sttp

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The HTTP client for Scala that you always wanted!

import com.softwaremill.sttp._

val sort: Option[String] = None
val query = "http language:scala"

// the `query` parameter is automatically url-encoded
// `sort` is removed, as the value is not defined
val request = sttp.get(uri"https://api.github.com/search/repositories?q=$query&sort=$sort")
  
implicit val backend = HttpURLConnectionBackend()
val response = request.send()

// response.header(...): Option[String]
println(response.header("Content-Length")) 

// response.unsafeBody: by default read into a String 
println(response.unsafeBody)                     

Goals of the project

  • provide a simple, discoverable, no-surprises, reasonably type-safe API for making HTTP requests and reading responses
  • separate definition of a request from request execution
  • provide immutable, easily modifiable data structures for requests and responses
  • support multiple execution backends, both synchronous and asynchronous
  • provide support for backend-specific request/response streaming
  • minimum dependencies

See also the introduction to sttp and sttp streaming & URI interpolators blogs.

Non-goals of the project

  • implement a full HTTP client. Instead, sttp wraps existing HTTP clients, providing a consistent, programmer-friendly API. All network-related concerns such as sending the requests, connection pooling, receiving responses are delegated to the chosen backend
  • provide ultimate flexibility in defining the request. While it's possible to define most valid HTTP requests, e.g. some of the less common body chunking approaches aren't available

How is sttp different from other libraries?

  • immutable request builder which doesn't impose any order in which request parameters need to be specified. Such an approach allows defining partial requests with common cookies/headers/options, which can later be specialized using a specific URI and HTTP method.
  • support for multiple backends, both synchronous and asynchronous, with backend-specific streaming support
  • URI interpolator with context-aware escaping, optional parameters support and parameter collections

Quickstart with Ammonite

If you are an Ammonite user, you can quickly start experimenting with sttp by copy-pasting the following:

import $ivy.`com.softwaremill.sttp::core:0.0.16`
import com.softwaremill.sttp._
implicit val backend = HttpURLConnectionBackend()
sttp.get(uri"http://httpbin.org/ip").send()

Adding sttp to your project

SBT dependency:

"com.softwaremill.sttp" %% "core" % "0.0.16"

sttp is available for Scala 2.11 and 2.12, and requires Java 7 if using an OkHttp based backend, or Java 8 otherwise. The core module has no transitive dependencies.

If you'd like to use an alternate backend, see below for additional instructions.

API

First, import:

import com.softwaremill.sttp._

This brings into scope sttp, the starting request (it's an empty request with the Accept-Encoding: gzip, defalte header added). This request can be customised, each time yielding a new, immutable request description (unless a mutable body is set on the request, such as a byte array).

For example, we can set a cookie, string-body and specify that this should be a POST request to a given URI:

val request = sttp
    .cookie("login", "me")
    .body("This is a test")
    .post(uri"http://endpoint.com/secret")

The request parameters (headers, cookies, body etc.) can be specified in any order. There's a lot of ways in which you can customize a request: just explore the API. And more will be added!

You can create a request description without knowing how it will be sent. But to send a request, you will need a backend. A default, synchronous backend based on Java's HttpURLConnection is provided out-of-the box. An implicit value of type SttpBackend needs to be in scope to invoke the send() on the request:

implicit val backend = HttpURLConnectionBackend()

val response: Response[String] = request.send()

By default the response body is read into a utf-8 string. How the response body is handled is also part of the request description. The body can be ignore (.response(ignore)), read into a sequence of parameters (.response(asParams)), mapped (.mapResponse) and more; some backends also support request & response streaming.

The default backend doesn't wrap the response into any container, but other asynchronous backends might do so. The type parameter in the Response[_] type specifies the type of the body.

URI interpolator

Using the URI interpolator it's possible to conveniently create Uri instances, which can then be used to specify request endpoints, for example:

import com.softwaremill.sttp._

val user = "Mary Smith"
val filter = "programming languages"

val endpoint: Uri = uri"http://example.com/$user/skills?filter=$filter"

Any values embedded in the URI will be URL-encoded, taking into account the context (e.g., the whitespace in user will be %-encoded as %20D, while the whitespace in filter will be query-encoded as +).

The possibilities of the interpolator don't end here. Other supported features:

  • parameters can have optional values: if the value of a parameter is None, it will be removed
  • maps, sequences of tuples and sequences of values can be embedded in the query part. They will be expanded into query parameters. Maps and sequences of tuples can also contain optional values, for which mappings will be removed if None.
  • optional values in the host part will be expanded to a subdomain if Some, removed if None
  • sequences in the host part will be expanded to a subdomain sequence
  • if a string containing the protocol is embedded as the very beginning, it will not be escaped, allowing to embed entire addresses as prefixes, e.g.: uri"$endpoint/login", where val endpoint = "http://example.com/api".

