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https://github.com/CleverCloud/pulsar4s

Idiomatic, typesafe, and reactive Scala client for Apache Pulsar
https://github.com/CleverCloud/pulsar4s

akka-streams async cats fs2 monix pulsar reactive reactive-streams scala scalaz

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Idiomatic, typesafe, and reactive Scala client for Apache Pulsar

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# pulsar4s - Apache Pulsar Scala Client



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pulsar4s is a concise, idiomatic, reactive, type safe Scala client for [Apache Pulsar](https://pulsar.apache.org/).

As a simple wrapper over the Java client, we benefit from the reliability and performance of that client while providing better integration with the Scala ecosystem and idioms.



* Supports different effects - [scala.concurrent.Future](https://docs.scala-lang.org/overviews/core/futures.html),

[monix.eval.Task](https://monix.io/docs/2x/eval/task.html),

[cats.effect.IO](https://typelevel.org/blog/2017/05/02/io-monad-for-cats.html),

[scalaz.concurrent.Task](https://github.com/indyscala/scalaz-task-intro/blob/master/presentation.md)

* Uses scala.concurrent.duration.Duration

* Provides case classes rather than Java beans

* [Akka Streams](https://github.com/sksamuel/pulsar4s#akka-streams) source and sink

* [FS2](https://github.com/typelevel/fs2) Reader and Writer

* Circe, SprayJson, PlayJson and Jackson implementations of Schema typeclass



## Warning!!



(This disclaimer was written on 2023-01-05.)



Starting in version 2.9.0, we support scala 3. This means we had to perform some

"aggressive" bumps on libs:



Libs that were bumped for everyone:

- play-json 2.10 (Currently in RC7)

- cats-effect 3.3 (was 2.x)

- ZIO 2.0 (was 1.x) & zio-cats-interop 23.0.0



Libs that come in different versions across scala versions:

- avro4s

  - for Scala 3: 5.0+

  - for Scala 2: 4.1+

- scala-java8-compat

  - for Scala ≥2.13: 1.0.2

  - for Scala 2.12: 0.8.0 (Was already the case before scala 3)



Check carefully that bumping pulsar4s will not break, especially with **cats-effect**! 



## Using the client



The first step is to create a client attached to the pulsar cluster, providing the service url.



```scala

val client = PulsarClient("pulsar://localhost:6650")

```



Alternatively, you can use an instance of `PulsarClientConfig` if you need to set further configuration

options such as authentication, tls, timeouts and so on.



```scala

val config = PulsarClientConfig("pulsar://localhost:6650", ...)

val client = PulsarClient(config)

```



Then we can create either a producer or a consumer from the client. We need an implicit schema in scope - more on that later.



To create a producer, we need the topic, and an instance of `ProducerConfig`.

We can set further options on the config object, such as max pending messages, router mode, producer name and so on.



```scala

implicit val schema: Schema[String] = Schema.STRING



val topic = Topic("persistent://sample/standalone/ns1/b")

val producerConfig = ProducerConfig(topic, ...)

val producer = client.producer[String](producerConfig)

```



To create a consumer, we need one or more topics to subscribe to, the subscription name, and an instance of `ConsumerConfig`.

We can set further options on the config object, such as subscription type, consumer name, queue size and so on.



```scala

implicit val schema: Schema[String] = Schema.STRING



val topic = Topic("persistent://sample/standalone/ns1/b")

val consumerConfig = ConsumerConfig(Seq(topic), Subscription("mysub"), ...)

val consumerFn = client.consumer[String](ConsumerConfig(, )

```



Note: Call `close()` on the client, producer, and consumer once you are finished. The client and producer also implement `AutoCloseable` and `Closeable`.



### Schemas



A message must be the correct type for the producer or consumer. When a producer or consumer is created,

an implicit `Schema` typeclass must be available. In the earlier examples, you saw that we added an implicit schema for String using `implicit val schema: Schema[String] = Schema.STRING`.



