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 sent and handle the response data. Backends do all the heavy-lifting. Typically, a single backend instance is created for the lifetime of the application.
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 the Akka backend
if you are using
Future
without Akka, use theHttpClientFutureBackend
if you are on Java11+, orAsyncHttpClientFutureBackend
Future otherwisefinally, 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 two type parameters:
F[_]
, the effects wrapper for responses. That is, when you invokesend(backend)
on a request description, do you get aResponse[_]
directly, or is it wrapped in aFuture
or aTask
?P
, the capabilities supported by the backend, in addition toEffect[F]
. IfAny
, no additional capabilities are provided. Might includeStreams
(the ability to send and receive streaming bodies) andWebSockets
(the ability to handle websocket requests).
Below is a summary of all the JVM backends; see the sections on individual backend implementations for more information:
Class |
Effect type |
Supported stream type |
Supports websockets |
Fully non-blocking |
---|---|---|---|---|
|
None ( |
n/a |
no |
no |
|
|
n/a |
no |
no |
|
|
|
yes (regular & streaming) |
yes |
|
|
n/a |
yes (regular) |
no |
|
|
n/a |
yes (regular) |
no |
|
|
|
yes (regular & streaming) |
no |
|
|
|
yes (regular & streaming) |
no |
|
|
n/a |
no |
no |
|
|
|
yes (regular & streaming) |
no |
|
|
n/a |
no |
yes |
|
|
n/a |
no |
yes |
|
|
|
no |
yes |
|
|
|
no |
yes |
|
|
n/a |
no |
yes |
|
|
|
no |
yes |
|
None ( |
n/a |
yes (regular) |
no |
|
|
n/a |
yes (regular) |
no |
|
|
|
yes (regular & streaming) |
no |
|
|
|
no |
no |
|
None ( |
n/a |
no |
no |
|
|
n/a |
yes (regular) |
no |
|
|
|
yes (regular & streaming) |
yes |
|
|
|
yes (regular & streaming) |
yes |
|
|
|
yes (regular & streaming) |
yes |
|
|
n/a |
no |
no |
The backends work with Scala 2.11, 2.12, 2.13 and 3 (with some exceptions for 2.11 and 3).
Backends supporting cats-effect are available in versions for cats-effect 2.x (dependency artifacts have the -ce2
suffix) and 3.x.
All backends that support asynchronous/non-blocking streams, also support server-sent events.
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.extendable logging backends (with an slf4j implementation) backends. See the dedicated section.
ResolveRelativeUrisBackend
to resolve relative URIs given a base URI, or an arbitrary effectful functionListenerBackend
to listen for backend lifecycle events. See the dedicated section.FollowRedirectsBackend
, which handles redirects. All implementation backends are created wrapped with this one.
In addition, there are also backends for Scala.JS:
Class |
Effect type |
Supported stream type |
Supports websockets |
---|---|---|---|
|
|
n/a |
yes (regular) |
|
|
|
yes (regular & streaming) |
|
|
n/a |
yes (regular) |
And a backend for scala-native:
Class |
Effect type |
Supported stream type |
Supports websockets |
---|---|---|---|
|
None ( |
n/a |
no |
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
.be-kind-rewind, a VCR testing library for Scala