A fully-featured example:

import com.softwaremill.sttp._
val secure = true
val scheme = if (secure) "https" else "http"
val subdomains = List("sub1", "sub2")
val vx = Some("y z")
val params = Map("a" -> 1, "b" -> 2)
val jumpTo = Some("section2")
uri"$scheme://$subdomains.example.com?x=$vx&$params#$jumpTo"

// generates:
// https://sub1.sub2.example.com?x=y+z&a=1&b=2#section2

Starting & cleaning up

In case of most backends, you should only instantiate a backend once per application, as a backend typically allocates resources such as thread or connection pools.

When ending the application, make sure to call backend.close(), which will free up resources used by the backend (if any). The close process might be asynchronous, that is it can complete after the close() method returns.

Note that only resources allocated by the backends are freed. For example, if you use the AkkaHttpBackend() the close() method will terminate the underlying actor system. However, if you have provided an existing actor system upon backend creation (AkkaHttpBackend.usingActorSystem), the close() method will be a no-op.

Supported backends

Summary

Class Result wrapper Supported stream type
HttpURLConnectionBackend None (Id) -
AkkaHttpBackend scala.concurrent.Future akka.stream.scaladsl.Source[ByteString, Any]
AsyncHttpClientFutureBackend scala.concurrent.Future -
AsyncHttpClientScalazBackend scalaz.concurrent.Task -
AsyncHttpClientMonixBackend monix.eval.Task monix.reactive.Observable[ByteBuffer]
AsyncHttpClientCatsBackend F[_]: cats.effect.Async -
AsyncHttpClientFs2Backend F[_]: cats.effect.Async fs2.Stream[F, ByteBuffer]
OkHttpSyncBackend None (Id) -
OkHttpFutureBackend scala.concurrent.Future -
OkHttpMonixBackend monix.eval.Task monix.reactive.Observable[ByteBuffer]

HttpURLConnectionBackend

The default synchronous backend. Sending a request returns a response wrapped in the identity type constructor, which is equivalent to no wrapper at all.

To use, add an implicit value:

implicit val sttpBackend = HttpURLConnectionBackend()

AkkaHttpBackend

To use, add the following dependency to your project:

"com.softwaremill.sttp" %% "akka-http-backend" % "0.0.16"

This backend depends on akka-http. A fully asynchronous backend. Sending a request returns a response wrapped in a Future.

Next you'll need to add an implicit value:

implicit val sttpBackend = AkkaHttpBackend()

// or, if you'd like to use an existing actor system:
implicit val sttpBackend = AkkaHttpBackend.usingActorSystem(actorSystem)

This backend supports sending and receiving akka-streams streams of type akka.stream.scaladsl.Source[ByteString, Any].

To set the request body as a stream:

import com.softwaremill.sttp._
import com.softwaremill.sttp.akkahttp._

import akka.stream.scaladsl.Source
import akka.util.ByteString

val source: Source[ByteString, Any] =   ...

sttp
  .streamBody(source)
  .post(uri"...")

To receive the response body as a stream:

import com.softwaremill.sttp._
import com.softwaremill.sttp.akkahttp._

import akka.stream.scaladsl.Source
import akka.util.ByteString

implicit val sttpBackend = AkkaHttpBackend()

val response: Future[Response[Source[ByteString, Any]]] = 
  sttp
    .post(uri"...")
    .response(asStream[Source[ByteString, Any]])
    .send()

AsyncHttpClientBackend

To use, add the following dependency to your project:

"com.softwaremill.sttp" %% "async-http-client-backend-future" % "0.0.16"
// or
"com.softwaremill.sttp" %% "async-http-client-backend-scalaz" % "0.0.16"
// or
"com.softwaremill.sttp" %% "async-http-client-backend-monix" % "0.0.16"
// or
"com.softwaremill.sttp" %% "async-http-client-backend-cats" % "0.0.16"

This backend depends on async-http-client. A fully asynchronous backend, which uses Netty behind the scenes.

The responses are wrapped depending on the dependency chosen in either a:

  • standard Scala Future
  • Scalaz Task. There's a transitive dependency on scalaz-concurrent.
  • Monix Task. There's a transitive dependency on monix-eval.
  • Any type implementing the Cats Effect Async typeclass, such as cats.effect.IO. There's a transitive dependency on cats-effect.

Next you'll need to add an implicit value:

implicit val sttpBackend = AsyncHttpClientFutureBackend()

// or, if you're using the scalaz version:
implicit val sttpBackend = AsyncHttpClientScalazBackend()

// or, if you're using the monix version:
implicit val sttpBackend = AsyncHttpClientMonixBackend()

// or, if you're using the cats effect version:
implicit val sttpBackend = AsyncHttpClientCatsBackend[cats.effect.IO]()

// or, if you'd like to use custom configuration:
implicit val sttpBackend = AsyncHttpClientFutureBackend.usingConfig(asyncHttpClientConfig)

// or, if you'd like to instantiate the AsyncHttpClient yourself:
implicit val sttpBackend = AsyncHttpClientFutureBackend.usingClient(asyncHttpClient)

Streaming using Monix

The Monix backend supports streaming (as both Monix and Async Http Client support reactive streams Publishers out of the box). The type of supported streams in this case is Observable[ByteBuffer]. That is, you can set such an observable as a request body:

import com.softwaremill.sttp._

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

val obs: Observable[ByteBuffer] =  ...

sttp
  .streamBody(obs)
  .post(uri"...")

