Fix HTML-in-JSON in ErrorView (#4500)

* fix html-in-json errors

* add tests

---------

Co-authored-by: hq1 <hq@mtod.org>

lib/plausible_web/views/error_view.ex

@@ -52,6 +52,14 @@ defmodule PlausibleWeb.ErrorView do
   end
 
   def template_not_found(template, assigns) do
+    if String.ends_with?(template, ".json") do
+      fallback_json_error(template, assigns)
+    else
+      fallback_html_error(template, assigns)
+    end
+  end
+
+  defp fallback_html_error(template, assigns) do
     assigns =
       assigns
       |> Map.put_new(:message, Phoenix.Controller.status_message_from_template(template))
@@ -59,4 +67,16 @@ defmodule PlausibleWeb.ErrorView do
 
     render("generic_error.html", assigns)
   end
+
+  defp fallback_json_error(template, _assigns) do
+    status =
+      String.split(template, ".")
+      |> hd()
+      |> String.to_integer()
+
+    message = Plug.Conn.Status.reason_phrase(status)
+    %{status: status, message: message}
+  rescue
+    _ -> %{status: 500, message: "Server error"}
+  end
 end

test/plausible_web/views/error_view_test.exs

@@ -13,4 +13,12 @@ defmodule PlausibleWeb.ErrorViewTest do
 
     refute error_html =~ "data-domain="
   end
+
+  test "renders json errors" do
+    assert Phoenix.View.render_to_string(PlausibleWeb.ErrorView, "500.json", %{}) ==
+             ~s[{"message":"Server error","status":500}]
+
+    assert Phoenix.View.render_to_string(PlausibleWeb.ErrorView, "406.json", %{}) ==
+             ~s[{"message":"Not Acceptable","status":406}]
+  end
 end