Response Transformation

The counterpart to Request Building is the ResponseTransformation trait, which is especially useful on the client-side when you want to transform an incoming HTTP response in a number of loosely coupled steps into some kind of higher-level result type (see also spray-client).

Just like with RequestBuilding the ResponseTransformation trait gives you the ~> operator, which allows you to “append” a transformation function onto an existing function producing an HttpResponse. Thereby it doesn’t matter whether the result is a plain response or a response wrapped in a Future.

For example, if you have a function:

import // for futures

val sendReceive: HttpRequest => Future[HttpResponse] = // ...

and a “response transformer”:

val removeCookieHeaders: HttpResponse => HttpResponse =
  r => r.withHeaders(r.headers.filter(_.isNot("set-cookie")))

you can use the ~> operator to combine the two:

import spray.httpx.ResponseTransformation._

val pipeline: HttpRequest => Future[HttpResponse] =
  sendReceive ~> removeCookieHeaders

More generally the ~> operator combines functions in the following ways:

X Y X ~> Y
A => B B => C A => C
A => Future[B] B => C A => Future[C]
A => Future[B] B => Future[C] A => Future[C]

Predefined Response Transformers

decode(decoder: Decoder): HttpResponse ⇒ HttpResponse
Decodes a response using the given Decoder (Gzip or Deflate).
unmarshal[T: Unmarshaller]: HttpResponse ⇒ T
Unmarshalls the response to a custom type using the in-scope Unmarshaller[T].
logResponse(...): HttpResponse ⇒ HttpResponse
Doesn’t actually change the response but simply logs it.