withRangeSupport

Signature

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.

Description

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 TooManyRangesRejection. Requests with unsatisfiable ranges are rejected with an UnsatisfiableRangeRejection.

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.

Example

val route =
  withRangeSupport {
    complete("ABCDEFGH")
  }

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

  val part2 = response(1)
  part2.contentRange === ContentRange(6, 7, 8)
  part2.entity should matchPattern {
    case HttpEntity.Strict(_, bytes) if bytes.utf8String == "GH" =>
  }
}