=htc #20793 make Marshaller.fromStatusCode emit empty entity for StatusCode with allowEntity=false

akka-http-core/src/main/scala/akka/http/scaladsl/model/StatusCode.scala

@@ -107,7 +107,7 @@ object StatusCodes extends ObjectRegistry[Int, StatusCode] {
   val Created                     = reg(s(201)("Created", "The request has been fulfilled and resulted in a new resource being created."))
   val Accepted                    = reg(s(202)("Accepted", "The request has been accepted for processing, but the processing has not been completed."))
   val NonAuthoritativeInformation = reg(s(203)("Non-Authoritative Information", "The server successfully processed the request, but is returning information that may be from another source."))
-  val NoContent                   = reg(s(204)("No Content", "", allowsEntity = false))
+  val NoContent                   = reg(s(204)("No Content", "The server successfully processed the request and is not returning any content.", allowsEntity = false))
   val ResetContent                = reg(s(205)("Reset Content", "The server successfully processed the request, but is not returning any content."))
   val PartialContent              = reg(s(206)("Partial Content", "The server is delivering only part of the resource due to a range header sent by the client."))
   val MultiStatus                 = reg(s(207)("Multi-Status", "The message body that follows is an XML message and can contain a number of separate response codes, depending on how many sub-requests were made."))

akka-http-testkit/src/main/scala/akka/http/scaladsl/testkit/MarshallingTestUtils.scala

@@ -5,10 +5,10 @@
 package akka.http.scaladsl.testkit
 
 import scala.concurrent.duration._
-import scala.concurrent.{ ExecutionContext, Await }
-import akka.http.scaladsl.unmarshalling.{ Unmarshal, FromEntityUnmarshaller }
+import scala.concurrent.{ Await, ExecutionContext }
+import akka.http.scaladsl.unmarshalling.{ FromEntityUnmarshaller, Unmarshal }
 import akka.http.scaladsl.marshalling._
-import akka.http.scaladsl.model.HttpEntity
+import akka.http.scaladsl.model.{ HttpEntity, HttpRequest, HttpResponse }
 import akka.stream.Materializer
 
 import scala.util.Try
@@ -17,6 +17,10 @@ trait MarshallingTestUtils {
   def marshal[T: ToEntityMarshaller](value: T)(implicit ec: ExecutionContext, mat: Materializer): HttpEntity.Strict =
     Await.result(Marshal(value).to[HttpEntity].flatMap(_.toStrict(1.second)), 1.second)
 
+  def marshalToResponse[T: ToResponseMarshaller](value: T, request: HttpRequest = HttpRequest())(implicit ec: ExecutionContext, mat: Materializer): HttpResponse = {
+    Await.result(Marshal(value).toResponseFor(request), 1.second)
+  }
+
   def unmarshalValue[T: FromEntityUnmarshaller](entity: HttpEntity)(implicit ec: ExecutionContext, mat: Materializer): T =
     unmarshal(entity).get
 

akka-http-tests/src/test/scala/akka/http/scaladsl/marshalling/MarshallingSpec.scala

@@ -23,7 +23,7 @@ class MarshallingSpec extends FreeSpec with Matchers with BeforeAndAfterAll with
   implicit val materializer = ActorMaterializer()
   import system.dispatcher
 
-  "The PredefinedToEntityMarshallers." - {
+  "The PredefinedToEntityMarshallers" - {
     "StringMarshaller should marshal strings to `text/plain` content in UTF-8" in {
       marshal("Ha“llo") shouldEqual HttpEntity("Ha“llo")
     }
@@ -39,7 +39,17 @@ class MarshallingSpec extends FreeSpec with Matchers with BeforeAndAfterAll with
     }
   }
 
