[R] Implement new save raw in R. (#7571)

R-package/R/xgb.save.raw.R

@@ -4,6 +4,14 @@
 #' Save xgboost model from xgboost or xgb.train
 #'
 #' @param model the model object.
+#' @param raw_format The format for encoding the booster.  Available options are
+#' \itemize{
+#'     \item \code{json}: Encode the booster into JSON text document.
+#'     \item \code{ubj}:  Encode the booster into Universal Binary JSON.
+#'     \item \code{deprecated}: Encode the booster into old customized binary format.
+#' }
+#'
+#' Right now the default is \code{deprecated} but will be changed to \code{ubj} in upcoming release.
 #'
 #' @examples
 #' data(agaricus.train, package='xgboost')
@@ -17,7 +25,8 @@
 #' pred <- predict(bst, test$data)
 #'
 #' @export
-xgb.save.raw <- function(model) {
+xgb.save.raw <- function(model, raw_format = "deprecated") {
   handle <- xgb.get.handle(model)
-  .Call(XGBoosterModelToRaw_R, handle)
+  args <- list(format = raw_format)
+  .Call(XGBoosterSaveModelToRaw_R, handle, jsonlite::toJSON(args, auto_unbox = TRUE))
 }