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.akka.http.javadsl.coding.Coder enum class.

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:

Scala
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()
Java
import akka.actor.ActorSystem;
import akka.http.javadsl.Http;
import akka.http.javadsl.coding.Coder;
import akka.http.javadsl.model.HttpRequest;
import akka.http.javadsl.model.HttpResponse;
import akka.http.scaladsl.model.headers.HttpEncodings;
import akka.stream.ActorMaterializer;
import akka.stream.Materializer;
import scala.concurrent.duration.FiniteDuration;

import java.util.Arrays;
import java.util.List;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.CompletionStage;
import java.util.concurrent.TimeUnit;
import java.util.function.Function;
import java.util.stream.Collectors;

public class HttpClientDecodingExampleTest {

  public static void main(String[] args) throws Exception {

    final ActorSystem system = ActorSystem.create();
    final Materializer materializer = ActorMaterializer.create(system);

    final List<HttpRequest> httpRequests = Arrays.asList(
      HttpRequest.create("https://httpbin.org/gzip"), // Content-Encoding: gzip in response
      HttpRequest.create("https://httpbin.org/deflate"), // Content-Encoding: deflate in response
      HttpRequest.create("https://httpbin.org/get") // no Content-Encoding in response
    );

    final Http http = Http.get(system);

    final Function<HttpResponse, HttpResponse> decodeResponse = response -> {
      // Pick the right coder
      final Coder coder;
      if (HttpEncodings.gzip().equals(response.encoding())) {
        coder = Coder.Gzip;
      } else if (HttpEncodings.deflate().equals(response.encoding())) {
        coder = Coder.Deflate;
      } else {
        coder = Coder.NoCoding;
      }

      // Decode the entity
      return coder.decodeMessage(response);
    };

    List<CompletableFuture<HttpResponse>> futureResponses = httpRequests.stream()
      .map(req -> http.singleRequest(req, materializer)
        .thenApply(decodeResponse))
      .map(CompletionStage::toCompletableFuture)
      .collect(Collectors.toList());

    for (CompletableFuture<HttpResponse> futureResponse : futureResponses) {
      final HttpResponse httpResponse = futureResponse.get();
      system.log().info("response is: " + httpResponse.entity()
                        .toStrict(1000, materializer)
                        .toCompletableFuture()
                        .get());
    }

    system.terminate();
  }
}
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