Pulsar Go client

Tips: Currently, the CGo client will be deprecated, if you want to know more about the CGo client, please refer to CGo client docs

You can use Pulsar Go client to create Pulsar producers, consumers, and readers in Go (aka Golang).

API docs available as well For standard API docs, consult the Godoc.

Installation

Install go package

You can install the pulsar library locally using go get.

$ go get -u "github.com/apache/pulsar-client-go/pulsar"

Once installed locally, you can import it into your project:

import "github.com/apache/pulsar-client-go/pulsar"

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's 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're using 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'll first need a Client object. You can create a client object using the NewClient function, passing in a ClientOptions object (more on configuration below). Here's an example:

import (
	"log"
	"time"

	"github.com/apache/pulsar-client-go/pulsar"
)

func main() {
	client, err := pulsar.NewClient(pulsar.ClientOptions{
		URL:               "pulsar://localhost:6650",
		OperationTimeout:  30 * time.Second,
		ConnectionTimeout: 30 * time.Second,
	})
	if err != nil {
		log.Fatalf("Could not instantiate Pulsar client: %v", err)
	}

	defer client.Close()
}

The following configurable parameters are available for Pulsar clients:

Name	Description	Default
URL	Configure the service URL for the Pulsar service. This parameter is required
ConnectionTimeout	Timeout for the establishment of a TCP connection	30s
OperationTimeout	Set the operation timeout. Producer-create, subscribe and unsubscribe operations will be retried until this interval, after which the operation will be marked as failed	30s
Authentication	Configure the authentication provider. Example: Authentication: NewAuthenticationTLS("my-cert.pem", "my-key.pem")	no authentication
TLSTrustCertsFilePath	Set the path to the trusted TLS certificate file
TLSAllowInsecureConnection	Configure whether the Pulsar client accept untrusted TLS certificate from broker	false
TLSValidateHostname	Configure whether the Pulsar client verify the validity of the host name from broker	false

Producers

Pulsar producers publish messages to Pulsar topics. You can configure Go producers using a ProducerOptions object. Here's an example:

producer, err := client.CreateProducer(pulsar.ProducerOptions{
	Topic: "my-topic",
})

_, err = producer.Send(context.Background(), &pulsar.ProducerMessage{
	Payload: []byte("hello"),
})

defer producer.Close()

if err != nil {
	fmt.Println("Failed to publish message", err)
}
fmt.Println("Published message")

Producer operations

Pulsar Go producers have the following methods available:

Method	Description	Return type
Topic()	Fetches the producer's topic	string
Name()	Fetches the producer's name	string
Send(context.Context, *ProducerMessage)	Publishes a message to the producer's topic. This call will block until the message is successfully acknowledged by the Pulsar broker, or an error will be thrown if the timeout set using the SendTimeout in the producer's configuration is exceeded.	(MessageID, error)
SendAsync(context.Context, *ProducerMessage, func(MessageID, *ProducerMessage, error))	Send a message, this call will be blocking until is successfully acknowledged by the Pulsar broker.
LastSequenceID()	Get the last sequence id that was published by this producer. his represent either the automatically assigned or custom sequence id (set on the ProducerMessage) that was published and acknowledged by the broker.	int64
Flush()	Flush all the messages buffered in the client and wait until all messages have been successfully persisted.	error
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 block until all pending publish requests have been persisted by Pulsar. If an error is thrown, no pending writes will be retried.

