Use JsValue not String for DCAR

Frontend posts the data for articles, fronts, tags pages and so on to DCAR as JSON, using `WSClient`. At the moment the following steps are taken to transform from an instance of a case class in frontend to the format that `WSClient` uses (`BodyWritable`):

```
case class instance -> JsValue -> String -> BodyWritable
```

The final transformation here, `String -> BodyWritable`, is handled by `WSClient`, as it defines an implicit way to get from one type to the other. However, it also defines a way to do this for a `play-json` `JsValue`, so we do not need to convert to a `String` beforehand. We should be able to pass a `JsValue` to `WSClient` directly, removing one of the transformation steps:

```
case class instance -> JsValue -> BodyWritable
```

The way to achieve this is by modifying our methods that use `WSClient.post` to take a `JsValue` payload instead of a `String`. We are then able to update the `toJson` methods on each of our models to remove the `Json.stringify` step. However, aside from `RemoteRender` requests, these `toJson` methods are also used to provide for `JsonFormat` requests via the `renderJson` method, which at the moment requires a `String`. This method, though, makes use of Play's `Writeable`, which also includes an implicit transformation to get from a `play-json` `JsValue`. So we can update it to take a `JsValue` instead, and save the additional `String` transformation step here too.

Note that there is one exception where we're using `circe` instead of `play-json`, for crosswords, so in that case we're transforming from one to the other via `String`.

applications/app/controllers/CrosswordsController.scala

@@ -23,6 +23,7 @@ import org.joda.time.{DateTime, LocalDate}
 import pages.{CrosswordHtmlPage, IndexHtmlPage, PrintableCrosswordHtmlPage}
 import play.api.data.Forms._
 import play.api.data._
+import play.api.libs.json.JsValue
 import play.api.libs.ws.WSClient
 import play.api.mvc._
 import renderers.DotcomRenderingService
@@ -117,7 +118,7 @@ class CrosswordPageController(
   }
   private def getDCRJson(crosswordPage: CrosswordPageWithContent, pageType: PageType)(implicit
       request: RequestHeader,
-  ): String =
+  ): JsValue =
     DotcomRenderingDataModel.toJson(
       DotcomRenderingDataModel.forCrossword(crosswordPage, request, pageType),
     )

applications/app/controllers/GalleryController.scala

@@ -7,6 +7,7 @@ import contentapi.ContentApiClient
 import model._
 import model.dotcomrendering.{DotcomRenderingDataModel, PageType}
 import pages.GalleryHtmlPage
+import play.api.libs.json.JsValue
 import play.api.libs.ws.WSClient
 import play.api.mvc._
 import play.twirl.api.Html
@@ -74,7 +75,7 @@ class GalleryController(
 
   private def getDCRJson(galleryPage: GalleryPage, pageType: PageType, blocks: Blocks)(implicit
       request: RequestHeader,
-  ): String = {
+  ): JsValue = {
     DotcomRenderingDataModel.toJson(DotcomRenderingDataModel.forGallery(galleryPage, request, pageType, blocks))
   }
 

applications/app/controllers/ImageContentController.scala

@@ -61,7 +61,7 @@ class ImageContentController(
 
   private def getDCRJson(content: ImageContentPage, pageType: PageType, mainBlock: Option[Block])(implicit
       request: RequestHeader,
-  ): String = {
+  ): JsValue = {
     DotcomRenderingDataModel.toJson(DotcomRenderingDataModel.forImageContent(content, request, pageType, mainBlock))
   }
 

applications/app/controllers/MediaController.scala

@@ -9,7 +9,7 @@ import implicits.{AppsFormat, JsonFormat}
 import model._
 import model.dotcomrendering.{DotcomRenderingDataModel, PageType}
 import pages.ContentHtmlPage
-import play.api.libs.json.{Format, JsObject, Json}
+import play.api.libs.json.{Format, JsObject, Json, JsValue}
 import play.api.libs.ws.WSClient
 import play.api.mvc._
 import renderers.DotcomRenderingService
@@ -96,7 +96,7 @@ class MediaController(
 
