Unified Scala.js + Scala HTTP client API
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Latest commit 602710c Dec 3, 2018



Build Status Latest release Scala.js

A human-readable scala http client API compatible with:


Add a dependency in your build.sbt:

Resolver.bintrayRepo("hmil", "maven")
libraryDependencies += "fr.hmil" %%% "roshttp" % "2.2.3"


The following is a simplified usage guide. You may find useful information in the API doc too.

Basic usage

import fr.hmil.roshttp.HttpRequest
import monix.execution.Scheduler.Implicits.global
import scala.util.{Failure, Success}
import fr.hmil.roshttp.response.SimpleHttpResponse

// Runs consistently on the jvm, in node.js and in the browser!
val request = HttpRequest("https://schema.org/WebPage")

    case res:Success[SimpleHttpResponse] => println(res.get.body)
    case e: Failure[SimpleHttpResponse] => println("Houston, we got a problem!")

Configuring requests

HttpRequests are immutable objects. They expose methods named .withXXX which can be used to create more complex requests.


The URI can be passed as argument of the request constructor or .withURI. The URI can be built using .withProtocol, .withHost, .withPort, .withPath, and .withQuery.... The latter is a bit more complex and is detailed below.

import fr.hmil.roshttp.Protocol.HTTP

  .withQueryParameter("city", "London")
  .send() // GET http://localhost:3000/weather?city=London


The whole querystring can be set to a custom value like this:

// Sets the query string such that the target url ends in "?hello%20world"
request.withQueryString("hello world")

.withQueryString(string) urlencodes string and replaces the whole query string with the result. To bypass encoding, use .withQueryStringRaw(rawString).


Most of the time, the query string is used to pass key/value pairs in the application/x-www-form-urlencoded format. HttpRequest offers an API to add, update and delete keys in the query string.

  .withQueryParameter("foo", "bar")
  .withQuerySeqParameter("table", Seq("a", "b", "c"))
  .withQueryObjectParameter("map", Seq(
    "d" -> "dval",
    "e" -> "e value"
    "license" -> "MIT",
    "copy" -> "© 2016"
  /* Query is now:

HTTP Method

import fr.hmil.roshttp.Method.PUT



Set individual headers using .withHeader

request.withHeader("Accept", "text/html")

Or multiple headers at once using .withHeaders

  "Accept" -> "text/html",
  "User-Agent" -> "Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; WOW64; Trident/5.0)"

Backend configuration

Some low-level configuration settings are available in BackendConfig. Each request can use a specific backend configuration using .withBackendConfig.


import fr.hmil.roshttp.BackendConfig

    // Uses stream chunks of at most 1024 bytes
    maxChunkSize = 1024

Cross-domain authorization information

For security reasons, cross-domain requests are not sent with authorization headers or cookies. If despite security concerns, this feature is needed, it can be enabled using withCrossDomainCookies, which internally uses the XMLHttpRequest.withCredentials method, but has no effect in non-browser environments. Also for same-site requests, setting it to true has no effect either.


Response headers

A map of response headers is available on the HttpResponse object:

request.send().map({res =>

Sending data

An HTTP request can send data wrapped in an implementation of BodyPart. The most common formats are already provided but you can create your own as well.
A set of implicit conversions is provided in body.Implicits for convenience.

You can post or put some data with your favorite encoding.

import fr.hmil.roshttp.body.Implicits._
import fr.hmil.roshttp.body.URLEncodedBody

val urlEncodedData = URLEncodedBody(
  "answer" -> "42",
  "platform" -> "jvm"
// or

Create JSON requests easily using implicit conversions.

import fr.hmil.roshttp.body.Implicits._
import fr.hmil.roshttp.body.JSONBody._

val jsonData = JSONObject(
  "answer" -> 42,
  "platform" -> "node"

File upload

To send file data you must turn a file into a ByteBuffer and then send it in a ByteBufferBody. For instance, on the jvm you could do:

import java.nio.ByteBuffer
import fr.hmil.roshttp.body.ByteBufferBody

val buffer = ByteBuffer.wrap(
        List[Byte](0x68, 0x65, 0x6c, 0x6c, 0x6f, 0x20, 0x77, 0x6f, 0x72, 0x6c, 0x64, 0x0a)

Note that the codec argument is important to read the file as-is and avoid side-effects due to character interpretation.


Use the MultiPartBody to compose request bodies arbitrarily. It allows for instance to send binary data with some textual data.

The following example illustrates how you could send a form to update a user profile made of a variety of data types.

import fr.hmil.roshttp.body.Implicits._
import fr.hmil.roshttp.body.JSONBody._
import fr.hmil.roshttp.body._

  // The name part is sent as plain text
  "name" -> PlainTextBody("John"),
  // The skills part is a complex nested structure sent as JSON
  "skills" -> JSONObject(
    "programming" -> JSONObject(
      "C" -> 3,
      "PHP" -> 1,
      "Scala" -> 5
    "design" -> true
  "hobbies" -> JSONArray(
  // The picture is sent using a ByteBufferBody, assuming buffer is a ByteBuffer
  // containing the image data
  "picture" -> ByteBufferBody(buffer, "image/jpeg")


Warning: Even though the streaming API works flawlessly on the JVM, it is an experimental feature as the JS implementation may leak memory or buffer things in the background.

