A mixin trait for using PBDirect with Akka HTTP for Protobuf support

ProtobufSupport.scala

import akka.http.scaladsl.marshalling.{Marshaller, ToEntityMarshaller}
import akka.http.scaladsl.model.MediaType.{NotCompressible, applicationBinary}
import akka.http.scaladsl.model.{ContentTypeRange, MediaType}
import akka.http.scaladsl.unmarshalling.{FromEntityUnmarshaller, Unmarshaller}
import pbdirect._

/**
  * This allows you to have a mixin trait for use with Akka HTTP endpoints that accept/return Protobuf.
  * This has been patterned after https://github.com/hseeberger/akka-http-json and uses
  * https://github.com/btlines/pbdirect for "proto-less" (i.e. no .proto schemas) serialization/
  * deserializaition of case classes
  *
  * Note that this uses the media type "application/protobuf".
  */
trait ProtobufSupport {

  def unmarshallerContentTypes: Seq[ContentTypeRange] =
    mediaTypes.map(ContentTypeRange.apply)

  def mediaTypes: Seq[MediaType.Binary] =
    List(applicationBinary("protobuf", NotCompressible))

  private val unmarshaller = Unmarshaller.byteArrayUnmarshaller
    .forContentTypes(unmarshallerContentTypes: _*)

  // this is from the pbdirect README.  an example of how to add PB support to a Java class
  import cats.syntax.invariant._
  implicit val instantFormat: PBFormat[java.net.URI] =
    PBFormat[String].imap(s => new java.net.URI(s))(u => u.toString)

  implicit def protobufMarshaller[T <: AnyRef](implicit writer: PBWriter[T]): ToEntityMarshaller[T] =
    Marshaller.byteArrayMarshaller(applicationBinary("protobuf", NotCompressible)).compose(_.toPB)

  implicit def protobufUnmarshaller[T <: AnyRef](implicit reader: PBParser[T]): FromEntityUnmarshaller[T] =
    unmarshaller.map(b => b.pbTo[T])
}