sink.scala

import java.security.MessageDigest
import akka.util.ByteString
import akka.stream.scaladsl.Sink
import scala.concurrent.ExecutionContext

trait SomeSink {
  def digest: MessageDigest
  
  def sink(implicit ec: ExecutionContext): Sink[ByteString, Future[String]] =
    Sink.fold[MessageDigest, ByteString](digest) { (digest, chunk) =>
      digest.update(chunk.toArray)
      digest
    }.mapMaterializedValue(_.map(_.digest))
}