There are built in schemas for bytes and strings, but other complex types required a custom schema.

Some people prefer to write custom typeclasses manually for the types they need to support.

Other people like to just have it done automagically. For those people, pulsar4s provides extensions

for the well known Scala Json libraries that can be used to generate messages where the body

is a JSON representation of the class.



An example of creating a producer for a complex type using the circe json library to generate the schema:



```scala

import io.circe.generic.auto._

import com.sksamuel.pulsar4s.circe._



val topic = Topic("persistent://sample/standalone/ns1/b")

val producer = client.producer[Food](ProducerConfig(topic))

producer.send(Food("pizza", "ham and pineapple"))

```



Note: The imports bring into scope a method that will generate an implicit schema when required.



The following extension modules can be used for automatic schemas



| Library | Module | Import |

|---------|------------------|--------|

|[Circe](https://github.com/travisbrown/circe)|[pulsar4s-circe](http://search.maven.org/#search%7Cga%7C1%7Cpulsar4s-circe)|import io.circe.generic.auto._ 
import com.sksamuel.pulsar4s.circe._|

|[Jackson](https://github.com/FasterXML/jackson-module-scala)|[pulsar4s-jackson](http://search.maven.org/#search%7Cga%7C1%7Cpulsar4s-jackson)|import com.sksamuel.pulsar4s.jackson._|

|Json4s|[pulsar4s-json4s](http://search.maven.org/#search%7Cga%7C1%7Cpulsar4s-json4s)|import com.sksamuel.pulsar4s.json4s._|

|Spray Json|[pulsar4s-spray-json](http://search.maven.org/#search%7Cga%7C1%7Cpulsar4s-spray-json)|import com.sksamuel.pulsar4s.sprayjson._|

|Play Json|[pulsar4s-play-json](http://search.maven.org/#search%7Cga%7C1%7Cpulsar4s-play-json)|import com.sksamuel.pulsar4s.playjson._|



### Producing



There are two ways to send a message - either with a plain value, or with an instance of `ProducerMessage`.

If you do not need to specify extra options on the message - such as key, event time, headers, etc - then you can just send

a plain value, and the client will wrap the value in a pulsar message. Alternatively, you can create an instance of `ProducerMessage`

to specify extra options.



Each method can be synchronous or asynchronous. The asynchronous methods return a `scala.concurrent.Future`.

If you are using another effect library, such as cats, scalaz or monix, then pulsar4s

also supports those effects. See the section on #effects.



If the send method is successful, you will receive the `MessageId` of the generated message. If an exception is generated, then in the synchronous methods, you will receive a `Failure` with the error. In the asynchronous

methods the exception will be surfaced as a failed Future.



To send a plain value, we just invoke `send` with the value:



```scala

producer.send("wibble")

```



Or to send a message, we first create an instance of `ProducerMessage`.



```scala

val message = DefaultProducerMessage(Some("mykey"), "wibble", eventTime = Some(EventTime(System.currentTimeMillis)))

producer.send(message)

```



### Consuming



To receive a message, create a consumer and invoke either the `receive`, `receive(Duration)`, or the `receiveAsync` methods.

The first two are synchronous and return an instance of `ConsumerMessage`, blocking if necessary, and the latter is asynchronous, returning

a Future (or other effect) with the `ConsumerMessage` once ready.



```scala

val message: Message = consumer.receive

```



or



```scala

val message: Future[T] = consumer.receiveAsync

```



Once a message has been consumed, it is important to acknowledge the message by using the message id with the ack methods.



```scala

consumer.acknowledge(message.messageId)

```



## Akka Streams



Pulsar4s integrates with the outstanding [akka-streams](https://doc.akka.io/docs/akka/2.5.5/scala/stream/index.html) library - it provides both a source and a sink.

To use this, you need to add a dependency on the `pulsar4s-akka-streams` module.



### Sources



To create a source all that is required is a function that will create a consumer on demand and the message id to seek.

The function must return a fresh consumer each time it is invoked.

