Pulsar's WebSocket API

Pulsar's WebSocket API is meant to provide a simple way to interact with Pulsar using languages that do not have an official client library. Through WebSockets you can publish and consume messages and use all the features available in the Java, Go, Python and C++ client libraries.

You can use Pulsar's WebSocket API with any WebSocket client library. See examples for Python and Node.js below.

Running the WebSocket service

The standalone variant of Pulsar that we recommend using for local development already has the WebSocket service enabled.

In non-standalone mode, there are two ways to deploy the WebSocket service:

embedded with a Pulsar broker
as a separate component

Embedded with a Pulsar broker

In this mode, the WebSocket service will run within the same HTTP service that's already running in the broker. To enable this mode, set the webSocketServiceEnabled parameter in the conf/broker.conf configuration file in your installation.

webSocketServiceEnabled=true

As a separate component

In this mode, the WebSocket service will be run from a Pulsar broker as a separate service. Configuration for this mode is handled in the conf/websocket.conf configuration file. You'll need to set at least the following parameters:

Here's an example:

configurationStoreServers=zk1:2181,zk2:2181,zk3:2181
webServicePort=8080
clusterName=my-cluster

Starting the broker

When the configuration is set, you can start the service using the pulsar-daemon tool:

$ bin/pulsar-daemon start websocket

API Reference

Pulsar's WebSocket API offers three endpoints for producing messages, consuming messages and reading messages.

All exchanges via the WebSocket API use JSON.

Producer endpoint

The producer endpoint requires you to specify a tenant, namespace, and topic in the URL:

ws://broker-service-url:8080/ws/v2/producer/persistent/:tenant/:namespace/:topic

Query param

Key	Type	Required?	Explanation
`sendTimeoutMillis`	long	no	Send timeout (default: 30 secs)
`batchingEnabled`	boolean	no	Enable batching of messages (default: false)
`batchingMaxMessages`	int	no	Maximum number of messages permitted in a batch (default: 1000)
`maxPendingMessages`	int	no	Set the max size of the internal-queue holding the messages (default: 1000)
`batchingMaxPublishDelay`	long	no	Time period within which the messages will be batched (default: 10ms)
`messageRoutingMode`	string	no	Message routing mode for the partitioned producer: `SinglePartition`, `RoundRobinPartition`
`compressionType`	string	no	Compression type: `LZ4`, `ZLIB`
`producerName`	string	no	Specify the name for the producer. Pulsar will enforce only one producer with same name can be publishing on a topic
`initialSequenceId`	long	no	Set the baseline for the sequence ids for messages published by the producer.
`hashingScheme`	string	no	Hashing function to use when publishing on a partitioned topic: `JavaStringHash`, `Murmur3_32Hash`

Publishing a message

{
  "payload": "SGVsbG8gV29ybGQ=",
  "properties": {"key1": "value1", "key2": "value2"},
  "context": "1"
}

Key	Type	Required?	Explanation
`payload`	string	yes	Base-64 encoded payload
`properties`	key-value pairs	no	Application-defined properties
`context`	string	no	Application-defined request identifier
`key`	string	no	For partitioned topics, decides which partition to use
`replicationClusters`	array	no	Restrict replication to this list of clusters, specified by name

Example success response

{
   "result": "ok",
   "messageId": "CAAQAw==",
   "context": "1"
 }

Example failure response

 {
   "result": "send-error:3",
   "errorMsg": "Failed to de-serialize from JSON",
   "context": "1"
 }

Key	Type	Required?	Explanation
`result`	string	yes	`ok` if successful or an error message if unsuccessful
`messageId`	string	yes	Message ID assigned to the published message
`context`	string	no	Application-defined request identifier

Consumer endpoint

The consumer endpoint requires you to specify a tenant, namespace, and topic, as well as a subscription, in the URL:

ws://broker-service-url:8080/ws/v2/consumer/persistent/:tenant/:namespace/:topic/:subscription

Query param

Key	Type	Required?	Explanation
`ackTimeoutMillis`	long	no	Set the timeout for unacked messages (default: 0)
`subscriptionType`	string	no	Subscription type: `Exclusive`, `Failover`, `Shared`
`receiverQueueSize`	int	no	Size of the consumer receive queue (default: 1000)
`consumerName`	string	no	Consumer name
`priorityLevel`	int	no	Define a priority for the consumer
`maxRedeliverCount`	int	no	Define a maxRedeliverCount for the consumer (default: 0). Activates Dead Letter Topic feature.
`deadLetterTopic`	string	no	Define a deadLetterTopic for the consumer (default: {topic}-{subscription}-DLQ). Activates Dead Letter Topic feature.
`pullMode`	boolean	no	Enable pull mode (default: false). See "Flow Control" below.

