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
.
Note that all fs2 backends also support any cats-effect effect, additionally supporting request & response streaming.
Also note that the http4s backend can also be created for a type implementing the cats-effect’s Async
typeclass, and supports streaming as in fs2.
Using HttpClient
Firstly, add the following dependency to your project:
"com.softwaremill.sttp.client3" %% "cats" % "3.10.2"
Obtain a cats-effect Resource
which creates the backend, and closes the thread pool after the resource is no longer used:
import cats.effect.IO
import sttp.client3.httpclient.cats.HttpClientCatsBackend
HttpClientCatsBackend.resource[IO]().use { backend => ??? }
or, by providing a custom Dispatcher
:
import cats.effect.IO
import cats.effect.std.Dispatcher
import sttp.client3.httpclient.cats.HttpClientCatsBackend
val dispatcher: Dispatcher[IO] = ???
HttpClientCatsBackend[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.cats.HttpClientCatsBackend
val httpClient: HttpClient = ???
val dispatcher: Dispatcher[IO] = ???
val backend = HttpClientCatsBackend.usingClient[IO](httpClient, dispatcher)
or, obtain a cats-effect Resource
with a custom instance of the HttpClient
:
import cats.effect.IO
import java.net.http.HttpClient
import sttp.client3.httpclient.cats.HttpClientCatsBackend
val httpClient: HttpClient = ???
HttpClientCatsBackend.resourceUsingClient[IO](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 Armeria
Creation of the backend 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.
Firstly, add the following dependency to your project:
"com.softwaremill.sttp.client3" %% "armeria-backend-cats" % "3.10.2" // for cats-effect 3.x
// or
"com.softwaremill.sttp.client3" %% "armeria-backend-cats-ce2" % "3.10.2" // for cats-effect 2.x
create client:
import cats.effect.IO
import sttp.client3.armeria.cats.ArmeriaCatsBackend
val backend = ArmeriaCatsBackend[IO]()
// You can use the default client which reuses the connection pool of ClientFactory.ofDefault()
ArmeriaCatsBackend.usingDefaultClient[IO]()
or, if you’d like the backend to be wrapped in cats-effect Resource
:
import cats.effect.IO
import sttp.client3.armeria.cats.ArmeriaCatsBackend
ArmeriaCatsBackend.resource[IO]().use { backend => ??? }
or, if you’d like to instantiate the WebClient yourself:
import cats.effect.IO
import com.linecorp.armeria.client.WebClient
import com.linecorp.armeria.client.circuitbreaker._
import sttp.client3.armeria.cats.ArmeriaCatsBackend
// 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 = ArmeriaCatsBackend.usingClient[IO](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
This backend doesn’t support non-blocking streaming.
Websockets
The backend doesn’t support websockets.