Caching and user data endpoint

app/controllers/HomeController.scala

@@ -1,15 +1,26 @@
 package controllers
 
-import javax.inject._
-import play.api._
-import play.api.mvc._
+import javax.inject.*
+import play.api.*
+import play.api.mvc.*
+import authentication.{AuthenticatedAction, AuthenticatedRequest}
+import caching.{Etagable, checkFresh}
+import models.User
+import play.api.libs.json.Json
+
+import java.nio.ByteBuffer
+import java.nio.charset.StandardCharsets.UTF_8
+import java.security.MessageDigest
+import java.util.Base64
 
 /**
  * This controller creates an `Action` to handle HTTP requests to the
  * application's home page.
  */
 @Singleton
-class HomeController @Inject()(val controllerComponents: ControllerComponents) extends BaseController {
+class HomeController @Inject()(val controllerComponents: ControllerComponents,
+                               authenticatedAction: AuthenticatedAction)
+  extends BaseController with Logging {
 
   /**
    * Create an Action to render an HTML page.
@@ -21,4 +32,26 @@ class HomeController @Inject()(val controllerComponents: ControllerComponents) e
   def index() = Action { implicit request: Request[AnyContent] =>
     Ok(views.html.index())
   }
+
+  def userData = authenticatedAction { implicit request: AuthenticatedRequest[AnyContent] =>
+    val user = request.user
+    request.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")
+    }
+  }
+
+  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())
+      }
+  }
 }

app/controllers/caching/caching.scala

@@ -0,0 +1,26 @@
+package controllers.caching
+
+import play.api.mvc.Results.NotModified
+import play.api.mvc.{Request, Result}
+
+import scala.concurrent.{ExecutionContext, Future}
+
+trait Etagable[A]:
+  extension (a: A) def etag: String
+
+
+extension [A, R[X] <: Request[X], E: Etagable](request: R[A]) {
+  def checkFreshAsync(entity: E)(onStale: => Future[Result])(using ec: ExecutionContext): Future[Result] = {
+    compareEtag(entity).fold(onStale)(
+      etag => Future.successful(NotModified.withHeaders("ETag" -> etag))
+    )
+  }
+
+  def checkFresh(entity: E)(onStale: => Result): Result = {
+    compareEtag(entity).fold(onStale)(
+      etag => NotModified.withHeaders("ETag" -> etag)
+    )
+  }
+
+  private def compareEtag(entity: E) = request.headers.get("If-None-Match").filter(e => e == entity.etag)
+}

app/models/models.scala

@@ -6,13 +6,11 @@ import java.time.Instant
 
 case class User(id: Option[Long], username: String, gid: String, passwordDigest: Option[String])
 object User {
-  given writes: Writes[User] = new Writes[User] {
-    override def writes(o: User): JsValue = Json.obj(
+  given writes: Writes[User] = (o: User) => Json.obj(
     "gid" -> o.gid,
     "username" -> o.username
   )
 }
-}
 
 case class AuthToken(id: Option[Long], userId: Long, token: String, createdAt: Instant, expiresAt: Instant)
 object AuthToken {

conf/application.conf

@@ -8,6 +8,7 @@ play.filters.csrf.header.bypassHeaders {
 }
 play.filters.cors {
     allowedOrigins = ["http://localhost:4321"]
+    exposedHeaders = ["ETag"]
 }
 
 play.modules.enabled += "mqttClient.Module"

conf/routes

@@ -9,6 +9,8 @@ GET     /                           controllers.HomeController.index()
 POST    /login                      controllers.authentication.SessionsController.login()
 DELETE  /logout                     controllers.authentication.SessionsController.logout()
 
+GET /user_data                      controllers.HomeController.userData()
+
 # Map static resources from the /public folder to the /assets URL path
 GET     /assets/*file               controllers.Assets.versioned(path="/public", file: Asset)