Download streams

Streaming a response is as simple as calling .stream() instead of .send(). HttpRequest#stream() returns a Future of StreamHttpResponse. A StreamHttpResponse is just like a SimpleHttpResponse except that its body property is an Observable. The observable will spit out a stream of ByteBuffers as shown in this example:

import fr.hmil.roshttp.util.Utils._

  .map({ r =>
    r.body.foreach(buffer => println(getStringFromBuffer(buffer, "UTF-8")))

Note that special care should be taken when converting chunks into strings because multibyte characters may span multiple chunks. In general streaming is used for binary data and any reasonable quantity of text can safely be handled by the non-streaming API.

HTTP methods

There is no shortcut method such as .post to get a streaming response. You can still achieve that by using the constructor methods as shown below:

import fr.hmil.roshttp.Method.POST

  .withBody(PlainTextBody("My upload data"))
  // The response will be streamed

Upload Streams

There are cases where you want to upload some very large data with minimal memory consumption. We've got you covered! The StreamBody takes an Observable[ByteBuffer] and streams its contents to the server. You can also pass an InputStream directly using RösHTTP's implicit converters:

import fr.hmil.roshttp.body.Implicits._

// On the JVM:
// val inputStream = new java.io.FileInputStream("video.avi")
    case _:Success[SimpleHttpResponse] => println("Data successfully uploaded")
    case _:Failure[SimpleHttpResponse] => println("Error: Could not upload stream")

Error handling

Have you ever been frustrated when an application fails silently or gives you a vague and insignificant error message? RösHTTP comes with a powerful error handling API which allows you to deal with exceptions at the granularity level of your choice!

Quick and easy error handling

Most applications only need to distinguish two failure cases: Application-level failures and lower-level failures.

Application-level errors occur when a bad status code is received. For instance:

  • The request contained invalid data (400)
  • The requested resource does not exist (404)
  • The server encountered an error (500)
  • etc...

Lower-level errors include timeouts, tcp and dns failures. They are beyond the scope of most applications and should be treated separately from application-level errors, especially in code tied to user interfaces.

import fr.hmil.roshttp.exceptions.HttpException
import java.io.IOException
  .recover {
    case HttpException(e: SimpleHttpResponse) =>
      // Here we may have some detailed application-level insight about the error
      println("There was an issue with your request." +
        " Here is what the application server says: " + e.body)
    case e: IOException =>
      // By handling transport issues separately, you get a chance to apply
      // your own recovery strategy. Should you report to the user? Log the error?
      // Retry the request? Send an alert to your ops team?
      println("There was a network issue, please try again")

note that HttpException is a case class which either contains a SimpleHttpResponse or a StreamHttpResponse depending on what you expect your response to be (see Streaming).

Fine-grain error handling

If you ever need very specific error details, here is the list of exceptions which can occur in the Future.

  • IOException All RösHTTP exceptions inherit from java.io.IOException
    • TimeoutException Receiving the response took longer than the configured response timeout threshold. Note that in this case the headers were already received and you can access them if needed (mainly for debugging purposes).
    • RequestException A transport error occurred while sending the request (eg. DNS resolution failure).
    • ResponseException A transport error occurred while receiving the response (for buffered responses). Note that in this case the headers were already received and you can access them if needed (mainly for debugging purposes).
    • UploadStreamException The stream used as a data source for the request body failed.
    • HttpException Application-level errors (ie. status codes >= 400)

Watch the issues for upcoming features. Feedback is very welcome so feel free to file an issue if you see something that is missing.

Known limitations

  • Streaming is emulated in the browser, meaning that streaming large request or response payloads in the browser will consume large amounts of memory and might fail. This problem has a solution
  • Some headers cannot be set in the browser (list).
  • There is no way to avoid redirects in the browser. This is a W3C spec.
  • Chrome does not allow userspace handling of a 407 status code. It is treated like a network error. See chromium issue.
  • The TRACE HTTP method does not work in browsers and PATCH does not work in the JVM.


Please read the contributing guide.



  • Add withCrossDomainCookies (by @nondeterministic)


  • Fix edge cases with require in JS environments
  • Add missing boolean and array JSON types


  • Update to monix v2.3.0
  • Update to scala v2.11.11


  • Update to monix v2.1.2


  • Renamed withQueryArrayParameter to withQuerySeqParameter
  • Timeout errors on body
  • Rename *Error classes to *Exception
  • Add streaming API
  • Add implicit Scheduler parameter
  • Add implicit execution context parameter


  • Fix bug on responses without Content-Type header
  • Detect key-value pairs during query string escapement


  • Fix NPE when reading empty error response



  • Remove general purpose StringBody
  • Add missing patch method
  • Make Method constructor public
  • Disambiguate withQueryArrayParameter and withQueryObjectParameter
  • Remove map parameters from .withQueryParameter(s) and .withHeaders


  • Support request body with post(), put() and options()
  • Add withHttpMethod()
  • Support HTTPS


  • First release