-  "The GenericMarshallers." - {
+  "The PredefinedToResponseMarshallers" - {
+    "fromStatusCode should properly marshal entities that are not supposed to have a body" in {
+      marshalToResponse(StatusCodes.NoContent) shouldEqual HttpResponse(StatusCodes.NoContent, entity = HttpEntity.Empty)
+    }
+    "fromStatusCode should properly marshal entities that contain pre-defined content" in {
+      marshalToResponse(StatusCodes.EnhanceYourCalm) shouldEqual
+        HttpResponse(StatusCodes.EnhanceYourCalm, entity = HttpEntity(StatusCodes.EnhanceYourCalm.defaultMessage))
+    }
+  }
+
+  "The GenericMarshallers" - {
     "optionMarshaller should enable marshalling of Option[T]" in {
 
       marshal(Some("Ha“llo")) shouldEqual HttpEntity("Ha“llo")
@@ -51,7 +61,7 @@ class MarshallingSpec extends FreeSpec with Matchers with BeforeAndAfterAll with
     }
   }
 
-  "The MultipartMarshallers." - {
+  "The MultipartMarshallers" - {
     "multipartMarshaller should correctly marshal multipart content with" - {
       "one empty part" in {
         marshal(Multipart.General(`multipart/mixed`, Multipart.General.BodyPart.Strict(""))) shouldEqual HttpEntity(

akka-http-tests/src/test/scala/akka/http/scaladsl/server/directives/CodingDirectivesSpec.scala

@@ -478,6 +478,27 @@ class CodingDirectivesSpec extends RoutingSpec with Inside {
     }
   }
 
+  "the default marshaller" should {
+    "allow compressed responses with no body for informational messages" in {
+      Get() ~> `Accept-Encoding`(HttpEncodings.compress) ~> {
+        encodeResponse {
+          complete { StatusCodes.Continue }
+        }
+      } ~> check {
+        status shouldBe StatusCodes.Continue
+      }
+    }
+    "allow gzipped responses with no body for 204 messages" in {
+      Get() ~> `Accept-Encoding`(HttpEncodings.gzip) ~> {
+        encodeResponse {
+          complete { StatusCodes.NoContent }
+        }
+      } ~> check {
+        status shouldBe StatusCodes.NoContent
+      }
+    }
+  }
+
   def compress(input: String, encoder: Encoder): ByteString = {
     val compressor = encoder.newCompressor
     compressor.compressAndFlush(ByteString(input)) ++ compressor.finish()

akka-http/src/main/scala/akka/http/scaladsl/marshalling/PredefinedToResponseMarshallers.scala

@@ -5,17 +5,15 @@
 package akka.http.scaladsl.marshalling
 
 import akka.http.scaladsl.common.EntityStreamingSupport
-import akka.stream.impl.ConstantFun
-
-import scala.collection.immutable
-import akka.http.scaladsl.util.FastFuture._
 import akka.http.scaladsl.model.MediaTypes._
 import akka.http.scaladsl.model._
-import akka.http.scaladsl.server.ContentNegotiator
 import akka.http.scaladsl.util.FastFuture
+import akka.http.scaladsl.util.FastFuture._
+import akka.stream.impl.ConstantFun
 import akka.stream.scaladsl.Source
 import akka.util.ByteString
 
+import scala.collection.immutable
 import scala.language.higherKinds
 
 trait PredefinedToResponseMarshallers extends LowPriorityToResponseMarshallerImplicits {
@@ -33,7 +31,10 @@ trait PredefinedToResponseMarshallers extends LowPriorityToResponseMarshallerImp
 
   implicit val fromStatusCode: TRM[StatusCode] =
     Marshaller.withOpenCharset(`text/plain`) { (status, charset) ⇒
-      HttpResponse(status, entity = HttpEntity(ContentType(`text/plain`, charset), status.defaultMessage))
+      val responseEntity =
+        if (status.allowsEntity) HttpEntity(status.defaultMessage)
+        else HttpEntity.Empty
+      HttpResponse(status, entity = responseEntity)
     }
 
   implicit def fromStatusCodeAndValue[S, T](implicit sConv: S ⇒ StatusCode, mt: ToEntityMarshaller[T]): TRM[(S, T)] =