def withRangeSupport(): Directive0
def withRangeSupport(rangeCountLimit: Int, rangeCoalescingThreshold:Long): Directive0

The signature shown is simplified, the real signature uses magnets. [1]

[1] See The Magnet Pattern for an explanation of magnet-based overloading.


Transforms the response from its inner route into a 206 Partial Content response if the client requested only part of the resource with a Range header.

Augments responses to GET requests with an Accept-Ranges: bytes header and converts them into partial responses if the request contains a valid Range request header. The requested byte-ranges are coalesced (merged) if they lie closer together than the specified rangeCoalescingThreshold argument.

In order to prevent the server from becoming overloaded with trying to prepare multipart/byteranges responses for high numbers of potentially very small ranges the directive rejects requests requesting more than rangeCountLimit ranges with a TooManyRangesRejectionTooManyRangesRejection. Requests with unsatisfiable ranges are rejected with an UnsatisfiableRangeRejectionUnsatisfiableRangeRejection.

The withRangeSupport() form (without parameters) uses the range-coalescing-threshold and range-count-limit settings from the akka.http.routing configuration.

This directive is transparent to non-GET requests.

See also: RFC 7233


val route =
  withRangeSupport {

Get() ~> addHeader(Range(ByteRange(3, 4))) ~> route ~> check {
  headers should contain(`Content-Range`(ContentRange(3, 4, 8)))
  status shouldEqual StatusCodes.PartialContent
  responseAs[String] shouldEqual "DE"

// we set "akka.http.routing.range-coalescing-threshold = 2"
// above to make sure we get two BodyParts
Get() ~> addHeader(Range(ByteRange(0, 1), ByteRange(1, 2), ByteRange(6, 7))) ~> route ~> check {
  headers.collectFirst { case `Content-Range`(_, _) => true } shouldBe None
  val responseF = responseAs[Multipart.ByteRanges].parts
    .runFold[List[Multipart.ByteRanges.BodyPart]](Nil)((acc, curr) => curr :: acc)

  val response = Await.result(responseF, 3.seconds).reverse

  response should have length 2

  val part1 = response(0)
  part1.contentRange shouldEqual ContentRange(0, 2, 8)
  part1.entity should matchPattern {
    case HttpEntity.Strict(_, bytes) if bytes.utf8String == "ABC" =>

  val part2 = response(1)
  part2.contentRange shouldEqual ContentRange(6, 7, 8)
  part2.entity should matchPattern {
    case HttpEntity.Strict(_, bytes) if bytes.utf8String == "GH" =>
import static akka.http.javadsl.server.Directives.complete;
import static akka.http.javadsl.server.Directives.withRangeSupport;

final Route route = withRangeSupport(() -> complete("ABCDEFGH"));

// test:
final String bytes348Range = ContentRange.create(RangeUnits.BYTES,
        akka.http.javadsl.model.ContentRange.create(3, 4, 8)).value();
final akka.http.javadsl.model.ContentRange bytes028Range =
        akka.http.javadsl.model.ContentRange.create(0, 2, 8);
final akka.http.javadsl.model.ContentRange bytes678Range =
        akka.http.javadsl.model.ContentRange.create(6, 7, 8);
final ActorMaterializer materializer = systemResource().materializer();

        .addHeader(Range.create(RangeUnits.BYTES, ByteRange.createSlice(3, 4))))
        .assertHeaderExists("Content-Range", bytes348Range)

// we set "akka.http.routing.range-coalescing-threshold = 2"
// above to make sure we get two BodyParts
final TestRouteResult response = testRoute(route).run(HttpRequest.GET("/")
                ByteRange.createSlice(0, 1), ByteRange.createSlice(1, 2), ByteRange.createSlice(6, 7))));

final CompletionStage<List<Multipart.ByteRanges.BodyPart>> completionStage =
                .runFold(new ArrayList<>(), (acc, n) -> {
                    return acc;
                }, materializer);
try {
    final List<Multipart.ByteRanges.BodyPart> bodyParts =
            completionStage.toCompletableFuture().get(3, TimeUnit.SECONDS);
    assertEquals(2, bodyParts.toArray().length);

    final Multipart.ByteRanges.BodyPart part1 = bodyParts.get(0);
    assertEquals(bytes028Range, part1.getContentRange());
            part1.toStrict(1000, materializer).toCompletableFuture().get().getEntity().getData());

    final Multipart.ByteRanges.BodyPart part2 = bodyParts.get(1);
    assertEquals(bytes678Range, part2.getContentRange());
            part2.toStrict(1000, materializer).toCompletableFuture().get().getEntity().getData());

} catch (Exception e) {
    // please handle this in production code
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