Monix backends

There are several backend implementations which are monix.eval.Task-based. These backends are asynchronous. Sending a request is a non-blocking, lazily-evaluated operation and results in a response wrapped in a Task.

Using HttpClient

Creation of the backend can be done in two basic ways:

• by creating a Task, which describes how the backend is created, or instantiating the backend directly. In this case, you’ll need to close the backend manually.

• by creating a Resource, which will instantiate the backend and close it after it has been used.

Firstly, add the following dependency to your project:

"com.softwaremill.sttp.client4" %% "monix" % "4.0.23"

and create the backend using:

import sttp.client4.httpclient.monix.HttpClientMonixBackend

HttpClientMonixBackend().flatMap { backend => ??? }

// or, if you'd like the backend to be wrapped in cats-effect Resource:
HttpClientMonixBackend.resource().use { backend => ??? }

// or, if you'd like to instantiate the HttpClient yourself:
import java.net.http.HttpClient
val httpClient: HttpClient = ???
val backend = HttpClientMonixBackend.usingClient(httpClient)

// or, obtain a cats-effect Resource with a custom instance of the HttpClient:
import java.net.http.HttpClient
val httpClient: HttpClient = ???
HttpClientMonixBackend.resourceUsingClient(httpClient).use { backend => ??? }

This backend is based on the built-in java.net.http.HttpClient available from Java 11 onwards.

Host header override is supported in environments running Java 12 onwards, but it has to be enabled by system property:

-Djdk.httpclient.allowRestrictedHeaders=host

Using OkHttp

To use, add the following dependency to your project:

"com.softwaremill.sttp.client4" %% "okhttp-backend-monix" % "4.0.23"

Create the backend using:

import sttp.client4.okhttp.monix.OkHttpMonixBackend

OkHttpMonixBackend().flatMap { backend => ??? }

// or, if you'd like the backend to be wrapped in cats-effect Resource:
OkHttpMonixBackend.resource().use { backend => ??? }

// or, if you'd like to instantiate the OkHttpClient yourself:
import okhttp3._
val okHttpClient: OkHttpClient = ???
val backend = OkHttpMonixBackend.usingClient(okHttpClient)

This backend depends on OkHttp and fully supports HTTP/2.

Using Armeria

To use, add the following dependency to your project:

"com.softwaremill.sttp.client4" %% "armeria-backend-monix" % "4.0.23"

add imports:

import sttp.client4.armeria.monix.ArmeriaMonixBackend

create client:

import monix.execution.Scheduler.Implicits.global
val backend = ArmeriaMonixBackend()

// You can use the default client which reuses the connection pool of ClientFactory.ofDefault()
ArmeriaMonixBackend.usingDefaultClient()

or, if you’d like to instantiate the WebClient yourself:

import com.linecorp.armeria.client.circuitbreaker.*
import com.linecorp.armeria.client.WebClient

// Fluently build Armeria WebClient with built-in decorators
val client = WebClient.builder("https://my-service.com")
             // Open circuit on 5xx server error status
             .decorator(CircuitBreakerClient.newDecorator(CircuitBreaker.ofDefaultName(),
               CircuitBreakerRule.onServerErrorStatus()))
             .build()
             
val backend = ArmeriaMonixBackend.usingClient(client)

Note

A WebClient could fail to follow redirects if the WebClient is created with a base URI and a redirect location is a different URI.

This backend is build on top of Armeria. Armeria’s ClientFactory manages connections and protocol-specific properties. Please visit the official documentation to learn how to configure it.

Streaming

The Monix backends support streaming. The streams capability is represented as sttp.client4.impl.monix.MonixStreams. The type of supported streams in this case is Observable[ByteBuffer]. That is, you can set such an observable as a request body (using the http-client backend as an example, but any of the above backends can be used):

import sttp.capabilities.monix.MonixStreams
import sttp.client4.*
import sttp.client4.httpclient.monix.HttpClientMonixBackend

import monix.reactive.Observable

HttpClientMonixBackend().flatMap { backend =>
  val obs: Observable[Array[Byte]] =  ???

  basicRequest
    .streamBody(MonixStreams)(obs)
    .post(uri"...")
    .send(backend)
}

And receive responses as an observable stream:

import sttp.capabilities.monix.MonixStreams
import sttp.client4.*
import sttp.client4.httpclient.monix.HttpClientMonixBackend

import monix.eval.Task
import monix.reactive.Observable
import scala.concurrent.duration.Duration

HttpClientMonixBackend().flatMap { backend =>
  val response: Task[Response[Either[String, Observable[Array[Byte]]]]] =
    basicRequest
      .post(uri"...")
      .response(asStreamUnsafe(MonixStreams))
      .readTimeout(Duration.Inf)
      .send(backend)
    response
}

Websockets

The Monix backend supports both regular and streaming websockets.

Server-sent events

Received data streams can be parsed to a stream of server-sent events (SSE):

import monix.reactive.Observable
import monix.eval.Task

import sttp.capabilities.monix.MonixStreams
import sttp.client4.impl.monix.MonixServerSentEvents
import sttp.model.sse.ServerSentEvent
import sttp.client4.*

def processEvents(source: Observable[ServerSentEvent]): Task[Unit] = ???

basicRequest.response(asStream(MonixStreams)(stream => 
  processEvents(stream.transform(MonixServerSentEvents.parse))))