Abhijit Sarkar Abhijit Sarkar - 8 months ago 133
Scala Question

Play Framework: How to modify the response body without blocking?

I'm cutting my teeth on Play using the book Reactive Web Applications: Covers Play, Akka, and Reactive Streams. Chapter 4, among other things, teaches how to write a filter, but the code shown in the book doesn't compile, because in Play 2.4.x,

used to be
and in 2.5.x it is

My version of the filter is as below:

class ScoreFilter @Inject()(implicit val mat: Materializer, ec: ExecutionContext) extends Filter {
override def apply(nextFilter: (RequestHeader) => Future[Result])(rh: RequestHeader) =
nextFilter(rh).map { result =>
if (result.header.status == OK || result.header.status == NOT_ACCEPTABLE) {
val correct = result.session(rh).get("correct").getOrElse(0)
val wrong = result.session(rh).get("wrong").getOrElse(0)

val score = s"\nYour current score is: $correct correct " +
s"answers and $wrong wrong answers"

val contentType = result.body.contentType
val scoreByteString = ByteString(score.getBytes(UTF_8))
val maybeNewBody = result.body.consumeData.map(_.concat(scoreByteString))

import scala.concurrent.duration._
val newBody = Await.result(maybeNewBody, 10 seconds)

result.copy(body = Strict(newBody, contentType))
} else {

In the book:

// result.body returns a play.api.http.HttpEntity which doesn't have an andThen method
val newBody = result.body andThen Enumerator(score.getBytes(UTF_8))
result.copy(body = newBody)

As you can see, my version of the filter works but it blocks on the future. I'm wondering if there's a better way to do this without blocking?

P.S.: Before dismissing my question as duplicate, please be aware that I've read all of the following threads and they convert the response body into a string, which isn't what I want.

Scala play http filters: how to find the request body

Play framework filter that modifies json request and response

Play 2.4: intercept and modify response body


if you want to avoid Await.result, you can do:

nextFilter(rh).flatMap { result =>
  maybeNewBody map { newBody =>
    result.copy(body = Strict(newBody, contentType))
} else Future.successful(result)

(note the change of map to flatMap)