Producer Example

How to use message router in producer

client, err := NewClient(ClientOptions{
	URL: serviceURL,
})

if err != nil {
	log.Fatal(err)
}
defer client.Close()

// Only subscribe on the specific partition
consumer, err := client.Subscribe(ConsumerOptions{
	Topic:            "my-partitioned-topic-partition-2",
	SubscriptionName: "my-sub",
})

if err != nil {
	log.Fatal(err)
}
defer consumer.Close()

producer, err := client.CreateProducer(ProducerOptions{
	Topic: "my-partitioned-topic",
	MessageRouter: func(msg *ProducerMessage, tm TopicMetadata) int {
		fmt.Println("Routing message ", msg, " -- Partitions: ", tm.NumPartitions())
		return 2
	},
})

if err != nil {
	log.Fatal(err)
}
defer producer.Close()

How to use delay relative in producer

client, err := NewClient(ClientOptions{
	URL: "pulsar://localhost:6650",
})
if err != nil {
	log.Fatal(err)
}
defer client.Close()

topicName := newTopicName()
producer, err := client.CreateProducer(pulsar.ProducerOptions{
    Topic:           topicName,
    DisableBatching: true,
})
if err != nil {
	log.Fatal(err)
}
defer producer.Close()

consumer, err := client.Subscribe(ConsumerOptions{
	Topic:            topicName,
	SubscriptionName: "subName",
	Type:             Shared,
})
if err != nil {
	log.Fatal(err)
}
defer consumer.Close()

ID, err := producer.Send(context.Background(), &ProducerMessage{
	Payload:      []byte(fmt.Sprintf("test")),
	DeliverAfter: 3 * time.Second,
})
if err != nil {
	log.Fatal(err)
}
fmt.Println(ID)

ctx, canc := context.WithTimeout(context.Background(), 1*time.Second)
msg, err := consumer.Receive(ctx)
if err != nil {
	log.Fatal(err)
}
fmt.Println(msg.Payload())
canc()

ctx, canc = context.WithTimeout(context.Background(), 5*time.Second)
msg, err = consumer.Receive(ctx)
if err != nil {
	log.Fatal(err)
}
fmt.Println(msg.Payload())
canc()

Producer configuration

Name	Description	Default
Topic	Topic specify the topic this consumer will subscribe to. This argument is required when constructing the reader.
Name	Name specify a name for the producer. If not assigned, the system will generate a globally unique name which can be access with Producer.ProducerName().
Properties	Properties attach a set of application defined properties to the producer This properties will be visible in the topic stats
MaxPendingMessages	MaxPendingMessages set the max size of the queue holding the messages pending to receive an acknowledgment from the broker.
HashingScheme	HashingScheme change the HashingScheme used to chose the partition on where to publish a particular message.	JavaStringHash
CompressionType	CompressionType set the compression type for the producer.	not compressed
MessageRouter	MessageRouter set a custom message routing policy by passing an implementation of MessageRouter
DisableBatching	DisableBatching control whether automatic batching of messages is enabled for the producer.	false
BatchingMaxPublishDelay	BatchingMaxPublishDelay set the time period within which the messages sent will be batched	1ms
BatchingMaxMessages	BatchingMaxMessages set the maximum number of messages permitted in a batch.	1000

Consumers

Pulsar consumers subscribe to one or more Pulsar topics and listen for incoming messages produced on that topic/those topics. You can configure Go consumers using a ConsumerOptions object. Here's a basic example that uses channels:

consumer, err := client.Subscribe(pulsar.ConsumerOptions{
	Topic:            "topic-1",
	SubscriptionName: "my-sub",
	Type:             pulsar.Shared,
})
if err != nil {
	log.Fatal(err)
}
defer consumer.Close()

for i := 0; i < 10; i++ {
	msg, err := consumer.Receive(context.Background())
	if err != nil {
		log.Fatal(err)
	}

	fmt.Printf("Received message msgId: %#v -- content: '%s'\n",
		msg.ID(), string(msg.Payload()))

	consumer.Ack(msg)
}

if err := consumer.Unsubscribe(); err != nil {
	log.Fatal(err)
}

Consumer operations

Pulsar Go consumers have the following methods available:

