Supported backends¶
sttp supports a number of synchronous and asynchronous backends. It’s the backends that take care of managing connections, sending requests and receiving responses: sttp defines only the API to describe the requests to be send and handle the response data. Backends do all the heavy-lifting.
Choosing the right backend depends on a number of factors: whether you are using sttp to explore some data, or is it a production system; are you using a synchronous, blocking architecture or an asynchronous one; do you work mostly with Scala’s Future
, or maybe you use some form of a Task
abstraction; finally, if you want to stream requests/responses, or not.
Which one to choose?
- for simple exploratory requests, use the synchronous
HttpURLConnectionBackend
, orHttpClientSyncBackend
if you are on Java11. - if you have Akka in your stack, use Akka backend
- otherwise, if you are using
Future
, use theAsyncHttpClientFutureBackend
Future backend - finally, if you are using a functional effect wrapper, use one of the “functional” backends, for ZIO, Monix, Scalaz, cats-effect or fs2.
Each backend has three type parameters:
F[_]
, the effects wrapper for responses. That is, when you invokesend()
on a request description, do you get aResponse[_]
directly, or is it wrapped in aFuture
or aTask
?S
, the type of supported streams. IfNothing
, streaming is not supported. Otherwise, the given type can be used to send request bodies or receive response bodies.WS_HANDLER
, the type of supported websocket handlers. IfNothingT
, websockets are not supported. Otherwise, websocket connections can be opened, given an instance of the handler
Below is a summary of all the JVM backends; see the sections on individual backend implementations for more information:
Class | Response wrapper | Supported stream type | Supported websocket handlers |
---|---|---|---|
HttpURLConnectionBackend |
None (Identity ) |
n/a | n/a |
TryHttpURLConnectionBackend |
scala.util.Try |
n/a | n/a |
AkkaHttpBackend |
scala.concurrent.Future |
akka.stream.scaladsl.Source[ByteString, Any] |
akka.stream.scaladsl.Flow[Message, Message, _] |
AsyncHttpClientFutureBackend |
scala.concurrent.Future |
n/a | sttp.client.asynchttpclient.WebSocketHandler |
AsyncHttpClientScalazBackend |
scalaz.concurrent.Task |
n/a | sttp.client.asynchttpclient.WebSocketHandler |
AsyncHttpClientZioBackend |
zio.Task |
zio.stream.Stream[Throwable, Byte] |
sttp.client.asynchttpclient.WebSocketHandler |
AsyncHttpClientMonixBackend |
monix.eval.Task |
monix.reactive.Observable[ByteBuffer] |
sttp.client.asynchttpclient.WebSocketHandler |
AsyncHttpClientCatsBackend |
F[_]: cats.effect.Async |
n/a | sttp.client.asynchttpclient.WebSocketHandler |
AsyncHttpClientFs2Backend |
F[_]: cats.effect.Async |
fs2.Stream[F, Byte] |
sttp.client.asynchttpclient.WebSocketHandler |
OkHttpSyncBackend |
None (Identity ) |
n/a | sttp.client.okhttp.WebSocketHandler |
OkHttpFutureBackend |
scala.concurrent.Future |
n/a | sttp.client.okhttp.WebSocketHandler |
OkHttpMonixBackend |
monix.eval.Task |
monix.reactive.Observable[ByteBuffer] |
sttp.client.okhttp.WebSocketHandler |
Http4sBackend |
F[_]: cats.effect.Effect |
fs2.Stream[F, Byte] |
n/a |
HttpClientSyncBackend |
None (Identity ) |
n/a | sttp.client.httpclient.WebSocketHandler |
HttpClientFutureBackend |
scala.concurrent.Future |
n/a | sttp.client.httpclient.WebSocketHandler |
HttpClientMonixBackend |
monix.eval.Task |
monix.reactive.Observable[ByteBuffer] |
sttp.client.httpclient.WebSocketHandler |
HttpClientZioBackend |
zio.RIO[Blocking, *] |
zio.stream.ZStream[Blocking, Throwable, Byte] |
sttp.client.httpclient.WebSocketHandler |
FinagleBackend |
com.twitter.util.Future |
n/a | n/a |
The backends work with Scala 2.11, 2.12 and 2.13 (with some exceptions for 2.11). Moreover, HttpURLConnectionBackend
, AsyncHttpClientFutureBackend
, AsyncHttpClientZioBackend
, HttpClientSyncBackend
, HttpClientFutureBackend
and HttpClientZioBackend
are additionally built with Dotty (Scala 3).
There are also backends which wrap other backends to provide additional functionality. These include:
TryBackend
, which safely wraps any exceptions thrown by a synchronous backend inscala.util.Try
OpenTracingBackend
, for OpenTracing-compatible distributed tracing. See the dedicated section.PrometheusBackend
, for gathering Prometheus-format metrics. See the dedicated section.- slf4j backends, for logging. See the dedicated section.
In addition, there are also backends for Scala.JS:
Class | Response wrapper | Supported stream type | Supported websocket handlers |
---|---|---|---|
FetchBackend |
scala.concurrent.Future |
n/a | n/a |
FetchMonixBackend |
monix.eval.Task |
monix.reactive.Observable[ByteBuffer] |
n/a |
And a backend for scala-native:
Class | Response wrapper | Supported stream type | Supported websocket handlers |
---|---|---|---|
CurlBackend |
None (Identity ) |
n/a | n/a |
Finally, there are third-party backends:
- sttp-play-ws for “standard” play-ws (not standalone).
- akkaMonixSttpBackend, an Akka-based backend, but using Monix’s
Task
&Observable
.