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" % "3.0.0-RC15"
And some imports:
import sttp.client3.asynchttpclient.fs2.AsyncHttpClientFs2Backend
import cats.effect._
import sttp.client3._
// an implicit `cats.effect.ContextShift` is required to create a concurrent instance for `cats.effect.IO`,
// as well as a `cats.effect.Blocker` instance. Note that you'll probably want to use a different thread
// pool for blocking.
implicit val cs: ContextShift[IO] = IO.contextShift(scala.concurrent.ExecutionContext.global)
val blocker: Blocker = Blocker.liftExecutionContext(scala.concurrent.ExecutionContext.global)
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 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
- by creating a
Resource
, which will instantiate the backend and close it after it has been used
A non-comprehensive summary of how the backend can be created is as follows:
AsyncHttpClientFs2Backend[IO](blocker).flatMap { backend => ??? }
or, if you’d like to use a custom configuration:
import org.asynchttpclient.AsyncHttpClientConfig
val config: AsyncHttpClientConfig = ???
AsyncHttpClientFs2Backend.usingConfig[IO](blocker, config).flatMap { backend => ??? }
or, if you’d like to use adjust the configuration sttp creates:
import org.asynchttpclient.DefaultAsyncHttpClientConfig
val sttpOptions: SttpBackendOptions = SttpBackendOptions.Default
val adjustFunction: DefaultAsyncHttpClientConfig.Builder => DefaultAsyncHttpClientConfig.Builder = ???
AsyncHttpClientFs2Backend.usingConfigBuilder[IO](blocker, adjustFunction, sttpOptions).flatMap { backend => ??? }
or, if you’d like the backend to be wrapped in cats-effect Resource:
AsyncHttpClientFs2Backend.resource[IO](blocker).use { backend => ??? }
or, if you’d like to instantiate the AsyncHttpClient yourself:
import org.asynchttpclient.AsyncHttpClient
val asyncHttpClient: AsyncHttpClient = ???
val backend = AsyncHttpClientFs2Backend.usingClient[IO](asyncHttpClient, blocker)
Using HttpClient (Java 11+)¶
To use, add the following dependency to your project:
"com.softwaremill.sttp.client3" %% "httpclient-backend-fs2" % "3.0.0-RC15"
And some imports:
import sttp.client3.httpclient.fs2.HttpClientFs2Backend
import cats.effect._
import sttp.client3._
// an implicit `cats.effect.ContextShift` is required to create a concurrent instance for `cats.effect.IO`,
// as well as a `cats.effect.Blocker` instance. Note that you'll probably want to use a different thread
// pool for blocking.
implicit val cs: ContextShift[IO] = IO.contextShift(scala.concurrent.ExecutionContext.global)
val blocker = Blocker.liftExecutionContext(scala.concurrent.ExecutionContext.global)
Create the backend using:
import sttp.client3.httpclient.fs2.HttpClientFs2Backend
HttpClientFs2Backend[IO](blocker).flatMap { backend => ??? }
or, if you’d like the backend to be wrapped in cats-effect Resource:
HttpClientFs2Backend.resource[IO](blocker).use { backend => ??? }
or, if you’d like to instantiate the HttpClient yourself:
import java.net.http.HttpClient
val httpClient: HttpClient = ???
val backend = HttpClientFs2Backend.usingClient[IO](httpClient, blocker)
This backend is based on the built-in java.net.http.HttpClient
available from Java 11 onwards.
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 sttp.capabilities.fs2.Fs2Streams
import sttp.client3._
import sttp.client3.asynchttpclient.fs2.AsyncHttpClientFs2Backend
import fs2.Stream
val effect = AsyncHttpClientFs2Backend[IO](blocker).flatMap { backend =>
val stream: Stream[IO, Byte] = ???
basicRequest
.streamBody(Fs2Streams[IO])(stream)
.post(uri"...")
.send(backend)
}
Responses can also be streamed:
import sttp.capabilities.fs2.Fs2Streams
import sttp.client3.asynchttpclient.fs2.AsyncHttpClientFs2Backend
import fs2.Stream
import scala.concurrent.duration.Duration
val effect = AsyncHttpClientFs2Backend[IO](blocker).flatMap { 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.capabilities.fs2.Fs2Streams
import sttp.client3.impl.fs2.Fs2ServerSentEvents
import sttp.model.sse.ServerSentEvent
import sttp.client3._
def processEvents(source: Stream[IO, ServerSentEvent]): IO[Unit] = ???
basicRequest.response(asStream(Fs2Streams[IO])(stream =>
processEvents(stream.through(Fs2ServerSentEvents.parse))))