Method	Description	Return type
Subscription()	Returns the consumer's subscription name	string
Unsubcribe()	Unsubscribes the consumer from the assigned topic. Throws an error if the unsubscribe operation is somehow unsuccessful.	error
Receive(context.Context)	Receives a single message from the topic. This method blocks until a message is available.	(Message, error)
Ack(Message)	Acknowledges a message to the Pulsar broker
AckID(MessageID)	Acknowledges a message to the Pulsar broker by message ID
Nack(Message)	Acknowledge the failure to process a single message.
NackID(MessageID)	Acknowledge the failure to process a single message.
Seek(msgID MessageID)	Reset the subscription associated with this consumer to a specific message id. The message id can either be a specific message or represent the first or last messages in the topic.	error
SeekByTime(time time.Time)	Reset the subscription associated with this consumer to a specific message publish time.	error
Close()	Closes the consumer, disabling its ability to receive messages from the broker

Receive example

How to use regx consumer

client, err := pulsar.NewClient(pulsar.ClientOptions{
    URL: "pulsar://localhost:6650",
})

defer client.Close()

p, err := client.CreateProducer(ProducerOptions{
	Topic:           topicInRegex,
	DisableBatching: true,
})
if err != nil {
	log.Fatal(err)
}
defer p.Close()

topicsPattern := fmt.Sprintf("persistent://%s/foo.*", namespace)
opts := ConsumerOptions{
	TopicsPattern:    topicsPattern,
	SubscriptionName: "regex-sub",
}
consumer, err := client.Subscribe(opts)
if err != nil {
	log.Fatal(err)
}
defer consumer.Close()

How to use multi topics Consumer

func newTopicName() string {
	return fmt.Sprintf("my-topic-%v", time.Now().Nanosecond())
}


topic1 := "topic-1"
topic2 := "topic-2"

client, err := NewClient(ClientOptions{
	URL: "pulsar://localhost:6650",
})
if err != nil {
	log.Fatal(err)
}
topics := []string{topic1, topic2}
consumer, err := client.Subscribe(ConsumerOptions{
	Topics:           topics,
	SubscriptionName: "multi-topic-sub",
})
if err != nil {
	log.Fatal(err)
}
defer consumer.Close()

How to use consumer listener

import (
	"fmt"
	"log"

	"github.com/apache/pulsar-client-go/pulsar"
)

func main() {
	client, err := pulsar.NewClient(pulsar.ClientOptions{URL: "pulsar://localhost:6650"})
	if err != nil {
		log.Fatal(err)
	}

	defer client.Close()

	channel := make(chan pulsar.ConsumerMessage, 100)

	options := pulsar.ConsumerOptions{
		Topic:            "topic-1",
		SubscriptionName: "my-subscription",
		Type:             pulsar.Shared,
	}

	options.MessageChannel = channel

	consumer, err := client.Subscribe(options)
	if err != nil {
		log.Fatal(err)
	}

	defer consumer.Close()

	// Receive messages from channel. The channel returns a struct which contains message and the consumer from where
	// the message was received. It's not necessary here since we have 1 single consumer, but the channel could be
	// shared across multiple consumers as well
	for cm := range channel {
		msg := cm.Message
		fmt.Printf("Received message  msgId: %v -- content: '%s'\n",
			msg.ID(), string(msg.Payload()))

		consumer.Ack(msg)
	}
}

How to use consumer receive timeout

client, err := NewClient(ClientOptions{
	URL: "pulsar://localhost:6650",
})
if err != nil {
	log.Fatal(err)
}
defer client.Close()

topic := "test-topic-with-no-messages"
ctx, cancel := context.WithTimeout(context.Background(), 500*time.Millisecond)
defer cancel()

// create consumer
consumer, err := client.Subscribe(ConsumerOptions{
	Topic:            topic,
	SubscriptionName: "my-sub1",
	Type:             Shared,
})
if err != nil {
	log.Fatal(err)
}
defer consumer.Close()

msg, err := consumer.Receive(ctx)
fmt.Println(msg.Payload())
if err != nil {
	log.Fatal(err)
}