NB: these parameter (except pullMode) apply to the internal consumer of the WebSocket service. So messages will be subject to the redelivery settings as soon as the get into the receive queue, even if the client doesn't consume on the WebSocket.

Receiving messages

Server will push messages on the WebSocket session:

{
  "messageId": "CAAQAw==",
  "payload": "SGVsbG8gV29ybGQ=",
  "properties": {"key1": "value1", "key2": "value2"},
  "publishTime": "2016-08-30 16:45:57.785"
}

Key	Type	Required?	Explanation
`messageId`	string	yes	Message ID
`payload`	string	yes	Base-64 encoded payload
`publishTime`	string	yes	Publish timestamp
`properties`	key-value pairs	no	Application-defined properties
`key`	string	no	Original routing key set by producer

Acknowledging the message

Consumer needs to acknowledge the successful processing of the message to have the Pulsar broker delete it.

{
  "messageId": "CAAQAw=="
}

Key	Type	Required?	Explanation
`messageId`	string	yes	Message ID of the processed message

Flow control

Push Mode

By default (pullMode=false), the consumer endpoint will use the receiverQueueSize parameter both to size its internal receive queue and to limit the number of unacknowledged messages that are passed to the WebSocket client. In this mode, if you don't send acknowledgements, the Pulsar WebSocket service will stop sending messages after reaching receiverQueueSize unacked messages sent to the WebSocket client.

Pull Mode

If you set pullMode to true, the WebSocket client will need to send permit commands to permit the Pulsar WebSocket service to send more messages.

{
  "type": "permit",
  "permitMessages": 100
}

Key	Type	Required?	Explanation
`type`	string	yes	Type of command. Must be `permit`
`permitMessages`	int	yes	Number of messages to permit

NB: in this mode it's possible to acknowledge messages in a different connection.

Reader endpoint

The reader endpoint requires you to specify a tenant, namespace, and topic in the URL:

ws://broker-service-url:8080/ws/v2/reader/persistent/:tenant/:namespace/:topic

Query param

Key	Type	Required?	Explanation
`readerName`	string	no	Reader name
`receiverQueueSize`	int	no	Size of the consumer receive queue (default: 1000)
`messageId`	int or enum	no	Message ID to start from, `earliest` or `latest` (default: `latest`)

Receiving messages

Server will push messages on the WebSocket session:

{
  "messageId": "CAAQAw==",
  "payload": "SGVsbG8gV29ybGQ=",
  "properties": {"key1": "value1", "key2": "value2"},
  "publishTime": "2016-08-30 16:45:57.785"
}

Key	Type	Required?	Explanation
`messageId`	string	yes	Message ID
`payload`	string	yes	Base-64 encoded payload
`publishTime`	string	yes	Publish timestamp
`properties`	key-value pairs	no	Application-defined properties
`key`	string	no	Original routing key set by producer

Acknowledging the message

In WebSocket, Reader needs to acknowledge the successful processing of the message to have the Pulsar WebSocket service update the number of pending messages. If you don't send acknowledgements, Pulsar WebSocket service will stop sending messages after reaching the pendingMessages limit.

{
  "messageId": "CAAQAw=="
}

Key	Type	Required?	Explanation
`messageId`	string	yes	Message ID of the processed message

Error codes

In case of error the server will close the WebSocket session using the following error codes:

Error Code	Error Message
1	Failed to create producer
2	Failed to subscribe
3	Failed to deserialize from JSON
4	Failed to serialize to JSON
5	Failed to authenticate client
6	Client is not authorized
7	Invalid payload encoding
8	Unknown error

The application is responsible for re-establishing a new WebSocket session after a backoff period.

Client examples

Below you'll find code examples for the Pulsar WebSocket API in Python and Node.js.

Python

This example uses the websocket-client package. You can install it using pip:

$ pip install websocket-client

You can also download it from PyPI.