The consumer is just a regular pulsar4s `Consumer` and can be created in the normal way, for example.



```scala

val topic = Topic("persistent://sample/standalone/ns1/b")

val consumerFn = () => client.consumer(ConsumerConfig(topic, subscription))

```



We pass that function into the source method, providing the seek. Note the imports.



```scala

import com.sksamuel.pulsar4s.akka.streams._

val pulsarSource = source(consumerFn, Some(MessageId.earliest))

```



The materialized value of the source is an instance of `Control` which provides a method called 'close' which can be used to stop consuming messages.

Once the akka streams source is completed (or fails) the consumer will be automatically closed.



### Sinks



To create a sink, we need a producer function similar to the source's consumer function.

Again, the producer used is just a regular pulsar4s `Producer`.

The function must return a fresh producer each time it is invoked.



```scala

val topic = Topic("persistent://sample/standalone/ns1/b")

val producerFn = () => client.producer(ProducerConfig(topic))

```



We pass that function into the sink method. Once again, take note of the imports.



```scala

import com.sksamuel.pulsar4s.akka.streams._

val pulsarSink = sink(producerFn)

```



A sink requires messages of type `ProducerMessage[T]` where T is the value type of the message. For example, if we were producing

String messages, then we would map our upstream messages into instances of `ProducerMessage[String]` before passing them to the sink.



```scala

import com.sksamuel.pulsar4s.akka.streams._

Source.fromIterator(() => List("a", "b", "c", "d").iterator)

  .map(string => ProducerMessage(string))

  .runWith(sink(producerFn))

```



A sink will run until the upstream source completes. In other words, to terminate the sink, the source must be cancelled or completed.

Once the sink completes the producer will be automatically closed.



The materialized value of the sink is a `Future[Done]` which will be completed once the upstream source has completed.



There is also an implementation of a 'multi-sink'.

Multi-sink allows to produce to multiple topics in Pulsar, while using just 1 sink.

Multi-sink expects, in addition to `ProducerMessage[T]`, a `Topic`, so the input format is `(Topic, ProducerMessage[T])`.

All producers in the sink are lazily-created, once a tuple with a new topic is received.

There is also a possibility to provide a collection of topics in the constructing function, to create those topics

ahead of time if the names are known. New topics read from the stream will also be created on-the-fly.



Example usage of a multi-sink:



```scala

import com.sksamuel.pulsar4s.akka.streams._



val topic1 = Topic("persistent://sample/standalone/ns1/b")

val topic2 = Topic("persistent://sample/standalone/ns1/bb")

val producerFn = (topic: Topic) => client.producer(ProducerConfig(topic))

val pulsarMultiSink = multiSink(producerFn)

# or to create those topics ahead of time:

val pulsarMultiSink2 = multiSink(producerFn, Set(topic1, topic2))

```



### Full Example



Here is a full example of consuming from a topic for 10 seconds, publising the messages back into another topic.

Obviously this is a bit of a toy example but shows everything in one place.



```scala

import com.sksamuel.pulsar4s.{ConsumerConfig, MessageId, ProducerConfig, PulsarClient, Subscription, Topic}

import org.apache.pulsar.client.api.Schema



implicit val system: ActorSystem = ActorSystem()

implicit val materializer: ActorMaterializer = ActorMaterializer()

implicit val schema: Schema[Array[Byte]] = Schema.BYTES



val client = PulsarClient("pulsar://localhost:6650")



val intopic = Topic("persistent://sample/standalone/ns1/in")

val outtopic = Topic("persistent://sample/standalone/ns1/out")



val consumerFn = () => client.consumer(ConsumerConfig(Seq(intopic), Subscription("mysub")))

val producerFn = () => client.producer(ProducerConfig(outtopic))



val control = source(consumerFn, Some(MessageId.earliest))

                .map { consumerMessage => ProducerMessage(consumerMessage.data) }

                .to(sink(producerFn)).run()



Thread.sleep(10000)

control.close()

```



## FS2 Support



Pulsar4s integrates with the [fs2](https://fs2.io/) library - it provides both a source and a sink.