Consumer configuration

Name	Description	Default
Topic	Topic specify the topic this consumer will subscribe to. This argument is required when constructing the reader.
Topics	Specify a list of topics this consumer will subscribe on. Either a topic, a list of topics or a topics pattern are required when subscribing
TopicsPattern	Specify a regular expression to subscribe to multiple topics under the same namespace. Either a topic, a list of topics or a topics pattern are required when subscribing
AutoDiscoveryPeriod	Specify the interval in which to poll for new partitions or new topics if using a TopicsPattern.
SubscriptionName	Specify the subscription name for this consumer. This argument is required when subscribing
Name	Set the consumer name
Properties	Properties attach a set of application defined properties to the producer This properties will be visible in the topic stats
Type	Select the subscription type to be used when subscribing to the topic.	Exclusive
SubscriptionInitialPosition	InitialPosition at which the cursor will be set when subscribe	Latest
DLQ	Configuration for Dead Letter Queue consumer policy.	no DLQ
MessageChannel	Sets a MessageChannel for the consumer. When a message is received, it will be pushed to the channel for consumption
ReceiverQueueSize	Sets the size of the consumer receive queue.	1000
NackRedeliveryDelay	The delay after which to redeliver the messages that failed to be processed	1min
ReadCompacted	If enabled, the consumer will read messages from the compacted topic rather than reading the full message backlog of the topic	false
ReplicateSubscriptionState	Mark the subscription as replicated to keep it in sync across clusters	false

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 recent unacked message). You can configure Go readers using a ReaderOptions object. Here's an example:

reader, err := client.CreateReader(pulsar.ReaderOptions{
	Topic:          "topic-1",
	StartMessageID: pulsar.EarliestMessageID(),
})
if err != nil {
	log.Fatal(err)
}
defer reader.Close()

Reader operations

Pulsar Go readers have the following methods available:

Method	Description	Return type
Topic()	Returns the reader's topic	string
Next(context.Context)	Receives the next message on the topic (analogous to the Receive method for consumers). This method blocks until a message is available.	(Message, error)
HasNext()	Check if there is any message available to read from the current position	(bool, error)
Close()	Closes the reader, disabling its ability to receive messages from the broker	error

Reader example

How to use reader to read 'next' message

Here's an example usage of a Go reader that uses the Next() method to process incoming messages:

import (
	"context"
	"fmt"
	"log"

	"github.com/apache/pulsar-client-go/pulsar"
)

func main() {
	client, err := pulsar.NewClient(pulsar.ClientOptions{URL: "pulsar://localhost:6650"})
	if err != nil {
		log.Fatal(err)
	}

	defer client.Close()

	reader, err := client.CreateReader(pulsar.ReaderOptions{
		Topic:          "topic-1",
		StartMessageID: pulsar.EarliestMessageID(),
	})
	if err != nil {
		log.Fatal(err)
	}
	defer reader.Close()

	for reader.HasNext() {
		msg, err := reader.Next(context.Background())
		if err != nil {
			log.Fatal(err)
		}

		fmt.Printf("Received message msgId: %#v -- content: '%s'\n",
			msg.ID(), string(msg.Payload()))
	}
}

In the example above, the reader begins reading from the earliest available message (specified by pulsar.EarliestMessage). The reader can also begin reading from the latest message (pulsar.LatestMessage) or some other message ID specified by bytes using the DeserializeMessageID function, which takes a byte array and returns a MessageID object. Here's an example:

lastSavedId := // Read last saved message id from external store as byte[]

reader, err := client.CreateReader(pulsar.ReaderOptions{
    Topic:          "my-golang-topic",
    StartMessageID: pulsar.DeserializeMessageID(lastSavedId),
})

How to use reader to read specific message

client, err := NewClient(ClientOptions{
	URL: lookupURL,
})

if err != nil {
	log.Fatal(err)
}
defer client.Close()

topic := "topic-1"
ctx := context.Background()

