Pulsar WebSocket API
Pulsar WebSocket API provides a simple way to interact with Pulsar using languages that do not have an official client library. You can use Pulsar WebSocket API with any WebSocket client library. See Python and Node.js examples for more details.
Through WebSocket, you can publish and consume messages and use features available on the Client Feature Matrix page.
Run 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:
configurationMetadataStoreUrl=zk1:2181,zk2:2181,zk3:2181
webServicePort=8080
clusterName=my-cluster
Security settings​
To enable TLS encryption on WebSocket service, configure the following parameters in the conf/broker.conf
file.
tlsEnabled=true
tlsAllowInsecureConnection=false
tlsCertificateFilePath=/path/to/client-websocket.cert.pem
tlsKeyFilePath=/path/to/client-websocket.key-pk8.pem
tlsTrustCertsFilePath=/path/to/ca.cert.pem
To enable encryption at rest on WebSocket service, add CryptoKeyReaderFactory factory class in classpath which will create CryptoKeyReader for WebSocket and that helps to load encryption keys for producer/consumer.
cryptoKeyReaderFactoryClassName=org.apache.pulsar.MyCryptoKeyReaderFactoryClassImpl
Start the broker​
When the configuration is set, you can start the service using the pulsar-daemon
tool:
bin/pulsar-daemon start websocket
Release notes​
For the changelog of Pulsar WebSocket APIs, see release notes.
API Reference​
Pulsar's WebSocket API offers three endpoints for producing, consuming, and reading messages.
All exchanges via the WebSocket API use JSON.
Authentication​
Browser javascript WebSocket client​
Use the query param token
to transport the authentication token.
ws://broker-service-url:8080/path?token=token
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 |
token | string | no | Authentication token, this is used for the browser javascript client |
encryptionKeys | string | no | Encryption key to encrypt published message only if encryption reader is configured using cryptoKeyReaderFactoryClassName config in websocket-configuration. |
Publish 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 , Key_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. |
negativeAckRedeliveryDelay | int | no | When a message is negatively acknowledged, the delay time before the message is redelivered (in milliseconds). The default value is 60000. |
token | string | no | Authentication token, this is used for the browser javascript client |
These parameters (except pullMode
) apply to the internal consumers of the WebSocket service.
So messages will be subject to the redelivery settings as soon as they get into the receive queue,
even if the client doesn't consume on the WebSocket.
Receive messages​
Server will push messages on the WebSocket session:
{
"messageId": "CAMQADAA",
"payload": "hvXcJvHW7kOSrUn17P2q71RA5SdiXwZBqw==",
"properties": {},
"publishTime": "2021-10-29T16:01:38.967-07:00",
"redeliveryCount": 0,
"encryptionContext": {
"keys": {
"client-rsa.pem": {
"keyValue": "jEuwS+PeUzmCo7IfLNxqoj4h7txbLjCQjkwpaw5AWJfZ2xoIdMkOuWDkOsqgFmWwxiecakS6GOZHs94x3sxzKHQx9Oe1jpwBg2e7L4fd26pp+WmAiLm/ArZJo6JotTeFSvKO3u/yQtGTZojDDQxiqFOQ1ZbMdtMZA8DpSMuq+Zx7PqLo43UdW1+krjQfE5WD+y+qE3LJQfwyVDnXxoRtqWLpVsAROlN2LxaMbaftv5HckoejJoB4xpf/dPOUqhnRstwQHf6klKT5iNhjsY4usACt78uILT0pEPd14h8wEBidBz/vAlC/zVMEqiDVzgNS7dqEYS4iHbf7cnWVCn3Hxw==",
"metadata": {}
}
},
"param": "Tfu1PxVm6S9D3+Hk",
"compressionType": "NONE",
"uncompressedMessageSize": 0,
"batchSize": {
"empty": false,
"present": true
}
}
}
Below are the parameters in the WebSocket consumer response.