To use this, you need to add a dependency on the `pulsar4s-{effect}` + `pulsar4s-fs2` module.



### Example



```scala

import com.sksamuel.pulsar4s._

import com.sksamuel.pulsar4s.cats.CatsAsyncHandler._

import com.sksamuel.pulsar4s.fs2.Streams



import org.apache.pulsar.client.api.Schema



implicit val schema: Schema[Array[Byte]] = Schema.BYTES



val client = PulsarClient("pulsar://localhost:6650")



val intopic = Topic("persistent://sample/standalone/ns1/in")

val outtopic = Topic("persistent://sample/standalone/ns1/out")



Streams.batch[IO, Array[Byte]](client.consumerAsync[Array[Byte], IO](ConsumerConfig(

  subscriptionName = Subscription("mysub"),

  topics = Seq(intopic),

  subscriptionInitialPosition = Some(SubscriptionInitialPosition.Earliest)

)))

  .map(_.map(ProducerMessage(_.value)))

  .through(Streams.committableSink(client.producerAsync[Array[Byte], IO](ProducerConfig(outtopic))))

  .compile

  .drain



```



## Example SBT Setup



```scala

val pulsar4sVersion = "x.x.x"

libraryDependencies ++= Seq(

  "com.clever-cloud.pulsar4s" %% "pulsar4s-core" % pulsar4sVersion,



  // for the akka-streams integration

  "com.clever-cloud.pulsar4s" %% "pulsar4s-akka-streams" % pulsar4sVersion,



  // if you want to use avro for schemas

  "com.clever-cloud.pulsar4s" %% "pulsar4s-avro" % pulsar4sVersion,



  // if you want to use circe for schemas

  "com.clever-cloud.pulsar4s" %% "pulsar4s-circe" % pulsar4sVersion,



  // if you want to use json4s for schemas

  "com.clever-cloud.pulsar4s" %% "pulsar4s-json4s" % pulsar4sVersion,



  // if you want to use jackson for schemas

  "com.clever-cloud.pulsar4s" %% "pulsar4s-jackson" % pulsar4sVersion,



  // if you want to use spray-json for schemas

  "com.clever-cloud.pulsar4s" %% "pulsar4s-spray-json" % pulsar4sVersion,



  // if you want to use play-json for schemas

  "com.clever-cloud.pulsar4s" %% "pulsar4s-play-json" % pulsar4sVersion,



  // if you want to use monix effects

  "com.clever-cloud.pulsar4s" %% "pulsar4s-monix" % pulsar4sVersion,



  // if you want to use scalaz effects

  "com.clever-cloud.pulsar4s" %% "pulsar4s-scalaz" % pulsar4sVersion,



  // if you want to use cats effects

  "com.clever-cloud.pulsar4s" %% "pulsar4s-cats-effect" % pulsar4sVersion,



  // if you want to use fs2

  "com.clever-cloud.pulsar4s" %% "pulsar4s-fs2" % pulsar4sVersion,



  // if you want to use zio

  "com.clever-cloud.pulsar4s" %% "pulsar4s-zio" % pulsar4sVersion

)

```



## Contributions

Contributions to pulsar4s are always welcome. Good ways to contribute include:



* Raising bugs and feature requests

* Improving the performance of pulsar4s

* Adding to the documentation



## License

```

This software is licensed under the Apache 2 license, quoted below.



Copyright 2017-2018 Stephen Samuel



Licensed under the Apache License, Version 2.0 (the "License"); you may not

use this file except in compliance with the License. You may obtain a copy of

the License at



    http://www.apache.org/licenses/LICENSE-2.0



Unless required by applicable law or agreed to in writing, software

distributed under the License is distributed on an "AS IS" BASIS, WITHOUT

WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the

License for the specific language governing permissions and limitations under

the License.

```