nats4cats

Small Scala cats-effect wrapper around the official nats.java library.

Features

• Scala 3 support

• cats-effect 3.5 support

Currently, the following features are supported: - Publish - Subscribe - Request

Roadmap

v0.x - Basic Publish/Subscribe/Request - Serializer/Deserializer of payloads - Scala 2 and 3 support

v1.x - fs2 integration

v2.x - JetStream support

v3.x - Replace nats.java with a pure Scala/cats-effect/fs2-io implementation

Usage

This library is currently available for Scala3.

To use the latest version, include the following in your build.sbt:

libraryDependencies ++= Seq(
  "de.thatscalaguy" %% "nats4cats" % "0.4.1",
  "de.thatscalaguy" %% "nats4cats-circe" % "0.4.1" // if you want to use circe integration
   "de.thatscalaguy" %% "nats4cats-service" % "0.4.1" // if you want to use service integration
)

Quickstart

1.) Add the dependency to your build.sbt

2.) Create a connection to the NATS server:

  import nats4cats.Nats

  for {
    nats <- Nats.connect[IO]() // Create a Resource[F,Nats[F]] managing the connection
  } yield ()

3.) Subscribe to a nats topic

import nats4cats.Nats
import nats4cats.Serializer.given   // including serializer for string
import nats4cats.Deserializer.given // including deserializer for string

for {
  nats <- Nats.connect[IO]()
  _    <- nats.subscribe[String]("foo") { 
            case Message(data, topic, _, _) => // Message hold data, topic, headers and replyTo(optional)
              IO.println(s"Received message on topic $topic: $data")
          }
  _    <- nats.publish[String]("foo", "Hello World!")
} yield ()

Circe integration

import nats4cats.circe.given // including circe serializer/deserializer
import io.circe.Codec

final case class Foo(bar: String) derives Codec.AsObject
for {
  nats <- Nats.connect[IO]()
  _    <- nats.subscribe[Foo]("foo") { 
            case Message(data, topic, _, _) => // Message hold data, topic, headers and replyTo(optional)
              IO.println(s"Received message on topic $topic: $data")
          }
  _    <- nats.publish[Foo]("foo", Foo("Hello World!"))
} yield ()

Service implementation

This feature is currently experimental and might change in the future.

See the example project for a full example.