Sending an http response with Json content using marshallers in Akka Http - json

Question

I want to send a Http error response with a message in JSON format in the body. I am having trouble using the PredefinedToResponseMarshallers.
I saw an implementation in the Akka docs but I tried a similar thing and it throws a compilation error.
import argonaut._, Argonaut._
import akka.http.scaladsl.marshalling.Marshal
import akka.http.scaladsl.server.Directives._
import akka.http.scaladsl.model.HttpResponse
import akka.http.scaladsl.model.headers._
import akka.http.scaladsl.model.StatusCodes._
import akka.http.scaladsl.marshalling.{ Marshaller, ToResponseMarshaller }
trait Sample extends Marshallers with Directives {
def login(user: Login): CRIX[HttpResponse] = {
for {
verification ← verify(user)
resp = if (verification) {
HttpResponse(NoContent, headers = Seq(
.........
))
}//below is my http Error response
else Marshal(401 → "It is an Unauthorized Request".asJson).to[HttpResponse]
} yield resp
}
}
It gives this compilation error :
Sample.scala:164: type mismatch;
[error] found : Object
[error] required: akka.http.scaladsl.model.HttpResponse
[error] } yield resp
[error] ^
[error] one error found
[error] (http/compile:compileIncremental) Compilation failed
I have just started Akka Http so forgive me if it is trivially easy.
TL;DR: I want(examples) to learn how to use ToResponseMarshallers in Akka Http.

Answer 1

Method to[HttpResponse] of negative condition takes on Future[HttpResponse]. At the same time positive condition returns HttpResponse.
Try something like (I assume verify takes on Future[T]):
for {
verification <- verify(user)
resp <- if (verification)
Future.successful(HttpResponse(NoContent, headers = Seq(.........)) )
else
Marshal(401 → "It is an Unauthorized Request".asJson).to[HttpResponse]
} yield resp