kafka4s - Functional programming with Kafka and Scala

kafka4s provides pure, referentially transparent functions for working with Kafka, and integrates with FP libraries such as cats-effect and fs2.

Quick Start

To use kafka4s in an existing SBT project with Scala 2.13 or a later version, add the following dependencies to your build.sbt depending on your needs:

resolvers += "confluent" at "https://packages.confluent.io/maven/"

libraryDependencies ++= Seq(
  "com.banno" %% "kafka4s" % "<version>"
)

Sending records to Kafka is an effect. If we wanted to periodically write random integers to a Kafka topic, we could do:

Stream
  .resource(ProducerApi.resource[F, Int, Int](BootstrapServers(kafkaBootstrapServers)))
  .flatMap { producer =>
    Stream
      .awakeDelay[F](1 second)
      .evalMap { _ =>
        Sync[F].delay(Random.nextInt()).flatMap { i =>
          producer.sendAndForget(new ProducerRecord(topic.name, i, i))
        }
      }
  }

Polling Kafka for records is also an effect, and we can obtain a stream of records from a topic. We can print the even random integers from the above topic using:

Stream.resource(
  ConsumerApi.resource[F, Int, Int](
    BootstrapServers(kafkaBootstrapServers),
    GroupId("example3"),
    AutoOffsetReset.earliest,
    EnableAutoCommit(true)
  )
)
  .evalTap(_.subscribe(topic.name))
  .flatMap(
    _.recordStream(1.second)
      .map(_.value)
      .filter(_ % 2 == 0)
      .evalMap(i => Sync[F].delay(println(i)))
  )

Learning more

To learn more about kafka4s, start with our Getting Started Guide, play with some example apps, and check out the kafka4s Scaladoc for more info.