And receive responses as an observable stream:

import com.softwaremill.sttp._
import com.softwaremill.sttp.asynchttpclient.monix._

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

implicit val sttpBackend = AsyncHttpClientMonixBackend()

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

It's also possible to use fs2s streams for sending request & receiving responses.

OkHttpClientBackend

To use, add the following dependency to your project:

"com.softwaremill.sttp" %% "okhttp-backend" % "0.0.16"
// or, for the monix version:
"com.softwaremill.sttp" %% "okhttp-backend-monix" % "0.0.16"

This backend depends on OkHttp, and offers:

  • a synchronous backend: OkHttpSyncBackend
  • an asynchronous, Future-based backend: OkHttpFutureBackend
  • an asynchronous, Monix-Task-based backend: OkHttpMonixBackend

OkHttp fully supports HTTP/2.

Custom backends, logging, metrics

It is also entirely possible to write your own backend (if so, please consider contributing!) or wrapping an existing one. You can even write completely generic wrappers for any delegate backend, as each backend comes equipped with a monad for the response type. This brings the possibility to map and flatMap over responses.

Possible use-cases for wrapper-backend include:

  • logging
  • capturing metrics
  • request signing (transforming the request before sending it to the delegate)

To pass some context to wrapper-backends, requests can be tagged. Each RequestT instance contains a tags: Map[String, Any] field. This is unused by http, but can be used e.g. to pass a metric name or logging context.

JSON

JSON encoding of bodies and decoding of responses can be handled using Circe by the circe module. To use add the following dependency to your project:

"com.softwaremill.sttp" %% "circe" % "0.0.16"

This module adds a method to the request and a function that can be given to a request to decode the response to a specific object.

import com.softwaremill.sttp._
import com.softwaremill.sttp.circe._

implicit val backend = HttpURLConnectionBackend()

// Assume that there is an implicit circe encoder in scope
// for the request Payload, and a decoder for the Response
val requestPayload: Payload = ???

val response: Either[io.circe.Error, Response] = 
  sttp
    .post(uri"...")
    .body(requestPayload)
    .response(asJson[Response])
    .send()

Request type

All request descriptions have type RequestT[U, T, S] (T as in Template). If this looks a bit complex, don't worry, what the three type parameters stand for is the only thing you'll hopefully have to remember when using the API!

Going one-by-one:

  • U[_] specifies if the request method and URL are specified. Using the API, this can be either type Empty[X] = None, meaning that the request has neither a method nor an URI. Or, it can be type Id[X] = X (type-level identity), meaning that the request has both a method and an URI specified. Only requests with a specified URI & method can be sent.
  • T specifies the type to which the response will be read. By default, this is String. But it can also be e.g. Array[Byte] or Unit, if the response should be ignored. Response body handling can be changed by calling the .response method. With backends which support streaming, this can also be a supported stream type.
  • S specifies the stream type that this request uses. Most of the time this will be Nothing, meaning that this request does not send a streaming body or receive a streaming response. So most of the times you can just ignore that parameter. But, if you are using a streaming backend and want to send/receive a stream, the .streamBody or response(asStream[S]) will change the type parameter.

There are two type aliases for the request template that are used:

  • type Request[T, S] = RequestT[Id, T, S]. A sendable request.
  • type PartialRequest[T, S] = RequestT[Empty, T, S]

Timeouts

Sttp supports read and connection timeouts:

  • Connection timeout - can be set globally (30 seconds by default)
  • Read timeout - can be set per request (1 minute by default)

How to use:

import com.softwaremill.sttp._
import scala.concurrent.duration._

// all backends provide a constructor that allows users to specify connection timeout
implicit val backend = HttpURLConnectionBackend(connectionTimeout = 1.minute)

sttp
  .get(uri"...")
  .readTimeout(5.minutes) // or Duration.Inf to turn read timeout off
  .send()

SSL

SSL handling can be customized (or disabled) when creating a backend and is backend-specific.

Depending on the underlying backend's client, you can customize SSL settings as follows:

  • HttpUrlConnectionBackend: when creating the backend, specify the customizeConnection: HttpURLConnection => Unit parameter, and set the hostname verifier & SSL socket factory as required
  • akka-http: when creating the backend, specify the customHttpsContext: Option[HttpsConnectionContext] parameter. See akka-http docs
  • async-http-client: create a custom client and use the setSSLContext method
  • OkHttp: create a custom client modifying the SSL settings as described on the wiki

Notes

  • the encoding for Strings defaults to utf-8.
  • unless explicitly specified, the Content-Type defaults to:
    • text/plain for text
    • application/x-www-form-urlencoded for form data
    • multipart/form-data for multipart form data
    • application/octet-stream for everything else (binary)

Other Scala HTTP clients

Contributing

Take a look at the open issues and pick a task you'd like to work on!

Credits