Some ETag refactoring

app/controllers/HomeController.scala

@@ -1,17 +1,15 @@
 package controllers
 
-import javax.inject.*
 import play.api.*
-import play.api.mvc.*
-import authentication.{AuthenticatedAction, AuthenticatedRequest}
-import caching.{Etagable, CheckFresh}
+import _root_.controllers.authentication.{AuthenticatedAction, AuthenticatedRequest}
+import _root_.controllers.caching.{CheckFresh, DigestEtagable}
 import models.User
 import play.api.libs.json.Json
+import play.api.mvc.*
 
-import java.nio.ByteBuffer
+import java.io.DataOutputStream
 import java.nio.charset.StandardCharsets.UTF_8
-import java.security.MessageDigest
-import java.util.Base64
+import javax.inject.*
 
 /**
  * This controller creates an `Action` to handle HTTP requests to the
@@ -37,21 +35,15 @@ class HomeController @Inject()(val controllerComponents: ControllerComponents,
     val user = request.user
     checkFresh(user) {
       // TODO: put the max-age somewhere into config
-      Ok(Json.toJson(user)).withHeaders("Etag" -> user.etag, "Cache-Control" -> "private, max-age=15, must-revalidate")
+      Ok(Json.toJson(user)).withHeaders("Cache-Control" -> "private, max-age=15, must-revalidate")
     }
   }
 
-  private given Etagable[models.User] with {
-    private val base64 = Base64.getUrlEncoder
-
-    extension (a: User)
-      override def etag: String = {
-        val md = MessageDigest.getInstance("SHA-1")
-        md.update(ByteBuffer.allocate(8).putLong(a.id.getOrElse(0)))
-        md.update(a.gid.getBytes(UTF_8))
-        md.update(a.username.getBytes(UTF_8))
-
-        base64.encodeToString(md.digest())
-      }
+  private given DigestEtagable[models.User] with {
+    override protected def writeDigestData(a: User, s: DataOutputStream): Unit = {
+      s.writeLong(a.id.getOrElse(0))
+      s.write(a.gid.getBytes(UTF_8))
+      s.write(a.username.getBytes(UTF_8))
+    }
   }
 }