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.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();
  }
}