.	`Array<Object>`
`getData()`	Getter method of message data.	`Buffer`
`getMessageId()`	Getter method of message id object.	`Object`
`getPublishTimestamp()`	Getter method of publish timestamp.	`Number`
`getEventTimestamp()`	Getter method of event timestamp.	`Number`
`getRedeliveryCount()`	Getter method of redelivery count.	`Number`
`getPartitionKey()`	Getter method of partition key.	`String`

Message ID object operations

In Pulsar Node.js client, you can get message id object from message object.

The message id object have the following methods available:

Method	Description	Return type
`serialize()`	Serialize the message id into a Buffer for storing.	`Buffer`
`toString()`	Get message id as String.	`String`

The client has static method of message id object. You can access it as Pulsar.MessageId.someStaticMethod too.

The following static methods are available for the message id object:

Method	Description	Return type
`earliest()`	MessageId representing the earliest, or oldest available message stored in the topic.	`Object`
`latest()`	MessageId representing the latest, or last published message in the topic.	`Object`
`deserialize(Buffer)`	Deserialize a message id object from a Buffer.	`Object`

Installation​

Requirements​

Compatibility​

Installation using npm​

Connection URLs​

Create a client​

Client configuration​

Producers​

Promise operation​

Producer operations​

Producer configuration​

Producer example​

Consumers​

Promise operation​

Consumer operations​

Consumer configuration​

Consumer example​

Readers​

Reader operations​

Reader configuration​

Reader example​

Messages​

Message object operations​

Message ID object operations​

Installation

Requirements

Compatibility

Installation using npm

Connection URLs

Create a client

Client configuration

Producers

Promise operation

Producer operations

Producer configuration

Producer example

Consumers

Promise operation

Consumer operations

Consumer configuration

Consumer example

Readers

Reader operations

Reader configuration

Reader example

Messages

Message object operations

Message ID object operations