   private def getDCRJson(content: MediaPage, pageType: PageType, blocks: Blocks)(implicit
       request: RequestHeader,
-  ): String = {
+  ): JsValue = {
     DotcomRenderingDataModel.toJson(DotcomRenderingDataModel.forMedia(content, request, pageType, blocks))
   }
 

article/app/controllers/ArticleController.scala

@@ -8,7 +8,7 @@ import model.Cached.{RevalidatableResult, WithoutRevalidationResult}
 import model.dotcomrendering.{DotcomRenderingDataModel, PageType}
 import model._
 import pages.{ArticleEmailHtmlPage, ArticleHtmlPage}
-import play.api.libs.json.Json
+import play.api.libs.json.{Json, JsValue}
 import play.api.libs.ws.WSClient
 import play.api.mvc._
 import renderers.DotcomRenderingService
@@ -91,7 +91,7 @@ class ArticleController(
 
   /** Returns a JSON representation of the payload that's sent to DCR when rendering the Article.
     */
-  private def getDCRJson(article: ArticlePage, blocks: Blocks)(implicit request: RequestHeader): String = {
+  private def getDCRJson(article: ArticlePage, blocks: Blocks)(implicit request: RequestHeader): JsValue = {
     val pageType: PageType = PageType(article, request, context)
     val newsletter = newsletterService.getNewsletterForArticle(article)
 

common/app/common/package.scala

@@ -10,7 +10,7 @@ import model.CacheTime.RecentlyUpdated
 import model.Cached.RevalidatableResult
 import model.{ApplicationContext, Cached, NoCache}
 import play.api.Logger
-import play.api.libs.json.{JsObject, JsString}
+import play.api.libs.json.{JsObject, JsString, JsValue}
 import play.api.mvc.{RequestHeader, Result}
 import play.twirl.api.Html
 import model.ApplicationContext
@@ -162,7 +162,10 @@ object `package`
       JsonComponent(page, json)
     }
 
-  def renderJson(json: String, page: model.Page)(implicit request: RequestHeader, context: ApplicationContext): Result =
+  def renderJson(json: JsValue, page: model.Page)(implicit
+      request: RequestHeader,
+      context: ApplicationContext,
+  ): Result =
     Cached(page) {
       RevalidatableResult.Ok(json)
     }

common/app/model/dotcomrendering/DotcomBlocksRenderingDataModel.scala

@@ -58,9 +58,9 @@ object DotcomBlocksRenderingDataModel {
     }
   }
 
-  def toJson(model: DotcomBlocksRenderingDataModel): String = {
+  def toJson(model: DotcomBlocksRenderingDataModel): JsValue = {
     val jsValue = Json.toJson(model)
-    Json.stringify(DotcomRenderingUtils.withoutNull(jsValue))
+    DotcomRenderingUtils.withoutNull(jsValue)
   }
 
   def apply(

common/app/model/dotcomrendering/DotcomFrontsRenderingDataModel.scala

@@ -98,8 +98,8 @@ object DotcomFrontsRenderingDataModel {
     )
   }
 
-  def toJson(model: DotcomFrontsRenderingDataModel): String = {
+  def toJson(model: DotcomFrontsRenderingDataModel): JsValue = {
     val jsValue = Json.toJson(model)
-    Json.stringify(DotcomRenderingUtils.withoutNull(jsValue))
+    DotcomRenderingUtils.withoutNull(jsValue)
   }
 }

