fs2 backend¶
The fs2 backend is asynchronous. It can be created for any type implementing the cats.effect.Async
typeclass, such as cats.effect.IO
. Sending a request is a non-blocking, lazily-evaluated operation and results in a wrapped response. There’s a transitive dependency on cats-effect
.
Using async-http-client¶
To use, add the following dependency to your project:
"com.softwaremill.sttp.client3" %% "async-http-client-backend-fs2" % "3.3.12" // for cats-effect 3.x & fs2 3.x
// or
"com.softwaremill.sttp.client3" %% "async-http-client-backend-fs2-ce2" % "3.3.12" // for cats-effect 2.x & fs2 2.x
This backend depends on async-http-client and uses Netty behind the scenes.
Next you’ll need to define a backend instance as an implicit value. This can be done in two basic ways:
- by creating a
Resource
, which will instantiate the backend (along with aDispatcher
) and close it after it has been used - by creating an effect, which describes how a backend is created, or instantiating the backend directly. In this case, you’ll need to close the backend manually, as well as provide a
Dispatcher
instance
Below you can find a non-comprehensive summary of how the backend can be created. The easiest form is to use a cats-effect Resource
:
import cats.effect.IO
import sttp.client3.asynchttpclient.fs2.AsyncHttpClientFs2Backend
AsyncHttpClientFs2Backend.resource[IO]().use { backend => ??? }
or, by providing a custom dispatcher:
import cats.effect.IO
import cats.effect.std.Dispatcher
import sttp.client3.asynchttpclient.fs2.AsyncHttpClientFs2Backend
val dispatcher: Dispatcher[IO] = ???
AsyncHttpClientFs2Backend[IO](dispatcher).flatMap { backend => ??? }
or, if you’d like to use a custom configuration:
import cats.effect.IO
import cats.effect.std.Dispatcher
import org.asynchttpclient.AsyncHttpClientConfig
import sttp.client3.asynchttpclient.fs2.AsyncHttpClientFs2Backend
val dispatcher: Dispatcher[IO] = ???
val config: AsyncHttpClientConfig = ???
AsyncHttpClientFs2Backend.usingConfig[IO](config, dispatcher).flatMap { backend => ??? }
or, if you’d like to use adjust the configuration sttp creates:
import cats.effect.IO
import cats.effect.std.Dispatcher
import org.asynchttpclient.DefaultAsyncHttpClientConfig
import sttp.client3.SttpBackendOptions
import sttp.client3.asynchttpclient.fs2.AsyncHttpClientFs2Backend
val sttpOptions: SttpBackendOptions = SttpBackendOptions.Default
val adjustFunction: DefaultAsyncHttpClientConfig.Builder => DefaultAsyncHttpClientConfig.Builder = ???
val dispatcher: Dispatcher[IO] = ???
AsyncHttpClientFs2Backend.usingConfigBuilder[IO](dispatcher, adjustFunction, sttpOptions).flatMap { backend => ??? }
or, if you’d like to instantiate the AsyncHttpClient yourself:
import cats.effect.IO
import cats.effect.std.Dispatcher
import org.asynchttpclient.AsyncHttpClient
import sttp.client3.asynchttpclient.fs2.AsyncHttpClientFs2Backend
val dispatcher: Dispatcher[IO] = ???
val asyncHttpClient: AsyncHttpClient = ???
val backend = AsyncHttpClientFs2Backend.usingClient[IO](asyncHttpClient, dispatcher)
Using HttpClient (Java 11+)¶
To use, add the following dependency to your project:
"com.softwaremill.sttp.client3" %% "httpclient-backend-fs2" % "3.3.12" // for cats-effect 3.x & fs2 3.x
// or
"com.softwaremill.sttp.client3" %% "httpclient-backend-fs2-ce2" % "3.3.12" // for cats-effect 2.x & fs2 2.x
Create the backend using a cats-effect Resource
:
import cats.effect.IO
import sttp.client3.httpclient.fs2.HttpClientFs2Backend
HttpClientFs2Backend.resource[IO]().use { backend => ??? }
or, if by providing a custom Dispatcher
:
import cats.effect.IO
import cats.effect.std.Dispatcher
import sttp.client3.httpclient.fs2.HttpClientFs2Backend
val dispatcher: Dispatcher[IO] = ???
