cats-effect backend¶
The Cats Effect backend is asynchronous. It can be created for any type implementing the cats.effect.Concurrent 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.
To use, add the following dependency to your project:
"com.softwaremill.sttp.client" %% "async-http-client-backend-cats" % "2.0.3"
This backend depends on async-http-client, uses Netty behind the scenes and supports effect cancellation.
Alternatively, the http4s backend can also be created for a type implementing the cats-effect’s Effect typeclass, and supports streaming as in fs2.
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 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
A non-comprehensive summary of how the backend can be created is as follows:
import sttp.client.asynchttpclient.cats.AsyncHttpClientCatsBackend
AsyncHttpClientCatsBackend().flatMap { implicit backend => ... }
// or, if you'd like to use custom configuration:
AsyncHttpClientCatsBackend.usingConfig(asyncHttpClientConfig).flatMap { implicit backend => ... }
// or, if you'd like to use adjust the configuration sttp creates:
AsyncHttpClientCatsBackend.usingConfigBuilder(adjustFunction, sttpOptions).flatMap { implicit backend => ... }
// or, if you'd like the backend to be wrapped in cats-effect Resource:
AsyncHttpClientCatsBackend.resource().use { implicit backend => ... }
// or, if you'd like to instantiate the AsyncHttpClient yourself:
implicit val sttpBackend = AsyncHttpClientCatsBackend.usingClient(asyncHttpClient)
Websockets¶
The backend supports websockets by wrapping a low-level Java interface, sttp.client.asynchttpclient.WebSocketHandler.