// create producer
producer, err := client.CreateProducer(ProducerOptions{
	Topic:           topic,
	DisableBatching: true,
})
if err != nil {
	log.Fatal(err)
}
defer producer.Close()

// send 10 messages
msgIDs := [10]MessageID{}
for i := 0; i < 10; i++ {
	msgID, err := producer.Send(ctx, &ProducerMessage{
		Payload: []byte(fmt.Sprintf("hello-%d", i)),
	})
	assert.NoError(t, err)
	assert.NotNil(t, msgID)
	msgIDs[i] = msgID
}

// create reader on 5th message (not included)
reader, err := client.CreateReader(ReaderOptions{
	Topic:          topic,
	StartMessageID: msgIDs[4],
})

if err != nil {
	log.Fatal(err)
}
defer reader.Close()

// receive the remaining 5 messages
for i := 5; i < 10; i++ {
	msg, err := reader.Next(context.Background())
	if err != nil {
	log.Fatal(err)
}

// create reader on 5th message (included)
readerInclusive, err := client.CreateReader(ReaderOptions{
	Topic:                   topic,
	StartMessageID:          msgIDs[4],
	StartMessageIDInclusive: true,
})

if err != nil {
	log.Fatal(err)
}
defer readerInclusive.Close()

Reader configuration

Name	Description	Default
Topic	Topic specify the topic this consumer will subscribe to. This argument is required when constructing the reader.
Name	Name set the reader name.
Properties	Attach a set of application defined properties to the reader. This properties will be visible in the topic stats
StartMessageID	StartMessageID initial reader positioning is done by specifying a message id.
StartMessageIDInclusive	If true, the reader will start at the StartMessageID, included. Default is false and the reader will start from the "next" message	false
MessageChannel	MessageChannel sets a MessageChannel for the consumer When a message is received, it will be pushed to the channel for consumption
ReceiverQueueSize	ReceiverQueueSize sets the size of the consumer receive queue.	1000
SubscriptionRolePrefix	SubscriptionRolePrefix set the subscription role prefix.	"reader"
ReadCompacted	If enabled, the reader will read messages from the compacted topic rather than reading the full message backlog of the topic. ReadCompacted can only be enabled when reading from a persistent topic.	false

Messages

The Pulsar Go client provides a ProducerMessage interface that you can use to construct messages to producer on Pulsar topics. Here's an example message:

msg := pulsar.ProducerMessage{
    Payload: []byte("Here is some message data"),
    Key: "message-key",
    Properties: map[string]string{
        "foo": "bar",
    },
    EventTime: time.Now(),
    ReplicationClusters: []string{"cluster1", "cluster3"},
}

if _, err := producer.send(msg); err != nil {
    log.Fatalf("Could not publish message due to: %v", err)
}

The following methods parameters are available for ProducerMessage objects:

Parameter	Description
Payload	The actual data payload of the message
Key	The optional key associated with the message (particularly useful for things like topic compaction)
Properties	A key-value map (both keys and values must be strings) for any application-specific metadata attached to the message
EventTime	The timestamp associated with the message
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.
SequenceID	Set the sequence id to assign to the current message
DeliverAfter	Request to deliver the message only after the specified relative delay
DeliverAt	Deliver the message only at or after the specified absolute timestamp

TLS encryption and authentication

In order to use TLS encryption, you'll need to configure your client to do so:

• Use pulsar+ssl URL type
• Set TLSTrustCertsFilePath to the path to the TLS certs used by your client and the Pulsar broker
• Configure Authentication option

Here's an example:

opts := pulsar.ClientOptions{
    URL: "pulsar+ssl://my-cluster.com:6651",
    TLSTrustCertsFilePath: "/path/to/certs/my-cert.csr",
    Authentication: NewAuthenticationTLS("my-cert.pem", "my-key.pem"),
}