HttpClientFs2Backend[IO](dispatcher).flatMap { backend => ??? }
or, if you’d like to instantiate the HttpClient
yourself:
import cats.effect.IO
import cats.effect.std.Dispatcher
import java.net.http.HttpClient
import sttp.client3.httpclient.fs2.HttpClientFs2Backend
val httpClient: HttpClient = ???
val dispatcher: Dispatcher[IO] = ???
val backend = HttpClientFs2Backend.usingClient[IO](httpClient, dispatcher)
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:
jdk.httpclient.allowRestrictedHeaders=host
Using Armeria¶
To use, add the following dependency to your project:
"com.softwaremill.sttp.client3" %% "armeria-backend-fs2" % "3.3.12" // for cats-effect 3.x & fs2 3.x
// or
"com.softwaremill.sttp.client3" %% "armeria-backend-fs2" % "3.3.12" // for cats-effect 2.x & fs2 2.x
create client:
import cats.effect.IO
import cats.effect.std.Dispatcher
import sttp.client3.armeria.fs2.ArmeriaFs2Backend
ArmeriaFs2Backend.resource[IO]().use { backend => ??? }
val dispatcher: Dispatcher[IO] = ???
// You can use the default client which reuses the connection pool of ClientFactory.ofDefault()
ArmeriaFs2Backend.usingDefaultClient[IO](dispatcher)
or, if you’d like to instantiate the WebClient yourself:
import cats.effect.IO
import cats.effect.std.Dispatcher
import com.linecorp.armeria.client.WebClient
import com.linecorp.armeria.client.circuitbreaker._
import sttp.client3.armeria.fs2.ArmeriaFs2Backend
val dispatcher: Dispatcher[IO] = ???
// 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 = ArmeriaFs2Backend.usingClient[IO](client, dispatcher)
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 built 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 fs2 backend supports streaming for any instance of the cats.effect.Effect
typeclass, such as cats.effect.IO
. If IO
is used then the type of supported streams is fs2.Stream[IO, Byte]
. The streams capability is represented as sttp.client3.fs2.Fs2Streams
.
Requests can be sent with a streaming body like this:
import cats.effect.IO
import fs2.Stream
import sttp.capabilities.fs2.Fs2Streams
import sttp.client3._
import sttp.client3.armeria.fs2.ArmeriaFs2Backend
import sttp.client3.asynchttpclient.fs2.AsyncHttpClientFs2Backend
val effect = AsyncHttpClientFs2Backend.resource[IO]().use { backend =>
val stream: Stream[IO, Byte] = ???
basicRequest
.streamBody(Fs2Streams[IO])(stream)
.post(uri"...")
.send(backend)
}
Responses can also be streamed:
import cats.effect.IO
import fs2.Stream
import sttp.capabilities.fs2.Fs2Streams
import sttp.client3._
import sttp.client3.asynchttpclient.fs2.AsyncHttpClientFs2Backend
import scala.concurrent.duration.Duration
val effect = AsyncHttpClientFs2Backend.resource[IO]().use { backend =>
val response: IO[Response[Either[String, Stream[IO, Byte]]]] =
basicRequest
.post(uri"...")
.response(asStreamUnsafe(Fs2Streams[IO]))
.readTimeout(Duration.Inf)
.send(backend)
response
}
Websockets¶
The fs2 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 cats.effect._
import fs2.Stream
import sttp.client3._
import sttp.capabilities.fs2.Fs2Streams
import sttp.client3.impl.fs2.Fs2ServerSentEvents
import sttp.model.sse.ServerSentEvent
def processEvents(source: Stream[IO, ServerSentEvent]): IO[Unit] = ???
basicRequest.response(asStream(Fs2Streams[IO])(stream =>
processEvents(stream.through(Fs2ServerSentEvents.parse))))