Validate media description length

Signed-off-by: marcin mikołajczak <git@mkljczk.pl>

test/pleroma/web/mastodon_api/update_credentials_test.exs

@@ -472,6 +472,33 @@ defmodule Pleroma.Web.MastodonAPI.UpdateCredentialsTest do
       assert user.avatar["name"] == "me and pleroma tan"
     end
 
+    test "limit", %{user: user, conn: conn} do
+      new_header = %Plug.Upload{
+        content_type: "image/jpeg",
+        path: Path.absname("test/fixtures/image.jpg"),
+        filename: "an_image.jpg"
+      }
+
+      assert user.banner == %{}
+
+      conn
+      |> patch("/api/v1/accounts/update_credentials", %{"header" => new_header})
+
+      description_limit = Config.get([:instance, :description_limit], 100)
+
+      description = String.duplicate(".", description_limit + 1)
+
+      conn =
+        conn
+        |> assign(:user, User.get_by_id(user.id))
+        |> patch("/api/v1/accounts/update_credentials", %{
+          "header_description" => description
+        })
+
+      assert %{"error" => "Banner description is too long"} =
+               json_response_and_validate_schema(conn, 413)
+    end
+
     test "Strip / from upload files", %{user: user, conn: conn} do
       new_image = %Plug.Upload{
         content_type: "image/jpeg",