Python producer

Here's an example Python producer that sends a simple message to a Pulsar topic:

import websocket, base64, json

TOPIC = 'ws://localhost:8080/ws/v2/producer/persistent/public/default/my-topic'

ws = websocket.create_connection(TOPIC)

# Send one message as JSON
ws.send(json.dumps({
    'payload' : base64.b64encode('Hello World'),
    'properties': {
        'key1' : 'value1',
        'key2' : 'value2'
    },
    'context' : 5
}))

response =  json.loads(ws.recv())
if response['result'] == 'ok':
    print 'Message published successfully'
else:
    print 'Failed to publish message:', response
ws.close()

Python consumer

Here's an example Python consumer that listens on a Pulsar topic and prints the message ID whenever a message arrives:

import websocket, base64, json

TOPIC = 'ws://localhost:8080/ws/v2/consumer/persistent/public/default/my-topic/my-sub'

ws = websocket.create_connection(TOPIC)

while True:
    msg = json.loads(ws.recv())
    if not msg: break

    print "Received: {} - payload: {}".format(msg, base64.b64decode(msg['payload']))

    # Acknowledge successful processing
    ws.send(json.dumps({'messageId' : msg['messageId']}))

ws.close()

Python reader

Here's an example Python reader that listens on a Pulsar topic and prints the message ID whenever a message arrives:

import websocket, base64, json

TOPIC = 'ws://localhost:8080/ws/v2/reader/persistent/public/default/my-topic'

ws = websocket.create_connection(TOPIC)

while True:
    msg = json.loads(ws.recv())
    if not msg: break

    print "Received: {} - payload: {}".format(msg, base64.b64decode(msg['payload']))

    # Acknowledge successful processing
    ws.send(json.dumps({'messageId' : msg['messageId']}))

ws.close()

Node.js

This example uses the ws package. You can install it using npm:

$ npm install ws

Node.js producer

Here's an example Node.js producer that sends a simple message to a Pulsar topic:

var WebSocket = require('ws'),
    topic = "ws://localhost:8080/ws/v2/producer/persistent/public/default/my-topic",
    ws = new WebSocket(topic);

var message = {
  "payload" : new Buffer("Hello World").toString('base64'),
  "properties": {
    "key1" : "value1",
    "key2" : "value2"
  },
  "context" : "1"
};

ws.on('open', function() {
  // Send one message
  ws.send(JSON.stringify(message));
});

ws.on('message', function(message) {
  console.log('received ack: %s', message);
});

Node.js consumer

Here's an example Node.js consumer that listens on the same topic used by the producer above:

var WebSocket = require('ws'),
    topic = "ws://localhost:8080/ws/v2/consumer/persistent/public/default/my-topic/my-sub",
    ws = new WebSocket(topic);

ws.on('message', function(message) {
    var receiveMsg = JSON.parse(message);
    console.log('Received: %s - payload: %s', message, new Buffer(receiveMsg.payload, 'base64').toString());
    var ackMsg = {"messageId" : receiveMsg.messageId};
    ws.send(JSON.stringify(ackMsg));
});

NodeJS reader

var WebSocket = require('ws'),
    topic = "ws://localhost:8080/ws/v2/reader/persistent/public/default/my-topic",
    ws = new WebSocket(topic);

ws.on('message', function(message) {
    var receiveMsg = JSON.parse(message);
    console.log('Received: %s - payload: %s', message, new Buffer(receiveMsg.payload, 'base64').toString());
    var ackMsg = {"messageId" : receiveMsg.messageId};
    ws.send(JSON.stringify(ackMsg));
});

Running the WebSocket service​

Embedded with a Pulsar broker​

As a separate component​

Starting the broker​

API Reference​

Producer endpoint​

Query param​

Publishing a message​

Example success response​

Example failure response​

Consumer endpoint​

Query param​

Receiving messages​

Acknowledging the message​

Flow control​

Push Mode​

Pull Mode​

Reader endpoint​

Query param​

Receiving messages​

Acknowledging the message​

Error codes​

Client examples​

Python​

Python producer​

Python consumer​

Python reader​

Node.js​

Node.js producer​

Node.js consumer​

NodeJS reader​

Running the WebSocket service

Embedded with a Pulsar broker

As a separate component

Starting the broker

API Reference

Producer endpoint

Query param

Publishing a message

Example success response

Example failure response

Consumer endpoint

Query param

Receiving messages

Acknowledging the message

Flow control

Push Mode

Pull Mode

Reader endpoint

Query param

Receiving messages

Acknowledging the message

Error codes

Client examples

Python

Python producer

Python consumer

Python reader

Node.js

Node.js producer

Node.js consumer

NodeJS reader