JavaScript (Fetch) backend

A JavaScript backend with web socket support. Implemented using the Fetch API.

Future-based

This is the default backend, available in the main jar for JS. To use, add the following dependency to your project:

"com.softwaremill.sttp.client3" %%% "core" % "3.5.2"

And create the backend instance:

val backend = FetchBackend()

Timeouts are handled via the new AbortController class. As this class only recently appeared in browsers you may need to add a polyfill.

As browsers do not allow access to redirect responses, if a request sets followRedirects to false then a redirect will cause the response to return an error.

Note that Fetch does not pass cookies by default. If your request needs cookies then you will need to pass a FetchOptions instance with credentials set to either RequestCredentials.same-origin or RequestCredentials.include depending on your requirements.

Monix-based

To use, add the following dependency to your project:

"com.softwaremill.sttp.client3" %%% "monix" % "3.5.2"

And create the backend instance:

val backend = FetchMonixBackend()

cats-effect-based

Any effect implementing the cats-effect Concurrent typeclass can be used. To use, add the following dependency to your project:

"com.softwaremill.sttp.client3" %%% "cats" % "3.5.2"

If you are on Cats Effect 2 (CE2) you will need to add the CE2 specific dependency instead:

"com.softwaremill.sttp.client3" %%% "catsce2 % "3.5.2"

And create the backend instance:

val backend = FetchCatsBackend[IO]()

Node.js

Using FetchBackend is possible with node-fetch module and ws with isomorphic-ws module for web sockets.

npm install --save node-fetch isomorphic-ws ws

It has to be loaded into your runtime. This can be done in your main method as such:

val g = scalajs.js.Dynamic.global.globalThis

val nodeFetch = g.require("node-fetch")

g.fetch = nodeFetch
g.Headers = nodeFetch.Headers
g.Request = nodeFetch.Request
g.WebSocket = g.require("isomorphic-ws")

Streaming

Streaming support is provided via FetchMonixBackend. Note that streaming support on Firefox is hidden behind a flag, see ReadableStream for more information.

To use, add the following dependency to your project:

"com.softwaremill.sttp.client3" %%% "monix" % "3.5.2"

An example of streaming a response:

import sttp.client3._
import sttp.client3.impl.monix._

import java.nio.ByteBuffer
import monix.eval.Task
import monix.reactive.Observable

val backend = FetchMonixBackend()

val response: Task[Response[Observable[ByteBuffer]]] =
  sttp
    .post(uri"...")
    .response(asStreamUnsafe(MonixStreams))
    .send(backend)

Note

Currently no browsers support passing a stream as the request body. As such, using the Fetch backend with a streaming request will result in it being converted into an in-memory array before being sent. Response bodies are returned as a “proper” stream.

Websockets

The backend supports both regular and streaming websockets.

Server-sent events

Received data streams can be parsed to a stream of server-sent events (SSE), when using the Monix variant:

import monix.reactive.Observable
import monix.eval.Task

import sttp.capabilities.monix.MonixStreams
import sttp.client3.impl.monix.MonixServerSentEvents
import sttp.model.sse.ServerSentEvent
import sttp.client3._

def processEvents(source: Observable[ServerSentEvent]): Task[Unit] = ???

basicRequest.response(asStream(MonixStreams)(stream => 
  processEvents(stream.transform(MonixServerSentEvents.parse))))