General parameters
Key Type Required? Explanation messageId
string yes Message ID payload
string yes Base-64 encoded payload publishTime
string yes Publish timestamp redeliveryCount
number yes Number of times this message was already delivered properties
key-value pairs no Application-defined properties key
string no Original routing key set by producer encryptionContext
EncryptionContext no Encryption context that consumers can use to decrypt received messages param
string no Initialization vector for cipher (Base64 encoding) batchSize
string no Number of entries in a message (if it is a batch message) uncompressedMessageSize
string no Message size before compression compressionType
string no Algorithm used to compress the message payload encryptionContext
related parameterKey Type Required? Explanation keys
key-EncryptionKey pairs yes Key in key-EncryptionKey
pairs is an encryption key name. Value inkey-EncryptionKey
pairs is an encryption key object.encryptionKey
related parametersKey Type Required? Explanation keyValue
string yes Encryption key (Base64 encoding) metadata
key-value pairs no Application-defined metadata
Acknowledge 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 |
Negatively acknowledge messages​
{
"type": "negativeAcknowledge",
"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 acknowledgments, 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 |
In this mode it's possible to acknowledge messages in a different connection.
Check if reach the end of topic​
Consumers can check if it has reached the end of a topic by sending the isEndOfTopic
request.
Request
{
"type": "isEndOfTopic"
}
Key | Type | Required? | Explanation |
---|---|---|---|
type | string | yes | Type of command. Must be isEndOfTopic |
Response
{
"endOfTopic": "true/false"
}
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 ) |
token | string | no | Authentication token, this is used for the browser javascript client |
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",
"redeliveryCount": 4
}
Key | Type | Required? | Explanation |
---|---|---|---|
messageId | string | yes | Message ID |
payload | string | yes | Base-64 encoded payload |
publishTime | string | yes | Publish timestamp |
redeliveryCount | number | yes | Number of times this message was already delivered |
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 acknowledgments, 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 |
Check if reach the end of topic​
Consumers can check if it has reached the end of a topic by sending the isEndOfTopic
request.
Request
{
"type": "isEndOfTopic"
}
Key | Type | Required? | Explanation |
---|---|---|---|
type | string | yes | Type of command. Must be isEndOfTopic |
Response
{
"endOfTopic": "true/false"
}
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
# If set enableTLS to true, your have to set tlsEnabled to true in conf/websocket.conf.
enable_TLS = False
scheme = 'ws'
if enable_TLS:
scheme = 'wss'
TOPIC = scheme + '://localhost:8080/ws/v2/producer/persistent/public/default/my-topic'
ws = websocket.create_connection(TOPIC)
# encode message
s = "Hello World"
firstEncoded = s.encode("UTF-8")
binaryEncoded = base64.b64encode(firstEncoded)
payloadString = binaryEncoded.decode('UTF-8')
# Send one message as JSON
ws.send(json.dumps({
'payload' : payloadString,
'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
# If set enableTLS to true, your have to set tlsEnabled to true in conf/websocket.conf.
enable_TLS = False
scheme = 'ws'
if enable_TLS:
scheme = 'wss'
TOPIC = scheme + '://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
# If set enableTLS to true, your have to set tlsEnabled to true in conf/websocket.conf.
enable_TLS = False
scheme = 'ws'
if enable_TLS:
scheme = 'wss'
TOPIC = scheme + '://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:
const WebSocket = require('ws');
// If set enableTLS to true, your have to set tlsEnabled to true in conf/websocket.conf.
const enableTLS = false;
const topic = `${enableTLS ? 'wss' : 'ws'}://localhost:8080/ws/v2/producer/persistent/public/default/my-topic`;
const ws = new WebSocket(topic);
var message = {
"payload" : new Buffer("Hello World").toString('base64'),
"properties": {
"key1" : "value1",
"key2" : "value2"
},
"context" : "1"
};
ws.on('open', function() {
// Send one message
ws.send(JSON.stringify(message));
});
ws.on('message', function(message) {
console.log('received ack: %s', message);
});
Node.js consumer​
Here's an example Node.js consumer that listens on the same topic used by the producer above:
const WebSocket = require('ws');
// If set enableTLS to true, your have to set tlsEnabled to true in conf/websocket.conf.
const enableTLS = false;
const topic = `${enableTLS ? 'wss' : 'ws'}://localhost:8080/ws/v2/consumer/persistent/public/default/my-topic/my-sub`;
const 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​
const WebSocket = require('ws');
// If set enableTLS to true, your have to set tlsEnabled to true in conf/websocket.conf.
const enableTLS = false;
const topic = `${enableTLS ? 'wss' : 'ws'}://localhost:8080/ws/v2/reader/persistent/public/default/my-topic`;
const 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));
});