common/app/model/dotcomrendering/DotcomNewslettersPageRenderingDataModel.scala

@@ -97,9 +97,9 @@ object DotcomNewslettersPageRenderingDataModel {
     )
   }
 
-  def toJson(model: DotcomNewslettersPageRenderingDataModel): String = {
+  def toJson(model: DotcomNewslettersPageRenderingDataModel): JsValue = {
     val jsValue = Json.toJson(model)
-    Json.stringify(DotcomRenderingUtils.withoutNull(jsValue))
+    DotcomRenderingUtils.withoutNull(jsValue)
   }
 
   private def convertNewsletterResponseToData(response: NewsletterResponseV2): NewsletterData = {

common/app/model/dotcomrendering/DotcomRenderingDataModel.scala

@@ -191,9 +191,9 @@ object DotcomRenderingDataModel {
     }
   }
 
-  def toJson(model: DotcomRenderingDataModel): String = {
+  def toJson(model: DotcomRenderingDataModel): JsValue = {
     val jsValue = Json.toJson(model)
-    Json.stringify(withoutNull(jsValue))
+    withoutNull(jsValue)
   }
 
   def forInteractive(

common/app/model/dotcomrendering/DotcomTagPagesRenderingDataModel.scala

@@ -132,8 +132,8 @@ object DotcomTagPagesRenderingDataModel {
     )
   }
 
-  def toJson(model: DotcomTagPagesRenderingDataModel): String = {
+  def toJson(model: DotcomTagPagesRenderingDataModel): JsValue = {
     val jsValue = Json.toJson(model)
-    Json.stringify(DotcomRenderingUtils.withoutNull(jsValue))
+    DotcomRenderingUtils.withoutNull(jsValue)
   }
 }

common/app/model/dotcomrendering/pageElements/EditionsCrosswordRenderingDataModel.scala

@@ -2,19 +2,21 @@ package model.dotcomrendering.pageElements
 
 import com.gu.contentapi.client.model.v1.Crossword
 import com.gu.contentapi.json.CirceEncoders._
-import io.circe.JsonObject
 import io.circe.syntax._
+import model.dotcomrendering.DotcomRenderingUtils
+import play.api.libs.json.{JsObject, Json, JsValue}
 
 case class EditionsCrosswordRenderingDataModel(
     quick: Crossword,
     cryptic: Crossword,
 )
 
 object EditionsCrosswordRenderingDataModel {
-  def toJson(model: EditionsCrosswordRenderingDataModel): String = {
-    JsonObject(
-      "quick" -> model.quick.asJson.dropNullValues,
-      "cryptic" -> model.cryptic.asJson.dropNullValues,
-    ).asJson.dropNullValues.noSpaces
-  }
+  def toJson(model: EditionsCrosswordRenderingDataModel): JsValue =
+    DotcomRenderingUtils.withoutNull(
+      Json.obj(
+        "quick" -> Json.parse(model.quick.asJson.toString()),
+        "cryptic" -> Json.parse(model.cryptic.asJson.toString()),
+      ),
+    )
 }

common/app/renderers/DotcomRenderingService.scala

@@ -25,6 +25,7 @@ import model.{
   RelatedContentItem,
   SimplePage,
 }
+import play.api.libs.json.JsValue
 import play.api.libs.ws.{WSClient, WSResponse}
 import play.api.mvc.Results.{InternalServerError, NotFound}
 import play.api.mvc.{RequestHeader, Result}
@@ -56,7 +57,7 @@ class DotcomRenderingService extends GuLogging with ResultWithPreconnectPreload
 
   private[this] def postWithoutHandler(
       ws: WSClient,
-      payload: String,
+      payload: JsValue,
       endpoint: String,
       timeout: Duration = Configuration.rendering.timeout,
   )(implicit request: RequestHeader): Future[WSResponse] = {
@@ -93,7 +94,7 @@ class DotcomRenderingService extends GuLogging with ResultWithPreconnectPreload
 
   private[this] def post(
       ws: WSClient,
-      payload: String,
+      payload: JsValue,
       endpoint: String,
       cacheTime: CacheTime,
       timeout: Duration = Configuration.rendering.timeout,