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.. _backends_summary:
Supported backends
==================
sttp suports 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. It's the backends where all the heavy-lifting is done.
Choosing the right backend depends on a number of factors: if 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.
Each backend has two type parameters:
* ``R[_]``, the type constructor in which responses are wrapped. That is, when you invoke ``send()`` on a request description, do you get a ``Response[_]`` directly, or is it wrapped in a ``Future`` or a ``Task``?
* ``S``, the type of supported streams. If ``Nothing``, streaming is not supported. Otherwise, the given type can be used to send request bodies or receive response bodies.
Below is a summary of all the backends. See the sections on individual backend implementations for more information.
================================ ============================ ================================================
Class Response wrapper Supported stream type
================================ ============================ ================================================
``HttpURLConnectionBackend`` None (``Id``) n/a
``TryHttpURLConnectionBackend`` ``scala.util.Try`` n/a
``AkkaHttpBackend`` ``scala.concurrent.Future`` ``akka.stream.scaladsl.Source[ByteString, Any]``
``AsyncHttpClientFutureBackend`` ``scala.concurrent.Future`` n/a
``AsyncHttpClientScalazBackend`` ``scalaz.concurrent.Task`` n/a
``AsyncHttpClientMonixBackend`` ``monix.eval.Task`` ``monix.reactive.Observable[ByteBuffer]``
``AsyncHttpClientCatsBackend`` ``F[_]: cats.effect.Async`` n/a
``AsyncHttpClientFs2Backend`` ``F[_]: cats.effect.Async`` ``fs2.Stream[F, ByteBuffer]``
``OkHttpSyncBackend`` None (``Id``) n/a
``OkHttpFutureBackend`` ``scala.concurrent.Future`` n/a
``OkHttpMonixBackend`` ``monix.eval.Task`` ``monix.reactive.Observable[ByteBuffer]``
================================ ============================ ================================================
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 in ``scala.util.Try``
* ``BraveBackend``, for Zipkin-compatible distributed tracing. See the :ref:`dedicated section <brave_backend>`.
* ``PrometheusBackend``, for gathering Prometheus-format metrics. See the :ref:`dedicated section <prometheus_backend>`.
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