Encoding / Decoding

The HTTP spec defines a Content-Encoding header, which signifies whether the entity body of an HTTP message is “encoded” and, if so, by which algorithm. The only commonly used content encodings are compression algorithms.

Currently Akka HTTP supports the compression and decompression of HTTP requests and responses with the gzip or deflate encodings. The core logic for this lives in the akka.http.scaladsl.coding package.

Server side

The support is not enabled automatically, but must be explicitly requested. For enabling message encoding/decoding with Routing DSL see the CodingDirectives.

Client side

There is currently no high-level or automatic support for decoding responses on the client-side.

The following example shows how to decode responses manually based on the Content-Encoding header:

import akka.actor.ActorSystem
import akka.http.scaladsl.Http
import akka.http.scaladsl.coding.{ Gzip, Deflate, NoCoding }
import akka.http.scaladsl.model._, headers.HttpEncodings
import akka.stream.ActorMaterializer

import scala.concurrent.Future

implicit val system = ActorSystem()
implicit val materializer = ActorMaterializer()
import system.dispatcher

val http = Http()

val requests: Seq[HttpRequest] = Seq(
  "https://httpbin.org/gzip", // Content-Encoding: gzip in response
  "https://httpbin.org/deflate", // Content-Encoding: deflate in response
  "https://httpbin.org/get" // no Content-Encoding in response
).map(uri ⇒ HttpRequest(uri = uri))

def decodeResponse(response: HttpResponse): HttpResponse = {
  val decoder = response.encoding match {
    case HttpEncodings.gzip ⇒
      Gzip
    case HttpEncodings.deflate ⇒
      Deflate
    case HttpEncodings.identity ⇒
      NoCoding
  }

  decoder.decodeMessage(response)
}

val futureResponses: Future[Seq[HttpResponse]] =
  Future.traverse(requests)(http.singleRequest(_).map(decodeResponse))

futureResponses.futureValue.foreach { resp =>
  system.log.info(s"response is ${resp.toStrict(1.second).futureValue}")
}

system.terminate()