Some ETag refactoring

app/controllers/caching/caching.scala

@@ -3,24 +3,55 @@ package controllers.caching
 import play.api.mvc.Results.NotModified
 import play.api.mvc.{Request, Result}
 
+import java.io.{ByteArrayOutputStream, DataOutputStream, OutputStream}
+import java.security.{DigestOutputStream, MessageDigest}
+import java.util.Base64
 import scala.concurrent.{ExecutionContext, Future}
+import scala.util.Using
 
 trait Etagable[A]:
   extension (a: A) def etag: String
 
 
+trait DigestEtagable[A] extends Etagable[A]:
+  private val base64 = Base64.getUrlEncoder.withoutPadding
+
+  protected def writeDigestData(a: A, s: DataOutputStream): Unit
+
+  extension (a: A) {
+    override def etag: String = {
+      val md = MessageDigest.getInstance("SHA-1")
+      Using(DataOutputStream(DigestOutputStream(OutputStream.nullOutputStream(), md))) { dos =>
+        writeDigestData(a, dos)
+        dos.flush()
+      }
+
+      base64.encodeToString(md.digest())
+    }
+  }
+
+
 trait CheckFresh {
   protected def checkFreshAsync[A, E: Etagable](entity: E)(onStale: => Future[Result])(using request: Request[A], ec: ExecutionContext): Future[Result] = {
-    compareEtag(request, entity).fold(onStale)(
-      etag => Future.successful(NotModified.withHeaders("ETag" -> etag))
+    compareEtag(request, entity).fold(
+      entityEtag => onStale.map(_.withHeaders("etag" -> entityEtag)),
+      requestEtag => Future.successful(notModified(requestEtag))
     )
   }
 
   protected def checkFresh[A, E: Etagable](entity: E)(onStale: => Result)(using request: Request[A]): Result = {
-    compareEtag(request, entity).fold(onStale)(
-      etag => NotModified.withHeaders("ETag" -> etag)
+    compareEtag(request, entity).fold(
+      entityEtag => onStale.withHeaders("etag" -> entityEtag),
+      requestEtag => notModified(requestEtag)
     )
   }
 
-  private def compareEtag[A, E: Etagable](request: Request[A], entity: E) = request.headers.get("If-None-Match").filter(e => e == entity.etag)
+  private def compareEtag[A, E: Etagable](request: Request[A], entity: E) = {
+    val entityEtag = entity.etag
+    request.headers.get("If-None-Match").filter(e => e == entityEtag) match {
+      case Some(etag) => Right(etag)
+      case None => Left(entityEtag)
+    }
+  }
+  private def notModified(etag: String) = NotModified.withHeaders("etag" -> etag)
 }